Current Report by Foreign Issuer (SEC Filing - 6-K)

Exhibit 99.1

2021 TECHNICAL REPORT

ON THE

PEBBLE PROJECT, SOUTHWEST ALASKA, USA

NORTHERN DYNASTY MINERALS LTD.

Effective Date - February 24, 2021

Issue date March 31, 2021

Qualified Persons

J. David Gaunt, PGeo.

James Lang, PGeo.

Eric Titley, PGeo.

Hassan Ghaffari, PEng.

Stephen Hodgson, PEng.

Table of Contents

1	SUMMARY	1
1.1	Introduction	1
1.2	Project Location	3
1.3	Property Description	4
1.4	Geological Setting and Mineralization	5
1.5	Mineral Resource	6
1.6	Mineral Processing and Metallurgical Testing	8
1.7	Environmental, Permitting and Social Conditions	10
1.8	Project Description	13
1.9	Interpretation and Conclusions	15
1.10	Recommendations	16
2	INTRODUCTION	17
2.1	Terms of Reference and Purpose	17
2.2	Sources of Information and Data	18
2.3	Qualified Persons	19
3	RELIANCE ON OTHER EXPERTS	20
4	Property Description and Location	21
4.1	Location	21
4.2	Description	21
4.3	Surface Rights	28
4.4	Environmental Liabilities	28
4.5	Permits	28
5	Accessibility, Climate, Local Resources, Infrastructure and Physiography Accessibility	29
5.1	Access	29
5.2	Climate	30
5.3	Infrastructure	30
5.4	Local Resources	31
5.5	Physiography	31
6	HISTORY	32
6.1	Overview	32
6.2	Historical Sample Preparation and Analysis	35
6.2.1	Sample Preparation	35
6.2.2	Sample Analysis	35
6.3	Historical Resource Estimates	36
6.4	Ownership History	37

Northern Dynasty Minerals Ltd. 2021 Technical Report on the Pebble Project, Southwest Alaska

7	GEOLOGICAL SETTING AND MINERALIZATION	39
7.1	Regional Geology	39
7.2	Property Geology	40
7.2.1	Kahiltna Flysch	40
7.2.2	Diorite and Granodiorite Sills	41
7.2.3	Alkalic Intrusions and Associated Breccias	42
7.2.4	Hornblende Granodiorite Intrusions	43
7.2.5	Volcanic-Sedimentary cover sequence	43
7.2.6	Hornblende Monzonite Porphyry Intrusions	43
7.2.7	Eocene Volcanic Rocks and Intrusions	44
7.2.8	Glacial Sediments	44
7.2.9	District Structure	44
7.3	Deposit Geology	46
7.3.1	Rock Types	46
7.3.2	Structure	47
7.4	Deposit Alteration Styles	53
7.4.1	Pre-hydrothermal Hornfels	53
7.4.2	Hydrothermal Alteration	53
7.4.3	Post-Hydrothermal Alteration	59
7.5	Deposit Mineralization Styles	60
7.5.1	Supergene Mineralization and Leached Cap	60
7.5.2	Hypogene Mineralization	60
8	DEPOSIT TYPES	65
8.1	Deposit Types	65
9	EXPLORATION	68
9.1	Overview	68
9.1.1	Geological Mapping	68
9.1.2	Geophysical Surveys	68
9.1.3	Geochemical Surveys	69
10	DRILLING	71
10.1	Location of all Drill Holes	71
10.2	Summary of Drilling 2001 to 2013	72
10.3	Bulk Density Results	78
11	SAMPLE PREPARATION, ANALYSES, AND SECURITY	79
11.1	Sampling Method and Approach	79
11.1.1	Northern Dynasty 2002 Drilling	80
11.1.2	Northern Dynasty 2003 Drilling	80
11.1.3	Northern Dynasty 2004 Drilling	80
11.1.4	Northern Dynasty 2005 Drilling	81
11.1.5	Northern Dynasty 2006 Drilling	81
11.1.6	Northern Dynasty and Pebble Partnership 2007 Drilling	81
11.1.7	Pebble Partnership 2008 Drilling	82
11.1.8	FMMUSA 2008 Drilling	82
11.1.9	Pebble Partnership 2009 Drilling	82
11.1.10	Pebble Partnership 2010 Drilling	82
11.1.11	Pebble Partnership 2011 Drilling	83
11.1.12	Pebble Partnership 2012 Drilling	83
11.1.13	Pebble Partnership 2013 Drilling	83
11.1.14	Pebble Partnership 2018 Drilling	83
11.1.15	Pebble Partnership 2019 Drilling	84

Northern Dynasty Minerals Ltd. 2021 Technical Report on the Pebble Project, Southwest Alaska

11.2	Sample Preparation	84
11.2.1	2002 Sample Preparation	84
11.2.2	2003 Sample Preparation	84
11.2.3	2004-2013 and 2018 Sample Preparation	85
11.3	Sample Analysis	85
11.3.1	2002 Sample Analysis	85
11.3.2	2003 Sample Analysis	87
11.3.3	2002, 2004-2013 and 2018 Sample Analysis	89
11.3.4	Bulk Density Determinations	94
11.4	Quality Control/Quality Assurance	94
11.4.1	Quality Assurance and Quality Control	94
11.4.2	Standards	96
11.4.3	Duplicates	97
11.4.4	Blanks	99
11.4.5	QA/QC on Other Elements	99
11.4.6	Rhenium Study	100
11.5	Bulk Density Validation	102
11.6	Survey Validation	103
11.7	Data Environment	104
11.7.1	Error Detection Processes	104
11.7.2	Analysis Hierarchies	105
11.7.3	Wedges	105
11.7.4	Control of QA/QC	106
11.8	Verification of Drilling Data	106
12	DATA VERIFICATION	108
13	MINERAL PROCESSING AND METALLURGICAL TESTING	111
13.1	Test Programs Summary	111
13.1.1	2003 to 2005 Testwork	111
13.1.2	2006 to 2010 Testwork	112
13.1.3	2011 to 2013 Testwork	113
13.2	Comminution Tests	114
13.2.1	Bond Grindability Tests	114
13.2.2	Bond Low Energy Impact Tests	116
13.2.3	SMC Tests	116
13.2.4	MacPherson Autogenous Grindability Tests	117
13.3	Flotation Concentration Tests	118
13.3.1	Recovery of Bulk Flotation Concentrate	118
13.3.2	Separation of Molybdenum and Copper	124
13.3.3	Rhenium Recovery into Molybdenum Concentrate	128
13.3.4	Pyrite Flotation	130
13.4	Gold Recovery Tests	131
13.4.1	Gravity Recoverable Gold Tests	131
13.5	MAP Tests for Molybdenum and Rhenium Recovery	131
13.5.1	Preliminary Leaching Tests	131
13.5.2	POX and Hot Cure Leaching Confirmation Tests	132
13.5.3	Metal Extractions from Pregnant Leach Solution Tests	133
13.6	Auxiliary Tests	135
13.6.1	Concentrate Filtration	135
13.7	Quality of Concentrates	135
13.8	Geometallurgy	136
13.8.1	Introduction	136
13.8.2	Description of Geometallurgical Domains	138
13.9	Metal Recovery Projection	141
13.9.1	Metal Projections of Copper, Gold, Silver and Molybdenum - 2014/2018, Tetra Tech	141
13.9.1.1	Metal Recovery Projection Basis - 2014/2018, Tetra Tech	141
13.9.1.2	Effects of Primary Grind Size on Metal Recoveries	143
13.9.2	Metal Recovery Projection Results	148
13.9.3	Rhenium Recovery Estimate - 2020	148

Northern Dynasty Minerals Ltd. 2021 Technical Report on the Pebble Project, Southwest Alaska

14	MINERAL RESOURCE ESTIMATES	149
14.1	Summary	149
14.2	Development of Rhenium Database for Estimation	151
14.2.1	Introduction	151
14.2.2	Data Used to Develop the Regression Equation	153
14.2.3	Data Analysis	154
14.2.4	Validation	156
14.3	Geological Interpretation For Estimation	160
14.4	Exploratory Data Analysis	163
14.4.1	Assays	163
14.4.2	Capping	169
14.4.3	Composites	171
14.5	Bulk Density	171
14.6	Spatial Analysis	172
14.7	Resource Block Model	174
14.8	Interpolation Plan	174
14.9	Reasonable Prospects of Economic Extraction	176
14.10	Mineral Resource Classification	177
14.11	Copper Equivalency	177
14.12	Block Model Validation	179
14.13	Comparison with Previous Estimate	182
14.14	Factors that may Affect the Resource Estimates	182
15	ADJACENT PROPERTIES	182
16	OTHER RELEVANT DATA AND INFORMATION	183
16.1	Project Setting	183
16.1.1	Jurisdictional Setting	183
16.1.2	Environmental and Social Setting	183
16.2	Baseline Studies - Existing Environment	186
16.2.1	Climate and Meteorology	188
16.2.2	Surface Water Hydrology and Quality	188
16.2.3	Groundwater Hydrology and Quality	190
16.2.4	Geochemical Characterization	191
16.2.5	Wetlands	191
16.2.6	Fish, Fish Habitat and Aquatic Invertebrates	193
16.2.7	Marine Habitats	194
16.3	Potential Environmental Effects and Proposed Mitigation Measures	196
16.4	Economy and Social Conditions	197
16.4.1	Community Consultation and Stakeholder Relations	199

Northern Dynasty Minerals Ltd. 2021 Technical Report on the Pebble Project, Southwest Alaska

16.5	Project Description and Permitting	202
16.5.1	Mining	205
16.5.2	Mineral Processing	207
16.5.3	Tailings Storage Facility (TSF)	211
16.5.4	Infrastructure	215
16.5.5	Permitting	227
16.5.6	Closure	234
17	INTERPRETATION AND CONCLUSIONS	235
17.1	General	235
17.2	Geology and Mineral Resource Estimate	235
17.2.1	Updating of Inferred Resource	236
17.2.2	Eastern Extension	236
17.3	Metallurgical Testwork and Process Design	237
17.4	Environmental	238
17.5	Other Studies	239
18	RECOMMENDATIONS	240
18.1	Recommended Program	240
19	REFERENCES	241
19.1	Geology	241
19.2	Mineral Processing	248
19.3	Environmental	249
20	CERTIFICATES	250

Northern Dynasty Minerals Ltd. 2021 Technical Report on the Pebble Project, Southwest Alaska

LIST OF TABLES

Table 1.5‑1 Pebble Resource Estimate August 2020	7
Table 1.6‑1 Projected Metallurgical Recoveries - 2018, Tetra Tech	10
Table 4.2‑1 Pebble Mineral Claims	23
Table 6.1‑1 Teck Drilling on the Sill Prospect to the End of 1997	33
Table 6.1‑2 Teck Drilling on the Pebble Deposit to the End of 1997	33
Table 6.1‑3 Total Teck Drilling on the Property to the End of 1997	34
Table 6.3‑1 Teck Resource Estimates	36
Table 10.2‑1 Summary of Drilling to December 2019	74
Table 10.3‑1 Summary of All Bulk Density (g/cm3) Results	78
Table 10.3‑2 Summary of Bulk Density (g/cm3) Results Used for Resource Estimation	79
Table 11.3‑1 ALS Aqua Regia Digestion Multi-Element Analytical Method ME-ICP41	85
Table 11.3‑2 ALS Additional Analytical Procedures	86
Table 11.3‑3 ALS Precious Metal Fire Assay Analytical Methods	86
Table 11.3‑4 SGS Copper Analytical Method ICAY50	87
Table 11.3‑5 SGS Gold Fire Assay Analytical Methods	88
Table 11.3‑6 SGS Aqua Regia Digestion Multi-Element Analytical Method ICP70	88
Table 11.3‑7 ALS Four Acid Digestion Multi-Element Analytical Method ME-ICP61a	89
Table 11.3‑8 ALS Four Acid Digestion Multi-Element Analytical Method ME-MS61	90
Table 11.3‑9 ALS Mercury Aqua Regia Digestion Analytical Methods	91
Table 11.3‑10 ALS Copper Speciation Analytical Methods	91
Table 11.3‑11 BVCCL Four Acid Digestion Multi-Element Analytical Method MA270	92
Table 11.3‑12 BVCCL Precious Metal Fire Assay Analytical Method	93
Table 11.4‑1 QA/QC Sample Types Used	95
Table 13.1‑1 Testwork Programs and Reports 2006 to 2010	112
Table 13.1‑2 Subsequent Testwork Programs and Reports, 2011 to 2014	114
Table 13.2‑1 Pebble West Rod Mill Data Comparison, SGS January 2012**	115
Table 13.2‑2 Pebble West Ball Mill Data Comparison, SGS January 2012**	115
Table 13.2‑3 Bond Low-Energy Impact Test Results, SGS January 2012	116
Table 13.2‑4 Major SMC Data Comparison on Pebble West Samples-SGS Test Report Sept.2014	117
Table 13.2‑5 Major SMC Data Comparison on Pebble East Samples - SGS Summary Report Sept. 2014	117
Table 13.2‑6 MacPherson Autogenous Grindability Test Results, SGS January 2012	117
Table 13.3‑1 Summary of Locked-Cycle Test Variability Test Results	121
Table 13.3‑2 Locked-Cycle Test Results on Pebble Variability Samples, SGS 2014	121
Table 13.3‑3 Locked-Cycle Test Results of Bulk Samples, SGS 2012	123
Table 13.3‑4 Locked-Cycle Test Results of Molybdenum Flotation, SGS 2011-2012	127
Table 13.3‑5 Molybdenum Recovery, G&T 2011	128
Table 13.3‑6 Molybdenum Open Cycle Cleaner Flotation Test Results (Mo-F13, SGS 2012)	129
Table 13.5‑1 MAP Test Samples Assay Results	133
Table 13.5‑2 POX and Alkaline Leach Test Results	133
Table 13.5‑3 (NH4)2MoO4 and MoO3 Analysis Results	135
Table 13.7‑1 LCT Cu-Mo Concentrate Major Elements Analysis Results - SGS 2014	135
Table 13.7‑2 LCT Cu Concentrate Major Elements Analysis Results - SGS 2014	136
Table 13.7‑3 LCT Mo Concentrate Major Elements Analysis Results - SGS 2014	136
Table 13.9‑1 Summary of Batch Recovery Change per 10µm Primary Grind Size Reduction	146
Table 13.9‑2 Summary of LCT Recovery Change per 10µm Primary Grind Size Reduction	147
Table 13.9‑3 Change in Metal Recovery for 10µm Primary Grind Size Reduction, P80 150µm to 300µm	147
Table 13.9‑4 Projected Metallurgical Recoveries - 2018 Tetra Tech	148

Table 14.1‑1 Pebble Deposit Mineral Resource Estimate August 2020	150
Table 14.2‑1 Correlation coefficients between rhenium and other elements	155
Table 14.2‑2 Predicted and actual rhenium for 50 withheld validation samples, at 10 ft scale and at 50 ft scale	158
Table 14.3‑1 Pebble Deposit Metal Domains	161
Table 14.4‑1 Pebble Deposit assay Database Descriptive Global Statistics	163
Table 14.4‑2 Pebble Deposit Capping Values	170
Table 14.4‑3 Pebble Deposit Composite Mean Values	171
Table 14.6‑1 Pebble Deposit Variogram Parameters	172
Table 14.6‑2 Pebble Deposit Search Ellipse Parameters	173
Table 14.7‑1 Pebble Deposit 2020 Block Model Parameters	174
Table 14.8‑1 Pebble Deposit Interpolation Domain Boundaries	175
Table 14.9‑1 Pebble Deposit Conceptual Pit Parameters	176
Table 16.5‑1 Summary Project Information	204
Table 16.5‑2 Mined Material Preproduction Phase	205
Table 16.5‑3 Mines Material - Production Phase	206
Table 16.5‑4 Environmental Permits Required for the Pebble Project	231

Northern Dynasty Minerals Ltd. 2021 Technical Report on the Pebble Project, Southwest Alaska

LIST OF FIGURES

Figure 1.2‑1 Property Location Map	4
Figure 4.2‑1 Mineral Claim Map with Exploration Lands and Resource Lands	22
Figure 5.1‑1 Property Location and Access Map	29
Figure 7.2‑1 Location of the Pebble Deposit & Regional Geological Setting of Southwest Alaska	41
Figure 7.2‑2 Rock Types in the Pebble District	45
Figure 7.3‑1 Geology of the Pebble Deposit Showing Section Locations	48
Figure 7.3‑2 Plan View of Alteration and Metal Distribution in the Pebble Deposit	49
Figure 7.3‑3 Geology, Alteration and Distribution of Metals on Section A-A'	50
Figure 7.3‑4 Geology, Alteration and Metal Distribution on Section B-B'	51
Figure 7.3‑5 Geology, Alteration and Metal Distribution on Section C-C'	52
Figure 7.5‑1 Drill Core Photograph Showing Chalcopyrite Mineralization	63
Figure 7.5‑2 Drill Core Photograph Showing Chalcopyrite and Bornite Mineralization	64
Figure 8.1‑1 Pebble Deposit Rank by Contained Copper	66
Figure 8.1‑2 Pebble Deposit Rank by Contained Precious Metals	67
Figure 10.1‑1 Location of all Drill Holes	71
Figure 10.2‑1 Location of Drill Holes - Pebble Deposit Area	73
Figure 11.3‑1 Pebble Project 2010 to 2013 Drill Core Sampling and Analytical Flow Chart	93
Figure 11.4‑1 Performance of the Copper Standard CGS-16 in 2008	95
Figure 11.4‑2 Performance of the Gold Standard CGS-16 in 2008	96
Figure 11.4‑3 Comparison of Gold Duplicate Assay Results for 2004 to 2010	98
Figure 11.4‑4 Comparison of Copper Duplicate Assay Results for 2004 to 2010	98
Figure 11.4‑5 Performance of Standard PLP-1 for Rhenium	100
Figure 11.4‑6 Performance of Control Sample PLP-2 for Rhenium	101
Figure 11.4‑7 Scatterplots in Log Format of Original vs 2020 Re-analysis for Copper and Molybdenum	102
Figure 13.3‑1 Basic Testwork Flowsheet, SGS 2011	120
Figure 13.3‑2 Basic Testwork Flowsheet, SGS 2011	125
Figure 13.3‑3 Rhenium Grade and Recovery Relationship (SGS 2012)	129
Figure 13.3‑4 Pyrite Flotation Kinetics Test Results	130
Figure 13.5‑1 Metal Extraction Steps Tested by SGS	134
Figure 13.9‑1 The Effect of Primary Grind Fineness of Copper Recovery to Rougher Concentrate	143
Figure 13.9‑2 Effect of Primary Grind Size on Cu, Au and Mo Recovery to Batch Copper Concentrate	144
Figure 13.9‑3 Cu, Au, and Mo Recovery into a 26% Batch Cu Concentrate	145
Figure 14.2‑1 Growth in the percentage of drill-hole sample intervals with rhenium assays.	152
Figure 14.2‑2 Block Model (red line); DDH Collars and Re analyses: Lacking (grey), Existing (yellow), 2020 Pulps (red)	154
Figure 14.2‑3 Rhenium Versus Molybdenum	156
Figure 14.2‑4 Rhenium predictions versus actual rhenium assays for withheld validation samples	157
Figure 14.3‑1 Pebble Deposit Plan View of Drill Holes and Block Model Extent (red rectangle)	162
Figure 14.4‑1 Pebble Deposit Copper Assay Domain Box-and-Whisker Plots	164
Figure 14.4‑2 Pebble Deposit Gold Assay Domain Box-and-Whisker Plots	165
Figure 14.4‑3 Pebble Deposit Molybdenum Assay Box-and-Whisker Plots	166
Figure 14.4‑4 Pebble Deposit Silver Assay Box-and-Whisker Plots	167
Figure 14.4‑5 Pebble Deposit Rhenium Assay Box-and-Whisker Plots	168
Figure 14.4‑6 Pebble Deposit Copper Grade Domains	169
Figure 14.12‑1 Pebble Deposit Vertical Section 2158700N Block and Composite Copper Grades; Section Line Location Shown in Figure 7.3‑1	179
Figure 14.12‑2 Copper Swath Plot at 2157000N	180
Figure 14.12‑3 Gold Swath Plot at 2157000N	180
Figure 14.12‑4 Molybdenum Swath Plot at 2157000N	181
Figure 14.12‑5 Rhenium Swath Plot at 2157000N	181
Figure 16.1‑1 Bristol Bay Watersheds	184
Figure 16.2‑1 Local Watershed Boundaries	189
Figure 16.5‑1 Potential Mine Site Layout	203
Figure 16.5‑2 Process Flow Sheet	208
Figure 16.5‑3 Key Elements of Water Management	221
Figure 16.5‑4 Diamond Point Port and Lightering Location	225
Figure 17.2‑1 Untested Exploration Potential East of Drillhole 6348	237

Northern Dynasty Minerals Ltd. 2021 Technical Report on the Pebble Project, Southwest Alaska Page 1

UNIT MEASURES AND ABBREVIATIONS
Above mean sea level	amsl
Acre	ac
Alaska Department of Environmental Conservation	ADEC
Alaska Department of Fish and Game	ADFG
Alaska Department of Natural Resources	ADNR
Alaska Peninsula Corporation	APC
Ampere	A
Annum (year)	a
Anadromous Waters Catalog	AWC
Acid Potential	AP
Acid Rock Drainage	ARD
Aqua Regia (HNO3-HCl)	AR
Atomic absorption spectroscopy	AAS
Billion	B
Billion years ago	Ga
Brittle-ductile fault	BDF
Centimetre	cm
Carbon-In-Leach	CIL
Clean Water Act	CWA
Cominco Exploration Research Laboratory	CERL
Cubic centimetre	cm3
Cubic feet per minute	cfm
Cubic feet per second	ft3/s
Cubic foot	ft3
Cubic inch	in3
Cubic metre	m3
Day	d
Days per week	d/wk
Days per year (annum)	d/a
Degree	°
Degrees Celsius	°C
Degrees Fahrenheit	°F
U.S. Environmental Protection Agency	EPA
Fire Assay	FA
Gram	g
Grams per cubic centimetre	g/cm3
Grams per litre	g/L
Grams per tonne	g/t
Gallons per minute	GPM
Greater than	>
Health, safety and environment	HSE
Hectare (10,000 m2)	ha
Horsepower	hp
Hours	h
Hours per day	h/d
Hours per week	h/w
Hours per year	h/a
Iliamna Natives Limited	INL
Inch	in

Induced Polarization geophysics	IP
Inductively coupled plasma atomic emission spectroscopy	ICP-AES
Inductively coupled plasma mass spectrometry	ICP-MS
Kaskanak Creek	KC
Kilo (thousand)	k
Kilogram	kg
Kilograms per hour	kg/h
Kilograms per square metre	kg/m2
Kilometre	km
Kilometres per hour	km/h
Kilopascal	kPa
Kilotonne	kt
Kilowatt	kW
Kilowatt hour	kWh
Kilowatt hours per tonne (metric ton)	kWh/t
Kilowatt hours per year	kWh/a
Least Environmentally Destructive Practicable Alternative	LEDPA
Less than	<
Litres	L
Litres per minute	L/m
Maximum potential acidity	MPA
Metal Leaching	ML
Metres	m
Metres above sea level	masl
Millions of years ago	Ma
Metric tonne	t
Microns	µm
Milligram	mg
Milligrams per litre	mg/l
Millilitre	mL
Millimetre	mm
Million	M
Million tonnes	Mt
Minute (plane angle)	'
Minute (time)	min
Month	mo
National Environmental Policy Act	NEPA
National Instrument 43-101	NI 43-101
Neutralizing Potential	NP
Neutralization potential ratio	NPR
North Fork Koktuli	NFK
Northern and Southern quartz vein domains	NQV and SQV
Ounce	oz
Parts per million	ppm
Parts per billion	ppb
Potentially acid generating	PAG
Percent	%

Northern Dynasty Minerals Ltd.

2021 Technical Report on the

Pebble Project, Southwest Alaska

Pounds	lb
Pounds per square inch	psi
Pounds per ton	lb/ton
Quality Control/Quality Assurance	QA/QC
Qualified Person	QP
Quartz Sericite Pyrite	QSP
Revolutions per minute	rpm
Rivers and Harbors Act	RHA

Semi-autogenous grinding	SAG
Sulphidize, acidify, recycle and thicken	SART
Second (plane angle)	'
Second (time)	s
Square	cm2
Square foot	ft2
Square inch	in2
Square kilometer	km2
Square metre	m2
South Fork Koktuli	SFK
Three dimensional	3D
Three Dimensional Model	3DM
Tonnes	t
Thousand tonnes (1,000 kg)	kt
Tons (imperial)	tons
Total dissolved solids	TDS
Upper Talarik Creek	UTC
U.S. Army Corps of Engineers	USACE
Vibrating wire piezometer	VWP
Volt	V
Week	wk
Year (annum)	a

Northern Dynasty Minerals Ltd. 2021 Technical Report on the Pebble Project, Southwest Alaska Page 3

The Pebble deposit was originally discovered in 1989 and was acquired by Northern Dynasty Minerals Ltd. (Northern Dynasty or the Company) in 2001. Since that time, Northern Dynasty and, subsequently, the Pebble Limited Partnership (Pebble Partnership) in which Northern Dynasty currently owns a 100% interest, have conducted significant mineral exploration, environmental baseline data collection, and engineering studies to advance the Pebble Project.

Since the acquisition by Northern Dynasty, work at Pebble has led to an overall expansion of the Pebble deposit, as well as the discovery of several other mineralized occurrences along an extensive northeast-trending mineralized system underlying the property. Over 1 million feet of drilling has been completed on the property, a large proportion of which has been focused on the Pebble deposit.

Comprehensive deposit delineation, environmental, socioeconomic and engineering studies of the Pebble deposit began in 2004 and continued through 2013. A previous estimate of the mineral resources in the Pebble deposit was stated in a technical report completed in 2018.

Northern Dynasty completed a Preliminary Assessment on the Pebble Project in February 2011. Since that time, after considering stakeholder feedback, the Pebble Partnership developed a plan for the Pebble Project on the basis of a substantially smaller mine facility footprint, and with other material revisions. As a result, the economic analysis included in the 2011 Preliminary Assessment is considered by Northern Dynasty to be out of date such that it can no longer be relied upon. In light of the foregoing and as noted in the Company's 2018 Technical Report, the Pebble Project is no longer an advanced property for the purposes of NI 43-101, as the potential economic viability of the Pebble Project is not currently supported by a preliminary economic assessment, pre-feasibility study or feasibility study.

A smaller mine facility formed the basis of the permit application under Section 404 of the Clean Water Act (CWA) and Section 10 of the Rivers and Harbors Act (RHA) submitted to the US Army Corps of Engineers (USACE) by the Pebble Partnership on December 22, 2017. On January 8, 2018, USACE accepted the permitting documentation and confirmed that an Environmental Impact Statement (EIS) level of analysis was required to comply with its National Environmental Policy Act (NEPA) review of the Pebble Project. The EIS process progressed through the scoping phase in 2018. The USACE delivered the Draft EIS in the first quarter of 2019 and completed a public comment period from March to July 2019. In the latter part of 2019 and early 2020, the USACE and its consultants advanced toward a Final EIS. The preliminary Final EIS was circulated to co-operating agencies for review in February 2020. As part of the EIS preparation process, the USACE and its consultants had undertaken a comprehensive alternatives assessment to consider a broad range of development alternatives and announced the conclusions of the draft Least Environmentally Damaging Practicable Alternative (LEDPA) in May 2020. The USACE published the Final Pebble EIS on July 24, 2020.

The CWA 404 Permit Application was submitted in December 2017, and the permitting process over the next three years involved the Pebble Partnership being actively engaged with the USACE on the evaluation of the Pebble Project. There were numerous meetings between representatives of the USACE and the Pebble Partnership regarding, among other things, compensatory mitigation for the Pebble Project. The Pebble Partnership submitted several draft compensatory mitigation plans to the USACE, each refined to address comments from the USACE and that the Pebble Partnership believed were consistent with mitigation proposed and approved for other major development projects in Alaska. In late June 2020, USACE verbally identified the 'significant degradation' of certain aquatic resources, with the requirement of new compensatory mitigation. The Pebble Partnership understood from these discussions that the new compensatory mitigation plan for the Pebble Project would include in-kind, in-watershed mitigation and continued its work to meet these new USACE requirements.

The USACE formally advised the Pebble Partnership by letter dated August 20, 2020 that it had made preliminary factual determinations under Section 404(b)(1) of the CWA that the Pebble Project as proposed would result in significant degradation to aquatic resources. In connection with this preliminary finding of significant degradation, the USACE formally informed the Pebble Partnership that in-kind compensatory mitigation within the Koktuli River watershed would be required to compensate for all direct and indirect impacts caused by discharges into aquatic resources at the mine site. The USACE requested the submission of a new compensatory mitigation plan to address this finding within 90 days of its letter. Accordingly, the Pebble Partnership developed a compensatory mitigation plan (CMP) to align with the requirements outlined by the USACE. This plan envisioned creation of a 112,445-acre Koktuli Conservation Area on land belonging to the State of Alaska in the Koktuli River watershed downstream of the Project. The plan was submitted to the USACE on November 4, 2020.

On November 25, 2020, the USACE issued a Record of Decision (ROD) rejecting the Pebble Partnership's permit application, finding concerns with the proposed CMP and determining that the project would be contrary to the public interest. The USACE concluded the proposed CMP is not compliant with USACE regulations.

The Pebble Partnership submitted its request for appeal of the ROD to the USACE Pacific Ocean Division on January 19, 2021. The request for appeal reflects the Pebble Partnership's position that the USACE's ROD and permitting decision - including its 'Significant Degradation' finding, its 'public interest review' findings, and its perfunctory rejection of the Pebble Partnership's CMP - are contrary to law, unprecedented in Alaska, and fundamentally unsupported by the administrative record, including the Pebble Project Final Environmental Impact Statement (FEIS). In a letter dated February 24, 2021, the USACE confirmed the Pebble Partnership's RFA is 'complete and meets the criteria for appeal.' While federal guidelines suggest the appeal should conclude within 90 days, the USACE has indicated the complexity of issues and volume of materials associated with Pebble's case means the review will likely take additional time.

On January 22, 2021, the State of Alaska, acting in its role as owner of the Pebble Deposit, also submitted a request for appeal. The state appeal was rejected on the basis that the State did not have standing to pursue an administrative appeal with the USACE.

As described in the 2018 and previous technical reports, the estimates suggest Pebble Deposit contains significant amounts of copper, gold, molybdenum and silver. The Pebble Deposit can also supply important products for alternative energy and other purposes of strategic national significance to the United States such as rhenium and palladium.

In September 2020, Northern Dynasty published a Technical Report on the Pebble Project. The purpose of that report was to document recent studies of the occurrence of rhenium and to estimate the rhenium mineral resources in the deposit. Previous work also determined palladium is also present, at least in parts of the deposit; however, insufficient analytical analyses have been completed to date to undertake a resource estimate. The report also summarized the proposed plan for the project as documented in the June 2020 Project Description and FEIS.

The purpose of this report is to update the current status of the EIS process for the Pebble Project, given the decisions of the USACE. No changes have been made to the resource estimate from the September 2020 Technical Report; however, information on closure has also been added to the Project Description and Permitting section.

The Pebble Project is located in southwest Alaska, approximately 200 miles southwest of Anchorage, 17 miles northwest of the village of Iliamna, 100 miles northeast of Bristol Bay, and approximately 60 miles west of Cook Inlet (Figure 1.2-1).

Figure 1.2-1 Property Location Map

Northern Dynasty holds, indirectly through Pebble East Claims Corporation and Pebble West Claims Corporation, wholly-owned subsidiaries of the Pebble Partnership, a 100% interest in a contiguous block of 2,402 mining claims and lease hold locations covering approximately 417 square miles (which includes the Pebble Deposit).

Pebble is a porphyry-style copper-gold-molybdenum-silver-rhenium deposit that comprises the Pebble East and Pebble West zones of approximately equal size, with slightly lower-grade mineralization in the center of the deposit where the two zones merge. The Pebble deposit is located at the intersection of crustal-scale structures that are oriented both parallel and obliquely to a magmatic arc which was active in the mid-Cretaceous and which developed in response to the northward subduction of the Pacific Plate beneath the Wrangellia Superterrane.

The oldest rock within the Pebble district is the Jurassic-Cretaceous age Kahlitna flysch, composed of turbiditic clastic sedimentary rocks, interbedded basalt flows and associated gabbro intrusions. During the mid-Cretaceous (99 to 96 Ma), the Kahlitna assemblage was intruded first by approximately coeval granodiorite and diorite sills and slightly later by alkalic monzonite intrusions. At approximately 90 Ma, hornblende diorite porphyry plutons of the Kaskanak batholith were emplaced. Copper-gold-molybdenum-silver-rhenium mineralization is related to smaller granodiorite plutons and dykes that are similar in composition to, and emplaced near and above the margins of, the Kaskanak batholith.

The Pebble East and Pebble West zones are coeval hydrothermal centers within a single magmatic-hydrothermal system. The movement of mineralizing fluids was constrained by a broadly vertical fracture system acting in conjunction with a hornfels aquitard that induced extensive lateral fluid migration. The large size of the deposit, as well as variations in metal grade and ratios, may be the result of multiple stages of metal introduction and redistribution.

Mineralization in the Pebble West zone extends from surface to approximately 3,000 ft depth and is centered on four small granodiorite plutons. Mineralization is hosted by flysch, diorite and granodiorite sills, and alkalic intrusions and breccias. The Pebble East zone is of higher grade and extends to a depth of at least 5,810 ft; mineralization on the eastern side of the zone was later dropped 1,970 to 2,950 ft by normal faults which bound the northeast-trending East Graben. East zone mineralization is hosted by a granodiorite plutons and dykes, and by adjacent granodiorite sills and flysch. The East and West zone granodiorite plutons merge with depth.

Mineralization at Pebble is predominantly hypogene, although the Pebble West zone contains a thin zone of variably developed supergene mineralization overlain by a thin leached cap. Disseminated and vein-hosted copper-gold-molybdenum-silver-rhenium mineralization, dominated by chalcopyrite and locally accompanied by bornite, is associated with early potassic alteration in the shallow part of the Pebble East zone and with early sodic-potassic alteration in the Pebble West zone and deeper portions of the Pebble East zone. Rhenium occurs in molybdenite and high rhenium concentrations are present in molybdenite concentrates. Elevated palladium concentrations occur in many parts of the deposit but are highest in rocks affected by advanced argillic alteration. High-grade copper-gold mineralization is associated with younger advanced argillic alteration that overprinted potassic and sodic-potassic alteration and was controlled by a syn-hydrothermal, brittle-ductile fault zone located near the eastern margin of the Pebble East zone. Late quartz veins introduced additional molybdenum into several parts of the deposit.

The current resource estimate is based on approximately 59,000 assays obtained from 699 drill holes. The resource was estimated by ordinary kriging and is presented in Table 1.5-1. The tabulation is based on copper equivalency (CuEq) that incorporates the contribution of copper, gold and molybdenum. Although the estimate includes silver and rhenium, neither were used as part of the copper equivalency calculation in order to facilitate comparison with previous estimates which did not consider the economic contribution of either of these metals. The highlighted 0.3% CuEq cut off is considered appropriate for deposits of this type in the Americas.

Table 1.5-1 Pebble Resource Estimate August 2020

Cutoff CuEq %	CuEq%	Metric Tonnes	Cu (%)	Au (g/t)	Mo (ppm)	Ag (g/t)	Re (ppm)	Cu Blb	Au Moz	Mo Blb	Ag Moz	Re Kkg
Measured
0.3	0.65	527,000,000	0.33	0.35	178	1.7	0.32	3.83	5.93	0.21	28.1	167
0.4	0.66	508,000,000	0.34	0.36	180	1.7	0.32	3.81	5.88	0.20	27.4	163
0.6	0.77	279,000,000	0.40	0.42	203	1.8	0.36	2.46	3.77	0.12	16.5	100
1.0	1.16	28,000,000	0.62	0.62	302	2.3	0.52	0.38	0.56	0.02	2.0	14
Indicated
0.3	0.77	5,929,000,000	0.41	0.34	246	1.7	0.41	53.58	64.81	3.21	316.4	2,443
0.4	0.82	5,185,000,000	0.45	0.35	261	1.8	0.44	51.42	58.35	2.98	291.7	2,271
0.6	0.99	3,455,000,000	0.55	0.41	299	2.0	0.51	41.88	45.54	2.27	221.1	1,748
1.0	1.29	1,412,000,000	0.77	0.51	343	2.4	0.60	23.96	23.15	1.07	109.9	853
Measured + Indicated
0.3	0.76	6,456,000,000	0.40	0.34	240	1.7	0.41	56.92	70.57	3.42	344.6	2,615
0.4	0.81	5,693,000,000	0.44	0.35	253	1.8	0.43	55.21	64.06	3.18	320.3	2,431
0.6	0.97	3,734,000,000	0.54	0.41	291	2.0	0.50	44.44	49.22	2.40	237.7	1,848
1.0	1.29	1,440,000,000	0.76	0.51	342	2.4	0.60	24.12	23.61	1.08	112.0	867
Inferred
0.3	0.55	4,454,000,000	0.25	0.25	226	1.2	0.36	24.54	35.80	2.22	170.4	1,603
0.4	0.68	2,646,000,000	0.33	0.30	269	1.4	0.44	19.24	25.52	1.57	119.1	1,154
0.6	0.89	1,314,000,000	0.48	0.37	292	1.8	0.51	13.90	15.63	0.85	75.6	673
1.0	1.20	361,000,000	0.68	0.45	377	2.3	0.69	5.41	5.22	0.30	26.3	251

Notes:

David Gaunt, P.Geo., a qualified person as defined under 43-101 who is not independent of Northern Dynasty, is responsible for the estimate.

Copper equivalent (CuEQ) calculations use metal prices: US$1.85/lb for Cu, US$902/oz for Au and US$12.50/lb for Mo, and recoveries: 85% Cu, 69.6% Au, and 77.8% Mo (Pebble West zone) and 89.3% Cu, 76.8% Au, 83.7% Mo (Pebble East zone).

Contained metal calculations are based on 100% recoveries.

A 0.30% CuEQ cut-off is considered to be appropriate for porphyry deposit open pit mining operations in the Americas.

The mineral resource estimate is constrained by a conceptual pit shell that was developed using a Lerchs-Grossman algorithm and is based in the following parameters: 42 degree pit slope; metal prices and recoveries of US$1,540.00/oz and 61% Au, US$3.63/lb and 91% Cu, US$20.00/oz and 67% Ag and US$12.36/lb and 81% Mo, respectively; a mining cost of US$1.01/ton with a US$0.03/ton/bench increment and other costs (including processing, G&A and transport) of US$6.74/ton.

All mineral resource estimates, cut-offs and metallurgical recoveries are subject to change as a consequence of more detailed analyses that would be required in pre-feasibility and feasibility studies.

The terms 'Measured Resources', 'Indicated Resources' and 'Inferred Resources' are recognized and required by Canadian regulations under 43-101. The SEC has adopted amendments to its disclosure rules to modernize the mineral property disclosure required for issuers whose securities are registered with the SEC under the US Securities Exchange Act of 1934, effective February 25, 2019, that adopt definitions of the terms and categories of resources which are 'substantially similar' to the corresponding terms under Canadian Regulations in 43-101. Accordingly, there is no assurance any mineral resources that we may report as Measured Resources, Indicated Resources and Inferred Resources under 43-101 would be the same had we prepared the resource estimates under the standards adopted under the SEC Modernization Rules. Investors are cautioned not to assume that all or any part of mineral deposits in these categories will ever be converted into reserves. In addition, Inferred Resources have a great amount of uncertainty as to their economic and legal feasibility. Under Canadian rules, estimates of Inferred Resources may not form the basis of feasibility or pre-feasibility studies, or economic studies except for a Preliminary Economic Assessment as defined under 43-101.

The mineral resource estimates contained herein have not been adjusted for any risk that the required environmental permits may not be obtained for the Pebble Project. The risk associated with the ability of the Pebble Project to obtain required environmental permits is a risk to the reasonable prospects for eventual economic extraction of the mineralisation and their definition as a mineral resource.

Metallurgical testwork for the Pebble Project was initiated by Northern Dynasty in 2003 and continued under the direction of Northern Dynasty until 2008. From 2008 to 2013, metallurgical testwork progressed under the direction of the Pebble Partnership.

Geometallurgical studies were initiated by the Pebble Partnership in 2008 and continued through 2012. The principal objective of this work was to quantify significant differences in metal deportment that may result in variations in metal recoveries during mineral processing. The results of the geometallurgical studies indicate that the deposit comprises several geometallurgical (or material type) domains. These domains are defined by distinct, internally consistent copper and gold deportment characteristics that correspond spatially with changes in silicate and sulphide alteration mineralogy.

Metallurgical testwork and associated analytical procedures were performed by recognized testing facilities with extensive experience with this analysis, with this type of deposit, and with the Pebble Project. The samples selected for the comminution, copper/gold/molybdenum bulk flotation, and copper molybdenum separation testing were representative of the various types and styles of mineralization at the Pebble deposit.

A conventional flotation process is proposed to produce copper concentrate and molybdenum concentrate. The flotation test results on variability samples derived from the 103 locked cycle flotation and the subsequent copper-molybdenum separation flotation tests indicate that marketable copper and molybdenum concentrates can be produced. The copper concentrate will also contain gold and silver contents that meet or exceed payable levels in representative smelter contracts; the molybdenum concentrate will contain significant rhenium (Re), with a reported grade range from 791 to 832 g/t Re observed in the locked cycle test (LCT) results of the copper-molybdenum separation.

A preliminary hydrometallurgical test program was performed on rougher and cleaner molybdenum concentrates to investigate the production of the marketable products of molybdenum trioxide (MoO3) and ammonium perrhenate (NH4ReO4). The test program included pressure oxidation leach, a series of metal extractions/purifications from the pregnant leach solution, and a calcination process. The tested methods were found technically feasible. Satisfactory dissolution rates of molybdenum and rhenium were obtained from the rougher molybdenum concentrate samples, while additional alkaline leach is required on the pressure oxidation leach residues for the cleaner molybdenum concentrate samples.

In this technical report, the metal recovery projections of copper, gold, silver and molybdenum stay the same as those published in the 2018 technical report. A rhenium recovery estimate at a high level has been completed and included. Table 1.6-1 provides projected metals recoveries via flotation concentration for metals and a gravity circuit for gold. The recovery estimate bases are summarized as follows:

Table 1.6-1 Projected Metallurgical Recoveries - 2018, Tetra Tech

Domain	Flotation Recovery %
Cu Con, 26% Cu	Mo Con, 50% Mo
Cu	Au	Ag	Mo	Re
Supergene:
Sodic Potassic	78.7	63.6	67.5	53.9	70.8
Illite Pyrite	72.1	46.5	67.8	66.3	70.8
Hypogene:
Illite Pyrite	89.8	45.6	66.6	76.1	70.8
Sodic Potassic	90.1	63.2	67.0	80.1	70.8
Potassic	93.7	63.6	66.5	85.4	70.8
Quartz Pyrophyllite	94.7	65.2	64.4	80.4	70.8
Sericite	89.6	40.6	66.5	75.9	70.8
Quartz Sericite Pyrite	89.8	32.9	66.9	86.1	70.8

The Pebble deposit is located on state land that has been specifically designated for mineral exploration and development. The project area has been the subject of two comprehensive land-use planning exercises conducted by the Alaska Department of Natural Resources (ADNR), the first in the 1980s and the second completed in 2005. ADNR identified five land parcels (including Pebble) within the Bristol Bay planning area as having 'significant mineral potential,' and where the planning intent is to accommodate mineral exploration and development. These parcels total 2.7% of the total planning area (ADNR, 2005).

Environmental standards and permitting requirements in Alaska are stable, objective, rigorous and science-driven. These features are an asset to projects like Pebble that are being designed to meet U.S. and international best practice standards of design and performance.

Northern Dynasty began an extensive field study program in 2004 to characterize the existing physical, chemical, biological, and social environments in the Bristol Bay and Cook Inlet areas where the Pebble Project might occur. The Pebble Partnership compiled the data for the 2004-2008 study period into a multi-volume Environmental Baseline Document (EBD, PLP, 2012). These studies have been designed to:

Additional data collected from the 2009-2013 period was compiled into the Supplemental EBD (PLP, 2018) and transmitted to USACE. In 2017, select environmental baseline studies were re-initiated and expanded. Monitoring data collected through 2019 has been provided to USACE.

The baseline study program includes:

surface water hydrology	wildlife
groundwater hydrology	air quality
surface and groundwater quality	cultural resources
Geochemistry	subsistence
snow surveys	land use
fish and aquatic resources	recreation
noise	socioeconomics
Wetlands	visual aesthetics
trace elements	climate and meteorology
fish habitat - stream flow modeling	Iliamna Lake
marine

The FEIS published by the USACE on July 24, 2020 culminated a 2 ½-year long, intensive review process under the National Environmental Policy Act (NEPA). Led by the USACE, the Pebble FEIS also involved eight federal cooperating agencies (including the US Environmental Protection Agency (EPA) and US Fish & Wildlife Service), three state cooperating agencies (including the Alaska Department of Natural Resources and the Alaska Department of Environmental Conservation), the Lake & Peninsula Borough and federally recognized tribes.

The FEIS was viewed by the Company as positive in that it found impacts to fish and wildlife would not be expected to affect subsistence harvest levels, there would be no measurable change to the commercial fishing industry including prices, and a number of positive socioeconomic impacts on local communities.

The CWA 404 Permit Application was submitted in December 2017, and the permitting process over the next three years involved the Pebble Partnership being actively engaged with the USACE on the evaluation of the Pebble Project. There were numerous meetings between representatives of the USACE and the Pebble Partnership regarding, among other things, compensatory mitigation for the Pebble Project. The Pebble Partnership submitted several draft compensatory mitigation plans to the USACE, each refined to address comments from the USACE and that the Pebble Partnership believed were consistent with mitigation proposed and approved for other major development projects in Alaska. In late June 2020, USACE verbally identified the 'significant degradation' of certain aquatic resources, with the requirement of new compensatory mitigation. The Pebble Partnership understood from these discussions that the new compensatory mitigation plan for the Pebble Project would include in-kind, in-watershed mitigation and continued its work to meet these new USACE requirements.

The USACE formally advised the Pebble Partnership by letter dated August 20, 2020 that it had made preliminary factual determinations under Section 404(b)(1) of the CWA that the Pebble Project as proposed would result in significant degradation to aquatic resources. In connection with this preliminary finding of significant degradation, the USACE formally informed the Pebble Partnership that in-kind compensatory mitigation within the Koktuli River watershed would be required to compensate for all direct and indirect impacts caused by discharges into aquatic resources at the mine site. The USACE requested the submission of a new compensatory mitigation plan to address this finding within 90 days of its letter. Accordingly, the Pebble Partnership developed a compensatory mitigation plan to align with the requirements outlined by the USACE. This plan envisioned creation of a 112,445-acre Koktuli Conservation Area on land belonging to the State of Alaska in the Koktuli River watershed downstream of the Project. The objective of the preservation of the Koktuli Conservation Area was to allow the long-term protection of a large and contiguous ecosystem that contains valuable aquatic and upland habitats. If adopted, the Koktuli Conservation Area would preserve 31,026 acres of aquatic resources within the 'aquatic resource of national importance'-designated Koktuli River watershed. The conservation area was selected to protect and preserve physical, chemical, and biological functions highlighted as important in the project review. Preservation of the Koktuli Conservation Area was proposed with the objective of minimizing the threat to, and preventing the decline of, aquatic resources in the Koktuli River watershed from potential future actions, with the objective of ensuring the sustainability of fish and wildlife species that depend on these aquatic resources, while protecting the subsistence lifestyle of the residents of Bristol Bay and commercial and recreational sport fisheries. The plan was submitted to the USACE on November 4, 2020.

On November 25, 2020, the USACE issued a ROD rejecting the Pebble Partnership's permit application. The ROD rejected the CMP as 'non-compliant' and determined the project would cause 'Significant Degradation' and be contrary to the public interest. Accordingly, the USACE rejected Pebble Partnership's permit application.

The Pebble Partnership submitted its request for appeal of the ROD on January 19, 2021. The request for appeal reflects the Pebble Partnership's position that the USACE's ROD and permitting decision - including its 'Significant Degradation' finding, its 'public interest review' findings, and its perfunctory rejection of the Pebble Partnership's CMP - are contrary to law, unprecedented in Alaska, and fundamentally unsupported by the administrative record, including the Pebble Project FEIS. The reasons for appeal asserted by the Pebble Partnership include: (i) the finding of 'Significant Degradation' by the USACE is contrary to law and unsupported by the record; (ii) the USACE's rejection of the CMP is contrary to the USACE regulations and guidance, including the failure to provide the Pebble Partnership with an opportunity to correct the alleged deficiencies; and (iii) the determination by the USACE that the Pebble Project is not in the public interest is contrary to law and unsupported by the public record. In a letter dated February 24, 2021, the USACE confirmed the Pebble Partnership's RFA is 'complete and meets the criteria for appeal.' The USACE has appointed a Review Officer to oversee the administrative appeal process. The appeal process will now move to consideration by the USACE of the merits of the appeal. The appeal will be reviewed by the USACE based on the administrative record and any clarifying information provided, and the Pebble Partnership will be provided with a written decision on the merits of the appeal at the conclusion of the process. The appeal is governed by the policies and procedures of the USACE administrative appeal regulations. While federal guidelines suggest the appeal should conclude within 90 days, the USACE has indicated the complexity of issues and volume of materials associated with Pebble's case means the review will likely take additional time.

On January 22, 2021, the State of Alaska, acting in its role as owner of the Pebble Deposit, announced that it also had filed a request for appeal. The state appeal was rejected on the basis that the State did not have standing to pursue an administrative appeal with the USACE.

On December 22, 2017, the Pebble Partnership submitted its CWA 404 permit application in which it is envisaged that the Pebble copper-gold-molybdenum porphyry deposit would be developed as an open pit mine, with associated on and off-site infrastructure. Over the course of past two years, additional engineering work completed to support the environmental assessment process, as well as recommendations from USACE in the FEIS, has resulted in some modifications to the plan and the Project Description has been updated accordingly. Project infrastructure includes:

Following four years of construction activity, the proposed Pebble mine will operate for a period of 20 years using conventional drill-blast-shovel operations. The mining rate will average 70 million tons per year, with 66 million tons of mineralized material processed through the mill each year (180,000 tons per day), for an extremely low life-of-mine waste to mineralized material ratio of 0.12:1.

The development proposed in Pebble's Project Description is substantially smaller than previous iterations, and presents significant new environmental safeguards, including:

The project proposed in the Project Description uses a portion of the currently estimated Pebble mineral resources. This does not preclude development of additional resources in other phases of the project in the future, but such development would require additional evaluation and would be subject to separate permitting processes.

The resource estimate documented herein confirms the presence of rhenium, a strategic metal, as a component of the Pebble deposit and demonstrates the Pebble Deposit is among the largest accumulations of rhenium in the world.

Products from mining this deposit, including rhenium, support development of alternative energy supply and other purposes of strategic national significance. The Pebble Project would have significant regional economic importance for southwest Alaska and the entire state through the creation of high-wage jobs and training opportunities, supply and service contracts for local businesses, and government revenue.

Based on the work carried out, this study should be followed by further technical and economic studies leading to an advancement of the project to the next level of development.

This study assessed and estimated the amount of rhenium in the Pebble deposit. Elevated levels of palladium, vanadium, titanium and tellurium have been noted in raw analytical data and in metallurgical studies. A scoping level program is recommended to determine their potential for inclusion in future resource estimates. Such a study would focus on these metals' deportment, distribution and the best approach to their quantification.

$100,000

Review metallurgical testwork to date to identify opportunities to optimize treatment of supergene mineralization within the deposit, and provide recommendations on future sampling and testwork.

$50,000

Complete an initial assessment of potential treatment methods of molybdenum concentrates to optimize the value of molybdenum and rhenium.

$50,000

The Pebble property hosts a globally significant deposit of copper, gold, molybdenum, silver and rhenium on state lands in southwest Alaska designated for mineral exploration and development.

Alaska was granted statehood in 1959 along with 28% of the state's land base for the explicit purpose of developing land and resources to support the state's government and citizenry. The Alaska State Constitution states: 'It is the policy of the State of Alaska … to encourage the development of its resources by making them available for maximum use consistent with the public interest.' The lands surrounding Pebble within the Bristol Bay Area Plan were received by the State from the U.S. government as part of the three-way Cook Inlet Land Exchange of 1976 and were recognized by the State at that time for their mineral prospectivity.

The Pebble deposit was originally discovered in 1989 and was acquired by Northern Dynasty in 2001. Since that time, Northern Dynasty and subsequently the Pebble Partnership1 have conducted significant mineral exploration, environmental baseline data collection, and engineering work on the Pebble Project.

Northern Dynasty commissioned this technical report to document the results of a study of rhenium to include rhenium in the mineral resource estimate and to update status of the Pebble Project based on work since 2017.

Northern Dynasty is a mineral exploration and development company based in Vancouver, Canada, and publicly traded on the Toronto Stock Exchange under the symbol 'NDM' and on the NYSE American exchange under the symbol 'NAK'. Northern Dynasty is currently the sole owner of the Pebble Partnership which owns the Pebble Project.

The authors have prepared this technical report for Northern Dynasty in general accordance with the guidelines provided in National Instrument (NI) 43-101 Standards of Disclosure for Mineral Projects.

The main purpose of this technical report is to update the status of the Pebble Project since the previous Technical Report was issued in September 2020. The resource estimate and Project Description incorporated in the September 2020 report have not been revised.

1Additional information on the history of the Pebble Partnership and Pebble Project is provided in Section 6.0.

Information and studies obtained from Northern Dynasty and the Pebble Partnership for the 2021 Technical Report include:

Information and studies from third-party sources used for this report are included in the references. The authors have reviewed and used information from the latter sources under the assumption that the information is accurate.

The principal units of measure used in this report are U.S. Standard Units. Exceptions are noted and include the mineral resource estimate, and other instances dictated by convention. Monetary amounts are in United States dollars, unless otherwise stated.

The Qualified Persons (QPs) responsible for this technical report and the dates of their most recent site visits2 are tabulated below.

Section	Report Section	Qualified Person & Professional Accreditation	Date of Last Site Visit
1.0	Summary	All; sign off by discipline
2.0	Introduction	Stephen Hodgson, PEng	Oct 2019
3.0	Reliance on Other Experts	Stephen Hodgson, PEng
4.0	Property Description and Location	Stephen Hodgson, PEng
5.0	Accessibility, Climate, Local Resources, Infrastructure and Physiography	Stephen Hodgson, PEng
6.0	History	Eric Titley, PGeo/ David Gaunt, PGeo/James Lang, PGeo
7.0	Geological Setting and Mineralization	James Lang, PGeo	July 2019
8.0	Deposit Types	James Lang, PGeo
9.0	Exploration	James Lang, PGeo
10.0	Drilling	Eric Titley, PGeo/ James Lang, PGeo
11.0	Sample Preparation, Analyses and Security	Eric Titley, PGeo	Sept 2011
12.0	Data Verification	All; sign off by discipline
13.0	Mineral Processing and Metallurgical Testing	Hassan Ghaffari, PEng	Sept 2010
14.0	Mineral Resource Estimates	David Gaunt, PGeo	Sept 2010
15.0	Adjacent Properties	James Lang, PGeo
16	Other Relevant Data and Information	Stephen Hodgson, PEng
17.0	Interpretation and Conclusions	All; sign off by discipline
18.0	Recommendations	All; sign off by discipline
19.0	References	All
20.0	Certificates

2All Qualified Persons are not independent of Northern Dynasty with the exception of Hassan Ghaffari.

Standard professional procedures were followed in preparing the contents of this report. Data used in this report has been verified where possible and the authors have no reason to believe that the data was not collected in a professional manner.

A QP has not independently verified the legal status or title of the claims or exploration permits, and has not investigated the legality of any of the underlying agreement(s) that may exist concerning the Pebble property, and has relied on legal counsel in terms of the confirmation of these matters.

In some cases, the QPs are relying on reports, opinions, and statements from experts who are not QPs for information concerning legal, environmental and socio-economic factors relevant to the technical report.

The following QPs who prepared this report relied on information provided by a number of experts who are not QPs:

The Pebble property is located in southwest Alaska, approximately 200 miles southwest of Anchorage, 17 miles northwest of the village of Iliamna, 100 miles northeast of Bristol Bay, and approximately 60 miles west of Cook Inlet (Figure 1.2-1).

The property is centred, approximately, at latitude 59°53′54' N and longitude 155°17′44' W, and is located on the United States Geological Survey (USGS) topographic maps Iliamna D6 and D7, in Townships 2-5 South, Ranges 33-38 West, Seward Meridian.

The Pebble Partnership uses the U.S. State Plane Coordinate System (as Alaska 5005) as the preferred grid, measured in feet.

Northern Dynasty holds indirectly through Pebble East Claims Corporation and Pebble West Claims Corporation, wholly-owned subsidiaries of the wholly-owned Pebble Partnership, a 100% interest in a contiguous block of 2,402 administratively active mining claims and leasehold locations covering approximately 417 square miles (which includes the Pebble Deposit). Teck Resources Limited (Teck) holds a 4% pre-payback net profits interest (after debt service), followed by a 5% after-payback net profits interest in any mine production from the Exploration Lands, which are shown in Figure 4.2-1 and further described in Section 6.0 History.

In June 2020, the Pebble Partnership established the Pebble Performance Dividend LLP to distribute a 3% Net Profits Royalty Interest in the Pebble Project to adult residents of Bristol Bay villages that have subscribed as participants. The Pebble Performance Dividend will distribute a guaranteed minimum annual payment of US $3 million each year the Pebble mine operates beginning at the outset of project construction.

State mineral claims in Alaska are kept in good standing by performing annual assessment work or in lieu of assessment work by paying $100 per year per 40 acre (0.06 square mile) mineral claim, and by paying annual escalating state rental fees each year. Assessment work is due annually by noon of September 1. However, credit for excess assessment work can be banked for a maximum of four years after work is performed, and can be applied as necessary to continue to hold the claims in good standing. The Project claims have a variable amount of assessment work credit available that can be applied in this way. Annual assessment work obligations for the property total some US$667,700 and annual state rentals for 2020 are approximately US$1,375,910 and are payable no later than 90 days after the assessment work is due (approximately December 1).

The details of the administratively active mining claims and leasehold locations are provided below in Table 4.2-1 (ADL refers to the Alaska Department of Lands).

The claim boundaries have not been surveyed.

Figure 4.2-1 Mineral Claim Map with Exploration Lands and Resource Lands

Table 4.2-1 Pebble Mineral Claims

Northern Dynasty Minerals Ltd.

2021 Technical Report on the

Pebble Project, Southwest Alaska

Page 27

Northern Dynasty currently does not own surface rights associated with the mineral claims that comprise the Pebble property. All lands are held by the State of Alaska, and surface rights may be acquired from the state government once areas required for mine development have been determined and permits awarded.

Environmental liabilities associated with the Pebble Project include removal of structures and equipment, closure of monitoring wells, and removal of piezometers. The State of Alaska holds a $2 million reclamation security associated with removal and reclamation of these liabilities.

Permits necessary for exploration drilling and other field programs associated with pre-development assessment of the Pebble Project are obtained as required each year.

The Pebble property is located in southwest Alaska (see Figure 5.1-1). The map shows a proposed infrastructure corridor for the project, as further described as the LEDPA in the FEIS and in Section 16.5 of this report.

Figure 5.1-1 Property Location and Access Map

Access to the property is typically via air travel from the city of Anchorage, which is situated at the northeastern end of Cook Inlet and is connected to the national road network via Interstate Highway 1 through Canada to the USA. Anchorage is serviced daily by several regularly scheduled flights to major airport hubs in the USA.

From Anchorage, there are regular flights to Iliamna through Iliamna Air Taxi. Charter flights may also be arranged from Anchorage. From Iliamna, access to the Pebble property is by helicopter.

The climate of the Pebble Project area is transitional; it is more continental in winter because of frozen water bodies and more maritime in summer because of the influence of the open water of Iliamna Lake and, to a lesser extent, the Bering Sea and Cook Inlet. Mean monthly temperatures in the deposit area range from about 11.4 °F in January to 50.8 °F in July (at the Pebble 1 meteorological station). The mean annual precipitation in the deposit area is estimated to be 54.6 inches (at the Pebble 1 meteorological station). About one-third of this precipitation falls as snow. The wettest months are August through October.

The climate is sufficiently moderate to allow a well-planned mineral exploration program to be conducted year-round (Rebagliati, C.M., and Haslinger, R.J., 2003) at Pebble.

There is a modern airfield at Iliamna, with two paved 4,920 ft airstrips, that services the communities of Iliamna and Newhalen. The runways are suitable for DC-6 and Hercules cargo aircraft and for commercial jet aircraft.

There are paved roads that connect the villages of Iliamna and Newhalen to the airport and to each other and a partly paved, partly gravel road that extends to a proposed Newhalen River crossing near Nondalton. The property is currently not connected to any of these local communities by road; a road would be planned as part of the project design.

There is no access road that connects the communities nearest the Pebble Project to the coast on Cook Inlet. From the coast, at Williamsport on Iniskin Bay, there is an 18.6 mile state-maintained road that terminates at the east end of Iliamna Lake, where watercraft and transport barges may be used to access Iliamna. The route from Williamsport, over land to Pile Bay on Iliamna Lake, is currently used to transport bulk fuel, equipment and supplies to communities around the lake during the summer months.

Also during summer, supplies have been barged up the Kvichak River, approximately 43.4 miles southwest of Iliamna, from Kvichak Bay on the North Pacific Ocean.

A small run-of-river hydroelectric installation on the nearby Tazamina River provides power for the three communities in the summer months. Supplemental power generation using diesel generators is required during winter months.

Iliamna and surrounding communities have a combined population of just over 400 people. As such, there is limited local commercial infrastructure except that which services seasonal sports fishing and hunting.

The property is situated at approximately 1,000 ft amsl in an area described as subarctic tundra. It is characterized by gently rolling hills and an absence of permafrost.

From Rebagliati, C.M., and Haslinger, J.M., 2003:

The Pebble property lies 80.5 km (50 miles) west of the Alaska Range in the Nushagak-Big River Hills, an area of rolling hills and low mountains separated by wide, shallow valleys blanketed with glacial deposits that contain numerous small, shallow lakes and are cut by several major meandering streams. The elevation ranges from 250 m (820 ft) amsl to 841 m (2,758 ft) amsl at Kaskanak Peak, the highest point on the property.

Tundra plant communities (mixtures of shrub and herbaceous plants) cover the project area. Willow is common only along streams, and sparse patches of dense alder are confined to better drained areas where coarse soils have developed. Poorly drained regions underlain by fine soils support dwarf birch and grasses (Detterman and Reed, 1973).

Cominco Alaska, a division of Cominco Ltd., now Teck Resources Limited (Teck), began reconnaissance exploration in the Pebble region in the mid-1980s and in 1984 discovered the Sharp Mountain gold prospect near the southern margin of the current property. Gold was discovered in drusy quartz veins of probable Tertiary age near the peak of Sharp Mountain (anonymous Teck report, 1984). Grab samples of veins in talus ranged from 0.045 oz/ton Au to 9.32 oz/ton Au and 3.0 oz/ton Ag. No record of further work is available, but similar quartz veins were encountered in 2004 during surface mapping of the property conducted by Northern Dynasty. Most of these veins trend north-south and dip steeply.

In 1987, examination and sampling of several prominent limonitic and hematitic alteration zones yielded anomalous gold concentrations from the Sill prospect, which was recognized as a precious-metal, epithermal-vein occurrence, and from outcrops over and surrounding what later became the Pebble area, but which at that time was of uncertain affinity. These discoveries were followed by several years of exploration including soil sampling, geophysical surveys and diamond drilling.

Geophysical surveys were conducted on the property between 1988 and 1997. The surveys were dipole-dipole induced polarization (IP) surveys for a total of 122 line-km, and were completed by Zonge Geosciences. This work defined a chargeability anomaly about 31.1 square miles in extent within Cretaceous age rocks which surround the eastern to southern margins of the Kaskanak batholith. The anomaly measures about 13 miles north-south and up to 6.3 miles east-west; the western margin of the anomaly overlaps the contact of the Kaskanak batholith, whereas to the east the anomaly is masked by Late Cretaceous to Eocene cover sequences. The broader anomaly was found to contain 11 distinct centres with stronger chargeability, many of which were later demonstrated to be coincident with extensive copper, gold and molybdenum soil geochemical anomalies. All known zones of mineralization of Cretaceous age on the Pebble property occur within the broad IP anomaly.

Diamond drilling was first conducted on the property during the 1988 exploration program which included 24 diamond drill holes at the Sill epithermal gold prospect soil sampling, geological mapping, two diamond drill holes at the Pebble target) and three holes totalling 893 ft on a target (later named the 25 Gold Zone by Northern Dynasty) located 3.7 miles south of the Pebble deposit.

Drilling at the Sill prospect intersected mineralization with gold grades that justified further exploration, but the initial Pebble drill holes yielded only modest encouragement. In 1989, an expanded soil-sampling program, the initial stages of the induced polarization (IP) surveys described above and nine diamond drill holes were completed at the Pebble target, 15 diamond drill holes were completed at the Sill prospect and three diamond drill holes were completed elsewhere on the property. Although limited in scope, the IP survey at Pebble displayed response characteristics of a large porphyry-copper system. Subsequent drilling by Teck intersected significant intervals of porphyry-style gold, copper and molybdenum mineralization, validating this interpretation.

Table 6.1-1 Teck Drilling on the Sill Prospect to the End of 1997

Year	No. of Drill Holes	Feet	Metres
1988	24	7,048	2,148
1989	15	3,398	1,036
Total	39	10,446	3,184

Table 6.1-2 Teck Drilling on the Pebble Deposit to the End of 1997

Year	No. of Drill Holes	Feet	Metres
1988	2	554	169
1989	9	3,131	954
1990	25	10,021	3,054
1991	48	28,129	8,574
1992	14	6,609	2,014
1997	20	14,696	4,479
Total	118	63,140	19,245

Exploration was accelerated when it became apparent that a significant copper-gold porphyry deposit had been discovered at Pebble. In 1990 and 1991, 25 and 48 diamond drill holes, respectively, were completed. In 1991, baseline environmental and engineering studies were initiated and weather stations were established. A preliminary economic evaluation was undertaken by Teck in 1991, and was updated in 1992 on the basis of 14 new diamond drill holes. In 1993, an IP survey and a four-hole diamond-drill program were completed at the target that was later named the 25 Gold Zone. In 1997, Teck completed an IP survey, geochemical sampling, geological mapping and 20 diamond drillholes within and near the Pebble deposit).

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From 1988 to 1995, Teck undertook several soil geochemical surveys on the property and collected a total of 7,337 samples (Bouley et al., 1995).

Table 6.1-3 Total Teck Drilling on the Property to the End of 1997

Year	No. of Drill Holes	Feet	Metres
1988	26	7,602	2,317
1989	27	7,422	2,262
1990	25	10,021	3,054
1991	48	28,129	8,574
1992	14	6,609	2,014
1993	4	1,263	385
1997	20	14,696	4,479
Total	164	75,741	23,086

Page 34

Teck drilled 125 holes in the Pebble area between 1988 and 1997 for a total of 65,295.5 ft. These holes include 118 holes drilled in what later became known as Pebble West and seven holes drilled elsewhere on the property. Of the Pebble West holes, 94 were drilled vertically and 20 were inclined from −45° to −70° at various orientations. Teck also completed 39 drill holes on the Sill prospect for a total of 10,445.5 ft in 1988 and 1989.

Teck drill core was transported from the drill site by helicopter to a logging and sampling site in the village of lIiamna. The core from within the Pebble deposit was typically sampled on 10 ft intervals and most core from Cretaceous age units was sampled. Samples from the Sill and other areas were typically 5 ft in length, with shorter samples in areas of vein mineralization. Samples consisted of mechanically-split drill core. The samples were transported by air charter to Anchorage and by air freight to Vancouver, BC. All coarse rejects from 1988 through 1997 and all pulps from 1988 and most from 1989 have been discarded. The remaining pulps were later shipped by Northern Dynasty to a secure warehouse at Surrey, BC, for long-term storage.

Teck samples collected prior to the 1997 program were prepared and analyzed by ALS Minerals (ALS) Laboratories in North Vancouver, BC (formerly Chemex Labs Inc.). The core samples were processed by drying, weighing, crushing to 70% passing 10 mesh and then splitting to a 250 g sub-sample and a coarse reject; the 250 g sub-sample was pulverized to 85% passing 200 mesh.

Teck systematically assayed for gold in the Cretaceous intersections from all drill holes completed on the property from 1988 through 1997. Copper analysis was added when the Pebble porphyry discovery hole was drilled in 1989, and single element copper analysis continued for all Cretaceous intersections in 1989. Selective single element molybdenum assays and single element silver analyses were added to some holes in 1989. In 1990, Teck added multi-element analysis to the analytical protocol, which included the determination of copper, molybdenum, silver and 29 additional elements. In 1991 and 1992, some sections of core were analyzed using the multi-element analysis and some were analyzed using single element copper analysis. Only four holes were drilled by Teck in 1993, on targets well south of the Pebble deposit, and these were only assayed for gold and copper. No drilling was completed from 1994 to 1996. Drill holes completed in 1997 were analyzed with a multi-element package.

During the 1997 program, drill core samples were prepared by ALS Laboratories in Anchorage. A 250 g pulp sample was then submitted to Cominco Exploration and Research Laboratory (CERL) in Vancouver, BC, for copper analysis using an aqua regia (AR) digestion with inductively coupled plasma atomic emission spectroscopy (ICP-AES) finish. Gold was analyzed using fire assay (FA) on a one assay-ton sample with atomic absorption spectroscopy (AAS) finish. Trace elements also were analyzed by AR digestion and ICP-AES finish. One blind standard was inserted for every 20 samples analyzed. One duplicate sample was taken for every 10 samples analyzed.

Teck analyzed a total of 6,987 core samples from 164 drill holes, including 676 samples analyzed from 39 drill holes on the Sill prospect.

Teck prepared several resource estimates on the Pebble deposit during the 1990s, employing block models estimated with either kriging or inverse distance (ID) weighting. The cut-off grade used was 0.3% CuEq based on metal prices of $1.00/lb of copper and $375/oz of gold. These estimates are summarized in Table 6.3-1.

Table 6.3-1 Teck Resource Estimates

Year	Tonnage (million)		Cu (%)	Au (oz/ton)
1990	200		0.35	0.01
1991	500		0.35	0.01
1992	460		0.40	0.01
2000	1,000		0.30	0.01

These historical estimates are considered both relevant and reliable, as the methodology was consistent with industry standards at the time of estimation. The historical estimates are classified as Inferred. However, no QP has done sufficient work to evaluate these historical estimates and Northern Dynasty is not treating the historical estimates as current Mineral Resources. More recent estimates are described in Section 14.0.

The following summary of historical property agreements is taken from Rebagliati et al (2010).

In October 2001, Northern Dynasty acquired, through its Alaskan subsidiary, a two-part Pebble Property purchase option previously secured by Hunter Dickinson Group Inc. (HDGI) from an Alaskan subsidiary of Teck Cominco Limited, now Teck Resources Limited (Teck). In particular, HDGI assigned this two-part option (the Teck Option) as 80% to Northern Dynasty while retaining 20% thereof. The first part of the Teck Option permitted Northern Dynasty to purchase (through its Alaskan subsidiary) 80% of the previously drilled portions of the Pebble Property on which the majority of the then known copper mineralization occurred (the 'Resource Lands Option'). Northern Dynasty could exercise the Resource Lands Option through the payment of cash and shares aggregating US$10 million prior to November 30, 2004. The second part of the Teck Option permitted Northern Dynasty to earn a 50% interest in the exploration area outside of the Resource Lands (the 'Exploration Lands Option'). Northern Dynasty could exercise the Explorations Lands Option by doing some 18,288 m (60,000 ft) of exploration drilling by November 30, 2004, which it completed on time. The HDGI assignment of the Teck Option also allowed Northern Dynasty to purchase the other 20% of the Teck Option retained by HDGI for its fair value.

In November 2004, Northern Dynasty exercised the Resource Lands Option and acquired 80% of the Resource Lands. In February 2005, Teck elected to sell its residual 50% interest in the Exploration Lands to Northern Dynasty for US$4 million. Teck still retains a 4% pre-payback advance net profits royalty interest (after debt service) and 5% after-payback net profits interest royalty in any mine production from the Exploration Lands portion of the Pebble property.

In June 2006, Northern Dynasty acquired, through its Alaska subsidiaries, the remaining HDGI 20% interest in the Resource Lands and Exploration Lands by acquiring HDGI from its shareholders and through its various subsidiaries had thereby acquired an aggregate 100% interest in the Pebble Property, subject only to the Teck net-profits royalties on the Exploration Lands described above [see Section 4. At that time, Northern Dynasty operated the Pebble Property through a general Alaskan partnership with one of its subsidiaries.

In July 2007, the Pebble Partnership was created and an indirect wholly-owned subsidiary of Anglo American plc (Anglo American) subscribed for 50% of the Pebble Partnership's equity effective July 31, 2007. Over the next 6 years, Anglo American spent US$573 million on exploration, resource estimation, environmental data collection and technical studies, with a significant portion spent on engineering of possible mine development models, as well as related infrastructure, power and transportation systems prior to withdrawing from the project. In December 2013, Northern Dynasty exercised its right to acquire Anglo American's interest in the Pebble Partnership and now holds a 100% interest in the Pebble Partnership.

On December 15, 2017 Northern Dynasty entered into a Framework Agreement ('Framework Agreement') with First Quantum Minerals Ltd. ('First Quantum') which contemplated that an affiliate of First Quantum would subsequently execute an option agreement with Northern Dynasty (the 'Option Agreement') with an option payment of US$150 million staged over four years. This option would entitle First Quantum to acquire the right to earn a 50% interest in the Pebble Partnership for US$1.35 billion. First Quantum made an early option payment of US$37.5 million to Northern Dynasty, applied solely for the purposes of progressing the permitting of the Pebble Project but withdrew from the project in 2018.

On June 29, 2010, Northern Dynasty entered into an agreement with Liberty Star Uranium and Metals Corp. and its subsidiary, Big Chunk Corp. (together, 'Liberty Star'), pursuant to which Liberty Star sold 23.8 square miles of claims (the 95 'Purchased Claims') to a U.S. subsidiary of Northern Dynasty in consideration for both a $1 million cash payment and a secured convertible loan from Northern Dynasty in the amount of $3 million. The parties agreed, through various amendments to the original agreement, to increase the principal amount of the Loan by $730,174. Northern Dynasty later agreed to accept transfer of 199 claims (the Settlement Claims) located north of the ground held 100% by the Pebble Partnership in settlement of the Loan, and subsequently both the Purchased Claims and the Settlement Claims were transferred to an Northern Dynasty subsidiary and ultimately to Pebble West Claims Corporation, a subsidiary of the Pebble Partnership.

On January 31, 2012, the Pebble Partnership entered into a Limited Liability Company Agreement with Full Metal Minerals (USA) Inc. (FMMUSA), a wholly-owned subsidiary of Full Metal Minerals Corp., to form Kaskanak Copper LLC (the LLC). Under the agreement, the Pebble Partnership could earn a 60% interest in the LLC, which indirectly owned 100% of the Kaskanak claims, by incurring exploration expenditures of at least US$3 million and making annual payments of $50,000 to FMMUSA over a period ending on December 31, 2013. On May 8, 2013, the Pebble Partnership purchased FMMUSA's entire ownership interest in the LLC for a cash consideration of $750,000. As a result, the Pebble Partnership gained a 100% ownership interest in the LLC, the indirect owner of a 100% interest in a group of 464 claims located south and west of other ground held by the Pebble Partnership. In 2014 the LLC was merged into Pebble East Claims Corporation, a subsidiary of the Pebble Partnership, which now holds title to these claims.

The tectonic and magmatic history of southwest Alaska is complex (Decker et al., 1994; Plafker and Berg, 1994). It includes formation of foreland sedimentary basins between tectonostratigraphic terranes, amalgamation of these terranes and their translation along crustal-scale strike-slip faults, and episodic magmatism and formation of related mineral occurrences. The overview presented here is based largely on Goldfarb et al. (2013) and its contained references.

The allochthonous Wrangellia superterrane comprises the amalgamated Wrangellia, Alexander and Peninsular oceanic arc terranes that approached North America from the southwest in the early Mesozoic. West-dipping subduction beneath the superterrane formed the Late Triassic to Early Jurassic Talkeetna oceanic arc, which is now preserved in the Peninsular terrane east of Pebble (Figure 7.2-1). Several foreland sedimentary basins dominated by Jurassic to Cretaceous flysch, including the Kahiltna basin that hosts the Pebble deposit (Kalbas et al., 2007), formed between Wrangellia and pericratonic terranes and previously amalgamated allochthonous terranes of the Intermontane belt (Wallace et al., 1989; McClelland et al., 1992). Basin closure occurred as Wrangellia accreted to North America by the late Early Cretaceous (Detterman and Reed, 1980; Hampton et al., 2010). Between approximately 115 to 110 Ma and 97 to 90 Ma, the strata in the foreland basins were folded, complexly faulted and subjected to low-grade regional metamorphism (Bouley et al., 1995; Goldfarb et al., 2013). Intrusions at Pebble are undeformed (Goldfarb et al., 2013) and were probably emplaced during a period when at least local extension occurred across southwest Alaska in the mid-Cretaceous (e.g. Pavlis et al., 1993). The relative importance of extensional versus compressional structures to the formation of the Pebble deposit is not well constrained, although an important syn-hydrothermal transpressional fault occurs in the eastern part of the deposit.

Since the early Late Cretaceous, deformation in southwest Alaska has occurred mostly on major dextral strike-slip faults that broadly parallel to the continental margin (Figure 7.2-1). The major Denali fault in central Alaska forms the contact between the Intermontane Belt and the collapsed flysch basins. Subparallel faults with less substantial displacement are located south of the Denali fault, and the Pebble district is located between what are probably terminal strands of the dextral Lake Clark fault zone (Figure 7.2-1) ; Shah et al., 2009). The Lake Clark fault zone marks the poorly defined boundary between the Peninsular terrane to the southeast and the Kahiltna terrane, which hosts Pebble, to the northwest (Figure 7.2-1). Haeussler and Saltus (2005) propose 16.1 miles of dextral offset along the Lake Clark fault zone, most of which is interpreted to have occurred prior to approximately 38 to 36 million years ago. Recent field studies of geomorphology along the Lake Clark fault indicate that this structure has not experienced seismic activity for at least the last 10,000 years (Haeussler and Saltus, 2005, 2011; Koehler, 2010; Koehler and Reger, 2011). Other sub-parallel strike-slip faults also form terrane boundaries in the region, including the Mulchatna and Bruin Bay faults (Figure 7.2-1). Goldfarb et al. (2013) propose that most or all movement on these smaller structures occurred during oroclinal bending in the Tertiary, after formation of the Pebble deposit.

The initiation of magmatism and metallogenesis in the Pebble district approximately coincides with the onset of dextral transpression during basin collapse (Goldfarb et al., 2013). Alkalic to subalkalic intrusions were emplaced between approximately 100 and 88 Ma (Bouley et al., 1995; Amato et al., 2007; Hart et al., 2010; Lang et al., 2013; Olson et al., 2017, 2020). Alaska-type ultramafic complexes were emplaced at Kemuk, which is enriched in platinum group elements (Iriondo et al., 2003; Foley et al., 1997), and a mineralogically similar alkalic ultramafic body, albeit probably emplaced at shallow depths and without known enrichment in platinum group elements, occurs at Pebble (Bouley et al., 1995). Porphyry Cu-Mo±Au±Ag mineralization in the region is associated dominantly with subalkalic, felsic to intermediate intrusions formed between 97 and 90 Ma, and includes deposits at Pebble, Neacola (Reed and Lanphere, 1973; Young et al., 1997) and possibly the undated Iliamna prospect (Figure 7.2-1). Late Cretaceous intermediate to felsic intrusions are subalkalic and were emplaced between 75 and 60 Ma (e.g., Couture and Siddorn, 2007; Goldfarb et al., 2013). Porphyry Cu-Au±Mo and/or reduced intrusion-related gold mineralization associated with these rocks (Figure 7.2-1) formed at the Whistler deposit (Hames and Roberts, 2020), located about 93.2 miles northeast of Pebble, at Kijik River (Kreiner et al., 2020), the Bonanza Hills (Anderson et al., 2013) and Shotgun (Rombach and Newberry, 2001). Late Cretaceous to intrusions are common in the Kahiltna terrane and widespread, voluminous Eocene volcanic rocks cover much of the Kahiltna terrane and are associated with epithermal precious metal mineralization (Bundtzen and Miller, 1997). Igneous rocks of the mid-Cretaceous, Late Cretaceous, and Eocene magmatic suites are present within the Pebble district.

The oldest rock type in the Pebble district is the Kahiltna flysch, which comprises basinal turbidites, interbedded basalt flows and lesser breccias, and minor gabbroid intrusions. The Kahiltna flysch forms a northeast-trending belt about 250 miles long, which has experienced multiple stages of igneous and hydrothermal activity (Figure 7.2-1; Goldfarb, 1997; Young et al., 1997). The flysch in the vicinity of Pebble is at least 99 to 96 million years old, based on the maximum age of cross-cutting intrusions. Sediments were predominately derived from intermediate igneous source rocks and consist of siltstone, mudstone, subordinate wacke and rare, thin, lensoidal beds of matrix-supported pebble conglomerate (Figure 7.2-1). Bedding ranges from laminar to thick and is commonly poorly defined. Bouma sequences (Bouley et al., 1995), graded beds and load casts demonstrate that the stratigraphy isright-way-up.

The flysch locally contains thick layers of basalt flows, lesser breccias and minor mafic volcaniclastic rocks located mostly in the southwest and northern parts of the district. Undated gabbros cut the flysch and volcanic rocks in several areas and are interpreted to be related either to the basaltic volcanic rocks within the flysch or to younger diorite sills.

Diorite and granodiorite sills intruded the Kahiltna flysch (Figure 7.2-2A) at approximately 96 Ma. These two rock types are interpreted to be approximately coeval, based on the similarity in their distribution and style of occurrence; they are only well documented within the Pebble deposit.

Figure 7.2-1 Location of the Pebble Deposit & Regional Geological Setting of Southwest Alaska

Diorite sills are laterally extensive and range from less than 10 ft to greater than 300 ft in thickness. They are most common as stacked sheets in the western part of the Pebble deposit. The sills are medium grained and weakly porphyritic, with common plagioclase and hornblende and minor pyroxene set in a very fine-grained groundmass of plagioclase and hornblende (Figure 7.2-2B).

Three laterally continuous granodiorite sills occur within the Pebble deposit. They are up to 1,000 ft thick, with the thickest portions in the northeast part of the deposit. The sills range from fine to medium grained, with common plagioclase and hornblende as well as minor amounts of apatite, in a very fine-grained groundmass of potassium feldspar and quartz with minor to accessory magnetite, apatite and zircon (Figure 7.2-2C).

A complex suite of alkalic porphyry intrusions, that ranges from biotite pyroxenite, monzodiorite, monzonite to syenomonzonite, monzonite and monzodiorite, and associated breccias extends occur in the southwest quadrant of the Pebble deposit and extend several miles to the south (Schrader, 2001; Hart et al., 2010; Goldfarb et al., 2013). Isotopic dates on diorite and granodiorite sills, biotite pyroxenite and alkalic intrusions indicate that they are approximately coeval and were emplaced between 99 and 96 Ma (Schrader, 2001; Olson, 2015). Early intrusions are medium-grained, biotite monzonite porphyries (Figure 7.2-2D) that commonly contain scattered potassium feldspar megacrysts up to a few centimetres in size. Later intrusions are fine-grained porphyritic biotite monzodiorite (Figure 7.2-2E). All intrusive phases contain angular to subrounded xenoliths of flysch, diorite and, in the younger monzodiorite phase, xenoliths of older alkalic intrusions. Many of the intrusions grade laterally into breccias.

Breccias in the alkalic complex are complicated. Subordinate intrusion breccias have angular to subangular fragments in a cement of a relatively younger porphyritic biotite monzodiorite intrusion. Fragments of diorite sills, early alkalic biotite monzonite porphyry intrusions and flysch are most common xenoliths. In the common breccias, the matrices dominantly consist of a rock flour composed of subangular to subrounded fragments of these same rock types (Figure 7.2-2F). Hydrothermal cement is absent, and fragments range from a few millimetres to tens of metres in size. Locally, intersections of diorite and granodiorite sills within the breccia bodies may correlate laterally with undisturbed sills. Due to the internal complexity of the alkalic rocks and breccias within the deposit, the complex is modeled as a single unit, loosely interpreted as a megabreccia.

Granodiorite intrusions include the Kaskanak batholith and numerous smaller bodies, mostly within or proximal to zones of porphyry-style mineralization around the margins of the batholith. All isotopic dates on these rocks are approximately 90 Ma (Bouley et al., 1995; Lang et al., 2013). The Kaskanak batholith is dominantly a medium-grained hornblende granodiorite porphyry, with minor equigranular hornblende quartz monzonite. Granodiorite intrusions spatially associated with porphyry-style mineralization throughout the Pebble district are all mineralogically and texturally similar to the main phase of the Kaskanak batholith (Figure 7.2-2G). All of these intrusions are characterized by common hornblende, plagioclase and minor quartz and titanite, set in a fine-grained groundmass of quartz, plagioclase, potassium feldspar, apatite, zircon and magnetite. Megacrysts of potassium feldspar are up to 0.6 in in size, increase in both size and concentration with depth (from less than 2% to greater than 5%) and poikilitically enclose plagioclase and hornblende phenocrysts.

Cretaceous rock types 90 Ma or older are unconformably overlain by well-bedded sedimentary and volcanic rocks (Figure 7.2-2H), informally called the cover sequence. The cover sequence is up to 2,200 ft thick over the eastern edge of the Pebble deposit, and basalt flows with lesser interbeds of clastic sedimentary rocks are up to at least 6,400 ft thick within the East Graben. The sequence occurs mostly on, and thickens toward, the east side of the district, and is widespread to the southwest, south and north of Pebble. Sedimentary rock types are facing right-way-up but have been tilted about 20o east in the deposit area, and include pebble to boulder conglomerate, wacke, siltstone and mudstone. Plant fossils are common in wacke, and coal-bearing seams up to approximately 1.5 ft thick have been intersected by drilling. Volcanic to sub-volcanic rocks include basalt flows and mafic dykes and sills. Volcaniclastic rocks are abundant and contain angular fragments ranging from basalt to rhyolite within a matrix of comminuted volcanic material. The cover sequence is cut by minor narrow, dykes and sills of felsic to intermediate composition. Lang et al., (2013) report that basalts in the East Graben are cut by 65 Ma hornblende monzonite porphyry intrusions, and Olson et al. (2017) assign sedimentary and volcanic rocks that overlie the eastern part of the deposit to the late Paleocene to Eocene Talarik Formation, which may correlate with the widespread Copper Lake Formation of Detterman and Reed (1980).

Two porphyry intrusions of hornblende monzonite, up to 820 ft thick, cut basalts within the East Graben and have been dated at approximately 65 Ma (Lang et al., 2013). They are medium-grained and porphyritic, with common plagioclase and lesser hornblende set in a fine-grained groundmass of potassium feldspar, plagioclase and minor magnetite. These intrusions are not hydrothermally altered.

Volcanic and sub-volcanic intrusive rocks on the east side of the district are dated at approximately 46 to 48 Ma (Bouley et al., 1995; Lang et al., 2013). These rocks are mostly exposed on Koktuli Mountain east of the deposit and in the East Graben; reconnaissance drill intersections suggest they are also common in the southeast part of the district beneath glacial cover. Rock types include felsic dykes, brecciated rhyolite flows, fine-grained, equigranular to porphyritic biotite-bearing hornblende latite intrusions and coarse-grained hornblende monzonite porphyry.

Unconsolidated glacial sediments of Pleistocene to recent age cover the valley floors and the flanks of the higher hills (Detterman and Reed, 1973; Hamilton and Klieforth, 2010). The sediments are typically less than 100 ft thick, but drill intersections range up to 525 ft in the wide valley in the southeast part of the district. Ice flow directions over the deposit were to the south-southwest, and the glaciers had retreated by approximately 11 Ka (Detterman and Reed, 1973; Hamilton and Klieforth, 2010).

The structural history of the district outside of the Pebble deposit is poorly understood due to a paucity of outcrop and marker horizons. The Kahiltna flysch exhibits shallow to moderate dips to the east, south and southeast, which may reflect doming around the margins of the Kaskanak batholith. Folds in the flysch are open, and most inter-limb angles are less than 20°. Folding and related deformation predate hydrothermal activity at Pebble (Bouley et al., 1995; Goldfarb et al., 2013).

Faults are abundant throughout the Pebble district. A metallogenically-significant northeast-trending, syn-hydrothermal brittle-ductile fault zone (BDF) is described later in this section. Most faults are brittle normal or normal-oblique structures that cut and displace all rock types in the district and, in many cases, have been inferred from discontinuities in airborne magnetic and electromagnetic data. The most prominent faults strike north-northeast and northwest, with fewer striking east. The most important of these faults bound the northeast-trending East Graben, which is believed to be a negative flower structure that down-drops high-grade mineralization on the east side of the Pebble deposit. Brittle faults cut Eocene rock types, but precursor structures may have been periodically active since the mid-Cretaceous (L. Rankin, pers. comm., 2011). There is no geological evidence to suggest that these faults have been recently active.

Figure 7.2-2 Rock Types in the Pebble District

Notes:

A: Kahiltna flysch with interbedded siltstone and wacke affected by biotite-rich potassic alteration.

B: Diorite sill cut by magnetite-rich veins with intense biotite-rich potassic alteration.

C: Granodiorite sill with crowded porphyritic texture and pervasive potassic alteration.

D: Biotite monzonite porphyry member of the alkalic suite.

E: Late biotite monzodiorite porphyry member of the alkalic suite with angular xenoliths of flysch.

F: Diatreme breccia from the alkalic suite with polylithic fragments in a matrix of rock flour.

G: Pebble East zone granodiorite porphyry pluton with relict hornblende phenocrysts selectively altered to biotite.

H: Sharp contact between mineralized granodiorite sill and overlying basal conglomerate of the cover sequence

at the top of the Pebble East zone.

The characteristics of the Pebble deposit are shown in plan view in Figure 7.3-1 and Figure 7.3-2, and in cross-section in Figure 7.3-3 to Figure 7.3-5 . Geological interpretation of the Pebble deposit is based almost entirely on diamond drill intersections. Greater detail on the geology of the Pebble deposit is available in Lang et al. (2013), Olson (2015), and Olson et al. (2017, 2020).

The deposit is hosted by Kahiltna flysch, diorite and granodiorite sills, alkalic intrusions and breccias, granodiorite stocks, and granodiorite to granite dykes Figure 7.3-1 and Figure 7.3-3. Within the deposit, the Kahiltna flysch is a well-bedded siltstone with less than 10% coarser-grained wacke interbeds; basalt and gabbro are absent. Bedding within the flysch typically dips less than 25o to the east. The flysch was intruded by diorite sills, granodiorite sills and rocks of the alkalic suite prior to hydrothermal activity. The diorite sills are found only in the western half of the deposit (Figure 7.3-3), whereas some granodiorite sills extend across the entire deposit. Intrusions and breccias of the alkalic suite occupy the southwest quadrant of the deposit (Figure 7.3-1).

The deposit is centered on a group of Kaskanak suite intrusions. Olson (2015) describes the sequence and composition of the intrusions within the Pebble deposit as: 1) earliest, voluminous equigranular granodiorite equivalent to the Kaskanak batholith; 2) transitionally porphyritic granodiorite stocks; 3) early-mineral granodiorite porphyry; 4) inter-mineral quartz granite porphyry; and 5) minor late-mineral high-silica quartz granite porphyry. Due to scale, the Kaskanak intrusions are simplified on Figure 7.3-1 and are shown as the larger Pebble East zone pluton and four smaller bodies in the Pebble West zone. The north contact of the Pebble East zone pluton is close to vertical, and its upper contact dips shallowly to the west; it remains undelineated to the south, and has been dropped into the East Graben by the ZG1 normal fault. Contacts of stocks in the Pebble West zone dip steeply to moderately outward. Drill intersections of equigranular granodiorite at depths more than ~3,300 feet below the deposit support the hypothesis that the observed porphyry dikes and stocks in the upper part of the deposit emanate and were derived from a deeper reservoir of granodiorite at depth that is part of the main mass of the Kaskanak batholith.

The Pebble East zone is entirely concealed by the east-thickening cover sequence. The contact between the flysch and the cover sequence ranges from sharp and undisturbed to structurally disrupted with slippage along the contact. The lower half of the sequence comprises a thick basal conglomerate with well-rounded cobbles and boulders of intrusive and volcanic rock types of unknown provenance, overlain by complex, interlayered, discontinuous lenses of pebble conglomerate, wacke, siltstone, and mudstone. The upper half of the sequence comprises volcanic and volcaniclastic rocks (Figure 7.3-3) dominated by basalt or andesite and intruded by minor felsic to intermediate sills and/or dykes.

The East Graben is filled by basalt flows and lesser sedimentary rocks that have an uncertain relationship to the cover sequence. The graben fill ranges from approximately 4,265 ft thick north of the ZE fault to a thickness of up to at least 6,400 ft to the south. Basalts in the lower half of the graben are cut by two ~65 Ma monzonite porphyry intrusions, which makes them older than the rocks that cover the Pebble East zone. The age of the upper part of the graben fill is unknown but similarities of the sedimentary layers to some rock types in the cover sequence suggests that they may be coeval.

Eocene rocks are rare within and proximal to the Pebble deposit. Where thus far encountered, they comprise narrow felsic dykes, a pink hornblende monzonite intrusion intersected at depth in the central part of the East Graben, and a rhyolite flow breccia at the top of the East Graben, south of the ZE fault.

Within the western part of the Pebble deposit, the Kahiltna flysch occurs as an open, M-shaped anticline with axes that plunge shallowly to the east-southeast (Rebagliati and Payne, 2006). The folding predates intrusive activity at Pebble and diorite sills are commonly thicker where they exploited the hinges of the folds. Folding did not affect the cover sequence.

A brittle-ductile fault zone (BDF) has been identified on the east side of the Pebble deposit (Figure 7.3-1) where it manifests a zone of deformation defined by distributed cataclastic seams and healed breccias. It strikes north-northeast, extends at least 1.86 miles along strike, is up to 650 ft wide and is vertical to steeply west-dipping. The BDF is truncated on the east by the ZG1 fault (Figure 7.3-3) and does not affect the cover sequence. Displacement was dextral-oblique/reverse (S. Goodman, pers. comm., 2008), and correlation of alteration domains across the fault limits post-hydrothermal lateral displacement to less than 1,310 ft. The BDF was active before, during and after hydrothermal activity. Deformation is most intense in flysch north of the Pebble East Zone pluton but is weaker within the intrusion, suggesting that the BDF was more active before or during emplacement of the stock. Syn-hydrothermal control on mineralization by the BDF is indicated by the much higher grades of copper and gold and higher vein density within the structural zone compared to adjacent, undeformed host rocks. The characteristics of deformation along the BDF, and its timing relative to hydrothermal activity at Pebble, support at least a local compressional to transpressional environment during the formation of the deposit. Local deformation of veins indicates some post-hydrothermal movement on the BDF.

Brittle faults within the Pebble deposit conform to the district-scale patterns described above (Figure 7.3-1). The ZB, ZC and ZD faults occur in the Pebble West zone and exhibit normal offset of diorite and granodiorite sills of between 50 ft and 300 ft. Normal displacement on the ZJ and ZI faults is not well constrained. The ZA fault has about 100 ft of apparent reverse movement. A minimum of 820 ft of normal displacement occurred across the steeply west-dipping ZF fault, juxtaposing mineralized sodic-potassic alteration in the east against poorly mineralized, propylitic and quartz-sericite-pyrite alteration to the west. Scissors-style, south-side-down normal displacement on the ZE fault increases from around 100 ft on its western end to about 980 ft on the east side of the deposit. The ZG1 fault forms the western boundary of the East Graben and has well-defined normal displacement of approximately 2,100 ft in the north and 2,900 ft in the south, based on offset of the contact between the deposit and the cover sequence (Figure 7.3-3). The ZG2 fault, which is parallel to the ZG1 fault, has between 880 ft and 1,800 ft of normal displacement. The ZH fault and possible parallel structures farther east mark the eastern margin of the East Graben but remain undelineated. Many of these brittle faults localized intermediate to mafic dykes and a date of 84 Ma for an andesite dyke by Schrader (2001) indicates that brittle faults were active at least from that time and likely continued at least until the Eocene (Olson, 2015).

Figure 7.3-1 Geology of the Pebble Deposit Showing Section Locations

Location of resource section shown in Figure 14.12.1

Cross-sections A-A', B-B' and C-C' are shown in Figure 7.3-3, Figure 7.3-4 and Figure 7.3-5, respectively.

The brittle-ductile fault zone (BDF) is indicated by the cross-hatched pattern.

The dashed outline of the estimated resources at a 0.3% CuEq cut-off is used as a reference point for alteration

and grade distribution in Figure 7.3-2 .

White areas are either undrilled or rock types below cover sequence unknown.

See Figure 7.2-1 for geology legend.

Figure 7.3-2 Plan View of Alteration and Metal Distribution in the Pebble Deposit

For geological reference, the resource outline matches that shown in Figure 7.3-1.

A simplified distribution of alteration types is shown on the map at upper left.

NQV and SQV are the northern and southern quartz vein domains (>50% quartz veins).

Figure 7.3-3 Geology, Alteration and Distribution of Metals on Section A-A'

Figure 7.3-4 Geology, Alteration and Metal Distribution on Section B-B'

Figure 7.3-5 Geology, Alteration and Metal Distribution on Section C-C'

Alteration styles are summarized below in the order of their interpreted relative ages.

Hornfels related to intrusion of the Kaskanak batholith pre-dates hydrothermal activity and is found in all Cretaceous rock types, except granodiorite plutons and dykes. The hornfels aureole to the batholith is narrow south of Pebble but extends well east of the batholith in the vicinity of the deposit, which suggests that the batholith underlies the deposit, a concept supported by magnetic data (Shah et al., 2009; Anderson et al., 2013). Hornfels-altered flysch is massive but highly susceptible to brittle fracture, although the narrow alteration envelopes around veins indicate that permeability between fractures was low. Hornfels in flysch outside the deposit comprises biotite, K-feldspar, albite, plagioclase and quartz with minor pyrite and other accessory minerals.

Numerous stages of hydrothermal alteration are present, including potassic (also sometimes called K- or potassium-silicate alteration), sodic-potassic, illite±kaolinite, pyrophyllite and sericite advanced argillic, quartz-illite-pyrite, propylitic, and quartz-sericite-pyrite associations, as well as a variety of vein types. Sericite is defined herein as fine-grained, crystalline white mica, whereas illite is very fine-grained, non-crystalline white mica (Harraden et al., 2013). Advanced argillic alteration follows the naming convention of Meyer and Hemley (1967), although there are some differences noted in Pebble alteration. Most metals were introduced during early potassic and sodic-potassic alteration, with significant enhancement of grade in areas overprinted by younger advanced argillic alteration.

Most copper-gold-molybdenum-silver-rhenium mineralization coincides with early potassic and sodic-potassic alteration. Potassic alteration occurs mostly in the upper part of the Pebble East zone, whereas sodic-potassic alteration occurs in the Pebble West zone and below potassic alteration in the Pebble East zone. Sodic-potassic alteration is distinguished from potassic primarily by the presence of albite and a higher concentration of carbonate minerals (Gregory and Lang, 2011, 2012; Gregory, 2017). Associated vein types are described below.

Potassic alteration occurs in all rock types and is most intense in flysch and granodiorite sills near the Pebble East zone pluton, within the Pebble East zone pluton and in small areas of the Pebble West zone (Gregory and Lang, 2009). It is weakest in the area between the Pebble East and Pebble West zone centers. The assemblage includes potassium feldspar, quartz and biotite with trace to minor ankerite or ferroan dolomite, apatite and rutile. Sulphides include disseminated chalcopyrite and pyrite with minor molybdenite and bornite (Gregory and Lang, 2009). The proportion of biotite to potassium feldspar correlates with the original Fe-Mg concentration of host rocks and, thus, is highest in flysch and diorite sills.

Intrusive rocks in the Pebble West zone are affected by early sodic-potassic alteration which comprises albite, biotite, potassium feldspar and quartz, accompanied by ankerite, ferroan dolomite, trace apatite, magnetite and, locally, siderite. The concentration of carbonate minerals increases with depth. Sulphides include pyrite and chalcopyrite that both generally decrease in concentration with depth. Sodic-potassic alteration of sedimentary rocks is mineralogically similar to that in the intrusions and is typically pervasive.

In the Pebble East zone, sodic-potassic alteration occurs below potassic alteration and is distinguished from similar alteration in the Pebble West zone by the presence of epidote and calcite and by lower metal grades. The potassic to sodic-potassic transition occurs over vertical distances of less than 330 ft. In the Pebble East zone pluton, cores and rims of zoned plagioclase phenocrysts are replaced by calcite-epidote and albite, respectively. Hornblende phenocrysts were replaced by biotite and then by chlorite. Hematitized igneous magnetite is also present. The igneous groundmass was replaced by fine-grained quartz, potassium feldspar, and variable albite. Mineralization is weak in this alteration and decreases with depth, and commonly comprises 2% pyrite and trace to minor chalcopyrite and molybdenite. This alteration is difficult to distinguish from peripheral propylitic alterationand its potential equivalence to well-mineralized sodic-potassic alteration in the Pebble West zone remains unclear.

Potassic alteration overprints sodic-potassic alteration but the two alteration types are interpreted to be coeval and therefore are treated as a single alteration event. The apparent relative timing is likely a consequence of telescoping and/or changing fluid chemistry during cooling. The paragenetic and spatial relationship between sodic-potassic alteration in the Pebble East and Pebble West zones and peripheral propylitic alteration is not established.

Four major quartz-sulphide vein types, comprising 80% of all veins in the deposit, are associated with early potassic and sodic-potassic alteration and are classified as types A, B, M and C. Each type includes varieties that broadly correlate with lateral and/or vertical position in the deposit. The naming conventions, while similar to common porphyry vein nomenclature, are not exact equivalents similarly named to vein types described from other deposits (e.g., Gustafson and Hunt, 1975; Clark, 1993; Gustafson and Quiroga, 1995). For clarity in the sections that follow, the term selvage is used to denote minerals lining the interior walls of a dilatant vein, whereas envelope refers to alteration in the host rock to a vein.

Total density of vein types A, B and C across most of the Pebble deposit is between 5 and 15 vol % (using the criteria of Haynes and Titley (1980) and excluding alteration envelopes). Lower concentrations occur near the margins of the deposit and at depth below the 0.3% CuEq resource boundary. Higher concentrations occur within or proximal to the Pebble East zone pluton and locally proximal to the smaller granodiorite plutons in the Pebble West zone. Vein density does not correlate consistently with rock type and, in most cases patterns extend smoothly across lithological contacts. Measurements in oriented drill core do not reveal any significant or consistent preferred vein orientations.

On the east side of the Pebble East zone there are two domains characterized by 50 to 90% quartz veins. These two zones are surrounded by and gradational with a larger zone that contains greater than 20% quartz veins of either the A1 or B1 vein subtypes (see below). These zones of high vein density probably reflect repeated refracturing and dilationthat accommodated repeated vein precipitation events. The first domain is located north of the ZE fault in a broadly cylindrical zone 330 to 1,640 ft wide and extending up to 1,970 ft below the cover sequence. Veins in this first zone are not deformed and controlling faults have not been identified. The second area forms a north-northeast-trending, nearly vertical, tabular zone that lies within the zone of brittle-ductile deformation (described above). This second area is truncated to the east by the ZG1 fault, continues into the East Graben and is open below depths of 4,920 ft. Veins in this zone are commonly deformed and locally brecciated and formed during syn-hydrothermal deformation along the BDF or a precursor structure.

Type A Veins

Type A veins are the oldest of the four types and include subtypes A1, A2 and A3. The A1 subtype is the most common and occurs mostly within the upper 2,300 ft of the Pebble East zone pluton. These veins are sinuous to anastomosing, discontinuous, and typically have diffuse contacts. They contain quartz, trace to minor potassium feldspar, less than 1 to 2% pyrite, lesser chalcopyrite, and rare molybdenite. Potassium feldspar alteration envelopes are commonly narrow, diffuse, and a few millimetres wide. They occur within zones of pervasive, weakly mineralized potassic alteration.

The A2 veins occur below approximately 3,300 ft in the Pebble East zone pluton and have characteristics transitional between quartz veins and pegmatites. They are characterized by potassium feldspar selvages and coarse-grained cores of euhedral to subhedral quartz. Coarse clots of biotite are locally present along with trace chalcopyrite, molybdenite and/or pyrite. The A2 veins are sinuous, discontinuous, irregular, have diffuse contacts and lack alteration envelopes.

A3 veins are transitional between vein types A1 and B1 and are most common below 2,500 ft in the Pebble East zone pluton. The A3 veins are typically anastomosing, sinuous to irregular and have diffuse contacts with prominent potassium feldspar envelopes. They contain quartz with trace to minor potassium feldspar and biotite, and locally contain up to 3% pyrite, minor chalcopyrite and rare molybdenite.

Type B Veins

Type B veins cut type A veins and include subtypes B1, B2 and B3. These are spatially coincident with potassic and sodic-potassic alteration, are the most widespread veins at Pebble and are most abundant within and proximal to the Pebble East zone pluton.

B1 veins are the most common subtype and are planar, continuous, have sharp contacts, and are typically 0.1 to 1.2 in wide. They are dominated by quartz with trace to minor biotite, potassium feldspar, apatite and/or rutile. The veins typically contain 2 to 5% of both pyrite and chalcopyrite with minor molybdenite and local bornite. Potassium feldspar (±biotite) alteration envelopes are ubiquitous, highly variable in width and contain disseminated chalcopyrite, pyrite and molybdenite.

B2 veins occur below 2,600 ft depth in the Pebble East zone and broadly coincide with sodic-potassic alteration. They contain quartz and minor K-feldspar and have narrow, weak potassium feldspar or biotite alteration envelopes. B2 veins transition upward into B1 veins and are distinguished from B1 veins by green chlorite pseudomorphs after coarse aggregates of locally preserved hydrothermal biotite and by minor calcite and epidote. The veins typically contain less than 2% pyrite, and minor chalcopyrite, and molybdenite.

B3 veins are most common in the north-central and south-central part of the Pebble East zone, and below 5,600 ft depth in the lower grade domain between the Pebble East and Pebble West zones. These veins are similar to B1 veins but contain molybdenite as the dominant sulphide and have only sporadic, weak, potassium feldspar alteration envelopes. B3 veins are planar and can be greater than 3.3 ft in width. B3 veins cut vein types A, B1, B2 and, locally, C veins; B3 veins are interpreted to represent a late substage of early alteration which locally introduced significant molybdenum to the Pebble deposit.

Type M Veins

Type M veins are associated with magnetite-bearing sodic-potassic alteration within and proximal to diorite sills in the Pebble West zone. Paragenetically they formed between vein types B1 and C. They are planar to irregular and are typically 0.4 to 2 inches wide. These veins comprise mostly magnetite and quartz with lesser ankerite and potassium feldspar as well as greater than 10% chalcopyrite and pyrite with minor molybdenite. The M veins have narrow potassium feldspar alteration envelopes.

Type C Veins

Type C veins are the most abundant veins in the western half of the deposit. The C veins cut A and B veins (except possibly the B3 subtype), and are contemporaneous with or slightly younger than M veins. C veins at Pebble are defined according to their relative timing and do not resemble the C veins defined by Gustafson and Quiroga (1995). The veins contain mostly quartz, locally abundant ankerite or ferroan dolomite, minor to trace potassium feldspar, magnetite and biotite, and 10% (locally up to 50%) sulphides. Sulphides include pyrite and chalcopyrite, variable molybdenite, trace arsenopyrite and rare bornite. The veins are planar, have sharp contacts, range from less than 0.4 in to approximately 2 in wide and commonly contain vugs along their central axis. Alteration envelopes are prominent with similar mineralogy to the veins and can be up to 10 times the width of the vein in the more permeable intrusive host rocks. Where the alteration envelopes to several C veins overlap, drill intersections up to approximately 15 ft in length can grade up to several percent copper.

Illite ± kaolinite alteration is coincident with and overprints early potassic and sodic-potassic alteration. Alteration intensity is highest at moderate depths within the Pebble East zone pluton. In these rocks, illite replaces phenocrysts of plagioclase previously altered to potassium feldspar and locally replaces the potassically-altered igneous matrix. This alteration style is weakest in flysch in the Pebble West zone. Minor pyrite co-precipitated with illite, but is likely a local reconstitution of older sulphides. Fracture or fault control is rarely apparent. Kaolinite accompanies illite in alteration of previously sodic-potassic altered areas where it replaces albite.

Advanced argillic alteration occurs only in the East Zone, where it is associated with the highest grades of copper and gold in the deposit. Advanced argillic alteration occurs within and adjacent to the BDF. This alteration comprises a pyrophyllite-quartz-sericite-chalcopyrite-pyrite zone within the BDF that is bounded to the west by an upwardly-flaring envelope of sericite-quartz-pyrite-bornite-digenite-chalcopyrite alteration to the west (cf., Khashgerel et al., 2009). Advanced argillic alteration is truncated on the east by the ZG1 fault but deep intersections in hole 6348 demonstrate that this alteration and its associated high grade mineralization continues eastward into the graben. Both the sericite and the pyrophyllite alteration types replace potassic and sodic alteration. The sericite alteration is locally replaced by younger quartz-sericite-pyrite alteration.

Pyrophyllite alteration is accompanied by quartz, sericite, pyrite and chalcopyrite. Pyrite concentration is commonly greater than 5% and is much higher than in adjacent early potassic alteration. Pyrophyllite alteration is coincident with but overprints the southern zone of high quartz vein density; quartz-sulphide veins within this zone are commonly deformed. Veins associated with pyrophyllite alteration are irregular, narrow, contain pyrite ± chalcopyrite in massive to semi-massive concentrations, contain variable quartz, and lack visible alteration envelopes. Pyrophyllite alteration has not been identified in the northern zone of high quartz vein density.

Pervasive sericite alteration forms an upward-flaring envelope west of the pyrophyllite alteration. Sericite alteration occurs in the upper 1,000 ft of the deposit on the downthrown southern side of the ZE fault. This alteration is pervasive and dominated by white sericite that replaces feldspars previously affected by potassic and illite alteration. Pyrite concentration is intermediate between pyrophyllite alteration and early potassic alteration and decreases with depth. Sericite alteration is distinguished by high-sulphidation hypogene copper minerals represented by various combinations of bornite, covellite, digenite, tennantite-tetrahedrite, and locally trace enargite. These minerals commonly replace the rims of chalcopyrite and pyrite precipitated during early potassic alteration. Minor quartz-rich veins with pyrite are related to this alteration, are narrow and irregular, and locally have well-developed envelopes with quartz, sericite, pyrite and high sulphidation copper minerals.

Propylitic alteration extends at least 3 miles south of the deposit and to the limit of drilling 1.4 miles to the north. Weak propylitic alteration also occurs throughout the eastern half of the Kaskanak batholith. This alteration comprises chlorite, epidote, calcite, quartz, magnetite and pyrite, minor albite and hematite, and trace chalcopyrite. Sulphide concentration is less than 3% and is mostly pyrite.

Type H veins occur locally and at low vein density throughout propylitic alteration. They contain calcite, hematized magnetite, quartz, albite, epidote, pyrite and trace to minor chalcopyrite. H veins are planar, less than 0.4 in wide and have alteration envelopes similar in mineralogy and width to the veins.

Polymetallic type E veins occur locally south of the deposit, in areas of propylitic and quartz-sericite-pyrite alteration. Rarely, E veins cut sodic-potassic alteration in the Pebble West zone. The E veins are planar, can be up to two feet in width, have sharp contacts with host rocks and locally have weak sericite alteration envelopes. These veins contain various combinations of quartz, calcite, pyrite (locally arsenian), sericite, sphalerite, galena, minor chalcopyrite and trace arsenopyrite, tennantite-tetrahedrite, freibergite, argentite and native gold.

The QSP alteration occurs closer to the centre of the deposit than does the propylitic alteration, but where these two alteration types overlap the QSP alteration is younger. QSP alteration, which is equivalent to classic phyllic alteration, is commonly texture-destructive and forms a halo around the deposit with inner and outer alteration fronts that dip steeply away from the core of the deposit. This halo extends at least 2.6 miles south of the deposit and 0.9 miles north; it is weakly developed west of the ZF fault where it partially overprints propylitic alteration. It occurs at depth in the north part of the East Graben but its full distribution east of the ZG1 fault is not established. In the Pebble East zone, the transition from potassic or advanced argillic alteration to intense, pervasive QSP alteration typically occurs over 50 to 60 ft. Weak QSP alteration occurs sporadically throughout the Pebble West zone with a more gradual outward transition than in the Pebble East zone.

Mineralogy of QSP alteration includes quartz, sericite, 8 to 20% pyrite, minor to trace ankerite, rutile and apatite, and rare pyrrhotite. Zones are cut by up to 10% pyrite-rich type D veins (Gustafson and Hunt, 1975) with variable amounts of quartz and trace rutile, chalcopyrite and ankerite. D veins are planar, have sharp contacts with host rocks and range from less than 1 in to 5 ft in width. Alteration envelopes are typically wider than the veins and form intense pervasive QSP alteration where they coalesce.

Quartz-illite-pyrite (QIP) alteration partially replaces potassic and/or sodic-potassic alteration in the upper, central part of the deposit. QIP alteration is interpreted as a zone of former weak to moderate, grade-destructive QSP alteration, located at the transition between sodic-potassic and potassic alteration, that was later overprinted by low-temperature illite alteration as the hydrothermal system waned. QIP alteration is texturally and mineralogically similar to QSP alteration, except that illite is the main phyllosilicate phase rather than sericite (Harraden et al., 2012). The pyrite concentration in QIP alteration is typically 5 to 10%, which occurs mostly in type D veins and their alteration envelopes. Domains between the QIP alteration envelopes preserve relict sodic-potassic alteration that host most of the copper mineralization that remains in this zone.

The youngest alteration at Pebble is clay alteration, which is common within 50 ft of the contact between the cover sequence and underlying Cretaceous rocks. Young, brittle faults that cut the deposit, in particular the ZG1 fault, host or are closely associated with basalt dikes related to volcanic rocks in the cover sequence. The faults and dikes are surrounded by narrow alteration zones of epidote, calcite, chlorite, and pyrite. An extremely small proportion of mineralization in the deposit is affected by this alteration.

Mineralization in the Pebble West zone is mostly hypogene, with a thin zone of mostly weak supergene overprint beneath a thin leached cap. Mineralization in the Pebble East zone is entirely hypogene with no preservation of leaching or paleo-supergene below the unconformity with the cover sequence.

A thin leached cap occurs at the top of the Pebble West zone. Strong leaching is rarely more than 33 ft thick but is highly variable, and weak oxidation along fractures locally extends to depths of up to 500 ft along or near brittle faults. Hypogene pyrite is commonly preserved in the leached zone, and minor malachite, chrysocolla and native copper are present locally.

Supergene mineralization occurs only in the Pebble West zone where the cover sequence is absent. Similar to the overlying leached cap, the thickness of supergene mineralization is highly variable. It locally extends to a depth of 560 ft in strongly fractured zones, but on average is closer to 200 ft in average thickness and tapers toward the margins of the resource. In the supergene zone, pyrite is typically rimmed by chalcocite, covellite and minor bornite, and complete replacement of pyrite is rare (Gregory and Lang, 2009; Gregory et al., 2012). The transition to hypogene mineralization with depth is gradational over vertical intervals of up to approximately 100 feet. Supergene processes increased copper grade up to approximately 50% across narrow intervals but the upgrading is typically much less.

Patterns of metal grades and ratios at Pebble correspond closely to alteration styles, with only weak or local relationships to host rock. The preserved deposit has a flat tabular geometry when the 20° post-hydrothermal tilt is removed. Copper and gold grades diminish below approximately 1,300 ft depth in the Pebble West zone but extend much deeper in the Pebble East zone, particularly within and proximal to the BDF. Laterally, grades decrease gradually toward the north and south margins of the deposit, where mineralization terminates over short distances due to the overprint by intense, grade-destructive QSP alteration. Moderate grades with the shortest vertical extent are observed in the middle of the deposit between the Pebble East and Pebble West zones. There is a general correspondence between copper and gold grades outside of the Pebble East zone pluton; within the Pebble East zone pluton, there is a closer correspondence between copper and molybdenum at low grades of gold, except where gold-rich advanced argillic alteration is present. On the west side of the deposit, mineralization extends to the normal/oblique ZF fault, but drilling has been too shallow to determine if the deposit continues to the west at depth. On the east side, the deposit was down-dropped by the ZG1 fault and continuation of high-grade mineralization into the East Graben has been confirmed by drilling. Molybdenum exhibits a more diffuse pattern, is open at depth and, in some areas, domains with strongly elevated grade corresponds with higher densities of molybdenite-rich type B3 veins.

Mineralization was primarily introduced during early potassic and sodic-potassic alteration. Copper is hosted primarily by chalcopyrite (Figure 7.5-1) that is locally accompanied by minor bornite (Figure 7.3-2) and trace tennantite-tetrahedrite. The pyrite to chalcopyrite ratio is typically close to one in potassic alteration in the Pebble East zone but is commonly much higher in the Pebble West zone where sulphide-rich type C and, locally, type D veins are present. Gold occurs primarily as electrum inclusions in chalcopyrite with minor amounts hosted by silicate alteration minerals and pyrite, and rarely as gold telluride inclusions in pyrite (Gregory et al., 2013). Diorite sills with magnetite-rich alteration and type M veins have relatively high gold concentrations. Molybdenite occurs in quartz veins and as intergrowths with disseminated chalcopyrite.

Incipient to weak illite±kaolinite alteration had little effect on grade, whereas strong alteration reduced the grade of copper and gold but left molybdenum largely undisturbed. Gold liberated during illite±kaolinite alteration was reconstituted as high-fineness inclusions (gold grains with less than 10 wt% Ag) in newly formed pyrite (Gregory and Lang 2009; Gregory et al., 2013). These patterns are consistent with the effects of illite alteration on grade in many porphyry deposits (e.g., Seedorf et al., 2005; Sillitoe, 2010).

Advanced argillic alteration zones have much higher grades of copper and gold but similar molybdenum compared to adjacent early potassic alteration. Pyrophyllite alteration precipitated high concentrations of pyrite and chalcopyrite and both minerals contain inclusions of high-fineness gold (Gregory et al., 2013). During sericite alteration, bornite, covellite, digenite and trace enargite or tennantite replaced chalcopyrite formed during early potassic alteration and also precipitated minor additional pyrite (Gregory and Lang, 2009). In general, gold occurs as high-fineness inclusions in later pyrite and high-sulphidation copper minerals, whereas electrum predominates in relict early chalcopyrite (Gregory et al., 2013).

The zone of high quartz vein density along the BDF is typically well-mineralized where it has been overprinted by pyrophyllite alteration. The northern zone of high quartz vein density has average to low grades of copper and gold except in small areas where higher grades reflect the presence of the sericite subtype of advanced argillic alteration.

The late QSP alteration is invariably destructive of both copper and molybdenum mineralization. Gold concentrations, however, remain consistent at 0.15 to 0.5 g/t, and locally exceed 1 g/t (Lang et al., 2008). The QIP alteration has a similar effect on copper, molybdenum and gold but is not completely pervasive, such that copper and molybdenum grades are reduced and some of the gold now occurs as high-fineness inclusions in pyrite formed by breakdown of older sulphides (Gregory et al., 2013).

Grade variation within the cores of the Pebble East and Pebble West zones shows a weak, local relationship to rock type. Higher than average copper and gold grades are spatially related to highly reactive, iron-rich diorite sills, a relationship common in porphyry deposits (e.g., Ray, Arizona; Phillips et al., 1974). On the margins of the deposit and in the lower grade area between the Pebble East and Pebble West Zones, relatively impermeable flysch affected by pre-hydrothermal hornfels has lower grades than adjacent, more permeable granodiorite sills.

Rhenium

The Pebble deposit is remarkable for its very large endowment in rhenium, for which a resource is estimated in Section 14 of this report that compares favourably with the largest known global resources of rhenium (Sinclair et al., 2009). Rhenium is one of the lesser known metals and is one of the rarest elements on earth, with a crustal abundance of less than one part per billion (John et al., 2017). The United States, under Executive Order 13817, has caused rhenium to be placed on its list of critical minerals, stating that it 'is essential to the economic and national security of the United States that has a supply chain vulnerable to disruption.' (US Department of the Interior news release, May 18, 2018). Rhenium typically does not form discrete minerals in nature, but because of its valence and atomic radius instead almost exclusively substitutes for molybdenum in the lattice of molybdenite (e.g., McCandless et al., 1993; Barton et al., 2019). Globally most rhenium is recovered from flue dust created during the roasting of molybdenite concentrates, most of which come from porphyry style deposits like Pebble (John et al., 2017). Elevated concentrations of rhenium occur throughout the Pebble deposit and, as expected, the concentrations of rhenium and molybdenum are very closely correlated. Molybenite concentrates produced during metallurgical testwork on the Pebble deposit, as described in Section 13 of this report, contain up to 960 ppm rhenium, which places Pebble in the upper echelon of porphyry deposits (e.g., McCandless et al., 1993; Barton et al., 2019). Detailed rhenium deportment studies have not yet been completed to determine if the concentation of rhenium in molybdenite varies spatially across the Pebble deposit or in paragenetically distinct stages of molybdenite precipitation, e.g., molybdenite in late B3 veins compared to molybdenite in earlier potassic or sodic-potassic alteration. Visual inspection of the 3D distribution of molybdenum to rhenium ratios in assay results across the Pebble deposit, however, suggests a general consistency with limited variation.

The Pebble deposit also contains elevated concentrations of the platinum group metal palladium, which is also considered a critical mineral by the Department of the Interior. This places Pebble among a very small minority of porphyry deposits known to contain significant palladium concentrations (e.g., McFall et al., 2018; Hanley et al., 2020). The highest concentrations of palladium at Pebble occur in or proximal to areas affected by advanced argillic alteration, but elevated palladium occurs in many parts of the deposit including within the proposed open pit. The deportment of palladium remains essentially unstudied at Pebble. A single sample of pyrite from the pyrophyllite alteration zone was analyzed by in-situ laser ablation ICP-MS and found to contain elevated palladium in undetermined form (Gregory et al. (2013). The deportment of palladium in porphyry deposits can be complex (e.g., Hanley et al., 2020) and a more detailed study of palladium deportment at Pebble is warranted to determine the degree to which this metal can be recovered to a chalcopyrite and/or pyrite concentrate.

Figure 7.5-1 Drill Core Photograph Showing Chalcopyrite Mineralization

Figure 7.5-2 Drill Core Photograph Showing Chalcopyrite and Bornite Mineralization

The Pebble deposit is classified as a copper-gold-molybdenum porphyry deposit. The principal features of porphyry copper deposits, as summarized recently by John et al. (2010), include:

These characteristics correspond closely to the principal features of the Pebble deposit as described in Section 7.0 of this report. This report focuses exclusively on the Pebble porphyry deposit; other deposits of intrusion-related skarn, vein and porphyry style mineralization have been encountered elsewhere on the Pebble property but have not been the subject of detailed exploration or delineation.

The Pebble deposit has many characteristics typical of porphyry deposits as a group, but it is unusual in terms of its sheer size and the variety and scale of its contained metal. Pebble has one of the largest metal endowments of any gold-bearing porphyry deposit currently known. Comparison of the current Pebble resource to other major copper and precious metal deposits shows that it ranks at or near the top in terms of both contained copper (Figure 8.1-1) and contained precious metals (gold and silver; Figure 8.1-2). Pebble is both the largest known undeveloped copper resource and the largest known undeveloped gold resource in the world today. Pebble also has a very large endowment in both molybdenum and, as cited previously, in rhenium. The presence of palladium further highlights its unusual character. The bases for these estimations of metal endowment in the Pebble deposit are fully described in Section 14.0 of this report.

Figure 8.1-1 Pebble Deposit Rank by Contained Copper

Source: Company filings, Metals Economics Group; BMO Capital Markets

Figure 8.1-2 Pebble Deposit Rank by Contained Precious Metals

Source: Company filings, S&P GlobalMarket Intelligence, street research; BMO Capital Markets

Note: Includes inferred resource.

1. Converted to Au Eq. at street consensus Au price of US$1,500/oz and Ag price of US$18.00/oz

2. At 0.30% Cu Eq. cut-off.

3. Source: World Gold Council (https://www.gold.org/about-gold/facts-about-gold) says that about 187,000 tonnes of gold have been mined since the beginning of civilization. Pebble resource represents 3,340 T (10,776,800,344 tonnes x 0.31 g/t = 3,340 T).

Geological, geochemical and geophysical surveys were conducted in the Pebble Project area from 2001 to 2007 by Northern Dynasty and since mid-2007 by the Pebble Partnership. The types of historical surveys and their results are summarized below. More detailed descriptions of historical exploration programs and results may be found in Rebagliati and Haslinger (2003), Haslinger et al. (2004), Rebagliati and Payne (2006 and 2007), Rebagliati and Lang (2009) and Rebagliati et al. (2005, 2008, 2009 and 2010).

Between 2001 and 2006, the entire Pebble property was mapped for rock type, structure and alteration at a scale of 1:10,000. This work provided an important geological framework for interpretation of other exploration data and drilling programs. A geological map of the Pebble deposit was also constructed but, due to a paucity of outcrop, was based solely on drillhole information. The content and interpretation of district and deposit scale geological maps have not changed materially from the information presented by Rebagliati et al. (2009 and 2010).

In 2001, dipole-dipole IP surveys totalling 19.3 line-mi were completed by Zonge Geosciences for Northern Dynasty, following up on and augmenting similar surveys completed by Teck.

During 2002, a ground magnetometer survey totalling 11.6 line-mi was completed at Pebble. The survey was conducted by MPX Geophysics Ltd., based in Richmond Hill, Ontario. The principal objective of this survey was to obtain a higher resolution map of magnetic patterns than was available from existing regional government magnetic maps. The focus of this work was the area surrounding mineralization in the 37 Skarn zone in the southern part of the Pebble district. A helicopter-based airborne magnetic survey was flown over the entire Pebble property in 2007. A total of 2,344 line-km (1,456.5 line-mi) were flown at 200 m (656 ft) line spacing, covering an area of 425 square km (164.5 square miles). The survey lines were flown at a mean terrain clearance of 60 m (196.8 ft) along flight lines oriented 135° at a line spacing of 200 m (656 ft), with tie lines oriented 045° at a spacing of 2 km (1.24 miles). Immediately over the Pebble deposit, an area of 23 square km (14.4 square miles) was surveyed at a 100 m (328 ft line) spacing for a total of 342 line-km (212.5 line-mi km), without additional tie lines.

During 2007, a limited magnetotelluric survey was completed by GSY-USA Inc., the U.S. subsidiary of Geosystem SRL of Milan, Italy, under the supervision of Northern Dynasty geologists. The survey focused on the area of drilling in the Pebble East zone and comprised 196 stations on nine east-west lines and one north-south line, at a nominal station spacing of 656 ft. Interpretation, including 3D inversion, was completed by Mr. Donald Hinks of Rio Tinto Zinc.

In July 2009, Spectrem Air Limited, an Anglo American-affiliated company based in South Africa, completed an airborne electromagnetic, magnetic and radiometric survey over the Pebble area. A total of 2,386 line-mi was surveyed in two flight block configurations:

The orientation of flight lines was 135° for both surveys, with additional tie-lines flown orthogonally. The objectives of this work included provision of geophysical constraints for structural and geological interpretation in areas with significant glacial cover.

Between the second half of 2009 and mid-2010, a total of 120.5 line-mi of IP chargeability and resistivity data were collected by Zonge Engineering and Research Organization Inc. (Zonge Engineering) for the Pebble Partnership. This survey was conducted in the southern and northern parts of the property and used a line spacing of about 0.5 miles; the objective of this survey was to extend the area of IP coverage completed prior to 2001 by Teck and during 2001 by Northern Dynasty.

During 2010, an airborne electromagnetic (EM) and magnetometer geophysical survey was completed on the Pebble property totalling 4,009 line-mi. This survey was conducted by Geotech Ltd. of Aurora, Ontario.

The USGS collected gravity data from 136 stations distributed over an area of approximately 2,317 square miles during 2008 and 2009.

Between 2001 and 2003, Northern Dynasty collected 1,026 soil samples (Rebagliati and Lang, 2009). Typical sample spacing in the central part of the large geochemical grid was 100 ft to 250 ft along lines spaced 122 to 400 ft to 750 ft apart; samples were more widely spaced near the north, west and southwest margins of the grid.

These sampling programs outlined high-contrast, coincident anomalies in gold, copper, molybdenum and other metals in an area that measures at least 5.6 miles north-south by up to 2.5 miles east-west, with strong but smaller anomalies in several outlying zones. All soil geochemical anomalies lie within the IP chargeability anomaly described above. Three very limited surficial geochemical surveys were completed by the Pebble Partnership in 2010 and 2011; no significant geochemical anomalies were identified. A total of 126 samples, comprising 113 till and 13 soil samples, were collected on the KAS claims located in the southern end of the property; samples were on lines spaced approximately 8,000 ft apart with a sample spacing of approximately 1,300 ft. A total of 109 soil samples were collected from two small areas located approximately 11 miles to the west-northwest and 15 miles west of the Pebble deposit; samples were spaced approximately 330 ft apart on lines that were irregularly spaced to accommodate terrain features.

Additional surveys were completed between 2007 and 2012 by researchers from the USGS and the University of Alaska Anchorage (see summary in Kelley et al., 2013 and contained references). The types of surveys that were completed by these groups include: (1) hydrogeochemical surveys in several parts of the Pebble property which obtained multi-element inductively coupled plasma mass spectrometry (ICP-MS) data from samples of surface waters; (2) determination of copper isotope ratios in surface waters; (4) heavy indicator mineral analyses of glacial till; and (4) orientation surveys which utilized a variety of weak extraction geochemical techniques. The results of these surveys were largely consistent with the results obtained by earlier soil sampling programs.

Extensive drilling totaling 1,048,509.8 ft has been completed in 1,389 holes on the Pebble Project. These drill campaigns took place during 19 of the 26 years between 1988 and 2013, and in 2018 and 2019. The spatial distribution and type of holes drilled is illustrated in Figure 10.1-1. A detail of the drilling in the 'Deposit Area' is shown in Figure 10.2-1.

Figure 10.1-1 Location of all Drill Holes

Drilling completed by Teck (1988 to 1997) is described briefly in Section 6.0 and will not be discussed further here.

All drill hole collars have been surveyed using a differential global positioning system (GPS). All holes were resurveyed in 2008 and 2009, with the exception of the Sill holes. A digital terrain model for the site was generated by photogrammetric methods in 2004. All post- Teck drill holes have been surveyed downhole, typically using a single shot magnetic gravimetric tool. A total of 989 holes were drilled vertically (-90°) and 192 were inclined from -42° to -85° at various azimuths.

The Pebble deposit has been drilled extensively (Figure 10.2-1). Drilling statistics and a summary of drilling by various categories to the end of the 2013 exploration program are compiled in Table 10.2-1. This includes seven drill holes completed by FMMUSA, drilled by Peak Exploration (USA) Corp. in the area in 2008; these holes were drilled on claims that are now part of the Pebble property and have been added to the Pebble dataset. Detailed descriptions of the programs and results for 2009 and preceding years may be found in technical reports by Rebagliati and Haslinger (2003 and 2004), Haslinger et al. (2004), Rebagliati and Payne (2005, 2006 and 2007), and Rebagliati et al. (2008, 2009 and 2010). Detailed information on the 2010 through 2013 drill programs may be found in technical reports by Gaunt et al. (2014 and 2018).

Most of the footage on the Pebble Project was drilled using diamond core drills. Only 18,716 ft was percussion-drilled from 229 rotary drill holes. Many of the cored holes were advanced through overburden, using a tricone bit with no core recovery. These overburden lengths are included in the core drilling total.

From early 2004 through 2013, all Pebble drill core was geotechnically logged on a drill run basis. Almost 70,000 measurements were made for a variety of geotechnical parameters on 737,000 ft of core drilling. Recovery is generally very good and averages 98.2% overall; two-thirds of all measured intervals have 100% core recovery. Detailed (domain-based) geotechnical logging and downhole surveys were also conducted between 2007 and 2012. Proper domain selection is the basis for rock mass classification and domain-based data is used extensively in open pit and underground mine design. In order to maximize the information from the 2007-2012 drill programs, several tools and techniques were added to a number of holes including: triple tube drilling, core orientation, acoustic televiewer probe and comprehensive point load testing complemented by laboratory UCS testing. Additionally, all Pebble drill core from the 2002 through 2013, 2018 and 2019 drill programs was photographed in a digital format.

Figure 10.2-1 Location of Drill Holes - Pebble Deposit Area

Table 10.2-1 Summary of Drilling to December 2019

	No. of Holes	Feet	Metres
By Operator
Teck 1	164	75,741.0	23,086
Northern Dynasty	578	495,069.5	150,897
Pebble Partnership 2	640	472,249.3	143,942
FMMUSA	7	5,450.0	1,661
Total	1,389	1,048,509.8	319,586
By Type
Core 1,5	1,160	1,027,671.9	313,234
Percussion 6	229	20,838.0	6,351
Total	1,389	1,048,509.8	319,586
By Year
1988 1	26	7,601.5	2,317
1989 1	27	7,422.0	2,262
1990	25	10,021.0	3,054
1991	48	28,129.0	8,574
1992	14	6,609.0	2,014
1993	4	1,263.0	385
1997	20	14,695.5	4,479
2002	68	37,236.8	11,350
2003	67	71,226.6	21,710
2004	267	165,567.7	50,465
2005	114	81,978.5	24,987
2006 3	48	72,826.9	22,198
2007 4	92	167,666.9	51,105
2008 5	241	184,726.4	56,305
2009	33	34,947.5	10,652
2010	66	57,582.0	17,551

2011	85	50,767.7	15,474
2012	81	35,760.2	10,900
2013	29	6,190.0	1,887
2018	28	4,374.2	1,333
2019	6	1,917.4	584
Total	1,389	1,048,509.8	319,586
By Area
East	149	450,047.3	137,174
West	447	349,128.7	106,414
Main 7	83	9,629.8	2,935
NW	215	49,951.1	15,225
North	84	30,927.0	9,427
NE	15	1,495.0	456
South	117	48,387.8	14,749
25 Zone	8	4,047.0	1,234
37 Zone	7	4,252.0	1,296
38 Zone	20	14,221.5	4,335
52 Zone	5	2,534.0	772
308 Zone	1	879.0	268
Eastern	5	621.5	189
Southern	147	64,374.4	19,621
SW	39	6,658.8	2,030
Sill	39	10,445.5	3,184
Cook Inlet	8	909.5	277
Total	1,389	1,048,509.8	319,586

Page 74

Notes to table:

1. Includes holes drilled on the Sill prospect.

2. Holes started by Northern Dynasty and finished by the Pebble Partnership are included as the Pebble Partnership.

3. Drill holes counted in the year in which they were completed.

4. Wedged holes are counted as a single hole including full length of all wedges drilled.

5. Includes FMMUSA drill holes; data acquired in 2010.

6. Percussion holes were drilled for engineering and environmental purposes. Shallow (<15 ft) auger holes not included.

7. Comprises holes drilled entirely in Tertiary cover rocks within the Pebble West and Pebble East areas.

Some numbers may not sum exactly due to rounding.

The drill hole database includes drill holes completed up until 2019; the drilling completed after 2012 is outside the area of the resource estimate. Highlights of drilling completed by Northern Dynasty and the Pebble Partnership between 2001 and 2019 include:

A re-survey program of holes drilled at Pebble from 1988 to 2009 was conducted during the 2008 and 2009 field seasons. For consistency throughout the project, the resurvey program referenced the control network established by R&M Consultants in the U.S. State Plane Coordinate System Alaska Zone 5 NAVD88 Geoid99. The resurvey information was applied to the drill collar coordinates in the database in late 2009.

In 2009 and 2013, the survey locations, hole lengths, naming conventions and numbering designations of the Pebble drill holes were reviewed. This exercise confirmed that several shallow, non-cored, overburden drill holes described in some engineering and environmental reports were essentially the near-surface pre-collars of existing bedrock diamond drill holes. As these pre-collar and bedrock holes have redundant traces, the geologic information was combined into a single trace in the same manner as the wedged holes. In addition, a number of very shallow (less than 15 ft), small diameter, water-monitoring auger holes were removed from the exploration drill hole database, as they did not provide any geological or geochemical information.

Bulk density measurements were collected from drill core samples, as described in Section 11.4. A summary of all bulk density results is provided in Table 10.3-1 and Table 10.3-2 shows a summary of bulk density drill holes used in the current mineral resource estimate.

Table 10.3-1 Summary of All Bulk Density (g/cm3) Results

Age	No. of Measurements	Density Mean	Density Median
Quaternary	34	2.60	2.61
Tertiary	2,703	2.57	2.57
Cretaceous	8,671	2.66	2.64
All	11,775	2.63	2.62

Table 10.3-2 Summary of Bulk Density (g/cm3) Results Used for Resource Estimation

Age	No. of Measurements	Density Mean	Density Median
Tertiary	3,026	2.56	2.57
Cretaceous	8,130	2.64	2.62
All	11,185	2.62	2.61

The Pebble deposit has been explored by extensive core drilling, with 81,188 samples taken from drill core for assay analysis. Nearly all potentially mineralized Cretaceous core drilled and recovered has been sampled by halving in 10 ft lengths. Similarly, all core recovered from the Late Cretaceous to Early Tertiary cover sequence (referred to as Tertiary3 here and in Sections 12.0 and 13.0) has also been sampled, typically on 20 ft sample lengths, with some shorter sample intervals in areas of geologic interest. Unconsolidated overburden material, where it exists, is generally not recovered by core drilling and therefore not usually sampled.

Rock chips from the 229 rotary percussion holes were generally not sampled for assay analysis, as the holes were drilled for monitoring wells and environmental purposes. Only 35 samples were taken from the drill chips of 26 rotary percussion holes outside the Pebble deposit area, which were drilled for condemnation purposes.

For details of the main rock units in the Pebble deposit and mineralization, see Section 7.0. Summaries of relevant sampling methods and procedures are in technical reports by Rebagliati and Haslinger (2003 and 2004), Haslinger et al. (2004), Rebagliati and Payne (2005, 2006 and 2007), and Rebagliati et al. (2008). Sampling methods and procedures for drill holes completed by Teck are described in these earlier reports, and will not be discussed further here.

Half cores remaining after sampling were replaced in the original core boxes and stored at Iliamna, AK in a secure compound. Later geological, metallurgical and environmental sampling took place on a small portion of this remaining core. Crushed reject samples from the 2006 through 2013 and the 2018 analytical programs are stored in locked containers at Delta Junction, AK. Drill core assay pulps from the 1989 through 2013 and the 2018 programs are stored at a secure warehouse in Surrey, BC.

3Tertiary in usage throughout this section is a collective reference to all unmineralized rocks of the cover sequence that directly overlies the Pebble deposit.

In 2002, 68 drill holes were completed by Quest America Drilling Inc. (Quest). All holes were NQ2 diameter (2 inches/5.08 cm). The core was boxed at the rig and transported daily by helicopter to the secure logging facility in Iliamna. A total of 2,467 core samples, averaging 10 ft long, were collected by Northern Dynasty personnel. Sampling was performed by mechanically splitting the core in half lengthwise.

In 2003, drilling was completed by contractor Quest. All core was NQ2 diameter. The core was boxed at the rig and transported daily by helicopter to the secure logging facility at the village of Iliamna. Samples averaged 10 ft long. Sampling was performed by mechanically splitting the core in half lengthwise. Coarse rejects were stored at SGS Mineral Services in Fairbanks, Alaska, until early 2005, and then discarded.

Most of the 2004 drilling was also completed by Quest, with some footage drilled by Boart Longyear Company (Boart Longyear) and Midnight Sun Drilling Co. Ltd. Core diameters included NQ2, HQ (2.5 in/6.35 cm diameter) and PQ (3.3 in/8.31 cm diameter). Thirty-three rotary percussion water well, engineering and environmental holes were also completed. The 2004 drilling program included 26 larger diameter (PQ and HQ) holes for metallurgical testing. The core was boxed at the rig and transported daily by helicopter to the secure logging facility in the village of Iliamna. A total of 12,865 Cretaceous (syn-mineralization) samples averaging 10 ft long were taken in 2004; 10,893 samples were mechanically split half-core samples and 1,972 samples were of the metallurgical type. The metallurgical samples were taken by sawing an off-centre slice representing 20% of the core volume, which was submitted for assay analysis. The remaining 80% was used for metallurgical purposes. No intact drill core remains after this type of metallurgical sampling, only assay reject and pulp samples. In addition, 904 Tertiary (post-mineralization) samples averaging 15 ft long were taken for trace element analysis. Tertiary samples were collected by mechanically splitting the core in half lengthwise. The average core recovery for all samples taken in 2004 was 97.6%.

In 2005, drilling was again completed by contractor Quest. Core diameters included NQ2, HQ and PQ core. The core was boxed at the rig and transported daily by helicopter to the secure logging facility in the village of Iliamna. A total of 4,378 Cretaceous samples and 1,435 Tertiary samples were collected. Of the Cretaceous samples, 3,541 were taken by sawing the core in half lengthwise. The remaining 837 Cretaceous samples and all Tertiary samples were from metallurgical holes, and were sampled using the 20% off-centre saw method described in Section 11.1.3. Cretaceous samples averaged 10 ft long and Tertiary samples averaged 20 ft long. The average core recovery for all 2005 core holes was 98.4%. In addition to the core drilling, a total of 6,100 ft was drilled in 71 rotary percussion holes by Foundex Pacific Inc. (Foundex) for water monitoring purposes. No samples were collected or analyzed from these holes.

The drilling contractors in 2006 were American Recon Inc. (American Recon) and Boart Longyear. Drill holes were NQ2 and HQ in diameter. A total of 13 shallow rotary percussion holes were also completed for environmental purposes by Foundex. The core was boxed at the rig and transported daily by helicopter to the secure logging facility at Iliamna. The 2,759 Cretaceous samples collected averaged 10 ft long and the 1,847 Tertiary samples averaged 20 ft long. The Cretaceous samples were collected by sawing the core in half lengthwise, and the Tertiary samples were collected by the 20% off-centre saw method described in Section 11.1.3. Average core recovery in 2006 was 98.7%.

The drilling contractors used in 2007 were American Recon, Quest and Boart Longyear. Drill holes were NQ2 and HQ in diameter, and were drilled for geological and metallurgical purposes. Additional drilling was completed by Foundex to establish monitoring wells, but core was not recovered from these holes. Several holes included wedges; in cases where the wedged hole successfully extended beyond the total depth of the parent hole, they were treated as extensions of their parent holes and overlapping information was ignored. The core was boxed at the rig and transported daily by helicopter to the secure logging facility at Iliamna. A total of 12,664 samples were taken from the 72 drill holes. The 9,485 Cretaceous samples averaged 10 ft long, and the 3,179 Tertiary samples averaged 20 ft long. The Cretaceous samples were collected by sawing the core in half lengthwise, and the Tertiary samples were collected by the 20% off-centre saw method described in Section 11.1.3. The average core recovery for 2007 drill holes was 99.7%.

The drilling contractors used in 2008 were American Recon, Boart Longyear and Foundex. Drill holes were NQ, HQ and PQ in diameter, and were drilled for delineation, geotechnical and metallurgical purposes. The core was boxed at the rig and transported daily by helicopter to the secure logging facility at Iliamna. The large 1.7 to 2.2 lb Cretaceous rock assay pulps and the 0.5 lb Tertiary waste rock pulps from these years are stored in a secure warehouse at Surrey, BC. A total of 12,701 samples were taken in 2008 by the Pebble Partnership. The 9,312 Cretaceous samples averaged 10 ft long and the 3,389 Tertiary samples averaged 20 ft long. The Cretaceous samples were collected by sawing the core in half lengthwise. The Tertiary samples and assay samples from metallurgical holes were collected using the 20% off-centre saw method described in Section 11.1.3. The remaining 80% of the core from the Cretaceous portions of the metallurgical holes were used for metallurgical testing.

In 2010, the Pebble Partnership acquired the data for seven holes with 414 samples drilled by FMMUSA in 2008. These drill holes are located near the Property on land that is now controlled by the Pebble Partnership, and provided information on the regional geology.

The drilling contractor used for 2009 drilling was American Recon. Drill holes were NQ, HQ and PQ in diameter. The core was boxed at the rig and transported daily by helicopter to the secure logging facility at Iliamna. A total of 2,835 mainstream samples were collected in 2009. The 2,555 Cretaceous samples averaged 10 ft long and the 280 Tertiary samples averaged 20 ft long. The Cretaceous samples were collected by sawing the core in half lengthwise. Tertiary samples were collected using the 20% off-centre saw method described in Section 11.1.3.

Drilling contractors used for 2010 drilling were American Recon and Foundex. Drill holes were NQ and HQ in diameter. The core was boxed at the rig and transported daily by helicopter to the secure logging facility at Iliamna. A total of 4,714 mainstream samples were taken in 2010. The 4,463 Cretaceous samples and the 251 Tertiary samples averaged 10 ft long. All samples were taken by sawing the core in half lengthwise.

Drill contractors American Recon, Quest and Foundex completed 85 holes in 2011. The hole numbering sequences are 11526 through 11542 for 17 district exploration holes and GH11-229 through GH11-296 for 68 geotechnical holes. Most of these holes were drilled vertically except for 11526, 11528, 11530, 11532, 11533 and 11539, which were inclined at -80°, and 11529, drilled at -75°. Among 68 geotechnical holes, 43 were sonic drilling. A total of 4,281 mainstream samples were taken. The 3,674 Cretaceous samples averaged 10 ft in length and the 607 Tertiary samples averaged 20 ft in length. Cretaceous samples were taken by sawing the core in half lengthwise. Tertiary samples were taken by the 20% off-centre saw-cut method described above.

Drill contractors Quest and Foundex completed 81 holes in 2012. The hole numbering sequences are 12543 through 12562 for 20 exploration, delineation and hydrological holes, and GH12-297 through GH12-357S for 61 geotechnical holes. Most of 12-series holes were drilled with dips of -65° to -80°, and azimuths of 90° to 270° except for 12546, 12554, 12558, 12559, 12561 and 12562, which were drilled vertically. All GH-series holes were drilled vertically. Among 61 geotechnical holes, 31 were completed by sonic drilling. Of the 81 holes, 14 h0les were drilled in the southern and western parts of the Pebble West zone; 6 holes were drilled in the broader claim area to test exploration targets to the south on the Kaskanak claim block to the northwest and south and the KAS claim block further south; and the 61 geotechnical and hydrogeological holes were drilled in the deposit area (45 holes), in Site A (8 holes) and in the area 50 miles to the southeast near Cook Inlet (8 holes). A total of 2,681 core samples (2,537 Cretaceous samples and the 144 Tertiary samples) were taken in 2012. The Cretaceous samples averaged 10 feet in length and were taken by sawing the core in half lengthwise. Tertiary samples averaged 20 ft in length and were taken by the 20% off-centre cut method.

Drill contractor Foundex completed vertical drilling in 37 holes at sites near the deposit in 2013. These holes numbered GH13-358 through GH13-383 were drilled PQ and HQ size for geotechnical and hydrogeological purposes. A total of 523 samples were taken: 1 from Quaternary, 124 from Tertiary and 398 from Cretaceous strata. The Cretaceous and Quaternary samples average 10 feet in length and were taken by sawing the core in half lengthwise. The Tertiary samples average 15 feet in length and were taken by the 20% off-centre cut method.

In 2018, 28 vertical geotechnical holes were drilled to test tailings and water storage facilities.

Six reverse circulation (RC) percussion holes were drilled by T&J Enterprises for hydrogeological site investigation in 2019 in support of the ongoing EIS process. The work consisted of drilling vertically through overburden and bedrock, followed by the installation of pumping wells, monitoring wells, and grouted-in vibrating wire piezometers (VWPs). These holes were not sampled for assay.

Essentially, all of the potentially mineralized Cretaceous rock recovered by drilling on the Pebble Project is subject to sample preparation and assay analysis for copper, gold, molybdenum and a number of other elements. Similarly, all Late Cretaceous to Early Tertiary cover sequence (Tertiary) rock cored and recovered during the drill program is also subject to sample preparation and geochemical analysis by multi-element methods. Since 2007, all sampling at Pebble has been undertaken by employees or contractors under the supervision of a QP. The QP believes these processes are acceptable for use in geological and resource modelling for the Pebble deposit.

In 2002, the samples were prepared at the Fairbanks laboratory of ALS, which has been certified under an International Organization for Standardization (ISO) 9001 since 1999. The sample bags were verified against the numbers listed on the shipment notice. In 2002, the entire sample of half-core was dried, weighed and crushed to 70% passing 10 mesh (2 mm), then a 250 g split was taken and pulverized to 85% passing 200 mesh (75 µm). The pulp was split, and approximately 125 g were shipped by commercial airfreight for analysis at the ALS laboratory in North Vancouver. The remaining pulps were shipped to a secure warehouse at Surrey, BC for long-term storage. The coarse rejects were held for several months at the Fairbanks laboratory until all quality assurance/quality control (QA/QC) measures were completed and were then discarded.

The 2003 samples were prepared at the SGS Mineral Services (SGS) sample preparation laboratory in Fairbanks. After verification of the sample bag numbers against the shipment notice, the entire sample of half-core was dried, weighed and crushed to 75% passing 10 mesh (2 mm). A 400 g split was taken and pulverized to 95% passing 200 mesh (75 µm), and pulps were shipped by commercial airfreight to the SGS laboratories in either Toronto, ON, or Rouyn, QC. The assay pulps were returned for storage at the Surrey warehouse. Coarse rejects were held for several months at the Fairbanks laboratory until all QA/QC measures were completed and were then discarded.

For the 2004 through 2013 and 2018 drill programs, the ALS sample preparation laboratory in Fairbanks performed the sample preparation work. The laboratory received the half-core Cretaceous samples and the off-centre saw splits from the Tertiary samples and metallurgical holes, verified the sample numbers against the sample shipment notice and performed the sample drying, weighing, crushing and splitting. ALS of North Vancouver pulverized the samples from 2004 through 2006 (as described for 2002 samples), and ALS Fairbanks pulverized the samples from 2007 through 2013 and 2018. Assay pulps were returned for long-term storage at the Surrey warehouse. Crushed reject samples from the 2006 through 2013 and 2018 analytical programs are stored in locked containers at Delta Junction, AK.

Analytical work for the 2002 drilling program was completed by ALS of North Vancouver, BC, an ISO 9002 certified laboratory. All samples were analyzed for copper, molybdenum, silver and additional elements by multi-element analysis and for gold by fire assay.

Multi-element analysis for 34 elements, including copper, molybdenum and silver, was by AR digestion of a 0.5 g sample with an ICP-AES finish (ALS code ME-ICP41 shown in Table 11.3-1).

Table 11.3-1 ALS Aqua Regia Digestion Multi-Element Analytical Method ME-ICP41

Element	Symbol	Units	Lower Limit	Upper Limit		Element	Symbol	Units	Lower Limit	Upper Limit
Silver	Ag	ppm	0.2	100		Magnesium	Mg	%	0.01	15
Aluminum	Al	%	0.01	15		Manganese	Mn	ppm	5	10,000
Arsenic	As	ppm	2	10,000		Molybdenum	Mo	ppm	1	10,000
Boron	B	ppm	10	10,000		Sodium	Na	%	0.01	10%
Barium	Ba	ppm	10	10,000		Nickel	Ni	ppm	1	10,000
Beryllium	Be	ppm	0.5	100		Phosphorus	P	ppm	10	10,000
Bismuth	Bi	ppm	2	10,000		Lead	Pb	ppm	2	10,000
Calcium	Ca	%	0.01	15		Sulfur	S	%	0.01	10
Cadmium	Cd	ppm	0.5	500		Antimony	Sb	ppm	2	10,000
Cobalt	Co	ppm	1	10,000		Scandium	Sc	ppm	1	10,000
Chromium	Cr	ppm	1	10,000		Strontium	Sr	ppm	1	10,000
Copper	Cu	ppm	1	10,000		Titanium	Ti	%	0.01	10
Iron	Fe	%	0.01	15		Thallium	Tl	ppm	10	10,000
Gallium	Ga	ppm	10	10,000		Uranium	U	ppm	10	10,000
Mercury	Hg	ppm	1	10,000		Vanadium	V	ppm	1	10,000
Potassium	K	%	0.01	10		Tungsten	W	ppm	10	10,000
Lanthanum	La	ppm	10	10,000		Zinc	Zn	ppm	2	10,000

A total of 1,715 samples from 26 drill holes exhibiting porphyry style copper-gold mineralization were assayed for copper by AR digestion with an AAS finish to the ppm level (ALS code Cu-AA46 shown in Table 11.3-2). Five copper assays greater than 10,000 ppm in hole 2037 were also assayed by this method. A further 271 samples from 5 drill holes were assayed for copper by four-acid (HNO3-HClO4-HF-HCl) digestion AAS (ALS code Cu-AA61 in Table 11.3-2) and 62 samples from drill hole 2034 were assayed for molybdenum by four-acid digestion with an AAS finish (ALS code Mo-AA61 shown in Table 11.3-2). Two samples with Pb and Zn concentrations >10,000 ppm by method ME-ICP41 were reanalyzed by four-acid digestion AAS (ALS codes Pb-AA46 and Zn-AA46 respectively, these methods also shown in Table 11.3-2).

Pebble Project, Southwest Alaska

Page 85

Table 11.3-2 ALS Additional Analytical Procedures

Element	Symbol	Method Code	Digestion	Instrument	Sample Mass (g)	Units	Lower Limit	Upper Limit
Copper	Cu	Cu-AA46	Aqua regia	AAS	0.4	%	0.01	50
Lead	Pb	Pb-AA46	Aqua regia	AAS	0.4	%	0.01	50
Zinc	Zn	Zn-AA46	Aqua regia	AAS	0.4	%	0.01	50
Copper	Cu	Cu-AA61	Four-acid	AAS	0.4	ppm	1	10000
Copper	Cu	Cu-AA62	Four-acid	AAS	0.4	%	0.01	50
Copper	Cu	Cu-OG62	Four-acid	ICP-AES	0.4	%	0.01	40

Gold concentrations were determined by 30 g FA fusion with lead as a collector and an AAS finish (ALS code Au-AA23 in Table 11.3-3). Four samples that returned gold results greater than 10,000 ppb (10 g/t), were re-analyzed by one assay ton FA fusion with a gravimetric finish (ALS code Au-GRAV21 in Table 11.3-3). Seven samples from hole 2013 were analyzed for gold, platinum and palladium by 30 g FA fusion with ICP finish (ALS code PGM-ICP23 in Table 11.3-3). In 2007, and additional 459 samples from 11 other 2002 holes were analyzed by this method.

Table 11.3-3 ALS Precious Metal Fire Assay Analytical Methods

Element	Symbol	Method Code	Instrument	Sample Mass (g)	Units	Lower Limit	Upper Limit
Gold	Au	Au-AA23	AAS	30	ppm	0.005	10
Gold	Au	Au-GRA21	Gravimetric	30	ppm	0.05	1000
Gold	Au	PGM-ICP23	ICP-AES	30	ppm	0.001	10
Platinum	Pt	PGM-ICP23	ICP-AES	30	ppm	0.005	10
Palladium	Pd	PGM-ICP23	ICP-AES	30	ppm	0.001	10

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Analytical work for the 2003 drilling program was completed by SGS Canada Inc. of Toronto, ON, an ISO 9002 registered, ISO 17025 accredited laboratory. All samples were assayed for copper by a total digestion ICP-AES method and for gold by FA. An AR digestion multi-element geochemical package was used for 33 additional elements including copper, molybdenum and silver.

Copper assays were completed at SGS Toronto, ON. Samples were fused with sodium peroxide, digested in dilute nitric acid and the solution analyzed by ICP-AES, with results in percent on SGS method ICAY50 as detailed in Table 11.3-4.

Table 11.3-4 SGS Copper Analytical Method ICAY50

Element	Symbol	Digestion	Instrument	Sample Mass (g)	Units	Lower Limit	Upper Limit
Copper	Cu	Sodium Peroxide Fusion	ICP-AES	0.2	%	0.01	10

Gold analyses were completed at SGS Rouyn, QC, by one assay ton (30 g) lead-collection FA fusion with AAS finish, with results reported in ppb. Ten samples that returned gold results greater than 2,000 ppb (2 g/t) were re-analyzed by 30 g FA fusion with a gravimetric finish, with results reported in g/t. The SGS analytical methods for gold are listed in Table 11.3-5.

Table 11.3-5 SGS Gold Fire Assay Analytical Methods

Element	Symbol	Method Code	Instrument	Sample Mass (g)	Units	Lower Limit	Upper Limit
Gold	Au	FA305	AAS	30	ppb	5	2000
Gold	Au	FA30G	Gravimetric	30	g/t	0.03	1000

All samples were subject to multi-element analysis for 33 elements including copper, molybdenum and sulphur by AR digestion with an ICP-AES finish at SGS Toronto by SGS method ICP70. The elements reported, units and detection limits are listed in Table 11.3-6.

Table 11.3-6 SGS Aqua Regia Digestion Multi-Element Analytical Method ICP70

Element	Symbol	Units	Lower Limit	Upper Limit		Element	Symbol	Units	Lower Limit	Upper Limit
Silver	Ag	ppm	0.2	10		Molybdenum	Mo	ppm	1	10000
Aluminum	Al	%	0.01	15		Sodium	Na	%	0.01	15
Arsenic	As	ppm	3	10000		Nickel	Ni	ppm	1	10000
Barium	Ba	ppm	1	10000		Phosphorus	P	%	0.01	1
Beryllium	Be	ppm	0.5	2500		Lead	Pb	ppm	2	10000
Bismuth	Bi	ppm	5	10000		Sulphur	S	%	0.01	10
Calcium	Ca	%	0.01	15		Antimony	Sb	ppm	5	10000
Cadmium	Cd	ppm	1	10000		Scandium	Sc	ppm	0.5	10000
Cobalt	Co	ppm	1	10000		Tin	Sn	ppm	10	10000
Chromium	Cr	ppm	1	10000		Strontium	Sr	ppm	0.5	5000
Copper	Cu	ppm	0.5	10000		Titanium	Ti	%	0.01	15
Iron	Fe	%	0.01	15		Vanadium	V	ppm	2	10000
Potassium	K	%	0.01	15		Tungsten	W	ppm	10	10000
Lanthanum	La	ppm	0.5	10000		Yttrium	Y	ppm	0.5	10000
Lithium	Li	ppm	1	10000		Zinc	Zn	ppm	0.5	10000
Magnesium	Mg	%	0.01	15		Zirconium	Zr	ppm	0.5	10000
Manganese	Mn	ppm	2	10000

In addition, 30 samples were analyzed for whole-rock geochemical analysis by lithium metaborate fusion with an x-ray fluorescence (XRF) finish. All duplicates were analyzed at ALS laboratory in North Vancouver, BC.

Analytical work in 2002, from 2004 to 2013 and 2018 was completed by ALS of North Vancouver. Total copper and molybdenum concentrations were determined by an intermediate-grade multi-element analytical method. A four-acid digestion was followed by ICP-AES finish (ALS code ME-ICP61a). This multi-element method was also used to determine 31 additional elements including sulphur. The elements reported, units and detection limits are listed in Table 11.3-7.

Table 11.3-7 ALS Four Acid Digestion Multi-Element Analytical Method ME-ICP61a

Element	Symbol	Units	Lower Limit	Upper Limit		Element	Symbol	Units	Lower Limit	Upper Limit
Silver	Ag	ppm	1	200		Molybdenum	Mo	ppm	10	50000
Aluminum	Al	%	0.05	50		Sodium	Na	%	0.05	30
Arsenic	As	ppm	50	100000		Nickel	Ni	ppm	10	100000
Barium	Ba	ppm	50	50000		Phosphorus	P	ppm	50	100000
Beryllium	Be	ppm	10	10000		Lead	Pb	ppm	20	100000
Bismuth	Bi	ppm	20	50000		Sulphur	S	%	0.05	10
Calcium	Ca	%	0.05	50		Antimony	Sb	ppm	50	50000
Cadmium	Cd	ppm	10	10000		Scandium	Sc	ppm	50	50000
Cobalt	Co	ppm	10	50000		Strontium	Sr	ppm	10	100000
Chromium	Cr	ppm	10	100000		Thorium	Th	ppm	50	50000
Copper	Cu	ppm	10	100000		Titanium	Ti	%	0.05	30
Iron	Fe	%	0.05	50		Thallium	Tl	ppm	50	50000
Gallium	Ga	ppm	50	50000		Uranium	U	ppm	50	50000
Potassium	K	%	0.1	30		Vanadium	V	ppm	10	100000
Lanthanum	La	ppm	50	50000		Tungsten	W	ppm	50	50000
Magnesium	Mg	%	0.05	50		Zinc	Zn	ppm	20	100000
Manganese	Mn	ppm	10	100000