Item 2. Properties
ITEM 2. PROPERTIES .
References to USD or $ refer to United States currency and AUD or A$ refer to Australian currency, all in thousands, unless specified otherwise.
Qualified Persons
The scientific and technical disclosures about Mt Todd in this annual report on Form 10-K have been reviewed and approved by John W. Rozelle, Senior Vice President of Vista. Mr. Rozelle is a qualified person as defined by S-K 1300 and NI 43-101. For a description of the key assumptions, parameters and methods used to estimate mineral reserves and mineral resources included in this Form 10-K, as well as data verification procedures and a general discussion of the extent to which the estimates may be affected by any known environmental, permitting, legal, title, taxation, sociopolitical, marketing or other relevant factors, please review the technical report summary of the Mt Todd FS (as described below) which is included as an exhibit to this Form 10-K.
Mt Todd Gold Project, Northern Territory, Australia
Summary Disclosure
The Company has one material mining property, the Mt Todd gold project located in the Northern Territory of Australia. We hold Mt Todd through our wholly owned subsidiary Vista Gold Australia Pty. Ltd. (“Vista Gold Australia”).
Technical Report Summary
The 2022 feasibility study for Mt Todd is the technical report summary, prepared pursuant to S-K 1300, that was filed on EDGAR on February 24, 2022 and is entitled “S-K 1300 Technical Report Summary - Mt Todd Gold Project - 50,000 tpd Feasibility Study – Northern Territory, Australia” with an effective date of December 31, 2022 and an issue date of February 9, 2022, as amended February 7, 2023 (the “Mt Todd FS”). The technical report summary remains current in all material respects.
A companion feasibility study for Canadian purposes, pursuant to NI 43-101, was filed on SEDAR on February 24, 2022 and is entitled “NI 43-101 Technical Report - Mt Todd Gold Project - 50,000 tpd Feasibility Study – Northern Territory, Australia” with an effective date of December 31, 2021 and an issue date of February 9, 2022. The companion report is referenced herein for informational purposes only.
The technical data and economic conclusions of these reports are materially identical, with differences in the formatting of the reports and details of certain assumptions resulting only from the respective disclosure requirements of S-K 1300 and NI 43-101. The reports were prepared by Sabry Abdel Hafez, Ph.D., P.Eng.; Rex Clair Bryan, Ph.D., SME RM; Thomas L. Dyer, P.E., SME RM; Amy Hudson, Ph.D., CPG, REM; April Hussey, P.E.; Chris Johns, M.Sc., P.Eng.; Max Johnson, P.E.; Deepak Malhotra, Ph.D., SME RM; Zvonimir Ponos, BE, MIEAust, CPeng, NER; Vicki J. Scharnhorst, P.E., LEED AP; and Keith Thompson, CPG, member AIPG, each of whom is a qualified person under S-K 1300 and NI 43-101.
The following description of Mt Todd has been derived, in part, from the Mt Todd FS and readers should consult the Mt Todd FS to obtain further particulars regarding Mt Todd. The Mt Todd FS is available for review at www.sec.gov and under our profile at www.sedar.com. The Mt Todd FS is not incorporated by reference into this annual report on Form 10-K.
Certain capitalized terms in this section not otherwise defined have the meanings ascribed to them in the Mt Todd FS.
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Table of Contents
Project Location and Access
Mt Todd is located 56 kilometers by road northwest of Katherine, NT, Australia, and approximately 290 kilometers by road southeast of Darwin, NT. Access is by existing paved public roads and approximately four kilometers of paved private road. We control and maintain the private paved road.
The area has a sub-tropical climate with a distinct wet season and dry season. The area receives most of its rainfall between the months of January and March. Temperatures are moderate, allowing for year-round mining operations. The topography is relatively flat. The tenements encompass a variety of habitats forming part of the northern Savannah woodland region, which is characterized by eucalypt woodland with tropical grass understories. Surface elevations are approximately 130 to 160 meters above sea level in the area of the previous and planned mine plant site and waste rock dumps.
Project Stage
The Mt Todd gold project is a development stage property with proven and probable mineral reserves.
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Table of Contents
Feasibility Study Results
The Mt Todd FS evaluates a 50,000 tpd project (“50,000 tpd Project”) that optimizes payable gold, capital efficiency, operating costs and net present value (“NPV”).
The 50,000 tpd Project highlights include:
● estimated proven and probable mineral reserves of 6.98 million ounces of gold (280 Mt at 0.77 g Au/t) at a cut-off grade of 0.35 g Au/t (1)(2) ;
● average annual production of 395,000 ounces of gold over the 16-year mine life, including average annual production of 479,000 ounces of gold per year during the first seven years of operations following commissioning and ramp-up;
● life of mine average cash costs of $817 per ounce, including average cash costs of $752 per ounce during the first seven years of operations following commissioning and ramp-up;
● a 16-year operating life;
● initial capital requirements of $892 million which assume an owner-operated mining fleet, power generated on-site by a third-party, and a locally based employee workforce;
● after-tax NPV 5% of $999.5 million and internal rate of return (“IRR”) of 20.6% at a gold price of $1,600 per ounce and an AUD:USD exchange rate of 0.71; and
● after-tax NPV 5% of $1.7 billion and IRR of 29.4% at a price of $1,900 per ounce of gold and an AUD:USD exchange rate of 0.71 based on the Gold Price and Foreign Exchange Sensitivity Table below.
(1) Note to investors: Proven and probable mineral reserves are estimated in accordance with S-K 1300 and CIM Definition Standards.
(2) See “Item 1. Business – Cautionary Note to Investors Regarding Estimates of Measured, Indicated and Inferred Resources and Proven and Probable Mineral Reserves” in this annual report on Form 10-K for additional information.
Key statistics of the 50,000 tpd Project are presented in the table below:
Years 1-7 (1)
Life of Mine (16 years) (2)
Average Plant Feed Grade (g Au/t) (3)
1.01
0.84
Average Annual Gold Production (koz)
479
395
Payable Gold Total (koz)
3,353
6,313
Average Recovery (%)
92.2
%
91.6
%
Cash Costs ($/oz) (4)
$
752
$
817
AISC ($/oz) (5)
$
860
$
928
Strip Ratio (waste:ore)
2.77
2.51
Initial Capital ($ millions)
$
892
After-tax NPV 5% ($ millions)
$
999.5
After-tax IRR
20.6
%
After-tax Payback (Months)
47
Note: Table economics presented using $1,600/oz gold and a A$1.00 :$0.71 exchange.
(1) Years 1-7 start after the 6-month commissioning and ramp up period.
(2) Life of mine is from start of commissioning and ramp up through the final closure.
(3) Post-sorting grinding circuit feed grade.
(4) Cash Costs per ounce is a non-U.S. GAAP financial measure; see Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations – Non-U.S. GAAP Financial Measures for additional disclosure.
(5) All-in Sustaining Costs (“AISC”) per ounce is a non-U.S. GAAP financial measure; see Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations – Non-U.S. GAAP Financial Measures for additional disclosure.
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Table of Contents
The following chart presents the 50,000 tpd Project annual cash flow using $1,600/oz gold and an A$1.00:$0.71 exchange rate:
The following table provides additional details of the 50,000 tpd Project economics at variable gold price and foreign exchange assumptions:
Gold Price and Foreign Exchange Rate Sensitivity Table ($ Millions)
Foreign
Gold Price
Exchange Rate
$1,300
$1,400
$1,500
$1,600
$1,700
$1,800
$1,900
($/A$)
NPV 5%
IRR
NPV 5%
IRR
NPV 5%
IRR
NPV 5%
IRR
NPV 5%
IRR
NPV 5%
IRR
NPV 5%
IRR
0.74
$214
8.6%
$453
12.4%
$674
15.5%
$911
19.0%
$1,144
22.1%
$1,372
25.0%
$1,589
27.7%
0.71
$304
10.2%
$541
14.0%
$762
17.3%
$999.5†
20.6%†
$1,229
23.7%
$1,458
26.7%
$1,674
29.4%
0.68
$393
11.9%
$626
15.6%
$851
18.9%
$1,085
22.3%
$1,313
25.7%
$1,543
28.5%
$1,758
31.3%
† Reflects the assumptions used for the economic analysis in the Mt Todd FS.
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Table of Contents
Key capital expenditures for the 50,000 tpd Project initial and sustaining capital requirements are:
Capital Expenditures ($ Millions, except per ounce amount)
Initial
Sustaining
Capital
Capital
Mining
$
81
$
531
Process Plant
474
28
Project Services
56
89
Project Infrastructure
45
8
Site Establishment & Early Works
24
—
Management, Engineering, EPCM Services
100
—
Preproduction Costs
27
—
Contingency
86
44
Sub-Total
$
892
$
700
Asset Sale and Salvage
—
(37)
Total Capital
$
892
$
663
(1)
Total Capital per Payable Ounce of Gold
$
141
$
105
(1)
Note: Amounts may not add to total due to rounding. Asset sale and salvage value assumptions include end of life re-sale values for mining and processing equipment; and recycle value for steel and pipe from the process plant and other facilities.
(1) Net of asset sales.
The Mt Todd FS contemplates an owner-operated mining fleet at initial capital of $86 million and sustaining capital of $565 million, inclusive of contingency. The study assumes the equipment will be sold when retired from operations, at an estimated salvage value of $21 million. Fleet operators, along with other employees, are expected to be community based, providing benefits by lower camp-related capital and operating costs. Mining equipment would be maintained through a full maintenance and repair contract with the manufacturer’s authorized dealer. Overall, this approach is expected to produce lower operating costs compared to contract mining.
The Mt Todd FS utilizes the efficiency of ore sorting across a broad range of head grades, the natural concentration of gold in the screen undersize material prior to sorting, the efficiency of fine grinding and the resulting improved gold recoveries at a final grind size of P 80 40 µm, and the selection of FLSmidth’s VXP mill (“VXP Mills”) as the preferred fine grinding mill.
The 50,000 tpd Project incorporates purchasing electrical power from a third-party. The power plant will be owned, operated, and provide power to the Project on a dedicated contract.
The following table presents a breakdown of 50,000 tpd Project operating costs.
Operating Cost
First 7 Years
Life of Mine Cost
Per ore tonne
Per ore tonne
processed
Per ounce
processed
Per ounce
Mining
$
8.52
$
316
$
6.79
$
302
Processing
9.39
348
9.44
419
Site General and Administrative
1.06
39
0.99
44
Jawoyn Royalty (1)
0.86
32
0.72
32
Water Treatment
0.26
10
0.29
13
Tailings Management
0.08
3
0.08
4
Refining Costs (1)
0.09
3
0.08
3
Total Cash Costs (2)
$
20.28
$
752
$
18.40
$
817
Note: Table may not add to total due to rounding
(1) Jawoyn Royalty (as defined below) and refining costs calculated at $1,600 per ounce gold and an A$1.00 : $0.71 exchange rate.
(2) Total Cash Costs is a non-U.S. GAAP financial measure; see Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations – Non-U.S. GAAP Financial Measures for additional disclosure.
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Table of Contents
In November 2020, we modified our agreement with the Jawoyn Association. The modified agreement provides the Jawoyn Association with a gross proceeds royalty (“GPR”) ranging between 0.125% and 2.0%, depending on prevailing gold prices and foreign exchange rates, instead of its previous right to become a 10% participating joint venture partner in Mt Todd (“Jawoyn Royalty”). The modified agreement did not affect the previously agreed 1.0% GPR. The combined GPR range is now from 1.125% to 3.0% and is reflected in the table above.
The life of mine production schedule contemplates 280.4 million tonnes of ore containing an estimated 6.98 million ounces of gold at an average grade of 0.77 g Au/t to be processed over a 16-year operating life of the Project. Total recovered gold is expected to be 6.31 million ounces. Average annual gold production over the life of the Project is expected to be 395,000 ounces, which includes averaging 479,000 ounces during the first seven years of commercial operations. Commercial operations are anticipated to begin after two years of construction and a six-month commissioning and ramp-up period.
The following table summarizes the production schedule. The shaded portion of the table highlights the impact of sorting which reduces the tonnage processed by 10%, increases the processed grade by a similar percentage, and results in cost savings in the grinding, leaching and tailings handling.
Years
Pit Ore Mined (kt)
Waste Mined (kt)
Ore Crushed (kt)
Crushed Grade (g/t)
Contained Ounces (kozs)
Ore to CIP (Post Sorting) (kt)
CIP Grade (g/t)
Contained Ounces (kozs)
Gold Produced (kozs)
Recovery (%)
(1)
7,188
14,066
0
0
0
0
0.00
0
0
0
1 †
18,216
25,904
12,334
1.10
436
11,100
1.21
431
399
92.6%
2
30,578
38,623
17,750
0.88
503
15,975
0.97
497
458
92.1%
3
19,696
63,199
17,750
1.04
594
15,975
1.14
587
542
92.5%
4
15,218
69,774
17,799
0.66
378
16,019
0.73
373
341
91.3%
5
27,591
66,264
17,750
0.79
451
15,975
0.87
445
408
91.7%
6
25,499
74,510
17,823
1.03
591
16,041
1.13
583
539
92.4%
7
13,229
77,291
17,750
0.97
554
15,975
1.06
546
504
92.3%
8
7,779
71,277
17,774
0.69
392
15,997
0.75
386
352
91.2%
9
13,866
59,499
17,774
0.52
295
15,997
0.57
291
261
89.8%
10
14,523
50,082
17,750
0.55
312
15,975
0.60
308
277
90.1%
11
20,830
40,490
17,750
0.61
347
15,975
0.67
343
311
90.7%
12
18,523
13,685
17,774
0.72
410
15,997
0.79
404
370
91.4%
13
11,307
4,388
17,774
0.76
433
15,997
0.83
428
391
91.6%
14
13,829
1,866
17,750
0.79
448
15,975
0.86
442
406
91.7%
15
9,149
412
17,750
0.78
446
16,120
0.85
440
403
91.6%
16 ‡
0
0
16,710
0.64
344
15,968
0.66
341
310
90.7%
17 ‡
0
0
2,612
0.54
45
2,612
0.54
45
41
89.8%
Total
267,021
671,331
280,375
0.77
6,979
253,673
0.84
6,891
6,313
91.6%
Note: Amounts may not add due to rounding.
† Six-month startup and commissioning period ahead of full production
‡ Total milled ore includes material from the existing heap leach pad that is processed in years 16 and 17.
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Table of Contents
Mineral Resources and Mineral Reserves Estimates
The mineral resources and mineral reserves reported in this section were prepared in accordance with both S-K 1300 standards and CIM Definition Standards. The table below presents the estimated mineral resources for the Project.
Mt Todd Gold Project – Summary of Gold Mineral Resources based on US$1,300/oz Gold
Batman Deposit
Heap Leach Pad
Quigleys Deposit
Total
Contained
Contained
Contained
Contained
Tonnes
Grade
Ounces
Tonnes
Grade
Ounces
Tonnes
Grade
Ounces
Tonnes
Grade
Ounces
(000s)
(g Au/t)
(000s)
(000s)
(g Au/t)
(000s)
(000s)
(g Au/t)
(000s)
(000s)
(g Au/t)
(000s)
Measured
—
—
—
—
—
—
594
1.15
22
594
1.15
22
Indicated
10,816
1.76
613
—
—
—
7,301
1.11
260
18,117
1.49
873
Measured & Indicated
10,816
1.76
613
—
—
—
7,895
1.11
282
18,711
1.49
895
Inferred
61,323
0.72
1,421
—
—
—
3,981
1.46
187
65,304
0.77
1,608
Notes:
● Measured & indicated resources exclude proven and probable reserves.
● The Point of Reference for the Batman and Quigleys deposits is in situ at the property. The Point of Reference for the Heap Leach is the physical Heap Leach pad at the property.
● Batman and Quigleys resources are quoted at a 0.40g-Au/t cut-off grade. Heap Leach resources are the average grade of the heap, no cut-off applied.
● Batman: Resources constrained within a US$1,300/oz gold Whittle TM pit shell. Pit parameters: Mining Cost US$1.50/tonne, Milling Cost US$7.80/tonne processed, G&A Cost US$0.46/tonne processed, G&A/Year 8,201 K US$, Au Recovery, Sulfide 85%, Transition 80%, Oxide 80%, 0.2g-Au/t minimum for resource shell.
● Quigleys: Resources constrained within a US$1,300/oz gold Whittle TM pit shell. Pit parameters: Mining cost US$1.90/tonne, Processing Cost US$9.779/tonne processed, Royalty 1% GPR, Gold Recovery Sulfide, 82.0% and Ox/Trans 78.0%, water treatment US$0.09/tonne, Tailings US$0.985/tonne.
● Differences in the table due to rounding are not considered material. Differences between Batman and Quigleys mining and metallurgical parameters are due to their individual geologic and engineering characteristics.
● Rex Bryan of Tetra Tech, Inc. is the QP responsible for the Statement of Mineral Resources for the Batman, Heap Leach Pad and Quigleys deposits.
● Thomas Dyer of RESPEC is the QP responsible for developing the resource Whittle TM pit shell for the Batman Deposit.
● The effective date of the Batman Deposit, Heap Leach Pad, and Quigleys Deposit mineral resources estimates under the requirements of SK-1300 is December 31, 2022. There have been no changes in the mineral resource estimates since December 31, 2021 because upon review the Company and the relevant qualified persons determined that the same material assumptions and estimates, including all economic parameters for resource estimation purposes, continued to apply as of December 31, 2022.
● The effective date of the Batman Deposit, Heap Leach Pad, and Quigleys Deposit mineral resource estimates under the requirements of NI 43-101 is December 31, 2021.
● Mineral resources that are not mineral reserves have no demonstrated economic viability and do not meet all relevant modifying factors.
There was no change in resource estimates as of December 31, 2022 compared to December 31, 2021 as the same material assumptions and criteria were determined to continue to apply to the resource estimates and there was no conversion of resources into reserves in the fiscal year ending December 31, 2022.
The mine plan in the Mt Todd FS includes both proven and probable mineral reserves and results in estimated total recovered gold of 6.31 million ounces.
29
Table of Contents
The table below presents the estimated mineral reserves for the Project.
Mt Todd Gold Project – Summary of Gold Mineral Reserves based on 50,000 tpd, 0.35 g Au/t cut-off and $1,125 per Ounce Pit Design
Batman Deposit
Heap Leach Pad
Total
Contained
Contained
Contained
Tonnes
Grade
Ounces
Tonnes
Grade
Ounces
Tonnes
Grade
Ounces
(000s)
(g Au/t)
(000s)
(000s)
(g Au/t)
(000s)
(000s)
(g Au/t)
(000s)
Proven
81,277
0.84
2,192
—
—
—
81,277
0.84
2,192
Probable
185,744
0.76
4,555
13,354
0.54
232
199,098
0.75
4,787
Proven & Probable
267,021
0.79
6,747
13,354
0.54
232
280,375
0.77
6,979
Economic analysis conducted only on proven and probable mineral reserves.
Notes:
● Thomas L. Dyer, P.E., is the QP responsible for reporting the Batman Deposit Proven and Probable reserves.
● Batman deposit reserves are reported using a 0.35 g Au/t cutoff grade.
● Deepak Malhotra is the QP responsible for reporting the heap-leach pad reserves.
● Because all the heap-leach pad reserves are to be fed through the mill, these reserves are reported without a cutoff grade applied.
● The reserves point of reference is the point where material is fed into the mill.
● The effective date of the mineral reserve estimates under the requirements of S-K 1300 is December 31, 2022. There have been no changes in the mineral reserve estimates since December 31, 2021 because the Company and the relevant qualified persons determined that the same material assumptions and criteria continued to apply as of December 31, 2022, including that the Company used a cutoff grade higher than the economic cutoff grade such that any intervening changes in the underlying economic assumptions were not material and did not require use of a cutoff grade greater than 0.35 g Au/t for mineral reserve estimation purposes.
● The effective date of the mineral reserve estimates under the requirements of NI 43-101 is December 31, 2021.
Cautionary note to investors: Proven and probable mineral reserves are estimated in accordance with S-K 1300 and CIM Definition Standards. A number of risk factors may adversely affect estimated mineral reserves and mineral resources, any of which may result in a reduction or elimination of reported mineral reserves and mineral resources. See “Item 1A. Risk Factors.”
There was no change in reserve estimates as of December 31, 2022 compared to December 31, 2021 as the same material assumptions and criteria were determined to continue to apply to the reserve estimates and there was no depletion of reserves in the fiscal year ending December 31, 2022 as the Mt. Todd Gold Project is in the development stage
The tables below show the resource classification criteria and variogram parameters for the Batman resource model.
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Table of Contents
Property Holdings
In 2006, through an agreement with Pegasus Gold Australia Pty. Ltd. (“Pegasus”), the NT Government, and the Jawoyn Association, we acquired the concession rights and access to Mt Todd. Also in 2006, through an agreement with the NT Government, we established the rights and obligations of Vista and the NT Government with respect to Mt Todd site care and maintenance and potential future development. In 2017, the latter agreement was extended through the end of 2023 and the Company has requested an additional extension.
Total land holdings controlled by Vista Gold Australia are approximately 1,705 Km 2 . A map showing the location of the mineral licenses (“MLs”) and exploration licenses (“ELs”) and a table with a list of MLs and ELs and the holding requirements are set out below. All of the estimated mineral reserves and resources are located within the boundaries of the MLs and substantially all of the estimated mineral reserves and resources at Mt Todd are located in the Batman deposit.
The Batman and Quigleys deposits are located within the MLs. Should a deposit be discovered on the ELs, the portion of the related EL would have to be converted to an ML before mining operations could start.
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Table of Contents
Mt Todd Land Holdings of Vista Gold Australia
Estimated Holding
Requirements
Annual Rent &
Annual Work
Annual
Surface
Location
Admin Fees
Requirement
Expenditure/
Area
Description
Location Date/
(thousands
(thousands
Technical
Mineral Licenses
(Km 2 )
(UTM)
Grant Date
Renewal Date
of A$)
of A$)
Reports Due
MLN 1070
39.8
Mining License Block
March 5, 1993
March 4, 2043
88
(due March 4)
N/A
May 4
MLN 1071
13.3
centered at
March 5, 1993
March 4, 2043
29
(due March 4)
N/A
May 4
MLN 1127
0.8
approximately
March 5, 1993
March 4, 2043
2
(due March 4)
N/A
May 4
MLN 31525
1.6
188555E, 435665N
September 4, 2017
September 3, 2042
4
(due September 3)
N/A
May 4
Subtotal
55.4
123
-
Estimated Holding
Requirements
Annual Rent &
Annual Work
Annual
Surface
Location
Admin Fees
Requirement
Expenditure/
Area
Description
Location Date/
(thousands
(thousands
Technical
Exploration Licenses
(Km 2 )
(UTM)
Grant Date
Renewal Date
of A$)
of A$)
Reports Due
EL29882
556
Centered at approximately 189100E, 84520000N
September 16, 2013
September 15, 2023
39
(due September 15)
125
May 14
EL29886
595
Centered at approximately 200300E, 8452000N
September 16, 2013
September 15, 2023
45
(due September 15)
77
May 14
EL30898
187
Centered at approximately 176100E, 8428700N
May 3, 2016
May 2, 2024
13
(due May 2)
12
May 14
EL32004
163
Centered at approximately 164000E, 8430550N
November 21, 2019
November 20, 2025
4
(due November 20)
30
May 14
ELA32005
149
Centered at approximately 160180E, 8445150N
Under application
Under application
Under application
Under application
Under application
Subtotal
1,650
101
244
Totals A$
224
244
Totals US$ (exchange rate of A$1.00 = $0.682 on December 31, 2022)
153
166
The surface land in the area of the contiguous MLs and ELs (excluding EL 32004) is freehold land owned by the Jawoyn Association. Because the Jawoyn Association have title to the land, such land is not part of the lands classified by the government as indigenous lands, and as a result such lands are not subject to an Indigenous land use agreement. Vista has a private agreement with the Jawoyn Association for access to the land.
Annually, we are required to submit a care and maintenance MMP to the DITT that details work to be done on the property. We have received approval for all work done on the Project to date and obtained approval for the EIS. We received our operational MMP in June 2021, which is the operating permit that sets out how mine operating strategy will be implemented throughout the mine life in compliance with the EIS and EPBC requirements. The MMP is in the process of being amended to align with the design changes in the Mt Todd FS. The remaining permitting processes are relatively straight-forward and are not expected to impede, to a material extent, our exploration and future development plans. Any future mining will require sufficient surety bonding to fund mine closure.
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Table of Contents
Infrastructure
Because Mt Todd was an operating mine, infrastructure exists that reduces initial capital expenditure and significantly reduces capital risk related to infrastructure construction, which has been a major source of capital cost overruns in the mining industry over the last decade. Existing mining infrastructure items include:
● a tailings storage facility with capacity for approximately 80 million tonnes of additional material;
● a fresh water storage reservoir that would receive a two-meter dam raise and would harvest stormwater expected to be sufficient to provide process water for year-round operations for a 50,000 tpd operation;
● a natural gas pipeline at site that can supply sufficient natural gas to meet the Project’s energy requirements which, coupled with the planned power generating plant, would save considerably on Project operating costs compared to grid-supplied power;
● a paved road to site; and
● current electrical connection to the NT electric grid.
In addition, we expect reduced earthworks costs due to the process plant location being the same as the previous process plant, which has already been cleared and graded.
Other benefits of Mt Todd’s NT location include:
● the Stuart highway – the main North / South highway in the NT is less than 10 kilometers from the Project site;
● rail line parallel to the Stuart highway; and
● the regional center of Katherine (population approximately 12,000) less than 40 kilometers from site and the NT capital of Darwin less than 290 kilometers from the Project site, which has port access.
The area has both historical and current mining activity and therefore a portion of the skilled workforce should be able to be sourced locally. In addition, Katherine offers the necessary support functions that are typically found in a medium-sized city with regard to supplies, accommodations, communications, etc.
Planned infrastructure for the site includes the following:
● ammonium nitrate and fuel oil facility;
● mine support facilities (heavy vehicle workshop, lube farm, washdown and tire change, warehouse, fuel farm, mining offices, core storage facility);
● heap leach facility;
● small accommodation camp for occasional contractor use;
● water treatment plant;
● power supply;
● pit dewatering;
● mine services;
● communications;
● gatehouse; and
● expanded existing and additional tailings storage facility.
Geological Setting, Mineralization, and Deposit Type
Mt Todd is situated within the southeastern portion of the Early Proterozoic Pine Creek Geosyncline. Meta-sediments, granitites, basic intrusives, acidic and intermediate volcanic rocks occur within this geological province. Within the Mt Todd region, the oldest outcropping rocks are assigned to the Burrell Creek Formation. These rocks consist primarily of interbedded greywackes, siltstones, and shales of turbidite affinity, which are interspersed with minor volcanics. The
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Burrell Creek Formation is overlain by interbedded greywackes, mudstones, tuffs, minor conglomerates, mafic to intermediate volcanics and banded ironstone of the Tollis Formation. The Burrell Creek Formation and Tollis Formation comprise the Finniss River Group. The Finniss River Group strata have been folded about northerly trending F1 fold axes. The folds are closed to open style and have moderate westerly dipping axial planes with some sections being overturned. A later north-south compression event resulted in east-west trending open style upright D2 folds. The Finniss River Group has been regionally metamorphosed to lower green schist facies. Late and Post Orogenic granite intrusions of the Cullen Batholith occurred from 1,789 Ma to 1,730 Ma and brought about local contact metamorphism to hornblende hornfels facies.
The Batman pit geology consists of a sequence of hornfelsed interbedded greywackes and shales with minor thin beds of felsic tuff. Bedding consistently strikes at 325 degrees, dipping 40 degrees to 60 degrees to the southwest. Northerly trending sheeted quartz sulfide veins and joints striking at 0 degrees to 20 degrees and dipping 60 degrees to the east are the major controls for mineralization in the Batman pit. The veins are 1 to 100 millimeters in thickness with an average thickness of around 8 to 10 millimeters and occur in sheets with up to 20 veins per horizontal meter. These sheeted veins are the main source of gold mineralization in the Batman pit. In general, the Batman pit extends 1,600 meters in length by 1,100 meters in width and has been drill tested to a depth of 800 meters down-dip. The deposit is open along strike and at depth.
The mineralization within the Batman pit is directly related to the intensity of the north-south trending quartz sulfide veining. The lithological units impact the orientation and intensity of mineralization. Sulfide minerals associated with the gold mineralization are pyrite, pyrrhotite and lesser amounts of chalcopyrite, bismuthinite and arsenopyrite. Galena and sphalerite are also present, but appear to be post-gold mineralization, and are related to calcite veining in the bedding plains and the east-west trending faults and joints. Two main styles of mineralization have been identified in the Batman pit. These are the north-south trending vein mineralization and bedding parallel mineralization.
Gold mineralization in the Batman deposit occurs in sheeted veins within silicified greywackes/shales/siltstones. The Batman deposit strikes north-northeast and dips steeply to the east. Higher grade zones of the deposit plunge to the south. The core zone is approximately 200-250 meters wide and 1.5 kilometers long, with several hanging wall structures providing additional width to the orebody. Mineralization is open at depth as well as along strike, although the intensity of mineralization weakens to the north and south along strike.
Historical Operations
The Batman gold prospect is located in the Pine Creek Geosyncline that was worked from early in the 20th century. Gold and tin were discovered in the Mt Todd area in 1889. Most deposits were worked in the period from 1902 to 1914. A total of 7.80 tonnes of tin concentrate was obtained from cassiterite-bearing quartz-kaolin lodes at the Morris and Shamrock mines. The Jones Brothers reef was the most extensively mined gold-bearing quartz vein, with a recorded production of 28.45 kg Au. This reef consists of a steeply dipping ferruginous quartz lode within tightly folded greywackes.
The Yinberrie Wolfram field, discovered in 1913, is located 5 kilometers west of Mt Todd. Tungsten, molybdenum and bismuth mineralization was discovered in greisenized aplite dykes and quartz veins in a small stock of the Cullen Batholith. Recorded production from numerous shallow shafts is 163 tonnes of tungsten, 130 kg of molybdenite and a small quantity of bismuth.
Exploration for uranium began in the 1950s. Small uranium prospects were discovered in sheared or greisenized portions of the Cullen Batholith in the vicinity of the Edith River.
Australian Ores and Minerals Limited (“AOM”) in a joint venture with Wandaroo Mining Corporation and Esso Standard Oil took out a number of mining leases in the Mt Todd area during 1975. Initial exploration consisted of stream sediment sampling, rock chip sampling, and geological reconnaissance for a variety of commodities. A number of geochemical anomalies were found primarily in the vicinity of old workings. Follow-up work concentrated on alluvial tin and, later, auriferous reefs. Backhoe trenching, costeaning, and ground follow-up were the favored mode of exploration. Two diamond drillholes were drilled at Quigleys. Despite determining that the gold potential of the reefs in the area was promising, AOM ceased work around Mt Todd.
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The Arafura Mining Corporation, CRA Exploration, and Marriaz Pty Ltd all explored the Mt Todd area at different times between 1975 and 1983. In late 1981, CRA Exploration conducted grid surveys, geological mapping and a 14 diamond drillhole program, with an aggregate meterage of 676.5 meters, to test the gold content of Quigleys Reef over a strike length of 800 meters. Following this program CRA Exploration did not proceed with further exploration.
During late 1986, Pacific Gold Mines NL (“Pacific”) undertook exploration in the area which resulted in small-scale open cut mining on the Quigleys and Golf reefs, and limited test mining at the Alpha, Bravo, Charlie and Delta pits. Ore was transported to a carbon in pulp (“CIP”) plant owned by Pacific at Moline. This continued until December 1987. Pacific ceased operations in the area in February 1988 having produced approximately 86,000 tonnes grading 4 g Au/t (historical reported production, not S-K 1300 or NI 43-101 compliant). Subsequent negotiations between the joint venture partners Shell Company of Australia (“Billiton”), Zapopan NL (“Zapopan”) and Pacific resulted in the acquisition of this ground and incorporation into the joint venture.
Billiton, who was the managing partner in an exploration program in the joint venture with Zapopan, discovered the Mt Todd mineralization, or more specifically the Batman deposit, in May 1988. In 1992, Pegasus acquired a shareholding in Zapopan, following which Zapopan acquired Billiton’s interest. Pegasus progressively increased their shareholding until they acquired full ownership of Zapopan in July 1995.
Historical preliminary studies (not S-K 1300 or NI 43-101 compliant) for Phase I, a heap leach operation which focused predominately on the oxide portion of the deposit, commenced during 1992 culminating in an engineering, procurement, construction management (“EPCM”) award to Minproc in November of that year. The Phase I project was predicated upon a 4 million tonne per year (“Mtpy”) heap leach plant, which came on stream in late 1993. The treatment rate was subsequently expanded to a rate of 6 Mtpy in late 1994.
Based on our review of the historical project files, we believe that approximately 21.4 million tonnes grading 1.05 grams gold per tonne and containing 723,795 ounces of gold were extracted between 1993 and the termination of mining in 2000. Processing was by a combination of heap leach production from oxide ore and cyanidation of sulfide ore. The remaining mineralization consists of sulfide mineralization lying below and along strike of the existing open pit, and in hanging wall structures parallel to the main zone in the existing open pit.
Historical heap leach production is shown in the table below:
Category
Historical Heap Leach Production Reported
Tonnes Leached (million)
13.2
Head Grade (g Au/t)
0.96
Recovery (%)
53.8
Gold Recovered (oz)
220,755
Cost/t (AUD)
8.33
Cost/oz (AUD)
500
NOTE: All tonnages and grades are historical production numbers that pre-date Vista’s ownership. The QPs and issuer consider historical estimates to be relevant but not current.
Phase II involved expanding to 8 Mtpy and treatment through a flotation and carbon-in-leach circuit. The feasibility study was conducted by a joint venture between Bateman Kinhill and Kilborne (“BKK”) and was completed in June 1995.
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The Pegasus board approved the project on August 17, 1995 and awarded an EPCM contract to BKK in October 1995. Commissioning commenced in November 1996. Final capital costs to complete the project were AUD232 million (USD181 million).
Design capacity was never achieved due to inadequacies in the third and fourth stages of the crushing circuit. A throughput rate of just under 7 Mtpy was achieved by mid-1997; however, problems with the flotation circuit which resulted in reduced recoveries necessitated closure of this circuit. Subsequently, high reagent consumption, as a result of cyanide soluble copper minerals, further hindered efforts to reach design production. Operating costs were above those predicted in the feasibility study. The spot price of gold deteriorated from above USD400 in early 1996 to below USD300 per ounce at the end of 1997. This, combined with underperformance of the project and higher operating costs led to the mine being closed and placed on care and maintenance on November 14, 1997.
In February 1999, General Gold Resources Pty. Ltd. (“General Gold”) agreed to form a joint venture with Multiplex Resources Pty Ltd (“Multiplex”) and Pegasus to own, operate, and explore the mine. Initial equity participation in the joint venture was General Gold 2%, Multiplex 93%, and Pegasus 5%. The joint venture appointed General Gold as mine operator, which contributed the operating plan in exchange for a 50% share of the net cash flow generated by the project, after allowing for acquisition costs and environmental sinking fund contributions. General Gold operated the mine from March 1999 to July 2000. Operations ceased in July 2000, and Pegasus, through the Deed Administrators, regained possession of various parts of the mine assets in order to recoup the balance of purchase price owed to it. Most of the equipment was sold in June 2001 and removed from the mine.
In March 2006, Vista acquired the concession rights from the Deed Administrators and surface rights from the Jawoyn Association and entered into a contract with the NT Government.
Exploration Licenses
Since acquiring the Mt Todd ELs, Vista has conducted an ongoing exploration program that includes prospecting, geologic mapping, rock and soil sampling, geophysical surveys and exploration drilling. Equipment and personnel were mobilized from the site or from an exploration base camp established in the central part of the ELs. The work was conducted by geologists and field technicians.
The exploration effort initially focused on follow-up work on targets developed by Pegasus during their tenure on the property. These included the RKD target, Tablelands, and Silver Spray. During a review of Pegasus’ airborne geophysical survey data, five distinct magnetic highs were observed located within sedimentary rocks that should have a low magnetic signature. These features are similar to those at Batman, which, as a result of the included pyrrhotite, exhibits a strong magnetic high. The geophysical targets were prioritized following review of historical work in the area and site visits. To date, two of the geophysical targets, Golden Eye and Snowdrop, have been drilled and a third, Black Hill, has been covered by soil sampling.
The Wandie target has a different magnetic signature. Field examination identified small-scale pits on an iron-rich outcropping.
There are no reportable mineral resources and mineral reserves on the ELs. No data from the ELs were used in the development of the Mt Todd FS results.
Exploration sampling summary:
Year
Soils
Rock Chips
2008
0
164
2009
1,333
45
2010
3,135
224
2011
1,925
79
2012
2,312
295
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2013
572
51
2014
2,601
143
2015
841
53
2016
241
27
2017
1,098
78
2018
341
132
2019
313
170
2020
278
9
2021
0
11
2022
60
556
Total Samples
15,050
2,037
Exploration Potential for MLs
Based on airborne geophysical survey data, we have identified several magnetic targets within our controlled land holdings surrounding the Batman pit. The targets are distinct magnetic highs located within sedimentary rocks that should have a low magnetic signature. These features are similar to those at Batman, which, as a result of the included pyrrhotite, exhibits a strong magnetic high.
Mineralization at the Quigleys deposit is interpreted to occur within a series of mineralized shears that strike north northwest and dip 30 to 35 degrees to the west. The main shear extends for nearly one kilometer along the strike and has been drilled to a vertical depth of 230 meters. The mineral resource estimate has been defined by 632 drill holes drilled by Pegasus and Billiton Australia Gold Pty. Ltd. in the late 1980s through the mid-1990s. Tetra Tech reviewed the integrity of the drill-hole database and developed a computer model to estimate and classify the estimated mineral resources. The model reflected Tetra Tech’s geological interpretation of the deposit, which constrained the mineralization to the shear zones using geological information and assays from 49,178 samples obtained from the drilling. Lower grade, erratic mineralization in the hanging wall of the shears has not been included in the mineral resource estimate.
Sampling and assaying were performed under the supervision of prior operators in conjunction with evaluation of the Batman pit and are discussed in the Mt Todd FS, as part of the overall Project sampling and assaying methodology.
Drilling
Batman Deposit
The Batman deposit resource drillhole database consists of both pre-Vista and Vista drill holes. All of the Vista resource drill holes are HQ-size core holes. Vista has drilled a total of 92 HQ diamond drill holes totaling 58,863 meters. All of the Vista diamond drill core samples were sawn into half splits for assaying purposes.
The pre-2007 exploration database (pre-Vista) consists of 743 drill holes, of which 226 are diamond drill holes and 517 are percussion drill holes. These drill holes total approximately 98,000 meters. The diamond core was a combination of NQ and HQ sizes, with the NQ core being sawed into half splits and the HQ core being sawed into quarter splits.
The table below shows a summary of Batman Deposit drilling from 1988 to 2017. A large percentage of the historical drilling was by reverse circulation (“RC”) of less than 100 meters in depth. The RC drilling was used for ore grade control during the mining operations of Pegasus and General Gold Resources. Vista’s drilling discovered a larger Batman Deposit resource by probing deeper with diamond drilling averaging 550 meters in depth.
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Batman Deposit Drilling History
Date
Reference
Holes (#)
Percussion (m)
Diamond (m)
RC
(m)
1988
Truelove
17
1,475
—
—
1989
Kenny, Wegmann, Fuccenecco
133
6,263
8,562
3,065
1990
Wegmann, Fuccenecco, Gibbs
122
—
5,060
8,072
1991
Billiton
149
501
202
3,090
1992
Zapopan
18
—
1,375
1,320
1993
Zapopan
16
—
—
2,814
1994-1997
Pegasus Gold
170
—
—
22,534
1998-2000
General Gold Resources
105
—
7,436
26,365
2007
Vista
25
—
9,883
—
2008
Vista
16
—
8,938
—
2010
Vista
12
—
6,864
—
2011
Vista
7
—
4,480
—
2012
Vista
27
—
17,439
—
2015
Vista
5
—
3,185
—
2016-2017
Vista
4
—
1,635
—
1988-2017
Batman Total
826
8,239
75,059
67,260
Vista Drilling 2012 – 2017
Between the fourth quarter of 2012 and the end of the first quarter of 2017, the Vista exploration program at the Batman Deposit consisted of 22 diamond core drillholes containing 12,530 meters that targeted both infill definitional drilling and step-out drilling.
The majority of drilling was angled so as to be approximately perpendicular to the mineralized core. This orientation more accurately transects the true thickness of the mineralization. The Batman Deposit mineralization forms a set of stacked plates that strike to the north and plunge steeply to the east. These mineralized zones have been defined by wireframes which are used to constrain the higher grades for resource estimation. Early drilling sampled the deposit near the surface allowing for shorter drillhole depths. Exploring the deeper portions of the deposit has required drill collars to be offset to the east with longer drillhole lengths to reach the mineralized zone. Recent Vista drilling in particular has targeted the deeper portions of the Batman Deposit. The positioning of the Vista drillhole collars was constrained to be outside of the flooded historical pit. Most Vista drilling has been oriented so as to transect the higher-grade mineralized zone.
While there are random high-grade intercepts outside of the core, the majority of higher-grade mineralization resides in the core zone of the deposit.
Quigleys
The table below shows the Quigleys Deposit drilling history. The Quigleys Deposit was mined from 1982 to 1987 during which the largest amount of drilling was percussion type used for ore grade control.
Relevant intervals of mineralization are contained within blanket-like zones which are modeled with 3-D wireframes for resource estimation. The mineralized zones have been defined by wireframes which are used to constrain the higher grades for the resource estimation. The majority of drilling was angled so as to be approximately perpendicular to the mineralized
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core. This orientation more accurately transects the true thickness of the mineralization. While there are random high-grade intercepts outside of the core, the majority of higher-grade mineralization resides within the defined zones. In 2011, Vista explored the potential for a deeper deposit with three diamond drillholes, each over 350 meters in depth.
Quigleys Deposit Drilling History
Date
Reference
Holes (#)
Percussion (m)
Diamond (m)
RC (m)
1975
Australian Ores and Minerals/Esso
2
—
200
—
1981
Arafura Mining Corp / CRA
14
—
676.5
—
1982-1987
Pacific Gold Mines NL (Small Scale Mining)
603
41,429
9710
4,013
1989
Pacific Gold Mines
9
501
202
—
2011
Vista
3
—
1,090
—
1988-2017
Quigleys Total
631
41,930
11,878
4,013
Drilling Results
The results of drilling at the Batman Deposit and Quigleys Deposit were used to determine the gold mineral reserves and resources estimates for the Batman Deposit and Quigleys Deposit. Vista’s drilling discovered a larger Batman resource by probing deeper with diamond drilling averaging 550 meters in depth. While there are random high-grade intercepts outside of the core, the majority of higher-grade mineralization at Batman resides in the core zone of the deposit. Relevant intervals of mineralization at Quigleys Deposit are contained within blanket-like zones which are modeled with 3-D wireframes for resource estimation. While there are random high-grade intercepts outside of the core zone, the majority of higher-grade mineralization at the Quigleys Deposit resides within the defined zones.
2020-2022 Drilling Program Results and Exploration Targets
Between late 2020 and early 2022, we completed an exploration drilling program designed to demonstrate that the Batman, Golf Tollis, and Quigleys deposits are not independent of each other but connected by structure and mineralization. This program consisted of 26 drill holes totaling 8,887 meters of HQ diamond core. The program consistently intersected mineralization predicted by our geologic model and demonstrated both horizontal and vertical continuity of the targeted structures. Additionally, the program identified four quality exploration targets as well as other potential structures along a 5.4-km portion of the 24-km Batman-Driffield Trend that contains the Batman, Golf Tollis, and Quigleys deposits.
Sampling, Analysis and Data Verification
The same sampling method and approach has been used for all diamond drillholes completed by Vista at Mt Todd. The drill core, upon removal from the core barrel, was placed into plastic core boxes. The plastic core boxes were transported to the sample preparation building where the core was marked, geologically logged, geotechnically logged, photographed, and cut into halves. One-half was placed into sample bags as nominal one-meter sample lengths, and the other half retained for future reference. The only exception to this was when a portion of the remaining core had been flagged for use in the ongoing metallurgical test work.
The bagged samples had sample tags placed both inside and on the outside of the sample bags. The individual samples were grouped into “lots” for submission to Northern Analytical Laboratories for sample preparation and analytical testing. All of this work was done under the supervision of a Vista geologist.
The following section describes the sample preparation, analyses and security undertaken by Vista through the Mt Todd FS resource update.
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The diamond drilling program was conducted under the supervision of the geologic staff composed of a chief geologist, several experienced geologists, and a core handling/cutting crew. The core handling crew was recruited locally.
Facilities for the core processing included an enclosed core logging shed and a covered cutting and storage area that was fenced in. Both of these facilities were considered to be limited access areas and kept secured when work was not in progress.
The diamond drill core was boxed and stacked at the rig by the drill crews. Core was then picked up daily by members of the core handling crew and transported directly to the core logging shed. Processing of the core included photographing, geotechnical and geologic logging, and marking the core for sampling. The nominal sample interval was one meter. When this process was completed, the core was moved into the core cutting/storage area where it was laid out for cutting and sampling. The core was logged using the following procedures:
● one-meter depth intervals were marked out on the core by a member of the geologic staff;
● core orientation (bottom of core) was marked with a solid line when at least three orientation marks aligned and were used for structural measurements. When orientation marks were insufficient an estimated orientation was indicated by a dashed line;
● geologic logging was then done by a member of the geologic staff. Assay intervals were selected at that time and a cut line marked on the core. The standard sample interval was one meter, with a minimum of 0.4 meters and a maximum of 1.4 meters;
● blind sample numbers were then assigned based on pre-labeled sample bags. Sample intervals were then indicated in the core tray at the appropriate locations; and
● each core tray was photographed and restacked on pallets pending sample cutting and stored on site indefinitely.
The core was then cut using diamond saws with each interval placed in sample bags. At this time, the standards and blanks were also placed in plastic bags for inclusion in the shipment. A reference standard or a blank was inserted at a minimum ratio of 1 in 10 and at suspected high-grade intervals additional blanks sample were added. Standard reference material was sourced from Ore Research & Exploration Pty Ltd and provided in 60 g sealed packets. When a sequence of five samples was completed, they were placed in a shipping bag and closed with a zip tie. All of these samples were kept in the secure area until crated for shipping.
Samples were placed in crates for shipping with 100 samples per crate (20 shipping bags) and sealed. The sealed crates were stacked outside the core logging shed until picked up for transport.
The following laboratories have been used for sample preparation, analyses, and check assays:
Laboratory
Address
Purpose
Abbreviation
Certifications
ALS | Minerals
31 Denninup Way
Malaga, WA 6090
Main assay analyses
ALS
ISO:9001:2008 and ISO 17025 Certified
ALS | Minerals
13 Price St
Alice Springs, NT 0870
Sample Preparation
ALS
Alice Springs
ISO 9001:2008 and ISO 17025 Certified
Genalysis Laboratory Services (Intertek Group)
15 Davison St Maddington, WA 6109
Check Analyses
Genalysis
Unable to verify
North Australian Laboratories Pty Ltd (“NAL”)
MLN 792 Eleanor Rd
Pine Creek, NT 0847
Alternative assay analyses
NAL
ISO 17025 Certified
NT Environmental Laboratories (Intertek Group)
3407 Export Dr
Berrimah, NT 0828
Check Analyses
NTEL
ISO 17025
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Vista is completely independent of each of the above listed analytical testing entities, other than the engagement of said entities as a service provider.
Each of the laboratories listed follow their own quality controls based on international standards. For example, ALS uses accredited methods specified by ISO/IEC 17025 in North America and Australia. The standards specify a recipe and set of quality control steps that the laboratory should follow including how the sample should be coded to obscure its relationship to the drilling geometry; how the received sample should be prepared; what analytical steps need be taken, given the required detection level and material analyzed, what instruments should be employed, what internal quality controls should be done such as: periodic assaying of duplicate samples, the insertion of certified calibration samples; utilizing blanks; and including a required number of randomized samples.
Mt Todd as a gold project requires assays to be done with the industry standard of fire assay. To get these fire assay results core samples from drillholes are split at Mt Todd into two with one archived and the other sent to an analytical laboratory. At the lab the sample is pulverized into a powder, with a subsample taken for fire assay. This subsample is then mixed with a fluxing agent. The remaining pulverized material is called a pulp archive, which can be used for within and between laboratory validations. The chosen sample is then heated in a furnace where it fuses and separates into a “button” which contains the gold. There are several methods to extract the gold from the button. The most common method is by combining the button with lead as a collector. The lead oxidizes and is absorbed into a cupel leaving a gold bead. Due to the relatively low concentration of gold at Mt Todd the lab must choose an analytical method able to detect at least 5ppb gold. The methods are generally by atomic absorption or inductively coupled plasma-mass spectrometry. The bead is dissolved in aqua regia or dissolved in hydrochloric acid and then analyzed by the selected instrument. The resultant assay values are reported by an assay certificate which is electronically or physically sent to the staff at Mt Todd. The assay results are entered with the drilling database.
Vista requires periodic rechecking of assays both within and between laboratories. As an example, prior to the 2011 drilling campaign, the majority of samples were transported first to ALS in Alice Springs, NT for sample preparation. After preparation, samples were then forwarded on to ALS in Malaga, WA for assay analyses. One in every 20 pulp or reject was sent from ALS in Alice Springs to NAL, Vista was notified by email which samples were sent to NAL. For the 2011-2012 drilling campaign samples for assay were sent to NAL lab in Pine Creek, NT. Following completion of assay results, all pulps and reject material was shipped back to the Mt Todd site and stored.
A comprehensive check of the quality of 12,365 assays in the database was undertaken by an outside auditor. Records were selected from among those that relate to mineralization that is still in situ. These were divided into three subsets, to be checked by three individual checkers. An additional 1,812 records were spot-checked in greater detail by a fourth individual. After the checking was done, from the original 12,365 records, 95% were selected that had gold value in the database and a gold assay in a source document such as an assay certificate. Of the assay pairs, 8,549 were “historical” in the sense of dating prior to Vista’s acquisition of the project and 3,262 assay pairs originate with Vista’s work. For context, Mt Todd assay table as of August of 2011 contained 118,550 records, 26,579 of them originating from Vista’s work.
Eight significant outliers were found with gold values in the database that differed from the source documents. Those eight were double-checked and were found to be real cases of the database containing data that differ from the source documents. The below table shows that most of the differences between the gold values in the database and those gleaned from the source documents are very small, although around economic cutoff grades the differences may well represent large percentages. More than 99% of the differences fall in the range -0.1 ppm Au to +0.1 ppm Au which is below the 0.4 ppm cutoff grade. However, a Mann-Whitney Test suggests that the differences between the two populations are not statistically different.
Prior to the 2011 drilling campaign, the majority of samples were transported first to ALS in Alice Springs, NT for sample preparation. After preparation, samples were then forwarded on to ALS in Malaga, Western Australia for assay analyses. One in every 20 pulp or reject was sent from ALS in Alice Springs to NAL, Vista was notified by email which samples were sent to NAL. For the 2011-2012 drilling campaign samples for assay were sent to NAL lab in Pine Creek, NT. Check assays on one in every 20 pulps or rejects were completed by NT Environmental Laboratories. Following completion of assay results, all pulps and reject material were shipped back to the Project site and stored.
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Comparison of Assay Values between the Database and Source Documents
Center of Cell Range in ppm
Au
Frequency
Percent
Cumulative
(+/- 0.1 ppm Au)
Percent
-1.2
0
0.00
0.00
-1
0
0.00
0.00
-0.8
1
0.01
0.01
-0.6
0
0.00
0.01
-0.4
0
0.00
0.01
-0.2
3
0.04
0.05
0
8,539
99.88
99.93
0.2
5
0.06
0.99
0.4
0
0.00
99.99
0.6
0
0.00
99.99
0.8
0
0.00
99.99
1
0
0.00
99.99
1.2
1
0.01
100.00
Differences with no rounding or truncation of data
The tables show the comparison of the gold grade assays within the database and source documents. One of the three data sets checked contained 3,262 assays from drilling campaigns by Vista in 2007 and 2008. Checks of the Vista data against original sources were done by one individual, using essentially the same procedures as had been used for checking the historical assays. A summary table of the findings is presented below. Of the 12 differences noted, two are significant. A gold value of 0.005 ppm Au in the database compared to the correct gold value of 0.8 ppm Au. A gold value of 1.08 ppm Au in the database compared to the correct gold value of 0.01 ppm Au. In addition, a separate detailed audit was done on 638 assays on Vista drillhole VB08-036. This audit shows that discrepancies within the database on the global resource estimate are not material.
Summary of Comparisons of Historical Assays
Historical Assays
Au in PPM
Differences, Source - Database in PPM
Database
Source
Average
0.79
0.70
0
Std Dev
1.48
1.48
0.01
Count
1171
1171
565
Max
33.44
33.45
0.255
Min
0.005
0.005
-0.29
Median
0.3
0.3
0
Differences > 0.01 ppm Au
20
Differences < 0.01 ppm Au
4
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Summary of Comparisons of Vista Assays
Vista Assays
Au in PPM
Differences, Source - Database in PPM
Database
Source
Average
0.79
0.78
0
Std Dev
1.89
1.89
0.02
Count
3262
3262
12
Max
55.37
55.37
0.79
Min
0.005
0.005
-1.07
Median
0.26
0.26
0
Differences > 0.01 ppm Au
3
Differences < 0.01 ppm Au
6
The Company requires periodic rechecking of assays both within and between laboratories. As an example, prior to the 2011 drilling campaign, the majority of samples were transported first to ALS in Alice Springs, NT for sample preparation. After preparation, samples were then forwarded on to ALS in Malaga, WA for assay analyses. One in every 20 pulps or rejects was sent from ALS in Alice Springs to NAL, Vista was notified by email which samples were sent to NAL. For the 2011-2012 drilling campaign samples for assay were sent to NAL lab in Pine Creek, NT. No bias in assays was found with a slope of 0.992 and a correlation of 99%. There was only one significant difference that was detected from a total of 2,948 comparisons. The Company’s assaying protocols are observed and required for every assay program, regardless of whether the exploration work is for resource estimation or metallurgical testing.
John W. Rozelle, Senior Vice President of Vista and a qualified person as defined by S-K 1300 and NI 43-101, has verified the data disclosed in this document, including sampling, analytical and test data underlying the information contained in the disclosure.
Sample Security
NAL is the primary laboratory we use for analysis of drill core assays. The NAL laboratory is located in the town of Pine Creek, approximately 50 kilometers distant by road from the Project site. Samples were picked up and transported by NAL employees.
Sample shipments were scheduled for approximately once a week. The sealed crates were picked up on site by NAL for direct road transport to the assay lab. A sample transmittal form was prepared and included with each shipment and a copy was filed in the geology office on site.
When the shipment left site, sample transmittals were prepared and e-mailed to NAL. When the shipment arrived at the preparation facility the samples were lined out and a confirmation of sample receipt was e-mailed back to Vista.
Statistical analyses of the various drilling populations and quality assurance/quality control samples have neither identified nor highlighted any reasons to not accept the data as representative of the tenor and grade of the mineralization estimated at the Batman deposit.
Mining Operations
The Project is designed to be a large open-pit mining operation that will utilize large-scale mining equipment in a drill/blast/load/haul operation. Ore is planned to be processed in a comminution circuit consisting of large-scale equipment, including: a gyratory crusher, cone crushers, high pressure grinding roll (“HPGR”) crushers followed by X-ray
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transmission (“XRT”) and laser sorting, and primary ball mills, followed by VXP Mills, as discussed in greater detail below. Vista plans to recover gold in a conventional CIP recovery circuit.
Mineral Processing
The flowsheet consists of open-circuit primary crushing, closed-circuit secondary crushing, closed-circuit tertiary crushing using HPGR crushers, ore sorting, two-stage grinding, cyclone classification, pre-leach thickening, leach and adsorption, elution electrowinning and smelting, carbon regeneration, tailings detoxification and disposal to conventional tailings storage facility.
The flowsheet for the Project is illustrated below.
Metallurgical Testing
Our metallurgical test work programs have confirmed: (1) ore hardness of the Batman deposit is consistent throughout the deposit and does not change at depth; (2) the selection of HPGR crusher technology as part of the comminution circuit; (3) the selection of ore sorting technology to eliminate low-grade material after crushing and prior to grinding; (4) estimated gold recovery rates based on optimized grind size and leach conditions; and (5) the processing of material from the historical heap leach pad at the end of the proposed mine life.
The test work results collated from the 2011 and 2012 testing campaigns and additional metallurgical and process test work conducted in 2016, 2017, 2018, and 2019, together with the process design criteria, were used to develop the process flow sheet and mass balance.
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Ore Hardness
Bond ball mill work indices (“BWi”) were determined at a grind size of P80 of 100 mesh for the various products, namely HPGR crusher, ore-sorting, composite samples and waste material.
The test results indicate the following:
● The BWi for the ore sorter feed (plus 5/8” screened HPGR crusher product) was higher than the composite samples prepared from the minus 5/8” screened HPGR crusher product. Hence, it is reasonable to conclude that the uncrushed material from the HPGR is harder than the crushed product.
● The rejected waste material had a BWi higher than both the composite sample prepared from the minus 5/8” HPGR crusher product and the XRT ore sorting product that is returned to the HPGR crushers.
● The BWi for the final HPGR product ranged from 23.10 to 26.63. A BWi of 24.50 was selected for the design of the primary ball mill circuit.
The results of this test work support two main conclusions: (1) that the hardness of ore at the Batman deposit is relatively constant; and (2) that ore hardness at the Batman deposit does not change at depth.
This test work validates the Company’s prior test work and supports Vista’s revised comminution circuit design, which is designed to crush and grind material with an average BWi of 26.2 kWh/t.
HPGR Crusher Selection
The proposed 50,000 tpd Project comminution circuit incorporates the use of a gyratory crusher and two cone crushers for the primary and secondary stages, respectively, and the use of two HPGR crushers as the third-stage of the crushing circuit.
The test work assessed the difference in power requirements between a primary/SAG/ball mill circuit, a conventional 3-stage crush/ball mill circuit, and a 3-stage HPGR crush/ball mill circuit (with 3 rd stage HPGR crushing and 2-stage grinding) to generate a P80 passing 40 μm product.
This test work also confirms our prior test work and supports our comminution circuit design. The use of HPGR crushers is anticipated to (a) produce a product that can be ground more efficiently (lower BWi); and (b) reduce energy requirements when compared to a SAG Mill design.
Ore Sorting
The bulk ore sorting tests comprised four, five-tonne composites; and one, one-tonne composite prepared from 3.75" drill core. In addition to these composites, three one-tonne composites were made from 2.75” drill core. Four of the 3.75” composites contained predominately sulfide mineralization and one composite contained mixed oxide/sulfide material that is encountered on the periphery of the deposit. The remaining three 2.75” drill core composites all contained sulfide material. The drill core was HPGR crushed and screened at 5/8” at the facilities of Thyssen Krupp Industries near Dusseldorf, Germany. The plus 5/8” material was sent to the test facility of Tomra Sorting Solutions near Hamburg, Germany where this material was initially sorted using XRT sorting. A total of 12 sorting tests were completed. The XRT rejects were then subjected to laser sorting to produce a final reject. All material (minus 5/8” HPGR crushed, XRT product, laser product and sorting reject) was sent to the metallurgical laboratory of Resource Development Inc. in Wheat Ridge, Colorado for subsequent sample preparation, assaying and additional metallurgical testing.
On a material mass basis, the combined XRT and laser sorting tests confirmed the Company’s expectation that it can reject approximately 10% of the run-of-mine feed as waste (test results range from 6.8% to 11.0%). The average grade of the rejected material is estimated to be 0.12 g Au/t (results range from 0.06 g Au/t to 0.23 g Au/t) compared to the mine cut-off grade of 0.35 g Au/t, resulting in a gold loss from the rejected waste of approximately 1.3%. The improvement in mill feed grade is expected to be approximately 8%, resulting in run-of-mine average mill feed grade of 0.84 g Au/t compared to the life-of-mine Batman Pit mineral reserve grade of 0.79 g Au/t.
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Gold Recoveries
We evaluated gold recoveries using two-stage grinding and a finer product size. This test work has confirmed that the introduction of ore sorting to reduce the leach tonnage by approximately 10% and finer grinding to P 80 of 40 µm yields an increase in recovery to ~91.6% on a weighted-average basis, net of solution losses.
A total of 71 additional leach tests were completed using the above mentioned two-staged grinding to confirm our resulting leach recoveries of 91.9%, net of solution losses. This test work has also confirmed a cyanide consumption rate of 0.88 kg per tonne.
Our recovery plant design utilizing a conventional, industry-proven, CIP circuit remains unchanged.
Existing Heap Leach Pad
In addition to analysis of freshly-mined material from the Batman deposit, Vista has analyzed the potential to process nearly 13.4 million tonnes of material from the existing heap leach pad at Mt Todd. The historical Mt Todd mine started as a heap leach operation with historical records indicating that the average grade of material placed on the pad was 0.96 g Au/t. Although the material was partially leached in the mid-1990s, Vista has drilled 24 air-rotary holes into the heap leach pad and assayed 361 samples, and Tetra Tech created a 3D resource model that has an average grade of 0.54 g Au/t.
Initial evaluation efforts focused on re-starting the heap leach pad. Bottle roll and column tests were completed, both of which supported the leachability of the material with gold recovery rates around 35%. However, poor in situ permeability rates caused Vista to ultimately abandon plans to re-start the heap.
A total of 16 tests were completed on composites taken from 11 of the heap leach pad drill holes. The samples were ground to the size of P80 of 40 μm and pre-treated with lime and 100 g/t of lead nitrate to suppress copper leaching. The material was then leached for 24 hours. These results ranged between 71 and 91% with the average being 82.2% for this material when processed through the proposed CIP flowsheet.
The Mt Todd FS assumes that the existing heap leach pad will be left in place and processed through the mill at the end of mine life. This ultimately is expected to reduce the scope of reclamation of the heap leach pad to the pad liner and regrading only.
Permitting
During September 2014, the EIS was approved. In its Assessment Report, the NT EPA advised that it had assessed the environmental impacts of Vista’s development plans for Mt Todd and concluded that it can proceed, subject to a number of recommendations which are outlined in the Assessment Report. The NT EPA Assessment Report includes 28 recommendations which are addressed as part of the MMP.
The approval of the EIS resulted in the requirement to obtain an authorization of a controlled activity as required under the EPBC as it relates to the Gouldian Finch. The EPBC authorization was granted by the Australian Commonwealth Department of Environment and Energy in January 2018.
In November 2018, we applied for the MMP approval, which is the operating permit that sets out how the mine operating strategy will be implemented throughout the mine life in compliance with the EIS and EPBC requirements. The MMP was approved in June 2021 and is in the process of being amended to align with the larger-scale design in the Mt Todd FS. The changes to the waste rock dump design have been referred to the NT EPA as required under the Environmental Protection Act 2019 for its consideration.
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Environmental, Social and Community Factors
A number of environmental studies have been conducted at Mt Todd in support of the EIS and as required for environmental and operational permits. Studies conducted have investigated soils, climate and meteorology, geology, geochemistry, biological resources, cultural and anthropological sites, socio-economics, hydrogeology, and water quality.
The E I S for the Project was submitted in June 2013 . The document was prepared by independent consultants, GHD Pty Ltd., to identify potential environmental, social, transport, cultural and economic impacts associated with reopening and operating the mine. NT EPA provided its final assessment of the Project in June 2014. Final approval was given in September 2014.
The Jawoyn people have been consulted with and involved in the planning of the Project. Areas of aboriginal significance have been designated, and the mine plan has avoided development in these restricted works areas.
Water Treatment
We obtained approval of a waste discharge license from the NT Government that authorized the release of treated water from the Mt Todd site during the wet season in accordance with an 80% protection limit environmental standard. We discharged treated water in compliance with the standards. The existing Batman pit has the capacity to contain approximately 11.5 gigaliters of water. At the end of December 2022, the pit contained approximately 0.7 gigaliters of water due to previous dewatering operations. The present volume of water in the pit will not present any major issues when resuming operations in the Batman pit.
2023 Project Development Plans
The Company is evaluating a smaller scale project at Mt Todd, targeting a significantly lower initial capital cost while maintaining operating costs very close to those estimated in the Mt Todd FS. A smaller project would be scalable, allowing for throughput expansion or mine-life extension. The completion of this study is expected in the first quarter of 2023.
The strategic process with CIBC Capital Markets is ongoing and remains a top priority.
Vista reduced its recurring costs in 2022, and reducing costs and maximizing effectiveness continue to be high priorities in 2023. Vista expects to incur expenditures of approximately $2,100 for its Mt Todd site maintenance and environmental stewardship activities.