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Exploration

History & Discovery

Gold mining in the Red Sea Hills and Nubian Desert of Sudan has taken place since ~3000 BC, with numerous documented sites of historic mining infrastructure throughout the terrane. Colonial gold mining occurred across the Red Sea Hills in the early 19th century, whilst there has been a rapid rise in artisanal gold mining activity since ~2008. Today, artisanal mining activities account for 90% of Sudan’s annual production (~100t in 2020).

The Block 14 concession is located ~900 km north of Khartoum and ~180 km due north of Abu Hamad. Wadi Doum is ~55 km due east of Galat Sufar South. Block 14 comprises of the Galat Surfar South and Wadi Doum deposits along with several unexplored targets.

Very little was known about the geology and mineralisation in the region and Orca used satellite imagery to identify ancient and modern mining activity.  All significant sites were then visited by geologists and occurrences ranked for follow up.

Timeline:

MAY 2012: Shark Minerals (the private pre-cursor to Orca) entered into a joint venture with the holders of the Block 14 Exploration Permit, Meyas Nub Multi Activities Company Ltd in May 2012 whereby Shark could earn up to a 70% interest.

JULY 2012: The GSS deposit was discovered in the summer of 2012 after follow-up of artisanal workings that were mining a sheared, hematite/sericite altered schist. The alteration package was systematically sampled and identified a broad zone of north trending mineralisation up to 100m wide with average surface grades >2.0 g/t gold.

NOVEMBER 2012: The first reverse circulation (RC) drill hole returned an intercept of 94m at 2.38g/t.

APRIL 2013: Shark Minerals was acquired by Canaco Resources which then changed its name to Orca Gold Inc trading on the Toronto Venture exchange under the symbol ORG.V.

EARLY 2014: A maiden resource was reported in early 2014 based on 35,637 metres of drilling. The Mineral Resource estimate using a cut-off grade of 1.0 g/t, comprised an Indicated Resource of 22.2Mt at 1.84g/t for 1.3 million ounces gold and an Inferred Resource of 6.5Mt at 1.9g/t for an additional 400,000 ounces gold.

EARLY 2015:  An updated resource was announced incorporating the Wadi Doum Discovery (55km east of GSS) and based on a total of 71,072 metres of drilling. The Mineral Resource estimate, using a cut-off grade of 1.0 g/t, comprised an Indicated Resource of 27.64Mt grading 1.83g/t for 1.63 million ounces of gold and an Inferred Resource of 10.28Mt grading 1.8g/t for an additional 0.59 million ounces.

SEPTEMBER 2016:  Preliminary Economic Assessment (“PEA”) was published and work commenced on a Pre-Feasibility Study (“PFS”).

FEBRUARY 2017: An updated Mineral Resource estimate was completed and using a cut-off grade of 1.0g/t, comprised an Indicated Resource of 30.6 Mt grading 1.82g/t for 1.792 Moz of gold and an Inferred Resource of 9.7 Mt grading 1.7g/t for an additional 0.536 Moz.

MAY 2017:  A new water resource was discovered 80km west of GSS based on the Area 5 aquifer and completed a Revised PEA based on an expanded plant throughput enabled by the new water discovery.

JANUARY 2018: Orca announced an Indicated resource of 72.7 Mt grading 1.30g/t Au for 3.05 Moz of gold and an Inferred resource of 19.8 Mt grading 1.2g/t Au for 0.75 Moz of gold. Th estimate was based on 98,754m of drilling in 688 holes.

SEPTEMBER 2018: Resources were updated as part of the Block 14 Feasibility Study with an Indicated resource of 79.9Mt grading 1.30g/t Au for 3.342 Moz of gold and an Inferred resource of 18.5Mt grading 1.2g/t Au for 0.711 Moz of gold (at a cut-off grade of 0.6g/t).

NOVEMBER 2018: The results of the Block 14 Feasibility Study were announced.

SEPTEMBER 2020: Revised Feasibility Study released with improved operating costs and NPV of $607M (based on $1,350/oz Au).

Mineralisation

The geological framework of Block 14 is dominated by two distinct geological domains ‐ the andesite

dominated Gabgaba terrain of the Arabian Nubian Shield (ANS) to the east and the marine sediments of the Keraf Suture in Western Gabgaba; these are separated by the Eastern Gabgaba Fault System (EGFS). The central part of the licence is dominated by the Northern Gabgaba Graben, a downthrown

portion of the Keraf that has been infilled by clastic sediments.

The geological framework of the Gabgaba terrane is relatively simple; the andesitic sequence is un-foliated and preserves its original mineralogy and textures and does not display evidence of folding. Where recognised, the primary layering in the volcano‐sedimentary rocks is east‐west.

The Keraf sediments are a thick sequence of folded / thrusted marine sediments dominated by pelites, marls and limestone units, with localised occurrences of coarser grained siliciclastic sediments. This is a significant geological formation in the region occurring along the length of the Keraf Suture. The Galat Sufar Andesite domain is an anomalous exposure of andesitic volcanic rocks within the thick sequence of Keraf sediments. It is interpreted as a doubly plunging antiformal fold created by complex inference folding, which exposes the andesitic volcanic‐sedimentary underlying the shallow marine sediments (the exact relationship between the andesites and sediments is unclear and is potentially structural). It is within this andesite domain that the Galat Sufar South deposit is located.

Mineralisation map

Galat Sufar South (GSS)

The GSS deposit is located in the central portion of the Galat Sufar Andesite Domain. The GSS deposit is located just south of the contact between marine sediments to the north (a remnant of the Keraf sediments) and an andesitic volcanic sequence to the south. The andesitic sequence is heterogeneous comprising lava flows, pyroclastic deposits and primary volcanic breccias.

Of importance to deposit formation, the andesite sequence contains a discrete 80 – 200 m wide volcaniclastic‐sedimentary horizon which contains dioritic sills / dykes. Mineralisation and alteration are concentrated in this unit, which is bordered to the north and south by increasingly unaltered andesitic flows and further volcaniclastics.

The host unit has been sequentially and intensely altered by the addition of albite, sericite, silica and lastly carbonate. Alteration grades from largely unaltered andesitic lavas and volcaniclastic host rocks to strongly altered and foliated silica – sericite schists in which the protolith cannot be identified. Pyrite is by far the most dominant sulphide with chalcopyrite, sphalerite, galena, tennantite / tetrahedrite occasionally seen in core and confirmed in petrological investigation. Gold is fine grained, typically <40 μm. With 95% of the gold being free gold, the remainder occurs as Petzite (Ag3AuTe3). The gold contains ± 20% silver.

The dominant foliation at the prospect scale (S1) is pervasively developed throughout the GSS deposit area. It is sub‐vertical and strikes towards the NW (330° ‐ 340°) at moderate to high angles to the orientation of the mineralised unit.

Wadi Doum (WD)

The main, high grade mineralization at WD outcrops at the base of the hill and is hosted by a strongly sulphidic volcaniclastic unit, which is in contact with a distinct rhyolite unit to the immediate east. The volcanoclastic unit dips at an angle of 20° to the southwest. This rhyolite is bounded to the east by a dacitic unit intruded by syn‐tectonic syenite / potassium altered diorite body which forms the summit of the main hill.

These lithologies are cut by thin (<0.75 cm), late, un‐mineralized felsic and mafic dykes. In contrast to the volcaniclastics, the rocks on the hill dip 75° to the east. Mineralization on the hill is associated with stringer zones within the syenite and in places smaller shears.

The high-grade mineralization is hosted within the volcanoclastic units which are confined by late felsic and mafic dykes. The mineralization is divided into a western volcaniclastic unit characterized by a dark colour caused by very fine-grained sulphides (>10 ‐ 15%), which contains some of the best intercepts and a central unit of paler, sulphide rich felsic volcaniclastics which contain deformed sulphide veinlets and a lower grade footwall unit of largely un‐deformed felsic volcaniclastics. The dominant sulphide is pyrite (85% in Qemscan analysis) with the remainder comprising a mix of sphalerite, galena, chalcopyrite and freibergite.

Alteration is confined to sericitisation within the felsic volcanics and a wider halo of carbonate alteration. Silicification is noticeably absent or weak within the high-grade part of the deposit (hence its location at the base of the hill.

The area is dominated by a strong and pervasive, north‐south trending schistosity, which is largely followed by the late dykes. The high-grade mineralization often appears un‐affected by structure, whereas the mineralization hosted by the syenite on and around the summit of the hill does appear structurally controlled.

Reserves & Resources

The Mineral Resource Estimates were updated in September 2018 (News Release September 18, 2018) by independent consultant MPR Geological Consultants of Perth, Western Australia using Multiple Indicator Kriging (MIK), and are shown below at a range of cut-off grades:

Deposit Cut Off Indicated Inferred
Mt Au g/t Ag g/t Au Koz Ag Koz Mt Au g/t Ag g/t Au Koz Ag Koz
Galat Sufar South 0.3 129.0 0.92 1.19 3,823 4,954 35.4 0.8 1.1 901 1,289
0.4 106.9 1.04 1.29 3,575 4,448 27.0 0.9 1.2 807 1,058
0.5 89.5 1.16 1.39 3,326 4,002 21.1 1.1 1.3 722 873
0.6 75.6 1.27 1.48 3,080 3,607 16.9 1.2 1.4 648 745
0.7 64.0 1.38 1.58 2,839 3,249 13.7 1.3 1.5 582 640
0.8 54.5 1.49 1.67 2,610 2,924 11.3 1.4 1.5 524 558
0.9 46.5 1.60 1.76 2,392 2,629 9.4 1.6 1.6 471 487
1.0 39.8 1.71 1.84 2,187 2,359 7.8 1.7 1.7 424 427
1.1 34.1 1.82 1.93 1,994 2,114 6.6 1.8 1.8 382 375
1.2 29.3 1.93 2.01 1,815 1,892 5.6 1.9 1.9 344 331
 
Wadi Doum 0.3 7.8 1.23 4.70 311 1,184 4.9 0.7 3.1 106 477
0.4 6.3 1.46 4.98 293 1,003 3.3 0.8 3.2 89 337
0.5 5.1 1.68 5.22 277 862 2.3 1.0 3.4 75 250
0.6 4.3 1.90 5.45 262 751 1.6 1.2 3.6 63 191
0.7 3.7 2.12 5.65 249 664 1.2 1.4 3.8 54 149
0.8 3.2 2.32 5.84 237 595 0.9 1.6 4.1 47 119
0.9 2.8 2.52 6.00 227 540 0.7 1.8 4.3 41 97
1.0 2.5 2.71 6.15 218 494 0.6 2.1 4.5 37 81
1.1 2.3 2.89 6.27 210 456 0.5 2.3 4.7 33 69
1.2 2.1 3.05 6.39 202 423 0.4 2.5 4.9 31 59
 
Combined 0.3 136.8 0.94 1.40 4,133 6,137 40.3 0.8 1.4 1,007 1,766
0.4 113.2 1.06 1.50 3,868 5,451 30.3 0.9 1.4 896 1,395
0.5 94.6 1.18 1.60 3,603 4,864 23.4 1.1 1.5 797 1,123
0.6 79.9 1.30 1.70 3,342 4,358 18.5 1.2 1.6 711 936
0.7 67.7 1.42 1.80 3,088 3,913 14.9 1.3 1.6 636 789
0.8 57.7 1.53 1.90 2,847 3,519 12.2 1.5 1.7 571 677
0.9 49.3 1.65 2.00 2,619 3,169 10.1 1.6 1.8 512 584
1.0 42.3 1.77 2.10 2,405 2,853 8.4 1.7 1.9 461 508
1.1 36.4 1.88 2.20 2,204 2,570 7.1 1.8 1.9 415 444
1.2 31.4 2.00 2.29 2,017 2,315 6.0 1.9 2.0 375 390

 

Notes:

  1. Mineral Resources are as defined by the 2014 CIM Definition Standards for Mineral Resources and Mineral Reserves
  2. Mineral Resources are inclusive of Mineral Reserves
  3. Mineral Resources are reported above a cut-off grade of 0.6g/t
  4. Mineral Resources which are not Mineral Reserves do not have demonstrated economic viability.
  5. Mineral Resources were estimated as of 29 January 2018
  6. Mr N Johnson was the Independent Qualified Person for Resource estimation being an employee of MPR Geological Consultants

The Mineral Resource has been estimated using the results of 111,761 metres of drilling in 756 holes completed between November 2012 and August 2018.

Importantly, the resource contains a higher-grade core within both the GSS and Wadi Doum deposits which enables the mining of higher grades in the early years of the project, significantly impacting economics.

Relative to the previous Mineral Resource Estimates, the September 2018 Mineral Resource Estimate is based on an additional 10,792m of drilling in 7 diamond holes and 57 reverse circulation (“RC”) holes completed at GSS and an additional 1,882m of drilling in 3 diamond holes and 8 RC holes completed at Wadi Doum.

Mineral Reserves

The November 2018 Mineral Reserve estimate is reported using topographic surfaces with no allowance for depletion by historic artisanal mining, which is considered to have a minor impact on the reported estimate.

 

  Classification Oxide Transitional Fresh Total
‘000 tonnes Au g/t ‘000 tonnes Au g/t ‘000 tonnes Au g/t ‘000 tonnes Au g/t
Main Probable 4,347 1.27 5,088 1.19 13,488 1.31 22,923 1.28
East Probable 8,302 0.89 11,236 0.89 30,729 1.05 50,267 0.99
North East Probable 1,606 0.84 2,192 0.85 367 0.90 4,166 0.85
Total GSS Probable 14,255 1.00 18,516 0.97 44,584 1.13 77,356 1.07
Wadi Doum Probable 527 1.90 119 2.37 1,941 2.49 2,588 2.36
Block 14 Total Probable 14,783 1.03 18,635 0.98 46,525 1.19 79,943 1.11

 

Notes:

  1. Mineral Reserves are as defined by the 2014 CIM Definition Standards for Mineral Resources and Mineral Reserves
  2. Mineral Resources are inclusive of Mineral Reserves
  3. Mineral Resources which are not Mineral Reserves do not have demonstrated economic viability.
  4. Mineral Reserves were estimated as of 7 November 2018
  5. Mr C Reardon was the Independent Qualified Person for reserves being an employee of Deswik Europe Ltd

Water Exploration

Water Exploration Water Exploration

Work undertaken by GCS Water and Environmental Consultants of South Africa (GCS) during the course of the pre-feasibility study showed that the HA8 water resource had limited expansion potential.

As a result, SkyTEM Surveys of Denmark, an airborne geophysical contractor specialising in water exploration were contracted to fly a 5,000km electromagnetic survey with the aim of expanding the HA8 discovery and investigating a new area to the west of Block 14 (Area 5) where two old production wells are located.

The survey in Area 5 returned positive results over a large area and has now been followed up with drilling. The aquifer, which is hosted within the Nubian Sandstone Formation (NSF) has been intersected in 19 boreholes over an area of +135km2 between 58m and 90m from surface. 48-hour pump test results have shown consistent aquifer yields and GCS are comfortable that the aquifer is able to sustain the output required for a 6.0Mtpa process plant.

The aquifer remains open to the north and south providing ample potential for expansion.

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