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Operations

GC Mine

  • Introduction
  • Mining
  • Mineral Processing
  • Exploration and Geology

Introduction

  • 99%-owned Gaocheng (GC) operations consist of a ~310 ktpa underground mine and a sulphide flotation plant

  • Located approximately 200 km west of Guangzhou, the capital city of Guangdong Province, China

  • Acquired from a private Chinese company in April 2008

  • Construction began shortly after mining permit receipt in late 2010. The permit covers a 5.5 km2 area and is valid until November 24, 2040

  • Achieved commercial production in 2014 and has since contributed over 5 Moz of silver and 190 Mlb of lead and zinc

  • Produces silver-lead, zinc and minor tin concentrates sold to smelters in China

  • Current reserves support mining through 2034

  • Mine life extension through resources to reserves conversion drilling and further generative exploration/development

Operation Snapshot

Mine Life1

13 Years

Silver Production

FY2021A: 716 koz

FY2022A: 640 koz

FY2023E: 0.7-0.8 Moz

AISC2

FY2021A: US$74.09/t

FY2022A: US$79.56/t

FY2023E: US$86.1-$92.0/t

  1. Gaocheng Technical Report effective March 31, 2021.
  2. AISC refers to all-in sustaining costs per tonne of ore processed.

Mining

 

GC1

Mine type

Ramp and shaft

supported underground

Mining method

Re-suing and shrinkage

Reserve tonnage2

4,131 kt

Reserve grades2

94 g/t silver

1.48% lead

3.22% zinc

Peak annual ore production

318 kt

Primary metal

Silver

By-product metals

Lead, zinc, tin

  1. Gaocheng Technical Report effective March 31, 2021.
  2. Mineral reserves estimate as of December 31, 2020.

Mineral Processing

  • The overall process consists of:
    • Two-stage crushing

    • Two-stage grinding

    • Sequential flotation of lead, zinc and pyrite concentrates

    • Concentrate de-watering by disc filtration

  • An experimental tin recovery (gravity) circuit was installed on pyrite flotation tails
  • Tailings are de-watered, then back-filled underground or dry-stacked
  • Mill throughput to date has generally been between 900 and 950 tpd (~310 ktpa)

Recent Work/Highlights

Silvercorp completed 72,878 m of underground drilling in 704 diamond drill holes at the GC mine from October 1, 2019 to June 30, 2021. The program targeted: 1) known silver-lead-zinc veins in and above the production area that were previously missed due to limited exploration, changes in the strikes/dips, and/or pinch-swelling of the pay-zones, and 2) the north and south sides of the resource area at higher elevations.

High-grade intercepts of known silver-lead-zinc veins within the production area:

  • Hole 20CK24A02 intersected a 6.13 m interval (6.01 m true width) of vein V2E1 grading 258 g/t silver, 7.05% lead, and 7.05% zinc from 53.41 m depth, at an elevation of -211 m, including a 1.10 m interval (1.08 m true width) grading 462 g/t silver, 25.57% lead, and 5.21% zinc.

  • Hole 20CK3025 intersected a 2.93 m interval (2.79 m true width) of vein NV28 grading 417 g/t silver, 19.22% lead, and 1.72% zinc from 38.96 m depth, at an elevation of -11 m, including a 1.48 m interval (1.34 m true width) grading 815 g/t silver, 37.47% lead, and 2.12% zinc.

High-grade intercepts of newly discovered silver-lead-zinc veins within the production area:

  • Hole 20CK11805 intersected a 0.74 m interval (0.74 m true width) of vein V18-3 grading 557 g/t silver, 1.21% lead, and 14.82% zinc from 104.30 m depth, at an elevation of -11 m.

  • Hole 20CK11808 intersected a 0.56 m interval (0.38 m true width) of vein V18-4 grading 533 g/t silver, 2.98% lead, and 7.51% zinc from 104.05 m depth, at an elevation of 24 m.

High-grade intercepts of newly discovered silver-lead-zinc veins south of the resource area:

  • Hole 20CK46A01 intersected a 0.87 m interval (0.46 m true width) of vein V33-2 grading 994 g/t silver, 5.18% lead, and 5.52% zinc from 57.56 m depth, at an elevation of 149 m. The hole also intersected a 0.74 m interval (0.56 m true width) of vein V33-1 grading 447 g/t silver, 2.04% lead, and 5.28% zinc from 72.76 m depth, at an elevation of 146 m

  • Hole 21CK4820 intersected a 2.16 m interval (1.30 m true width) of vein V35 grading 539 g/t silver, 8.06% lead, and 3.23% zinc from 47.55 m depth, at an elevation of 140 m.

High-grade intercepts of newly discovered silver-lead-zinc veins north of the resource area:

  • Hole 20CK4802 intersected a 0.47 m interval (0.46 m true width) of vein NV6 grading 115 g/t silver, 0.54% lead, and 18.05% zinc from 135.29 m depth, at an elevation of 39 m.

Data from the 2020-2021 exploration program underpinned an updated mineral resources and reserves estimate in August 2021 (effective December 31, 2020). Compared to the previous estimate (effective June 30, 2019):

  • Combined Proven and Probable tonnes increased by 8%.

  • Measured tonnes increased by 57% due to new discoveries, new vein interpretations, and conversion of Indicated tonnes (decreased by 17%).

  • Inferred tonnes increased by 17%.

In fiscal year 2023, Silvercorp plans to complete 61,400 m of exploration drilling (capitalized and expensed) at GC. The current drill program is complemented by 20,800 m of exploration and development tunnels (capitalized and expensed).

Mineral Resources:

The Mineral Resource estimates for the Gaocheng property were prepared by Mr. Shoupu Xiang, Resource Geologist of Silvercorp, and were reviewed by independent Qualified Person, Ms. Dinara Nussipakynova, P.Geo of AMC who takes responsibility for the estimates. The data used in the Mineral Resource estimation includes results of all drilling carried out on the Property to 31 December 2020. The estimation was carried out in Micromine™ software. Interpolation was carried out using inverse distance squared (ID2) for all the veins.

The Mineral Resources are reported above a cut-off of 105 g/t silver equivalent (AgEq). Cut-off grades are based on in situ values in AgEq terms in grams per tonne (after application of mining recovery and payable values) and incorporate all mining and processing costs provided by Silvercorp and reviewed by AMC.

The estimated Mineral Resources and metal content for the property as of December 31, 2021 are detailed in Table 1 below.

Gaocheng Property - Measured & Indicated, and Inferred Mineral Resources

(Inclusive of Mineral Reserves)

Resource Classification Tonnes (Mt) Ag (g/t) Pb (%) Zn (%) Contained Metal
Ag (koz) Pb (Mlbs) Zn (Mlbs)
Measured 5.286 88 1.3 3.1 14,906 154 360
Indicated 4.747 75 1.1 2.5 11,457 111 259
Measured and Indicated 10.033 82 1.2 2.8 26,363 265 619
Inferred 8.441 87 1.0 2.4 23,562 195 442

Notes: 

• CIM Definition Standards (2014) were used for reporting the Mineral Resources.

• Mineral Resource are reported at a silver equivalent (AgEq) cut-off grade of 105 g/t AgEg.

• The equivalency formula is Ag g/t+50.46*Pb%+43.53*Zn% using prices of US$18.20/oz Ag, US$0.94/lb Pb, and US$1.08/lb Zn and estimated recoveries of 82.6% Ag, 89.5% Pb, and 87.3% Zn.

• Sample results up to 31 December 2020.

• Mineral Resources have been depleted to account for mining to 31 December 2020.

• Veins factored to a minimum extraction width of 0.4 m.

• Mineral Resources are inclusive of Mineral Reserves reported in Section 15.

• Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability. An Inferred Mineral Resource is that part of a Mineral Resource for which quantity and grade or quality are estimated on the basis of limited geological evidence and sampling and must not be converted to a Mineral Reserve. It is reasonably expected that the majority of Inferred Mineral Resources could be upgraded to Indicated Mineral Resources with continued exploration.

• The numbers may not compute exactly due to rounding.

Mineral Reserves:

The Mineral Reserve estimates for the Property were prepared by Silvercorp under the guidance of independent QP, Mr H. Smith, P.Eng., who takes QP responsibility for those estimates.

The Mineral Reserve estimation is based on the assumption that current stoping practices will continue at the Gaocheng property, namely predominantly shrinkage stoping but also with some cut and fill resuing. Minimum mining widths of 1.0 m for shrinkage and 0.5 m for resuing, and minimum dilution of 0.20 m total for shrinkage and 0.10 m for resuing cut and fill stopes are assumed. Full breakeven COGs used are 215 g/t AgEq for shrinkage and 275 g/t AgEq for resuing.

Table summarizes the Mineral Reserves estimate for the Gaocheng mine. 63% of the Mineral Reserve tonnage is categorized as Proven and 37% is categorized as Probable.

Gaocheng Property - Proven and Probable Mineral Reserves

Reserve classification Tonnes (Mt) Ag (g/t) Pb (%) Zn (%) Contained metal
Ag (koz) Pb (Mlbs) Zn (Mlbs)
Proven 2.587 93 1.5 3.3 7,743 84 189
Probable 1.544 95 1.5 3.0 4,740 51 103
Proven + Probable 4.131 94 1.5 3.2 12,483 135 293

Notes to Mineral Reserve Statement:

• Canadian Institute of Mining, Metallurgy and Petroleum Standards (2014) were used for reporting the Mineral Reserves.

• Full breakeven cut-off grades: Shrinkage = 215 g/t AgEq: Resuing = 275 g/t AgEq.

• Marginal material cut-off grade: Shrinkage = 185 g/t AgEq; Resuing = 250 g/t AgEq.

• Dilution (zero grade) assumed as a minimum of 0.1 m on each wall of a shrinkage stope and 0.05 m on each wall of a resuing stope.

• Mining recovery factors assumed as 92% for shrinkage and 95% for resuing.

• Metal prices: Silver US$18.20/troy oz, lead US$0.94/lb, zinc US$1.08/lb, with respective payables of 65.5%, 86.2%, and 66.3%.

• Processing recovery factors: Ag – 82.6%, Pb – 89.5%, Zn – 87.3%.

• Effective date 31 December 2020.

• Exchange rate assumed is RMB6.80: US$1.00.

• Rounding of some figures may lead to minor discrepancies in totals.

Geological Background

The GC property is located on the east margin of the Luoding basin, within the north portion of the Yunkai uplift of the South China Orogenic Belt, at the intersection between the Wuchuan-Sihui Deep Fault zone and Daganshan Arc-ring structural zone. Basement rocks within the project area consist of sedimentary clastics and carbonates belonging to the Sinian Daganshan Formation, the Triassic Xiaoyunwushan Formation, and the Cretaceous Luoding Formation. These rocks are intruded by Palaeozoic medium-grained biotite granite and Mesozoic fine- to medium-grained adamellite, brownish, fine-grained, biotite mylonite, granite porphyry, quartz porphyry, diabase, and aplite. The Mesozoic units intruded along the south and southwest contacts of the Palaeozoic granites. The majority of silver-zinc-lead mineralization is hosted by the Mesozoic granite, which dips south and strikes approximately WNW, parallel to many of the mineralized veins on the property.

GC is a mesothermal vein deposit hosted within a WNW-ENE trending, 4.8 km long by 2 km wide fault zone. The zone contains numerous variably oriented veins, including:

  • The more common WNW veins with 90-150° strike and 55° to sub-vertical drip. The average vein thickness is 0.76 m.

  • East-west veins with 50-130° strike and 65° to sub-vertical drip. The average vein thickness is 0.77 m.

  • Veins sub-parallel to the major NE striking faults F25 and F27, with 10-80° strike and 60-75° dip. The average vein thickness is 0.76 m.

Primary silver-zinc-lead mineralization represents 95% of GC’s current Mineral Resources. Pyrite is the dominant sulphide species, typically comprising up to 13% of the vein. Other metallic constituents include:

  • A few percent of sphalerite, galena, pyrrhotite, arsenopyrite and magnetite.

  • Less than one percent of chalcopyrite and cassiterite.

  • Trace amount of argentite, native silver, bornite, wolframite, scheelite and antimonite.

Metallic minerals occur in narrow massive bands, veinlets and as disseminations in gangues.

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