The poly-metallic mineralization of the GC deposit belongs to the mesothermal vein infill style of deposit and exhibits the following characteristics:

• The mineralization occurs as veins which are structurally controlled within broader alteration zones. The alteration can reach more than a few metres along the faults distributing in both hangingwall and footwall.
• The veins have a sharp contact with the host rocks and steeply dip at angles between 60 – 85°.

In general, the Ag-Zn-Pb mineralization occurs along the strike of the faults. The veins have true widths varying from just over 0.1 m to over 10 m. They have been traced for over 1,250 m along strike, and approximately 550 m down dip.

Ag-Zn-Pb mineralization at the GC deposit can be divided into two types: primary and oxidized. The primary mineralization is mainly composed of galena-sphalerite-silver minerals which occur sparsely, as disseminations, veinlets and lumps. Primary mineralization accounts for 95% of the entire Mineral Resource. Oxide mineralization occurs on and near the surface.

Mineralized veins in the GC area occur in relatively permeable fault-breccia zones. These zones are extensively oxidized from the surface to depths of about 40 m. Veins in this zone exhibit open space and boxwork lattice textures resulting from the leaching and oxidation of sulphide minerals. Secondary minerals present in varying amounts in this zone include kaolinite, hematite, and limonite.

The dominant sulphide mineral is pyrite, typically comprising a few percent to 13% of the vein. Other constituents are a few percent of sphalerite, galena, pyrrhotite, arsenopyrite, magnetite, and less than a percentage of chalcopyrite and cassiterite. Metallic minerals in much smaller amounts include argentite, native silver, bornite, wolframite, scheelite, and antimonite. Metallic minerals occur in narrow massive bands, veinlets or as disseminations in the gangue. Gangue minerals include chlorite, quartz, fluorite, feldspar, mica, hornblende, with a small or trace amount of kaolinite, tremolite, actinolite, chalcedony, garnet, zoisite, apatite, and tourmaline.

Alteration minerals associated with the GC vein systems include quartz, sericite, pyrite, and chlorite, together with clay minerals and limonite. Silicification commonly occurs near the centre of the veins. Chlorite and sericite occur near and slightly beyond the vein margins.

Quartz, pyrite, fluorite, and chlorite are closely related to the mineralization.

Mining to date has been conducted in two stages that are horizontally defined by mine sections and vertically by elevations, with a general description as follows:
1 Stage 1: +150 mRL to -50 mRL between local Mine Sections 10 to 36 for development and 12 to 32 for production - west side of project.
2 Stage 2: +100 mRL to -50 mRL between Mine Sections 36 to 54 for development and 32 to 54 for production. From -50 m RL to -300 mRL between Mine Sections 12 to 50 for both development and production.

Stage 1 essentially targeted bringing the project into production as soon as practicable using mobile rubber-tired diesel-powered equipment (development jumbo, loader, and truck) with surface declines access down to -50 mRL.

Stage 2 development from -50 mRL down to -300 mRL employs conventional tracked equipment (battery powered locomotives, rail cars, electric rocker shovels and pneumatic handheld drills) via a surface shaft access.

Selective stoping methods - shrinkage and resuing - are employed with stope production drilling conducted with pneumatic jackleg drilling. In-stope rock movement is by gravity to draw points or hand-carting to steel-lined passes.

Stage 1 production mucking used load-haul-dump loaders (LHD) with trucks hauling ore to the surface ROM stockpile, and ore was re-handled from the ROM stockpile to the primary crusher feed bin using a ROM front-end-loader (FEL).

Stage 2 and ongoing production mucking uses electric-powered over-throw rail loaders with rail cars and battery powered locomotives transporting ore to level ore passes at each level. Ore is hoisted using a double-story cage (holding four cars, i.e. two cars each story) to a surface stockpile where a loader conveys ore to the surface crusher feed bin.

Shrinkage stoping and resue stoping are the methods employed.

Shrinkage stoping
The method begins with establishing a sill drive along the vein to expose the vein at 2.4 m height. An access drive (conventionally a footwall drive) is also developed parallel to the vein at 2.4 m wide x 2.4 m high at a minimum stand-off distance of 6 m. Cross-cuts between the access and vein drives are developed at approximately 7.5 m strike spacing (actual spacing is dependent on the loader used, loader dimensions and the rib pillar thickness required for rib stability). The cross-cuts act as draw points for the mucking of the stope ore. Travelway raises that are also used for services are established between the levels at each end of the stope block. Waste packs are built on each void side of the raise as stoping proceeds upwards. Each stoping block is normally 50 m strike length by 50 m height.

Jackleg miners use pneumatic drills to drill a 1.8 – 2.0 m stope lift that is drilled and blasted as inclined up-holes with a forward inclination of 75 – 85o (“half-uppers”). The typical drill pattern uses a drill burden of 0.6 – 0.8 m and spacing of 0.8 – 1.2, depending on vein thickness. Holes are charged with cartridge explosives and ignited with tape fuse. The powder factor is generally 0.4 – 0.5 kg/t. Stope blasting fills the void below with ore as the mining proceeds upwards. While mining upwards, only 30 – 35% of the stope ore may be mucked until the entire stope is mined. At this point, all ore is mucked from the stope, leaving the stoping void effectively empty. A crown pillar is maintained for the stope to provide regional stability and to minimize dilution from up-dip stopes. Ventilation, compressed air, and water are carried up the travelway raises to the stoping level. Loading of the ore from the draw points is by rubber-tired LHD into trucks (Stage 1) or electric rail over-throw loaders into rail cars.

Resue stoping
Vein and access development preparation is essentially the same as for shrinkage stoping except that an elevated sill drive (3 m on-dip height) is established along with draw points (generally limited to two or three) to provide access to the raise positions (raises equipped with steel liners as mill holes).

Resue stoping veins are typically higher-grade and generally between 0.20 m (minimum extraction width 0.3 m) and 0.80 m width. Resue stoping involves separately blasting and mucking the high-grade narrow vein and waste required to achieve a minimum stoping work width.

The mining crew consists of jackleg miners using pneumatic drills. Half-uppers lifts are drilled and blasted in essentially the same manner as for shrinkage stoping. After an ore lift is blasted and mucked, the footwall is blasted and used to fill the space mined out. This process is repeated until the crown pillar is reached. The entire stope is left filled with waste from the slashing of the footwall.

The blasted ore is transported by wheelbarrow and / or hand shovelling to the steel lined mill-hole. The steel pass is constructed in lift segments as the stope is mined upwards. The base of the steel pass is held in place with a timber set. The footwall waste is then slashed (blasted) to maintain a minimum mining width (typically 0.8 m for GC) and to provide the working platform for the next stope lift. In contrast to shrinkage stoping, the mined-out stope is left filled with waste from the slashing of the footwall necessary to maintain a minimum mining thickness and to provide a working platform.

The order of vein extraction and footwall slashing is generally dependent on the condition of the vein hangingwall contact. Where the vein hangingwall contact is distinct and stable, the vein is extracted first; otherwise the footwall waste is extracted first followed by vein slashing.

Rubber mats and / or belting are placed on top of the levelled waste after each waste lift to minimize ore intermingling with the waste (ore losses) and also to minimize over-mucking of the waste (dilution). Mucking of the ore consists of hand lashing (shovelling) and hand carting to the steel pass which connects to the mill hole crosscut. The rubber mats and / or belt are rolled up and removed for reuse prior to slashing the footwall and forming the next platform lift.

In-stope ore transporting may potentially be improved by using scraper winches with small hoes.

AMC understands that Silvercorp has previously considered the application of a cemented backfill system to fill some of the mined-out stopes and that provision is now being made for introduction of such a system.

Crushing
The crushing circuit consists of a run-of-mine ore bin from which the ore is drawn by a vibratory feeder into the primary jaw crusher. The jaw crusher product is screened on a vibrating screen with the -10 mm fines being conveyed forwards to the fine ore bin while the +10 mm material feeds the secondary cone crusher via a buffer storage bin to maintain choke feeding of the crusher. The fine ore bin has a capacity of 1,600 t.

Grinding
In similar fashion to the crushing section, the two-stage grinding circuit is sized for 1,600 tpd.

Given that 1,600 tpd could be the ultimate throughput, four mills with 400 kW motors have been installed.

Typical of Chinese practice and conforming to the design successfully used at Silvercorp’s Ying mine, the grinding circuit consists of a grate-discharge ball mill in closed circuit with screw classifier followed by an overflow ball mill in closed circuit with hydrocyclones, to achieve the desired flotation feed size of 80% passing 75 µm (P80 of 75 µm) in the cyclone overflow. The primary mills have weightometers fitted to the feed conveyors linked to a variable speed belt motor for mill feed control.

The circuit is configured in two parallel trains, each of 800 tpd capacity, for reasons of flexibility and ease of maintenance.

The overall process consists of crushing, grinding, sequential flotation of lead, zinc, and pyrite concentrates, and concentrate dewatering by disc filtration. An experimental tin recovery gravity separation circuit is installed on pyrite flotation tails.

Two-stage crushing is carried out, with the second stage in closed circuit. Run of mine ore at -350 mm is reduced to crusher product at -10 mm. This is followed by two-stage grinding in ball mills to a product size of 80% passing 75 µm (P80 of 75 µm).

The flotation process consists of a standard flotation of lead, with three-stage cleaning of the lead concentrate, then flotation of zinc concentrate with three-stage cleaning; leaving pyrite tailings as S concentrate. Concentrates are dewatered by conventional thickening and filtration.

The experimental tin recovery circuit treats Zn scavenger flotation tailings. It comprises spiral classification, followed by coarse and fine gravity concentration using ........