Silvercorp, through its wholly owned subsidiary Victor Mining Ltd, is party to a cooperative joint venture agreement dated 12 April 2004 under which it earned a 77.5% interest in Henan Found Mining Co. Ltd (Henan Found), the Chinese company holding (with other assets) the Ying silver, lead, and zinc project (the Ying Project). In addition, Silvercorp, through its wholly owned subsidiary Victor Resources Ltd, is party to a cooperative agreement dated 31 March 2006, under which it initially obtained a 60% interest in Henan Huawei Mining Co. Ltd (Henan Huawei), the beneficiary owner of the project in Haopinggou (the HPG Project) and the project in Longmen (the LME Project). Since that time, Silvercorp’s interest in Henan Huawei has increased to 80%.
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Summary:
Mineralization
The Ying Property contains multiple mesothermal silver-lead-zinc-rich quartz-carbonate veins in steeply-dipping fault-fissure zones which cut Archean gneiss and greenstone. To date, significant mineralization has been defined or developed in at least 308 discrete vein structures, and many other smaller veins have been found but not as yet well explored.
Structurally, the vein systems throughout the district are all somewhat similar in that they occur as sets of veins of generally similar orientation enclosed by fault-fissure zones which trend most commonly northeast-southwest, less commonly north-south, and rarely northwest-southeast. The structures extend for hundreds to a few thousand metres along strike. They are often filled by altered andesite or diabase dikes together with quartz-carbonate veins or as discrete zones of altered bedrock (mainly gneiss) associated with local selvages of quartz-carbonate veinlets. From one-third to one-half of the structures exposed at the surface are conspicuously mineralized as well as altered.
The vein systems consist of narrow, tabular or splayed veins, often occurring as sets of parallel and offset veins. The veins thin and thicken abruptly along the structures in classic “pinch-and-swell” fashion with widths varying from a few centimetres up to a few metres. “Swells” formed in structural dilatant zones along the veins often forming mineralized “shoots”. At the SGX mine, these shoots range from 30 m to more than 60 m in vertical and horizontal dimensions over true vein widths of 0.4 m to 3.0 m. The vertical dimension of the SGX shoots is commonly twice or more the horizontal dimension. Longitudinal sections constructed along the veins indicate that many of the shoots have a steep, non-vertical rake.
The vein systems of the various mine areas in the district are also generally similar in mineralogy, with slight differences between some of the separate mine areas and between the different vein systems within each area. These differences have been attributed to district-scale mineral zonation at different levels of exposure. This subtle zonation is thought to be perhaps analogous to the broad-scale zonation patterns observed in the Coeur d’Alene District (USA) and characteristic of many other significant mesothermal silver-lead-zinc camps in the world (Broili et al. 2008, Broili et al. 2010).
SGX area
Currently defined Ag-Pb-Zn mineralization in the SGX area occurs within 82 veins which occur in eight major and two minor vein systems. Three of the 82 veins contain high gold values. The five largest veins, S19, S8, S2, S7-1, and S71, based on Measured and Indicated Mineral Resources expressed as silver equivalent metal, account for 33% of this mineralization.
HZG area
The HZG mine area, south of the SGX area, has 23 Ag-Pb-Zn veins in which mineralization has been defined to date. Underground and surface sampling and drilling indicates that 14% to 23% of the vein-filling material in these veins is strongly mineralized over a true weighted average width of 0.55 m (ranging from 0.30 m to 2.64 m). The veins contain distinctly more copper but lower zinc than the district’s many other veins. For example, one of the largest HZG veins defined to date, HZ20, contains an average of 0.688% copper, which occurs mostly in chalcopyrite and tetrahedrite. The tetrahedrite commonly forms massive lenses, probably filling tension gashes that are distributed in relay-like fashion near the vein margins and in ladder-like fashion near the centre of the veins. The chalcopyrite occurs as disseminated crystals in the gangue and in the tetrahedrite. Other sulphides include galena (up to several percent locally) and pyrite.
HPG area
The HPG mine area is located in the central part of the district, immediately north-east of the SGX mine. Figure 7.6 shows the tunnels and veins in the HPG area. Table 7.3 describes the attributes of the ten biggest veins. Mineralization is currently defined in 47 veins. The five largest veins, H17, H15, H16, H15W, and H15_1 based on Measured and Indicated Mineral Resources expressed as silver equivalent metal, account for 49% of the mineralization. Sampling at various levels in workings along these vein structures indicates that from 27% to 50% or more of the vein material is mineralized, ranging from 0.30 m to 5.76 m in width, averaging 0.77 m.
TLP and LM area
As the mineralization style is similar at the TLP, LME, and LMW mines, they are discussed together here. There are 76 known veins at TLP and 88 at LMW and 30 at LME. Figure 7.7 shows the distribution of veins in the TLP and LM area. Table 7.4 to Table 7.6 describe the attributes of the ten biggest veins for each mine. TLP contains no gold-rich veins. LME has one gold-rich vein, LM4E2. LMW has four gold-rich veins, LM22, LM26, LM50, and LM51.
DCG area
The DCG project area is located in the north-east part of the district, immediately north of the TLP mine. Mineralization is currently defined in ten veins. The largest two veins, C76 and C9 based on Measured and Indicated Mineral Resources expressed as silver equivalent metal, account for 80% of the Mineral Resources defined to date at DCG. Sampling in workings along vein structures indicates that from 18% to 35% or more of the vein material is mineralized, ranging from 0.30 m to 6.99 m in width, averaging 0.67 m. C76 and C9 are the gold-rich veins at DCG. Vein C9 has a different orientation from the other veins in that it extends north-northwest with dip direction around 70-90°, while the other veins extend north-east.
Deposit types
The deposits described in this report are epigenetic vein deposits that have mesothermal characteristics. Mesothermal vein systems typically occur in rocks associated with orogenic belts, in the case of the Ying district, the Qinling orogenic belt. Mineralization is associated with deep-seated shear zones that cut the metamorphic rocks. The veins form in a temperature range of 200 – 300°C, at pressure depths from 600 m to 5,000 m. The veins occur in sets with the major veins in the system tending to be continuous for over 1,000 m in lateral and vertical sense.