The Ying silver-lead-zinc mine complex in the Henan province of China encompasses the SGX, HZG, HPG, TLP, LME, and LMW underground mines, as well as the DCG project.
Canadian mining company Silvercorp holds a 77.5% stake in the Chinese holding company Henan Found Mining that owns the flagship SGX mine as well as the TLP mine within the Ying silver-lead-zinc property.
Silvercorp also holds an 80% stake through its wholly-owned subsidiary Victor Resources in Henan Found Mining that owns the HPG, LME, and the LMW mines within the Ying mining district.
Operator Silvercorp received the mining permit for the SGX mine after two years of exploration and development in March 2006, while the mine commenced commercial production started the following month in April.
The HPG mine commenced operations in January 2007, while the LME and the LMW mines were brought into production in March 2008.
The Ying mine complex produced 5.59 million ounces (Moz) of silver, 25,598 tonnes (t) of lead, and 3,328t of zinc in the year ending March 2020.
Location and geology
The Ying silver-lead-zinc mining district is located approximately 145km south-west of Luoyang and 240km west-southwest of the capital city of Zhengzhou, in Henan province of China.
The mining complex is situated in the Qinling orogenic belt which is a 300km-long, west-northwest trending belt. The Ying poly metals ore deposit is underlain by a highly metamorphosed Archean basement of mafic to felsic gneisses, derived from mafic to felsic volcanic and sedimentary rock units.
The lowest part of the basement is a north-northeast trending, 1km-thick mafic gneiss with local gabbroic dikes and sills that dip 30° to 60° in the south-east. The lower basement is overlain by a much thicker, thin-bedded quartz-feldspathic gneiss sequence. The gneisses are locally intruded by small granite porphyry stocks of Proterozoic to Paleozoic age.
Mineralisation and reserves
The mineralisation at the Ying silver-lead-zinc property occurs as a multi mesothermal silver-lead-zinc-rich quartz-carbonate deposit with veins occurring in steeply-dipping fault-fissure zones which cut Archean gneiss and greenstone.
The mineralised zones are found to be hosted in up to 308 discrete vein structures throughout the property with several other smaller vein structures yet to be explored. The vein systems consist of narrow, tabular, or splayed veins that thin and thicken abruptly in pinch-and-swell fashion varying in widths from a few centimetres up to a few metres.
As of December 2019, the total proven and probable reserves at the Ying silver-lead-zinc property were estimated to be approximately 12 million tonnes (Mt) grading 257 g/t silver (Ag), 0.13 g/t gold (Au), 3.81% lead (Pb), and 1.41% zinc (Zn), containing 99 million ounces (Moz) of silver, 50,000 ounces (oz) gold, 456,000 tonnes (t) of lead, and 169,000t of zinc.
The SGX mine alone was estimated to hold 5.2Mt of proven and probable reserves, while the measured and indicated resources at the Ying mine complex were estimated to be 20.12Mt.
Mining equipment and method
The underground mining operations at the Ying silver-lead-zinc are carried out using 20t tonne trucks, single-boom jumbos, electric and diesel locomotives, rail cars, electric rocker shovels, and pneumatic hand-held drills.
The underground access to each of the mines is via adits at various elevations, inclined haulage ways, shafts, and declines.
The mining extraction sequence is top-down between levels, and generally outwards from the central shaft or main access location while the stope extraction sequence is bottom-up with shrinkage and resuing as the primary methods. Jacklegs are used in stope blast drilling.
SGX and HZG mines
The SGX mine, the biggest underground mine within the mine complex is located on the western part of the property. The mine is accessed via eight adits and a 2.9km-long ramp which will further extend to 5.6km with the extension of an inclined-haulage way expected to be completed by 2021.
The SGX mine is divided into 13 production systems, each with an independent transport and muck-hoisting system. A total of up to 75 mineralised veins have been discovered within the SGX mine area.
The HZG mine is a satellite of the SGX mine with 21 known mineralised veins and five production systems. The underground access portals comprise five adits located approximately 4km south of the SGX mine. A ramp measuring 2.1km-long is being developed for the mine which is expected to be completed in 2021.
HPG, TLP, LME, and LMW mines
The HPG mine is located in the central part of the Ying mining property, to the north-east of the SGX mine. The underground operations are accessed via six adits and the mine has five production systems. A total of 36 mineralised veins have been identified in the HPG mine.
The TLP mine is located approximately 11km east–southeast from the SGX mine. The mine is accessed from eight adits while a 3.3km-long ramp is expected to be completed by 2021. The mine has seven production systems and 77 known westward dipping mineralised veins.
The LME mine is located immediately south of the TLP mine, approximately 12km away from the SGX mine. The LME underground operations are accessed a single audit and two inclined haulage ways. A 2.5km-long ramp is being developed for the mine which is scheduled for completion by 2021. A total of 23 mineralised veins have been identified at the LME mine.
The LMW mine is located adjacent to the LME mine. It is accessed via four audits, two shafts, and one ramp. A total of 72 mineralised veins have been identified for the mine.
The DCG project details
The DCG project which is currently in the development stage is located approximately 2.7km north-west of the TLP mine.
The mine has three identified mineral veins with north-east strike and north-west dips. The mine is accessible via a ramp and a 1,768m transportation decline from the TLP is expected to be completed by April 2021.
Mining operations at the DCG mine are expected to be started by 2022.
The Ying silver-lead-zinc project has two processing plants namely, Plant 1 and Plant 2 that are located within a distance of 2km from each other. The two processing plants have a combined processing capacity of 2,600tpd.
The crushing units for the processing plants are closed circuits, consisting of jaw-cone crushers with a vibrating screen, and secondary cone crushers which feed the milling circuit.
The crushed ore from the live bins is conveyed to a closed milling circuit comprising two trains, each with a grate-discharge ball mill and a screw classifier.
The fine product from the classifiers feeds the lead rougher conditioning tanks which in turn feeds the lead rougher flotation cells. The lead concentrates slurry from the flotation cells are transferred to a concrete settling containment structure. The settled slurry containing up to 60% solids is dewatered in a ceramic filter to produce a lead concentrate filter cake with up to 10% water content.
The medium grade lead concentrate from Plant 1 is sent to Plant 2 to be blended with high-grade lead concentrate from Plant 2 to optimise the profitability. The blended concentrates are then packaged for shipping to clients.
Offtake agreements for the Ying mine
The monthly lead concentrate supply contracts for the Ying mine have been signed with smelters mostly within the Henan province which include Henan Yuguang Gold and Lead Smelting, JiyuanWanyang Smelting, JiyuanJinli Smelting, Lingbao Xinling Smelting, and Anyang Minshan Smelting.
The monthly zinc supply contract for zinc concentrate is in place with Henan Yuguang Zinc Industry.
The Ying silver-lead-zinc property is accessible via a 56km-long paved road from Luoning which leads up to the mill site located in the central part of the mine complex.
The power supply is received from the Chinese National Grid via a 35kV transmission line from the Luoning Guxian 110kV substation, and two 10kV high-voltage lines from the Luoning-Chongyang 35kV substation. Two 1500 kW and one 1,200 kW backup generators are available in the mine complex.
The water requirement for the mine complex is received from the Guxian Reservoir via 89mm diameter pipelines, as well as from the nearby creeks, springs, and underground sources.
Canada-based AMC Mining Consultants was engaged by Silvercorp Metals to prepare the 2020 Technical Report for the Ying silver-lead-zinc project.
The contractors engaged for the underground mining operations include Luoyang Xinsheng Mining Engineering, Lushi County Jingsheng Tunnelling Engineering, Henan Sanyi Mine Construction Engineering, Hongji Construction Engineering, Zhejiang Xinlong Construction Engineering, and Shandluo Shunan Tunnelling Engineering.