This report details the processing facilities and metallurgical performance for the Ying silver-lead-zinc property in Henan Province, China.
Report context
This technical report update for the Ying Ag-Pb-Zn Property in Henan Province, People's Republic of China, dated 2022, provides information on the processing operations for Silvercorp Metals Inc. The report covers two operating processing plants (Plant 1 and Plant 2) and a third plant under construction, with production data generally referenced from FY2019 through Q3 of FY2022 (1 April 2018 to 31 December 2021).
Processing route
Plant 1 (Xiayu Plant)
Plant 1, also known as the No.1 Mill or Xiayu Plant, has been in operation since March 2007. The plant was designed with a capacity of 600 tpd, later expanded to 800 tpd, based on lab tests completed by HNMRI in 2005. The plant currently operates at an actual capacity of 700 tpd with 330 days per year plant availability.
The flowsheet includes a crusher circuit with closed-circuit two-stage crusher-screen operation (jaw crusher, one cone crusher, vibrating screen, dust collectors, and two ore storage bins). Crushing is operated with a primary jaw crusher (Model: PEF 500 x 750) having a closed-side setting of 80 mm. Discharge is conveyed to a 15 mm aperture vibrating screen, with oversize material conveyed to a secondary cone crusher (Model: PYH-2X cone crusher) with a 15 mm closed-side setting. Product undersize feeds fine-ore bins with 100 t live storage capacity.
The milling classification circuit consists of two trains, each with a grate-discharge ball mill (Model: MQCG 2100 x 3600) and a screw classifier (Model: FG-200). The ball charge uses Mn-steel balls with diameters from 60 mm to 120 mm. The target grind size is 61% to 63% passing 200 mesh, with overflow density maintained at 40% solids w/w.
Plant 1 was upgraded by adding a gravity separation circuit following metallurgical testing by Changchun Gold Research Institute (CCGRI) in 2021. This circuit includes a set of hydrocyclones to replace the spiral classifier, a Knelson concentrator to recover coarse gold, a linear screen to screen coarse particles greater than 2 mm, and a shaking table for cleaning the Knelson concentrate.
The lead flotation circuit consists of one train with conventional Pb flotation arrangement capable of processing 800 tpd. The flotation bank includes one stage of roughing, two stages of scavenging (BF-4 type cells), and three stages of cleaning (BF-1.2 type cells). The zinc flotation circuit exists but is not currently in operation due to low zinc in the feed ore to Plant 1.
The following minor changes were made to the original Plant 1 design: addition of one cone crusher to increase ball mill capacity from 600 to 800 tpd; coarsening of the original ball mill grinding size target from 70% to 60% (-200 mesh), later adjusted to 61% to 63% (-200 mesh) in 2014 resulting in increased Pb recovery of 0.41% and Ag recovery of 2.16 g/t; addition of gravity separation circuit; and replacement of lime slurry by NaOH/Na2CO3 for pH control.
Plant 2 (Zhuangtou Plant)
Plant 2, also known as the No.2 Mill or Zhuangtou Plant, is located 2 km west of Plant 1. Phase I (1,000 tpd design) has been in production since December 2009, and Phase II (also 1,000 tpd design) has been in production since October 2011. The plant currently operates at an actual capacity of 1,800 tpd with 330 days per year plant availability.
The flowsheet includes a crusher circuit with three-stage crushing-screening (one jaw crusher, two cone crushers, vibration screen, dust collectors, ore storage bins) as one train. The primary jaw crusher (Model: PEF 800 x 1000) has a closed-side setting of 80 mm. Discharge is conveyed to a secondary cone (Model: PYHD-3CC) with 15 mm closed-side setting, then to a 15 mm aperture vibrating screen. Oversize material is conveyed to a tertiary cone crusher (Model: PYH-3CC) with 15 mm closed-side setting. Undersize product feeds ore bins with 1,000 t live capacity.
The milling classification circuit consists of two trains, each with a grate-discharge ball mill (Model: MQG 2.7 m dia. x 4.0) and 15" hydrocyclone/spiral classifiers (Model: 2FG2.4).
The flotation circuit includes lead sulphide flotation and zinc sulphide flotation with rougher-scavenger-cleaner cells and chemical reagent preparation tanks, configured as two trains of 1,000 tpd each. There is no copper flotation. The flotation cells are larger than those in Plant 1 (BF-16 and BF-4).
Plant 3 (Under Construction)
Plant 3, with a design capacity of 3,000 tpd, is currently under construction and scheduled to be operating by mid-2024. The plant is planned to replace Plant 1 and Plant 2. A third tailings management facility is also being built to accommodate tailings from Plant 3.
Plant 3 is designed by Changchun Gold Design Institute (CGDI) according to the results of their metallurgical testing and operating experience at Ying. The flowsheet is similar to that of Plant 2 but with larger equipment, greater processing capacity, more advanced technology, and more flexible operation. It can handle silver-lead-zinc ore, silver-lead ore, copper-lead ore, and gold ore.
The flowsheet includes a crusher circuit (one train, 200 tph), grinding with semi-autogenous grinding (SAG) milling (6.0 m dia. x 3.0 m SAG mill), ball milling (4.5 m dia. x 6.4 m ball mill), and hydrocyclone classification (one set of 500 mm dia. hydrocyclones) arranged as one circuit with 3,000 tpd capacity. Gravity concentration includes a Knelson concentrator, a vertical mill for regrinding Knelson gold concentrate, and a concentrate shaking table. The flotation circuit includes lead flotation, zinc flotation, and copper/lead separation flotation.
Ore Supply and Handling
Ore from the Ying mines is shipped via truck to processing Plants 1 and 2. SGX/HPG lumps (rich, large-size galena lumps with characteristic specular, silver-grey appearance) may be hand-sorted at the mine sites, crushed, and shipped by dedicated trucks to Plant 1. These lumps are milled in a dedicated facility and sold directly or mixed with flotation PbS concentrate for sale, bypassing the flotation circuit. No hand-sorting was done between January 2020 and December 2021.
An ore transportation tunnel from SGX to HPG has been constructed and the haul road from HPG to the plants has been upgraded. A transportation tunnel from TLP to DCG was completed in October 2020 to haul ore from DCG via TLP to the plants by truck.
Concentrate Handling
Lead concentrate from Plant 1 and Plant 2 are blended to optimize profitability. High grade lead concentrate (55% to 65% Pb) from Plant 2 is blended with medium grade lead concentrate (40% to 50% Pb) from Plant 1 before shipping blended concentrate to clients.
Process Control
An ore crushing control centre in Plant 2 controls and monitors the crushing and screening equipment. In 2019, a PCL system was installed in the crushing building in Plant 2 to allow automatic control of the entire crushing system. Ore feed to the ball mill is controlled via an electronic scale. Chemical reagent dosages are controlled via a localized PLC system, adjusted based on assay feedback (each half hour). The central monitoring room in the grinding-flotation building allows monitoring of key points via TV imaging.
Plant 3 is to be equipped with advanced industry-standard monitoring and process control instruments and systems, including a central control room and video monitoring system for the whole plant.
Key reported parameters
| Parameter | Plant 1 | Plant 2 (Phase I) | Plant 2 (Phase II) | Plants 1+2 |
|---|---|---|---|---|
| First year in operation | Mar 2007 | Dec 2009 | Oct 2011 | – |
| Design capacity (tpd) | 800 | 1,000 | 1,000 | 2,800 |
| Actual capacity (tpd) | 700 | 900 | 900 | 2,500 |
| Plant availability (day/yr) | 330 | 330 | 330 | 330 |
| Major ore feed | LM/TLP/HZG | All | All | All |
| Tailings pond | P1-Zhuangtou | P2-Shiwagou | P2-Shiwagou | P1+P2 |
Project website: https://silvercorpmetals.com/silvercorp-announces-filing-of-updated-technical-reports-for-the-ying-mining-district/
| Design metallurgical performance | Pb recovery (%) | Zn recovery (%) | Ag recovery (%) |
|---|---|---|---|
| Plant 1 design (600 tpd basis) | 90.00 | 85.00 | – |
| Plant 2 design (1,000 tpd per phase) | 93.00 | 81.50 | – |
| Average actual (FY2019-FY2022Q3) | 95.80 | 59.87 | 95.28 |
| Design target | 90 | 85 | 90 |
| Concentrate quality (design vs actual average) | Pb (%) | Zn (%) | Ag (g/t) |
|---|---|---|---|
| Pb concentrate design | 60 | 1.95 | – |
| Pb concentrate actual average | 53.35 | 3.54 | 3,655 |
| Zn concentrate design | 0.95 | 45 | – |
| Zn concentrate actual average | 0.75 | 52.10 | 284 |
| Mill power consumption | Plant 1 | Plant 2 | Plant 3 (planned) |
|---|---|---|---|
| Total installed power (kW) | 3,124 | 9,260 | 12,391 |
| Crushing and milling power (kW) | 963 | 3,260 | 5,411 |
| Average mill power consumption (kWh/t) | 32.1 | 38.9 | 48.06 |
| 2021 average (kWh/t) | 29.4 | 40.95 | – |
| Ore supply by mine (FY2019-FY2022Q3 totals) | Tonnes | Contribution (%) |
|---|---|---|
| SGX | 942,794 | 39 |
| HZG | 198,815 | 8 |
| HPG | 226,658 | 9 |
| TLP | 634,043 | 26 |
| LME | 178,299 | 7 |
| LMW | 244,712 | 10 |
| Total | 2,425,320 | 100 |
Technical qualifications
The following limitations are noted from the report:
- Plant 1 is averaging 480 tpd which is less than the current stated capacity of 700 tpd and is run only in campaigns depending on ore supply. Plant 2 is operating at 1,500 tpd which is below the current stated capacity of 1,800 tpd.
- Lead and silver recovery targets are being met; however, zinc recovery is lower than design, attributed to lower than planned zinc feed grades.
- The average Pb grade in lead concentrate is still lower than the design value of 60%.
- With the proportion of SGX ore decreasing, the challenge is to maintain similar metallurgical performance on lower grade feedstock.
- The design of Plant 3 is based on locked-cycle flotation test results for different ore types, and the actual metallurgical performance will be determined after commissioning.
- Water usage data for Plant 3 is projected, not actual.
- The zinc flotation circuit in Plant 1 is not currently in operation due to low Zn in the feed ore.
Source: NI 43-101 Technical Report Update on the Ying Ag-Pb-Zn Property in Henan Province, People's Republic of China, Silvercorp Metals Inc., 2022, Section 17 Recovery methods.
