Baiyunpu’s Idle 500 t/d Flotation Plant to Be Replaced by a 1,500 t/d Mill on the Same Flowsheet

This report documents the historical 500 tpd processing facility, its metallurgical performance during 2011 operations, and the proposed replacement with a 1,500 tpd plant following an identical flowsheet.

Report context

This National Instrument 43-101 Mineral Resource Technical Report for the Baiyunpu Project is dated 30th April 2019. At the time of report writing, Silvercorp had not prepared an estimate of mineral reserves. The existing 500 tpd processing facility on site had been idle for more than 4 years and was in need of repair or replacement. The Company intended to dismantle the 500 tpd plant and replace it with a 1,500 tpd processing plant that follows the same process flowsheet. The plant was used to process both lead-zinc sulphide and gold mineralized material, treated separately in campaigns. Lead-zinc flotation used both flotation circuits to produce lead and zinc concentrates, whereas gold flotation used only the lead flotation circuit to produce a gold-bearing pyrite concentrate.

Processing route

Historical 500 tpd Plant

The historical plant consisted of a two-stage crushing circuit followed by classification and dual flotation circuits (lead and zinc). Crushing comprised a jaw crusher (Model PE 400×600) with a closed side setting of 90 mm, followed by a cone crusher (Model PYD 1200) with a closed side setting of 25 mm, in closed circuit with a 25 mm aperture vibrating screen (Model YA1536). Discharge from the screen fed ore bins with a live capacity of 100 tons. Dust from crushing and screening was collected in a bag house and transferred as slurry to a pre-flotation tank.

The milling circuit was a closed circuit consisting of two grate ball mills (Model MQCG 1500 x 4000 mm) and two spiral classifiers (Model FG-15). The ball charge was made of Mn-steel balls with diameters ranging from 60 mm to 120 mm. The target grind size was 70% passing 200 mesh (74 micron). Overflow density was maintained at 40% solids by weight for feeding to conditioning tanks for lead flotation.

Flotation comprised a lead circuit and a zinc circuit. The lead flotation bank consisted of one stage of roughing, two stages of scavenging, and three stages of cleaning. Lead scavenger tails flowed to zinc flotation, which consisted of one stage of roughing, two stages of scavenging, and four stages of cleaning.

Both lead and zinc concentrates were discharged to six settling bays for dewatering by evaporation. Moisture averaged 14-16% in final concentrate products.

Proposed 1,500 tpd Plant

The Company intends to dismantle the 500 tpd plant and replace it with a 1,500 tpd plant that follows the same process flowsheet. The same reagents will be used for the planned 1,500 tpd processing plant. Tailings will be pumped to a surface plant constructed for paste backfill, with half used for underground backfill and the remainder dewatered and sold to third party cement plants.

Process Control

There was no centralized automation station or control room for entire plant process monitoring or control. Ore feed to ball mill was controlled via an electronic scale, and water addition was controlled via slurry density and experience. Pulp density of mill spiral classifiers was monitored and adjusted to maintain between 28% and 35% solids. Chemical dosages were controlled via a localized PLC system for each set of equipment, adjusted in a narrow range based on assay feedback every half hour. Automatic sampling of key metallurgical accounting streams was conducted. A central control room in the grinding-flotation building allowed TV imaging of key production flow points. Samples were taken every 0.5 hour for quality control, mass balance, and recovery calculation.

Ancillary Facilities

The on-site laboratory was equipped with sample preparation, wet chemistry, basic photometric analytical equipment, and metallurgical testing equipment for crushing, grinding, flotation, gravity separation, and fire assay. The laboratory processed up to 100 samples per day and conducted routine analysis of ores and concentrates, water quality, and environmental testing. Silvercorp’s QA/QC procedures included inserting standards in sample batches and submitting duplicate pulps to an independent external laboratory on an intermittent basis. The on-site laboratory had been idle for more than 4 years, and most measuring instruments needed repair or replacement.

During historical production, daily maintenance was serviced through section-specific workshops equipped with cranes, welding capability, and basic machine-shop facilities. Current maintenance workshops needed to be restored before providing basic maintenance services.

Key Inputs

Mill power (10 kV power line) was drawn from the town of Baiyunpu, Hunan Province power authority grid, 7 km from the mine. Another power source (30 kV power line) was planned from the town of Jukoupu, 1.74 km away. To meet 1,500 tpd mining capacity, one 1000 KVA transformer would be used for underground operation, one 630 KVA transformer for fill station, and two 500 KVA transformers for the processing plant.

Net fresh water usage was approximately 1 cubic metre per tonne of ore. Recycled water from the tailings dam helped maintain a zero-discharge water balance for most of the year, with wet season discharges via a water treatment facility.

Reagents used included depressants/modifiers (sodium sulfide, zinc sulfate, sodium sulphite, copper sulfate), collectors (di-ethyl dithiocarbamate, ammonium dibutyl dithiophosphate, butyl xanthate), and frother (MIBC). Reagent storage and mixing was located adjacent to the grinding/flotation plant.

Key reported parameters

Technical qualifications

• At the time of report writing, Silvercorp had not prepared an estimate of mineral reserves.
• The word “ore” was used in a generic sense and does not imply that mineral reserves had been estimated.
• The historical metallurgical data (Table 17-1) represents production data from 2011; feed tonnage of 420 tpd (strikethrough in original) and certain concentrate values were presented with strikethrough formatting in the original table.
• The existing 500 tpd processing facility had been idle for more than 4 years and was in need of repair or replacement.
• The on-site laboratory had been idle for more than 4 years, with most measuring instruments needing repair or replacement.
• The existing 500 tpd plant was to be dismantled and replaced, not upgraded or expanded.
• No centralized automation station or control room existed for entire plant process monitoring or control; the planned level of process control and automation was described as basic but adequate.
• Current maintenance workshops needed to be restored before providing basic maintenance services.

*Source: National Instrument 43-101 Mineral Resource Technical Report , Baiyunpu Project, 30th April 2019, Section 17 Recovery Methods.*