Terronera Project — Updated Preliminary Feasibility Study (Recovery Methods)

The Updated Preliminary Feasibility Study for the Terronera Project proposes a Flash flotation beneficiation plant to recover gold and silver into a marketable concentrate, with testwork indicating enhanced recovery at a grind size of 80 percent passing 150 mesh.

Report context

This recovery methods section is taken from the Terronera Project Updated Mineral Resource Estimate & Updated Preliminary Feasibility Study (UPFS). The metallurgical program included work by Resource Development Inc. (RDi) and additional flotation studies conducted by ALS Metallurgy in Kamloops, B.C., Canada. SFA conducted analysis of the ALS data to develop estimated gold and silver recovery levels. Composite samples were assembled and provided by Endeavour Silver’s Geology department.

Processing route

Grinding and Flash flotation

The proposed plant uses a grind of 80 percent passing 150 mesh (Tyler), equivalent to approximately 100 microns. Flash flotation technology was selected based on testwork indicating it will provide enhanced precious metal recovery at this grind size. The grinding circuit design consists of two lines (A and B), each with a single stage of primary ball milling. A portion of the cyclone underflow slurry feeds the Flash flotation cell, which is installed in the grinding circuit area. Dilution water is added to the cell to allow flotation of liberated values. Flash flotation tailings are directed to the mill feed box, while the concentrate reports directly to the final concentrate thickener.

Flotation and cleaning

After grinding, the ground slurry at approximately 23 percent solids is sent to a trash screen for debris removal, then to a conditioning tank where flotation reagents are added. The flotation circuit comprises two lines of Rougher followed by Scavenger cells. Rougher and Scavenger concentrates are sent to a regrind circuit to achieve optimum liberation. Cyclone overflow from the regrind circuit feeds a two-stage cleaning circuit. First cleaner tailings are returned to the head of Rougher flotation. Second cleaner concentrate reports to the concentrate thickener.

Concentrate handling

Final concentrate is filtered, producing a filter cake with moistures ranging from 15 to 20 percent. The cake is stored and air dried in a warehouse prior to shipment. Each shipment will be sampled and analyzed for precious metal and moisture contents, with impurities quantified and evaluated prior to shipment.

Tailings management

Flotation tails are sent to a thickener, and the higher-density slurry is filtered using two ceramic disk filters. The filter cake is stockpiled at the dry tailings filter plant before transport by truck to the dry stack tailings storage facility (DTSF). A radial stacker places the filtered tailings in a stockpile, with front-end loaders and compaction equipment used to load, spread and compact the material. The report lists advantages of a dry stack tailings system as water reclaim maximization, no embankment needed, minimal area required for placement, improved drainage control, and lower reclamation cost.

Crushing circuit

The crushing circuit is designed to process 1,500 dry tpd in 18 hours of operation. It includes a 24-tonne dump ore pocket with a stationary grizzly having 10-inch by 10-inch openings, with grizzly oversize broken by a hydraulic breaker. An apron feeder sends ore to a primary jaw crusher that reduces material to minus 85 mm. Crushed material and dust fines are transported to subsequent stages of screening and closed-circuit crushing to further reduce material to minus 9 mm. Conveyor belts transport intermediate and fine crushed materials. The circuit includes weigh scales, a crushed ore sampling system, and magnetic separators to protect the cone crusher from tramp iron. Fine crushed product is transported to two fine ore bins (A and B), each with 750 metric tonnes live capacity.

Plant design and expansion

The design basis is 750 dry tpd for Years 1 and 2 of operation. In Year 3, throughput will increase to 1,500 tpd by the addition of line B grinding and flotation circuits. The beneficiation plant will operate continuously 365 days per annum with an assumed availability of 92 percent.

Key reported parameters

Reagents and dosage (testwork basis)

Technical qualifications

The report states that results from testing mineralized material may not always represent metallurgical results obtained from a production-scale processing plant following a defined mine production plan. The process design is consistent with metallurgical data developed from samples tested by ALS for this study, but calculated levels of precious metal recovery may change as more metallurgical data become available from future testing. The composite samples are believed to be representative of materials originating from the Terronera deposit. The report also notes that optimization of the grinding circuit design will be necessary to ensure the desired grind is achieved during normal operation. Reagent dosage optimization studies will allow for reduction of costs associated with flotation and sedimentation.

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Source: *Terronera Project Updated Mineral Resource Estimate & Updated Preliminary Feasibility Study*, Section 17 Recovery Methods.