Segovia 2021 PFS Update NI 43-101 Technical Report

This technical report details the processing methods, plant expansion plans, and historical operating performance for the Maria Dama process plant at the Segovia project.

Report context

This NI 43-101 Technical Report, dated May 2022, provides an update to the 2021 Pre-Feasibility Study for the Segovia project, which is operated by Gran Colombia Gold (GCM). The report describes the existing 1,500 t/d Maria Dama process plant and a planned expansion to 2,000 tpd capacity by July 2022.

Processing route

Crushing Circuit

Run-of-mine ore from GCM’s mining operations is crushed to -15 mm in a two-stage crushing circuit. The circuit includes a 20 inch x 36-inch primary jaw crusher that discharges to a RoM ore bin. Primary crushed ore is screened at 15 mm on a 1.9 m x 4.7 m double-deck screen (1 ½ inch top deck and ¾ inch bottom deck). Screen oversize is conveyed to a 4 ft secondary cone crusher (CH-440 Sandvik) operated in closed circuit with a secondary vibrating screen (1.8 m x 6 m). The final 15 mm crushed product is sampled with a primary cross-cut sampler and a secondary rotary sampler as it is conveyed to the fine ore bin. Two Sandvik CH-430 cone crushers serve as backup when the CH-440 crusher is down for maintenance.

Ore delivered by mining contractors is already crushed before arrival and is dumped into a receiving bin. Contractor ore is sampled with both a primary cross-cut sampler and a secondary rotary sampler as it is conveyed from the receiving bin to a separate fine ore bin, with samples assayed by an outside commercial laboratory (SGS). GCM ore samples are assayed by the on-site analytical laboratory.

Grinding Circuit

GCM’s and the contractor’s ore are conveyed to a single conveyor belt feeding the grinding circuit. The circuit consists of a 12.5 ft x 23 ft ball mill operated in a closed circuit with a cluster of Cavex 250 cyclones to produce a final grind of 80% passing 150 µm in the cyclone overflow, which advances to the flotation circuit. A portion of the cyclone underflow is diverted to the gravity concentration circuit, which consists of a single QS-40 Knelson centrifugal concentrator operated in closed circuit with the grinding circuit. Approximately 30% of the contained gold is recovered into a primary gravity concentrate, which is further upgraded in the refinery on a Gemini table. Feed to the grinding circuit is continuously weighed on a belt-scale and hand-sampled every hour.

Flotation and Regrind Circuit

Cyclone overflow from the grinding circuit advances to the flotation circuit where it is first conditioned with flotation reagents. Conditioned slurry is then subjected to one stage of rougher flotation in a 40 m³ tank cell manufactured by Prominer, three stages of scavenger flotation in a bank of three 30 m³ WEMCO flotation cells, and finally one cleaner cell. Rougher/scavenger flotation concentrate is upgraded in one stage of cleaner flotation and combined with the rougher flotation concentrate. The combined rougher/scavenger cleaner concentrate, representing about 7 wt% of the plant feed, is thickened to about 55% solids (w/w) and reground in a 4 ft x 8 ft ball mill to approximately 80% passing 45 µm prior to the cyanidation circuit. The regrind ball mill is operated in closed circuit with 6-inch Krebs cyclones.

Cyanidation and Counter-Current-Decantation Circuit

The reground flotation concentrate is thickened and then processed through a conventional cyanidation circuit consisting of four agitated leach tanks operated in series to provide a total leach retention time of about 96 hours. The cyanide concentration is adjusted to 450 ppm NaCN in the first leach tank and is allowed to naturally attenuate to about 200 ppm NaCN in the last leach tank. The pH of the leach slurry is maintained at about 10.5 to 11 with lime.

Discharge from the fourth agitated leach tank flows to the CCD circuit, which consists of two 24 ft diameter thickeners and one 42 ft diameter thickener and serves to wash the pregnant leach solution (PLS) from the leach residue. The PLS from the first thickener overflow advances to the Merrill Crowe gold recovery circuit, and the thickener underflow from the third thickener is discharged to the TSF.

Merrill-Crowe and Refining

The PLS is processed in the Merrill Crowe circuit to recover solubilized gold and silver values from solution. This is accomplished by clarifying the PLS to remove any remaining suspended solids, de-aerating the solution to less than 1 ppm dissolved oxygen, and then precipitating the gold and silver values by the addition of zinc dust. The resulting gold and silver precipitate is recovered in three plate and frame pressure filters. The gold and silver precipitate is smelted using a flux composed of borax (40%), sodium nitrate (30%), soda ash (15%), and silica (3%). Approximately 650 kg of flux is blended with 600 kg of precipitate and smelted in a gas-fired furnace to produce a final doré product.

The gravity concentrate produced from the Gemini table located in the refinery is directly smelted using a flux formula in which flux is added in the ratio of two parts flux to one-part gravity concentrate. The flux composition includes borax (40%), sodium nitrate (30 to 33%), soda ash (7.5%), and silica (6%).

Tailings

Final leached tailings from the CCD circuit are detoxified with hydrogen peroxide and then pumped to lined dewatering cells identified as Bascula, Bolivia-1, Bolivia-2 and Bolivia-3. Effluent from the dewatering cells is then recycled back to the process plant. Flotation tailings are pumped to the El Chocho TSF where they are thickened and filtered to about 15% moisture prior to dry stack placement at the TSF. Thickener overflow and filtrate solutions are recycled back from the TSF to the process plant.

Proposed Plant Expansion

GCM is expanding the capacity of the Maria Dama process plant and expects to be able to process ore at the rate of 2,000 tpd by July 2022. The plant expansion includes the following components:

• Expansion of the ore stockpile area and upgrades to the crushing circuit designed to increase crushing capacity from 70 to 150 t/h.
• Installation of a new 40 m³ tank flotation cell to the rougher flotation circuit.
• Installation of a new Merrill-Crowe circuit for recovery of gold from the leach solution using conventional zinc precipitation technology.
• Replacement of the old thickeners in the CCD circuit with new thickeners.
• Upgrading the process water distribution system.
• Installation of a second tailings pressure filter at the El Chocho dry stack TSF.

The plant expansion is budgeted at a cost of US$9.57 million, allocated as follows: second tailings pressure filter (US$4.16 million), ore stockpile and crusher upgrade (US$3.96 million), new Merrill-Crowe circuit (US$0.24 million), process water distribution (US$0.14 million), new thickeners (US$0.76 million), and new rougher flotation tank cell (US$0.31 million).

Key reported parameters

Technical qualifications

This report is based on the original technical report titled "Segovia 2021 PFS Update NI 43-101 Technical Report" dated May 2022. The processing methods described show the existing Maria Dama process plant and proposed expansion as designed by GCM. Historical production data covers the period from 2002 to 2021, with detailed operating data from 2019 to 2021. The report notes that although silver occurs in the ore, silver recovery is not monitored. Reagent consumption data and operating costs are provided from actual plant operations for 2018 through 2021. The flowsheet figures and general arrangement drawings referenced in the original report (Figures 17-1 and 17-2) are not reproduced here. Equipment specifications are based on the major equipment list provided by GCM in 2022.

Source: Segovia 2021 PFS Update NI 43-101 Technical Report, May 2022, Section 17 Recovery Methods