NI 43-101 Technical Report – Krumovgrad Project

This report describes the proposed process plant design for the Krumovgrad gold project, based on crushing, grinding, and froth flotation to produce a gold bearing concentrate.

Report context

The NI 43-101 Technical Report for the Krumovgrad Project (Report Number: R135.2014) documents a 2012 mining study that described a mine and process facility with design treatment rates of nominal 0.85 and 1.1 Mtpa. The process flowsheet incorporated a relatively fine (P80 30 microns) primary grind, recovery of precious metals by flotation, and tailings being thickened and co-deposited with mining waste in an integrated mine waste facility (IMWF). No changes were made to the original concepts; however, the base assumptions for each component were interrogated to ensure optimum production through the life of the operation.

Processing route

Crushing

All ore will be reclaimed from the run-of-mine pad by a front-end loader and fed to the feed bin, which will be fitted with a static grizzly to prevent oversize rocks from entering the bin. Ore will be drawn from the ROM bin via a variable speed feeder and discharged into a jaw crusher to produce a crushed product P100 of 200 mm and P80 of 125 mm. The primary crusher product will discharge onto a conveyor belt that transfers the product to the Coarse Ore Silo for storage prior to the grinding circuit. Surge capacity is provided in a 3,000 tonne capacity silo located between the crushing and grinding circuits. The crushing plant is designed to operate on a 12 hours per day basis.

Grinding circuit

Ore will be withdrawn from the silo by one of two apron feeders and fed onto the grinding circuit feed conveyor. The grinding circuit comprises a single stage open circuit SAG mill with pebble crushing in closed circuit with cyclones to produce a product of P80 of 100 to 75 μm. The SAG mill will discharge over a trommel screen, with the oversize (pebbles and steel pieces) discharging onto conveyors feeding the pebble crusher. Tramp steel will be removed using an overhead belt magnet, and the pebbles will feed into a cone crusher to produce a crushed product P100 of 16 mm. The pebble crusher product will discharge back onto the mill feed conveyor belt.

The trommel undersize slurry will gravitate to the mill discharge hopper where it is diluted with water and pumped to a cluster of hydrocyclones for classification. The overflow from the hydrocyclones (ground product) will gravitate through a trash removal screen to the tertiary grinding circuit, while the hydrocyclone underflow will be returned by gravity to the SAG mill for further grinding. The trash screen undersize slurry will gravitate to the combined cyclone feed hopper prior to final classification in hydrocyclones, with the underflow forming the feed to the tertiary mills.

The tertiary grinding circuit comprises two vertical mills in parallel, selected for more efficient use of energy for fine grinding compared to a conventional ball mill. The discharge product will be pumped to a cluster of hydrocyclones for classification. The overflow from the hydrocyclones (the final grinding circuit product) will gravitate as feed to the flotation circuit at the required grind size P80 of 30 microns. Mill operations are designed for 24 hours per day basis.

Flotation circuit

Concentrate from the first stage of the Rougher/Scavenging flotation (4 units for each stage) will be sent for regrind in the tertiary grinding circuit (to a P80 of 15 μm), and then cleaned in the first cleaner (2 units) to produce final concentrate. Tails from the Rougher circuit will be scavenged and the concentrate recycled back to the Rougher feed. Tails from the first cleaner are retreated in the cleaner/scavenger bank (5 units), the tails from which return to the feed to the rougher. The Scavenger cleaner concentrate will be recleaned in the second cleaner (4 units) producing final concentrate, with the tails being recycled back to the feed of the cleaner/scavenger bank.

Concentrate handling

Final concentrate will be thickened and then dewatered in a pressure filter, with the product being stored in bags prior to shipment from site in sealed containers.

Tailings

The discharge from the Scavenger Flotation bank will be pumped to the head of the IMWF, where it will be dewatered in a deep cone thickener to produce an underflow with a minimum of 56% w/w solids. The thickened underflow slurry is conveyed by gravity pipeline and combined with mine waste and placed in the disposal area of the IMWF. The thickener overflow water is returned to the reclaim water tank in the mill circuit area.

Key reported parameters

*Source: Table 64, Krumovgrad Gold Project – Summary Design Parameters (Ref. Project Design Criteria Document – KGP100-20001100-DCS-0001)*

Technical qualifications

The report states that the 2012 mining study design incorporated the flowsheet developed from the extensive test program completed at SGS and the subsequent FLEET circuit modelling program. The grinding circuit development included trade-off studies, with final selection being a single stage SAG mill in closed circuit with cyclones. The report notes that actual plant throughput will be limited by the proportion of the wall component of ore treated in any one year. The flotation circuit design incorporated Staged Flotation Reactor (SFR) units based on trade-off studies and operational experience at the Chelopech operation. The design parameters are based on the Project Design Criteria Document (KGP100-20001100-DCS-0001).

Source: NI 43-101 Technical Report – Krumovgrad Project, Report Number: R135.2014, Section 17 Recovery Methods.