South Africa

Lace Mine

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Categories

Overview

Mine TypeUnderground
Commodities
  • Diamond
Mining Method
  • Longhole open stoping
Mine Life25 years (as of Jan 1, 2016)
ShapshotStatus: flooded as of July 2021

Owners

SourceSource
CompanyInterestOwnership
BEE 30 % Indirect
Almas Resources Ltd 70 % Indirect

Deposit type

  • Kimberlite

Summary:

The Lace Mine lies within the south central Archean Kaapvaal Craton within a subcluster of kimberlites referred to as the Kroonstad Group II Kimberlite Cluster (Howarth, 2010) of which only Lace and nearby Voorspoed have seen formal mining. Four other small kimberlite blows and several dykes are known within the cluster.

The Lace Mine lies within the south central Archean Kaapvaal Craton within a subcluster of kimberlites referred to as the Kroonstad Group II Kimberlite Cluster (Howarth, 2010) of which only Lace and nearby Voorspoed have seen formal mining. Four other small kimberlite blows and several dykes are known within the cluster.

Drilling from surface through the wallrocks into the kimberlites in 1997-98 outlined a relatively simple stratigraphy of Karoo shales to ~60m, Ventersdorp volcanics to ~300m, an intercalated shale/volcanic sequence to ~350m, clean lavas again to 380m, and then Kameeldoorns Formation shales again to ~550m, the deepest wall rock drilling to date, in hole Crown-1. We therefore do not believe that Transvaal Supergroup rocks are present at Lace based on drilling to date.

The Lace kimberlites have been dated at 133.2 +/- 2.8 Ma by the 40Ar/39Ar technique on ground mass phologopite grains, similar to the early Cretaceous ages of the other Kroonstad kimberlites and to other Group II kimberlites in South Africa including Finsch.

Reserves

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Mining Methods

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Comminution

Crushers and Mills

Milling equipment has not been reported.

Summary:

A front-end-loader (FEL) will feed 200tph run of mine material into a heavy duty scalping unit which have 500mm spacings. All +500mm dump oversize will be removed by the scalping unit and broken up by a rock pecker. The -500mm ore is fed by a conveyor into a VGF (vibrating grizzly feeder). The VGF has 150mm spacings which drops out the -150mm onto a conveyor and thus bypasses the primary jaw crusher – the +150mm ore is fed into the jaw crusher which is set at 120mm (CCS). The crusher discharge drops onto the same conveyor belt as the -150mm ore and is transported to the primary scrubber. This conveyor is fitted with a weightometer for tonnage measurement and an overband magnet for tramp iron removal. The scrubber feed conveyor discharges into the primary 2.4m diameter by 6.0m length scrubber complete with a double skin trommel. The scrubber feed material is mixed with water at a ratio of 1:1 in the scrubber and the material is disagglomerated.\ Primary scrubber discharge is classified and dewatered with the trommel with -1mm material gravitating to the primary screen under pan; +80mm gravitating to the oversize conveyor and -80+1mm gravitating to the secondary scrubber. Secondary scrubber feed is mixed with fresh water at a ratio of 1:1 and disagglomerated in a 2.0m by 5.0m scrubber. This scrubber is fitted with a bell mouth discharge. -28+1mm material is conveyed to the DMS classifying screen above the DMS surge bins. This material is classified on the screen into -10mm and +10mm fractions. The primary reason for this separation is that the DMS feed can be processed utilising smaller diameter cyclones, thereby improving DMS cyclone efficiencies and in turn assisting with the recovery of fine diamonds. Both the Fines and Coarse module utilise conventional DMS technology. In the case of both modules material is de-slimed on feed preparation screens, -1mm is gravitated to the effluent sump and clean screen product is discharged into a mixing box. The material is mixed with correct medium Ferrosilicon (FeSi) slurry in the mixing box and is pumped with thecyclone feed pump to the cast separating cyclones at the correct density. The +6mm floats from the 100TPH Floats screen and the Coarse Floats are conveyed to the 40T re-crush surge bin. The surge bin ensures choke feed on the Oremaster VSI (vertical spindle impactor) crusher. DMS concentrate is stored in a 20T storage hopper. A vibrating feeder extracts concentrate from the bin and feeds a 1.0m by 3.0m scrubber. This concentrate is scrubbed to polish the material before final concentration. Scrubber discharge is jet pumped to the final recovery building.

Processing

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Production

CommodityUnitsLOM (Projected)
Diamond carats 478,274

Production Costs

Commodity production costs have not been reported.

Heavy Mobile Equipment

Fleet data has not been reported.

Aerial view:

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