Modder East Gold Mine

 mine, gold mine

Modder East, Gold One's flagship mine, is the first new mine built on the East Rand of South Africa's Gauteng Province in 28 years. On 21 July 2009, Gold One announced that it had poured its first 240 ounces of gold from underground Modder East ore, well ahead of schedule, following on from the successful commissioning of the Modder East plant in June 2009 using low grade third party surface material. Continuous and commercial production was declared on 1 December 2009.


Situated approximately 30 kilometres to the east of Johannesburg, Modder East is located in one of South Africa's richest historic gold mining districts. The Modder East project consists of both the Modder East gold mine and the UC prospect areas, where the Black Reef and the UK9a Reef (Kimberley Reef) have been identified.


The Modder East mine encompasses a shallow underground mine (300 metres to 530 metres below surface) and a dedicated gold treatment facility. Mining at Modder East employs a combination of conventional and mechanised mining techniques. Access to the ore body is via a trackless decline from surface to the footwall of the reef horizons. The decline serves as a roadway for vehicles to transport material into the mine and transports rock out of it. A vertical shaft provides transport in and out of the mine for personnel as well as additional ventilation.


Geology and Mineralisation

Modder East is located in the East Rand Basin, which lies in the northeastern quadrant of the Witwatersrand Basin. Most gold mineralisation in the East Rand is hosted in quartz-pebble conglomerate beds or reefs.


The Black Reef is the principal target at Modder East and dips shallowly at approximately 3° to the south. It contains three distinct facies. At the top is the Buckshot Pyrite Leader Zone (BPLZ), which averages 0.5 metres in width and is the primary mining target. The BPLZ is a placer deposit, with gold present within a heavy mineral suite dominated by pyrite and hosted within a conglomerate. The BPLZ overlies the Blanket Facies, a 1.3 metres thick quartzite which has relatively low gold grades and is not a principal target at Modder East. At the base of the Black Reef is the Channel Facies, a 3 metre thick erosional feature.


The UK9a Reef and UK5a Reef dip shallowly to the south between 6° and 12° with mineralisation contained within sedimentary channel features. These channels range from several tens of metres to hundreds of metres in width. At the Modder East gold project, the UK9a and UK5a reefs have been drilled and evaluated between 290 metres and 530 metres below surface.


Mining Method

Support of the development and stopes is based on a pillar system which protects the surface from any impact caused by mining. It also ensures a safe and stable mining environment underground. Rock bolting and timber support are used where necessary for additional safety.


The mining method employed is conventional narrow reef mining as practiced widely throughout the South African mining industry. Though the mining is serviced by a trackless infrastructure, all access to the reefs and all on-reef workings is mined in the conventional manner. Mined material from the reefs is cleaned with scraper winches and fed into ore passes, to be loaded into 30 tonne low profile underground haulage trucks. Material is then transported to a central silo system, while dedicated 50 tonne haul trucks transport the ore to surface for processing.


Processing Method

The Modder East mine utilises a carbon-in-leach (CIL) plant to process Black Reef and Kimberley ores. The plant comprises a single stage semi-autogenous grinding (SAG) mill, which operates in closed circuit with hydrocyclones, CIL adsorption, elution, electrowinning and smelting.

Reference:
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