Mponeng

Overview

Mponeng is an underground gold mine located about 65 km southwest of Johannesburg, South Africa.

The mine is owned by AngloGold Ashanti and is part of the company’s West Wits operations. TauTona and Savuka mines are located immediately north of Mponeng.

At Mponeng mining is conducted at depths of between 2,800 m and 3,400 m below surface. Gold reefs are accessed through two deep shafts. A sequential-grid mining method is employed as to better deal with the geological complexity of the orebody.

In 2011, the mine produced 600,000 ounces of gold and had a mineral reserve estimated to contain 14 million ounces gold.

Location

Mponeng is located between the towns of Carletonille and Fochville on the border between the South African provinces of Gauteng and North West. It is 43 km northeast of the city of Potchefstroom on the northwestern rim of the Witwatersrand Basin.

South Africa is a country located at the southern tip of the African continent. It is a multi-ethnic nation and has diverse cultures and languages.

Gauteng – the Place of Gold in local Sesotho language - is South Africa’s smallest province but at the same time the most populous. It is the country’s most important economic hub and contributes heavily in the financial, manufacturing, transport, technology and telecommunications sectors, amongst others.

Geology & Mineralization

The only gold reef mined at Mponeng Is the Ventersdorp Contact Reef (VCR). The reef is up to 3 m thick and consists of quartz pebble conglomerates that overlie the uppermost angular unconformity of the Witwatersrand Supergroup. The VCR is capped by the Ventersdorp lavas that stopped the formation of new gold conglomerates. The footwall is made of different types of rocks – protoquartzites, shales and siltstones from the Central Rand Group.

At the base of the Central Rand Group there is another gold reef - the Carbon Leader Group (CLR) – which is only 20 cm in width and is being mined at the adjacent Savuka and Tau Tona mines. The CLR is situated 900 m deeper than the VCR. Mponeng mine would also target the CLR gold reef in the near future.

Both reefs are frequently faulted and are cross-cut by a series of igneous dykes and sills.

To the south of the Mponeng lease area is the Western Ultra Deep Levels (WUDLS) area which has the potential to increase the Mineral Resource of the mine once it has effectively been explored.

As of December 31, 2011, mineral reserves were estimated at 42.71 million tonnes at 10.21 g/t gold for 14.02 million ounces gold.

Mining & Operation

Mining at Mponeng is conducted at depths of between 2,800m to 3,400m below surface. The mine operates two vertical hoisting shafts, a sub-shaft and two service shafts. Twin shaft sinking from surface commenced in 1981 and the shafts were commissioned along with the gold plant complex in 1986.

To the south of the Mponeng lease area is the Western Ultra Deep Levels (WUDLS) area which has the potential to increase the Mineral Resource of the mine once it has effectively been explored.

In 2011, Mponeng mining operations produced 600,000 ounces of gold.

Processing

The hoisted ore is milled and smelted at the Mponeng Plant. The plant has a capacity of 160,000 tonnes per year.

Ore from Mponeng is treated through semi-autogenous grinding (SAG) mills, followed by a conventional gold leach with liquid oxygen injection. Gold extraction is by means of CIP technology. The recovery of gold from carbon for Mponeng, Savuka and the TauTona mines, is done at the central elution plant and smelthouse, which forms part of the Mponeng Plant. Advanced AARL elution circuits are used, followed by stainless steel electrowinning. Smelting is done both by electric and induction furnaces.

Environment & Community

Safety
Tragically, there were four fatalities at Mponeng during 2010. Two of the fatalities were of undetermined causes and are still pending classification upon completion of the DMR enquiry. The all injury frequency rate deteriorated to 15.93 per million hours worked from a rate of 14.31 in 2009.
The mine embarked on a number of safety initiatives in 2010. 

Health
During 2010, some 111 new cases of occupational tuberculosis (TB) were diagnosed at Mponeng, at an annual incidence of 2%. By year-end, 58 employees were still receiving daily treatment for TB. In addition, 852 Mponeng employees were seen at the Wellness Clinic in the six-month period to December 2010, representing approximately 19% of the group 3-8 workforce. A total of 512 employees had received anti-retroviral therapy by the end of the year.

Environment
In order to prevent the mine from impacting surface and ground water, a number of risk assessments and environmental investigations were conducted during the year.

An ISO 14001 first advancement assessment audit was conducted at Mponeng in August 2010, with the mine retaining its accreditation.