Overview

Finding the orebody

A global exploration programme identifies targets and undertakes exploration, on its own or in conjunction with joint venture partners.

Creating access to the orebody

There are two types of mining which take place to access the orebody, these are underground and open-pit.

Underground: A vertical or decline shaft (designed to transport people and/or materials) is first sunk deep into the ground, after which horizontal development takes place at various levels of the main shaft or decline. This allows for further on-reef development of specific mining areas where the orebody has been identified.

Open-pit: The top layers of topsoil or rock are removed in a process called stripping' to uncover the reef.

Removing the ore by mining or breaking the orebody

In underground mining, holes are drilled into the orebody, filled with explosives and then blasted. The blasted ‘stopes' or ‘faces' are then cleaned and the ore released is now ready to be transported out of the mine.

In open-pit mining, drilling and blasting may also be necessary to release the goldbearing rock; excavators then load the material onto the ore transport system.

Transporting the broken material from the mining face to the plants for treatment

Underground ore is transported by means of vertical and/or horizontal transport systems. Once on surface, conveyor belts usually transport the ore to the treatment plants.

Open-pit mines transport ore to the treatment plants in vehicles capable of hauling huge, heavy loads.

Services

Mining activities require extensive services, both on the surface and underground, including:

•            mining engineering services;

•            mine planning;

•            ventilation;

•            provision of consumable resources;

•            engineering services;

•            financial, administration and human resource services; and

•            environmental/permitting services.

Processing

Comminution is the breaking up of ore to make gold available for treatment. Conventionally, this process occurs in multistage crushing and milling circuits. Modern technology is based on large mills fed directly with run-of-mine material.

Gold ores can typically be classified into refractory ores, where the gold is locked within a sulphide mineral and not readily available for recovery by the cyanidation process; or free milling, where the gold is readily available for recovery by the cyanidation process.

Refractory ore treatment - after fine grinding, the sulphide materials are floated away from the barren gangue material to produce a high-grade sulphide concentrate. The sulphide concentrate is oxidised by either roasting or bacterial oxidation (BIOX). The oxidation process oxidises the sulphide minerals liberating the gold particles making them amenable to recovery by the cyanidation process.

Free milling and oxidised refractory ores are processed for gold recovery by agitator leaching the ore in an alkaline cyanide leach solution followed generally by adsorption of the gold cyanide complex onto activated carbon-in-pulp (CIP).

The alternative process is the heap-leach process. Generally considered applicable to only high-tonnage, low-grade ore deposits.

Gold adsorbed onto activated carbon is recovered by a process of re-dissolving the gold from the activated carbon (elution), followed by precipitation in electro-winning cells and subsequent smelting of that precipitate into doré bars that are shipped to the gold refineries.

The retreatment of tailing stockpile from previous decades' operations can also practised. The old tailings are mined by water sluicing followed by agitator leaching in alkaline cyanide solution and recovery of dissolved gold onto activated carbon.

Refining

The doré bars, are transported to a refinery for further refining, to as close to pure gold as possible - good delivery status. This gives the assurance that the bar contains the quantity and purity of gold as stamped on the bar.

To view the Process of Producing Gold please see the Virtual Gold Mine Tour created by one of our Members, AngloGold Ashanti