Exploration strategy and application at Ashanti's Obuasi operations

The Ashanti mine is located within the Lower Proterozoic Birimian of Ghana, and covers a concession of 474 square kilometres at its Obuasi operations which comprise large scale underground, surface and tailings treatment faci lities. The mine had operated for a century at the end of 1997 and had prod uced nearly 25 million ounces of gold, a significant proportion of which ca me from the underground operations. This paper covers the strategy under which exploration for both surface and underground mineral resources was instrumental in enabling the expansion p rogramme to go ahead together with the methodologies and results that have developed in the exploration area over the last five years. Within capital expenditure constraints, the objective on surface is to repl ace oxide depletion with a secondary objective of discovering new sulphides in areas other than the main trend. In the underground, the exploration strategy is directed at replacement of both underground and surface sulphide depletion, minimising finding costs a nd assisting the development of long lead time infrastructure. The exploration application describes the methodologies in use for both sur face and underground exploration that have been developed in recent years i n conjunction with a description of a major review conducted in 1995/96 of the exploration database, using an integrated approach, geochemistry, geoph ysics, remote sensing and structural geology. A revisit of soil geochemical data in particular, and modification of explo ration methodology led to the success in finding relatively significant: ne w oxides in 1997.