Application of geophysics to gold exploration in Ghana: examples from Newmont projects

Abstract

Ghana has been a producer of gold since the 16th century and today boasts one of the largest and richest reserves of the precious metal in the world. The principal gold producing areas of Ghana occur within Palaeoproterozoic Birimian meta-volcanic and meta-sedimentary rocks, and within the marginally younger, overlying Tarkwaian meta-sedimentary succession. The giant 40+ million ounce (Moz) Ashanti deposit at Obuasi and 38+ Moz deposit at Tarkwa are 2 monstrous examples located in Ghana. Other deposits include Prestea/Bogoso (7 Moz), Konongo (2 Moz), Damang/Aboso (3Moz), Bibiani (5 Moz), and Chirano (2 Moz). Gold exploration in the past was primarily conventional stream sediment and soil sampling, followed by trenching and drilling. This methodology was used to discover a majority of the deposits. However, completely unexplored grounds in Ghana, where cursory, first-pass reconnaissance surface sampling methods lead to a major discovery, are virtually nonexistent. The modern phase of exploration calls for a more interdisciplinary approach involving the use of geophysics, geochemistry, and regolith mapping, as well as detailed structural and geologic observations. Newmont is one such company that integrates geophysics extensively in its gold exploration programmes in Ghana. Some of the geophysical techniques used are airborne magnetics, radiometrics and electromagnetics. Ground based geophysical tools include gravity, magnetics and IP/Resistivity. Geophysical data are used to help with ground selection, direct drill targeting, and to help produce interpreted geology and regolith maps. Newmont Ghana has trained Ghanaian nationals to conduct a majority of the data collection, processing and interpretation. Several example data sets are shown.