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Abstract:
The geology of Jamaica is reviewed with reference to gold. Two geochemical surveys, one employing stream sediments for mineral exploration in selected regions of Jamaica considered a priori to have greater mineral potential, and the other an island-wide low-density soil survey to meet agro-environmental objectives, were undertaken in 1986 and 1988, respectively. The paper presents an interpretation of the previously unpublished soil data for gold, and undertakes a comparison of the two surveys in terms of their effectiveness for gold exploration. The stream sediment survey (1 site per 1 km2) led to the discovery of three new gold occurrences, one of which became a producing mine in 2001, and the recognition of two previously known auriferous districts. The low-density soil survey (1 site per 64 km2) identified the host rocks of three of these auriferous districts as having gold potential, including those of the producing mine, demonstrating its value as a broad-scale regional mineral reconnaissance tool. Geochemical studies of gold in Jamaica are complicated by the presence of transported palaeo-anomalies, related to Miocene ash-falls, in terra rossa soils in karst terrain. The Fe/Na ratio is an index of soil maturity and increases over two-and-a-half orders of magnitude with increasing soil age and mature. The plotting of Au versus the Fe/Na ratio in soils offers a simple procedure for identifying samples most likely to be related to gold occurrences in bedrock, i.e. high Au and low Fe/Na ratio. It is concluded that in the specific instance of Jamaica's high relief terrain and the apparent limitation of gold occurrences to the Cretaceous Inliers and Eocene Wagwater Trough underlying those high relief areas, stream sediment sampling is the most effective mineral exploration tool