Geochemical dispersion patterns associated with the Lake Yindarlgooda sulphide mineralization, Western Australia

Abstract

Geochemical investigations have been carried out in the Lake Yindarlgooda area, 40 km east of Kalgoorlie, Western Australia, where sulphide deposits and black shales occur in a sequence of metavolcanics and metasediments of the Eastern Goldfields greenstone belt. The studies were made in order to understand the processes of element migration and the formation of dispersion patterns in semi-arid regions having partly lateritic weathering conditions. Outcrop exposure in the vicinity of the mineralized zones is limited to the siliceous caprock and gossans. Mineralogical data, and geochemical data on the distribution of Cu, Ni, Co, Zn, Pb and other elements, have been obtained from unweathered and weathered rocks, and different horizons of the overlying soil in the area surrounding the mineralized zones of Lake Yindarlgooda, Scotia and Ringlock. The results indicate, in principle, two different kinds of weathering environment: (1) playa lakes, with the development of solonchaks; and (2) Tertiary peneplains outside the playa lakes, with lateritic soils, solonized brown soils or desert loams. The trace element distribution patterns in the solonchaks are determined only by the initial element content of the alluvial sediments. Therefore, sampling of solonchaks generally cannot be recommended for geochemical exploration surveys, but sampling of weathered bedrock below the solonchaks is highly recommended in the playa lake environment. By sampling of the bedrock, the non-outcropping continuation of the Lake Yindarlgooda sulphide body has been precisely delineated. In areas of the Tertiary peneplains outside the playa lakes, lateritic soils, solonized brown soils or desert loams cover the weathered bedrock. Comparative geochemical investigations in these areas in the vicinity of the nickel sulphide deposits at Scotia and Ringlock have shown that the migration of elements in solution is restricted, a result of the very low water table. In this area the main process of dispersion is mechanical. Therefore, the secondary dispersion haloes of Scotia and Ringlock are narrow, restricted to a few tens of metres, and sampling at closer intervals is needed to locate the orebodies.