GEOLOGICAL SETTING, CHARACTERISTICS AND REGIONAL EXPLORATION FOR GOLD IN THE VOLCANIC ARCS OF NORTH SULAWESI, INDONESIA

Recent exploration has highlighted North Sulawesi as a significant gold province located within a series of spatially overlapping Tertiary volcanic arcs. In the western ensialic portion, rhyodacitic volcanics overlie quartzo-feldspathic metamorphic basement. In contrast, the central and eastern ensimatic areas comprise marine basaltic basement overlain by andesitic volcanic, the centres of which have migrated progressively eastwards from the Early Miocene until the present day. Four major categories of gold mineralisation are recognised; gold-copper porphyries within which gold is distinctly partitioned, gold and base-metal bearing breccias, and gold in both high- and low-sulphidation epithermal systems. A regional exploration technique, comprising fractional analyses of gold in stream sediments and pan concentrates, is able to detect all mineralisation types. Gold in the finer-size fractions of these media gives better discriminated anomalies and more repeatable results. Copper and silver in stream sediments may be used to further discriminate anomalies in terms of their character of source mineralisation. This has proved particularly useful in situations where different styles of mineralisation occur in close proximity. In a number of the cases described soil geochemistry has enabled differentiation between mineralisation styles and thus guided ongoing exploration in areas of sparse outcrop. © 1990.