Relationships Among Carbonate-Replacement Gold Deposits, Gold Skarns, and Intrusive Rocks, Bau Mining District, Sarawak, Malaysia

Abstract

Three distinct styles of gold mineralization are spatially associated with Miocene microgranodiorite porphyry stocks in the Bau mining district, Sarawak, Malaysia. These include: (1) gold-bearing calcic skarns; (2) several varieties of veins near and distal to calcic skarns; and (3) carbonate-replacement ore bodies in sedimentary rocks peripheral to the veins and typically furthest from the stocks. Most of the gold produced to date from the Bau district originated from the carbonate-replacement deposits. These deposits exhibit strikingly similar mineralogical and geochemical features with Carlin-type deposits that occur in the western United States.
Similarities in key mineralogical and chemicall features of the ores indicate that all three styles of mineralization are not only spatially, but genetically, related to the microgranodiorite porphyry stocks. Preliminary fluid inclusion measurements on quartz from the three gold ore types suggest decreasing thermal and salinity gradients with increasing distance from the stocks.