Some notes on quinine and its associated alkaloids

Abstract

The Ojolali region in Sumatra, Indonesia contains two main epithermal gold–silver deposits: (i) Tambang, a Ag–Au intermediate-sulfidation deposit with base-metal sulfides and Mn-carbonate in the ore assemblage; and (ii) Bukit Jambi, a high-level, low-sulfidation Au–Ag deposit related to a zone of near-surface steam-heated acid sulfate alteration, overprinted by supergene oxidation, with most of the ore hosted in the oxide zone. Alteration and mineralisation are hosted in a window of Miocene intermediate to mafic volcanics, related to NNE-trending silicified structures identifiable in regional resistivity and ground magnetic maps. All units are from the same fractionation sequence. The Tambang footwall was determined to be more mafic in composition than other units across the region, including the Bukit Jambi footwall. In comparing the intermediate-sulfidation state, base-metal and carbonate-rich assemblage at Tambang against the high-level, low-sulfidation / steam-heated alteration assemblage at Bukit Jambi, it is inferred that Tambang was more proximal to the magmatic fluid source, with lateral fluid movement and equilibration with host rock occurring between Tambang and Bukit Jambi. Although the basin is floored by basalt, the geochemistry of this and the overlying andesitic units suggests that they are comagmatic and of calc-alkaline affinity. Similar settings should occur elsewhere within the Sunda Arc and these should also be highly prospective for epithermal gold–silver deposits.