Ore Shoot Targeting by Recognition of Upflow and Outflow, Low Sulphidation Epithermal Gold Deposits

摘要

Two types to low suphidation epithermal deposits that have different gangue mineralogies and ore shoot geometries are recognised. One has laterally near-continuous ore shoots over a significant vertical interval that consist of quartz, chalcedony, pyrite, minor base metal sulphides and adularia, with electrum. The other type of deposit has discrete near-vertical ore shoots of a lesser vertical extent, that consist of quartz, pyrite, base metal sulphides, sulphosalts, electrum and in their upper parts barite, which are enclosded in veins of earlier quartz. The gold mineralisation in both deposit types is consdiered to be a co-precipitate of pyrite, with that in the first type of deposit produced by mixing, a deep water primed for gold deposition by prior limited boiling, with an iron-bearing oxidised condensate of the steam released by the boiling, with an iron-bearing oxidised condensate of the steam released by the boiling, in an outflow of a hydrothermal system (Outflow Deposits); an example is Thames in New Zealand.