Carlin–type gold deposit

Geology

The Carlin type deposits show enrichment in the elements gold, arsenic, antimony, mercury, thallium and barium. This enrichment is created by hydrothermal circulation with a temperature of up to 300 °C. The underlying rocks out of which the minerals are dissolved are normally silty carbonates, although silicates and other sediments are possible. The source of the heating for the water in the hydrothermal circulation is still under discussion. The material in the deposit is altered in a way that the carbonate minerals are either dissolved or converted to the silicates by silicate rich hydrothermal water. For example, dolomite is transformed into jasperoid. Another alteration is the formation of clay minerals by interaction of water and feldspar. The absence of base metal sulfides and the even distribution of the pyrite and arsenopyrite in the host rock are the most obvious difference to other sulfide deposits.

During the Eocene, fluids flowed through the lower plate of thrust faults and the underlying fractured carbonates. These fluids were magmatic, meteoric, and metamorphic in origin. A low pH in the fluids allowed for a significant amount of carbonate rocks to dissolve. The presence of carbonate in the water kept the fluids reduced. This reduction facilitated the movement of gold within sulfate rich epithermal fluids. The low temperature, low salinity fluids replaced the carbonate rocks with ore deposits that included gold. Later, when the Basin and Range began its extension, normal faulting took place, and the ore deposits were downfaulted and buried under alluvial sediment.