Hydrothermal fluid chemistry in exploration. Acoustic decrepitation as a method of locating potentially auriferous quartz systems formed from CO2 rich fluids

Abstract

There is a well documented relationship between Au mineralized quartz and CO2 rich fluid inclusions within that quartz, indicating the CO2 rich nature of the parent hydrothermal fluids. This relationship has been suggested to be a function of CO2 buffering the Ph of the geothermal fluids in a range which enhances gold solubility. It is also known that the acoustic decrepitation method can identify quartz formed from fluids which had high CO2 contents, as CO2 rich fluid inclusions decrepitate upon heating at temperatures well below that of aqueous inclusions trapped under the same pressure and temperature conditions. CO2 contents at least as low as 5 mole % are readily detectable using the acoustic decrepitation method.The decrepitation method has been applied to a number of gold deposits in Victoria and shows that CO2 is a common but not ubiquitous constituent of the fluid systems which deposited the quartz and gold. Although the precise relationship between CO2 and gold is not clear, the method provides a means to “fingerprint” quartz veins as an exploration guide. Samples from the Meguma terrane in Nova Scotia also show widespread but variable levels of CO2 rich fluids in the gold deposits.Knowledge of the CO2 contents of quartz systems is a valuable exploration tool and the acoustic decrepitation method is the easiest way to acquire this information for exploration purposes as it is an automated and quick instrumental procedure.