Precipitation of gold in a low-sulfidation epithermal gold deposit: Insights from a submillimeter-scale oxygen isotope analysis of vein quartz

The physical and chemical mechanisms of gold precipitation in the typical l ow- sulfidation epithermal gold deposit at Hishikari (southern Japan) were quantified by submillimeter-scale oxygen isotope analyses of vein quartz. I n situ CO2 laser-ablated fluorination was used to measure temporal delta O- 18 excursions. The calculated oxygen isotope compositions of the ore-formin g fluid indicate a dynamic process of epithermal vein formation. Intermitte nt opening of the vein allowed introduction of metal-bearing deep fluid to the epithermal system, and associated boiling and subsequent mixing with me teoric water caused precipitation of precious metals.