PIXE analysis of contrasting fluid inclusion types in intrusion-related gold systems of the Tintina Gold Province, Yukon, Alaska

Abstract

The chemistry of fluid inclusions in shallow (coexisting brine and carbon dioxide-bearing vapour inclusions) and deep (low salinity carbon dioxide±methane-rich aqueous fluids) intrusion-related gold systems in the Tintina Gold Belt, Alaska and Yukon, has been measured using proton induced x-ray emission (PIXE) in order to compare and contrast these different fluid types. Both the high and low salinity fluid inclusions have high K/Ca ratios (> 1) consistent with granite-derived or granite equilibrated fluids, and low Mn/Fe ratios (< 0.24) consistent with the reduced conditions in which the ore systems formed. Fluid inclusions in the shallow level deposits are characterized by higher base metals contents due to the greater abundance of chlorine. Nonetheless, the copper contents are significantly lower (< 1000 ppm) than those found in porphyry copper systems. Tungsten is more elevated in the low salinity carbon dioxide-bearing fluid inclusions consistent with high tungsten contents in deeper level deposits, and likely due to tungsten’s preference to form tungstate complexes rather than chloride complexes. Arsenic was found in both high and low salinity fluid inclusions, and may be explained by its ability to complex with other elements such as sulfur (e.g., thioarsenite) in addition to chlorine. Arsenic may be used as a proxy for gold due to their similar chemical behaviour and explain why both shallow and deep level deposits contain gold despite the diverse fluid types present.