Precambrian orogens and their hypozonal orogenic gold ores

High-temperature (hypozonal) orogenic gold deposits formed at conditions of 500 − 700ºC and 2-7 kbar in syn- to post-peak metamorphic shear zones, and appear to be restricted to the Precambrian. Their formation occurred between ca. 3030 Ma (New Consort, South Africa) and ca. 550 Ma (Navachab, Namibia), at an apparent geothermal gradient of 40−80◦C/km, which is similar to mesozonal orogenic gold deposits. The PT conditions of orogenic gold formation define a linear trend resembling terrane exhumation, largely below the granite wet solidus and in the 1-phase stability field for aqueous-carbonic ore fluid compositions (Kolb et al., 2015).