Gold deposits of the Bardoc Tectonic Zone: a distinct style of orogenic gold in the Archaean Eastern Goldfields Province, Yilgarn Craton, Western Australia

The Bardoc Tectonic Zone is an similar to 80 km-long and up to 12 km wide, intensely sheared corridor of Late Archaean supracrustal rocks that is bounded by pre- to syn-tectonic granites in the Eastern Goldfields Province, Yllgarn Craton. This zone has produced over 100 t of gold from a range of deposits, the largest being Paddington (similar to 40 t Au). This shear system is connected along strike to the Boulder-Lefroy Shear Zone, which hosts considerably larger deposits including the giant Golden Mile Camp (> 1500 t produced Au). In contrast to the diverse characteristics of gold deposits associated with the Boulder Lefroy Shear Zone, mineralogical and geochemical data from five representative localities in the Bardoc Tectonic Zone have relatively uniform features. These ore: (i) quartz-carbonate veins in competent mafic units with wall-rock alteration characterised by carbonate + quartz + muscovite + chlorite + biotite + sulf-arsenide + sulfide + oxide + gold assemblages; (ii) arsenopyrite as the dominant sulfur-bearing mineral; (iii) a unique three-stage paragenetic history, commencing with pyrrhotite, and progressing to arsenopyrite and then to pyrite-dominated alteration; (iv) a lock of minerals indicative of oxidising conditions, such as hematite and sulfates; (V) delta(34) sulfur compositions of pre- to syn-gold iron sulfides ranging from 1 to 9%; and (vi) a lack of tellurides. These features characterise a coherent group of moderately sized orogenic-gold deposits, and when compared with the larger gold deposits of the Boulder-Lefroy Shear Zone, potentially highlight the petrological and geochemical differences between high-tonnage and smaller deposits in the Eastern Goldfields Province.