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 ～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, Yilgarn Craton. This zone has produced over 100 t of gold from a range of deposits, the largest being Paddington (～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 are: (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 lack of minerals indicative of oxidising conditions, such as hematite and sulfates; (v) δ³⁴ 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.