THE GEOLOGY OF THE BROKEN HILL-TYPE PINNACLES PB-ZN-AG DEPOSIT, WESTERN NEW-SOUTH-WALES, AUSTRALIA

The Pb-Zn-Ag Pinnacles deposit lies in the Proterozoic rocks of the Willyama Supergroup of western New South Wales and consists of a series of stacked strata-bound sulfide lenses, hosted in a mixed suite of pelites, psammopelites, and inferred meta-exhalites. Sulfur isotope data for the orebodies have deltaS-34 values close to zero, but show some variation between sulfide lenses. Meta-exhalites include garnetites, quartz-gahnite rocks, and quartz-garnet rocks in immediate association with the mineralized rocks and the quartz-magnetite rocks as country rocks nearby. The deposit has been subject to granulite facies prograde metamorphism and kyanite-grade retrograde metamorphism, and is associated with four phases of folding (D1-4) and crosscutting retrograde shear zones (D5). The Pinnacles and Broken Hill deposits have many features in common, e.g., associated rock types and geochemical trends (including isotopic composition and REE concentrations). However, there are also several important differences including lithological associations, Fe/Mn ratios, inferred f(O)2 during sulfide precipitation, and size. These similarities and differences have direct bearing on genetic models for the formation of Broken Hill-type deposits. The geologic setting of the Pinnacles deposit is discussed in terms of temporal and/or spatial facies changes. The implications of these findings and observations are significant for the exploration of Broken Hill-type deposits.