Abstract

Within the central and southern mine leases at Broken Hill, the Broken Hill lead-zinc-silver lodes and three other zones of lead-zinc-silver mineralization--White Leeds, Western Mineralization, and Centenary Mineralization--are hosted in the psammites of unit 4.7 of suite 4 (the Broken Hill Group) within the Willyama Supergroup. Descriptions of the suite 4 stratigraphic sequence for each of the four zones of mineralization show that, although the compositional and distributional character of the units low in the sequence are similar in each zone, the lithologies and their distribution within the upper portions of the sequence are unique in each zone. Gamma signatures from geophysical well logs through the sequence are used to diagnose trends in the succession and reveal coincidences of mineralization with upward-coarsening psammites. Thus, the Pb-Zn lodes and associated mineralization are spatially associated with the upper members of a stratigraphic succession representing a major upward-coarsening cycle of sedimentation interpreted to have been deposited in a prograding deltaic environment. Consequently the rocks of suite 4 (excluding amphibolites) in the mine leases are clastic sediments, although some, such as the Potosi gneiss, are considered to have a substantial immature volcanic component. The psammite-hosted orebodies and mineralization are enclosed within pelitic and psammopelitic sediments and appear to lack any close association with felsic volcanic rocks.

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