The Broken Hill Province is best known for the Broken Hill orebody, originally containing about 300 million tonnes of economic and sub economic Pb- Zn- Ag mineralisation, and occurring in highly deformed, lower granulite-grade metamorphics of the Early Proterozoic Willyama Supergroup. The outcropping Willyama Supergroup also contains an abundance of small metalliferous and non-metallic deposits, and exploration for economically mineable deposits continues both in areas of outcrop and areas covered by sediment. The types of deposit considered to have greatest potential in the Willyama Supergroup are Broken Hill-type stratiform Pb-Zn deposits and deposits containing base metals andlor gold, associated with iron formations. Other types with some potential include base metals and scheelite in calc-silicate rocks, cobaltiferous pyrite in albite-rich rocks, Pb, Ag, Zn, Cu andlor Au-bearing veins (either on their own merits, or as leaders to a larger accumulation), PGE- Ni- Cu associated with ultramafic intrusions, scheelite in quartzo-feldspathic gneiss, and granite-related breccias with magnetite and pyrite. Very little mineralisation is known from the Late Proterozoic Adelaidean sequence, but various types of base metal and gold mineralisation occur in stratigraphically equivalent rocks in South Australia, and base-metal and uranium deposits are being mined in very similar rocks in southern Africa. The potential of the Adelaidean rocks is very poorly tested. Extensive areas of Willyama and Adelaidean rocks are covered by 50- 200 m of Mesozoic/Cainozoic sediments below the Mundi Mundi Plains and in the Tindara area to the north. Drilling in probable Willyama Supergroup rocks below the Mundi Mundi Plains has detected a wide interval of low grade Pb-Zn mineralisation, interpreted to be in the Broken Hill Group , and significant Cu- Au- Ag mineralisation in magnetite-rich ironstone in the interpreted Thackaringa Group. No mineralisation is known in the Tindara area, but there is no outcrop, and pre-Mesozoic basement has been penetrated in only 11 drill holes, in an area approximately 100 km by 40 km. Exploration of deeply covered Willyama Supergroup rocks depends largely on aeromagnetics; in the Adelaidean, exploration can be approached both by conceptual modelling and by empirical techniques. Broken Hill-type deposits are difficult targets, because they may have no discernible geophysical signature and because of their essentially one-dimensional shape, which requires a different approach to drilling.
