Stratiform and stratabound tungsten mineralisation in the Broken Hill Block, N.S.W.

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Abstract
The Early‐Middle Proterozoic Broken Hill Block contains three types of W occurrences, which show close stratigraphic control. All three types occur within a relatively narrow stratigraphic interval (the ‘Mine Sequence’ Suite of Stevens et al., 1980) comprising a highly variable group of metamorphosed silicic and mafic volcanics, clastic sediments, and exhalative and chemical sediments containing base metals. The first type includes occurrences of W and base metals in bedded calc‐silicate rocks. In the second type, W occurs in layered to non‐layered calcsilicate rocks associated with amphibolite; these are intimately associated in a narrow stratigraphic interval containing abundant, small, Broken Hill type deposits. The third type comprises stratabound, W‐bearing pegmatites, which have been remobilised from quartz‐feldspar‐biotite gneiss and bedded quartz‐tourmaline rocks. Tungsten has been mined only from the third type and only in small quantities. The three types of tungsten deposits show a close spatial relationship with stratiform and stratabound Pb‐Zn mineralisation, including the Broken Hill type. The Pb‐Zn and W deposits are inferred to be genetically related.