STRATA-BOUND SCHEELITE IN META-EVAPORITES, BROKEN-HILL, AUSTRALIA

The Middle Proterozoic Willyama Supergroup of the Broken Hill block, A ustralia, as undergone multiphase coeval deformation and high temperat ure-low pressure metamorphism. The Willyama Supergroup is interpreted as a sequence of intracontinental rift sediments, volcanics, and hot s pring precipitates. Scheelite occurs in regional calc-silicate rocks e nriched in F and Zn within a sequence of carbonaceous-sulfidic metapel ite, tourmalinite, and amphibolite; it overlies a felsic gneiss-metase diment sequence, part of which is interpreted as meta-evaporites. The distribution of scheelite is unrelated to syntectonic pegmatite or pos t-tectonic granitic rocks. Finally, scheelite has undergone minor remo bilization during tectonism. The calc-silicate rocks are interpreted a s dolomitic limey sediment which formed part of a playa-lake sequence into which B-, W-, Zn-, and F-rich alkaline hot springs debouched. Coe val sudden deepening, an increased geothermal gradient, deposition of the Broken Hill Pb-Zn-Ag sulfide orebodies, and siliceous exhalite dep osition occurred after deposition of the evaporite sequence. Some comp onents for the highly saline Broken Hill Pb-Zn-Ag ore fluid may have b een leached from the underlying evaporites and redeposited higher in t he stratigraphy.