ZINC-LEAD SKARN DEPOSITS AT LEADVILLE, NEW-SOUTH-WALES, AUSTRALIA, AND THEIR DISTINCTION FROM VOLCANIC-HOSTED MASSIVE SULFIDES

Exploration of Zn-rich sulphide deposits at Leadville, northern Lachla n Fold Belt, New South Wales, for over two decades has been largely on the premise that the mineralisation represents felsic volcanic-hosted massive sulphides (VHMS). Deposits are hosted by ?Silurian felsic met avolcanic, psammopelitic and calcareous metasedimentary rocks which ha ve been intruded by the late Carboniferous I-type Gulgong Granite. Evi dence for an epigenetic replacement (skarn) origin of the deposits, ra ther than representing metamorphosed volcanogenic massive sulphides, i ncludes the proximity of evolved granitic intrusives and reactive carb onate rocks, a skarn mineral assemblage (with characteristic prograde and retrograde stages), lack of textural or lithological indications o f an exhalative origin, and gossan and sulphide compositions consisten t with Zn-Pb skarns and atypical of Lachlan Fold Belt VHMS deposits. F urthermore, sulphide lead isotope ratios are significantly more radiog enic than signatures for VHMS deposits in the Lachlan Fold Belt. Carbo nate delta(13)C and delta(18)O and sulphide delta(34)S values are cons istent with the interaction of magmatic hydrothermal fluids with Palae ozoic carbonate rocks and a largely magmatic source of sulphur. It is concluded that the Leadville deposits are of skarn type, genetically r elated to the Gulgong Granite.