NONCARBONATE, SKARNLIKE AU-BI-TE MINERALIZATION, LUCKY-DRAW, NEW-SOUTH-WALES, AUSTRALIA

Gold-bismuth-tellurium mineralization at the Lucky Draw mine is associ ated with pods, lenses, and veins of Fe-Mg-Al silicates, adjacent to t he late Carboniferous Burraga Granodiorite. Alteration and mineralizat ion is enclosed by micaceous quartzite and quartz-mica schist of the T riangle Group, immediately below ultramafic shoshonitic volcanic rocks of the Rockley Volcanics. Geologic relationships imply that mineraliz ation and alteration are probably synchronous with later stages of con tact metamorphism and, hence, postdate upper greenschist facies region al metamorphism. Barren stage I assemblages consisting of combinations of gedrite, biotite, staurolite, cordierite, quartz, albite, ilmenite , and hercynite are overprinted by stage II assemblages of chlorite, a lmandine, and biotite. Stage III alteration, consisting of green-brown biotite, is developed where the granodiorite intrudes stage II altera tion. Stage I assemblages are poorly constrained to T approximate to 6 00 degrees C at 2 to 3 kbars, whereas garnet-chlorite thermometry and phase equilibria indicate T approximate to 550 degrees C for stage II assemblages. Native Bi, bismuthinite, native Au, maldonite, and Variou s Bi tellurides were deposited interstitial to chlorite grains and alo ng chlorite cleavage planes, during stage II alteration. Ore minerals are characterized by low melting points (less than or equal to 370 deg rees C) but are in apparent equilibrium with stage II assemblages; thi s can be reconciled if the ore minerals collected as melts at higher t emperatures. Laminae of heavy minerals, which are present in stage I a nd II alteration assemblages, are identical to those marking bedding a nd crossbedding in unaltered metasedimentary rocks enclosing the miner alization. Whole-rock immobile element concentrations of the alteratio n assemblages are very similar to unaltered metasedimentary rocks of t he local Triangle Group. However, stage I assemblages and mineral comp ositions have some similarities with local occurrences of cordierite-o rthoamphibole rocks derived from altered mafic volcanics. Therefore, s ilicate assemblages at Lucky Draw may be the product of contact metamo rphism and metasomatic alteration of quartz-rich metasedimentary and i nterbedded, mafic volcanic rocks.