Experimental petrology may be used to accurately
constrain PTX conditions in order to calibrate and understand geologic
processes. This method may be used to answer postulated questions, by recreating
known geologic conditions and observing changes in the experimental charges. The
purpose of this project was to determine the eutectic composition and
temperature in the ternary system PbS-FeS-ZnS (Ag2S), at ambient and
elevated pressures and elucidate if the sulfides of the Broken Hill orebody may
have been partially molten during highgrade (granulite facies) metamorphism. The
study determined the eutectic temperature and composition in the system
PbS-FeS-ZnS to be 8002C and 62.5% PbS, 30.5%FeS, 7% ZnS respectively, at one atmosphere, and the
eutectic temperature at 27 kbars was found to be 960C10C, with a eutectic
composition enriched in ZnS relative to the one atmosphere eutectic. the
addition of lwt.% Ag2S to the system depresses the eutectic
temperature to 7722C at 1 atmosphere and below 8105C at 5 kbars. The
conditions of peak metamotphism for the cental and southern areas of the Broken
Hill Block,
New
South Wales,
Australia
, lie above the solidus of
the PbS-FeS-ZnS-Ag2S system, strongly suggesting that partial melting
occurred in the orebody.