Abstract

Fluid inclusion studies on quartz and fluorite from the Rex Hill orebody indicate that they were deposited from aqueous solutions of variable salinity and relatively high K/Na and Li/Na ratios. Corrected filling temperatures of the inclusions (assuming a pressure of 300 atmospheres) indicate that the formation temperature of quartz and fluorite varied from about 260 degrees to 410 degrees C with most deposition occurring between 330 degrees and 350 degrees C. Fractionation of S 32 and S 34 between coexisting sphalerite and galena, which are intimately intergrown with the quartz and fluorite, is relatively uniform. This confirms that there was no marked departure from equilibrium during their deposition, thus supporting independent evidence of textural equilibrium. Fractionation factors from coexisting galena-sphalerite pairs indicate a general range of temperature of deposition from 335 degrees to 460 degrees C with a mean of 392 degrees C. This temperature is at least 50 degrees C higher than that expected from the fluid inclusion studies, although the temperature ranges do overlap. The FeS contents of sphalerites show no correlation with their formation temperatures indicated by isotope fractionation, and their erratic compositions are consistent with the textural disequilibrium they display with respect to pyrite. The compositions of arsenopyrites are broadly compatible with the temperature ranges indicated by fluid inclusion data and isotope fractionation.

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