Abstract

The unusually large and high-grade orebody developed as a result of infiltration metasomatism shortly following the epizonal intrusion of an Upper Cretaceous, peraluminous, biotite monzogranite pluton. Thermal metamorphism attained the pyroxene-hornfels facies and was accompanied by the formation of minor folds and a foliation parallel to contact in the inner aureole. Subsequently, following a temperature drop of 50 degrees to 100 degrees C, initial hydrothermal activity at 450 degrees to 500 degrees C generated a zoned array of anhydrous and hydrous reduced skarn facies. Skarn formation occurred under a confining pressure of ca. 1 + or - 0.3 kb (from sphalerite geobarometry) and was associated with extensive brittle and ductile deformation of the exoskarn contact zone. Scheelite, abundant in all skarn facies except the garnet-pyroxene, is everywhere strongly correlated with pyrrhotite and shows little textural evidence of dissolution in the course of skarn development. The hydrothermal fluid was a predominantly, or entirely, nonboiling moderately saline (4-14 equiv. wt % NaCl) brine which is inferred to have contained CaCl 2 , FeCl 2 , MgCl 2 , and KCl, in addition to NaCl. The skarn-generating fluids apparently remained essentially constant in composition during the protracted mineralizing event.--Modified journal abstract.

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