Abstract

A mineral assemblage consisting of calcite–tremolite–quartz–clinozoisite–diopside–muscovite has been found associated with a small, stratiform pod of galena–sphalerite–chalcopyrite–pyrite–pyrrhotite. This alteration assemblage resembles that of a skarn, although lacking, significantly, some typical minerals including garnet, wollastonite, and vesuvianite. Limits on possible condition of T, Pfluid, and graphic can be estimated for the formation of the assemblage. The assemblage must have formed in a water-rich fluid, as graphic is sharply restricted by the reaction 2 clinozoisite + CO2 = calcite + 3 anorthite + H2O. In PfluidT space, the assemblage is stable between the univariant curves for the assemblages tremolite + calcite + quartz + diopside at fixed graphic and clinozoisite + anorthite + grossular + quartz + calcite. These curves bracket the kyanite–sillimanite boundary. As kyanite and sillimanite occur in the wall rocks, the minimum PfluidT are those of the aluminosilicate triple point. Measurement of sphalerite–sphalerite/galena dihedral angles in the thermally annealed area yielded a calculated temperature of 390 °C. Metamorphic conditions suggest that a sequence of progressive contact metamorphic reactions of an original talc and (or) chlorite–quartz–calcite assemblage produced the presently observed assemblage. Proximity to a later granitic batholith is believed to have brought about these changes by reactions in the original alteration mineral assemblage.

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