A pseudo-tactite assemblage in the footwall of a massive sulfide occurrence, Savant Lake – Sturgeon Lake Greenstone Terrains, Ontario

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 [Formula: see text] can be estimated for the formation of the assemblage. The assemblage must have formed in a water-rich fluid, as [Formula: see text] is sharply restricted by the reaction 2 clinozoisite + CO2 = calcite + 3 anorthite + H2O. In Pfluid–T space, the assemblage is stable between the univariant curves for the assemblages tremolite + calcite + quartz + diopside at fixed [Formula: see text] and clinozoisite + anorthite + grossular + quartz + calcite. These curves bracket the kyanite–sillimanite boundary. As kyanite and sillimanite occur in the wall rocks, the minimum Pfluid–T 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.