The pluton interior is generally free from inclusions and yet is the most contaminated based on geochemical evidence. This leads to the conclusion that this rock was exposed to a lot of wall and/or roof rock material, presumably as xenoliths, which have all been assimilated. Fluorite occurs as fracture fillings obviously emplaced in the solid or largely solid and brittle rock. Late stage mineralization with Li, Cu, Mn, Mo, W, Sn, and U is found in the central region of the pluton. The main thing to see here is cordierite, which sadly is mostly hydrothermally altered and weathers out as rectangular pits on the outcrop surface. Thin section photos are shown here.
Purple fluorite vein cutting rusty-weathering granite.
Closeup of a purple fluorite vein cutting the granite.
Flow-aligned feldspar phenocrysts. The black, generally rectangular pits are places where the hydrothermally altered cordierite has weathered out, at least according to the description at the outcrop. My sample had no matrix cordierite and the likely weathered material was altered Ca-rich plagioclase cores.
Closeup of the largest K-feldspar phenocryst in the photo above. The rectangular pits are weathered out, altered plagioclase cores (or possibly altered cordierite) are visible both in the matrix and inside the phenocryst. My two thin sections have no cordierite or altered cordierite within the K-feldspars. Orange spots are lichens starting to grow.
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Schenectady, NY 12308 U.S.A. |