Altered andsite thin section, Reko Diq, Pakistan by Ian Butler

154 images taken with a a modified Meiji microscope in cross polarised light using a Nikon D60 and direct objective projection using a Zeiss objective. Bright spots at frame centres were minimised by altering the substage condenser position, but they were still a problem. As it turns out, using a different adapter with a lens on the D60 solves the bright spots but really messes up the flat field of the Zeiss objective.

Reko Diq is a porphyry Cu-Au deposit in the Balochistan region of Pakistan. The sample is a thin section of andesite which has seen a little alteration, probably from meteoric water circulation associated with the mineralisation. Plagioclase in the groundmass is the most altered, but within the section jewel-like amphibole phenocrysts have mostly survived and show complex twinnng and zoning under crossed polars.