Low-Temperature Secondary Minerals from Tarbela
Abstract
Several types of sulphates and other minerals, believed to have formed at low temperatures, were found in a remedial excavation site overlooking Tunnel 3 and 4 on the right bank of the Tarbela Dam. Identified with the help of optical properties, XRD and chemical analyses, these include gypsum, pickeringite, potassium alum, hydrated iron sdphate, epsomite, lecontite, natroalunite, hantite, halloysite, (?) leonite and (?) starkeyite. Optical and chemical data for most of the samples studied are presented in the paper. The sulphates are thought to have formed in connection with the weathering and alteration of pyrite commonly present in the metasediments of the host Salkhala formation. The huntite has formed by the action of ground water on dolomitic rocks, or gabbros and pyroxene/hornblende peridotites, and the halloysite from alkali feldspar-rich intrusive rocks of the Tarbela "alkaline" complex.
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