Studies on lead-zinc mineralization in Karempudi area, Guntur District, Andhra Pradesh

Abstract

The geological formations near Karempudi area in Guntur District of Andhra Pradesh (Lat. 16°20' and 16°26'; Long. 79° 38'40" and 79°45') consist of slaty shales of Cumbum, Irlakonda quartzites, Kolumnala slates and shales with intercalations of siliceous dolomitic limestones and Sreesailam quartzites of Krishna Series, forming a perfect conformable sequence, all the formations striking N.E.-S.W. and dipping on average 25°S.E. The Srisailam quartzites are overlaid unconformably by Palnad limestones (Narjis) of Jammalamadugu stage of Kurnool Series with a constant dip of 8-12° in the same direction. The Krishna Series were subjected to local but intense structural disturbances resulting in an overfold. Subsequent to the overfolding, lead mineralization has taken place in dolomitic limestones. The lead-zinc minerals of Karempudi consist of Galena, Sphalerite, Jamesonite, Tetrahedrite as primary minerals, and Anglesite as secondary mineral; there is association of chalcopyrite with Sphalerite. The textures are due to replacement and unmixing. The paragenetic sequence of the minerals is established to be sphalerite, chalcopyrite, galena, jamesonite, tetrahedrite and anglesite. Correlation of field to laboratory studies revealed that the minerals are of hydrothermal (hypogene) origin. The structural and lithological favourability and controlling of the mineralisation are also explained. Anglesite owes its origin to the oxidation of galena due to air-water processes. The mineralization is surmised to have taken place in Pre-Palnads and Post-Krishna times.