A Note on the Occurrence of Carbonatite in the Nellur Schist Belt, Near Vinjamur, Udayagiri Taluk, A.P.

About 80 km north-north-west of Nellore, in the northern portion of the Nellore schist belt (referable to the Dharwar and older metamorphics) linear bands of rock of considerable strike length made up of Calcite, dolomite, siderite, with concentrations of baryte and phlogopite, Occur as conformable sheets within a cogenetic volcanic sequence of intermediate to acid rocks. The volcanic sequence into which the carbonatites are emplaced is part of a group of rocks, locally called the Udayagiri group.

The Carbonatites occurring here can be classified essentially into two groups: (1) Fine grained siderite-rich rock exhibiting flow banding, vugs and other features suggestive of flow. This variety is rich in baryte and euhedral phlogopite plates; (2) Sheets of carbonate rich rock emplaced in conformity with the litho-layering trends of the enclosing meta-volcanics. These are medium to coarse grained, deep brownish rocks made up of siderite, clacite, dolomite, baryte and soda-amphibole, with magnetite and apatite in lesser amounts. Also found are micro-layers of a green mineral which has a characteristic fluorescence, and is strongly suspected to be a cerium-lanthanum rare earth mineral. The first type is seen about 1 km ssw of Bandakindipalli (14°52'30": 79°44') while the second is near Kodandarama baryte mine at 4.5 km wsw of Vinjamur (14°50': 79°35').