A note on ‘composite dike’ in basement granite in the vicinity of Srisailam sub-basin near Akkavaram,Telangana

A composite dike has been noticed in basement granite in the vicinity of Srisailam sub-basin near village Akkawaram, Mahabubnagar district, Telangana. It is trending N-S and traced over an extent of 600m in eastern flank of Akkavaram outlier and comprises rocks of mafic and felsic composition characterized by both gradational and abrupt contacts. On the basis of petrographic studies, felsic part of dike is designated as bostonite and mafic as dolerite. Geochemically, they are grouped into (i) trachyte to trachydacite and (ii) basalt categories. Such dissimilar mineralogical and chemical characters in a single dike may be due to coexistence of magma of contrasting composition and provides vital information for understanding the two phase liquid. Interestingly, high uranium values (0.022% U₃O₈) recorded in parts of felsic portion.     

Grain size, geochemistry, magnetic susceptibility: Proxies in identifying sources and factors controlling distribution of metals in a tropical estuary, India

The aim of this study is to understand the various sources and factors controlling the abundance and distribution of the metals through the analyses of selected metals (iron, manganese, chromium, copper, zinc and cobalt), sand, silt, clay, organic carbon and magnetic susceptibility of the surface sediments of Zuari estuary in three different seasons. Total suspended matter (TSM) concentration and salinity of near surface and bottom waters were also measured. The study undertaken for three seasons, based on 18 selected stations all along the estuary, indicated that the concentration of most of the metals were comparatively higher during pre-monsoon than in monsoon and post-monsoon seasons. Further, along the length of the estuary, high concentrations were observed at lower middle and lower estuary and also at few stations at the upstream end. Salinity, distribution of TSM, size of the sediment, organic matter, geomorphological setup, fresh water input from land and release of industrial waste within the estuary played a role in distribution and concentration of metals. Magnetic measurements indicated the dominance of haematite like minerals and helped in understanding the source and depositional processes.