Abstract:
The association of pyrite, gold and uraninite is found in Indus basin and most of the major rivers and their tributaries in Gilgit area of Kohistan, including the Hunza valley north of the Indus suture zone. This association is similar to the mineralization in the Witwatersrand Basin of South Africa, which has been extensively studied and is the best example of Paleo placer gold uraninite deposits. However, in the Kohistan area of northern Pakistan and in the Indus basin this system has not yet been studied systematically. In this work an attempt has been made to study and examine the factors controlling the dissolution of uraninite and assess its stability, as a detrital mineral in recent alluvial sands of the Indus basin. Moreover, the probable sources of pyrite-gold-uraninite assemblage have been discussed. The distribution of radioactivity, percentage of pyrite and number of gold flakes in different rivers and streams in the region were studied chemically using SEM on panned concentrate samples. The concentration of pyrite varies in different valleys and some valleys such as Bagrot, Pisan, Shamshal and Hasis valleys (Ishkuman) contain>45% pyrite in panned concentrate samples. Pyrite is mostly fresh and occurs as euhedral cubes but there are also some grains showing rounded margins, corrosion and alteration. The microprobe study of pyrite grains from Bagrot valley shows some high values (several hundred ppm) for gold. Gold flakes have different shapes (rounded, tabular, ellipsoidal and irregular) and sizes (6mm) which probably show different distances they traveled from their sources. Investigations indicate that the radioactive material consists mainly of thorium-uraninite with lesser uraninite, and monazite grains. Grains of the radioactive minerals are very fresh and show well-defined crystal faces, some have cubic forms with little evidence of corrosion. However, there are a few grains which show rounded margins and corrosion. As far as the size is concerned, they are in the very fine-to fine range of the sand size.
Page(s):
297-311
DOI:
DOI not available
Published:
Journal: Proceedings of 5th Pakistan Geological Congress , Volume: 0, Issue: 0, Year: 2007