Geochemical Dispersion Pattern of some Heavy Metals in Upper Alaknanda Catchment: Application in Mineral Exploration and Environmental Implications

Geochemical characteristics of active stream and river sediment from part of the main Alaknanda catchment including main tributaries (Nandakini, Pindar and Mandakini) in Garhwal Himalaya were investigated. Economically important and environmentally sensitive selected trace element (Cr, Ni, Pb, Zn, Cu, Th and U) abundance in the sediments were studied to evaluate their spatial distribution in relation to lithotectonic control, mineral prospects and environmental geochemistry. The background concentrations, as median values, are found perceptibly enriched for these elements with respect to upper crustal average. Distribution patterns of U, Th and Pb are distinctive and show intrinsic relationship with the medium-grade deformed rocks (granitoids) of central crystallines and are generally enriched, whereas Cu is depleted in the same area. Background concentration of Cr is many fold enriched as compared to crustal abundance. 5 However, Ni in relation to Cr is not so high. There is a good correlation between Cr and Ni in the areas of mafic volcanic occurrences within low-grade metasedimentry rocks. But the same is not true in case of Nandakini valley within Baijnath central crystallines where Cr enrichment is anomalously high with Ni showing antagonistic relationship. High U and Th content in sediments are observed within or near the central crystalline thrust sheets, whereas the Cu and Zn anomaly zones are restricted within the Garhwal group of rocks. Some of these anomalies are significant and seems to have a definite structural (thrust/Fault) and lithological control, such as crystallines for U and Th and carbonates for Cu and Zn. The present study, thus also provides some useful clues for mineral exploration. Whereas the high anomaly areas are highly potential for economic mineral deposits of Cu, Zn, U and Th, but at the same time are equally prone to toxic exposure of U and Th as well as risk of arsenic and cadmium contamination that are normally associated with Cu and Zn sulphides.