Geochemical aspects of uranium in the Sumayar valley, northern areas of Pakistan
Abstract
The Sumayar valley is located opposite to the Hunza township in the Northern Areas of Pakistan. The area is in the southern extreme of the Karakoram Block and close to the Main Karakoram Thrust (MKT) where medium to high-grade metamorphic rocks are exposed. The Sumayar Pluton, which is a Tertiary tourmaline leucogranite, crops out in the middle part of the valley. The upperpart of the valley is filled by the Silkiang Glacier and there is a range of glacial sediments deposited downstream of the glacier,
As part of a study to establish parameters for further detailed geochemical exploration programs in the region, stream sediments were collected from 12 paired sites representing adjacent high and low energy hydraulic environments. The coarse fraction (125-180 µm), fine fraction (< 125 µm) and a pan concentrate (pancon) at each site was analysed. Samples were also collected from adjacent talus fans. glacial deposits, avalanche and lacustrine deposits, This paper focuses on the U data from this sample set.
Uranium contents in the stream sediments range from 1.7 to 35 ppm in the coarse and fine fractions and 1.5 to 184 ppm in the pancons. Elevated U concentrations are spatially associated with the granite in both the stream sediments and talus fans. The presence of slightly elevated U (2 ppm) in one moraine sample indicates U mineralisation possibly extends further towards south under the cover of ice, Uranium contents are typically correlated with Sn, Pb, Zr, Ga, Hf and Lu but negatively correlation with Cr, Cu and Ni. Factor and cluster analysis indicates a strong relationship between U and other elements typically enriched in leucogranites,
The strongest response to the presence of the U-rich Sumayar Pluton is observed in the U contents of the fine stream sediments (<125 µm) and there does not appear to be a Strong hydraulic influence on this fraction suggesting the U is either hydromorphically transported or associated with very fine-grained heavy minerals.
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