Geology of the Gilgit-Hispar area, Gilgit Agency, Pakistan

Abstract

The Gilgit-Hispar area contains a large variety of igneous and metamorphic rocks, which have been grouped into seven general lithologic units, five composed largely of metamorphic rocks and two of intrusive rocks. The metamorphic units consist of probable correlatives of the Precambrian(?) Salkhala Series; the upper Paleozoic, slightly metamorphosed schists, quartzites, and calcareous rocks of the Chalt Schist; the higher metamorphosed (garnet and staurolite grades) schists, gneisses, and marbles of the Baltit Group; the Pasu Slate; and the Triassic(?) and older(?) greenstone complex consisting in large part of metavolcanic rocks. The metamorphism of the area is due at least in part to the intrusions of two huge silicic to intermediate batholiths of Cretaceous to Tertiary age composed largely of biotite granodiorite. The structural grain is west-northwest throughout the area and represents a part of the structural pattern whose focus is the Hazara-Kashmir syntaxial bend. Although steep faults and isoclinal folds are present, no large thrust faults were seen. The area apparently is structurally less complicated than comparable parts of the Hindu Kush mountains farther west in Chitral State. Deeply incised streams and elevated terraces indicate very recent uplift of considerable magnitude. Although traces of potential ore minerals are common in the Gilgit-Hispar area, deposits of possible commercial value were not seen. Heavy-mineral samples of stream sands contain fairly high concentration of scheelite. The radioactivity of the stream sands is in large part due to the thorium and uranium content of zircon. Radiometric traverses showed slightly higher radioactivity over gneisses and quartzites than over other rocks, but no unusually high values were recorded.