Origin and tectonic setting of stratabound tungsten mineralization within the Hindu Kush of Pakistan

Stratabound scheelite mineralization has been discovered in the Hindu Kush range of northern Pakistan as a result of a geochemical drainage survey. The mineralization occurs predominantly in clinozoisite-bearing calcsilicate quartzite beds within a sequence of mica schist and subordinate graphitic phyllite, mica quartzite, tourmalinite and feldspathic gneiss, but not in adjacent calcite marble. The sequence is intruded by a small leucogranite stock emplaced after the climax of Barrovian-type metamorphism during the later of two deformation phases which are related to continent-arc collisions in the Cretaceous and Eocene. In the calcsilicate quartzites, scheelite crystal-lized simultaneously with clinozoisite prior to the leucogranite emplacement and is clearly of metamorphic origin. Tungsten-rich brines, generated from hot springs in an extensional tectonic environment, are thought to have been concentrated in the relatively porous precursor of the calcsilicate quartzite during diagenesis. Subsequent metamorphism recrystallized the tungsten as scheelite along with metamorphic silicate minerals and caused limited mobility of the element into veins.