Mineralogy and geochemistry of leucogranite from Miniki Gol (Chitral), northern Pakistan: implications for petrogenesis and mineralisation

Abstract

A body of two-mica leucogranite occurs in the Miniki Gol area of Chitral, northern Pakistan. Exposed at a distance of just 400 m from scheelite mineralisation in the area, the leucogranite consists of quartz, albite, orthoclase, muscovite and garnet together with minor amounts of biotite, tourmaline and apatite. Consistent with these mineralogical features, the geochemical details of the Miniki Gol leucogranite (MGL) manifest its peraluminous trait. The average values of Li, Rb, Pb, Be, W, Ta and U are distinctly higher in MGL than those in low-Ca granites. The average W and Ta abundances in the MGL samples are higher also than the Himalayan (Manaslu) leucogranite. Besides, the abundance of Sn in all the MGL samples is markedly higher than both the low-Ca granite and the Himalayan leucogranite. On the other hand, the levels of Zr, Hf, Y, Th, Nb, Sr, Ba, Zn, V and Ni abundance are distinctly lower in MGL than the average low-Ca granite. The MGL geochemical profile also displays very low levels of light rare earth element (LREE) relative to HREE, negative Eu anomalies and good sympathetic relationships between FeO* and MgO, Sn and Ta, Sr and Ba, Zr and Th and Zr and LREE. All these features signify a high degree of magmatic differentiation, i.e. the highly evolved character of MGL and derivation of its parent melt from a pelitic protolith in a collisional environment. The high levels of Pb, W, Sn, Ta and Be in the MGL point to its metallogenic significance. As the enrichment in these elements, especially Sn and Ta, seems to be a diagnostic feature of Sn, W-bearing granites, the MGL could be potential ore-bearing granite. Furthermore, the occurrence and Zr, Ta-richer character of scheelite in the associated metasedimentary rocks and the presence of beryl in the Miniki Gol pegmatite suggest that the investigated leucogranite may have played a key role in the mineralisation of both tungsten and beryllium in the Miniki Gol area.