Genesis of stratabound scheelite and stratiform Pb-Zn mineralisation: Chitral, northern Pakistan, and its comparison with S-W England tin-tungsten deposits.
thesisposted on 2015-11-19, 09:05 authored by Mohammad Zahid. Khan
Tungsten mineralisation lies within the Asian plate to the north-west of Main Karakoram Thrust, which marks the suture zone between the Kohistan complex (Northern Pakistan) and Asian plate. Scheelite has been found mainly in the calc-silicate quartzites and subordinate tourmalinites associated with metapelites at Miniki Gol. This succession is intruded by leucogranites emplaced after the culmination of amphibolite facies metamorphism followed by retrogression. The area has undergone at least two deformational events and scheelite seems to be structurally controlled. Miniki Gol leucogranites are exposed 400 m away from the scheelite mineralisation and tungsten appears to be genetically related to these leucogranites. The chemistry of these leucogranites particularly high levels of Li, Be, W, Sn and Ta fairly coordinate with the specialised granite. The trace element chemistry and the chemical composition of clinozoisite, sphene, amphibole, grossular garnet, biotite, chlorite and scheelite of the calc-silicate rocks indicate a pronounced hydrothermal activity at Miniki Gol. The chemical composition of the tourmaline and spessartine-rich garnet of the tourmalinites is similar to that of tourmaline and spessartine-rich garnet of the leucogranite reflecting a genetic linkage. The occurrence of scheelite-bearing skarn at Miniki Gol further support a genetic relationship between scheelite mineralisation and leucogranite. In addition, the geochemical data of the Miniki Gol tourmalinites have been found similar to that of schist and hence can not be considered as siliceous chemical precipitates. Background level of tungsten is slightly higher than those of the average shale but not anomalous that rules out the possibility of the pre-granitic enrichment of tungsten at the study area. The consistency of the fluid inclusions both within leucogranites and calc-silicate rocks also signify a genetic link between the scheelite mineralisation and the possible post-magmatic hydrothermal fluids. The Miniki Gol W mineralisation has been compared with Cornubian Sn-W deposits. In both the areas tungsten seems to be enriched after the emplacement of granites. The stratiform and stratabound lead-zinc mineralisation is mainly confined to the marble horizon at Besti Gol. The conformability of the sulphide mineralisation with the host marble indicates that these mineralisations have been precipitated in synsedimentary environment.
Date of award1996-01-01
Awarding institutionUniversity of Leicester