Genesis of tourmalinite from Chitral, Northern Pakistan
Abstract
Miniki Gol scheelite-bearing tourmalinite occurs within the Jurassic Arkari Formation. The Arkari Formation is located near the Pak-Afghan border within the Eastern Hindu Kush and is composed of garnet mica schist, phyllite, marble, mica quartzite, calc-silicate quartzite and subordinate tourmalinite. The extension of tourmalinite is vet)' limited and has been identified at three locations within the mica schist. Tourmalinite is dominantly composed of tourmaline, spessartine-rich garnet, quartz and scheelite. Tourmaline reaches up to by volume in some tourmalinites. The chemical composition of tourmaline and garnet of the tourmalinite fairly corresponds with those of the nearby exposed leucogranite. The values of K2O, MnO, Zn, Rb and Ba of Miniki Gol tourmalinite, are not markedly different from the associated schist and thus cannot be considered as siliceous chemical precipitates (exhalites). The limited extension of the tourmalinite is also inconsistent with the occurrence of exhalites. The lack of Sb, Hg, Ag, F and P in the tourmalinite also rules out the possibility of the exhalative activity in the study area.
A linear relationship between LREE and elements of obvious igneous origin such as Zr, Hf and Be in the tourmalinite indicates a post-magmatic metasomatic activity. The Miniki Gol leucogranite can be considered as potential source for the extreme enrichment of boron in the tourmalinite.
References
Deer, W. A., Howie, R. A. & Zussman, J., 1982. Rock-forming minerals, orthosilicates. Vol. IA, Longman, London.
Fletcher, C. J. N., 1985. Gold, antimony and tungsten mineralisation in the Chitral District, Northwest Frontier Province, Pakistan. Unpublished report for Sarhad Development Authority, Peshawar.
Hayden, H. H., 1915. Notes on the geology of Chitral, Gilgit and the Pamirs. Ind. Geol. Surv. Records, 45, 271-235.
Henry, D. J. & Guidotti, C. V., 1985. Tourmaline as a petrogenetic indicator mineral: an example from the staurolite grade metapelites of NW Maine. Am. Min., 70, 1-15.
Leake, R. C., Fletcher, C. J. N., Has-lam, H. W., Khan, B. & Shakirullah. 1989. Origin and tectonic setting of stratabound tungsten mineralisation within the Hindu Kush of Pakistan. J. Geol. Soc. London, 146, 1003-1016.
Lottermoser, B. G., 1989. Rare-earth element study of exhalites within the Willyama Supergroup, Broken Hill Block, Australia. Mineral. Deposita, 24, 92-99.
Miller, C. F. & Stoddard, E. F., 1981. The role of manganese in the paragenesis of magmatic garnet: an example from the Old Woman-Piute Range, California. J. Geology, 89, 233-
Plimer, I. R., 1984. The role of fluorine in the submarine exhalative systems with special reference to Broken Hill, Australia. Mineral. Deposita, 19, 19-25.
Plimer, I. R., 1986. Tourmalinites from the golden dyke dome, Northern Australia. Mineral. Deposita, 21, 263-270.
Plimer, I. R., 1987. The association of tourmalinite with stratiform scheelite deposits. Mineral. Deposita, 22, 282-291.
Pudsey, C. J., Coward, M. P., Luff, I. W., Shackleton, R. M., Windley, B. F. & Jan, M. Q., 1985. Collision zone between the Kohistan arc and the Asian plate in NW Pakistan. Trans. Roy. Soc. Edinburgh, 76, 463-479.
Slack, J. F., 1982. Tourmaline in Appalachian-Caledonian massive sulphide deposits and its exploration significance. Trans. Inst. Min. Metall. (Sect. B: Appl. Earth sci.), 91, B81-B89.
Slack, J. F., Herriman, N., Barnes, R. G, & Plimer, I. R., 1984. Stratiform tourmalinites in metamorphic terranes and their geologic significance. Geology, 12, 713-716.
Slack, J. E., Palmer, M. R. Stevens, B. P. J. & Barnes, R. G., 1993. Origin and significance of tourmaline-rich rocks in the Broken Hill District, Australia. Econ. Geol., 88, 505-541.
Sonnet, P., Verkaeren, J. & Crevola, G., 1985. Scheelite bearing calc-silicate gneisses in the Provence crystalline basement (Var, France). Bull. De Min., 108, 377-390.
Talent, J. A., Conaghan, P. J., Mawson, R., Molloy, P.D. & Pickett, J., 1982. Intricacy of tectonics in Chitral (Hindu Kush): faunal evidence and some regional implications. Geol. Surv. India Miscel. Pub., 41, 77-101.
Turekian, K. K. & Wedepohl, K. H., 1961. Distribution of the elements in some major units of the earth crust. Geo. Soc. Am. Bull., 72, 175-192.
Zahid, M., 1996. Genesis of stratabound scheelite and stratiform Pb-Zn mineralisation Chitral, Northern Pakistan, and its comparison with S-W England tin-tungsten deposits. Unpubl. Ph.D. thesis Univ. Leicester.
