Exploration and extraction of placer gold in the terraces of Bagrot valley, Gilgit, northern Pakistan
Abstract
The upper reaches of Chitral, Gilgit and the Indus river, in northern pans of Pakistan, are well known for the placer gold occurrences. The extraction of gold by gold-washers, using primitive tools, has been practiced since long period in the region. Due to the recent advancement in technology, there has been a rapid growth in gold production from placer deposits world over. However, mining of placer gold in Pakistan has not been given due consideration so far. The study of the placer deposit of Bagrot valley has, therefore, been carried out to determine the mineralogy of these placer deposits, which could help in investigating the source rock for gold and also to design methods for the extraction of placer gold in more economic manner.
The placer deposits of the Bagrot valley are mainly composed of glacio-fluvial and fluvial sediments in the form of terraces of various sizes. Representative samples of the sediments from each terrace in Chirah, Farfooh and Bulchi villages of the Bagrot valley 'were collected during fieldwork.
The glacio-fluvial and fluvial terraces of the study area have similar mineralogy with only difference in the size and shape of the gold particles in concentrates. The gold particles of the fluvial terraces have smaller size and more roundness in shape as compared to those of glacio-fluvial terraces. The sediment load in both types of terraces is mainly composed of rock fragments, magnetite, quartz, biotite, muscovite, chlorite and epidote. Garnet, tourmaline, amphibole, pyroxene, olivine. pyrite and chalcopyrite are present in lesser amounts while zircon and sphene occur in traces. Chemically, maximum gold and silver have been noticed in the concentrates while rest of the media (middling and Tail) have negligible gold and silver. Both mineralogical and chemical studies suggest that gold in the source rock is present as coarse-grained native form and, therefore, the gravity separation method is the most appropriate method for the extraction of placer gold in the area.
The size and morphology of gold in the concentrates of both glacio-fluvial and fluvial terraces of the study area have been evaluated to understand the proximal or distal nature of the gold source. The general characteristics of studied gold particles suggest that gold in glacio-fluvial and fluvial terraces has been derived and transported from a distal source at least more than a few tens of kilometers, up-stream.
References
Ahmed, Z. & Chaudhry, M.N., 1976. Petrology of the Babusar area, Diamir district, Gilgit, Pakistan. Geol. Bull. Punjab Univ., 12, 67-78.
Austromineral, 1976. Final report (feasibility study), Indus gold project: submitted to Pakistan Mineral Development Corporation by Austromineral, Vienna, Austria, 1-235.
Austromineral, 1978. Feasibility study (final report), Mineral exploration and mining development, Chitral District: submitted to Sarhad Development Authority, Peshawar, Pakistan by Austromineral, Vienna, Austria, l- 289.
Bard, J.P., Maluski, H., Matte, P.H. & Proust. F., 1980. The Kohistan sequence; Crust and mantle of an obducted island arc. Geol. Bull. Univ. Peshawar, 13, 87-93.
Boyle, R. W., 1979. The geochemistry of gold and its deposits. Geol. Surv. Canada Bull. 280, 584 p.
Butler, R.W.H. Prior, D.L. & Knipe, R.J., 1989. Neoectonics Syntaxis, Pakistan and crustal stacking in the northwest Himalayas. Earth Planet. Sci. Lett., 94, 329-343.
Butler, R.W.H., and Prior, D.J., 1988. Tectonic control on the uplift of the Nanga Parbat Massif, Pakistan Himalayas. Nature, 333, 247-250,
Chamberlain, C.P., Zeitler, P.K. & Erickson E., 1991. Constraints on the tectonic evolution of the northwestern Himalaya from geochronologic and petrologic studies of Babusar Pass, Pak. J. Geol., 99, 829-849.
Coward, M.P., Butler, R.W.H., Khan, M.A. & Knipe, R.J., 1987. The tectonic history of Kohistan and its implications for Himalayan structure. J. Geol. Soc. London, 144, 377-391.
Coward, M.P., Jan, M.Q., Rex, D., Tarney, J., Thirlwall, M. & Windley, B.F., 1982. Structural evolution of a crustal section in the western Himalaya. Nature, 295(5844), 22-24.
Coward, M. P., Windley, B.F., Broughton, R.D., Luff, I.W., Petterson, M.G., Pudsey, C.J., Rex, D.C. & Khan, M.A., 1986. Collision tectonics in the NW Himalayas. In: Collision Tectonics (M.P. Coward, & A.C. Ries, eds.). Geol. Soc. Lond., Spec. Publ. 19, 203-219.
Dilabio, R.N.W., 1990. Classification and interpretation of the shapes and surface textures of gold grains from till on the Canadian Shield. In Current Research, Part C. Geological Survey of Candad, Paper 90-1C, 323-329.
Freyssinet, P.H., Lawrence, L.M. & Butt, C.R.M., 1989, Geochemistry and morphology of gold in lateritic pro-files in Savanna and semi-arid Climates. Abstract, Chem. Geol. 84, 61-63.
Giusti, L., 1986. The morphology, mineralogy and behaviour of "finegrained" gold from placer deposits of Alberta: Sampling and implications for mineral exploration. Canad. Jour. Earth Sci., 23, 1662-1672.
Halfpenny, R. & Mazzucchelli, R.R., 1999. Regional multi-element drainage geochemistry in the Himalayan mountains, northern Pakistan. J. Geochem. Explor., 67, 223-233.
Hanson, C.R., 1989. The northern suture in the Shigar valley, Baltistan, northern Pakistan.
Herail, G., Fornari, M., Viscarra, G. & Miranda, V., 1990. Morphological and chemical evaluation of gold grains during the formation of a polygenetic fluviatile placer, the Mio-Pleistocene Tipuani placer example (Andes, Bolivia). Chronique de la Recherche miniere, No.500, 41-49.
Herail., G., 1984. Geomorphologie et gitologie de 1' or detritique. Piemonts et basins intramontagneux due Nord-Ouest de I 'Espagne. Centre National de la recherché scientifique. Paris, 456 p,
Kazmi, A.H. & Jan, M.Q., 1997. The geology and tectonic of Pakistan. Graphic Publishers, Karachi, Pakistan.
Khan, M.A., 1988. Petrology and Structure of the Chilas Ultramafic-Mafic Complex. N. Pakistan. Unpubl. Ph.D. thesis, Univ. Lond. UK.
Khan, M.A., Jan, M.Q., Windley, B.F., Tarney, J., & Thirlwall, M.F., 1989. The Chilas mafic-ultramafic igneous complex; the root of the Kohistan island arc in the Himalaya of northern Pakistan. 1m Tectonics of the Western Himalayas (L.M. Malinconico, Jr. & R.J. Lillie, eds.). Geol. Soc. Am., Spec. Pap. 232, 75-94.
Khan, Khan, M.A. & Jan, M.Q, 1994. Geology of a part of the Kohistan terrane between Gilgit and Chilas, northern areas, Pakistan. Geol. Bull. Univ. Peshawar, 27, 99-112.
Kolesov, S. V., 1971, Flattening and hydrodynamic sorting of placer gold. Intern-. Geol, Rev., 17, p. 940-944.
Le Fort, P., Lernennicier, Y., Lombardo, B., Pecher, A., Pertusati, P., Pognante, H. & Rolfo, F., 1995. Preliminary geological map and description of the Himalayan-Karakorum junction in Chogo Lungma to Turmik area (Baltistan, northern Pakistan). J. Nepal Geol. Soc., 11, 17-38.
Lindgren, W., 1933. Mineral Deposits (4th ed.). McGraw-Hill., New York.
Loen, J.S., 1993. Implications of changes in placer gold morphology, Pioneer district, Montana. Northwest Geology. Department of Earth Sciences, Montana State University, Bozeman, Montana, 22, 29-42.
Searle, M.P., 1991. Geology and Tectonics of the Karakoram Mountains. Wiley & Sons, New York.
Sweatman, T.R., Clavarino, J.G. & Dawney, R.L., 1995. Drainage geochemical exploration and mineral potential of Northern Pakistan, Third report by Rex Sweatman and Associates for Australian Agency for International Development.
Tahirkheli, R.A.K. & Jan, M.Q. (eds.). 1979. Geology of Kohistan, Karakoram Himalaya, northern Pakistan. Geol. Bull. Univ. Peshawar, 1l (Spec. Issue), 187p
Tahirkheli, R. A.K., 1974. Alluvial gold prospects in the north-west, West Pakistan. Information Release No. 7, Geol. Surv. Pakistan. 1-48.
Tahirkheli, R.A.K., 1982. Geology of the Himalaya, Karakoram and Hindukush in Pakistan. Geol. Bull. Univ. Peshawar, 15 (Spec. Issue), 1-51.
Zeitler, P.K., Johnson, N.M., Nasser, G. W. & Tahirkheli, R.A.K., 1982. Fission track evidence for Quaternary uplift of the Nanga Parbat region, Pakistan. Mature, 298, 255-257.
Zeitler, P.K. & Chamberlain, C.P., 1991. Petrologic and tectonic significance of young leucogranites from the north Western Himalaya, Pakistan. Tectonics, 10, 729-741.
Zeitler, P.K., 1985. Cooling history of the NW Himalaya, Pakistan. Tectonics, 4, 127-151.
Zeitler, P.K., Chamberlain, C.P. & Smith, H.A., 1993. Synchronous anatexis, metamorphism, and rapid denudation at Nanga Parbat (Pakistan Himalaya). Geology, 21, 347-350
Zeitler, P.K., Sutter, J.F., Williams, I.S., Zartman, RE & Tahirkheli, R.A.K., 1989. Geochronology and temperature history of the Nanga Parbat-Haramosh massif, Pakistan. In: Tectonics of the Western Himalayas (L.L. Malinconico & R.J. Lillee eds.), Geol. Soc. Am., Spec. Pap, 232, 1-22.
