Petrography, mineralogy and geochemistry of Baran Lak magnesite and associated rocks, Khuzdar, Balochistan, Pakistan
Abstract
The Baran Lak massif, displays a complete ophiolitic sequence in the northern part of Bela Ophiolite. Magnesite veins are irregular and intersect each other at different angles forming netting pattern within ultramafic rocks. Geochemical, mineralogical and petrographical investigations of magnesite and associated ophiolitic rocks (Aptian- Maastachian) of Baran Lak area, Balochistan, were conducted to specify the nature of these deposits. Quantitative estimation of important major elements of magnesite has been carried out. Mutual plots between CaO, MgO, I.R. and R2O3 suggest that the magnesite is mainly derived from high Mg and low Fe bearing olivines and pyroxenes. The low contribution of alumina-silicates (feldspars) is also reflected in country rock by low R2O3. The plot of MgO vs. MgO/CaO ratio is evidenced for gradual depletion of Mg at the expense of Ca, probably due to interaction with groundwater. Chemically they are MgCO3 in which MgO ranges 42-44 % with minor amount of CaO (av. 3 %), insoluble residue, Fe and Al. X-ray studies revealed magnesite occurs as the major mineral along with chlorite as minor one.
Petrographic studies of host rocks revealed partly to completely serpentinized equivalents of harzburgite, dunire, wehrlite and pyroxenite. These ultramafic rocks are highly altered into serpentine with subordinate amount of chlorite and sericite. At places small lenses of dunite and wehrlite and some basic intrusive rocks (sill/dyke) consisting of gabbro and diorite were also identified in the area.
References
Ahmed, Z., 1993. Leucocratic rocks from the Bela ophiolite, Khuzdar District, Pakistan. In: Himalayan Tectonics (P.J. Treloar, P.J. & M.P. Searle, eds.) Geol. Soc. London Spec. pub. 74, 89-100.
Ahmed, Z., 1992. Composition of chromite from the northern part of Bela ophiolite, Khuzdar district, Pakistan. Acta Mineralogica Pakistanica, 6, 4-20.
Ahmed, Z., 1991. Basalt geochemistry and supra-subduction zone origin of the Bela ophiolites, Pakistan, Acta Mineralogica Pakistanica, 5, 83-98.
Ahsan, S.N. & Quaraishi, I.H., 1997. Mineral/Rock Resources of Lasbela and Khuzdar districts, Balochistan, Pakistan, Geol. Bull. Univ. Peshawar, 30, 41-51.
Ahsan, S.N., Akhtar, T. & Khan, Z.A., 1988. Petrology of Bela Khuzdar Ophiolite Balochistan, Pakistan. Geol. Surv. Pakistan, I.R. No. 307.
Arif, M., Jan, M.Q. & Ahsan, S.N., 1997. Mineral chemistry of the chromite occurrences from the Bela ophiolite in Khuzdar, Balochistan, Western Pakistan, Proc, Nation. Symp. Econ. Geol. Pakistan, 111-134.
Babien, J., 1991, Enclaves in plagiogranites of the Guevgueli ophiolite complex, Greece, In: Enclaves and granite petrology (J. Didier, & Barbarih, eds.), 200-219.
Dickson, T., 1990. Carbonate mineralogy and chemistry. In: Carbonate Sedimentology. (E. Tucker & V.P. Wright, eds.). Blackwell Sc. Pub, Oxford.
Gauher, S.H., 1966. Magnesite deposits in Pakistani Geol. Surv. Pak., Pre-publ. Issue. No.57.
Gnos, E., Khan, M., Mahmood, K., Khan, A.S., Shafique, N. A. & Villa, I. M., 1998. Bela oceanic lithosphere assemblage and its relation to the reunion hotspot. Terra Nova, 10, 90-95.
Hirayama, J., Mononobe, S. & Karim, T., 1995, A proposal for the use of Phosphorite and Magnesite in Hazara Division, N, W.F.P., Pakistan. Geologica I, 97-103.
Kazmi, A.H. & Jan, M.Q., 1997. Geology and Tectonics of Pakistan, Graphic Publishers, Karachi.
Kazmi, A.H. and Abbas, S.G., 2001. Metallogeny and mineral deposits of Pakistan. Graphic Publishers, Karachi.
Lefond, S.J., 1975. Industrial Minerals and Rocks, port City Press, Baltimore, Maryland.
Luitingh, J.V.N., 2001. Magnesite. USGS mineral Bureau.
MacKenzie, W.S., Donaldson, CH. & Guilford, C., 1982. Atlas of igneous rocks and their textures. Longman.
Miller. J., 1988. Microscopical techniques; Slices, slides, stains and peel, 86-107.
Mononobe, S., Hirayama, J. & Karim, T., 1992. A preliminary report on the reserve of Kumhar Magnesite mine. Proceed. Geosci. Colloq,, 3, 11-22.
Naseem, S., Sheikh, S.A. & Qadeeruddin, M., 1996-97. Geochemistry and tectonic setting of Gadani-Phuari segment of Bela ophiolites, Balochistan, Pakistan, J. King Abdulaziz Univ. Earth Sci. Jeddah, 9, 127-144.
Naseem, S., Sheikh, S.A. & Qadeeruddin, M., 2002. Petrography and Geochemistry of Wadh Plagiogranites and associated Gabbros from Bela Ophiolite, Pakistan. J. Geol. Soci. Philippines, 57, 1-18.
Naseem, S. & Sheikh, S.A., 2002. Biogeochemical Prospecting of Sulphide Minerals in Winder Valley, Balochistan, Pakistan. Resour. Geol. Japan, 52, 59-66.
Nicolas, A., 1989. Structures of ophiolites and dynamics of oceanic lithosphere, Kluwer Academic Pb., Dordrecht.
Pearce, J. A., Lippard, S. J. & Roberts, S., 1994. Characteristics and tectonic significance of supra-subduction zone ophiolites. In: Marginal Basin Geology: volcanic and associated sedimentary and tectonic processes in modern and ancient marginal basins (B.P. Kokelaar & M.F. Howels, eds.). Geol. Soc. London Spec. Publ.16, 77-94.
Sarwar, G., 1992. Tectonic setting of the Bela ophiolite, southern Pakistan. Tectonophysics, 207, 359-381.
Sarwar, G. & Dejong, K.A., 1984. Composition and origin of Kanar melange, southern Pakistan, Geol. Soc. London. Spec. Pap. 198, 127-137.
Siddiqui, S.H., Khalid, M. & Zaidi, S.A.H., 1996. Substitution of dolomite with serpentine in sintering. Pak. Steel Res. J.
