Alkali-feldspar from Koga syenites, Ambella grantitic complex, NW Pakistan
Abstract
The Koga syenites are intruded by at least two carbonatite intrusions, having different Na/K ratios. The carhonatite with high Na/K ratio has produced Na-feniles, while the other formed K-fenites. XRD study of low albile indicates that changes occur in the structural state of albite with increasing grade of fenitization. The Na-feldspar in the unfenilized rocks is low alhite, while in the fenitized rocks is anomalous low albite. The degree of Order ness increases with the increasing intensity of fenilizalion. The K-feldspar is maximum microcline in both the fenitized and unfenitized rocks. The lie lines between the co-existing Na- and K-feldspars deviate from the generally agreed magmatic trend.
References
Chaudhary, M. N., Ashraf, M. & Hussain, S. S., 1982. Petrology of Koga Nepheline syenites and pegmatites of Swat district. Geol. Bull. Punjab Univ., 16, 1-14.
Goldsmith. J. R. & Laves, F., 1954. Potassium feldspar structurally intermediate between microcline & sanidsine. Geo chi m. Cosmochim. Acta., 6, 100-118.
Le Bas. M. J., Mian, I. & Rex. D. C., 1987. Age and nature of carbonatite emplacement in North Pakistan. Geol. Rund., 76. 317-323.
Martin, R. F., 1969. The hydrothermal synthesis of low albite. Contr. Mineral. Petrol., 23, 323-339.
Mian, I., 1987. The mineralogy and geochemistry of the carbonatites, syenites and fenites of N.W.F.P. Pakistan. Unpub. Ph. D. thesis, Univ. of Leicester, U. K.
Mian, I. & Le Bass, M. J., 1988. Feldspar solid solution series in fenites from Loe Shilman Carbonatite Complex, NW Pakistan. Geol. Bull. Univ. Peshawar, 21, 71-83
Rafiq, M., 1987. Petrology and Geochemistry of the Ambella granitic Complex, N.W. F. P. Pakistan. Unpubl. Ph.D. thesis, Univ. Peshawar, Pakistan.
Siddiqui, F. A., 1967. Noté on the discovery of carbonatite rocks in the Chamla area, Swat State, West Pakistan. Geol. Bull. Punjab Univ., 6, 85-88.
Siddiqui, F. A., Chaudhary, M. N. & Shakoor, A., 1968. Geology & petrology of feldspathoidal Syenites and associated rocks of the Koga area, Chamla, Valley, Swat, West Pakistan. Geol. Bull. Punjab Univ., 7, 1-30.
Siemiatkowska, K. M. & Martin, R. F. , 1975. Fenitization of Missagi Quartzite, Sudbury Area, Ontario. Geol. Soc. Amer. Bull., 86, 1109-1122.
Stephenson, D., 1976. The South Qoroq Centre nepheline syenites, South Greenland. Petrology, felsic mineralogy and petrogenesis. Bull. Greenlands Geol. Unders., 118, 1-55.
Vartiainen, H. & Woolley, A. R., 1976.The petrology. mineralogy and geochemistry of the fenites of the Sokli Carbonatite intrusion, Finland. Geol. Surv. Finland, Bull., 280, 87.
Woolley, A. R., 1969.Some aspects of fenitization with particular reference to Chilwa Island and Kangankunde, Malawi. British M us. (Nat. Hist.). Bull. Mineral., 2, 191-219
Wright, T. L., 1967. The microcline-orthoclase transformation in the contact aureole of the Eldora Stock. Amer. Mineral., 52, 117-136.
Wright, T. L., 1968. X-ray and optical study of alkali feldspar II. An x-ray method of determining the composition and structural state from measurement of 20 values for three reflections. Amer. Mineral, 54, 88-104.
Wright, T. L. & Stewart, D. B., 1968 and optical study of alkali feldspar: 1. Determination of composition and structural state from refined unit-cell parameters and 2V. Amer. Mineral., 53, 38-87.
