NS  Vol.4 No.9 , September 2012
SHRIMP zircon U-Pb dating of the mafic and felsic intrusive rocks of the Saza area in the Lupa goldfields, southwestern Tanzania: Implication for gold mineralization
Abstract: The Lupa Goldfield (LGF) is one of the eight structural terranes in the NW – SE striking Ubendian Belt of SW Tanzania. The LGF is comprised of granitic gneisses with bands of amphibolites which are intruded by mafic intrusions including gabbros, granodiorites, diorites; and various granites as well as metavol-canics. These rocks are cross-cut by narrow mafic dykes and aplites. SHRIMP zircon U-Pb data are presented for the granodiorite and a mafic dyke that cross-cut the granodiorites in the Saza area of the LGF, with the aim of constraining the mafic and felsic magmatism and their implication to gold mineralization. The zircon U-Pb data shows that the Saza granodiorites were emplaced at 1924 ± 13 Ma (MSWD = 2.6) whereas the cross-cutting mafic dyke yielded a zircon U-Pb age of 1758 ± 33 Ma (MSWD = 0.88). The dated granodiorite sample was in sheared contact with an altered mafic intrusive rock, most likely a diorite, along which an auriferous quartz vein occurs. The 1924 ± 13 Ma age of granodiorites is within error of the reported molybdenite Re-Os age of 1937 Ma determined for the gold mineralization event in Lupa Goldfields. Although auriferous quartz veins are younger than the granodiorites, the more or less similar ages between the emplacement of granodiorites and the mineralizing event indicate that the granodiorites might be the heat source (or driver) of hydrothermal fluids responsible for gold mineralization in the Lupa goldfields. This would further suggest that gold mineralization in the LGF is intrusion-related type. The mafic dykes represent the youngest rocks to have been emplaced in the area and hence the 1758 ± 33 Ma age of the mafic dykes conclude the magmatic evolution in the Lupa goldfields during the Palaeoproterozoic.
Cite this paper: Manya, S. (2012) SHRIMP zircon U-Pb dating of the mafic and felsic intrusive rocks of the Saza area in the Lupa goldfields, southwestern Tanzania: Implication for gold mineralization. Natural Science, 4, 724-730. doi: 10.4236/ns.2012.49096.

[1]   McConnell, R. (1950) Outline of the geology of Ufipa and Ubende. Geological Survey of Tanganyika Bulletin, 19, 62.

[2]   Daly, M.C., Klerkx, J. and Nanyaro, J.T. (1985) Early proterozoic terranes and strike-slip accretion in the Ubendian Belt of southwest Tanzania. Terra Cognita, 5, 257.

[3]   Daly, M.C. (1988) Crustal shear zones in central africa: A kinematic approach to proterozoic tectonics. Episodes, 11, 5-11.

[4]   Boniface, N., Schenk, V. and Appel, P. (2012) Paleoproterozoic eclogites of MORB-type chemistry and three proterozoic orogenic cycles in the Ubendian Belt (Tanzania): Evidence from monazite and zircon geochronology, and geochemistry. Precambrian Research, 192-195, 16- 33.

[5]   Hanson, R.E. (2003) Proterozoic geochronology and tectonic evolution of southern Africa. In proterozoic east Gondwana: Supercontinent assembly and break up. Geological Society of London, 427-463.

[6]   Mnali, S.R. (1999) Palaeoproterozoic felsic magmatism and associated gold-quartz vein mineralization in western part of the Lupa Gold Field, south-western Tanzania. Ph.D. Thesis, University of Dar es Salaam, Dar es Salaam.

[7]   Nanyaro, J.T. (1987) Proterozoic gold-base metal veins in the Mpanda Mineral Field, western Tanzania. Ph.D. Thesis, University of Dar es salaam, Dar es Salaam.

[8]   McKenzie, C., Sheets, R., Moore, J. and Selby, D. (2009) Ubendian mineralization in the Lupa Goldfields, southwestern Tanzania: New discoveries and geochronology.

[9]   Wiedenbeck, M., Alle, P., Corfu, F., Griffin, W.L., Meier, M., Oberli, F., von Quadt, A., Roddick, J.C. and Spiegel, W. (1995) Three natural zircon standards for U-Th-Pb, Lu-Hf, trace element and REE analyses. Geostandards Newsletter, 19, 1-23. doi:10.1111/j.1751-908X.1995.tb00147.x

[10]   Williams, I. (1998) U-Th-Pb Geochronology by Ion Microprobe. Application of microanalytical techniques to understanding mineralizing processes, vol. 7. In: McKibben, M., Shanks, W.J. and Ridley, W., Eds., Reviews in Economic Geology, The Society, Toronto, 1-35.

[11]   Ludwig, K.R. (1999) User’s manual for Isoplot/Ex, version 2.10, a geochronological toolkit for microsoft excel. Berkeley Geochronology Center Special Publication, Berkeley.

[12]   Ludwig, K.R. (2000) SQUID 1.00, a user’s manual. Berkeley Geochronology Center Special Publication, Berkeley.

[13]   Sillitoe, R.H. (1991) Intrusion-related gold deposits. In: Foster, R.P., Ed., Gold metallogeny and exploration. Blackie and Son Ltd., Glassgow, 165-209.

[14]   McCoy, D., Newberry, R.J., Layer, P., DiMarchi, J.J., Bakke, A., Masrerman, J.S. and Minehand, D.L. (1997) Plutonic-related gold deposits of interior Alaska. In: Goldfarb, R.J. and Miller, L.D., Eds., Economic geology monogram, Economic geology publishing Company, El Paso, 9. doi:10.2113/gsecongeo.86.6.1187

[15]   Lenoir, J.L., Liegeois, J.P., Theunissen, K. and Klerkx, J. (1994) The palaeoproterozoic Ubendian shear belt in Tanzania: Geochronology and structure. Journal of African Earth Sciences, 19, 169-184. doi:10.1016/0899-5362(94)90059-0

[16]   Boven, A., Theunissen, K., Sklyarov, E., Klerkx, J., Melnikov, A., Mruma, A. and Punzalan, L. (1999). Timing of exhumation of a high-pressure mafic granulite terrane of the paleoproterozoic Ubende Belt (west Tanzania). Precambrian Research, 93, 119-137. doi:10.1016/S0301-9268(98)00101-6