Geochemical features of the granitoids of South Mada complex and their relation to Sn, Nb, W mineralization

The South Mada complex is an anorogenic peraluminous granite complex which outcrops over an area of 14 x 13 km of Central Nigeria. The main mass of the complex consists of biotite granite emplaced within a mix assemblage of metamorphic and granitic rocks, and surrounded by a discontinuous polygonal ring dyke of granite porphyry. Endogenous cassiterite-bearing veins and tungsten mineralization occur within the biotite granite. Petrochemically the major elements show only subtle variations typical of rocks from the Nigerian province, while the trace elements in contrast show marked variations from the early to late stage rocks, a trend probably suggestive of fractional crystallization. However, locally there is evidence of fluid phase transfer which also caused postmagmate metasomatic alteration of the granite and the formation of the hypothermal mineralization. The biotite granites are characterized by anomalously high contents of F, Li, Rb, Sn, Nb, W and low Ba, Sr, and Zr. The inter-relationships of these elements as reflected by factor analysis indicate that element groupings can be explained by mineralization and postmagmatic processes. The most important mineralization event is marked by the lithophile factor heavily loaded by Li, Rb, F, W, Sn and Th. (author)