Granites of the Saldania mobile belt, South Africa: radioelements and P as discriminators applied to metallogeny.

Abstract A method is provided to classify highly fractionated 550 Ma–510 Ma S-, I- and A-type granitic plutons of the Saldania mobile belt into those with potential mineralization and those that are most likely to be barren. Particular A-type granites of the Saldania belt have the potential for breccia-related Mo–Cu ± Au mineralization, specific S-type plutons for Sn–W mineralization and specific I-type plutons for skarn-related W–Mo–REE mineralization. As a result of their highly fractionated state, the geochemical features of these granitoids tend to be similar. As a first step in the discrimination process the P and Th content of granites are utilized to separate S-, I- and A-type plutons. Gamma-ray spectrometric radioelement (U and Th) contents are used to discriminate between barren and mineralized S-type plutons. The distinction between barren and mineralized A-type plutons is made by a combination of gamma-ray spectrometry and Zr/Nb ratio. No radiometric distinction can be drawn between barren and mineralized I-type plutons. To achieve this, parameters utilizing a combination of P and Th were developed and expressed as two diagrams, the P 2 O 5 * 100/Th – B (where B = millicationic Fe + Mg + Ti) and P 2 O 5 * 100/Th – (U + Th) – (Th − U) diagrams. The results of this investigation may be applied to the equivalents of the Cape Granite Suite in the Ross Orogeny and possibly the younger phases of the Dom Feliciano Belt in Brazil.