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Title:: Why the Geochemistry of Igneous Rocks Needs Constraints by Geological, Petrological and Mineralogical Evidences?

Author(s):: LUO Zhao-hua; State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China

Keywords:: numerical petrology; magmatic mineral system; geochemistry of igneous rock; transmagmatic fluid; Fe-Ti oxide deposit; Sichuan

Abstract:: Many contributions to the numerical or chemical petrology of igneous rocks are published in recent years. However, the volume of scientific issues is not decreased, but more and more problems are emerged. The major causes inducing such difficult condition are that many investigations are insufficient to be constrained by the geological, petrological and mineralogical evidences, and that many researchers do not concern to the developments in igneous theory. A typical example is the origin of magmatic deposit. Accordingly, the factors causing diversity of the geochemical interpretations were analyzed; the general features of magma systems were introduced; taking Baima Fe-Ti oxide deposit in Panxi area of Sichuan as an example, the methodology to constrain geochemical data by the geological, petrological and mineralogical evidences was discussed. The results show that ①the numerical petrology has real geological implications only then when it is constrained by geological, petrological and mineralogical evidences, because the bulk composition essentially do not include the genetic information about igneous rocks, but the compatible elements may present the potential phase proportion, and the incompatible elements may present the fluid processes undergone in rocks; ②the formation of giant ore deposit also needs a huge volume of the ore-bearing fluid, and hence, the transmagmatic fluid model can more reasonably explain the origin of Baima Fe-Ti oxide deposit.