Elemental behavior during the fractionation of felsic magma at Hobenzan polymetallic province, SW Japan

We have performed PIXE microprobe analysis of rock-forming minerals in granitoids at the Hobenzan polymetallic region of unique CuBiAsCoWB mineralization. The analysis was carried out at CSIRO using 5 to 30 μm beam of 3 MeV protons, and the following elements were detected: Cr, Mn, Fe, Ni, Cu, Zn, Ga, As, Rb, Sr, Y, Zr, Nb, Mo and Sn. In the case of biotite, incompatible elements such as Rb and Y show positive correlation with the Differentiation Index (DI) of the rocks. Ore forming elements such as Zn and Sn have similar trend to that of the incompatible elements. This fact implies that some of the ore forming elements do not directly enter the magmatic fluid that is evacuated from parental magma but they need to be extracted from minerals through water/rock interaction to be components of the mineralizing fluid. Our result also indicated that biotite is an ideal mineral to monitor the elemental behavior during the evolution of a magmatic-hydrothermal system.