Chlorine and Fluorine Contents of the Neogene Granitic Rocks in Kyushu

Abstract

Chlorine and fluorine contents of the Neogene granitic rocks in Kyushu were analyzed by an X-ray fluorecence analyzer and a specific ion electrode. Based on the petrography, Kyushu is divided into the. Inner zone, the Outer zone I and the Outer zone II from NW to SE. With some exceptions, chlorine and fluorine decrease as SiO₂ increases in each granitic mass. From the halogen contents in large granitic masses in the three zones, it is suggested that the chlorine content decreases and the F/Cl ratio increases toward the Pacific Ocean side. These trends correspond with those of other geochemical data which have been explained by the differences in modes of generation and granitic magma emplacement. On the other hand, the hypabyssal rocks in this region show a different pattern of halogen content from the plutonic rocks, indicating that the mode of emplacement affects the behaviour of halogen elements.
Granitic rocks of the Inner zone associated with base metal mineralization are rich in chlorine. Those of the Outer zone I are characterized by rather high fluorine content. Whereas, some hypabyssal rocks closely related to tin mineralization in the Outer zone I contain high chlorine concentrations or minerals with high chlorine contents. Hence, it is thought that chlorine plays an important role in transportation of tin, but that fluorine is enriched during differentiation process or by later greinsenization. There are some small tungsten-tin ore deposits in the Outer zone II. It is thought that there is no intense mineralization in the Outer zone II, because of the low chlorine content of the granitic rocks..