Chlorine and fluorine contents of granitoids as indicatiors for base metal and tin mineralizations

Abstract

Recent efforts to use the chlorine content in rocks and minerals as a tool for exploration of base metal deposits, on the basis of chloride-complex model for magmatic hydrothermal ore deposits, seem to have resulted in discouraging conclusion on biotite and bulk samples. Yet we obtained extremely high chlorine values on unaltered granitoids from the lead-zinc mine area at Taishu, and some anomalies in other copper mine areas. In these examples, the chlorine anomalies are found to be largely due to fluid inclusions of high salinity. It appears that the chlorine content in bulk rock analysis can be useful in base metal exploration, if rock types (e.g., magnetite-bearing series or magnetite-free series) and degree and kind of alteration are examined carefully in advance. From the chlorine data together with some geological evidence, a possible area for future exploration of base metal deposits, perhaps of porphyry type, is proposed in the eastern part of the Chugoku batholith. Tin and greisen-type wolframite deposits occur in granitoids belts that have high F/C1 ratios. Fluorine contents of unaltered granitoids spatially related to the ore deposits have some connection with intensity of these mineralizations. It is recommended, however, to use both fluorine and tin in exploration of these types of ore deposits.