The role of fluorine in submarine exhalative systems with special reference to Broken Hill,Australia

Fluorine-bearing minerals are uncommon in submarine exhalative ores, exhalites and associated alteration zones, probably because of the low solubility of CaF₂. The Broken Hill (Australia) deposit contains fluorapatite and fluorite with one lens containing 1.35% F and greater than 3 volume % F-bearing minerals. The calcite-fluorite-fluorapatite assemblage at Broken Hill indicates that ore deposition was probably from hypersaline fluorine-bearing fluids which decreased in pH by base leaching reactions which released Ca²⁺ and mixing with seawater promoting the rapid and simultaneous precipitation of calcite, fluorite and fluorapatite as a result of temperature and salinity decrease and pH and Ca²⁺] increase. The abundance of fluorine minerals in the Broken Hill ore and the association of F and B minerals with stratigraphically equivalent W- and Sn-bearing exhalites suggest that F complexes are important for ore transport in some exhalative systems. The Fe/Mn ratio decreases and the F/Cl ratio increases in fluorapatite in exhalites with increasing proximity to the Broken Hill deposit.