Chlorine-bromine-iodine systematics as tracer of fluid and metal sources in Sn-W mineralized magmatic-hydrothermal systems

Granite-hosted Sn-W ore systems constitute one of the most important types of magmatic-hydrothermal ore deposits in Europe, especially due to their increasingly recognized critical metal potential (Li, Be, Ga, Nb, Ta and In). Their formation is closely linked to the waning stages of magmatic activity in shallow granitic complexes, particularly the exsolution of magmatic-hydrothermal fluids during fractional crystallization. These fluids give rise to a multitude of mineralization styles whose formation depends on complex interplays of fluid-rock and fluid-fluid interaction processes, and which range from Sn-W greisen and sheeted vein systems to skarns and distal polymetallic sulfide ores. This complexity still represents a major obstacle in identifying fluid and metal sources in such systems, as well as the first order mechanisms controlling metal enrichment and precipitation. The heavier halogens (Cl, Br, I) have long since been recognized to be sensitive recorders of crustal fluid reservoirs and to behave largely conservatively in most fluid-rock interaction processes. They have a high potential to trace fluid and metal sources even in complex Sn-W magmatic-hydrothermal systems with protracted fluid flow histories, but their applicability remains limited to date for a number of reasons. While the Cl-Br-I halogen signatures of S-type granitic melts are known to be regionally distinct, it is not clear how these convert into halogen signatures in associated magmatic-hydrothermal fluids in light of processes such as fractional crystallization and fluid saturation. Furthermore, very little is known about how hydrothermal halogen signatures develop in response to processes such as fluid phase separation. Taken together, this severely limits interpretability and robustness of the scarce reference data on halogens in magmatic-hydrothermal fluids. This proposal seeks funding for an integrated study tracing the fate of the heavier halogens (Cl, Br, I) throughout the evolution of a magmatic-hydrothermal Sn-W ore deposit systems, from melt composition and fractional crystallization to fluid saturation and the subsequent evolution of the exsolved magmatic-hydrothermal fluids. This will be done using a combination of combustion ion chromatography (CIC) for determination of halogen signatures in granitic rocks and mineral separates and LA-ICP-MS fluid inclusion microanalysis of fluids from all stages of the magmatic-hydrothermal system. In conjunction with ore metal concentration data in the fluids, it will be possible to link hydrothermal halogen signatures to the critical ore forming processes during all stages of a magmatic-hydrothermal Sn-W mineralized system. Development of a robust tracer tool for the identification of first order parameters controlling metal sources, mobility and precipitation in such systems will make a significant contribution to the stated goals of the DOME priority program (SPP 2238).