Despite their well-known economic potential, the genesis of deposits associated with magmatic-hydrothermal fluids derived from granitic plutons is still not fully understood. The Cornubian batholith (SW England) represents an example of those: it was intensely mined for Sn and Cu, but also hosts W mineralizations and Li-rich granitic rocks.
This study explores the use of halogens as tracers for the formation of such critical element enrichments, across the transition from magmatic to hydrothermal conditions in this well-studied natural laboratory of a Variscan S-type system. Given the high incompatibility of heavy halogens (Cl, Br, I) in most minerals, they are reliable indicators of fluid provenance and evolution and readily discern geofluid reservoirs, but questions remain as to halogen behaviour during crucial ore-forming processes such as fluid exsolution or phase separation.
In situ LA-ICP-MS analysis of fluid inclusions and whole-rock combustion ion-chromatography will provide a detailed assessment of halogen behaviour across the magmatic-hydrothermal transition in samples ranging from granites and pegmatites, to greisens and mineralized Sn-W-Cu hydrothermal veins.
Preliminary results show a progressive dilution of fluids with magmatic Br/Cl - I/Cl signatures and elevated concentrations of Cu, Sn and W as the main factor controlling mineralization.