Gold metallogenesis in the Scottish Dalradian: the role of late-stage, low-temperature brines

摘要

Fluid inclusion studies of mesothermal vein-type gold deposits show a strong genetic association with high-temperature, low-salinity, volatile-rich fluids. Although fluid models for this type of mineralization are well established, they commonly ignore several important facts that indicate a role for low-temperature fluids. 'Visible' gold is invariably fracture-controlled and, hence, is related to fluid processes represented by later (secondary) fluid inclusions. In the limited number of cases where these have been studied a multiple fluid history involving low-temperature brines (<250 deg C) is commonly observed. Gold is often associated with a suite of minerals characterized by sulphosalts, tellurides, sulpho-tellurides and rare gold alloys. Some of these are only stable below 275 deg C, indicating an association with low-temperature processes.Fluid inclusion and mineralogical data representing the major styles of mineralization (e.g. Cononish and Calliachar Burn (Au-quartz); Lagalochan (porphyry Cu+-Au); Tomnadashan (igneous-related Cu); Tyndrum, Castleton and Inverneil (Pb-Zn); Strochullin and Corrie Buie (Pb-Zn+-Au)) were collated with data on regional fluids (e.g. Loch Lomond) in the Scottish Dalradian. Six fluid types are identified.