Fluid inclusions and mineralization at Cligga Head, Cornwall, England

Abstract

Thermometric and salinity data are presented for fluid inclusion populations in samples of hydrothermal vein material (quartz intergrown with wolframite, cassiterite, stannite, arsenopyrite, pyrite/chalcopyrite, hematite and limonite) and in metasomatic quartz over-growths in granite, greisen and kaolinized granite. These data indicate that multistage high temperature (Th 200– 400°C) and single or multistage low temperature (Th 70–150°C) hydrothermal events occurred within the Cligga Head granite stock and its environs. Although fluid inclusion salinities were low (2–12 equiv, wt. % NaCl) throughout the hydrothermal history of the stock, there is a general tendency for the salinity of the vein fluids to decrease with decreasing temperature. The homogenization temperature and salinity of the vein fluids of the wolframite-cassiterite mineralization are similar to those of another Cornish Sn-W deposit at St Michae¾s Mount. Low to moderate salinity fluids in the Th range 300–400°C appear to be a characteristic of the cassiterite-wolframite mineralization in the Cornubian metallogenic province.