ABSTRACT
The high sensitivity of the Auger Electron Spectroscopy (AES) makes it useful for searching trace fluid composition preserved on mineral surfaces and grain boundaries. In this study we used AES to investigate the surface composition of country rocks and ores of the Golden Giant gold deposit of Hemlo, Ontario.The Hemlo gold deposits are situated within a sequence of Archean metasedimentary and metavolcanic supracrustal rocks that are part of the Hemlo-Heron Bay greenstone belt within Wawa subprovince of Superior structural province, The greenstone belt has been subjected to a complicated history of deposition, magmatism, deformation, metamorphism and metasomatism,
The country rocks investigated include oligoclase-biotite-quartz schist, quartz-oligoclase-muscovite schist, quartz-oligoclase prophyritic breccia, quartz-eye muscovite schist and quartz-eye microcline granofels. The ores investigated include quartz-microcline siliceous ore, muscovitic ore, baritic ore and biotitic ore. In most samples chloride films with minor S and K are preserved on grain boundaries showing that Cl-bearing fluids were involved in formation of the rocks and ores. The country rocks close to the ore zones have high Cl content on mineral surfaces. The baritic ore contains distinctly high surface Cl (up to 6.3 wt%). The study of fluid inclusions in quartz veinlets from the Golden Giant deposit supports the AES results. The fluid inclusions are highly saline (19–29 NaCl wt%, equivalent). Analysis of fluid inclusion brine residues produced by evaporation shows that NaCl dominates, with variable amounts of CaCl2 and carbonate species. It is surprising that the fluid inclusions have such low homogenization temperatures, ranging from 167 to 227°C. The data seems to support an epithermal model for some of the veins.
