Deep drill hole in the Devonian South Mountain batholith, Nova Scotia: A potential for hidden mineral deposits within the batholith

Abstract

The drill hole near Digby in southwestern Nova Scotia is the deepest on-shore hole in the Canadian Appalachians, and penetrated to a depth of about 1.5 km. The site of the drill was selected at the periphery of the Devonian South Mountain batholith, which contains important mineralization of tin and uranium. The drill hole intersected texturally uniform megacrystic biotite granodiorite, which does not display any pronounced primary vertical zonation. At depth, the drill core contains zones of alteration, fracturing, and brecciation. The alteration is mainly due to fluid flow along the fractures. Some fractures are mineralized and contain galena, sphalerite, pyrrhotite, chalcopyrite, pyrite, hematite, quartz, and carbonate minerals. Common occurrence of alteration zones in the hole suggests that such zones are widespread in the batholith and point to abundant hydrothermal activity deep within the massif. It is inferred that the potential for hidden economic mineral deposits within the batholith is much greater than is suggested by surface features. The association of mineralization as seen in the drill core with the most primitive rocks of the batholith further indicates that mineral deposits in granitoid rocks are not always hosted by the most evolved and fractionated rocks. Extensive fracturing demonstrates that the batholith is not a suitable candidate for the storage of radioactive waste material. High temperature measured in the drill hole (∼68°C at a depth of about 1,450 m) suggests that the pluton has promise as a source of geothermal energy.