A review of the mesothermal gold deposits of the Meguma Group, Nova Scotia, Canada

Abstract

The gold province of the Meguma Terrane in Nova Scotia contains several classic examples of turbidite-hosted mesothermal gold deposits. There are over 300 gold occurrences and deposits hosted by the Cambro–Ordovician Meguma group rocks in southern Nova Scotia, Canada. The Meguma Group consists of two formations: (1) a lower, sand-dominated flysch (Goldenville Formation) and (2) an upper shaley flysch (Halifax Formation). Subdivision of the Goldenville Formation into several map units is leading to a better understanding of the stratigraphic constraints on the gold mineralization. Although detailed stratigraphic investigations in all of the major gold-producing areas is still ongoing, it is evident that the Steve's Road–Beaverbank and the Mt. Uniacke stratigraphic intervals contain most of the major past gold producers in the province. The Meguma Group rocks are variably deformed into upright gently to moderately doubly-plunging folds with multiple cleavages. The strata are metamorphosed from greenschist to amphibolite facies and are subsequently intruded by ca. 370 Ma peraluminous granites and minor mafic intrusions. The gold deposits can be divided into three main types: (1) high grade (approximately 15 g/t Au) narrow gold-bearing quartz veins; (2) low-grade (0.5–4 g/t Au) slate/argillite hosted; and (3) low-grade meta-sandstone hosted. A combination of two or more of the above can also occur. Almost all of the historic production (47 million g Au) has come from the high-grade veins within 200 m of surface. A variety of vein types occur although most of the gold produced came from bedding concordant, stockwork and fissure veins. Isotopic investigations and dating of the vein minerals indicate that the mineralization was related to migration of metamorphic fluids from multiple reservoirs in the waning stages of the Acadian Orogeny. Disseminated low-grade gold, with minor electrum and associated intermetallic compounds and metal alloys have recently been recognized in host rocks at several of the former gold mining areas in Nova Scotia. The presence of disseminated gold in combination with high-grade vein mineralization greatly enhances the economic viability of gold deposits in the Meguma Group. The association of disseminated gold and narrow vein-hosted deposits has important exploration implications for similar mesothermal gold districts elsewhere.