The Barry Gold Deposit, Abitibi Subprovince, Canada: A Greenstone Belt-Hosted Gold Deposit Coeval with Late Archean Deformation and Magmatism

摘要

The Barry gold deposit is an example of an Archean greenstone-hosted lode gold deposit located in the Urban-Barry greenstone belt in the Abitibi subprovince of Quebec, Canada. The host mafic volcanic rocks are part of the 2717 Ma Macho Formation of the Northern Volcanic zone. They are cut by a series of weakly foliated preore diorite, pre- and postore quartz-feldspar porphyry (QFP), and quartz monzonite dikes and plugs, providing a unique opportunity to evaluate the age of the gold mineralization. Auriferous zones are spatially associated with northeast-trending ductile shear zones with moderate southeasterly dip. Gold mineralization occurs within straight N64° E/64° SE and folded N20° E/60°SE, on average, albite-carbonate-quartz veins and within the surrounding carbonate-quartz-pyrite, and locally within biotitecarbonate alteration zones of the host mafic volcanic rocks. The auriferous veins comprise 5 to 15 vol percent of the mafic volcanic rocks, are 1 to 5 cm wide, and are locally boudinaged. Although the volcanic units strike N55-60° E and dip 40°SE, the ore envelope (>2 g/t Au) is constrained from surface to a depth of 30 m in an antiformal shape. Gold generally occurs as microinclusions in pyrite but is also present as free gold in albitecarbonate- quartz veins, synmineralization altered host rocks, and locally within quartz veins cutting early QFP dikes. The deposit has an indicated resource of 309,500 oz Au (7,701,000 t at 1.25 g/t Au) and an inferred gold resource of 471,950 oz Au (10,411,000 t at 1.41 g/t Au). U-Pb dating of single zircon grains from the premineralization diorite and postmineralization QFP yielded indistinguishable ages, averaging 2697 ± 0.6 Ma, which is interpreted as the age of gold mineralization at the Barry deposit. This age and the field relationships reveal that lode gold mineralization was coeval with regional deformation and magmatism, similar to that documented at the Kiena, Norlartic, and Siscoe (Main zone) deposits of the Val d’Or district. These deposits represent the earlier orogenic gold event in the Abitibi greenstone belt, which preceded the postmagmatic, quartz-tourmaline auriferous veins such as those present at Sigma. Barry, Kiena, Norlartic, and Siscoe share many similarities with other orogenic gold deposits worldwide that are spatially associated with felsic and intermediate intrusions. The genesis for these deposits is not well constrained, as it is not obvious to distinguish whether the auriferous fluids were derived from the coeval magmas or whether both magmas and fluids were derived from a thermal event from the deep crust, or possibly the mantle.