Structural controls and age constraints on sulphide mineralization, southern Taltson magmatic zone, northeastern Alberta

Abstract

Northeastern Alberta is underlain by Precambrian rocks of the Taltson magmatic zone, a composite continental magmatic arc/collisional orogen developed between Rae craton (Archean) and the Buffalo Head terrane (Paleoproterozoic). Rutledge River basin (2.13-2.08 Ga) received pelitic/quartzitic sediments that probably covered the basement of the Taltson magmatic zone, and much of the western Rae Province, prior to Taltson magmatism (1.99-1.90 Ga). The basin was dismembered by the intrusion of Taltson plutons, and by development of a complex northward-trending regime of early granulite facies, mainly sinistral strike-slip shearing and subordinate thrusting (ca. 1.93 Ga), and later greenschist facies brittle-ductile dextral and sinistral shearing (ca. 1.86-1.80 Ga). The Taltson magmatic zone contains three types of sulphide mineral occurrences. The first type is stratiform pyrite-arsenopyrite-gold mineralization, initially developed within pelitic gneisses of Rutledge River basin, commonly within 100 m of the contact with the underlying basement. The second type occurs in zones in which initial stratiform mineralization was subsequently remobilized within regions of greenschist grade deformation overprinting layer-parallel high-grade fabrics in pelitic gneisses. Gold values to 600 ppb and arsenic values to 3600 ppm were reported from these gneisses. The third type is pyrite-pyrrhotite, copper-gold mineralization found in greenschist grade shear zones associated with sheared amphibolite gneisses, with copper values ranging to 900 ppm. 40Ar/39Ar dating of micas indicates a 1.86 to 1.80 Ga age for regional greenschist grade deformation. This is inferred to be the time of recrystallization- reconcentration of mineralization in stratiform and shear zone-hosted occurrences.