Geology, U–Pb zircon geochronology, and geochemistry of PGE-bearing Neoarchean and Paleoproterozoic gabbroic rocks of the Peter Lake domain, southern Hearne craton, Canada

Abstract

The Peter Lake domain, a component of the Hearne craton in Saskatchewan, includes several intrusive complexes ranging in age from 2.70 to 1.83 Ga. Two gabbroic complexes (Swan River and Porter Bay) together represent one of the largest accumulations of Precambrian mafic intrusion, both metamorphosed at amphibolite facies. Sulfide-poor PGE occurrences are found in both complexes and share many textural and lithological characteristics with magmatic contact-type PGE–(Ni–Cu) deposits such as the chaotic Lac des Iles pluton and with layered stratiform deposits of large layered intrusions such as Bushveld or Stillwater. Lithologically, both complexes are dominated by leucocratic gabbronorite and gabbro, locally characterized by cumulate layering, cross-bedding, brecciated, and pegmatitic textures. U–Pb zircon crystallization ages between 2562 and 2560 Ma were obtained for the Swan River complex. sulfide formation is interpreted to be of magmatic origin rather than remobilized, as had been speculated by exploration geologists, and is therefore of the same age as the host gabbro. Geochemical data support the interpretation of a mantle plume origin in a subduction environment for the Swan River complex. The Porter Bay complex is much more restricted in areal extent and a leucocratic gabbronorite yielded a U–Pb zircon age of 1913 ± 1 Ma, which is interpreted as the crystallization age and the time of sulfide formation. Major and trace element geochemical data of Porter Bay complex rocks show a considerably more evolved character than the Swan River complex, and is interpreted as indicating emplacement in a continental arc environment.