Stratigraphy, geochronology, and geochemistry of the Georgie River area, northwest British Columbia, and implications for mineral exploration

Abstract

Georgie River area is underlain by greenschist facies volcanic, clastic, and plutonic rock. High precision U–Pb isotopic ages on zircon enable regional stratigraphic correlation by constraining the Lower to lower Middle Jurassic depositional history. A sample from pyroxene-phyric tholeiitic basalt is Upper Triassic and (or) Lower Jurassic in age; its upper age limit is constrained by a crosscutting intrusion dated at 189.8 ± 0.3 Ma. The Bulldog Creek pluton, at 193.0 ± 0.3 Ma, is significantly older than the previously reported K–Ar age. Hazelton Group strata include a coarse-grained volcaniclastic and volcanic unit overlain by a fine-grained clastic and bimodal volcanic flow unit. The coarse volaniclastic unit is coeval and probably cogenetic with the Outram Lake porphyry intrusion (189.7 ± 0.3 Ma) and near the top includes andesitic tuff (189.8 ± 0.6 Ma). These data constrain the age of deposition of the unit and support correlation with the Lower Jurassic Hazelton Group and members of the Texas Creek plutonic suite. Age of the fine clastic and bimodal volcanic unit is no older than the youngest detrital zircons (ca. 185 Ma) near its base. That age and the age of a rhyolite unit (176.6 ± 1.1 Ma) at the top support correlation with the Middle Jurassic Salmon River Formation of the Hazelton Group. Resolution of the litho- and chronostratigraphy of the area reveal close similarities in age, rock types, succession, and composition with strata that host the base- and precious metal-rich stratiform Eskay Creek deposit, revealing the potential for Eskay-type volcanogenic massive sulphide (VMS) deposits in the Georgie River area.