Geochronology and lithogeochemistry of granitoid rocks from the central part of the Central plutonic belt, New Brunswick, Canada: implications for Sn-W-Mo exploration

摘要

The central part of the Central plutonic belt in New Brunswick is underlain by numerous plutons of calc-alkaline,foliated and unfoliated granite that intrude Cambrian to Early Ordovician metasedimentary rocks. U-Pb (zircon)dating demonstrates that granites range in age from Middle Ordovician to Late Devonian, although most are lateSilurian to Early Devonian. An age of 467 ± 7 Ma has been obtained on the foliated McKiel Lake Granite, whereasunfoliated intrusions yield ages of 423.2 ± 3.2 Ma (Bogan Brook Granodiorite), 420.7 +1.8/-2.0 Ma (NashwaakGranite), 419.0 ± 0.5 Ma (Redstone Mountain Granite), 416.1 ± 0.5 Ma (Beadle Mountain Granite), 415.8 ± 0.3 Ma(Juniper Barren Granite), 409.7 ± 0.5 Ma (Lost Lake Granite), and 380.6 ± 0.3 Ma (Burnthill Granite). All plutonsexhibit mixed arc-like and within-plate geochemical signatures, although the Redstone Mountain and Burnthillgranites are dominantly within-plate type. Trace element data reveal a close overall geochemical similarity betweenOrdovician and Silurian – Devonian plutons, indicating that all were generated by partial melting of similar crustalsources and/or share a similar petrogenesis. Late Silurian to Early Devonian plutons mainly comprise biotite and/ormuscovite-bearing, peraluminous granite and are considered prospective for granophile-element mineralization.All plutons contain Sn well in excess of the granite global average abundance, and several contain average tinvalues comparable to productive stanniferous granites elsewhere. The Burnthill, Lost Lake, Beadle Mountain andNashwaak granites are geochemically most evolved and enriched in Sn and W. The Burnthill Granite in particularhas experienced late-stage hydrothermal processes that have resulted in local enrichments of these elements.