Chemostratigraphy at the Brunswick No. 6 Volcanic-Sediment-Hosted Massive Sulfide Deposit, New Brunswick: Resolving Geometry from Drill Core in Deformed Felsic Volcanic Rocks

摘要

Diamond-drill hole DDH-B357, located 1.5 km north of the Brunswick No. 6 Zn-Pb-Cu-Ag volcanic-sediment-hosted massive sulfide (VSHMS) deposit, intersects three exhalative horizons within variably altered felsic volcanic rocks of the Nepisiguit Falls and Flat Landing Brook formations. These three petrographically indistinguishable iron formation intervals (Fe₂O₃T 21.4 wt.%) likely represent cogenetic hydrothermal sedimentary units because they display a common geochemical signature: Fe₂O₃T = 42.9 ± 10.5 wt.%, MnO = 5.4 ± 3.1 wt.%, elevated base metal values (Zn+Pb = 1999 ± 1091 ppm), strong enrichment in additional exhalative components (CaO = 5.3 ± 3.9 wt.%; P₂O₅ = 1.43 ± 1.00 wt.%), oxidized signature (Fe/Mn = 10 ± 6), as well as a common immobile element signature (Zr/TiO₂ = 0.025 ± 0.007) representative of a pelagic source. The calc-alkaline to transitional host volcanic rocks can be discriminated by Zr/TiO₂, and to a lesser extent by Th/Nb: Nepisiguit Falls Formation: Zr/TiO₂ = 0.053 ± 0.004, Th/Nb = 1.08 ± 0.37; Flat Landing Brook Formation: Zr/TiO₂ = 0.107 ± 0.043, Th/Nb = 0.86 ± 0.17. A symmetrical repetition of the footwall–iron formation–hanging wall stratigraphic sequence is observed in DDH-B357, with distinct felsic volcanic rock domains separated by the three iron formations. This is best explained by parasitic F₂ folds on the west flank of the south-plunging Brunswick antiform, similar to the fold closures known to host massive sulfide accumulations in the Brunswick No. 6 and No. 12 mines. Iron formation geochemistry and felsic volcanic rock chemostratigraphy from drill core sampling can provide an effective mineral exploration tool for the structurally complex rocks of the Bathurst Mining Camp.