Open Collections

Miller, Emily Ann

University of British Columbia

The Stewart-Iskut district contains a >200 km long belt of porphyry Cu-Au and epithermal Au mineralisation hosted in the Stikine Terrane of northwestern British Columbia. The porphyry deposits in the district are associated with a short-lived, (~6 M.y.) but significant, latest Triassic to Early Jurassic tectono-magmatic shift during which time most of the known copper resources in British Columbia accumulated. The tectonic and structural setting of porphyry emplacement in the region is obscured by mid-Cretaceous shortening related to the formation of the east-vergent Skeena fold-and-thrust belt and later Eocene deformation. Recent studies in this district propose that small, pull-apart basins served to localise emplacement of the Kerr-Sulphurets-Mitchell Cu-Au porphyry systems. The Big Bulk Cu-Au porphyry deposit is located near the southern extent of the Stewart-Iskut district in the Kitsault River Map area, 50 km southeast of Stewart. Detailed mapping (1:10,000 scale) in the area recognised conglomerates at the base of the Hazelton Group, informally referred to herein as the Kinskuch conglomerates, which contain locally-derived megaclasts (up to 120 m long). They are bound to the west by a prominent northeast-trending dextral fault (Tabletop fault). We propose that the Tabletop fault, and likely other faults in the area, had an early (latest Triassic) history with oblique strike-slip movement, and that releasing step-overs, splays, or double bends in this fault network created a local zone of north-south extension, easterly trending normal faults, and local pull-apart basin into which the Kinskuch conglomerate was deposited. The multi-phase Big Bulk diorite stock (204.61±0.18 Ma, CA-TIMS, U-Pb zircon), which hosts the Big Bulk porphyry system, cuts the lower part of the Hazelton Group and was emplaced in the southern portion of the proposed basin. The east-west elongated geometry of the Big Bulk stock and east-west orientation of sheeted porphyry-related veins are consistent with emplacement along easterly-trending normal faults and/or emplacement under north-south directed extension, consistent with that proposed for the pull-apart basin. Hence, like other porphyry deposits in the district, a local pull-apart basin appears to have influenced or controlled emplacement of the Big Bulk porphyry system.

Text

2024-01-10

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87205

Geological Sciences

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/