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TitleSulfide immiscibility induced by wall-rock assimilation in a fault-guided basaltic feeder system, Franklin Large Igneous Province, Victoria Island (Arctic Canada)
AuthorHayes, B; Bédard, J H; Hryciuk, M; Wing, B; Nabelek, P; MacDonald, W D; Lissenberg, C J
SourceEconomic geology and the bulletin of the Society of Economic Geologists vol. 110, 2015 p. 1697-1717, Open Access logo Open Access
Alt SeriesEarth Sciences Sector, Contribution Series 20140542
PublisherSociety of Economic Geologists
Mediapaper; on-line; digital
File formatpdf
AreaVictoria Island
Lat/Long WENS-120.0000 -107.0000 73.0000 71.0000
Subjectsigneous and metamorphic petrology; igneous rocks; igneous petrology; magmatism; dykes; diabase dykes; dykes, mafic; sills; petrography; petrographic analyses; Franklin Lip; Franklin Large Igneous Province; Minto Inlier
Illustrationslocation maps; tables; block diagrams; plots; stereonets
ProgramGEM: Geo-mapping for Energy and Minerals PGE/Base Metals - Victoria Island (NWT and Nunavut)
Released2015 09 22
AbstractThe Southern Feeder Dike Complex is part of the Franklin Large Igneous Province (LIP), exposed in the Minto Inlier of Victoria Island in the Canadian Arctic. Previous field and geochemical studies on the Franklin LIP considered its igneous rocks to be prospective for Fe-Ni-Cu mineralization. The Southern Feeder Dike Complex comprises a series of NW-SE-trending gabbroic intrusions and sedimentary hosts. Field and textural relationships show that the Complex intrusions were emplaced contemporaneously with Neoproterozoic normal faulting. Faulted contact zones correspond to prominent first derivative magnetic lineaments. Gabbroic dikes have intrusive contacts against brecciated country rock, and diabasic microxenoliths in basaltic matrices indicate multiple intrusive/brecciation events. Intrusive breccias are commonly overprinted by hydrothermal greenschist facies assemblages, with calcite + pyrite veins filling open spaces between breccia fragments. Late dikes emplaced into these heterogeneous breccias contain disseminated globular and net-textured sulfides suggesting that sulfide immiscibility was triggered on a local scale by assimilation of local wall rock. This inference is supported by elevated d34S values of sulfides in these dikes, consistent with assimilation of country rocks. Wall-rock assimilation would have been facilitated by fault-related brecciation and cataclasis, which would expose extensive xenolith surface areas to fresh magma. Gossanous and meter-scale semimassive sulfide showings associated with dikes and sills located upsection from the Southern Feeder Dike Complex suggest that immiscible sulfide liquids may have been flushed downstream (or upsection) during replenishment of composite dike systems. Fault-mediated melt ascent along northwest-southeast faults has been documented elsewhere in the Minto Inlier, providing equivalent opportunities for wall-rock assimilation and consequent triggering of sulfide immiscibility and sulfide melt redistribution. The evidence preserved in the Complex confirms the Fe-Ni-Cu potential of the Franklin LIP and informs current models of ore deposit formation in conduit-type magmatic plumbing systems.
Summary(Plain Language Summary, not published)
This paper provides detailed observations of a fault-guided magmatic feeder system to the Franklin magmatic suite on Victoria island. Some of the basaltic intrusions have elevated sulfur isotope signatures (34S) and contain immiscible blebs of sulfide, suggesting that assimilation of sedimentary wallrock triggered sulfide immiscibility. This implies that Franklin magmas with elevated 34S isotopic signatures may be most prospective for Cu-Ni-PGE deposits.

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