Sulfide Immiscibility Induced by Wall-Rock Assimilation in a Fault-Guided Basaltic Feeder System, Franklin Large Igneous Province, Victoria Island (Arctic Canada)

Ben Hayes,Jean H Bédard,Boswell Wing,Peter Nabelek,C Johan Lissenberg,William D Macdonald,Matthew Hryciuk

doi:10.2113/econgeo.110.7.1697

Abstract

The 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 δ34S 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.

Highlights

The Southern Feeder Dike Complex on Victoria Island in the Canadian Arctic is part of the Franklin Large Igneous Province (LIP), which extends across northern Canada and into Greenland
The part of the Franklin LIP exposed on Victoria Island is primarily composed of gabbroic sills, with subordinate NNW- to NW-trending feeder dikes
Igneous breccias cemented by basalt and drag folds within wall rocks indicate that Franklin magmas were emplaced contemporaneously with regional Neoproterozoic normal faulting

Summary

Introduction

Dike-like magma conduits are dynamic systems that provide opportunities for magma-crust interaction (Naldrett, 1992; Li et al, 2000; Maier et al, 2001; Mungall, 2007; Ding et al, 2010; Hughes et al, 2015; Lightfoot and Evans-Lamswood, 2015) and are important sites of Fe-Ni-Cu mineralization (Naldrett, 1992; Ripley and Li, 2011). In conduit-type deposits, upgrading would most likely occur in open magmatic systems, whereas previously concentrated sulfide melt would see its metal tenor upgraded during magma throughflow (Naldrett, 1992, 2004)

Methods

Discussion

Conclusion