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

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 δ 34 S 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.

Distinct sulfur saturation histories within the Palaeogene Magilligan Sill, Northern Ireland: implications for Ni – Cu – platinum group element mineralisation in the North Atlantic Igneous Province

“…13), the source composition of the magma supply in the conduit system shifted to a more primitive composition so that subsequent magma replenishment in the Magilligan Sill formed the olivine gabbros. S-saturation likely occurred earlier (perhaps deeper) in the magma plumbing system, as indicated by the upgrading processes envisaged for sulfides in the olivine interpreted in a similar way, also featuring evidence of conduit-focused magma replenishment and sulfide cycling at different depths in its plumbing system (Hayes et al 2015). Given that the second-generation sulfides contain PGE, Ni, Cu, Co, and Ag, a higher volume concentration of in situ mineralisation of similar or higher tenor nearer the depth at which Ssaturation occurred could provide an interesting target for further exploration, despite the Magilligan Sill itself being sub-economic.…”

“…Sulfide liquids formed during contamination-driven S-saturation in the ascending magma may be cycled upwards in the plumbing system by subsequent magma pulses, towards their final resting horizon (e.g. Hayes et al 2015). This will subject them to multistage dissolution upgrading, wherein the sulfides are partially dissolved during transportation, reducing their volume and S content while retaining their chalcophile element concentrations (e.g.…”

Application of Gravity Survey for Tin Exploration at Bongsu Granite, Kulim, Kedah, Malaysia

“…The THD regional gravity anomaly map ( Figure 5) shows dominantly three elliptical high anomalies which indicate either nearly vertical rock boundaries or faults in deep subsurface. These faults are considered as deep source of geothermal area including magma feeders (Hayes et al 2015;Salem et al 2005;Vigneresse et al 1996). The THD residual gravity anomaly map ( Figure 5) shows at least two prominent bending lines tipping southeastward and three ring features of high anomalies.…”

Serial interaction of primitive magmas with felsic and mafic crust recorded by gabbroic dikes from the Antarctic extension of the Karoo large igneous province

“…Such interactions are likely to be concentrated in magma chambers and conduits within intermediate to deep (≥ 10 km) crust, where the residence times are longer and the wallrock is warmer, compared to shallower systems (e.g., Tegner et al 2005;Heinonen et al 2019). Nevertheless, evidence of assimilation has also been observed or indicated for some shallower feeder systems (e.g., Lightfoot and Naldrett 1989;Neumann et al 2011;Yallup et al 2013;Hayes et al 2015). Overall, as the magmas travel through a lithologically and geochemically heterogeneous lithosphere, multiple stages of contamination may take place (see, e.g., Neumann et al 2011).…”