Understanding Sulfide Mineralization in the Reinfjord Ultramafic Complex: Field study, microanalysis and thermodynamic modeling

Sulfide minerals are important from both resource and environmental perspectives, as they constitute a wide-range of exploitable metals and are the primary constituent of acid rock drainage. The Reinfjord Ultramafic Complex (RUC) in Northern Norway consists of layered dunites, wehrlites and olivine clinopyroxenites, formed through a series of magmatic recharge events. The RUC is a part of the Seiland Igneous Province (SIP), which comprises over 50,000 km³of mafic, ultramafic and alkaline melts that were emplaced into the lower continental crust under an extensional regime at about 560 - 570 Ma at pressures of 0.8-1 GPa. Understanding the genesis of sulfide mineralizations within the RUC and SIP can allow us to better predict and describe the occurrence of sulfide mineralizations at these uncommonly exposed depths of magmatic ore-forming activity. This study uses detailed mapping and field relations, as well as light microscopy, quantitative EDS and XRD analysis, and thermodynamic modeling to describe the formation of the sulfide mineralizations in a specific magmatic, metamorphic, and structural geological setting. We find that sulfide mineralizations formed at multiple events during the development of the RUC, both at the magmatic stage and subsequently when magmatic volatiles infiltrated the lithologies at 550 - 650°C and approximately 0.6 Gpa.