Critical Controls on the Formation of Contact-Style PGE-Ni-Cu Mineralization: Evidence from the Paleoproterozoic Monchegorsk Complex, Kola Region, Russia

Abstract

The Paleoproterozoic Monchegorsk Complex, located in the Russian part of the Fennoscandian Shield, constitutes one of the largest mafic-ultramafic layered intrusions in Europe. The complex hosts extensive contact-style PGE-Ni-Cu sulfide mineralization along its margin, irrespective of the host lithology, which ranges from peridotite to pyroxenite and gabbronorite. The mineralized intervals reach up to 3 ppm Pt + Pd and attain a thickness of up to 50 m in the central portions of the intrusion, thinning towards the periphery. Our study shows that the key process controlling the size and grade of a contactstyle deposit in the Monchegorsk Complex, was the efficiency of sulfide collection in distinct zones of the intrusion. Strongly mineralized basal contacts are always associated with intense brecciation and the presence of large amounts of felsic pegmatite, suggesting a multi-stage emplacement of the mafic-ultramafic succession. Thermal modeling demonstrates that multiple episodes of magma influx are required to allow for significant partial melting of the basement. Moreover, the interaction between magma and basement led to the local addition of water and potentially carbon dioxide to the magma, resulting in partial melting of cumulus phases and a reduction in viscosity of the interstitial melt. This increased the porosity of the mush in the vicinity of the lower intrusion contact, which promoted preferential sulfide liquid accumulation at the base, while the local decrease in magma viscosity facilitated gravitational settling of sulfide droplets. These factors led to an efficient collection of sulfide liquid, especially in the center of the complex, where permeability was maintained the longest due to slower cooling relative to more peripheral parts.

Low-Sulfide Platinum–Palladium Deposits of the Paleoproterozoic Fedorova–Pana Layered Complex, Kola Region, Russia

“…The remaining ore samples of the Fedorova-Pana Complex have similar patterns to those of gabbronorite from the marginal zone at Mt. Travyanaya and to the metagabbronorite of the Vuruchuayvench massif of the Monchegorsk Complex ( Figure 7E,F) [60,61]. Notably, most samples from Fedorova-Pana are characterized by relatively strong negative Nb-Ta anomalies similar to the Monchegorsk Complex [60]; however, the exceptionally primitive reefs of the Fedorova intrusion ( Figure 7B) as well as the most primitive ophitic orthopyroxenite from Monchegorsk ( Figure 10B in [60]) lack this feature, which may indicate that the parental magma to the most primitive rocks at both intrusions may not have necessarily featured a negative Nb-Ta anomaly.…”

The Main Anorthosite Layer of the West-Pana Intrusion, Kola Region: Geology and U-Pb Age Dating

“…Assuming that the most significant PGE enrichments in the Kola Region are associated with additional intrusions of sulfide-saturated and somewhat PGE-enriched magmas, as suggested for the Monchegorsk Complex [45,46] and the Fedorova intrusion [1], it is likely that the gabbronorites, overlying the Main Anorthosite Layer, also formed as a result of a late-stage intrusion of sulfide-saturated, PGE-enriched magma into the pre-existing cumulate pile. Further evidence for this mechanism is provided by the presence of a thin, discontinuous norite layer, as well as abundant hornfels xenoliths directly above the anorthosite layer ( Figure 3).…”

“…Further evidence for this mechanism is provided by the presence of a thin, discontinuous norite layer, as well as abundant hornfels xenoliths directly above the anorthosite layer ( Figure 3). This late-stage intrusion may have led to the infiltration of PGE-enriched sulfide melt into the interstitial space of the underlying anorthosite cumulates [47,48], somewhat similar to contact-style sulfide mineralization, infiltrating basement lithologies that are in direct contact with the intrusion [46,49].…”

Программное Приложение Для Термального Моделирования Интрузий

“…Предпосылкой разработки приложения для термального моделирования явилась гипотеза о критическом значении температурного фактора при формировании контактовых месторождений элементов платиновой группы в расслоенных интрузиях (Karykowski et al, 2018). Такие месторождения приурочены к мафит-ультрамафитовым расслоенным комплексам, которые, как правило, были образованы в результате нескольких внедрений магмы.…”

“…где n i T -температура на глубине i×Dx м через n×Dt лет. Подробный вывод уравнения приведён в (Karykowski et al, 2018). Вся моделируемая толща мощностью H (м) разбивается на элементарные слои толщиной Dx (м), в каждом из которых температура принимается постоянной.…”