Linking the Siberian Flood Basalts and Giant Ni‐Cu‐PGE Sulfide Deposits at Norilsk

• Published in: Journal of geophysical research. Solid earth Vol. 126; no. 3
• Main Authors: Yao, Zhuo‐sen, Mungall, James E.
• Format: Journal Article
• Language: English
• Published: 01-03-2021
• Subjects: fluid dynamics simulation; Norilsk‐Talnakh deposits; shallow dike‐sill transition; Siberian LIP; sulfide‐laden magma; two‐stage assimilation
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2020JB020823

The world‐class magmatic sulfide deposits in the Norilsk region exhibit a remarkable spatial and temporal association with the Siberian large igneous province (LIP). However, the details of the causal connection between the Siberian LIP and the ore deposits have remained contentious. Here we address the problem by modeling of assimilation, crystallization and flow behavior of magmas based on aggregated data from the Norilsk camp. Crustal assimilation at depth by mantle‐derived picritic magma can account for the compositional and isotopic variations of the early tholeiitic basalts and the sequestering of sulfide liquid in a mid‐crustal conduit system. When the rate and volume of asthenospheric magma production dramatically increased, the metal tenors of the mid‐crustal sulfide reservoir were first upgraded by consequent reaction with the fresh, undepleted magmas, then entrained and flushed to higher crustal levels. The resulting sulfide‐rich emulsions were too dense to reach the surface to form lavas but were instead emplaced in multiple pulses within blind sill‐like bodies at shallow depth. Sulfide ores transported from the mid‐crust were deposited at the bases of the upper‐crustal sills, where sedimentary host rocks were assimilated wholesale by the already sulfide‐charged replenishing magmas; this shallow assimilation was itself not instrumental in forming the ores. Although the evolution and dynamics of flood basalts are thus inextricably linked with coeval subvolcanic economic intrusions, the mineralization itself is argued not to occupy feeders with direct links to the overlying lavas, suggesting major implications for exploration in other LIPs.
Plain Language Summary
The Siberian Large Igneous Province is the largest subaerial accumulation of volcanic rocks on Earth. Its associated magmatic activity generated Norilsk Ni‐Cu‐Pd‐Pt deposit group, which is the world's single most valuable concentration of mineral deposits. It also caused emissions of widely thought to have provoked the most catastrophic mass extinction event in the history of multicellular life on Earth. In this work we propose a new model for the origins of the mineral deposits that honors the entirety of the available geochemical, petrological, and structural data. We suggest that the ore‐forming magmatic sulfide liquid initially formed in the mid‐crust and later was elevated to its current site immediately beneath the pile of lava flows by a major increase in the rate of magma production after a brief hiatus in magmatism. The ores were emplaced as dense slurries of crystals and globules of immiscible sulfide liquid carried by the freshly introduced basaltic magma. Whereas they are commonly referred to as feeders through which magma flowed before erupting to form the stack of lavas, also termed chonoliths, we argue that, due to their high density, these intrusions failed to reach the surface and therefore cannot be regarded as flow‐through systems.
Key Points
Causal connection between Norilsk‐Talnakh deposits and overlying Siberian large igneous province (LIP)
Flow behavior of sulfide‐laden magma during sill‐dike transition and emplacement
Re‐entrainment of sulfides from deep‐seated reservoir into blind sill‐like body