Olivine and pyroxene as evidences of petrology and mineral resource of basic–ultrabasic intrusions in the Norilsk area, Siberian Traps Province

The Norilsk region, the largest metallogenic province in the world, is located in the northern part of Eastern Siberia. This area contains many basic–ultrabasic intrusive bodies related to the Siberian Traps, some of which contain very rich platinum-group element (PGE)–copper–nickel ore deposits, such as Talnakh, Oktyabr'sky, and Norilsk 1. To discover new massifs with sulfide mineralization, the composition of rock-forming minerals, such as olivine and pyroxene, was studied using EPMA, LA ICP-MS, and SIMS methods in ten intrusive bodies with different volumes of sulfide mineralization. It was found that all the massifs exhibit strong variations in mineral composition across vertical cross-sections: olivine varies from Fo₈₂ to Fo₄₃ and pyroxene changes from Mg# 87 to Mg# 52. Additionally, for the first time, it was shown that the composition of minerals within each horizon (picritic, tacxitic, and olivine-bearing gabbro-dolerite) varies in trace elements, particularly in Ti for pyroxene and Ni and Y (HREEs) for olivine. Similar horizons from different intrusions, especially picritic ones, are characterized by different trends in the Fo (Mg#)-trace element coordinates on diagrams. This feature allows us to separate ore-bearing intrusions from all studied massifs. The specific features of intrusions with high sulfur content were demonstrated using statistical methods, as their olivine is enriched in Ni, Ca, Ti, and HREE as compared to barren intrusions. The composition of the parental melts of ore-bearing intrusions was determined by studying melt inclusions in olivine and pyroxene, which corresponds to typical intraplate magmas with normal volatile component contents (H₂O, CO₂, Cl, B). Thus, mineral compositions, rather than rock compositions, aid in recognizing mineralized intrusions. This seems to be based on the difference in f_O2 of barren and sulfide-containing magmas during crystallization.

This study was supported by state assignment of the Ministry of Science and High Education of Russian Federation for GEOKHI RAS.