Magmatic Ni-Cu-(PGE) deposits in magma plumbing systems: Features, formation and exploration

The three most crucial factors for the formation of large and super-large magmatic sulfide deposits are: (1) a large volume of mantle-derived mafic-ultramafic magmas that participated in the formation of the deposits; (2) fractional crystallization and crustal contamination, particularly the input of sulfur from crustal rocks, resulting in sulfide immiscibility and segregation; and (3) the timing of sulfide concentration in the intrusion. The super-large magmatic Ni-Cu sulfide deposits around the world have been found in small mafic-ultramafic intrusions, except for the Sudbury deposit. Studies in the past decade indicated that the intrusions hosting large and super-large magmatic sulfide deposits occur in magma conduits, such as those in China, including Jinchuan (Gansu), Yangliuping (Sichuan), Kalatongke (Xinjiang), and Hongqiling (Jilin). Magma conduits as open magma systems provide a perfect environment for extensive concentration of immiscible sulfide melts, which have been found to occur along deep regional faults. The origin of many mantle-derived magmas is closely associated with mantle plumes, intracontinental rifts, or post-collisional extension. Although it has been confirmed that sulfide immiscibility results from crustal contamination, grades of sulfide ores are also related to the nature of the parental magmas, the ratio between silicate magma and immiscible sulfide melt, the reaction between the sulfide melts and newly injected silicate magmas, and fractionation of the sulfide melt. The field relationships of the ore-bearing intrusion and the sulfide ore body are controlled by the geological features of the wall rocks. In this paper, we attempt to demonstrate the general characteristics, formation mechanism, tectonic settings, and indicators of magmatic sulfide deposits occurring in magmatic conduits which would provide guidelines for further exploration

The origin of the Zhubumafic-ultramafic intrusion of the Emeishan large igneous province, SW China: Insights from volatile compositions and C-Hf-Sr-Nd isotopes

The Zhubu mafic-ultramafic intrusion of the Permian Emeishan large igneous province (LIP), SW China hosts a magmatic Ni, Cu and platinum-group element (PGE) deposit. It consists of a layered sequence with sub-horizontal modal layering wrapped by a sub-vertical marginal zone. Our new zircon U-Pb isotopic dating gives a mean age of 263.2 +/- 5.6 Ma for the layered sequence. The volatiles extracted from the mineral separates of the Zhubu intrusion are composed of predominant H2O (11,769.84 mm(3) . STP/g, STP-standard temperature and pressure) and minor H-2 and CO2. The layered sequence has lower H2O but higher H-2, CO2, H2S and SO2 contents than themarginal zone. The CO2 and CH4 extracted at 400-900 degrees C and 900-1200 degrees C have light delta(CCO2)-C-13 varying from 17.45% to-7.10% and delta(CCH4)-C-13 varying from - 41.35% to - 22.88%. The pyroxene separates have significantly lower (Sr-87/Sr-86)(i) values (0.705882 to 0.708912) and slightly higher e(Nd) (t= 263 Ma) values (-2.8 to 0.7) than the whole rocks. The epsilon(Hf) (t= 263 Ma) values of zircon crystals vary from-3.05 to+1.90. The chemical compositions of volatiles from the Zhubu intrusion indicate a slightly reduced condition and aH(2)O-rich parentalmagma. The C-Hf-Sr-Nd isotopes for the Zhubu intrusion are consistent with similar to 15 wt% assimilation of the upper crust by a mantle-derived magma. The carbon isotopes indicate that a thermogenic component from sedimentary organic materials was present in the contaminated magma. A weak positive correlation between volatile and PGE contents, together with the C-Hf-Sr-Nd isotopes, indicates that sulfide saturation in the Zhubu magmawas triggered by crustal contamination including the addition of volatiles. (C) 2017 Elsevier B. V. All rights reserved