Field Relationships and Geochemical Constraints on the Emplacement of the Jinchuan Intrusion and its Ni-Cu-PGE Sulfide Deposit, Gansu, China

Abstract

International audienceField mapping and petrological-geochemical investigation of the Jinchuan intrusion in north-central China clarifies how the intrusion was emplaced and provides a new model that explains how its large and rich Ni-Cu-platinoid deposits may have formed. The intrusion was emplaced into high-grade gneisses and marbles along a disconformity at the base of an overlying cover sequence, indicating that it was emplaced as a sill, not a near-vertical dike, as previously proposed. After emplacement the intrusion was rotated to its present orientation and deformed and metamorphosed under greenschist-facies conditions. Relative enrichment of incompatible trace elements coupled with negative U-Th and Nb-Ta anomalies in all samples from the intrusion provide evidence that the parental magma assimilated granitoid rocks in the lower crust. The presence of abundant marble xenoliths, now decarbonatized to diopside-rich skarns, and chemical indices such as high CaO/SiO2, indicate that the magma assimilated carbonate on reaching its present site. This contamination may be linked to the formation of the Ni-Cu platinoid ores. We propose that the assimilation of carbonate-rich fluids increased the oxygen fugacity of the magma and led to the segregation of metal-rich sulfides

The Uitkomst intrusion and Nkomati Ni-Cu-Cr-PGE deposit, South Africa: trace element geochemistry, Nd isotopes and high-precision geochronology

“…Several important magmatic ore deposits are associated with carbonaceous rocks, such as the Platreef/Flatreef of the Bushveld Complex (McDonald and Holwell 2011), the Noril'sk I (Naldrett and Li 2009), Jinchuan (Lehmann et al 2007), and Aguablanca Ni-Cu sulphide deposits (Piña et al 2009), and the Panzihua magnetite deposit in China (Ganino et al 2008). We propose that in all these cases, devolatisation of floor carbonate played an important, and possibly critical role in ore formation.…”

Multiple S isotopes, zircon Hf isotopes, whole-rock Sr-Nd isotopes, and spatial variations of PGE tenors in the Jinchuan Ni-Cu-PGE deposit, NW China

“…2c). However, based on structural reconstruction, some researchers Lehmann et al 2007) believe that the original geometry of the Jinchuan intrusion was a subhorizontal sheet. The four major fault-bounded segments of the Jinchuan intrusion from west to east were numbered as ΙΙΙ, Ι, ΙΙ, and ΙV by the mine geologists based on the order of mine development (Fig.…”

“…However, such models require a dyke-like geometry for each of the ore zones that have different PGE tenors. Detailed mapping shows that the original geometry of the Jinchuan intrusion is more likely a subhorizontal sheet for most parts of the intrusion (Lehmann et al 2007).…”

“…It contains more than 500 million metric tons of ores with 1.1 wt% Ni and 0.7 wt% Cu (Tang et al 2009). Recently, many studies on the deposit and its host intrusion have been carried out (e.g., Chai and Naldrett 1992a, b;Chen et al 2013;de Waal et al 2004;Li et al 2004;Lehmann et al 2007;Song et al 2006Song et al , 2009Song et al , 2012Su et al 2008;Tang 1993;Tonnelier 2010). These studies have improved our understanding of the genetic relationship between magma evolution and ore genesis.…”

How did the Alxa Block respond to the Indo-Eurasian collision?

“…A strike-slip fault along the northern foothills of the Longshoushan is the main fault in the famous Jinchuan nickel mine in Gansu province (Lehmann et al 2007); this fault was active in the late Cenozoic, and minor (Fig. 1).…”