Structural, lithological, and geochemical constraints on the dynamic magma plumbing system of the Jinchuan Ni-Cu sulfide deposit, NW China
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Song, X-Y and Danyushevsky, LV and Keays, RR and Chen, L-M and Wang, Y-S and Tian, Y-L and Xiao, J-F, Structural, lithological, and geochemical constraints on the dynamic magma plumbing system of the Jinchuan Ni-Cu sulfide deposit, NW China, Mineralium Deposita, 47, (3) pp. 277-297. ISSN 0026-4598 (2012) [Refereed Article]
Copyright 2011 Springer-Verlag
Eastern and western portions of the Jinchuan ultramafic intrusion have previously been interpreted as dismembered segments of a single elongate intrusion by late faults. However, the different stratigraphic sequences of the two portions indicate that they are originally two separate intrusions, referred to as Eastern and Western intrusions in this study. The Eastern intrusion is characterized by a concentric distribution of rock types with a core of sulfide dunite enveloped by lherzolite, whereas the Western intrusion is composed of the Upper and Lower units, interpreted as magmatic mega cycles with regular variations in lithology and chemistry. In the Western intrusion, the Upper unit consists of fine-grained dunite, lherzolite, and pyroxenite from its base to its top. The MgO contents decrease upward from the dunites (42-45 wt.%) to the lherzolites (36-41 wt.%), while Al 2O 3 and incompatible elements increase upward. In contrast, the Lower unit consists of coarse-grained dunites and lherzolites containing 37-40 and 28-35 wt.% MgO, respectively. Sharp contacts between the Upper and Lower units and fine-grained dunite xenoliths at the top of the Lower unit indicate that the Lower unit intruded along the base of the Upper unit. Disseminated and net-textured sulfides primarily occur in the Lower unit and comprise the no. 24 ore body. Very low S contents (<100 ppm) of the wall rocks at Jinchuan indicate that they were not the source of S causing sulfide immiscibility. Sulfide segregation more likely occurred in deep-seated magma chambers, and sulfides were deposited in the Western intrusion when sulfide-bearing magmas passed through the intrusion. In contrast, the Eastern intrusion was formed by injections of sulfide-free and sulfide-bearing olivine-crystal mushes, respectively, from another deep-seated staging magma chamber. The Eastern and Western intrusions and the deep-seated magma chambers comprise a complicated magma plumbing system at Jinchuan. Normal faults played a significant role in the formation of the magma plumbing system and provided pathways for the magmas. © 2011 Springer-Verlag.
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