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Gao J.-F.,University of Hong Kong | Zhou M.-F.,University of Hong Kong | Zhou M.-F.,Chinese Academy of science | Lightfoot P.C.,Vale | And 2 more authors.
Economic Geology | Year: 2012

The Kalatongke Cu-Ni sulfide deposit in the Paleozoic Altay orogenic belt, NW China, is hosted in a Permian mafic intrusion consisting of norite, troctolite, gabbro, and diorite. Disseminated Ni-Cu, massive Ni-Cu, and massive Cu-rich sulfide ores are mainly hosted in norite and gabbro. Some massive Ni-Cu ores also occur in the Carboniferous sedimentary rocks. The geologic and compositional relationships between various sulfide ores and the rocks of Kalatongke offer a new interpretation of the sequence of emplacement of the magmas, which underpins an understanding of the compositions of the ores and the formation of the Kalatongke deposit. Olivine grains from disseminated Ni-Cu ores have Fo values ranging from 71.6 to 78.0 mol % and Ni contents from 1,000 to 2,200 ppm. Typically, Ni decreases from the cores to the rims from 2,000 to 1,000 ppm at constant Fo content, indicating the reaction of early-formed olivine with later-segregated sulfide melt. Cr spinels at Kalatongke are highly enriched in Fe 3+ and Fe 2+, with relatively low Cr, Al, and Ti, reflecting reaction with evolved trapped intercumulus melt. Norites are depleted in Nb, Ta, Zr, Hf, and Th and enriched in Sr and Ba, whereas disseminated Ni-Cu sulfide ores have considerable depletion of Rb and enrichment of Sr and Ba and lack depletion of Nb, Ta, Zr, and Hf, indicating their different origins. Disseminated Ni-Cu sulfide ores have bulk compositions with variable Cu and Ni contents which are much lower than those of massive Cu-rich and Ni-Cu ores, but disseminated and massive Ni-Cu ores have similar PGE contents with relatively low Pd/Ir ratios. Massive Cu-rich ores have much higher Pd and Pt with very high Pd/Ir ratios. The Kalatongke Cu-Ni sulfide deposit appears to have formed from two different pulses of PGE-poor and Cu-rich basaltic magmas that underwent different degrees of assimilation and fractional crystallization. The first magma pulse gained sulfide saturation because of minor crustal contamination and fractionated a small amount of sulfide (<0.03%); the evolved melt then intruded and assimilated crustal materials to attain sulfide saturation again. Sulfide liquid segregated from the magma to form the massive sulfide melts and residual magma formed the noritic rocks in the shallow magma chamber. The segregated massive sulfide melts then underwent further fractionation to form massive Ni-Cu and massive Cu-rich ores. The second pulse of magma after removal of sulfides (<0.02%) experienced more crustal contamination and re attained S saturation. This new S-saturated and phenocryst-laden magma intruded the earlier formed massive sulfide ores and norites and formed the disseminated sulfide ores. © 2012 Society of Economic Geologists, Inc. Source

Deposits of Ni-Cu-Co-(PGE) sulfide often occur in association with small differentiated intrusions that reside within local transtensional spaces in strike-slip fault zones. These faults often develop in response to incipient rifting of the crust and the development of large igneous provinces due to far-field stresses generated by plume-induced continental drift. We review the geology of a number of large and small nickel sulfide deposits and the associated intrusions, and show that the geometry of the host intrusion and localization of the mineral zones can be classified into three main groups. Further, we show that the morphology of each is controlled by space created in response to deformation on structures. One group of intrusions has the plan shape of an asymmetric rhomboid with the long axis sub-parallel to a fault zone, and contacts which have often been structurally modified during and/or after emplacement of themagma. The typical cross section is a downward-closing cone shape with curved walls and often a dyke-like keel at the base. This morphology is found in the Ovoid and Discovery Hill Zones of the Voisey's Bay Deposit (Canada), the Jinchuan, Huangshan, Huangshandong, Hongqiling, Limahe, Qingquanshan, and Jingbulake (Qingbulake) Intrusions in China, and the Eagle and Eagle's Nest deposits in the USA and Canada, respectively. A second group of deposits is associated with conduits within dyke and sheet-like intrusions; these deposits are often associated with discontinuities in the dyke which were created in response to structural controls during emplacement. Examples include the Discovery Hill Deposit and the Reid Brook Zone of the Voisey's Bay Intrusion, where there are plunging domains of thicker dyke which control the mineralization inside the dyke, and thin discontinuous segments of the dyke which are associated with structurally controlled mineralization in the surrounding country rock gneisses. The Oktyabrysk, Taimyrsk, Komsomolsk, and Gluboky Deposits in the Noril'sk Region of Russia are localized at the base of thicker parts of the Kharaelakh Intrusionwhich appear to be a conduit that follows synformal features in the country rocks located west of the Noril'sk-Kharaelakh Fault. Other examples of dyke-like bodies with both variation inwidth and the development of discontinuities are the Copper Cliff and Worthington Offset Dykes which radiate away from the Sudbury Igneous Complex (Canada). The distribution of ore bodies in these Sudbury Offset Dykes is principally controlled by variations in the thickness of the dyke, interpreted to reflect the presence of conduits within the dyke. A third group ofmineralized intrusions locatedwithin structural corridors have the geometry of oblate tubes; examples include Kalatongke in China, Northeastern Talnakh and Noril'sk 1 in Russia, Babel-Nebo in Australia, and Nkomati in South Africa. Sometimes these oblate tube-like intrusions formin bridging structures between larger intrusions hosted in themore significant structures. Examples include the Tamarack Intrusion in Minnesota, USA, and the Current Lake Complex in Ontario, Canada, both ofwhich containmagmatic Ni-Cu sulfide mineralization. In all of these deposits, the intrusions appear to be open system magma pathways, and so the term "chonolith" can be applied to describe them as a group. All of these intrusions are characterized by a high ratio of sulfide/silicate; there are 1-3 orders ofmagnitude more sulfide in the intrusion than themagma contained in the intrusion is capable of dissolving. The formation of these deposits is considered to have taken place in open systemmagma conduits. It is possible that the metal tenor of the sulfideswere upgraded by equilibration of successive batches of silicate magma passing through the conduit, and equilibrating with a stationary pool of magmatic sulfide. At Voisey's Bay there appears little doubt that the sulfides were injected through a conduit dyke into higher level magma chambers. A similar model has been proposed for the formation of the deposits at Jinchuan and Noril'sk-Kharaelakh. Economically significant nickel sulfide deposits that tend to be high in Ni tenor, are often related to the late injection ofmagma that formdistinct parts of the intrusion, and the localization of mineralization tends to be related to changes in the geometry of the magma chamber. Strongly deformed and metamorphosed komatiite-associated deposits (e.g. Pechenga, Thompson, and the Yilgarn komatiite associations)appear to be the remains of open system magma conduits which are now represented by segmented and boudinaged ultramafic bodies as a result of more than 4 phases of post-emplacement deformation. LIP activity at craton margins has long been recognized as a key control on the genesis of magmatic sulfide deposits; we showthat the principal regional controls of strike-slip tectonics underpin the local geometry of the intrusions, and we provide an explanation for why so many of the global nickel sulfide ore deposits are associated with intrusions that share commonmorphologies and characteristics. Thismodel provides a framework for more detailed structural investigations of nickel sulfide deposits, and it is a predictive framework for mineral exploration. © 2014 Elsevier B.V. Source

Shnorhokian S.,McGill University | Mitri H.S.,McGill University | Thibodeau D.,Vale
International Journal of Rock Mechanics and Mining Sciences | Year: 2014

Numerical models are increasingly being used to assess the stability of mine openings, and forming an integral part of operational and safety decisions. A key factor in obtaining realistic model results is the correct simulation of the pre-mining stress regime in a heterogeneous rockmass with complex geometries. When in-situ stress measurement results are available, or if an estimate can be made based on the vertical stress gradient in the region, the model can be calibrated based on these values and relied upon to replicate the rockmass behavior in the field. The calibration of a numerical model with a heterogeneous rockmass cannot be reduced to analytical solutions due to the numerous variables involved, especially under elastoplastic conditions or in the vicinity of geological structures. In this paper, a systematic and iterative calibration methodology is presented - based on two different methods of in-situ stress determination - that uses boundary tractions for a mine-wide numerical model of a deep Canadian mine. The effects of lateral and vertical model dimensions, as well as mesh density, are examined to verify the adaptability of the methodology to these changes under linear elastic conditions. In addition, the model is calibrated under elastoplastic conditions and in the presence of a shear zone. It is shown that regardless of any of the modifications, model calibration can be conducted with the proposed methodology. © 2014 Elsevier Ltd. Source

Lightfoot P.C.,Vale | Keays R.R.,Monash University | Evans-Lamswood D.,Vale Newfoundland and Labrador Ltd | Wheeler R.,Vale Newfoundland and Labrador Ltd
Mineralium Deposita | Year: 2012

The Voisey's Bay deposit is hosted in a 1.34-Ga intrusion composed of troctolite, olivine gabbro, and ferrogabbro. The sulfide mineralization is associated with magmatic breccias that are enveloped by weakly mineralized olivine gabbros and troctolites, and also occurs as veins along structures in adjacent paragneiss. A dyke is connected to the base of the north wall of the Eastern Deeps Intrusion, and the entry point of this dyke into the chamber is the locus of the Eastern Deeps nickel sulfide deposit. A detailed exploration in the area between the Eastern Deeps and the Ovoid has shown that these intrusions and ore deposits are connected by a splayed dyke. The Eastern Deeps Deposit is surrounded by a halo of moderately to weakly mineralized variable-textured troctolite (VTT) that reaches a maximum thickness above the axis of the Eastern Deeps Deposit along the northern wall of the Eastern Deeps Intrusion. The massive sulfides and breccia sulfides are petrologically and chemically different when compared to the disseminated sulfides in the VTT, and there is a marked break in Ni tenor of sulfide between the two. Sulfides hosted in the dyke tend to have low metal tenors ([Ni] 100 = 2.5-3. 5%), sulfides in Eastern Deeps massive and breccia ores have intermediate Ni tenors ([Ni] 100 = 3.5-4%), and disseminated sulfides in overlying rocks have high Ni tenors ([Ni] 100 = 4-8%). Four principal processes control the compositions of the Voisey's Bay sulfides. Coarse-grained loop-textured ores consisting of pyrrhotite crystals separated by chalcopyrite and pentlandite exhibit a two orders of magnitude variation in the Pd/Ir ratio which is due to mineralogical variations where pentlandite is enriched in Pd and Ir is dispersed throughout the mineral assemblage. A decrease in Ir and Rh from the margin of the Ovoid toward cubanite-rich parts at the central part of the Ovoid is consistent with fractionation of the sulfide from the margins toward the center of the Ovoid. The Ovoid ores have higher Ni and Pd tenor than the Eastern Deeps massive sulfides; this is consistent with both a higher R factor and greater degree of silicate parental magma evolution in the Ovoid than the Eastern Deeps. The disseminated sulfides surrounding the Eastern Deeps deposit have some of the highest Ni and Pd tenors at Voisey's Bay, which are indicative of not only more primitive magmas but also higher R factors than the Ovoid or the Eastern Deeps. VTT and normal-textured troctolite of the Eastern Deeps that contain trace sulfide have 0.1-3 ppb Pt and 0.1-3 ppb Pd, whereas weakly to heavily mineralized variable troctolites in the same unit have one to two orders of magnitude higher abundances of Pt and Pd. Troctolites and olivine gabbros from other parts of the Voisey's Bay Intrusion and other Nain Plutonic Suite Intrusions, including the Kiglapait, Newark Bay, Barth Island, Mushua, and Nain Bay South Intrusion, also have low platinum group element abundances. Although it is possible that this is a signature of a widespread sulfide saturation event that pre-dated ore formation at Voisey's Bay, it is more likely that platinum group element (PGE) depletion is a product of the source melting process where low degrees of melting resulted in the retention of PGE in the mantle source. If so, this indicates that PGE depletion should be used with caution as an exploration tool in the Nain Plutonic Suite. © 2011 Springer-Verlag. Source

Gao J.-F.,University of Hong Kong | Gao J.-F.,CAS Guangzhou Institute of Geochemistry | Zhou M.-F.,University of Hong Kong | Lightfoot P.C.,Vale | And 3 more authors.
Economic Geology | Year: 2013

The eastern Tianshan orogenic belt, northwestern China, hosts ∼120 mafic-ultramafic intrusions and at least six of them host significant Ni-Cu sulfide mineralization of which the Permian Huangshandong intrusion is the largest. The mafic-ultramafic rocks of the Huangshandong intrusion comprise lherzolite, gabbronorite, gabbro, and diorite. Individual orebodies are composed of pyrrhotite, pentlandite, and chalcopyrite as disseminated to net-textured or massive to semimassive sulfide mineralization. Oxide-bearing sulfide mineralization contains 1 to 5% magmatic magnetite that has ilmenite and spinel exsolution lamellae. Silicate rocks and sulfide mineralization have variable whole-rock platinum group elements (PGE; 0.38?362 ppb), Cu (42?97,000 ppm), and Ni (26?33,000 ppm) concentrations. The mineralization is broken out into two types termed oxide rich and oxide poor. The oxide-rich sulfide mineralization has high PGE concentrations with low 187Re188Os ratios (38.9?151), whereas oxide-poor sulfide mineralization has low PGE concentrations with high 187Re188Os (159?781). Both oxide-rich and -poor sulfide mineralization have highly variable γOs values (49?189 and 30?278, respectively). Oxide-rich sulfide mineralization contains magnetite with variable amounts of MgO, TiO2, Al2O3, FeO total, Cr, V, Zn, and Sn, indicating that they crystallized from different stages during magma differentiation. We propose that the host intrusion and associated sulfide mineralization were derived from high Mg basaltic magmas from a mantle source that was previously modified by subducted oceanic slab. Oxide-poor sulfide mineralization of the Huangshandong intrusion formed from a magma that underwent <0.03% sulfide removal before emplacement and was thus PGE depleted. Oxide-rich sulfide mineralization formed from magma that had much lower amounts of sulfide (<0.003%) removed in the early stage before entering the Huangshandong magma chamber. An early sulfide saturation event was likely associated with fractionation of silicate minerals in a deep-staging magma chamber. The second sulfide saturation event that formed the sulfide mineralization was probably triggered by selective crustal contamination and fractionation in the high-level chamber where mixing of magmas and accumulation of immiscible sulfide occurred. © 2013 Society of Economic Geologists, Inc. Source

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