Magmatic Ni‐Cu and PGE Deposits: Geology, Geochemistry, and Genesis, Volume 17 of Reviews in Economic Geology

Magmatic Ni-Cu and PGE Deposits: Geology, Geochemistry, and Genesis, Volume 17 of Reviews in Economic Geology , edited by Chusi Li and Edward M Ripley , Society of Economic Geologists, Inc. , ISBN : 978-1-934969-35-9 , Price USD 80 (nonmember), 64 (member) Derived from a SEG Short Course at the 2011 GSA meeting in Minneapolis, Minnesota, USA, this volume consists of 13 papers that are designed for specialists in magmatic sulfide deposits. The volume is a superb collection of papers that were delivered in the short course and which contain the most current knowledge about the geology, geochemistry and genesis of the deposits. The first chapter by Anthony J. Naldrett covers the development of some basic concepts and histories in the study of magmatic sulfide deposits, and includes a classification of Ni-Cu and PGE deposits in the world. Some basic features of these deposits are also introduced, such as mineralization styles and factors that control the formation of such deposits. A wide range of world-class sulfide deposits are described in the book, covering the basic geology and genetic models for individual deposits. Although the examples are limited, their models have implications for future exploration of similar deposits elsewhere. Barnes et al. present a case study for the Perseverance and Mount Keith nickel deposits in the Yilgarn Craton, Western Australia. This group of deposits is hosted in lenticular bodies of high-Mg cumulates derived from komatiitic magmas, possibly of mantle plume origin. The authors emphasize the importance of external sulfur from a felsic volcanic country-rock sequence in the formation of the Ni-Cu deposits. Houle and Lesher deal with the Ni-Cu-(PGE) deposits in the Abitibi greenstone belt, Superior Province, Canada. These deposits are hosted in komatiites and are considered to be derived from S-undersaturated komatiitic magmas. The authors further suggest that a juvenile tectonic setting and low density of continental crust are not favorable for the formation of large deposits in the Abitibi greenstone belt. They highlight the significance of environments that acted as pathways for komatiite magmas in the formation of Ni-Cu-PGE deposits, where external sulfur was possible for the magmas to assimilate. Layton-Matthews et al. focus on the mineralogy and geochemistry of the komatiite-associated nickel deposits in the Thompson belt, Manitoba, Canada. They suggest that the sulfide ores were emplaced prior to peak metamorphism and deformation, and that metamorphism did not significantly mobilize the metals of the deposits. Hanski et al. present new Re-Os and sulfur isotopic data for feeder dikes associated with the Pechenga Ni-Cu sulfide deposits, northwestern Russia. Their results reveal a significant component of radiogenic Os in the magma and stratigraphic decoupling of sulfur isotopic compositions between ore-bearing intrusions and sedimentary wall rocks. They argue that a reevaluation is needed for the model in which immediate country rocks are the main source of sulfur and radiogenic Os in the formation of the Ni-Cu deposits. Li and Ripley provide new insights about the tectonic setting, magma evolution, ore genesis, and exploration implications of the Jinchuan Ni-Cu-PGE deposit in the western part of the North China Craton. They suggest that the Jinchuan mafic-ultramafic intrusion formed from magmas originated from an enriched lithospheric mantle source with significant fractional crystallization and crustal contamination. They argue that the ∼830-Ma intrusion was emplaced in the North China Craton, not in the Yangtze Craton. Ripley and Li's chapter is a comprehensive review about conduit-related Ni-Cu-PGE sulfide mineralization. Based on the similar geology and geochemistry of the Voisey's Bay deposit, Labrador, and the Eagle deposit, northern Michigan, these authors propose that these deposits may have formed in both near vertical and horizontal portions of the conduits. The role of magma-country rock interaction is emphasized for triggering sulfide saturation and thus its role in the formation of these deposits. Arndt revisits the Norilsk-Talnakh Ni-Cu-PGE sulfide deposits associated with a large igneous province in Siberia, and provides a new and improved genetic model for their formation. Low-Ti tholeiitic magmas are considered to have originated from high degrees of partial melting due to an ascending mantle plume. Assimilation of granitic rocks at a mid-crustal level strongly modified magma compositions, but assimilation of sulfur-rich evaporitic sediments triggered the sulfide segregation. Maier et al. provide a review of the ore-forming processes of the Kabanga Ni sulfide deposits, Tanzania. They highlight the variable metal tenors of sulfides within individual intrusions, and the association of high-grade ores with olivine-rich lithological units, high R factors, S-rich country rocks and remobilization of sulfides. This case study has important implications for camp-scale Ni sulfide exploration. Naldrett et al. report a comprehensive geochemical dataset especially for samples from a number of drill holes of the Merensky Reef and chromitite seams of the Bushveld complex. The authors propose that the presence of PGE-enriched zones strongly depends on chromite crystallization, which would occur because of contamination of the mafic magma with a melt having an average upper crustal composition. McDonald and Holwell describe Ni-Cu-PGE deposits of the Bushveld complex, and reconsider the genesis of the Platreef. PGE-rich sulfide deposits of the Platreef are thought to have been derived from the same magmas that formed the Merensky Reef or, alternatively, to have formed in pre-Platreef staging chambers. Oberthiir describes the PGE mineralization of the main sulfide zone, Great Dyke, Zimbabwe, presents new PGE and PGM data for the mineralization, and discusses genetic models. This study emphasizes that sulfur saturation of the evolving magma leading to sulfide segregation is the most important factor in the primary magmatic concentration of the PGE. Finally, Barnes and Gomwe focus on the petrology and geochemistry of the Pd deposits of the Lac des Iles complex, northwestern Ontario, Canada. The authors demonstrate that the PGE compositions of the rocks vary with grain size and that the matrix and fragment samples have different compositions. They further highlight the significance of sulfide mineral formation from a sulfide liquid and low-temperature alteration in the control of PGE enrichment. Like other volumes of Reviews in Economic Geology, this book should be considered an important benchmark in the study of magmatic sulfide deposits. Many of the examples contained in the volume will be of critical importance in guiding exploration for the same type of deposits. The book is indeed the most complete record of knowledge in the field and is a compelling review that provides useful suggestions for future research. The book can be ordered from the following website of the Society of Economic Geologists (http://www.segweb.org/Store/detail.aspx?id=REV17).

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