Lithos 164–167 (2013) 1
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Editorial
Ore deposits and the role of the lithospheric mantle
Introduction to the Special Issue of LITHOS The role of the lithospheric mantle in magma generation has been controversial since the 1970s, when evidence for significant, regionally homogenous “crustal components” was first found in some continental flood-basalt provinces (e.g. Karoo, Parana, and Ventersdorp). Some authors have interpreted this signature as reflecting magma derivation from the sub-continental lithospheric mantle (SCLM), a model that has subsequently been applied to more primitive magmas, including some komatiites. Recent Re/Os studies have provided evidence that the Bushveld Complex in South Africa contains an important SCLM component, consistent with e.g., the location of most PGE deposits along the margins of cratons, or at sutures between cratonic blocks. The question of the role of the SCLM is not only important in magma genesis, but also relevant to the formation of many types of mineral deposits; for example, partial melts of the SCLM may have provided some PGE to the magmas from which the Bushveld Complex formed. Furthermore, recent studies have suggested that the metals in IOCG and orogenic gold deposits may be derived from the SCLM. In view of the increasing demand for metals across the world, these questions are of considerable importance to mineral exploration strategies. Our understanding of ore-deposit formation has expanded significantly over the last few years, allowing an improved evaluation of the interaction between mantle-derived magmas and the SCLM. The present thematic issue focuses on the role of the lithospheric mantle in the formation of orogenic gold, chromite, PGE, Ni–Cu, and porphyry Cu deposits. Lorand et al. present a general review on platinumgroup-element systematics and petrogenetic processing of the continental upper mantle. Negishi et al. describe sulfide-rich dunites within a thick Moho transition zone in the northern Oman ophiolite and their implications for the origin of the Cyprus-type sulfide deposits. Their work suggests a rather heterogeneous S distribution in the mantle, which has important implications for the mobility of chalcophile metals in the mantle. Malitch et al. present data on Hf–Nd isotopes from the Noril'sk Cu–Ni–PGE-mineralized intrusions, pointing to the interaction of magmas from distinct sources that include the SCLM. Dolgopolova et al. have studied the Sr–Nd–Pb–Hf-isotope systematics of the Oyu Tolgoi Cu–Au deposit in Mongolia and argue that the magmas originated predominantly from lithophile-element-depleted source material within the lithospheric mantle. Mathur et al. have measured Re/Os isotopes in Au-bearing sulfides and native gold from the Witwatersrand gold
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fields in South Africa. Their data indicate mixing of Os components derived from both the asthenospheric mantle, and SCLM or crustal sources at 2.7 Ga. They argue for the introduction of a significant portion of the Au after the formation of the conglomerates. Another group of papers addresses the formation of the chromite deposits associated with ophiolites. Gonzalez-Jimenez et al. use the fractionation of Re–Os isotopes during melting, melt–rock reaction and melt transport in the SCLM, as exposed in the Ojen lherzolite massif in the Betic Cordillera (Spain), to study the processes involved in the formation of ophiolitic chromitites. Ghosh et al. have characterized the chromian spinels from the mantle sequence of the Andaman ophiolite (India), and studied their paleogeodynamic implications. Taken together, the papers presented in this volume illustrate the current state of thinking about the possible role of the SCLM in the genesis of a range of important mineral deposit types worldwide. We hope that the volume may serve as a benchmark in a rapidly changing scientific landscape. Finally, we thankfully acknowledge all the reviewers of this special issue for their valuable comments and suggestions to improve the quality of the articles. Sisir K. Mondal Department of Geological Sciences, Jadavpur University, 188 Raja S.C. Mullik Road, Kolkata-700032, India Department of Earth and Planetary Sciences, American Museum of Natural History, Central Park West @ 79th Street, New York, NY 10024, USA Corresponding author at: Department of Geological Sciences, Jadavpur University, 188 Raja S.C. Mullik Road, Kolkata-700032, India. E-mail addresses:
[email protected],
[email protected]. William L. Griffin GEMOC/CCFS, Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia E-mail address: bill.griffi
[email protected]. Wolfgang Maier Department of Geology, University of Oulu, Oulu-90014, Finland E-mail address: wolfgang.maier@oulu.fi. 19 December 2012
