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Processes and Ore Deposits of Ultramafic-Mafic Magmas through Space and Time focuses on the fundamental processes that control the formation of ore deposits from ultramafic-mafic magmas, covering chromite, platinum-group element (PGE), Ni-sulfides and Ti-V-bearing magnetite. The exploration, exploitation and use of these magmatic ores are important aspects of geology and directly linked to the global economy. Magmatic ores form from ultramafic-mafic magmas and crystallize at high-temperature after emplacement into crustal magma chambers, and are genetically linked to the evolution of the parental magmas through space and time. This book features recent developments in the field of magmatic ore deposits, and is an essential resource for both industry professionals and those in academia.Elucidates the relationships between tectonic settings and magmatic ore mineralizationProvides the links between magma generation in the mantle and ore mineralization at crustal levelsFeatures the latest research on changing patterns in magmatic ore mineralization through time and their bearing on the chemical evolution of the Earth's mantle

The chromium isotope system has been proven to be a redox-sensitve proxy in ancient and modern environmental studies (e.g. [1], [2]). In this study we investigated Cr isotope fractionation during soil formation from Archean (3.1-3.3 Ga) ultramafic rocks, intruded into metamorphic rocks of the Iron Ore Group in the southern Singhbhum Craton (Orissa, India)[3]. A modern weathering profile was logged in an active open cast chromite mine (Sukinda valley). The Cr isotope data of samples from the weathering profile are fractionaed. While the least weathered horizons at the base of the profile reflect mantle inventory values (-0.124±0.101‰ [4]), the δ53Cr values from the more weathered upper part of the profile are as low as -1.28±0.08‰, indicative of the loss of an isotopically heavy (53Cr enriched) fraction to the runoff. Mass-balance calculations show that the highly weathered horizons are characterised by a Cr loss of up to 74 %. These data are consistent with the findings of Crowe et al. [2] who also studied the effects of weathering of ultramafic rocks in Indonesia on the Cr isotope system. These authors demonstrate that oxidation of Cr(III) to Cr(VI) in the soils is accompanied by isotopic shifts. Thereby the Cr(VI) lost to runoff is enriched in the heavier 53Cr, while the lighter 52Cr preferentially remains in the residual Cr(III) pool of the soils. We measured high (up to 1.2 ppm) concentrations of total dissolved Cr in the mine drainage waters. Isotopically the mine waters are slightly heavier than mantle inventory, indicating input of 53Cr enriched Cr(VI) during continious rock weathering. δ53Cr values in the main river (Damsal Nala) which discharges its dissolved loads into the Indian Ocean are positivley fractionated with values up to 0.7‰. [1] Ellis et al (2002) Science 295, 2060-2062. [2] Crowe et al (submitted) EPSL. [3] Mondal et al (2006) Precambrian Res. 148, 45-66. [4] Schoenberg et al (2008) Chem.

The Nuggihalli greenstone belt is part of the older greenstone belts (3.4 - 3.0 Ga) in the Western Dharwar Craton, southern India. This greenstone sequence consists of conformable metavolcanic and metasedimentary supracrustal rock assemblages that belong to the Sargur Group. Sill-like ultramafic-mafic plutonic bodies are present within these supracrustal rocks (schist rocks) which are in turn enclosed by tonalite-trondhjemite-granodiorite gneiss (TTG). The sill-like ultramafic-mafic rocks are cumulates derived from a high-Mg parental magma that are represented by chromitite-hosted serpentinite and tremolite-chlorite-actinolite- schist (altered peridotite), anorthosite, pyroxenite, and gabbro hosting magnetite bands. The first whole-rock Sm-Nd data for the peridotite anorthosite- pyroxenite-gabbro unit has been obtained yielding an age of 3125 ± 120 Ma (MSWD = 1.3) which is similar to reported ages for the komatiitic suite of the associated schist belts in the craton within the limits of errors. A whole rock Pb-Pb errorchron age of 2801 ± 110 Ma (MSWD = 102) has been obtained for the entire plutonic ultramafic-mafic suite; this represents a younger metamorphic age and is in agreement with previous geochronological studies. The magmatic activity of the younger greenstone belts in the Western Dharwar Craton has reset the Pb isotope systematics, which thus yield younger ages. The whole rock Rb-Sr data has been perturbed such that no age data is obtainable. Whole-rock major and trace element geochemistry indicates that the sill-like ultramafic-mafic rocks are cogenetic and related by fractional crystallization. The metavolcanic schist rocks are inferred to be cogenetic with the plutonic suite, and are also fractionated. The subchondritic to chondritic REE abundances of the chromitites, serpentinites, peridotites, and anorthosites, along with the flat heavy REE patterns, resemble the pattern of Al-undepleted komatiites and indicate high degrees of partial m