Abstract Among the basaltic large igneous provinces (LIPs) world over, the Deccan Large Igneous Province (DLIP) is considered barren of metalliferous sulfide deposits, and especially platinum group minerals (PGMs). The tholeiitic basaltic magmas of the DLIP were found to lack sulfur saturation at all stages of its evolution. However, we found some incidences of Fe–Ni–platinum group element (PGE) mineralization in the cumulate gabbros of the Phenai Mata Igneous Complex (PMIC), as well as intrusive dykes of lamprophyre, picrobasalt and basalt in adjoining areas. To examine the metal potential of the gabbros, we adopted the following approach: (a) whole-rock PGE analysis of selected rocks; (b) preconcentration of the samples by communition, sieving and gravity-magnetic separation, followed by froth floatation, Ni-sulfide fire assay and geochemical analysis of the concentrates; and (c) direct scanning of samples using an electron probe microanalyser (EPMA). The geochemical proxies – namely, Pd/Ir, Cu/Ir, Ni/Pd and Ni/Cu – indicate that PMIC has distinct geochemical signatures compared to other parts of the DLIP. The results have further indicated an interesting suite of minerals comprising metal sulfides of Fe–Cu–Zn–Pb–Co–Ni. This metal-rich suite in the otherwise ‘barren’ Deccan Trap tholeiites is a result of accidental fertilization of metals into their sulfides due to the mixing of crustal sulfur.

Abstract Proterozoic to Cenozoic lamprophyres, lamproites and related rock types hold a unique potential for the investigation of processes affecting mantle reservoirs. They originated from primary mantle-derived melts that intruded both cratons and off-craton regions, which were parts of former supercontinents – Columbia, Rodinia and Gondwana–Pangaea. Well known for hosting economic minerals and elements such as diamonds, base metals, platinum-group elements and Au, they are also significant for our understanding of deep-mantle processes, such as mantle metasomatism and mantle plume–lithosphere interactions, as well as large-scale geodynamic processes, including subduction-related tectonics and supercontinent amalgamation and break-up. This Special Publication presents an overview of the state of the art and recent advances as achieved by individual research groups from different parts of the world, and outlines future research directions. Mineralogical, geochemical, geochronological and isotope analyses are used to decipher the complex petrogenetic and metallogenetic evolution of these extraordinary rocks and unravel a complete history of tectonic events related to individual supercontinent cycles. The Special Publication including this introductory chapter also deals with some issues related to the classification of these rocks.

Abstract: The genetic connection between Large Igneous Province (LIP) and carbonatite is controversial. Here, we present new major and trace element data for carbonatites, nephelinites and Deccan basalts from Amba Dongar in western India, and probe the linkage between carbonatite and the Deccan LIP. Carbonatites are classified into calciocarbonatite (CaO, 39.5–55.9 wt%; BaO, 0.02–3.41 wt%; ΣREE, 1025–12 317 ppm) and ferrocarbonatite (CaO, 15.6–31 wt%; BaO, 0.3–7 wt%; ΣREE, 6839–31 117 ppm). Primitive-mantle-normalized trace element patterns of carbonatites show distinct negative Ti, Zr–Hf, Pb, K and U anomalies, similar to that observed in carbonatites globally. Chondrite-normalized REE patterns reveal high LREE/HREE fractionation; average (La/Yb) N values of 175 in carbonatites and approximately 50 in nephelinites suggest very-low-degree melting of the source. Trace element modelling indicates the possibility of primary carbonatite melt generated from a subcontinental lithospheric mantle (SCLM) source, although it does not explain the entire range of trace element enrichment observed in the Amba Dongar carbonatites. We suggest that CO 2 -rich fluids and heat from the Deccan plume contributed towards metasomatism of the SCLM source. Melting of this SCLM generated primary carbonated silicate magma that underwent liquid immiscibility at crustal depths, forming two compositionally distinct carbonatite and nephelinite magmas. Supplementary material: Detailed sampling locations and descriptions, major and trace element composition of apatite in carbonatite and nephelinite, analytical reproducibility for major and trace elemental analyses, and details of trace element modelling are available at https://doi.org/10.6084/m9.figshare.c.3819457