Abstract There are three large intracratonic basins (Vindhyan, Cuddapah and Chattisgarh) and several smaller basins (Kaladgi, Bhima, Pakhal, Penganga, Indravati, Khariar, Sabari and Kolhan) covering a large part of peninsular India. They are not known to host any significant metallic resource – except for a substantial uranium resource and Pb–Zn sulphide mineralization in the Cuddapah Basin, uranium in Bhima and Kaladgi basins and manganese in the Penganga sequence – but are nevertheless the repository of vast resources of industrial rocks (limestone, dolomite, phosphorite, aluminous laterite, building materials) and minerals (including pyrite, barite and diamond) in the country. The temporal distribution of these resources indicates a Mesoproterozoic age for all the deposits and occurrences except the uranium deposits in the Vempalle dolostones in the southwestern fringe of the Cuddapah Basin, which are Palaeoproterozoic in age. The Cuddapah Basin is the most intensely mineralized Proterozoic basin, with the Cumbum Formation in the Nallamalai belt hosting stratabound base metals and barite, dated c. 1.6 Ga, all the way from north to south. Potential mineralization, still undiscovered in the basin, is a large SEDEX-type Pb–Zn orebody in the vicinity of the Mangampet barite deposit and unconformity-proximal U deposits in the Kurnool Group, similar to those of the Bhima Basin.

Results of sulfur and oxygen isotopic studies of sedimentary-exhalative (SEDEX) Zn-Pb(-Ag-Au-Ba-F) deposits hosted in metamorphosed Paleozoic clastic and carbonate rocks of the Nome Complex, Seward Peninsula, Alaska, are consistent with data for similar deposits worldwide. Stable isotopic studies of the Nome Complex are challenging because the rocks have undergone Mesozoic blueschist- and greenschistfacies metamorphism and deformation at temperatures estimated from 390 to 490 °C. Studies of sulfur and oxygen isotopes in other areas suggest that, in the absence of chemical and mineralogical evidence for metasomatism, the principal effect of metamorphism is re-equilibration between individual minerals at the temperature of metamorphism, which commonly leads to a narrowing of the overall range of isotope values for a suite of rocks but generally does not significantly modify the average whole-rock value for that suite. Sulfur isotopic studies of the stratabound and locally stratiform sulfide lenses at the Aurora Creek–Christophosen deposit, which is of possible Late Devonian–Early Carboniferous age, show a large range of δ 34 S sulfide values from –9.7‰ to 39.4‰, suggesting multiple sulfur sources and possibly complex processes of sulfide formation that may include bacterial sulfate reduction, thermochemical sulfate reduction in a restricted sulfide basin, and Rayleigh distillation. Low δ 34 S values probably represent bacterial sulfide minerals remobilized from the host metasedimentary rocks either during the original seafloor mineralization or are related to a Cretaceous mineralizing event that produced Au-vein and base-metal replacement deposits; the latter process is supported by Pb isotope data. The Wheeler North deposit is similar to Aurora Creek–Christophosen but does not have negative δ 34 S values. It probably formed in an euxinic subbasin. The stratabound Nelson deposit, and the deformed veins at the Galena and Quarry deposits, may be older than the Aurora Creek–Christophosen and Wheeler North deposits. The Nelson deposit has a lower and narrower range of δ 34 S values (1.9‰–10.4‰), averaging ~8‰. The Galena and Quarry vein deposits display δ 34 S values that are similar to those of the stratabound Nelson deposit. Barite samples from the Aurora Creek–Christophosen, Wheeler North, and Quarry deposits have 34 S-enriched δ 34 S values between 25‰ and 30‰ that are consistent with derivation of the sulfur from coeval (Paleozoic) seawater sulfate. Given their δ 34 S values, it is likely that the Aurora Creek–Christophosen and Wheeler North deposits formed in closed subbasins with euxinic conditions that led to extreme Rayleigh distillation to produce the very large range and very high δ 34 S values. The Nelson deposit probably formed within an anoxic but not euxinic subbasin. At Nelson, sulfide was likely derived by a subsurface thermochemical sulfate reduction (TSR) reaction, similar to reactions that are inferred to have produced the sulfides in the Galena and Quarry deposits, which are interpreted as feeder veins for the stratabound deposits. Calculations of oxygen isotope temperatures are based on the assumption that evolved seawater with δ 18 O of 3‰ was the mineralizing and altering fluid related to the formation of the sulfide deposits. Temperatures of aluminous alteration and sulfide mineralization were between 109 and 209 °C, determined on the basis of oxygen isotope fractionations between the mineralizing fluid and proportionate amounts of quartz and muscovite in the rocks. These temperature estimates agree well with known temperatures of SEDEX mineralization worldwide. Sulfur isotope values also are generally consistent with the known ranges in SEDEX deposits worldwide (δ 34 S ≈ −5‰ to 25‰).