Combining metal and nonmetal isotopic measurements in barite to identify mode of formation

Abstract:

Barite (BaSO₄) is a highly stable and widely-distributed mineral found in magmatic, metamorphic, and sedimentary rocks (of all ages), as well as in soils, aerosol dust, and extraterrestrial material. Today, barite can form in a variety of settings in the oceans (hydrothermal, cold seeps, water column, sediments) and on the continents – where supersaturation and precipitation of barite typically occurs from the mixing of fluids – one containing Ba and another containing sulfate. Sulfur (δ³⁴S) and oxygen (δ¹⁸O) isotopes together with ⁸⁷Sr/⁸⁶Sr and stable Sr-isotopic signatures (δ^88/86Sr) of modern authigenic continental barite are compared to modern pelagic marine barite and marine hydrothermal and cold seep barite to investigate the potential for their combined use to indicate mode of barite formation. The ⁸⁷Sr/⁸⁶Sr in barite cleary identifies the source of fluid for any particular type of barite (as previously noted, see Paytan et al., 2002). The highest (most radiogenic) ⁸⁷Sr/⁸⁶Sr values are measured in continental barite samples. There is no unique δ^88/86Sr signature for any particular type of barite, but coretop marine (pelagic) barite has a consistent value measured from samples collected in different ocean basins. The highest and lowest δ^88/86Sr values were measured in continental barite samples. The combination of isotopic systems result in unique δ^88/86Sr and δ¹⁸O relationships and distinct δ^88/86Sr and δ³⁴S relationships for different types of barites investigated. Data suggest that the combined use of these metal and nonmetal isotopic measurements in barite could be useful as a new geochemical proxy to identify mode of barite mineralization for use in earth science applications including understanding ancient barite deposits.