Siderite separation from other diagenetic carbonates and pyrite

Siderite is a common diagenetic mineral and is also considered to be part of the highly reactive iron pool. The presence and characteristic of siderite in sediments are important indicators of diagenetic processes. Also, its presence in sedimentary aquifer has significant implications for groundwater quality. Siderite is often found with calcite and other diagenetic carbonates, such as dolomite and ankerite, and occasionally it can be associated with pyrite. Traditionally, sequential extraction methods focus isolating carbonates as a group, leaving aside the separation and description of each carbonate phase. Separation of siderite from other carbonates has been described as complex due to its incomplete dissolution by conventional sequential extraction methods that focus on iron speciation. This issue complicates the quantification and geochemical characterization of siderite in sediments. We will present a new extraction method for carbonates that is currently under development. The goal of the method is separating the different carbonate phases (calcite-dolomite-ankerite-siderite) and iron sulphur phases (AVS and pyrite) in sediment samples. This will be achieved by optimizing the parameters controlling the kinetics of the acid dissolution of the different minerals. The progress of dissolution of the different phases is determined by simultaneously monitoring the changes in solution composition and the concomitant release of CO2 and H2S. These gasses are trapped in NaOH and AgNO3 solutions. The new method will also be used to measure the δ13C and δ34S values of the produced CO2 and H2S.