부산대학교 도서관

Trace element changes in fluids associated with ore-forming events in sedimentary basins may be recorded by contemporaneous cements, especially zoned carbonate minerals (microstratigraphy). Cement analysis using advanced mapping and analytical techniques including scanning electron microscopy cathodoluminescence (SEM-CL), charge contrast imaging, high-resolution X-ray computed tomography (XCT), and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) documents geochemical changes associated with Mississippi Valley-type mineralization in solution-collapse breccias of the Cambrian-Ordovician Knox Group (Tennessee and Kentucky, USA). Dolomite cement zonation coincident with changes in Fe and Mn can be observed with optical microscope CL in bands as narrow as 5 µm, whereas panchromatic SEM-CL reveals microfractures and cement subzones coincident with changes in La and Ce concentrations in bands as narrow as 0.1 µm. XCT scans image a high-density (Fe-rich) dolomite zone at the onset of late sulfide precipitation. The transition from pre-ore to ore-stage cementation is marked by increased Fe, Mn, Zn, Cd, Ga, Pb, and Sr and decreased La and Ce concentrations. Fine-scale metal depletion cycles during this transition may record metal precipitation from brine in response to the availability of reduced sulfur. Except for Fe and Mn, post-ore dolomite zones generally have low metal concentrations. Thus, dolomite microstratigraphy tracks systematic changes in brine metal concentrations modified by episodes of localized sulfide mineral precipitation.