Secondary Ion Mass Spectrometry (SIMS) Analyses of Trace Elements in Seafloor Massive Sulfides

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This project involves development of Secondary Ion Mass Spectrometry (SIMS) as a valid and useful technique for quantifying concentrations of trace elements in specific sulfide mineral phases. We plan to use this technique to investigate the processes of formation and early evolution of modern seafloor sulfide deposits through examination of trace elements at the ppm to sub-ppm level on a scale of 10s of microns. Sulfide-rich deposits form on the seafloor from mixtures of hydrothermal fluid and seawater, and record a history of reactions and changes in hydrothermal activity through space and time. Trace elements (Co, Se, Mo, As, Sb, Pb, Cd, Mn, Ag, Au) reside in sulfide minerals and can provide valuable information about depositional conditions (e.g., temperature), aspects of source fluid compositions, and the processes of metal remobilization and chemical zoning in ore deposits and in sea-floor hydrothermal vent deposits. The three steps in achieving our objectives are: 1) To create standards and establish methods using SIMS to measure the concentrations of the trace elements Co, Se, Mo, As, Sb, Cd, Pb, Ag, Ni, Bi, and U in sulfide grains (pyrite, chalcopyrite, pyrrhotite, marcasite, and bornite). 2) To examine the distribution of trace elements on a scale of 10s of microns in primary precipitates in seafloor chimneys where the conditions during mineral precipitation are well characterized. 3) To examine trace element distribution associated with replacement and recrystallization within black smoker chimneys, and within Fe-rich massive sulfides. Development of SIMS as a technique to measure trace elements in sulfide minerals will not only benefit studies of seafloor sulfide deposits, but will have wider application for studies of sulfides from a variety of environments.