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doi:10.2204/iodp.proc.304305.203.2009

Method development

Attempts at TEM analysis of standard petrographic thin sections proved unfruitful, as the sulfide mineral grains are typically small (commonly <50 µm) and the total abundance of sulfide mineral is commonly <1 mod%. Eventually, we settled on grain mount preparations derived from pulverizing the samples to <1 mm grain size and then deriving a heavy mineral separate using a dense sodium polytungstate solution.

After the sulfides were separated from the bulk material, they were mixed in ethanol solutions and deposited on Cu grids, which were previously glow discharged in order to achieve better dispersions. TEM measurements were carried out using a JEOL 2010 TEM system at a working voltage of 200 kV. All imaging magnifications were calibrated using the standards of SiC lattice fringes (Luo, 2006) for high magnifications and commercial cross-line grating replica for low magnifications. EDS, which was used to determine chemical composition, was done using an Oxford Instruments EDS detector with an INCA energy platform. Electron micrographs were digitalized using an Epson (Long Beach, CA) Projection 3200 scanner at 1200 dpi.

Reflected light petrography and electron microprobe analyses were performed on representative samples of the various major lithologies for comparison with TEM results. Analyses of sulfide minerals were performed using the CAMECA SX-50 electron microprobe. Analyses were performed using a 50 nA beam current, an accelerating voltage of 15 keV, and a 1 µm beam. Count times range from 10 to 40 s. Standards used included pyrite (S and Fe); sphalerite (Zn); and pure Co, Ni, and Cu wire.

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