(Table 3) Concentration of Au, Pd, and Pt in the interstitial waters of ODP Leg 125 samples

Palladium, platinum, and gold were analyzed for 20 interstitial water samples from Leg 125. No Pd or Pt was detected in fluids from serpentinite muds from Conical Seamount in the Mariana forearc, indicating that low-temperature seawater-peridotite interaction does not mobilize these elements into the serpentinizing fluids to levels above 0.10 parts per billion (ppb) in solution. However, Au may be mobilized in high pH solutions. In contrast, fluids from vitric-rich clays on the flanks of the Torishima Seamount in the Izu-Bonin forearc have Pd values of between 4.0 and 11.8 nmol/L, Pt values between 2.3 and 5.0 nmol/L and Au values between 126.9 and 1116.9 pmol/L. The precious metals are mobilized, and possibly adsorbed onto clay mineral surfaces, during diagenesis and burial of the volcanic-rich clays. Desorption during squeezing of the sediments may produce the enhanced precious metal concentrations in the analyzed fluids. The metals are mobilized in the fluids probably as neutral hydroxide, bisulfide, and ammonia complexes. Pt/Pd ratios are between 0.42 and 2.33, which is much lower than many of the potential sources for Pt and Pd but is consistent with the greater solubility of Pd compared with Pt in most natural low-temperature fluids.

本研究针对大洋钻探第125航次（Leg 125）采集的20件孔隙水（interstitial water）样品，分析了其中钯（Palladium）、铂（Platinum）和金（Gold）的含量。在马里亚纳前弧（Mariana forearc）锥形海山（Conical Seamount）的蛇纹岩泥（serpentinite muds）流体中未检出钯与铂，这表明低温海水-橄榄岩相互作用（seawater-peridotite interaction）无法将这些元素迁移进入蛇纹石化流体（serpentinizing fluids），使其溶液浓度高于0.10十亿分之一（parts per billion, ppb）。然而，金可在高pH值溶液中发生迁移。与之相反，伊豆-小笠原前弧（Izu-Bonin forearc）鸟岛海山（Torishima Seamount）侧翼的富玻璃质黏土（vitric-rich clays）流体中，钯含量介于4.0~11.8纳摩尔每升（nmol/L），铂含量介于2.3~5.0纳摩尔每升（nmol/L），金含量介于126.9~1116.9皮摩尔每升（pmol/L）。在富火山岩黏土的成岩作用（diagenesis）与埋藏过程中，贵金属会发生迁移，且可能吸附于黏土矿物表面。沉积物挤压过程中的解吸作用（desorption）可能是导致分析流体中贵金属浓度升高的原因。流体中的金属元素大概率以中性氢氧化物（hydroxide）、硫氢根配合物（bisulfide）以及氨配合物（ammonia complexes）的形式发生迁移。铂/钯比值（Pt/Pd ratios）介于0.42~2.33，这一比值远低于铂与钯的诸多潜在源区比值，但与多数天然低温流体中钯的溶解度高于铂的规律相符。