Petrologic, Geochemical, and Isotopic Investigation of Gulf Coast Salt Dome Cap Rocks

美国墨西哥湾沿岸地区的盐丘含锌-铅-钡-银矿床为沉积地体中含金属卤水和矿床的起源和演化提供了独特的信息。盐丘矿床与密西西比河谷型锌铅钡矿床和沉积喷淋型锌铅银钡矿床有亲缘关系。我们以往的研究大多集中在矿石矿物的岩石学和地球化学上，表明这些矿床明显是在盖层形成期间和之后，由沿盐层边缘向上泄漏的相对热流体形成的。我们建议继续我们的研究，更多地关注盖层形成的过程，而不是矿石的形成(1)，以更好地建立盆地盐水、盖层和硫化物/硫酸盐矿床之间的联系；(2)确定沉积剖面或盐层下方的哪些成分提供了金属和硫。详细的岩石学研究将结合C、O、Sr、Pb和S同位素、REE和流体包裹体研究盖层和伴生矿物。我们建议确定沉积盆地中产生盐丘矿床必须发生的事件的相对顺序，以表征含硫和含金属流体的性质，研究硬石膏盖层与含盐硬石膏之间的同位素关系，以了解在盖层形成过程中发生了涉及硬石膏的哪些反应。并研究不同盐盆地中的流体如何产生盆地内盐丘盖岩的不同同位素特征。

Salt dome hosted Zn-Pb-Ba-Ag deposits in the Gulf Coast Region of the United States offer unique information about the origin and evolution of metal-bearing brines and ore deposits in sedimentary terranes. The salt dome mineral deposits have genetic affinities with Mississippi Valley Type Zn-Pb-Ba deposits and sedimentary exhalative Zn-Pb-Ag-Ba deposits. Our previous studies, most of which have focused on the petrology and geochemistry of ore minerals, indicate that these deposits were apparently emplaced during and after the formation of cap rocks from relatively hot fluids leaking upward along the salt stock margins. We propose to continue our study, concentrating more on the processes of cap rock formation than ore mineral formation (1) to better establish the links between basin brines, cap rocks, and sulfide/sulfate mineral deposits, and (2) to determine what constituents in the sedimentary section or beneath the salt stock provided metals and sulfur. Detailed petrographic studies will be integrated with C, O, Sr, Pb, and S isotope, REE, and fluid inclusion studies cap rocks and associated minerals. We propose to determine the relative sequence of events that must take place in a sedimentary basin to produce salt dome mineral deposits, to characterize the nature of sulfur- and metal-bearing fluids, to investigate the isotopic relationships between anhydrite cap rocks and salt- hosted anhydrite to see what reactions involving anhydrite take place during cap rock formation, and to investigate how fluids in different salt basins may give rise to distinct isotopic signatures of salt dome cap rocks within that basin.