Oxygen, Sulfur and Carbon Isotopic Study of Pore Fluid Evolution in the Creede Formation

该项目涉及对在科罗拉多州西南部克里德组钻探期间获得的岩心样品进行综合岩石学和稳定同位素研究，目的是记录在克里德热液系统成岩和热液活动过程中从孔隙流体中析出的次生矿物的氧、硫和碳同位素组成的逐步变化。将研究孔隙充填、裂缝充填和围岩蚀变矿物的结构关系和矿物组成，以确定次生矿物沉淀的相对时间。将尽可能采用基于激光的原位提取技术来测量细粒矿物中的氧和硫同位素，并测试矿物中的同位素变化。将测量适当矿物之间的氧(以及较小程度的硫和碳)同位素分配，并将其与实验和理论推导的分馏系数相结合，以限制降水温度。测量的次生矿物中氧、硫和碳的同位素组成将结合温度约束和矿物-流体分馏系数来计算矿物从其中沉淀出来的溶液的稳定同位素组成。根据次生矿物数据重建的稳定同位素变化序列将用于评估封闭系统过程(如局部流体-岩石反应)和开放系统过程(如地下水或热液流入)在控制孔隙流体中氧、硫和碳的同位素组成方面的相对重要性。

This project involves an integrated petrographic and stable isotopic study of samples selected from core obtained during drilling in the Creede Formation of southwestern Colorado for the purpose of documenting progressive changes in the oxygen, sulfur and carbon isotopic compositions of secondary minerals which precipitated from pore fluids during the course of diagenesis and hydrothermal activity in the Creede hydrothermal system. The textural relationships and mineral compositions of pore-filling, fracture-filling, and wall rock alteration minerals will be examined in order to establish the relative timing of secondary mineral precipitation. Laser-based in situ extraction techniques will be employed whenever possible to measure oxygen and sulfur isotopes in fine-grained minerals and test for isotopic variation within minerals. Oxygen (and to a lesser extent sulfur and carbon) isotopic partitioning between appropriate minerals will be measured and combined with experimentally and theoretically derived fractionation factors in order to constrain temperatures of precipitation. The measured isotopic compositions of oxygen, sulfur, and carbon in secondary mineral minerals will be combined with temperature constraints and mineral-fluid fractionation factors to calculate the stable isotopic compositions of the solutions from which the minerals precipitated. The sequence of stable isotopoic variation reconstructed from data for the secondary minerals will be used to assess the relative importance of closed-system processes (e.g. local fluid-rock reaction) and open-system processes (e.g. groundwater or hydrothermal fluid influx) in controlling the isotopic compositions of oxygen, sulfur, and carbon in the pore fluids.