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首页> 外文期刊>American Journal of Science >INTERACTIONS OF MIXED VOLATILE-BRINE FLUIDS IN ROCKS OF THE SOUTHWESTERN FOOTWALL OF THE DULUTH COMPLEX, MINNESOTA: EVIDENCE FROM AQUEOUS FLUID INCLUSIONS
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INTERACTIONS OF MIXED VOLATILE-BRINE FLUIDS IN ROCKS OF THE SOUTHWESTERN FOOTWALL OF THE DULUTH COMPLEX, MINNESOTA: EVIDENCE FROM AQUEOUS FLUID INCLUSIONS

机译：明尼苏达州Dulth Complex西南麓岩层中混合的挥发性盐卤流体的相互作用：流体包裹体的证据

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Drillcore samples of troctolites and gabbros were studied along the southwest footwall of the Duluth Complex, Minnesota. The rocks were intruded into an active rifting environment, which enhanced melt-wallrock interaction. The samples analyzed contain variable, sub-economic amounts of Fe—Ti oxides and Cu—Fe—Ni sul-fides and some uneconomic enrichments of platinum-group elements (PGE). The goal of the study was to investigate the nature of the aqueous fluids that interacted with the igneous rocks and possibly affected the concentration and distribution of ore minerals. Microthermometric and Raman microprobe analyses were done on about 150 fluid inclusions hosted by quartz and apatite in hydrously altered mafic rocks. The aqueous fluids range from 0 to 48 wt percent total dissolved salt (assuming NaCl + CaCl_2) with CaCl_2/(NaCl + CaCl_2) weight ratios up to 0.9. Homogenization temperatures range from about 100° to over 400℃. The inclusion data suggest that the Complex experienced significant interactions with mixed aqueous (NaCl + CaCl_2 + KCl)-volatile (CH4 + N_2 ± CO_2) fluids over a temperature range from above 700° to below 200℃ at about 2 kb pressure. The aqueous components were derived from metasediments of the Thompson Formation and from the mafic igneous melt, whereas organic components of the metasediments are the major source of the C—O—H—N volatiles in the fluids. The high salinities of some of these brines were achieved by separation of a magmatic fluid component, reaction of fluid with igneous and metasedi-mentary rocks, development of brine-brine immiscibility at high temperatures and brine-gas immiscibility at lower temperatures, removal of a gas phase by effervescence through surface-penetrating fractures, and removal of water into hydrous alteration phases. The hot, highly saline fluids were capable of transporting ore components such as Cu, Fe, Ni, and PGE. In principle, the development of brine-brine and brine-gas immiscibility in these fluids has strong ore-forming potential. However, the sporadic PGE concentrations at Duluth may be due to: (1) the insufficient concentration of PGE in the original magmas; (2) the repeated intrusion of mafic melts, which caused ore components to be dispersed by overlapping hydrothermal cells; and (3) the reduced nature of the fluids, making them less capable of transporting ore components.
机译：沿明尼苏达州德卢斯综合体的西南下盘研究了闪长石和辉长岩的钻芯样品。岩石被侵入活跃的裂谷环境，增强了熔岩与围岩的相互作用。分析的样本包含可变的亚经济量的Fe-Ti氧化物和Cu-Fe-Ni硫化物以及一些不经济的铂族元素（PGE）富集。该研究的目的是研究与火成岩相互作用并可能影响矿石矿物的浓度和分布的含水流体的性质。在含水蚀变镁铁质岩石中，对石英和磷灰石所含的约150种流体包裹体进行了显微热计量和拉曼探针分析。水性流体的总溶解盐（假设NaCl + CaCl_2）的重量百分比范围为0至48％，CaCl_2 /（NaCl + CaCl_2）的重量比最高为0.9。均质温度范围从大约100°到超过400℃。包裹体数据表明，在约2 kb的压力下，从700°C至200°C以下的温度范围，该络合物与混合的（NaCl + CaCl_2 + KCl）挥发性水（CH4 + N_2±CO_2）流体发生了显着的相互作用。含水成分来源于汤普森组的沉积物和镁铁质火成岩熔体，而沉积物的有机成分是流体中CHN-NH挥发物的主要来源。通过分离岩浆流体成分，流体与火成岩和准沉积岩的反应，在高温下形成盐水与盐水的不溶混性以及在较低温度下去除盐水与气体的混溶性，去除水中的卤水，可以实现其中一些盐水的高盐度。通过表面渗透性裂缝的冒泡形成气相，并将水去除为含水蚀变相。高温，高盐分的流体能够运输矿石成分，例如Cu，Fe，Ni和PGE。原则上，在这些流体中盐水-盐水和盐水-气体不混溶的发展具有很强的成矿潜力。但是，Duluth处零星的PGE浓度可能是由于：（1）原始岩浆中PGE浓度不足； （2）镁铁质熔体的反复侵入，致使矿石成分被重叠的热液单元分散； （3）减少了流体的性质，使它们传输矿石成分的能力降低。

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