The ~4500-m-deep Iceland Deep Drilling Project (IDDP) borehole IDDP-2 in Iceland penetrated the root of an active seawater-recharged hydrothermal system below the Mid-Atlantic Ridge. As direct sampling of pristine free fluid was impossible, we used fluid inclusions to constrain the in situ conditions and fluid composition at the bottom of the hydrothermal convection cell. The fluid temperature is ~600 °C, and its pressure is near-hydrostatic (~45 MPa). The fluid exists as two separate phases: an H2O-rich vapor (with an enthalpy of ~59.4 kJ/mol) and an Fe-K–rich brine containing 2000 μg/g Cu, 3.5 μg/g Ag, 1.4 μg/g U, and 0.14 μg/g Au. Occasionally, the fluid inclusions coexist with rhyolite melt inclusions. These findings indicate that the borehole intersected high-energy steam, which is valuable for energy production, and discovered a potentially ore-forming brine. We suggest that similar fluids circulate deep beneath mid-ocean ridges worldwide and form volcanogenic massive sulfide Cu-Zn-Au-Ag ore deposits.

中文翻译：

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600℃洋中脊热液地热能与成矿潜力

冰岛约 4500 米深的冰岛深钻项目 (IDDP) 钻孔 IDDP-2 穿透了大西洋中脊下方活跃的海水补给热液系统的根部。由于无法对原始游离流体进行直接采样，因此我们使用流体包裹体来限制热液对流室底部的原位条件和流体成分。流体温度约为 600 °C，其压力接近静水压 (~45 MPa)。流体以两个独立的相存在：富含 H2O 的蒸汽（焓为 ~59.4 kJ/mol）和富含 Fe-K 的盐水，其中含有 2000 μg/g Cu、3.5 μg/g Ag、1.4 μg/g U , 和 0.14 μg/g Au。偶尔，流体包裹体与流纹岩熔体包裹体共存。这些发现表明钻孔与高能蒸汽相交，这对能源生产很有价值，并发现了一种潜在的成矿卤水。我们认为，类似的流体在全球洋中脊下方深处循环，形成火山成因的块状硫化物 Cu-Zn-Au-Ag 矿床。