ULTRA - Ultramafic-hosted mineral Resource Assessment

总结：大洋中脊（莫尔）上的海底块状硫化物（SMS）热液矿床自相矛盾;其规模似乎与火山活动量成反比。虽然热液SMS在快速扩展的莫尔中更频繁，但最大的矿床发生在火山作用似乎最小的地方。在这里，在缓慢和超缓慢扩张的山脊上所谓的amagmatic段，来自下地壳和上地幔的超镁铁岩被长期的断层挖掘出来;这一过程被认为影响了缓慢扩张山脊长度的50%。在这些环境中，超镁铁质海底块状硫化物形成了一些已知的最大矿床，含有高浓度的Au、Cu、Ni、E-tech元素（Co、Pt）。虽然岩浆驱动力的火山托管SMS存款是公认的，它仍然是有争议的muSMS。同样，虽然有模型的次表面结构和范围的火山主办的SMS，很少有人知道muSMS。对于某些muSMS，喷口流体化学表明，可能由于主岩的蛇纹化作用而与pH屏障发生相互作用，可能存在大量海底下金属沉淀的潜力。此外，物理，化学和微生物的机制，影响muSMS后，他们的形成受到很大的限制。我们的研究旨在测试这一假设，即muSMS矿床形成广泛的地下矿化，并在高度可变的pH值条件的影响下，与超镁铁岩相互作用和蛇纹石化过程中，在海底和海底下进行了显着的后期改造。我们的计划是将联合收割机新的地球物理技术（电磁感应和反向井下地震层析成像）与地表测绘和海底下钻探（回收主岩、硫化物、沉积物和流体）相结合，对存款及其周围环境的三维结构和组成进行成像。样品的矿物学、地球化学和同位素特征将揭示矿床的共生历史，包括形成、重结晶、金属活动、蚀变和海水渗透。热液流体样品将揭示驱动存款形成和主岩相互作用的热源的性质，并结合对含金属沉积物的研究，在后期蚀变过程中限制金属的流动性。这些过程的年龄将受到放射性测年的限制。过程的速度将受到现场和实验室的非生物氧化和微生物蚀变实验的限制。我们将利用热物理化学数值模拟将这些观测结果汇总在一起，以构建对当今海洋中这些大型多金属muSMS矿床的形成和保存的连贯理解。我们的方法需要两次巡航，以最大的已知和最具特色的muSMS领域在13度30分钟N，大西洋中脊（MAR）。尽管在技术上雄心勃勃，但我们从欧盟资助的蓝色采矿项目中获得的经验以及学术和工业合作伙伴的参与，贡献了实物数据和成本，大大降低了研究的风险。

Summary: Hydrothermal seafloor massive sulphide (SMS) deposits on mid-ocean ridges (MOR) are paradoxical; their size seems to be inverse to the amount of volcanic activity. While hydrothermal SMS are more frequent at fast-spreading MOR, the largest deposits occur where volcanism appears to be a minimum. Here, at so-called amagmatic segments on slow- and ultra-slow spreading ridges, ultramafic rocks from the lower-crust and upper-mantle are exhumed by long-lived faulting; a process that is thought to affect 50% of the length of slow-spreading ridges. Ultramafic-hosted seafloor massive sulphides (muSMS) in these settings form some of the largest deposits known, hosting high metal concentrations of Au, Cu, Ni, E-tech elements (Co, Pt). Whereas the magmatic driving force for volcanic-hosted SMS deposits is well established, it remains contentious for the muSMS. Similarly, while there are models for the sub-surface structure and extent of volcanic-hosted SMS, little is known about muSMS. For some muSMS, vent fluid chemistry indicates the potential for extensive sub-seafloor metal precipitation, possibly by interaction with pH barriers due to serpentinisation of the host rock. Furthermore, the physical, chemical and microbial mechanisms affecting muSMS after their formation are poorly constrained. Our study aims to test the hypothesis that muSMS deposits form extensive sub-surface mineralisation and undergo significant post-formational modification at and beneath the seafloor under the influence of highly variable pH conditions as a result of interaction with ultramafic rocks and during serpentinisation. Our plan is to combine novel geophysical techniques (electromagnetic induction and inverted down-hole seismic tomography) with surface mapping and sub-seafloor drilling (recovering host rocks, sulphides, sediment and fluids) to image the 3D structure and composition of the deposit and its surroundings. The mineralogy, geochemistry and isotope signatures of the samples will reveal the paragenetic history of the deposits including formation, recrystallisation, metal mobilisation, alteration and penetration by seawater. Hydrothermal fluid samples will reveal the nature of the heat source driving deposit formation and host-rock interactions and, combined with studies of metalliferous sediment, constrain metal mobility during later alteration. Ages of these processes will be constrained by radiometric dating. Rates of processes will be constrained by in situ and lab-based, abiotic oxidation and microbial alteration experiments. We will draw these observations together using thermo-physio-chemical numerical modelling to construct a coherent understanding of the formation and preservation of these large polymetallic muSMS deposits in todays-oceans. Our approach requires two cruises to the largest known and best characterised muSMS field at 13degrees30minutesN, Mid-Atlantic Ridge (MAR). Despite being technically ambitious, our experience from the EU-funded Blue Mining project and the involvement of both academic and industrial partners, contributing in-kind data and costs, significantly de-risks the research.