ULTRA - Ultramafic-hosted mineral Resource Assessment

ULTRA - 超镁铁质托管的矿产资源评估

• 批准号: NE/S004319/1
• 负责人: Crispin Little
• 金额: $ 9.81万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FS004319%2F1
• 关键词: ULTRA; Ultramafic; hosted; mineral; Resource

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 mineralization and undergo significant post-formational modification at and beneath the seafloor under the influence of highly variable pH conditions. 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, recrystallization, 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 metaliferous 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 physiochemical 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 the largest known and best characterised muSMS field at 13degree30minuteN, 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.

摘要：水热海底硫化物（SMS）沉积在中山脊（MOR）是自相矛盾的；它们的大小似乎与火山活动的数量相反。虽然在快速传播的MOR中，水热SMS更为频繁，但最大的沉积物发生在火山主义似乎最小的情况下。在这里，在慢速和超慢的山脊上所谓的杂乱无章的细分市场中，从下壳和上胸腔的超镁铁质岩石被长期寿命的断层所挖掘出来。该过程被认为会影响慢速山脊长度的50％。在这些环境中，超缺乏托管的海底巨大硫化物（肌肉）构成了一些已知的最大沉积物，具有高金属浓度的AU，Cu，Ni，E-Tech元素（CO，PT）。尽管已经确定了火山托管SMS沉积物的岩浆驱动力，但对肌肉仍然有争议。同样，尽管有一些用于火山托管SMS的地下结构和程度的模型，但对肌肉的了解鲜为人知。对于某些肌肉，排气流体化学表明可能由于宿主岩石的蛇形化而与pH障碍物相互作用，可能会出现广泛的下层状金属沉淀。此外，形成后影响肌肉后的物理，化学和微生物机制受到限制。我们的研究旨在检验以下假设：在高度可变的pH条件下，肌肉沉积会形成广泛的地下矿化，并在海底进行大量的形成后修饰。我们的计划是将新颖的地球物理技术（电磁感应和倒孔的地震层析成像）与表面映射和层次钻探（恢复宿主岩石，硫化物，沉积物和流体）相结合，以形象沉积物的3D结构和组成。样品的矿物学，地球化学和同位素特征将揭示沉积物的副校长历史，包括形成，重结晶，金属动员，改变和海水穿透。水热流体样品将揭示热源驱动沉积物形成和宿主岩石相互作用的性质，并结合对金属沉积物的研究，限制了以后的变化中金属迁移率。这些过程的年龄将受到辐射测定的约束。过程速率将受到原位和基于实验室的，非生物氧化和微生物改变实验的限制。我们将使用生理化学数值建模一起绘制这些观察结果，以构建对当今范围内这些大型聚合肌肉沉积的形成和保存的连贯理解。我们的方法需要两次巡游是中大西洋山脊（MAR）13degree30minuten的最大和最佳特征肌场。尽管在技术上是雄心勃勃的，但我们来自欧盟资助的蓝色矿业项目的经验以及学术和工业伙伴的参与，贡献了实物数据和成本，大大降低了这项研究的风险。