Search Results (9)

Several Jurassic, ophiolite-hosted Cu-Zn VMS deposits occur in Tuscany. They are hosted by tectonic units of oceanic affinity (Ligurian Units), such as the well-known deposits of nearby Liguria. Industrial production was small and definitively ceased in the 1960s. Locally, massive ore (chalcopyrite-bornite-chalcocite) with an exceptionally high grade was found. The Montecatini Val di Cecina mine exploited the largest “bonanza” and, for few decades in the 19th century, became one of the most profitable copper mines in Europe. This study provides an updated review of these deposits. Tuscan Cu-Zn VMSs mostly occur in proximity of the contact between the serpentinite-gabbro basement and the overlying basalts. Chalcopyrite-pyrite stockworks occur in serpentinite-gabbro cut by dolerite dykes, while the largest massive sulphide bodies are hosted by polymictic-monomictic breccias at the base of pillow basalts. Early chalcopyrite ores were mechanically–chemically reworked and upgraded to bornite-rich nodular ore embedded in a chlorite, calcic amphibole, Fe-rich serpentine, quartz, andradite, ilvaite, and xonotlite assemblage. This bornite-rich ore contains substantial amount of sphalerite and pyrite and ubiquitous grains of clausthalite, hessite, tellurium, and gold. They represent a prime example of the sub-seafloor portion of a hybrid mafic-ultramafic oceanic hydrothermal system formed in an OCC along the slow spreading ridge of the Jurassic Piedmont-Ligurian Ocean. The peculiar mineralogical–textural character of the bornite-rich ore was driven by an interface coupled dissolution–precipitation process mediated by fluids. Full article

Deep-sea mining is a multidimensional concept that requires interdisciplinary research and development to close the current knowledge gaps. This study conducts a bibliometric analysis of the research focus, publishing structures and international and inter-institutional cooperation as evident in academic publishing. This could aid in the identification of knowledge gaps, research opportunities, potential inter-institutional cooperation and the need for strategic investment and policy development. The analysis is based on a sample of 1935 journal papers (from 1968 to 2021) obtained by searching Elsevier’s Scopus database for publications containing an explicit reference to deep-sea mining (or equivalent terms) in their title, abstract or keywords. Publication numbers are broken down by publication year, subject area, author affiliations and source. The scientific output mirrors the commercial interest and the growing environmental concern. A detailed analysis of content is performed on the 2017–2021 subset, containing one third of the total publications. Here, China (152 publ.), the United Kingdom (133), the United States (115) and Germany (107) are the top contributors. China has had a comparatively stronger focus on engineering aspects and produces very few publications with international co-authorship. Almost half of the 2017–2021 publications focus on environmental aspects, whereas engineering aspects (especially vertical transport) are addressed by close to one third. Little is published on site remediation and ore processing, or specifically on ferromanganese crusts. Full article

The future extraction of mineral resources may irreversibly damage ocean floor geodiversity in the Southwest Pacific Ocean. Therefore, understanding of the spatial distribution of ocean floor geodiversity in relation to mineral resources is important. For that purpose, we first developed a geodiversity index map of the western Pacific Ocean including spatial information of openly available digital layers of four components: seafloor geomorphology, sediment thickness, bathymetry and seafloor roughness. Second, we analysed how these components contributed to the geodiversity index. Finally, correlations between three mineral resources (seafloor massive sulphides, polymetallic nodules and cobalt-rich crusts) and the geodiversity index, its components, and the ocean floor age were calculated. The results showed that the ocean floor environment and the time necessary for the formation of the three mineral resources were predominantly related to the bathymetry component and the age of the ocean floor, and to a lesser extent to the seafloor roughness, geomorphology and sediment thickness components. We conclude that the ocean floor geodiversity index and its components contribute to an improved understanding of the spatial distribution of abiotic seafloor diversity and can be optimized by using higher resolution data. We suggest that ocean floor geodiversity could be considered in future resource extraction to support responsible mining and help limit environmental damage. Full article

Seafloor massive sulphide (SMS) deposits are hosts to a wide range of economic minerals, and may become an important resource in the future. The exploitation of these resources is associated with considerable expenses, and a return on investment may depend on the availability of multiple deposits. Therefore, efficient exploration methodologies for base metal deposits are important for future deep sea mining endeavours. Underwater hyperspectral imaging (UHI) has been demonstrated to be able to differentiate between different types of materials on the seafloor. The identification of possible end-members from field data requires prior information in the form of representative signatures for distinct materials. This work presents hyperspectral imaging applied to a selection of materials from the Loki’s Castle active hydrothermal vent site in a laboratory setting. A methodology for compensating for systematic effects and producing the reflectance spectra is detailed, and applied to recover the spectral signatures from the samples. The materials investigated were found to be distinguishable using unsupervised dimensionality reduction methods, and may be used as a reference for future field application. Full article

The Semyenov-2 hydrothermal field located at 13°31′N of the Mid-Atlantic Ridge (MAR) is associated with an oceanic core complex (OCC) and hosted by peridotites and basalts with minor amounts of gabbro and plagiogranites. Seafloor massive sulphides (SMS) are represented by chimneys with zonality, massive sulphides without zonality and sulphide breccia cemented by opal and aragonite. The mean value of Au (20.6 ppm) and Te (40 ppm) is much higher than average for the MAR SMS deposits (3.2 ppm and 8.0 ppm, respectively). Generally, these high concentrations reflect the presence of a wide diversity of Au and Te minerals associated with major mineral paragenesis: primary native gold, melonite (NiTe₂) and tellurobismuthite (Bi₂Te₃) are related to high-temperature chalcopyrite (~350 °C); electrum (AuAg)₁, hessite (Ag₂Te) and altaite (PbTe) are related to medium- and low-temperature Zn-sulphide and opal assemblages (260–230 °C). Calaverite (AuTe₂) and Te-rich “fahlore” Cu₁₂(Sb,As,Te)₄S₁₃ are texturally related to the chalcopyrite-bornite-covellite. Enrichment of Au in sulphide breccia with opal and aragonite cement is driven by the re-deposition and the process of hydrothermal reworking of sulphide. The low-temperature fluid mobilizes gold from primary sulphide, along with Au and Te minerals. As a result, the secondary gold re-precipitate in cement of sulphide breccia. An additional contribution of Au enrichment is the presence of aragonite in the Cu-Zn breccia where the maximal Au content (188 ppm) is reached. Full article

Loki’s Castle on the Arctic Mid-Ocean Ridge (AMOR) is an area of possible seafloor massive sulphide (SMS)-style mineralisation under Norwegian jurisdiction, which, due to mounting social pressure, may be a strategic future source of base and precious metals. The purpose of this study is to characterise mineralised material from a hydrothermal vent system on the AMOR in detail for the first time, and to discuss the suitability of methods used; reflected light microscopy, X-ray diffraction (XRD), whole rock geochemistry, electron probe micro-analysis (EPMA), and QEMSCAN. The primary sulphide phases, identifiable by microscopy, are pyrite and marcasite with minor pyrrhotite and galena, but multiple samples from the Loki’s Castle contain economically interesting quantities of copper (hosted in isocubanite and chalcopyrite) and zinc (hosted in sphalerite), as well as silver and gold. This reinforces the notion that slow spreading ridges may host significant base metal deposits. Micro-textures (chalcopyrite inclusions and exsolutions in sphalerite and isocubanite respectively) are typically undefinable by QEMSCAN, and require quantitative measurement by EPMA. QEMSCAN can be used to efficiently generate average grain size and mineral association data, as well as composition data, and is likely to be a powerful tool in assessing the effectiveness of SMS mineral processing. Full article

Noble gases have become a powerful tool to constrain the origin and evolution of ore-forming fluids in seafloor hydrothermal systems. The aim of this study was to apply these tracers to understand the genesis of newly discovered polymetallic sulphide deposits along the ultraslow-spreading Southwest Indian Ridge (SWIR). The helium, argon, and sulphur isotope compositions of metal sulphide minerals were measured for a number of active/inactive vent fields in the Indian Ocean. The helium concentrations and isotopic ratios in these ore samples are variable (⁴He: 0.09–2.42 × 10⁻⁸ cm³STP∙g⁻¹; ³He: 0.06–3.28 × 10⁻¹³ cm³STP∙g⁻¹; ³He/⁴He: 1.12–9.67 R_a) and generally greater than the modern atmosphere, but significantly lower than those in massive sulphides from the fast-spreading East Pacific Rise (EPR), especially for three Cu–Fe-rich samples from the ultramafic-hosted Tianzuo and Kairei vent fields. On the contrary, most of the SWIR sulphide deposits have somewhat higher ⁴⁰Ar/³⁶Ar ratios of trapped fluids (ranging from 290.6 to 303.4) when compared to the EPR ore samples. Moreover, the majority of sulphide minerals from the Indian Ocean have much higher δ³⁴S values (3.0‰–9.8‰, ~5.9 on average, n = 49) than other basaltic-hosted active hydrothermal systems on the EPR. Overall, these He–Ar–S results are well within the range of seafloor massive sulphide deposits at global sediment-starved mid-ocean ridges (MORs), lying between those of air-saturated water (ASW) and mid-ocean ridge basalt (MORB) end members. Therefore, our study suggests that the helium was derived mainly from the MORB mantle by degassing during the high-temperature stage of hydrothermal activity, as well as from a mixture of vent fluids with variable amounts of ambient seawater during either earlier or late-stage low-temperature hydrothermal episodes, whereas the argon in ore-forming fluids trapped within sulphide minerals was predominantly derived from deep-sea water. Additionally, relatively high δ³⁴S values exhibit a great estimated proportion (up to nearly 40%) of seawater-derived components. In summary, sub-seafloor extensive fluid circulation, pervasive low-temperature alteration, shallow seawater entrainment, and mixing processes, may make a larger contribution to the SWIR hydrothermal ore-forming systems, compared to fast-spreading centres. Full article

The Permian (~273–274 Ma) Ice volcanogenic massive sulphide (VMS) deposit represents a mound shaped Cyprus (mafic)-type VMS deposit (~4.5 Mt @ 1.5% Cu) hosted in basaltic rocks of Slide Mountain terrane. The deposit consists of massive sulphides that are underlain by a chlorite-sulphide-hematite-rich stringer pipe, and overlain by a hematite-(pyrite)-rich exhalative chert. The sulphides are divided into five facies: (1) pyrite-rich; (2) pyrite-bornite-rich; (3) pyrite-chalcopyrite-rich; (4) hematite-pyrite; and (5) stringer sulphide. The sulphides have a distinct paragenetic and textural evolution in the massive sulphide that reflect: (1) an early, low temperature stage (<250 °C dominated by Fe-Zn-Cu-rich mineralization; (2) an intermediate, high temperature stage (>300 °C) dominated by Cu-Fe-rich mineralization; and (3) a late, low temperature phase (<150 °C) dominated by Fe-rich mineralization. In situ sulphur isotope data pyrite and chalcopyrite (by secondary ion mass spectrometry (SIMS)) range from δ³⁴S = +1.8‰ to +8.2‰, but vary as a function of paragenesis and temperature of deposition. Both early and late forming sulfides were dominated by sulphur from partial thermochemical sulphate reduction (TSR) of seawater sulfate, whereas intermediate, high temperature mineralization was dominated leached, igneous sulphur from basement rocks. These results are similar to modern seafloor vents and many ancient VMS deposits. Full article

This paper reports the leaching of seafloor massive sulphides (SMS) from the Loki’s Castle area at the Arctic Mid-Ocean Ridge in sulphuric acid with manganese dioxide and sodium chloride. The results presented are of various leaching experiments conducted under different conditions in order to optimise the dissolution of copper and silver. It was shown that the main copper bearing minerals in the SMS were chalcopyrite and isocubanite, while silver could occur as an admixture in the crystallographic lattice of sulphides or as disseminated micro inclusions. Based on the results, the leaching mechanism was discussed and elucidated. It was shown that the dissolution of the SMS was mainly due to galvanic interactions between the primary marine minerals of SMS and manganese dioxide. Addition of sodium chloride promoted the extraction mechanism. Full article