Massive Sulfide Deposits Research Articles

Evolution of the Garmab-e-Paein native copper-rich volcanogenic massive sulfide deposit from northeast Iran: Insights from sulfur isotope and chlorite chemistry

The Garmab-e-Paein Cu-Ag volcanogenic massive sulfide (VMS) deposit occurs as stratiform and stratabound orebody within a specific stratigraphic horizon in a Late Cretaceous volcano-sedimentary sequence of the Sabzevar zone, northeast Iran. The host rocks to mineralization are andesitic-trachyandesitic volcanic and volcaniclastic rocks. Based on textural and mineralogical studies, the VMS mineralization is comprised of four ore facies: 1) vein-veinlets (stringer) containing chalcopyrite, pyrite and minor magnetite, 2) massive ore, dominated by pyrite and minor chalcopyrite, 3) bedded ore containing laminated pyrite, and 4) exhalite containing Fe-Mn oxide-hydroxides such as hematite, psilomelane and pyrolusite. Wall rock alteration styles are chloritic, minor silicic and secondary argillic. There is a distinct metal zonation in the massive sulfide orebody; Au, Pb, As, and Ag contents and the Cu/Zn ratio increase vertically from the stringer to the massive facies, but decrease laterally from the stringer to the bedded facies. Zinc and Mn increase from the stringer to the bedded ore facies. Sulfur isotope values for pyrite range from −1.7 to +5.1‰, with average +1.4‰. The δ34S values of massive ore facies (−1.7 and +2.7‰) increase downward toward the stockwork (+2.2 to +4.3‰) and laterally outward toward the bedded (+5.1‰) zones. The near-zero sulfur isotope values indicate that most of the sulfur was derived from leaching of underlying host volcanic rocks by hydrothermal fluids circulating in the high temperature reaction zone.Extensive disseminations and vein-veinlets of native copper mineralization formed within the hanging wall Late Cretaceous volcanic rocks and younger Paleocene conglomerates. The native copper mineralization is accompanied by chlorite and zeolite alteration, and both formed after formation of the Garmab-e-Paein VMS deposit during diagenesis, burial metamorphism and uplift. The deposit is now potentially economic due to the native copper mineralization.Two generations of chlorite are observed in the deposit: Chl-I is accompanied pyrite and chalcopyrite, in the VMS mineralization system, and the second Chl-II occurs along with zeolite and native copper mineralization. The EPMA results show that Chl-I is more Fe-rich than Chl-II.

Geochemistry of Sphalerite from the Permian Volcanic-Hosted Massive Sulphide (VHMS) Deposits in the Tasik Chini Area, Peninsular Malaysia: Constraints for Ore Genesis

The Bukit Botol and Bukit Ketaya deposits are two examples of volcanic-hosted massive sulphide (VHMS) deposits that occur in the Tasik Chini area, Central Belt of Peninsular Malaysia. The mineralisation is divided into subzones distinguished by spatial, mineralogical, and textural characteristics. The primary sulphide minerals include pyrite, chalcopyrite, sphalerite, and galena, with lesser amounts of Sn- and Ag-bearing minerals, with Au. However, pyrrhotite is absent from both deposits. This study presents the results of sphalerite chemistry analysed by using an electron microprobe. Two types of sphalerite are recognised: sphalerite from the Bukit Botol deposit reveals a range of <DL to 24.0 mole% FeS, whereas sphalerite from the Bukit Ketaya deposit shows a range of <DL to 3 mole% FeS. Significant variations are shown in Zn, Cu, Cd, and Ag levels. Although the sphalerite has a wide variation in composition, a discernible decreasing Fe trend is exhibited from the stringer zone towards massive sulphide. This compositional variation in sphalerites may in part reflect variable temperature and activity of sulphur in the hydrothermal fluids during ore formation. Alternatively, the bimodal composition variations suggest that mineral chemistry relates to contrasting depositional processes. The Zn/Cd ratios for sphalerite from both these deposits are similar to those exhibited by volcano−sedimentary deposits with a volcanic origin. Therefore, the consistently low Cd concentrations and moderate to high Zn/Cd ratios suggest mixing of seawater and minor magmatic fluids controlling the chemistry of sphalerite at both deposits during their formation.

Refining the Paleoproterozoic tectonothermal history of the Penokean Orogen: New U-Pb age constraints from the Pembine-Wausau terrane, Wisconsin, USA

Abstract An enduring problem in the assembly of Laurentia is uncertainty about the nature and timing of magmatism, deformation, and metamorphism in the Paleoproterozoic Wisconsin magmatic terranes, which have been variously interpreted as an intra-oceanic arc, foredeep or continental back-arc. Resolving these competing models is difficult due in part to a lack of a robust time-frame for magmatism in the terranes. The northeast part of the terranes in northern Wisconsin (USA) comprise mafic and felsic volcanic rocks and syn-volcanic granites thought to have been emplaced and metamorphosed during the 1890–1830 Ma Penokean orogeny. New in situ U-Pb geochronology of igneous zircon from the volcanic rocks (Beecher Formation), and from two tonalitic plutons (the Dunbar Gneiss and Newingham Tonalite) intruding the volcanic rocks, yielded crystallization ages ranging from 1847 ± 10 Ma to 1842 ± 7 Ma (95% confidence). Thus, these rocks record a magmatic episode that is synchronous with bimodal volcanism in the Wausau domain and Marshfield terrane farther south. Our results, integrated with published data into a time-space diagram, highlight two bimodal magmatic cycles, the first at 1890–1860 Ma and the second at 1845–1830 Ma, developed on extended crust of the Superior Craton. The magmatic episodes are broadly synchronous with volcanogenic massive sulfide mineralization and deposition of Lake Superior banded iron formations. Our data and interpretation are consistent with the Penokean orogeny marking west Pacific-style accretionary orogenesis involving lithospheric extension of the continental margin, punctuated by transient crustal shortening that was accommodated by folding and thrusting of the arc-back-arc system. The model explains the shared magmatic history of the Pembine-Wausau and Marshfield terranes. Our study also reveals an overprinting metamorphic event recorded by reset zircon and new monazite growth dated at 1775 ± 10 Ma suggesting that the main metamorphic event in the terranes is related to the Yavapai-interval accretion rather than the Penokean orogeny.

Late Cretaceous hydrothermal vent communities from the Troodos ophiolite, Cyprus: systematics and evolutionary significance

AbstractModern hydrothermal vent communities are based on chemosynthesis by microbial primary producers. Molecular phylogenetic divergence estimates indicate that many of the dominant vent taxa arose during the Cenozoic and Cretaceous; however, the fossil record of vent communities from these time periods is poor. One occurrence of such Cretaceous vent communities pertains to six volcanogenic massive sulphide deposits in the Troodos ophiolite of Cyprus. These deposits represent hydrothermal activity on deep (2500–5000 m) arc‐related spreading ridge(s) in the Neotethyan Ocean over several million years during the late Cenomanian and earliest Turonian. The Cyprus vent communities consist of worm tubes, representing possible vestimentiferans and serpulids, together with a moderate diversity of abyssochrysoid gastropods, belonging to eight new species (Desbruyeresia kinousaensis sp. nov., Desbruyeresia memiensis sp. nov., Desbruyeresia kambiaensis sp. nov., Hokkaidoconcha morisseaui sp. nov., Ascheria canni sp. nov., Cyprioconcha robertsoni gen. et sp. nov., Paskentana xenophontosi sp. nov. and Paskentana dixoni sp. nov.) in five genera and three families; none of the species is shared between vent sites. A single gaudryceratid ammonite from one of the vent sites most likely represents a water‐logged shell that sank from surface waters. The gastropod fauna contains the first representatives of the genera Desbruyeresia, Hokkaidoconcha, Ascheria and Paskentana from hydrothermal vents, and also the youngest representative of the last‐named genus in any environment. The Cypriot vent communities share tube worms with slightly older (Cenomanian) and younger (Turonian–Santonian) vent communities elsewhere in the western part of the Neotethyan Ocean.

The Role of Mineral Assemblages in The Environmental Impact of Cu-Sulfide Deposits: A Case Study from Norway

Metallic mineral deposits represent natural geochemical anomalies of economically valuable commodities but, at the same time, their weathering may have negative environmental implications. Cu-sulfide mineral deposits have been recognized as deposits with a particularly large environmental footprint. However, different Cu deposits may result in significantly different environmental impacts, mostly depending on weathering conditions, but also on geological characteristics (mineralogy, geochemistry, host-rock lithology) of the Cu mineralization. This study presents new mineral and geochemical data from the Repparfjord Tectonic Window sediment-hosted Cu deposits and the Caledonian volcanogenic massive sulfides (VMS) deposits. The deposits share similar mineral features, with chalcopyrite and bornite as the main ore minerals, but they differ according to their trace element composition, gangue mineralogy, and host lithology. The studied sediment-hosted Cu deposits are depleted in most toxic metals and metalloids like Zn, As, Cd, and Hg, whereas the Røros Caledonian VMS mineralization brings elevated concentrations of Zn, Cd, In, Bi, As, and Cd. The conducted leaching experiments were set to simulate on-land and submarine weathering conditions. A high redox potential was confirmed as the main driving force in the destabilization of Cu-sulfides. Galvanic reactions may also contribute to the destabilization of minerals with low rest potentials, like sphalerite and pyrrhotite, even under near-neutral or slightly alkaline conditions. In addition, the presence of carbonates under near-neutral to slightly alkaline conditions may increase the reactivity of Cu sulfides and mobilize Cu, most likely as CuCO3 (aq).

Development of a laser ablation ICP-MS method for the analysis of fluid inclusions associated with volcanogenic massive sulfide deposits

There is increasing acceptance of the presence of variable magmatic contributions to the mineralizing fluids in the formation of volcanogenic massive sulfide (VMS) deposits. The world-class Windy Craggy Cu-Co-Au deposit (>300 MT @ 2.12 wt% Cu) in northwestern British Columbia is of interest because, unlike most VMS deposits, fluid inclusions in quartz from within the deposit range from relatively low to intermediate salinity (most 6–16 wt% equivalent). In this study we used an excimer (193 nm) laser ablation system interfaced to a quadrupole inductively coupled plasma mass spectrometer to quantify key metals and metalloids that are considered by many to be indicative of magmatic contributions to hydrothermal ore deposits. Although LA-ICP-MS signals from these low-salinity inclusions are highly transient, we were able to quantify Na, Mg, K, Ca, Mn, Fe, Co, Cu, Zn, Sr, Sn, Ba, Ce, Pb and Bi consistently – of the 34 elements that were monitored. Furthermore, Cl, Sb, Cd, Mo, Rb, Br and As were also measured in a significant number of inclusions. Comparison of the fluid inclusion chemistry with unaltered and altered mafic volcanic and sedimentary rocks and mineralized samples from the deposit indicate that enrichment in the main ore metals (Cu, Zn, Fe, Pb) in the inclusions reflects that of the altered rocks and sulfides. Metals and metalloids that may indicate a magmatic contribution typically show much greater enrichments in the fluid inclusions over the host rocks at the same Cu concentration; in particular Bi, Sn and Sb are significantly elevated when compared to the host rock samples. These data are consistent with the ore-forming fluids at Windy Craggy having a strong magmatic contribution. Supplementary material: fluid inclusion data for temperature of homogenization and salinity, and full analytical results for laser ablation ICP-MS analyses of individual inclusions for the two analytical sessions are available at https://doi.org/10.6084/m9.figshare.c.5443094

Metallogeny of a Pan-African oceanic arc: VHMS and gold deposits in the Ariab-Arbaat belt, Haya terrane, Red Sea Hills (Sudan)

Gold in the Ariab district (Red Sea Hills, Sudan) is mined in gossans developed over volcanogenic massive sulphide (VHMS) deposits formed in the context of a Tonian ensimatic arc of the Haiya terrane, in the Neoproterozoic Arabo-Nubian Shield. All the primary gold occurrences of the Ariab belt, whatever their style (VHMS-, quartz lode- or shear-zone-hosted), appear, however, to have been syn-to late-kinematic, i.e., formed in the context of the final Pan-African collision leading to the Arabian-Nubian Shield (D3 event), and therefore are post-VHMS. Gold is thus found associated with either galena or bismuth telluride in late syn- to post-metamorphic sets of (micro)cracks, mostly within earlier pyrite or arsenopyrite. Gold deposition as native gold or electrum occurred when an intense fluid circulation of metamorphic CO2-H2O rich fluids underwent significant decompression from lithostatic to hydrostatic pressures at temperatures decreasing from 400 to 430 °C at around 8 km depth down to 300 °C. Although no clear evidence of volatile unmixing was observed, the decompression, together with a temperature decrease due to dilution by aqueous rich fluids, favoured gold deposition.The late-D3 gold event in the Ariab belt has all the makings of an orogenic gold system, notably similar to the Late Carboniferous gold event in the West European Variscan belt. Thus, it is possible to propose that, at the end of the collision events, fluids released from the newly formed terrane root were channelled towards the upper crust through the major D3 shear zones such as the Oko shear zone. The fluids outpouring from these major drains were then conveyed through fault plays and damaged zones, up to specific chemical traps within massive sulphide ore bodies or quartz veins systems. Thus, the Ariab gold district could be classified as a representative of the class of orogenic gold deposits.

LA-ICP-MS sphalerite and galena trace element chemistry and mineralization-style fingerprinting for carbonate-hosted Pb-Zn deposits: Perspective from early Devonian Huodehong deposit in Yunnan, South China

The Sichuan-Yunnan-Guizhou metallogenic province (SYGMP) in the southwestern margin of the Yangtze block is an important Pb-Zn province in China. In the SYGMP, over 400 Pb-Zn deposits are mostly hosted in the Sinian, Lower Cambrian and Carboniferous sedimentary rocks and rarely in the Devonian carbonate rocks (e.g., Houdehong). For Houdehong, however, its ore-forming conditions and deposit type remain unclear due to limited geological and geochemical data available. In this study, LA-ICP-MS spot analysis and mapping were conducted to determine the trace element features in the sphalerite and galena from Huodehong. The results show that the sphalerite is characterized by enrichments in Ge and Tl but depletions of Fe, Mn, and Co. Most of these elements have widely varying concentrations and occur as solid solutions in the sphalerite crystal lattice. The critical element of Ge enters sphalerite through coupling substitution with Mn2+ for Zn2+ and/or Cd2+. The results calculated by empirical formula show that the sphalerite mineralization occurred under low-temperature conditions (<180℃). Meanwhile, the Houdehong galena contains low Se, Cd, Tl and Bi, and very low Ag (<1.0 ppm) and Sb (<5.0 ppm) concentrations, which is likely controlled by the original ore-fluid compositions. Trace element compositions of the Houdehong sulfides are generally similar to that of the sulfides from Mississippi Valley-type (MVT) deposits and many other Pb-Zn deposits in the SYGMP, but markedly different from those of volcanogenic massive sulfide (VMS), sedimentary exhalative (SEDEX) and skarn Pb-Zn deposits. Considering also the deposit geological and geochemical features, we considered that the Huodehong Pb-Zn deposit is of MVT. Our findings provide further geological and geochemical evidence for understanding the Devonian carbonate-hosted Pb-Zn mineralization in the region.

Seismic imaging across fault systems in the Abitibi greenstone belt – an analysis of pre- and post-stack migration approaches in the Chibougamau area, Quebec, Canada

Abstract. Two high-resolution seismic reflection profiles acquired north and south of Chibougamau, located in the northeast of the Abitibi subprovince of Canada, help understand historic volcanically hosted massive sulfide (VMS) deposits and hydrothermal Cu–Au mineralization found there. Major faults crossed by the profiles include the Barlow fault in the north and the Doda fault and the Guercheville fault in the south, all targets of this study that seeks to determine spatial relationships with a known metal endowment in the area. Common-offset DMO corrections and common-offset pre-stack time migrations (PSTMs) were considered. Irregularities of the trace midpoint distribution resulting from the crooked geometry of both profiles and their relative contribution to the DMO and PSTM methods and seismic illumination were assessed in the context of the complex subsurface architecture of the area. To scrutinize this contribution, seismic images were generated for offset ranges of 0–9 km using increments of 3 km. Migration of out-of-plane reflections used cross-dip element analysis to accurately estimate the fault dip. The seismic imaging shows the thickening of the upper-crustal rocks near the fault zones along both profiles. In the northern seismic reflection section, the key geological structures identified include the Barlow fault and two diffraction sets imaged within the fault zone that represent potential targets for future exploration. The south seismic reflection section shows rather a complicated geometry of two fault systems. The Guercheville fault observed as a subhorizontal reflector connects to a steeply dipping reflector. The Doda fault dips subvertical in the shallow crust but as a steeply dipping reflection set at depth. Nearby gold showings suggest that these faults may help channel and concentrate mineralizing fluids.

HIGH-PRECISION CA-ID-TIMS AGE CONSTRAINTS ON THE NIBLACK Cu-Zn-Au-Ag DEPOSITS: A NEOPROTEROZOIC VOLCANIC-HOSTED MASSIVE SULFIDE DEPOSIT IN THE NORTH AMERICAN CORDILLERA

Abstract The Neoproterozoic-Cambrian Wales Group and Ordovician-early Silurian Moira Sound unit of Prince of Wales Island, Alaska, USA, host numerous volcanic-hosted massive sulfide (VHMS) deposits and occurrences, including the Niblack VHMS deposits. Previous attempts to determine the age of the felsic volcanic host rocks in the Niblack area have resulted in conflicting results and interpretations. We have utilized chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb zircon geochronology to acquire highly precise crystallization and maximum depositional ages for a total of six samples of felsic volcanic and intrusive rocks from Niblack. This study establishes age constraints for the Niblack felsic succession of (1) crystallization ages of 565.1 ± 0.9 and 564.8 ± 1.0 Ma for coherent rhyolite flows, (2) maximum depositional ages of 565.3 ± 0.9 and 565.2 ± 0.9 Ma for felsic volcaniclastic rocks, (3) a crystallization age of 565.2 ± 0.9 Ma for a quartz-feldspar-phyric subvolcanic sill, and (4) a crystallization age of 564.8 ± 1.0 Ma for a felsic dike that crosscuts the Niblack felsic succession. These results indicate that the ~200-m-thick Niblack felsic succession and VHMS deposits formed during one episode of felsic volcanism at ca. 565.1 ± 0.9 Ma and are thus confirmed as part of the Neoproterozoic Wales Group. Results of this study provide the first chronostratigraphic framework for felsic volcanism associated with VHMS deposit formation at Niblack and have implications for mineral exploration on Prince of Wales Island and elsewhere in the Alexander terrane.

Recognizing subsurface breccias in Archean terranes: Implications for district scale metallogeny

Breccias are common in ancient and modern volcanic terranes, where they form at and below surface through volcanic, hydrovolcanic, magmatic, or tectonic mechanisms. They are critical for volcanic reconstruction as stratigraphic markers and indicators of geodynamic change and since they can be associated with mineralization their genesis is also important from an exploration perspective. Their origin can be difficult to ascertain in ancient terranes that have undergone polyphase deformation and associated metamorphism. The Joliet Breccia is a subeconomic Cu-Ag prospect within the Neoarchean Rouyn-Noranda mining district, in the Abitbi greenstone belt, Canada. It was previously interpreted as a phreatic breccia formed on the seafloor. This study presents new data indicating that the Joliet Breccia is a subsurface magmatic-hydrothermal breccia. Specifically, the recognition of gradational contacts with host rocks and between internal breccia domains, lack of sedimentary features and the spatial and temporal association with a tonalite intrusion strongly supports this interpretation. The angular, poorly sorted, lithic clasts derived from the immediate host rocks, hydrothermal cement, complete absence of a rock flour matrix, and presence of a radial and concentric fracture pattern extending into the host rocks, further support a subsurface magmatic-hydrothermal emplacement mechanism.A new TIMS U-Pb zircon age of 2698.0 ± 0.9 Ma (2σ) for a tonalite block within the breccia constrains the maximum age of brecciation. Four LA-ICP-MS U-Pb dates on hydrothermal monazite (2693.7 ± 1.0/8.9 Ma; 2696.9 ± 0.45/8.9 Ma; 2698.7 ± 1.4/8.9 Ma; 2701.2 ± 0.33/8.9 Ma; 2 s/2ssys) found in the cement of the Breccia indicate brecciation and mineralization occurred shortly after the emplacement of the tonalite. Similarly, the ca. 2697 Ma St. Jude intrusive breccia indicates a localized ca. 2699–2695 Ma magmatic-hydrothermal event superimposed on ca. 2704–2701 Ma strata. These breccias are temporally correlative with the youngest units of the Blake River Group strata and associated ca. 2698–2695 Ma volcanogenic massive sulfide (VMS) deposits, which suggests an indirect genetic link between these two hydrothermal systems. The VMS deposits may represent the near surface, distal manifestations of a deeper magmatic-hydrothermal system akin to the porphyry-intermediate sulfidation epithermal continuum in modern subaerial volcanic arcs.

Differentiating between hydrothermal and diagenetic carbonate using rare earth element and yttrium (REE+Y) geochemistry: a case study from the Paleoproterozoic George Fisher massive sulfide Zn deposit, Mount Isa, Australia

Carbonate minerals are ubiquitous in most sediment-hosted mineral deposits. These deposits can contain a variety of carbonate types with complex paragenetic relationships. When normalized to chondritic values (CN), rare-earth elements and yttrium (REE+YCN) can be used to constrain fluid chemistry and fluid-rock interaction processes in both low- and high-temperature settings. Unlike other phases (e.g., pyrite), the application of in situ laser ablation-inductively coupled plasma-mass spectroscopy (LA-ICP-MS) data to the differentiation of pre-ore and hydrothermal carbonates remains relatively untested. To assess the potential applicability of carbonate in situ REE+Y data, we combined transmitted light and cathodoluminescence (CL) petrography with LA-ICP-MS analysis of carbonate mineral phases from (1) the Proterozoic George Fisher clastic dominated (CD-type) massive sulfide deposit and from (2) correlative, barren host rock lithologies (Urquhart Shale Formation). The REE+YCN composition of pre-ore calcite suggests it formed during diagenesis from diagenetic pore fluids derived from ferruginous, anoxic seawater. Hydrothermal and hydrothermally altered calcite and dolomite from George Fisher is generally more LREE depleted than the pre-ore calcite, whole-rock REE concentrations, and shale reference values. We suggest this is the result of hydrothermal alteration by saline Cl--rich mineralizing fluids. Furthermore, the presence of both positive and negative Eu/Eu* values in calcite and dolomite indicates that the mineralizing fluids were relatively hot (>250°C) and cooled below 200–250°C during ore formation. This study confirms the hypothesis that in situ REE+Y data can be used to differentiate between pre-ore and hydrothermal carbonate and provide important constraints on the conditions of ore formation.

Mineralogical and geochemical characteristics and ore-forming mechanism of hydrothermal sediments in the middle and southern Okinawa Trough

In this study, analysis of mineralogy and geochemistry of fifteen surface sediment samples from four hydrothermal fields in the middle and southern Okinawa Trough is presented. Sediment samples can be divided into two types: (1) Metalliferous group (MS group) containing large amounts of sulfides and sulfate are enriched in Pb, Zn, Cu, Fe, Au, Ag, Ba, As, Hg, Se, Sb, Mo, slightly enriched in U, V, and have rare earth elements (REE) patterns similar to those of hydrothermal vent fluids and sulfides, indicating formation by a complex combination of wasting and erosion primary massive sulfide deposits and plume fallout of sulfides and sulfate. The occurrence of sphalerite with high contents of Fe and of co-existing pyrrhotite as major Fe-sulfide indicate that these minerals are formed at high temperature with low-sulfur fugacity in the Clam and Jade hydrothermal sites. The enrichment of Pb, Zn, Cu, Au, Ag, Ba, As, Hg, Se, Sb, and Mo is related to the presence of galena, sphalerite, Cu-sulfides, stibnite, and realgar in the sediments. (2) Non-metalliferous group (non-MS group) containing small amounts of pyrite are slightly enriched in Pb, Zn, Cu, Au, Ag, As, Hg, Se, Sb, and Mo relative to the East China Sea (ECS) continental shelf sediments, with REE exhibiting a “shale-like flat” patterns and close to Taiwan sediments in a REE discrimination plot, indicating formation by a large amount of terrigenous materials originated from Taiwan Island and a small amount of particles of sulfides in the hydrothermal nonbuoyant plume. The slight enrichment of Pb, Zn, Cu, Au, Ag, As, Hg, Se, Sb, and Mo maybe caused by co-precipitation with the fine-grained sulfides settling from the nonbuoyant plume. The positive relationships between the HREE fractionation index (Gd/Yb)N, heavy mineral proportion, and δEu suggest that (Gd/Yb)N can be used as a sensitive indicator for reflecting the effect of hydrothermal activity on the sediments.

3D geostatistical modeling of metal contents and lithofacies for mineralization mechanism determination of a seafloor hydrothermal deposit in the middle Okinawa Trough, Izena Hole

Seafloor hydrothermal deposits in the Okinawa Trough have been regarded as a modern analog of kuroko-type volcanogenic massive sulfide (VMS) deposits on land. VMS deposit is one of the primary producers of base metals (e.g. Cu, Pb, Zn) and precious metals (e.g. Au, Ag). However, owing to difficulties in accessing subseafloor samples/data without costly drilling operations, the spatial distribution of metal contents below the seafloor remains poorly constrained. We apply a combination of four spatial modeling methods: (1) principal component analysis; (2) k-means clustering; and (3, 4) conditional geostatistical simulations of turning bands and pluri-Gaussian. These modeling methods are based on the whole-rock geochemical data using inductively coupled plasma-quadruple mass spectrometry, together with lithologic log data obtained from onboard visual core descriptions, and X-ray diffraction analyses from the middle Okinawa Trough, Izena Hole, during the cruise CK16-05 (Expedition 909) in 2016 by D/V Chikyu. The primary goal is to construct plausible 3D models for the contents of base metals and silver as well as lithotypes. The constructed models successfully map the configuration and zonation of subseafloor metal deposits with hydrothermal flow paths, which sheds light on hydrothermal circulation systems and metal accumulation mechanisms. This approach is shown to be effective for geologic and mineralization modeling and exploration of (sub)seafloor hydrothermal deposits.

Subseafloor sulphide deposit formed by pumice replacement mineralisation

Seafloor massive sulphide (SMS) deposits, modern analogues of volcanogenic massive sulphide (VMS) deposits on land, represent future resources of base and precious metals. Studies of VMS deposits have proposed two emplacement mechanisms for SMS deposits: exhalative deposition on the seafloor and mineral and void space replacement beneath the seafloor. The details of the latter mechanism are poorly characterised in detail, despite its potentially significant role in global metal cycling throughout Earth’s history, because in-situ studies require costly drilling campaigns to sample SMS deposits. Here, we interpret petrographic, geochemical and geophysical data from drill holes in a modern SMS deposit and demonstrate that it formed via subseafloor replacement of pumice. Samples from the sulphide body and overlying sediment at the Hakurei Site, Izena Hole, middle Okinawa Trough indicate that sulphides initially formed as aggregates of framboidal pyrite and matured into colloform and euhedral pyrite, which were replaced by chalcopyrite, sphalerite and galena. The initial framboidal pyrite is closely associated with altered material derived from pumice, and alternating layers of pumiceous and hemipelagic sediments functioned as a factory of sulphide mineralisation. We infer that anhydrite-rich layers within the hemipelagic sediment forced hydrothermal fluids to flow laterally, controlling precipitation of a sulphide body extending hundreds of meters.

Innovative seismic imaging of volcanogenic massive sulfide deposits, Neves-Corvo, Portugal — Part 1: In-mine array

To evaluate and upscale the feasibility of using exploration tunnels in an operating mine for active-source seismic imaging, a seismic experiment was conducted at the Neves-Corvo mine, in southern Portugal. Four seismic profiles were deployed in exploration drifts approximately 650 m beneath the ground surface, above the world-class Lombador volcanogenic massive sulfide deposit. In addition to the tunnel profiles, two perpendicular surface seismic profiles were deployed above the exploration tunnels. The survey was possible due to a newly developed prototype global positioning system (GPS) time transmitter enabling accurate GPS synchronization of cabled and nodal seismic recorders, below and on the surface. Another innovative acquisition aspect was a 1.65 t broadband, linear synchronous motor (LSM) driven — electric seismic vibrator (e-vib) used as the seismic source along two of the exploration tunnels. We have evaluated the challenges and innovations necessary for active-source tunnel seismic acquisition, characterized by high levels of vibrational noise from the mining activities. In addition, we evaluated the LSM vibrator’s signal and overall seismic-data quality in this hard rock mining environment. Our processing results from the tunnel data and 3D reflection imaging of the Lombador deposit below the exploration tunnels were checked for consistency through constant-velocity 3D ray-tracing traveltime forward modeling. For imaging purposes, 3D Kirchhoff prestack depth and poststack time-migration algorithms were used, with both successfully imaging the targeted deposit. The results obtained show that active-source-seismic imaging using subsurface mining infrastructure of operational mines is possible. However, it requires innovative exploration strategies, a broadband seismic source, an accurate GPS-time system capable of transmitting GPS-time hundreds of meters below the surface, and careful processing. The results obtained open up possibilities for similar studies in different mining or tunneling projects.

Sulfide remobilization and trace element redistribution during metamorphism and deformation at the Xitieshan Pb-Zn deposit, NW China

The effects of post-ore metamorphism and deformation on trace element concentrations in sulfides have recently received increasing attention. In this study, we report comprehensive petrographic observations combined with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) trace element analysis data of pyrite, sphalerite, and chalcopyrite to evaluate the influence of regional metamorphism and deformation on sulfide remobilization and trace element distribution in the metamorphosed volcanic-sediment-hosted Xitieshan deposit, NW China. The Xitieshan deposit, located in the central segment of the North Qaidam orogenic belt along the northeastern margin of the Tibetan Plateau, is one of the largest Pb-Zn producers in China. Marble-hosted mineralization accounts for approximately 80% of the total mineral resources with the rest hosted in schist in this deposit. Petrographic studies coupled with detailed field work revealed that sulfide minerals in marble-hosted mineralization generally preserve the primary ore textures well with respect to the original mineralization. In contrast, sulfide minerals in schist-hosted ores exhibit various brittle and ductile deformation textures, including cataclasis, recrystallization, annealing, Durchbewegung, fracture healing textures, and veinlets, indicating that sulfide remobilization during metamorphism and deformation was most likely achieved by the combination of mechanical and chemical processes.LA-ICP-MS trace element data for pyrite grains with inclusion-rich cores (Py1b) inside “clean” inclusion-free overgrowth (Py3) indicate that the recrystallization of pyrite both expels trapped inclusions and liberates trace elements such as Cr, Mn, Ni, Cu, Zn, Ag, In, Sn, and Sb. Py3 contains more As than Py1, suggesting that the enrichment of As into recrystallized pyrite occurred during metamorphism. Compared to primary sphalerite (Sp1), the deformed counterpart (Sp2) is characterized by the depletion of In, which could be attributed to (a) remobilization of In into recrystallized chalcopyrite, and/or (b) remobilization and diffusion of In out of primary sphalerite and subsequent formation of the indium-bearing mineral during metamorphism. Indium, Sn, and Ag concentrations were significantly higher in recrystallized chalcopyrite grains than in other analyzed sulfide minerals, indicating that these elements are preferentially incorporated into chalcopyrite under metamorphic conditions.Trace element signatures for deformed and recrystallized pyrite, sphalerite, and chalcopyrite resemble previously reported data from other massive sulfide deposits that have undergone metamorphism and deformation elsewhere. Original mineralization at Xitieshan formed in a high-temperature, magmatically-driven hydrothermal system, which is indicated by the high Co/Ni ratios in pyrite, elevated concentrations of Sn in chalcopyrite and indium in sphalerite, and high calculated temperatures (350–420 ℃) by using the novel “Ga-Ge-In-Mn-Fe in sphalerite” geothermometer.

Resource estimation of the sulfide-rich deposits of the Yuhuang-1 hydrothermal field on the ultraslow-spreading Southwest Indian Ridge

Abstract Seafloor massive sulfide (SMS) deposits are important deep-sea mineral resources expected to occur predominantly on slow- and ultraslow-spreading mid-ocean ridges. Resource estimates are already available for some of the largest SMS deposits on slow-spreading ridges but not on ultraslow-spreading ridges. Based on geological mapping and sampling, this study investigates the distribution and content of sulfide-rich deposits in the Yuhuang-1 hydrothermal field (YHF), located on the ultraslow-spreading Southwest Indian Ridge. The sulfide-rich deposits in the YHF are composed of two areas ~500 m apart: the southwest sulfide area (SWS) and the northeast sulfide area (NES). We calculated the volume of sulfide-rich moundsin the YHF and arrived at a total accumulation of ~10.6 × 106 tons, including at least ~7.5 × 105 tons of copper and zinc and ~18 tons of gold. Furthermore, considering the coverage of layered hydrothermal sediment mixed with sulfide-rich breccias, which may have underlying massive sulfide deposits, the maximum total mass was estimated at ~45.1 × 106 tons. This suggests that the YHF is one of the largest SMS deposits worldwide and confirm that ultraslow-spreading ridges have the greatest potential to form large-scale SMS deposits.

A Devonian age for the Sarhlef Formation (Jebilet Massif, Morocco) – evidence from new biostratigraphic data based on metamorphosed conodonts

The Sarhlef Formation, which hosts the massive sulphide deposits of the Moroccan Meseta, has been considered as Carboniferous in age. Moreover, palynological analysis of the black shales hosting the Draa Sfar deposit (Central Jebilet) has allowed to restrict the age of the Sarhlef Formation to the late Visean (Asbian). However, this age is not compatible with geochronological data of various magmatic intrusions present in Central Jebilet. New biostratigraphic results based on metamorphosed conodonts from 34 samples (three cores, DS170, DF306 and DS125) of the Draa Sfar deposits provide a new biostratigraphic framework of the Sarhlef Formation. The collected fauna is affected by pyritization, silicification and tectonic deformation. Some non-pyritised or partially pyritized conodonts show a conodont color alteration (CAI) change varying from black to translucent (CAI 5 to CAI 8). The conodont fauna comprise representatives of the genera Icriodus, Polygnathus, Ancyrodella, Palmatolepis, Ancyrognathus, Ancyroides, and Palmatolepis showing that age spans from the Frasnian to Late Famennian. This age is more compatible with the radiometric data of the intrusive magmatic rocks. In core DS170, the Upper Kellwasser Horizon at the Frasnian-Famennian boundary has been identified by lithological characteristics and stratigraphy. The proposed Late Devonian age of the Sarhlef Formation provides new insights on the geological evolution and stratigraphy of the entire region.

U-Pb zircon SHRIMP dating of a protracted magmatic setting and its volcanic emplacement: Insights from the felsic volcanic rocks hosting the sulphide ore of the giant Aljustrel deposit, Iberian Pyrite Belt

• A protracted (~50 Ma) magmatic activity is suggested. • Upper Devonian subvolcanic activity (~373–365 Ma) took place before main volcanism . • Early Carboniferous long-lasting volcanism was identified (353–359 Ma) • Data suggests diachronism of sulphide deposition between different sub-basins. • Pb loss effects are attributed to the Variscan deformation and metamorphism . A geochronological study using SHRIMP U-Pb analysis of zircon grains has been conducted to date felsic volcanic rocks hosting the six massive sulphide deposits of the giant Aljustrel mining district in the Iberian Pyrite Belt. A multiple method age calculation approach was used to validate and ponder calculated Concordia ages (emplacement and inherited), which included weighted average, probability density peak(s), Tuff Zirc and Unmix functions. This approach was particularly useful to interpret the wide continuous single U-Pb ages (320–405 Ma) recorded in the Aljustrel volcanic rocks. The volcanic pile (>250 m) that hosts the Aljustrel deposits was emplaced between 359 and 353 Ma. Upper Devonian inheritance, representing subvolcanic activity, is well-represented in the volcanic rocks of Aljustrel (373–365 Ma). Older Devonian inherited zircon ages at 405 Ma, 388 Ma and 380 Ma were retrieved, hypothetically representing deep plutonism or other melting episodes, which suggests a long-lasting (~50 Ma) magmatic activity in the Aljustrel district. Older pre-Devonian inherited ages, uppermost Silurian and early to late Cambrian, and post-emplacement ages (~330–345 Ma) were also detected, with the latter reflecting Pb loss most likely driven by the main Variscan orogenic event. Maximum ages obtained for the volcanic rocks in the different deposits open the possibility that the last pulses of volcanic activity and subsequent deposition of the massive sulphides were diachronic in the different Aljustrel sub-basins. Additionally, results imply that, contrary to previously assumed, Gavião and São João-Moinho deposits are probably not the same ore lens disrupted by tardi-Variscan faults. This opens new opportunities for mining exploration and targeting in the Aljustrel district and points out the importance of high-resolution geochronological studies in mining and brownfield areas.