Massive Sulfide Deposits Research Articles

Syn-metamorphic sulfidation of the Gamsberg zinc deposit, South Africa

The Mesoproterozoic Aggeneys-Gamsberg ore district, South Africa, is one of the world´s largest sulfidic base metal concentrations and well-known as a prime example of Broken Hill-type base metal deposits, traditionally interpreted as metamorphosed SEDEX deposits. Within this district, the Gamsberg deposit stands out for its huge size and strongly Zn-dominated ore ( >14 Mt contained Zn). New electron microprobe analyses and element abundance maps of sulfides and silicates point to fluid-driven sulfidation during retrograde metamorphism. Differences in the chemistry of sulfide inclusions within zoned garnet grains reflect different degrees of interaction of sulfides with high metal/sulfur-ratio with a sulfur-rich metamorphic fluid. Independent evidence of sulfidation during retrograde metamorphism comes from graphic-textured sulfide aggregates that previously have been interpreted as quenched sulfidic melts, replacement of pyrrhotite by pyrite along micro-fractures, and sulfides in phyllic alteration zones. Limited availability of fluid under retrograde conditions caused locally different degrees of segregation of Fe-rich sphalerite into Zn-rich sphalerite and pyrite, and thus considerable heterogeneity in sphalerite chemistry. The invoked sulfur-rich metamorphic fluids would have been able to sulfidize base metal-rich zones in the whole deposit and thus camouflage a potential pre-metamorphic oxidation. These findings support the recently established hypothesis of a pre-Klondikean weathering-induced oxidation event and challenge the traditional explanation of Broken Hill-type deposits as merely metamorphosed SEDEX deposits. Instead, we suggest that the massive sulfide deposits experienced a complex history, starting with initial SEDEX-type mineralization, followed by near-surface oxidation with spatial metal separation, and then sulfidation of this oxidized ore during medium- to high-grade metamorphism.

Classification of Rock Mineral in Field X based on Spectral Data (SWIR & TIR) using Supervised Machine Learning Methods

The massive development of science and technology in the industrial era 4.0 includes artificial intelligence, which is purposed to produce research output in the field of geology more accurately and can be completed in a short time using large amounts of data. Machine learning is a part of artificial intelligence that can provide learning processes on computers independently without explicit programming. The process of identifying rocks through classification can be done using machine learning. The study area is in the Manjimup region, Western Australia which consists of Volcanogenic Massive Sulphide (VMS) deposits. This study purposed to determine the classification of rock minerals using accuracy values from the evaluation of models generated using supervised machine learning based on spectral data, namely Short-Wavelength Infrared (SWIR), and Mid or Thermal Infrared (TIR) acquired from electromagnetic spectrum measurements to identify rock mineral features. The spectral data comes from five rock drilling data in the study area. The supervised machine learning method used to determine the best accuracy consists of 5 types of methods, which are K-Nearest Neighbors (K-NN), Support Vector Machine (SVM), Decision Tree (DT), Random Forest (RF), and Multi-layer Perceptron (MLP). Machine learning is completed by supervised method because the research data contains information about label data, which is the type of rock mineral so that it can produce a classification based on the level of accuracy for each type of rock mineral data. The SVM method produces the best accuracy on SWIR data with 82.5% accuracy and the MLP method produces the best accuracy on TIR data with 82% accuracy for rock mineral classification.

Vectors to ore in replacive volcanogenic massive sulfide (VMS) deposits of the northern Iberian Pyrite Belt: mineral zoning, whole rock geochemistry, and application of portable X-ray fluorescence

Abstract. In this work we have performed a detailed study of vectors to ore to a representative volcanic-rock-hosted replacive volcanogenic massive sulfide (VMS) deposit located in the northern Iberian Pyrite Belt (Spain), the Aguas Teñidas deposit. The investigated vectors include the following: (1) mineralogical zoning, (2) host sequence characterization and mineralized unit identification based on whole rock geochemistry discrimination diagrams, (3) study of the characteristics and behaviour of whole rock geochemical anomalies around the ore (e.g. alteration-related compositional changes, characteristics and extent of geochemical halos of indicative elements such as Cu, Zn, Pb, Sb, Tl, and Ba around the deposit), and (4) application of portable X-ray fluorescence (p-XRF) analysis to the detection of the previous vectors. In the footwall, a concentric cone-shaped hydrothermal alteration zone bearing the stockwork passes laterally, from core to edge, from quartz (only local) to chlorite–quartz, sericite–chlorite–quartz, and sericite–quartz alteration zones. The hydrothermal alteration is also found in the hanging wall despite being tectonically allochthonous to the orebody: a proximal sericite alteration zone is followed by a more distal albite-rich one. Whole rock major elements show an increase in alteration indexes (e.g. AI, CCPI) towards the mineralization, a general SiO2 enrichment, and FeO enrichment as well as K2O and Na2O depletion towards the centre of the hydrothermal system, with MgO showing a less systematic behaviour. K2O and Na2O leached from the centre of the system are transported and deposited in more external areas. Copper, Pb, and Zn produce proximal anomalies around mineralized areas, with the more mobile Sb, Tl, and Ba generating wider halos. Whereas Sb and Tl halos form around all mineralized areas, Ba anomalies are restricted to areas around the massive sulfide body. Our results show that proposed vectors, or adaptations designed to overcome p-XRF limitations, can be confidently used by analysing unprepared hand specimens, including the external rough curved surface of drill cores. The data presented in this work are not only applicable to VMS exploration in the Iberian Pyrite Belt, but on a broader scale they will also contribute to improving our general understanding of vectors to ore in replacive-type VMS deposits.

Mineralization styles, alteration mineralogy, and sulfur isotope geochemistry of volcanogenic massive sulfide deposits in the Shadli Metavolcanics Belt, South Eastern Desert, Egypt: Metallogenic implications

Three distinct occurrences of Zn–Cu–Pb mineralization (Um Samiuki, Hilgit, and Maaqal) in Neoproterozoic island arcs of the Shadli Metavolcanics Belt, South Eastern Desert, Egypt, have been investigated in this study. The Shadli Metavolcanics Belt erupted in two magmatic cycles, with the Older Um Samiuki Metavolcanics group getting overlain by the Younger Hamamid Metavolcanics (YHM) group. The YHM group is characterized by two distinct cycles of volcanism. The studied deposits are mainly hosted by volcanic and volcaniclastic rocks that belong to the first cycle of the YHM group. The host-rock succession was interpreted to have been formed by back-arc extensional volcanism and was then deformed and metamorphosed to the lower greenschist facies. The relationship between the mineral occurrences and host rocks remains poorly constrained and controversial. We report new field observations, paragenetic data, mineral chemistry analyses, and in situ sulfur isotopes to characterize the sulfide mineralization and to gain insights into its genesis. Two mineralization styles have been identified in these deposits. The first style in the Um Samiuki deposit is expressed by two massive mineralized bodies that are mostly stratiform. It is distinguished by sphalerite, chalcopyrite, pyrite, galena, and Ag-bearing minerals; followed by bornite and covellite in decreasing abundance. Less abundant supergene phases include secondary copper minerals and iron oxyhydroxides. The hydrothermal alteration is characterized by sericitization, chloritization, epidotization, and silicification. The second style represents disseminated and vein-type sulfides mainly encountered in Hilgit and Maaqal occurrences. It is characterized by pyrite with minor sphalerite and chalcopyrite. The δ34SV-CDT values range from + 5.44‰ to + 9.08‰ with an average of + 8.11‰ ±1.1‰ (n = 18) for massive mineralized zones and from − 2.25‰ to + 3.78‰ with an average of + 1.06‰ ±2.3‰ (n = 8) for disseminated and vein sulfides. Such a variation in the sulfur isotope signatures may imply that both mineralization styles were derived from the thermochemical sulfate reduction (TSR) of seawater and leaching of basement lithologies in varying quantities, consistent with Volcanogenic Massive Sulfide (VMS) deposits of back-arc basins. The negative δ34SV-CDT values of some sulfides from the disseminated and vein mineralization may be seen as evidence for magmatic SO2 disproportionation. The studied VMS deposits display a close spatial and genetic association with submarine felsic volcanism of the YHM group, and their temporal distribution corresponds closely with the Mozambique Ocean closure stage of the Pan-African Orogeny.

Zinc, cadmium and sulphur isotopic compositions reveal biological activity during formation of a volcanic-hosted massive sulphide deposit

Zinc and Cd isotopes fractionate strongly within a range of hydrothermal systems; consequently, metal stable isotopes have been used to understand the formation of hydrothermal ore deposits. We investigated the Zn–Cd–S isotopic compositions of sulphides from the Carboniferous-Permian Xiaobaliang Cu–Au deposit, Inner Mongolia, China. This ancient seafloor hydrothermal system is the only known Cyprus-type volcanic-hosted massive sulphide (VHMS) deposit in the Central Asian Orogenic Belt. The S isotopic compositions of sulphide minerals are highly variable with δ34SCDT values ranging from −21.2‰ to 25.2‰. We infer that negative δ34SCDT values reflect mixing of volcanogenic S and S derived from bacterial sulphate reduction (BSR), and that positive δ34SCDT values reflect mixing of volcanogenic S with S derived from thermochemical sulphate reduction (TSR). Zinc isotopic compositions are relatively consistent at the deposit; δ66Zn values range from 0.10‰ to 0.70‰. These values are similar to those reported for modern seafloor sulphides. We infer that consistency of δ66Zn values relates to the Zn species ([ZnCl4]2−) present in the ore-forming fluids during sulphide precipitation. All of the sulphides are enriched in the light Cd isotopes; δ114/110Cd values range from −0.74‰ to −0.08‰. Zinc and Cd can be affected by biological activity, and we infer that biological activity caused the negative δ114/110Cd values at this deposit because: (1) biological processes (e.g., bacterial activity) enrich fluids in the light Cd isotopes, leading to the precipitation of sulphides with negative δ114/110Cd values; and (2) the Cd isotopic composition of ore-forming fluid is readily modified because the concentration of Cd is much lower than that of Zn in ore and basalt. Our results indicate that Cd isotopes might record ancient biological activity, and that organisms might play a more important role than previously thought in the formation of VHMS systems.

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.