Volcanogenic Massive Sulfide Research Articles

Gold enrichment and the Au–Te association in the Huangtan Au–Cu–Zn volcanogenic massive sulfide deposit, Kalatag, East Tianshan, China: An in-situ LA–ICP–MS analysis

Huangtan Au–Cu–Zn is an auriferous VMS deposit hosted in tuff breccia, and tuff of Silurian age in the Kalatag area that located in the northern part of East Tianshan. Mineralization can be divided into two principal ore facies: massive, semimassive ore and stockwork ore. Pyrite, chalcopyrite, and sphalerite, as the predominant sulfide minerals and Au–bearing minerals, were investigated using a combination of ore microscopy, EMPA, SEM–EDS, and in situ LA–ICP–MS. There is no clear systematic variation in the trace element distribution with different types of pyrite, chalcopyrite, and sphalerite in the massive ore, stockwork ore, and hydrothermal alteration zone. Combined with mineralogical characteristics, this deposit is considered to be the product of the same ore-forming fluid and belongs to the VMS metallogenic system. Gold in the Huangtan deposit is present in three main mineralogical forms: auriferous tellurides, “invisible” gold, and native gold. Tellurides identified in the Huangtan deposit include: calaverite, sylvanite, petzite, native tellurium, hessite, altaite, and tellurobismuthite. LA–ICP–MS depth profiles, and mapping imaging for Au, Ag, and Te suggest that the invisible gold in pyrite, chalcopyrite, and sphalerite are micro- to nanoscale inclusions of Au–Ag–Te assemblages. Native gold contains smaller amounts of Ag, Bi, Te, and Se. The concentrations of trace elements Au, Te, Ag, Bi, and Se in pyrite, chalcopyrite, and sphalerite are strongly correlated, indicating that the ore-forming fluid was likely of magmatic origin. In addition, the sulfur isotope compositions (–3.3‰ to 2.3‰) of different types of major sulfides have a narrow range, indicating a homogeneous sulfur source, and show that sulfur sources were mainly derived from magmatic sulfur. The mineral assemblages reveal that Au–Te precipitated under variable redox conditions with log ƒTe2 being less than −8 in the massive ore, and log ƒTe2 being greater than −12.5 in the stockwork ore. The formation of tellurides is sensitive to the temperature of the mineralization system. With the decreasing temperature, the auriferous tellurides gradually precipitated and formed the Huangtan Au–Cu–Zn deposit with an auriferous telluride ore body.

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.

Potential for Volcanogenic Massive Sulfide Mineralization at the A6 Anomaly, North-West British Columbia, Canada: Stratigraphy, Lithogeochemistry, and Alteration Mineralogy and Chemistry

The Middle Jurassic A6 Anomaly is located 30 km southeast of Eskay Creek, north-central British Columbia and consists of thick, altered felsic igneous rocks overlain by a mafic volcano-sedimentary package. Lithogeochemistry on igneous rocks, X-ray diffraction on altered felsic units, and electron probe microanalysis and secondary ion mass spectrometry on illite and quartz were applied to explore the volcanogenic massive sulfide (VMS) potential, characterize alteration, and determine fluid conditions at the A6 Anomaly. Lithogeochemistry revealed calc-alkaline rhyodacite to trachyte of predominantly FII type, tholeiitic basalts with Nb/Yb < 1.6 (i.e., Group A), and transitional to calc-alkaline basalts and andesites with Nb/Yb > 2.2 (i.e., Group B). The felsic units showed weakly to moderately phyllic alteration (quartz–illite with minor orthoclase and trace chlorite–pyrite–calcite–barite–rutile). Illite ranged in composition from illite/smectite (K = 0.5–0.69 apfu) to almost endmember illite (K = 0.69–0.8 apfu), and formed from feldspar destruction by mildly acidic, relatively low temperature, oxidized hydrothermal fluids. The average δ18O composition was 10.7 ± 3.0‰ and 13.4 ± 1.3‰ relative to Vienna Standard Mean Ocean Water for illite and quartz, respectively. Geothermometry involving illite composition and oxygen isotope composition on illite and quartz yielded average fluid temperatures of predominantly 200–250 °C. Lithogeochemical results showed that the A6 Anomaly occurred in a late-Early to Middle Jurassic evolving back-arc basin, further east then previously recognized and in which transitional to calc-alkaline units formed by crustal assimilation to enriched Mid-Ocean Ridge Basalt (EMORB) (i.e., felsic units, Group B), followed by thinning of the crust resulting in tholeiitic normalized MORB basalts (i.e., Group A) with a minor crustal component. The alteration assemblage is representative of distal footwall alteration, and metal transport in this zone was limited despite favorable temperature, pH, and redox state, indicating a metal depleted source (i.e., felsic units).

Geochemical and Volcanological Criteria in Assessing the Links between Volcanism and VMS Deposits: A Case on the Iberian Pyrite Belt, Spain

VMS deposits in the Iberian Pyrite Belt (IPB), Spain and Portugal, constitute the largest accumulation of these deposits on Earth. Although several factors account for their genetic interpretation, a link between volcanism and mineralization is generally accepted. In many VMS districts, research is focused on the geochemical discrimination between barren and fertile volcanic rocks, these latter being a proxy of VMS mineralization. Additionally, the volcanological study of igneous successions sheds light on the environment at which volcanic rocks were emplaced, showing an emplacement depth consistent with that required for VMS formation. We describe a case on the El Almendro–Villanueva de los Castillejos (EAVC) succession, Spanish IPB, where abundant felsic volcanic rocks occur. According to the available evidence, their geochemical features, εNd signature and U–Pb dates suggest a possible link to VMS deposits. However, (paleo)volcanological evidence here indicates pyroclastic emplacement in a shallow water environment. We infer that such a shallow environment precluded VMS generation, a conclusion that is consistent with the absence of massive deposits all along this area. We also show that this interpretation lends additional support to previous models of the whole IPB, suggesting that compartmentalization of the belt had a major role in determining the sites of VMS deposition.

Gold accumulation in the metavolcanic-hosted orogenic gold deposit constrained by pyrite paragenesis coupled with in-situ trace elements and sulfur isotope: The Sarekuobu example in the Chinese Altay Orogen

Origin and accumulation process of gold in the metavolcanic-hosted orogenic gold deposits is still open to debate. Approximately fifteen gold-bearing deposits are hosted in the metamorphosed volcanics of the Chinese Altay Orogen, NW China. Among them, the representative Sarekuobu gold deposit, occurs as lodes in a Devonian volcanic-sedimentary succession that was deformed into a series of multiple overturned synclines and metamorphosed to (garnet)-biotite-chlorite schists. In previous studies, little attention has been paid to pyrite varieties and their in situ geochemistry to constrain their genetic understanding. Herein, five types of pyrite with distinct textures and mineral assemblages at Sarekuobu are divided into four generations based on the crosscutting and replacing relationship. The earliest pyrite (PyI) occurs as magnetite-pyrite parallel laminated layers comparable to those in VMS deposits, and some of its beddings are crosscut by PyⅡ that is scattered in foliation of the host greenschists and likely formed during syn-deformation. The colloidal PyIIIa and inclusion-rich PyIIIb are present in the same auriferous quartz veins continuously cutting across the PyⅡ-rich schists. It is notable that PyIIIb acts as the most important gold-bearing pyrite containing some micro-mineral inclusions such as visible gold and chalcopyrite. The final inclusion-poor PyⅣ with coarse and euhedral grains replaces or envelops all above three pyrite generation. The highest gold concentrations are presented in PyIIIa and PyIIIb by LA-ICP-MS spot analysis, with the maximum values up to 16 ppm and 426 ppm, respectively. In contrast to the substituted invisible Au nano-particles in lattice structures with time-resolved LA-ICP-MS signal parallel to Fe, the visible Au occurs as sizeable micro-inclusions in PyIIIb revealed by highly variable LA-ICP-MS signal spectrum. Further LA-ICP-MS trace element mapping show Au and other trace elements (e.g., Cu, Pb, Zn, Bi, Sb and Ag) are unevenly distributed in PyIIIb but barren in coexisting PyⅣ, in agreement with the microscopic textures of inclusion-rich PyIIIb and inclusion-poor PyⅣ. Another mapping displays these trace elements are homogeneously distributed along colloidal layers in PyIIIa but depleted in the coexisting PyI. Collectively, PyIIIb is believed to experience relatively longer-time crystallization co-precipitating with native gold and chalcopyrite, whereas PyIIIa is rapidly deposited from the same auriferous ore fluids without sufficient time for crystallization and captures some clay minerals and organic matters. In-situ δ34SV-CDT values of four pyrite generations by fsLA-MC-ICP-MS range from +2.34 to + 10.14‰, and gradually decrease from PyI (mean, +9.59‰), through PyⅡ (+8.67‰), PyIIIa (+6.16‰) and PyIIIb (+4.97‰), to final PyⅣ (+3.66‰). In combination with published sulfur isotope composition of host rocks (maximum, +18.7‰), the formation of the auriferous fluids and deposition of Au in pyrite at Sarekuobu might be attributed to the sulfur pathway of progressively enhanced thermal sulfate reduction (TSR) in the Devonian marine strata. Thus, two process including the Devonian seafloor sedimentation and Triassic orogeny-related metamorphism are critical for formation of the Sarekuobu gold deposit.

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.

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

Two-phase mineralization of Hongtaiping Cu polymetallic deposit in Yanbian area (NE China): Evidence from sulfide Rb–Sr dating and in-situ trace element analysis

The Hongtaiping Cu polymetallic deposit in Yanbian area (NE China) is located in the tectonic junction between the eastern Central Asian Orogenic Belt and the North China Craton. Two mineralization types are identified at the Hongtaiping deposit, i.e., stratiform mineralization hosted in the pyroclastic rocks of the Middle Permian Miaoling Formation (Fm.) and the quartz-sulfide vein-type mineralization controlled by fractures. To determine temporal and genetic relations between the two mineralization types, sulfide Rb–Sr dating and in-situ LA–ICP–MS trace element analysis were conducted. Seven sulfide samples from stratiform orebodies yielded a Rb–Sr isochron age of 268.3 ± 2.6 Ma, which is similar to the reported zircon U–Pb age of ore-hosting pyroclastic rocks of the Miaoling Fm., suggesting that the stratiform mineralization was syngenetic. The initial 87Sr/86Sr ratios of these sulfide samples show value of 0.7102–0.7103 (average of 0.7103), implying a major crustal origin, with certain mantle-derived input, for the ore-forming materials of the stratiform mineralization. Sulfides from the stratiform and vein-type ores have distinct trace elemental features. High Co/Ni ratio and low Se content in pyrite, and high Sn content and low Zn content in chalcopyrite reflect high temperature and vice versa. In the pyrite from stratiform and vein-type ores, average Se contents are 19.72 ppm and 9.70 ppm, and average Co/Ni ratios are 0.20 and 2.46, respectively. Whilst in the chalcopyrite from stratiform and vein-type ores, average Sn contents are 2.49 ppm and 60.31 ppm and average Zn contents are 346.55 ppm and 236.17 ppm, respectively, indicating that the temperature of the stratiform mineralization is lower than that of the vein-type mineralization. Integrating the geological and geochronological features of the two types of mineralization and wall rocks, as well as trace element compositions of the sulfides, we inferred that the stratiform mineralization at the Hongtaiping deposit can be classified as volcanogenic massive sulfide (VMS)-type, associated with the Middle Permian submarine volcanism caused by the subduction of the Paleo-Asian Ocean. The vein-type mineralization was likely related to the Late Triassic felsic magmatism. In a word, two-phase mineralization implies the VMS-hydrothermal reworking-type for the Hongtaiping deposit.

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.

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.

Genetic discrimination of the Dingjiashan Pb-Zn deposit, SE China, based on sphalerite chemistry

The Dingjiashan Pb-Zn deposit (5.35 Mt Pb + Zn @ 1.14% Pb and 4.07% Zn) is hosted by pyroxene-dominated skarn occurring along the contact zones between Proterozoic quartz mica schist and marble in the central Fujian region of southeastern China. The ore genesis of Proterozoic volcanogenic massive sulfide (VMS) vs. Late Mesozoic skarn type has long been debated. In this study, two types of sphalerite (sphalerite I and sphalerite II) were identified based on the mineral assemblages in the sulfide stage of the Dingjiashan deposit. Sphalerite I (including sphalerite Ia and sphalerite Ib subtypes), with a dark gray-blue to black coloring, is predominantly associated with pyrrhotite, whereas sphalerite II (including sphalerite IIa and sphalerite IIb subtypes) shows a light to dark gray-blue coloring and is mainly associated with galena and chalcopyrite. Geological features indicate that sphalerite I predates sphalerite II. Representative time-resolved depth profiles and mapping images based on the LA-ICP-MS method, coupled with inter-element correlation analyses, collectively illustrated that: 1) Fe, Mn, Cd, Co, In, Ga and Ge are present in solid solution; 2) Cu may occur both as solid solution and as micro-inclusions; 3) Ag, Pb and Bi may be intimately associated with galena inclusions hosted by sphalerite. The characteristics of trace and minor elements (such as Fe, Mn, In, Co, Ga, Ge, etc.), along with the results of GGIMFis geothermometer studies, indicate that the main mineralization stage occurred at high-temperature conditions (>300 °C). Compared to Pb-Zn deposits (including 6 VMS deposits and 9 skarn deposits) worldwide, sphalerite from the Dingjiashan Pb-Zn deposit exhibits similar ore-forming temperatures and trace/minor element compositions to those from skarn deposits, but is different to those from VMS deposits. This finding is of great significance for further exploration in the Dingjiashan deposit and—more broadly—the entire central Fujian region. It also provides an important future guide for the differentiation of VMS and skarn deposits.

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.

Rift structures and magmatism focus VMS and gold mineralisation in the Paleoproterozoic Bryah Rift Basin, Australia

• Geophysical interpretation reveals syn -rift structures and magmatic centres. • Magmatic centres control syn -rift VMS and post-rift orogenic gold mineralisation . • Long-lived structures favour high endowment mineralisation. The interaction of structure development and magmatism in rift-settings provides systemic controls on the emplacement of ore deposits both during rifting and subsequently, and a knowledge of these may help to predict better the likely locations of major deposits. The Paleoproterozoic Bryah Rift Basin includes substantial mafic magmatism and deep-crust penetrating structures and possesses syn -rift volcanogenic massive sulphide (VMS) and later gold mineralisation, providing a good opportunity to study interactions between magmatism, structures, and mineralisation. The volcano-sedimentary Bryah Group was deposited in a continental rift developed within the broader Yerrida Basin on the northern margin of the Yilgarn Craton at ca. 2030 Ma. Multi-scale interpretation and forward modelling of gravity and magnetic data were applied to characterise the magmatic and structural patterns of the Bryah Group, enabling a better understanding of its tectono-magmatic development and controls on VMS and gold mineralisation. The interpretation highlights the bounding extensional faults and the inward-deepening structural pattern of the Bryah Rift Basin that reflects the initial rift geometry. Deep-rooted gravity sources show magmatism focused in the southern-central part of the basin, where mafic rocks' thickness can reach more than 10 km. At shallower levels, the rift magmatism extends in three east to east-northeast trending magmatic corridors with an en-echelon arrangement along the rift, oblique to major structures. These magmatic corridors have an intrinsic relationship with the internal structure of the rift. VMS mineralisation associated with mafic magmatism shows a spatial connection with magmatic corridors and major syn -rift faults, whereas VMS mineralisation associated with felsic volcanic rocks is related with off-axis volcanism and regional pre-rift faults. Later orogenic gold mineralisation is also spatially associated with the borders of the magmatic centres and rift faults, despite occurring ~200 Ma later. These associations suggest that primary rift architecture has substantially focused syn -rift VMS mineralisation and also later gold mineralisation, as a consequence of rheological and compositional contrasts.

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.

Geology, mineralization and short wave infrared alteration mapping of the Khan Altai Au deposit, Mongolia

AbstractKhan Altai Au deposit is located near the N margin of the Neoproterozoic‐Cambrian Lake terrain in SW Mongolia, about 5 km from its contact with the Proterozoic‐Archean Baydrag craton, and 18 km SE of the Khantaishir ophiolite, which was emplaced in the Late Cambrian. The host rocks are strongly deformed and metamorphosed to lower greenschist facies, and of uncertain age. They comprise a sequence of rhyolitic volcaniclastics and porphyritic flows interbedded with laminated siltstone, basaltic andesite and faulted against dolomite. Low‐grade gold mineralization (up to 2 ppm Au) is hosted mainly in rhyolitic volcanics and extends over an area of about 1,100 × 160 m with a vertical extent of about 200 m. It is associated with disseminated pyrite (2–10% by vol) but includes high‐grade zones (up to 183 ppm Au over 1 m) related to cm‐wide quartz‐native Au‐pyrite veins. The Au mineralized zone also encompasses VMS mineralization (currently of minor extent), characterized by massive pyrite‐sphalerite lenses and quartz‐chalcopyrite stringer zones. A larger VMS deposit (Ereen Budagt, about 10 Mt sulfide ore) is found 6 km to the SSE in a similar geological setting. The main alteration assemblage is quartz‐white mica‐albite, but with minor carbonate, chlorite, epidote‐actinolite and pyrophyllite‐diaspore‐dickite alteration. Gold mineralization is related to zones of strong tectonic foliation and formation of phengitic white mica, with an outward zonation to high Al white mica. Pyrite is typically euhedral, and exhibits concentric growth zones, as well as quartz pressure shadows to enclosing foliation, consistent with syngenetic growth during metamorphism and deformation. Other sulfides include arsenopyrite, sphalerite and possible marcasite. Preliminary LA‐ICPMS mapping shows pyrite rims are enriched in Au, As, Co, Cu, Ni, Pb, Ag, Mo and Se, the pyrite core is enriched in Co, Bi, Te, and rhyolitic host rock is enriched in K, Ba, V and Tl. Whole rock geochemistry of basaltic andesite to rhyolite, shows N‐MORB characteristics for basaltic andesite, as well as a subduction signature for all rocks, and high MgO (~8%), TiO2 (~1%) and low Ni, Cr content in basalt, compatible with a back arc tectonic setting.