Ancient Volcanogenic Massive Sulfide Research Articles

Ore genesis of the Tieshajie Cu deposit: Implications for Cu mineralization in the Qin-Hang Metallogenic Belt, South China

The Tieshajie Cu deposit, located in the northeastern part of the Qin-Hang Metallogenic Belt (QHMB), South China, has long been regarded as a representative Meso-Neoproterozoic volcanogenic massive sulfide (VMS) deposit. Here we present a hydrothermal titanite U-Pb age, Re-Os and in-situ S-Cu isotope data for chalcopyrite to constrain the timing and ore genesis of the Tieshajie deposit. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb dating of titanite from the disseminated Cu ore yielded a weighted mean 206Pb/238U age of 160.1 ± 4.4 Ma. Chalcopyrite from different ore types has low 187Os/188Os (0.85–3.60) and 187Re/188Os (46.1–614.0) ratios, combined with initial 187Os/188Os (0.74–2.00), excluding a mantle source. A Re-Os isochron age (188 ± 30 Ma) for five chalcopyrite samples is consistent with the titanite U-Pb age within errors. Moreover, the variations in Cu isotope compositions (δ65Cu: −1.13 to +0.12 ‰) and δ34S values (+3.8 to +7.7 ‰) of chalcopyrite are inconsistent with those reported from the ancient VMS deposits in previous studies. Therefore, our results are indicative of a Late Jurassic magmatic-hydrothermal origin instead of a VMS origin for the Tieshajie deposit. In combination with previous studies, we propose that the Tieshajie Cu deposit belongs to the distal part of the Mid-Late Jurassic (170–150 Ma) porphyry-skarn Cu mineralization event in the QHMB, likely triggered by the subduction of the Paleo-Pacific plate during the Late Mesozoic. This study also has new insights into the genesis of Cu mineralization in the QHMB and further provides implications for future exploration.

Relics of near-bottom fauna in massive sulfide ores

The additional study of ancient volcanogenic massive sulfide deposits in various regions revealed microtextures, probably of biogenic origin, which could represent varieties of the shells of mineralized fauna. The new finds expand the list of sites containing relics of bioforms associated with hydrothermal vents of "black smokers".

A missing link between ancient and active mafic-hosted seafloor hydrothermal systems – Magmatic volatile influx in the exceptionally preserved Mala VMS deposit, Troodos, Cyprus

Reconciling observations between ancient volcanogenic massive sulfide (VMS) and actively forming seafloor massive sulfide (SMS) deposits is critical for understanding the sources and processes that govern metal enrichment in marine hydrothermal systems. For a mafic VMS deposit, the Mala VMS mound located within the Troodos ophiolite, Cyprus, is unusual as pyrite is enriched in magmatic volatile elements (Au, Cu, Te and Se), sulfide δ34S values average − 3.8‰ ± 1.9‰ (1σ, n = 28), and gypsum averages +14.5‰ ± 2.0‰ (1σ, n = 26) - in stark contrast to the bulk of Troodos VMS pyrite, which averages +4.6‰ ± 2.8‰. To date, this combination of features has only been observed in actively forming SMS deposits in immature, subduction-influenced environments and rarely in ancient VMS deposits hosted in felsic environments. Traditionally, the leaching of igneous rocks is considered as the primary source of metals in mafic VMS deposits. However, at Mala, and perhaps other active SMS deposits in mafic environments, we suggest that Au, Cu, Te and Se were initially sourced from the direct contribution of a magmatic volatile phase where SO2 underwent disproportionation, a signature that is later overprinted by reacted seawater during deposit maturation and is therefore not usually preserved in ancient analogues. Thus, the exceptional preservation of Mala provides evidence of a magmatic volatile contribution in the early stages of mafic VMS deposit formation.

Textural, mineralogical, and geochemical characteristics of non-volcanogenic Fe–Mn deposit of Motuosala, western Tianshan, northwestern China

Modern and ancient volcanogenic massive sulfide (VMS) systems commonly have associated Fe–Si–(Mn) occurrences that typically are hosted by volcanic suites. However, the Motuosala Fe–Mn deposit in western Tianshan, northwestern China, which shows similar geological features with the Fe–Si–(Mn) occurrences in VMS systems, is hosted by volcanic-free sedimentary sequences and has no clear relationship in space with VMS mineralization. In this paper, textural, mineralogical, and geochemical studies were conducted to unravel the genesis of the Motuosala Fe–Mn deposit. The hematite ores from the Motuosala deposit consist predominantly of fine-grained hematite, barite, and quartz, with minor amounts of galena and chalcopyrite. The jasper samples are mainly composed of amorphous silica with little micro-sized hematite, barite, and galena. Geochemically, the hematite ore and jasper samples all are characterized by enrichment of Cu, Pb, Zn, and Ba, positive Eu anomaly, slightly light rare earth elements enrichment, and negligible Ce anomalies. Based on these results, we proposed that the Fe-, Si-, and Mn-rich layers at Motuosala are the diagenetic products of ancient seafloor hydrothermal sediments which have not suffered significantly replacement by post-precipitation hydrothermal alteration and deformation. This study implies that Fe–Si–(Mn) sediments in volcanic rock-free areas also can be the distal product of submarine hydrothermal system, which can be considered as the proxy for identifying associated submarine volcanogenic iron oxide or VMS mineralization.

Life on the edge: Microbial biomineralization in an arsenic- and lead-rich deep-sea hydrothermal vent

Unravelling complex microbial activity in modern hydrothermal vents can provide crucial insights into the evolution of ancient life on Earth. It is well established that microorganisms in hydrothermal vents have a significant impact on the cycling of metals and mineral formation. However, the detailed roles played by microorganisms in driving sulfide deposition and cycling of toxic metals, like arsenic (As) and lead (Pb), in high-temperature deep-sea hydrothermal vents remain unknown. The understanding of these mechanisms in extreme environments is of particular importance as As has been postulated as a driver of microbial activities on the early Earth. Here, we present the first geologic evidence of PbAs rich microbial filamentous clusters observed in a modern high-temperature black smoker from the Manus back-arc basin, Papua New Guinea. The clusters occur as net-like structures on the surface of barite and sulfides and are composed of multiple filaments and fine-grained PbAs sulfosalt. Each of the filaments includes an As-Pb-rich sulfosalt core and organic-rich shell structure with elevated carbon, nitrogen and phosphorus. Further synchrotron X-ray absorption near edge structure analysis shows that the clusters contain a mixture of As (II) and As (III). Additionally, those filaments show a close association with realgar (As4S4), by penetrating and dissolving this As-sulfide mineral. We interpret the filaments to be a result of As-related microbial activity in As- and Pb-enriched hydrothermal environments. The findings show possible processes through which extremophiles live in Pb and As-rich environments during chimney growth. In addition, as hydrothermal vents are regarded as modern analogs of ancient volcanogenic massive sulfide deposits, the observed biominerals present the potential to be used as proxies to trace the signatures of early life in ancient geological systems.

Evolution of a volcanogenic hydrothermal system recorded by the behavior of LREE and Eu: Case study of the Key Tuffite at Bracemac–McLeod deposits, Matagami, Canada

The distribution of rare earth elements (REE) in the alteration zones surrounding modern and ancient volcanogenic massive sulfide (VMS) deposits is often characterized by a wide range of variations comprising both gains and losses of light REE (LREE: La to Sm) and europium. The evolution of the hydrothermal system is recorded by mineral assemblages and their chemical composition. To address the behavior of the REE in such a context, the Bracemac–McLeod Archean VMS deposits of the Matagami district are used. There, mineralization was formed mainly by subsea-floor replacement along a tuffaceous marker unit (Key Tuffite) of homogenous andesitic composition, hence providing a single protolith to account for mineral and chemical variations in relation to ore position. We combine whole-rock and mineral REE data in both distal sericite and proximal chlorite alteration surrounding the mineralization. A model, integrating observed textural relationships, geochemical data and current understanding of mineral stabilities, is proposed to explain the redistribution of the REE during the evolution of the VMS hydrothermal system. The distal sericite zone represents the early, low temperature alteration. It is characterized by the destruction of volcanic glass and plagioclase leading to a negative Eu anomaly in the whole-rock analyses and the depletion of LREE. The proximal chlorite zone was formed during the thermal evolution of a fertile VMS hydrothermal system. It is generally characterized by gains of LREE and Eu, although some chloritized samples are depleted in LREE. Petrographic observations suggest that the coprecipitation of allanite with chlorite explains the increase of LREE, whereas a mass balance calculation indicates that the precipitation of apatite (±carbonates) essentially controls the Eu. Local silicification, occurring as pulses during the hydrothermal system life, is also of interest because it could preserve an intermediate alteration state and thus provide additional information on the evolution of the hydrothermal system. The mobility of REE is indicative of specific hydrothermal conditions, which may reflect the efficiency of a mineralizing hydrothermal system. At Matagami, the mobility of LREE and Eu could be used for vectoring in exploration, especially Eu which has an anomalous behavior that extends far beyond the limit of the sulfide zone, into the distal sericitic low-temperature alteration (up to 400m from the ore zones).

The Tiger Sulfide Chimney, Yonaguni Knoll IV Hydrothermal Field, Southern Okinawa Trough, Japan: The First Reported Occurrence of Pt–Cu–Fe‐Bearing Bismuthinite and Sn‐Bearing Chalcopyrite in an Active Seafloor Hydrothermal System

AbstractA sulfide chimney ore sampled from the flank of the active Tiger vent area in the Yonaguni Knoll IV hydrothermal field, south Okinawa trough, consists of anhydrite, pyrite, sphalerite, galena, chalcopyrite and bismuthinite. Electron microprobe analysis indicates that the chalcopyrite contains up to 2.4 wt% Sn, whereas bismuthinite contains up to 1.7 wt% Pt, 0.8 wt% Cu and 0.5 wt% Fe. The Sn‐rich chalcopyrite and Pt–Cu–Fe‐bearing bismuthinite are the first reported occurrence of such minerals in an active submarine hydrothermal system. The results confirm that Sn enters the chalcopyrite as a solid solution towards stannite by the coupled substitution of Sn4+Fe2+ for Fe3+Fe3+, whereas Pt, Cu and Fe enter the bismuthinite structure as a solid solution during rapid nucleation. The fluid inclusions homogenization temperatures in anhydrite (220–310°C) and measured end‐member temperature of the vent fluids on‐site (325°C) indicate that Sn‐bearing chalcopyrite and Pt–Cu–Fe‐bearing bismuthinite express the original composition of the minerals that precipitated as metastable phases at a temperature above 300°C. The result observed in this study implies that sulfides in ancient volcanogenic massive sulfide deposits have similar trace element distribution during nucleation but it is remobilised during diagenesis, metamorphism or supergene enrichment processes.

Mineralogy and Formation of Black Smoker Chimneys from Brothers Submarine Volcano, Kermadec Arc

Brothers caldera volcano is a submarine volcano of dacitic composition, located on the Kermadec arc, New Zealand. It hosts the NW caldera vent field perched on the steep slope of the caldera walls and includes numerous, active, high-temperature (max 302°C) chimneys and a greater amount of dead, sulfide-rich spires. Petrographic studies of these chimneys show that three main zones can occur within the chimneys: a chalcopyrite-rich core, surrounded by a sulfate-dominated zone, which is in turn mantled by an external rind of Fe oxides, calcite, and silicates. Four chimney types are identified based on the relative proportions of the chalcopyrite and sulfate layers and the presence or absence of anhydrite. Two are Cu rich, i.e., chalcopyrite-sulfate and chalcopyrite-bornite chimneys, and two are Zn rich, i.e., sphalerite-barite and sphalerite-chalcopyrite. Chimney growth begins with the formation of a sulfate wall upon which sulfides precipitate. Later, zone refining results in a chalcopyrite-rich core with pyrite/marcasite and sphalerite occurring predominantly near the outer margins. In chalcopyrite-bornite chimneys, the chalcopyrite core rapidly loses permeability and limits the thickness of the surrounding sulfate layer. In these chimneys, bornite, chalcocite, and covellite form along the outer margin of the chalcopyrite zone as a result of oxidation by seawater. Zinc-rich chimneys display a more vertical zonation and their growth involves an upward-advancing barite cap followed by chalcopyrite deposition (if present) nearer the base. The vertical zonation and lack of anhydrite in these chimneys also implies that larger chalcopyrite and anhydrite deposits may exist subsea floor. The different chimney types are related to subsea-floor permeability, the amount of fluid mixing that occurs prior to venting, and heterogeneous fluid compositions. The occurrence of specular hematite and Bi or Au tellurides associated with chalcopyrite are consistent with magmatic contributions to the NW caldera vent site. These tellurides are the first gold-bearing phase to be identified in these chimneys, and the Bi-Au association suggests that gold enrichment up to 91 ppm is due to scavenging by liquid bismuth. The presence of tellurides in Brothers chimneys have implications for other telluride-bearing deposits, such those in the Urals. Likewise, other aspects of the mineralogy (i.e., textures) and zonation, including the implied subsea-floor deposition, presented here from an active, undeformed environment can aid in understanding ancient volcanogenic massive sulfide (VMS) deposits that have undergone various degrees of metamorphism.

PGE distribution in massive sulfides from the PACMANUS hydrothermal field, eastern Manus basin, Papua New Guinea: implications for PGE enrichment in some ancient volcanogenic massive sulfide deposits

PGE distribution in massive sulfides from the PACMANUS hydrothermal field, eastern Manus basin, Papua New Guinea: implications for PGE enrichment in some ancient volcanogenic massive sulfide deposits

PGE distribution in massive sulfides from the PACMANUS hydrothermal field, eastern Manus basin, Papua New Guinea: implications for PGE enrichment in some ancient volcanogenic massive sulfide deposits

The distribution of platinum group elements (PGE) in Cu- and Zn-rich samples from the Roman Ruins and Satanic Mills vent sites in the PACMANUS hydrothermal field (Papua New Guinea) was studied and compared to that from selected ancient volcanogenic massive sulfide (VMS) deposits. Samples from the Satanic Mills site are enriched in Pd and Rh when compared to samples from Roman Ruins and reach highest values in active and inactive Cu-rich black smoker chimneys and chalcopyrite-cemented dacite breccias (up to 356 ppb Pd and up to 145 ppb Rh). A significant positive correlation was established between Cu and Pd and Rh in samples from both vent sites. Comparisons of chondrite normalized patterns and values of Pd/Pt and Pd/Ir ratios in Cu-rich sulfides and probable source rocks (felsic volcanic rocks/MORB) along with the evidence for a magmatic component in the PACMANUS hydrothermal system indicate that leaching of back-arc volcanic rocks together with addition of magmatic volatiles to the convecting hydrothermal system was the most important factor for PGE enrichment at PACMANUS and likely at some PGE-enriched ancient VMS deposits.

The aqueous geochemistry of the rare earth elements and yttrium: VI. Stability of neodymium chloride complexes from 25 to 300°C

The stability and stoichiometry of Nd (III) chloride complexes have been experimentally determined in the temperature range 40 to 300°C, P = Psat. The solubility of AgCl (s) was measured in solutions of fixed HC1 + NaC1 concentration (0.01 to 5.0 m) and varying ΣNd/ΣCl molar ratio (0.0 to 0.5), following the method of Gammons (1995). The results of over 250 individual solubility experiments were regressed to obtain the following smoothed values for the first and second cumulative association constants for the Nd(III) chloride complexes: Nd3+ + Cl− = NdC12+ (β1); Nd3+ + 2Cl− = NdCl2+ (β2):25°C50°C100°C150°C200°C250°C300°log β10.060.210.661.312.173.224.48±.50±.30±.20±.20±.15±.30±.50log β2——0.131.082.524.456.87±.50±.30±.15±.50c]±.50These are the first experimentally determined equilibrium constants for chloride complexes of any rare earth element (REE) at elevated temperature. At 25°C, neodymium exists mainly as Nd3+ in the absence of high concentrations of Cl− and other ligands (F−, CO3−, SO4−). However, complexation with chloride is greatly enhanced by increase in temperature, such that NdC12+, NdC12+, and possibly NdCl30 become the dominant species for NaClHClH2O brines at 300°C. The experimental data indicate a higher degree of complexation than predicted from earlier theoretical studies (Wood, 1990b; Haas et al., 1995), particularly in the case of log β2.Calculations of monazite solubility in seafloor hydrothermal systems (Wood and Williams-Jones, 1994) are re-evaluated in light of our new experimental data. Chloride complexes are shown to dominate the aqueous Nd socciation at 300°C, and lead to solubilities that are (1) much higher than previously estimated and (2) much closer to the maximum concentrations that have been reported from active black smokers. However, the large fluxes of REEs in altered rock beneath ancient massive sulfide deposits are still difficult to explain assuming that modern seafloor hydrothermal systems are direct analogs to ore-forming processes. Significant differences in fluid chemistry (e.g., lower pH, higher Cl− or F− concentrations) and/or duration and intensity of hydrothermal activity (higher water/rock ratio) are required to explain the REE systematics in ancient volcanogenic massive sulfide deposits.

Hydrothermally precipitated mixed-layer illite-smectite in recent massive sulfide deposits from the sea floor

Mixed-layer illite-smectite (I/S) in recent massive sulfide deposits from a seamount near the East Pacific Rise has been studied by X-ray powder diffraction (XRD) and scanning and transmission electron microscopy (SEM, TEM). The I/S fills pore space between quartz and sulfides, and XRD and TEM analyses indicate that the I/S contains ∼25%-45% smectite, with R1-type ordering (ISISIS). Microprobe and analytical electron-microscope analyses indicate a rectorite-like composition, K being the dominant interlayer cation. The occurrence of the I/S within a hydrothermally precipitated sulfide deposit, the pore-filling texture, and the internal structure of the I/S are all consistent with direct precipitation from hydrothermal solutions. Direct precipitation of I/S from solution has two important implications. First, some sericite in ancient volcanogenic massive sulfide deposits may have similarly originated as hydrothermal precipitates rather than as alteration products, with implications for mobility and transport of Al. Second, direct precipitation of R1-ordered I/S from fluid implies that during diagenetic evolution of smectite to illite, the sequence of smectite → random I/S → ordered I/S → illite may not be followed.