Types Of Hydrothermal Ore Deposits Research Articles

Mineralogical distribution and genetic aspects of cobalt at the active Fåvne and Loki’s Castle seafloor massive sulfide deposits, Arctic Mid-Ocean Ridges

The demand for responsibly sourced cobalt has increased dramatically as a result of the global transition to ‘fossil-free’ electromobility. However, the distribution, mineralogical expressions and mechanisms of concentration of Co in different types of hydrothermal ore deposits remain poorly constrained, inhibiting resource assessments and exploration. Here we report Co and other metal concentrations in ores from the active Fåvne and Loki’s Castle seafloor massive sulfide (SMS) deposits located along the Mohns Ridge and assess some genetic aspects of Co. The assemblages from the recently discovered Fåvne deposit are dominated by either pyrrhotite-isocubanite or sphalerite, in both cases with abundant anhydrite and local Fe-oxides. They show high whole-rock Co concentrations (average 0.31 wt%, up to 0.98 wt%) and Co is enriched in the Cu-rich relative to the Zn-rich assemblages. No independent Co-minerals are observed; rather, Co is variably hosted in pyrrhotite (up to 1.03 wt%), isocubanite (up to 0.71 wt%), sphalerite (up to 0.14 wt%) and magnetite (∼100 ppm). The assemblages from Loki’s Castle are dominated by pyrrhotite, isocubanite, sphalerite, amorphous silica and barite, and they exhibit distinctly lower Co concentrations in both whole-rock samples (average 62 ppm, up to 368 ppm) and in individual minerals (up to 152, 148 and 99 ppm in isocubanite, sphalerite and pyrrhotite, respectively). At both deposits, Co is interpreted to enter the Fe-, Cu-Fe- and Zn-sulfides and Fe-oxides via simple Co2+ ↔ (Fe,Zn)2+ substitutions and its mineralogical distribution reflects a combination of crystal-chemical controls (e.g., spin state compatibility between Co2+ and the divalent cation) and changing hydrothermal fluid conditions (e.g., temperature) during mineral formation. Based on a comparison with global SMS and VMS deposits, we suggest that the ‘diffuse’ high-temperature venting at Fåvne can in part explain the enrichment of Co in the surficial sulfides, whereas at Loki’s Castle more Co-rich sulfides might occur in the interior of the deposit. Furthermore, Fåvne and several Co-rich deposits elsewhere show evidence for the involvement of saline hydrothermal fluids with enhanced capacity to mobilize and transport Co during their evolution. While their future role as a source of Co and other critical commodities remains uncertain, active SMS deposits provide unique insights into the processes and conditions associated with formation of hydrothermal Co mineralization that will aid both deep-sea and onshore exploration.

Fluid Evolution and Scheelite Precipitation Mechanism of the Large-Scale Shangfang Quartz-Vein-Type Tungsten Deposit, South China: Constraints from Rare Earth Element (REE) Behaviour during Fluid/Rock Interaction

Unlike classic skarn-type scheelite deposits directly acquiring sufficient Ca2+ from surrounding limestones, all of the scheelite orebodies of the Shangfang tungsten (W) deposit occur mainly in amphibolite, and this provides a new perspective on the mineralization mechanism of W deposits. The ability of hydrothermal scheelite (CaWO4) to bind REE3+ in their Ca2+ crystal lattices makes it a useful mineral for tracing fluid-rock interactions in hydrothermal mineralization systems. In this study, the REE compositions of scheelite and some silicate minerals were measured systematically in-situ by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to assess the extent of fluid-rock interactions for the Late Mesozoic quartz-vein-type Shangfang W deposits. According to the variations in CaO and REE among scheelite and silicate minerals, the amphibole and actinolite in amphibolite may be able to release large amounts of Ca2+ and REE3+ into the ore-forming fluids during chlorite alteration, which is critical for scheelite precipitation. Furthermore, an improved batch crystallization model was adopted for simulating the process of scheelite precipitation and fluid evolution. The results of both the in-situ measurements and model calculations demonstrate that the precipitation of early-stage scheelite with medium rare-earth elements (MREE)-rich and [Eu/Eu*]N 1. Even though the partition coefficient of REE is constant, the later-stage scheelite will also inherit a certain degree of MREE-depletion and [Eu/Eu*]N future from the residual fluids. As a common mineral, sheelite forms in various types of hydrothermal ore deposits (e.g., tungsten and gold deposits). Hence, the improved batch crystallization model is also possible for obtaining detailed information regarding fluid evolution for other types of hydrothermal deposits. The results from model calculations also illustrate that the Eu anomalies of scheelite are not an effective index correlated to oxygen fugacity of fluids but rather are dominantly controlled by the continuous precipitation of scheelite.

Mineralogical Distribution of Germanium, Gallium and Indium at the Mt Carlton High-Sulfidation Epithermal Deposit, NE Australia, and Comparison with Similar Deposits Worldwide

Germanium, gallium and indium are in high demand due to their growing usage in high-tech and green-tech applications. However, the mineralogy and the mechanisms of concentration of these critical elements in different types of hydrothermal ore deposits remain poorly constrained. We investigated the mineralogical distribution of Ge, Ga and In at the Mt Carlton high-sulfidation epithermal deposit in NE Australia, using electron probe microanalysis and laser ablation inductively-coupled plasma mass spectrometry. Parageneses from which selected minerals were analyzed include: Stage 1 acid sulfate alteration (alunite), Stage 2A high-sulfidation enargite mineralization (enargite, argyrodite, sphalerite, pyrite, barite), Stage 2B intermediate-sulfidation sphalerite mineralization (sphalerite, pyrite, galena) and Stage 3 hydrothermal void fill (dickite). Moderate to locally high concentrations of Ga were measured in Stage 1 alunite (up to 339 ppm) and in Stage 3 dickite (up to 150 ppm). The Stage 2A ores show enrichment in Ge, which is primarily associated with argyrodite (up to 6.95 wt % Ge) and Ge-bearing enargite (up to 2189 ppm Ge). Co-existing sphalerite has comparatively low Ge content (up to 143 ppm), while Ga (up to 1181 ppm) and In (up to 571 ppm) are higher. Sphalerite in Stage 2B contains up to 611 ppm Ge, 2829 ppm Ga and 2169 ppm In, and locally exhibits fine colloform bands of an uncharacterized Zn-In mineral with compositions close to CuZn2(In,Ga)S4. Barite, pyrite and galena which occur in association with Stage 2 mineralization were found to play negligible roles as carriers of Ge, Ga and In at Mt Carlton. Analyzed reference samples of enargite from seven similar deposits worldwide have average Ge concentrations ranging from 12 to 717 ppm (maximum 2679 ppm). The deposits from which samples showed high enrichment in critical elements in this study are all hosted in stratigraphic sequences that locally contain carbonaceous sedimentary rocks. In addition to magmatic-hydrothermal processes, such rocks could potentially be important for the concentration of critical elements in high-sulfidation epithermal deposits.

Injection-Driven Swarm Seismicity and Permeability Enhancement: Implications for the Dynamics of Hydrothermal Ore Systems in High Fluid-Flux, Overpressured Faulting Regimes—An Invited Paper

Many types of hydrothermal ore deposits form at overpressured conditions during high fluid flux through fault zones in the continental seismogenic regime. These include many orogenic gold deposits, some types of Fe oxide Cu-Au systems, and a variety of intrusion-related deposits, including some high-sulfidation epithermal systems. The internal structures of these deposits indicate formation while faults were active, in a regime involving episodic slip. Partial to complete sealing of fault zones by precipitation of hydrothermal minerals occurs between slip episodes. Such ore deposits occur typically within low displacement faults, or networks of such faults. Lodes seldom occupy areas much greater than 1 km 2 of fault surfaces, and net slip accumulated during ore formation is typically less than 150 m. Fluid injection experiments in low-permeability rocks, and seismicity styles in hydrothermally active settings, provide new insights about the dynamics of ore formation in high fluid-flux faults. In particular, they indicate that swarm seismicity is the characteristic response to injection of large volumes of overpressured fluids into intrinsically low-permeability rock. Injection-driven swarm seismicity and related permeability enhancement involves repeated sequences of thousands of ruptures, mostly with moment magnitude M w in the range −2 w 2 ; maximum cumulative slip is usually less than a few centimeters. Diffusion-like migration of a seismicity front away from the injection source at rates up to hundreds of meters per day is a key characteristic of injection-driven seismicity, and correlates with migration of a fluid pressure front along activated faults. By analogy with injection experiments and natural injection-driven swarm seismicity, the formation of fault-related ore deposits in overpressured, high fluid-flux regimes is interpreted to involve swarm seismicity, rather than mainshock-aftershock sequences. Recurrence intervals of swarms in contemporary injection-driven swarm sequences indicate that the total slip associated with formation of fault-hosted lodes can accumulate in periods as short as 104 to 105 years, during thousands of swarm episodes, and commonly involve >10 6 ruptures with −2 w 4 to 10 5 m 3 of fluid at injection rates of at least several tens of L.s −1 . Up to tens of kg Au are deposited per swarm. Cascades of thousands of microseismic ruptures and associated permeability enhancement, coseismic dilatancy, and fluid pressure changes during individual injection-driven swarm sequences create very dynamic hydrologic and reaction regimes. Ore formation involving transitory bursts of rapid flow, abrupt fluctuations in flow rates and fluid pressures, and possibly also fluid temperatures, is likely to promote severe chemical disequilibrium. This has implications for controls on ore deposition and grade distribution in many fault-related ore systems.

Structure and Thermodynamics of Subduction Zone Fluids from Spectroscopic Studies

Fluids1 in subduction zones have been a subject of growing interest for at least the last 20 years. Subduction zones are the major places on Earth for mass transfer, element recycling and chemical differentiation through magmatic processes in which fluids released from the slab play a central role. Hydrous subduction zone magmas are essential in the formation of numerous types of hydrothermal ore deposits and are the driving force behind magmatic-hydrothermal and geothermal systems in volcanic arcs. It is widely recognized that the characteristic geochemical signature of arc magmas results from the metasomatism of the magma source by a slab-derived flux (McCulloch and Gamble 1991; Elliott 2003). Large uncertainties remain however concerning the chemical composition and nature of the slab flux (aqueous fluid, hydrous melt or supercritical fluid?) and, ultimately, about the mechanisms of mass transfer from the slab to the mantle wedge. Correlating inputs and outputs in subduction zones to quantitatively estimate mass transfer and element recycling relies on thermodynamic modeling of fluid-rock interactions at pressure-temperature above 5 GPa and 1500 K (Manning 2004a). Key constraints on these models are the phase relations, mineral solubility, the behavior of trace elements (partition coefficients) and the physico-chemical and thermodynamic properties of high-pressure fluids at relevant conditions. Unfortunately, quantitative information on fluid properties at relevant P - T conditions are in most cases not available due to experimental difficulties associated with the non-quenchable character of fluid phases. New experimental designs, especially those using laser or synchrotron-based spectroscopic techniques combined with high temperature diamond anvil cells (Basset et al. 1993), are now opening the possibility for monitoring in situ the chemical composition of fluid phases and for the determination of structural parameters and thermodynamic quantities. In this chapter, I review recent progress in determining the thermodynamic properties and molecular-scale structure of …

Fluid bubbles in melt inclusions and pillow-rim glasses: high-temperature precursors to hydrothermal fluids?

Hypotheses for the formation of many types of hydrothermal ore deposits often involve the direct contribution of magma-related fluids (e.g., Cu–Mo–Au porphyries) or their superimposition on barren hydrothermal cells (e.g., volcanic-hosted massive sulfide deposits). However, the chemical and phase compositions of such fluids remain largely unknown. We report preliminary results of a comprehensive study of fluid bubbles trapped inside glassy melt inclusions in primitive olivine phenocrysts and pillow-rim glasses from basaltic magmas from different tectonic environments, including mid-ocean ridges (Macquarie Island, SW Pacific and Mid-Atlantic Ridge 43°N Fracture Zone), ocean islands (Hawaii) and a variety of modern and ancient backarc–island arc settings (eastern Manus Basin, Okinawa and Vanuatu Troughs, Troodos, New Caledonia and Hunter Ridge–Hunter Fracture Zone). Fluid bubbles from all localities, studied using electron microscopy with EDS and laser Raman spectroscopy, are composed of CO 2-(±H 2O±sulfur)-bearing vapor and contain significant amounts of amorphous (Na–K–Ca–Fe alumino-silicates and dissorded carbon) and crystalline phases. The crystals are represented mainly by carbonates (magnesite, calcite, ankerite, dolomite, siderite, nahcolite and rhodochrosite), sulfates (anhydrite, gypsum, barite and anglesite), and sulfides (pyrite, arsenopyrite, chalcopyrite and marcasite), though other minerals (brukite, apatite, halite, clinoenstatite, kalsilite, nepheline, amphibole and mica) may occur as well. We argue that chemical components (e.g., C, H, S, Cl, Si, Al, Na, K, Fe, Mn, Cr, Ca, Mg, Ba, Pb and Cu) that later formed precipitates in fluid bubbles were originally dissolved in the magmatic fluid, and were not supplied by host glasses or phenocrysts after entrapment. Magma-related fluid rich in dissolved metals and other non-volatile elements may be a potential precursor to ore-forming solutions.

Sulfur Isotopic Variation of Yanshanian Magmatic-hydrothermal Deposits in Southern China

Abstract: Sulfur isotope data (δ34S) of sulfides of more than 6700 samples from 157 ore deposits associated with Early and Late Yanshanian granitic and volcanic activities in South China are reviewed and summarized. Averaged δ34S values of individual deposits vary from -9. 3 to +20. 6%, and show a normal distribution pattern with the average of +2%. About 88 % of the ore deposits have values within the range, −2.5 ˜ +13.6‰, of associated Yanshanian granitoids. There is a temporal-spatial variation of δ34S values of the ore deposits. However, no clear zonal distribution parallel to geotectonic NNE lineaments was observed. Spatial distribution of ore sulfide δ34S values in most of the NE part of the whole studied area coincides with that of Yanshanian granitoids and volcanic rocks. A downward tendency of the average values in time is: +3. 0% (n=7, J1) → +1. 6% (n=29, J2) → +1. 7% (n=68, J3) → +1. 8% (n=37, K1) → −1. 5% (n=16, K2). There is an “island” of high and variable δ34S values (0˜ +16.5‰) occurring within a generally low trough zone (−8 ˜ 0%) of N-S about 800 km and E-W 100 to 300 km, bounded by 110°E ˜ 116°E longitudes and 22°N ˜ 31°N latitudes. The island occurs at the junction of three tectonic units and a NE-trending crustal matching line implying a variety of magmatism occurred at the junction. The low trough zone coincides with a low ferric/ferrous ratio zone of Early Yanshanian granitoids, indicating their genetic relationship. Different genetic types of ore deposits show different histogram patterns suggesting different relationships to magmatic rocks and host strata. Granite/greisen/pegmatite type deposits are most closely associated with granitoids, with average ore sul-fide δ34S values for individual ore deposits ranging between -2. 0 and +4. 1%, and an average of +0. 5% (n = 15) close to type meteoric value of 0%. Porphyry-type deposits have also narrow range of −2.2 ˜ + 4.9‰, with an average value of +1. 1% (n = 18). Skarn-type dominated ore deposits have a nearly normal distribution pattern with an average of +1. 6% (n = 62), ranging from -5. 3 to +11. 5%. Volcano-subvolcanic ore deposits range between -3. 1 and +5. 9% with an average of +2. 3% (n = 19). Other types of hydrothermal ore deposits have averaged δ34S values of individual ones from -9. 3 to +20. 6%, with average value of +1. 3% (n=43). Vertical and horizontal zonations of δ34S values of ore deposits around their associated granitoid plutons are observed in several localities. Such zonations may be caused by interaction between magma and/or magmatic fluids and host sedimentary rocks, as well as the evolution of physico-chemical conditions of ore-forming fluids. Spatial distribution of ore sulfur isotope compositions is also clearly controlled by tectonics and deep faults. Ore sulfur isotope composition is sometimes strongly affected by host sedimentary rocks, especially by evaporite sulfur with much higher δ34S value and partly by biogenic sulfur with low δ34S value. The δ34S values of Yanshanian granitoids are from -2. 5 to +13. 6% for both rock samples and pyrite/pyrrhotite separates from granitic rocks, with similar spatial distribution pattern to those of associated ore deposits. The ore deposits associated with ilmenite-series granitoids have δ34S values ranging between -7. 5 and +10. 4% with an average of +1. 0%, while the ore deposits associated with magnetite-series granitoids ranging between −8.0 ˜ +11.5‰ with an average of +1. 1%. δ34S values of ore deposits tend to converge to +3% as the Fe2O3/FeO ratio of associated granitoids increases from 0. 45 to 8. 7.

The role of komatiitic and picritic magmatism and S-saturation in the formation of ore deposits

The introduction of high temperature, high magnesium komatiitic and picritic magmas into the Earth's upper crust has given rise either directly or indirectly to many of the world's major ore deposits. There is a direct association between komatiitic magmatism and Kambalda-style NiCuPGE deposits. The link between magma type and mineralization is not as clear cut in the case of the Noril'sk CuNiPGE deposits, but nevertheless there is an association between picritic magmatism and ore deposit development. Komatiitic and/or picritic magmatism may also have contributed to the formation of many types of hydrothermal ore deposits. Recent Nd isotope data generated by Kent et al. (1994) provide strong evidence for the hypothesis proposed by Keays in 1983 that the Au in Archaean Au deposits was derived either directly or indirectly from komatiites through the action of metamorphic fluids. The importance of komatiitic and picritic magmas in ore forming processes arises from the fact that they are among the few mafic/ultramafic magma types that are S-undersaturated at the time of magma formation. S-saturation of magmas leads to marked depletion in the chalcophile metals. For example, Czamanske and Moore (1977) estimated that a third of the original Cu and Ni contents of MORB were lost from the magmas due to extraction into magmatic sulphides. The depletion in Au and the PGE is much greater due to their much larger partition coefficients (Keays and Scott, 1976). Komatiitic and picritic magmas are S-undersaturated because they are high temperature magmas produced by large degrees of partial melting of upper mantle sourc regions that were already depleted in S through earlier partial melting events. Most mafic magmas, produced by less than 25% partial melting, are S-saturated and hence depleted in the ore forming chalcophile elements. In contrast, komatiitic and picritic magmas have their full complement of chalcophile metals. When they do become S-saturated, they form sulphides that are strongly enriched in Ni, Cu, Au, PGE and other strongly, chalcophile metals; these may accumulate to form ore deposits directly (e.g. magmatic NiCuPGE sulphides) or be dispersed in komatiitic/picritic rocks or their fractionation products making these source rocks for hydrothermal Au or VMS deposits.

The role of komatiitic and picritic magmatism and S-saturation in the formation of ore deposits

The introduction of high temperature, high magnesium komatiitic and picritic magmas into the Earth's upper crust has given rise either directly or indirectly to many of the world's major ore deposits. There is a direct association between komatiitic magmatism and Kambalda-style NiCuPGE deposits. The link between magma type and mineralization is not as clear cut in the case of the Noril'sk CuNiPGE deposits, but nevertheless there is an association between picritic magmatism and ore deposit development. Komatiitic and/or picritic magmatism may also have contributed to the formation of many types of hydrothermal ore deposits. Recent Nd isotope data generated by Kent et al. (1994) provide strong evidence for the hypothesis proposed by Keays in 1983 that the Au in Archaean Au deposits was derived either directly or indirectly from komatiites through the action of metamorphic fluids. The importance of komatiitic and picritic magmas in ore forming processes arises from the fact that they are among the few mafic/ultramafic magma types that are S-undersaturated at the time of magma formation. S-saturation of magmas leads to marked depletion in the chalcophile metals. For example, Czamanske and Moore (1977) estimated that a third of the original Cu and Ni contents of MORB were lost from the magmas due to extraction into magmatic sulphides. The depletion in Au and the PGE is much greater due to their much larger partition coefficients (Keays and Scott, 1976). Komatiitic and picritic magmas are S-undersaturated because they are high temperature magmas produced by large degrees of partial melting of upper mantle sourc regions that were already depleted in S through earlier partial melting events. Most mafic magmas, produced by less than 25% partial melting, are S-saturated and hence depleted in the ore forming chalcophile elements. In contrast, komatiitic and picritic magmas have their full complement of chalcophile metals. When they do become S-saturated, they form sulphides that are strongly enriched in Ni, Cu, Au, PGE and other strongly, chalcophile metals; these may accumulate to form ore deposits directly (e.g. magmatic NiCuPGE sulphides) or be dispersed in komatiitic/picritic rocks or their fractionation products making these source rocks for hydrothermal Au or VMS deposits.

Формализованные геохимические модели эндогенного оруденения рудных месторождений

Formalized geochemical models have been constructed in the relative metrics of a standard in the primary halo contour of the main component. They arc based on geochemical zonality studi esand on the similarity method. Formalized models of gold and polymetallic ore formations were built for the first time in Bulgaria on the example of the copper-gold-polymetallic deposits in Vozdol in the Chelopech ore field. For that purpose were used investigations on the relationships belween the alterations in gold productivity and on the total amount of lead and zinc and the changes in the ore zones in depth. Taking into account the models the range of two types of ore depos its as well as the prognostication of metal resources according to geochemical data were determined. The prospects of gold and lead-zinc formation in an ore deposit were specified. A model of the gold formation for the whole field of the ore deposit was created according to the for ecast resources assessment. The numeriacal values of the factor for the estimation of the prognostication resources of gold in genetically similar deposits differing in sizes were found. The obtained models confirmed the well-known generalization of the endogenous ore formation. They can be used further for the estimation of similar sites in the ore field of Panagjurishte. On the example of the lead-zinc deposits in Rouen and Mali Rouen from the Ossogovo ore region, as well as the copper-pyrites deposits Radka in Panagjurishte ore region, it has been demonstrated how the real extent of the standard can be enlar ged and how the necessary number of zone indices may be chosen so that the formalized models of endogenous ore formation are constructed more effectively. This method is suitable for the creati on of the formalized models of the main industrial types of hydrothermal ore deposits in Bulgaria on the basis of the available data.

Oxygen isotope, aeromagnetic, and gravity anomalies associated with hydrothermally altered zones in the Yankee Fork mining district, Custer County, Idaho

Epithermal Ag-Au vein and disseminated deposits in the Yankee Fork district are hosted in altered volcanic rocks having low delta 18 O values, low magnetic susceptibilities, low remanent magnetizations, and relatively high densities. These isotopic and physical quantities provide sensitive indices of rock alteration that can be contoured over areas that are much larger than zones of strong visible alteration. Such contour maps reveal a marked spatial association between the ore deposits, the steepest delta 18 O gradients, and the perimeter of zones where the rocks have extremely low total magnetizations. The oxygen isotope results indicate that the ore zones coincide with steep gradients in temperature and water/rock ratio in two fossil hydrothermal convective systems that involved fluids derived from Tertiary meteoric waters. Our magnetic measurements suggest that these same high-gradient zones also coincide with oxidation-reduction boundaries. Low aeromagnetic intensities and positive Bouguer anomalies are also associated with the altered zones in the Yankee Fork district. The intensities of these geophysical features are consistent with the size of the altered zones and with the contrast in physical properties between altered and unaltered rocks. Contour maps of the magnetic and isotopic properties of host rocks should find application in exploration for a variety of types of hydrothermal ore deposits, as well as in the study of ore controls and conditions of mineralization.

The surrounding medium as an important factor in the formation of mineral types of hydrothermal ore deposits

The surrounding medium as an important factor in the formation of mineral types of hydrothermal ore deposits