scholarly journals Assessing Thallium Elemental Systematics and Isotope Ratio Variations in Porphyry Ore Systems: A Case Study of the Bingham Canyon District

Minerals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 548 ◽  
Author(s):  
Angus Fitzpayne ◽  
Julie Prytulak ◽  
Jamie Wilkinson ◽  
David Cooke ◽  
Michael Baker ◽  
...  
Keyword(s):  
Low Temperature ◽  
Gold Mineralization ◽  
Isotope Ratios ◽  
Gold Deposits ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Fluid Composition ◽  
New Information ◽  
Two Samples ◽  
Element Enrichment

The Bingham Canyon porphyry deposit is one of the world’s largest Cu-Mo-Au resources. Elevated concentrations of thallium (Tl) compared to average continental crust have been found in some brecciated and igneous samples in this area, which likely result from mobilization of Tl by relatively low temperature hydrothermal fluids. The Tl-enrichment at Bingham Canyon therefore provides an opportunity to investigate if Tl isotope ratios reflect hydrothermal enrichment and whether there are systematic Tl isotope fractionations that could provide an exploration tool. We present a reconnaissance study of nineteen samples spanning a range of lithologies from the Bingham district which were analysed for their Tl content and Tl isotope ratios, reported as parts per ten thousand (ε205Tl) relative to the NIST SRM997 international standard. The range of ε205Tl reported in this study (−16.4 to +7.2) is the largest observed in a hydrothermal ore deposit to date. Unbrecciated samples collected relatively proximal to the Bingham Canyon porphyry system have ε205Tl of −4.2 to +0.9, similar to observations in a previous study of porphyry deposits. This relatively narrow range suggests that high-temperature (>300 °C) hydrothermal alteration does not result in significant Tl isotope fractionation. However, two samples ~3–4 km away from Bingham Canyon have higher ε205Tl values (+1.3 and +7.2), and samples from more distal (~7 km) disseminated gold deposits at Melco and Barneys Canyon display an even wider range in ε205Tl (−16.4 to +6.0). The observation of large positive and negative excursions in ε205Tl relative to the mantle value (ε205Tl = −2.0 ± 1.0) contrasts with previous investigations of hydrothermal systems. Samples displaying the most extreme positive and negative ε205Tl values also contain elevated concentrations of Tl-Sb-As. Furthermore, with the exception of one sample, all of the Tl isotopic anomalies occur in hydrothermal breccia samples. This suggests that ε205Tl excursions are most extreme during the migration of low-temperature hydrothermal fluids potentially related to sediment-hosted gold mineralization. Future investigation to determine the host phase(s) for Tl in breccias displaying both chalcophile element enrichment and ε205Tl excursions can potentially provide new information about hydrothermal fluid composition and could be used to locate sites for future porphyry exploration.

scholarly journals Oxygen Fugacity and Volatile Content of Syntectonic Magmatism in the Neoarchean Abitibi Greenstone Belt, Superior Province, Canada

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 966
Author(s):  
Baptiste Madon ◽  
Lucie Mathieu ◽  
Jeffrey H. Marsh
Keyword(s):  
Oxygen Fugacity ◽  
Greenstone Belt ◽  
Inductively Coupled Plasma ◽  
Gold Mineralization ◽  
Gold Deposits ◽  
Hydrothermal Systems ◽  
Chemical Diversity ◽  
Temporal Association ◽  
Volatile Content ◽  
Abitibi Subprovince

Neoarchean syntectonic intrusions from the Chibougamau area, northeastern Abitibi Subprovince (greenstone belt), may be genetically related to intrusion related gold mineralization. These magmatic-hydrothermal systems share common features with orogenic gold deposits, such as spatial and temporal association with syntectonic magmatism. Genetic association with magmatism, however, remains controversial for many greenstone belt hosted Au deposits. To precisely identify the link between syntectonic magmas and gold mineralization in the Abitibi Subprovince, major and trace-element compositions of whole rock, zircon, apatite, and amphibole grains were measured for five intrusions in the Chibougamau area; the Anville, Saussure, Chevrillon, Opémisca, and Lac Line Plutons. The selected intrusions are representative of the chemical diversity of synvolcanic (TTG suite) and syntectonic (e.g., sanukitoid, alkaline intrusion) magmatism. Chemical data enable calculation of oxygen fugacity and volatile content, and these parameters were interpreted using data collected by electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry. The zircon and apatite data and associated oxygen fugacity values in magma indicate that the youngest magmas are the most oxidized. Moreover, similar oxygen fugacity and high volatile content for both the Saussure Pluton and the mineralized Lac Line intrusion may indicate a possible prospective mineralized system associated with the syntectonic Saussure intrusion.

scholarly journals Coupled partitioning of Au and As into pyrite controls formation of giant Au deposits

2019 ◽  
Vol 5 (5) ◽  
pp. eaav5891 ◽  
Author(s):  
C. Kusebauch ◽  
S. A. Gleeson ◽  
M. Oelze
Keyword(s):  
Partition Coefficients ◽  
Hydrothermal Fluid ◽  
Iron Sulfide ◽  
Gold Deposits ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Balance Model ◽  
Mass Balance Model ◽  
Depositional Process ◽  
Partitioning Behavior

The giant Carlin-type Au deposits (Nevada, USA) contain gold hosted in arsenic-rich iron sulfide (pyrite), but the processes controlling the sequestration of Au in these hydrothermal systems are poorly understood. Here, we present an experimental study investigating the distribution of Au and As between hydrothermal fluid and pyrite under conditions similar to those found in Carlin-type Au deposits. We find that Au from the fluid strongly partitions into a newly formed pyrite depending on the As concentration and that the coupled partitioning behavior of these two trace elements is key for Au precipitation. On the basis of our experimentally derived partition coefficients, we developed a mass balance model that shows that simple partitioning (and the underlying process of adsorption) is the major depositional process in these systems. Our findings help to explain why pyrite in Carlin-type gold deposits can scavenge Au from hydrothermal fluids so efficiently to form giant deposits.

scholarly journals Significance of Calcite Trace Elements Contents and C-O Isotopic Compositions for Ore-Forming Fluids and Gold Prospecting in the Zhesang Carlin-Like Gold Deposit of Southeastern Yunnan, China

Minerals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 338
Author(s):  
Jiasheng Wang ◽  
Jinyang Chang ◽  
Chao Li ◽  
Zhenchun Han ◽  
Tao Wang ◽  
...  
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Gold Deposit ◽  
Meteoric Water ◽  
Gold Mineralization ◽  
Mining Area ◽  
Gold Deposits ◽  
Hydrothermal Fluids ◽  
Magmatic Fluid ◽  
Isotopic Compositions

The Zhesang gold deposit of southeastern Yunnan is an important component of the Dian-Qian-Gui (Yunnan, Guizhou, and Guangxi) “Golden Triangle”, which hosts a multitude of Carlin-like gold deposits (CLGDs). Calcite is one of the most common gangue minerals in Zhesang. The calcites that have been found in the mining area are classified as ore-stage and post-ore calcites. The ore-stage calcite exhibits a clear paragenetic relationship with gold-bearing arsenopyrite and with an alteration halo that has been cut by the post-ore calcite. To elucidate the origin of the ore-forming fluids of the Zhesang gold deposit and to investigate the possibility of utilizing calcite geochemistry as prospecting indicators, the rare earth elements (REEs), Y, Fe, Mn and Mg contents, and C-O isotopic compositions of calcites from Zhesang have been analyzed. The ore-stage calcite is enriched in middle rare earth elements (MREEs) relative to light rare earth elements (LREEs) and heavy rare earth elements (HREEs) (MREE/LREE = 1.11–1.61, MREE/HREE = 6.12–8.22), whereas post-ore calcite exhibits an enrichment in LREE (LREE/HREE = 4.39–14.93, MREE/LREE = 0.35–0.71). The ore-stage and post-ore calcites were both formed by hydrothermal fluids; however, these hydrothermal fluids may have different sources. The Fe contents of the ore-stage calcite are significantly higher than those of post-ore calcite (4690–6300 μg/g versus 2030–2730 μg/g). Ore-stage calcite also has significantly lower δ18OV-SMOW values than post-ore calcite (11.03–12.49‰ versus 16.48–17.14‰). These calcites with an MREE/LREE ratio greater than 0.92, MREE/HREE ratio greater than 5.69, Fe content greater than 3827 μg/g, and δ18OV-SMOW value less than 14.40‰ represent ore-stage calcites and are important prospecting guidelines. According to the REE, C-O isotopic characteristics of the calcites and the previous findings, it is inferred that the ore-forming fluids of the Zhesang gold deposit were a mixture of crustal fluid by meteoric water leaching wall rocks and a small amount of basic magmatic fluid. The formation of post-ore calcite might be derived from meteoric water and marine carbonates interaction. The ore-forming fluids of the Zhesang gold deposit may be associated with the intrusion of diabase that outcrops in the mining area, and that the basic magmatic activities of the Indosinian period also provided some of the ore-forming materials and heat for gold mineralization.

Mineralization, antiforms and crustal extension in andesitic arcs

1994 ◽  
Vol 131 (2) ◽  
pp. 231-242 ◽  
Author(s):  
A. H. G. Mitchell ◽  
J. C. Carlile
Keyword(s):  
Gold Mineralization ◽  
Porphyry Copper ◽  
Geothermal Gradient ◽  
Gold Deposits ◽  
Hydrothermal Fluids ◽  
Plate Motion ◽  
Epithermal Gold ◽  
Crustal Extension ◽  
Copper Mineralization ◽  
High Level

AbstractThe distribution and stratigraphic position of porphyry copper and epithermal gold deposits in andesitic arcs of the western Pacific and eastern Europe suggest that porphyry copper and epithermal vein deposits of adularia–sericite type develop successively under different stress regimes in an evolving arc, rather than being genetically related as commonly supposed. Absence of coeval high-level stocks in the root zones of many adularia-sericite deposits suggests that circulation of the dominantly meteoric hydrothermal fluids is not driven by shallow intrusions. The location of several world-class deposits on basement geanticlines, and on more localized antiforms of which at least one has been interpreted as a metamorphic core complex, implies that elevation of the arc, emplacement of magmatic sills at depth and adularia–sericite type gold mineralization are genetically related to subduction-induced crustal extension. Ascent of deep hydrothermal fluids, predominantly meteoric but with a metamorphic or magmatic component, may be controlled by regional low-angle structures at depth, analogous to those inferred for some mesothermal gold deposits. Mineralization at shallow (epithermal) depths in high-angle structures largely reflects the high geothermal gradient and mixing of deep fluid with cool meteoric water in or at the base of the permeable volcanic cover. Andesitic magmatism may resume following porphyry copper mineralization, adularia–sericite epithermal gold mineralization, or continued extension to form a ‘back arc’ spreading system, depending on the relative plate motion.

scholarly journals Effect of paleoseawater composition on hydrothermal exchange in midocean ridges

2017 ◽  
Vol 114 (47) ◽  
pp. 12413-12418 ◽  
Author(s):  
Michael A. Antonelli ◽  
Nicholas J. Pester ◽  
Shaun T. Brown ◽  
Donald J. DePaolo
Keyword(s):  
Low Temperature ◽  
Negative Feedback ◽  
Chemical Exchange ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Sr Isotope ◽  
Seawater Chemistry ◽  
Quartz Veins ◽  
Midocean Ridges ◽  
Temperature Exchange

Variations in the Mg, Ca, Sr, and SO4 concentrations of paleoseawater can affect the chemical exchange between seawater and oceanic basalt in hydrothermal systems at midocean ridges (MOR). We present a model for evaluating the nature and magnitude of these previously unappreciated effects, using available estimates of paleoseawater composition over Phanerozoic time as inputs and 87Sr/86Sr of ophiolite epidosites and epidote-quartz veins as constraints. The results suggest that modern hydrothermal fluids are not typical due to low Ca and Sr relative to Mg and SO4 in modern seawater. At other times during the last 500 million years, particularly during the Cretaceous and Ordovician, hydrothermal fluids had more seawater-derived Sr and Ca, a prediction that is supported by Sr isotope data. The predicted 87Sr/86Sr of vent fluids varies cyclically in concert with ocean chemistry, with some values much higher than the modern value of ∼0.7037. The seawater chemistry effects can be expressed in terms of the transfer efficiency of basaltic Ca and Sr to seawater in hydrothermal systems, which varies by a factor of ∼1.6 over the Phanerozoic, with minima when seawater Mg and SO4 are low. This effect provides a modest negative feedback on seawater composition and 87Sr/86Sr changes. For the mid-Cretaceous, the low 87Sr/86Sr of seawater requires either exceptionally large amounts of low-temperature exchange with oceanic crust or that the weathering flux of continentally derived Sr was especially small. The model also has implications for MOR hydrothermal systems in the Precambrian, when low-seawater SO4 could help explain low seawater 87Sr/86Sr.

scholarly journals Quartz Rb-Sr Isochron Ages of Two Type Orebodies from the Nibao Carlin-type Gold Deposit, Guizhou, China

Minerals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 399 ◽  
Author(s):  
Zheng ◽  
Yang ◽  
Gao ◽  
Chen ◽  
Liu ◽  
...  
Keyword(s):  
Low Temperature ◽  
Gold Deposit ◽  
Fluid Inclusions ◽  
Large Scale ◽  
Gold Mineralization ◽  
Gold Deposits ◽  
Quartz Veins ◽  
Golden Triangle ◽  
Mineralization Age ◽  
Gold Bearing

The Nibao gold deposit, which includes both fault-controlled and strata-bound gold orebodies, constitutes an important part of the Yunnan–Guizhou–Guangxi “Golden Triangle” region. Defining the mineralization age of these gold orebodies may provide additional evidence for constraining the formation ages of low-temperature orebodies and their metallogenic distribution in South China. Petrographic studies of gold-bearing pyrites and ore-related quartz veins indicate that these pyrites coexist with quartz or filled in vein-like quartz, which suggests a possible genetic relationship between the two from Nibao gold deposit. Minerals chemistry shows that Rb and Sr are usually hosted in fluid inclusions in quartz ranging from 0.0786 to 2.0760 ppm and 0.1703 to 2.1820 ppm, respectively. The Rb–Sr isotopic composition of gold-bearing quartz-hosted fluid inclusions from the Nibao gold deposit were found to have Rb–Sr isochron ages of 142 ± 3 and 141 ± 2 Ma for both fault-controlled and strata-bound orebodies, respectively, adding more evidence to previous studies and thus revealing a regional gold mineralization age of 148–134 Ma. These results also confirm the Middle-Late Yanshanian mineralizing events of Carlin-type gold deposits in Yunnan, Guizhou, and Guangxi Provinces of Southwest China. In addition, previous studies indicated that antimony deposits in the region which were formed at ca. 148–126 Ma have a close affinity with gold deposits. This illustrates that the regional low-temperature hydrothermal gold mineralization is related in space and time to the Yanshanian (ca. 146–115 Ma) magmatic activity. Specifically, the large-scale gold and antimony mineralization are considered to be inherently related to mantle-derived mafic and ultramafic magmatic rocks associated with an extensional tectonic environment. Based on the initial 87Sr/86Sr ratios of 0.70844 ± 0.00022 (2σ) and 0.70862 ± 0.00020 (2σ) for gold-bearing quartz veins from fault-controlled and strata-bound gold orebodies, respectively, at the Nibao gold deposit, as well as the C, H, O, and S isotopic characteristics of gold deposits located in the Golden Triangle region, we suggest that the mantle-derived material can be involved in the formation of the Nibao gold deposit and that the ore-forming fluid can be derived from a mixed crust–mantle source.

Chapter 7: Paleoproterozoic Gold Deposits of the Loulo District, Western Mali

2020 ◽  
pp. 141-162
Author(s):  
Andrew Allibone ◽  
David Lawrence ◽  
John Scott ◽  
Mark Fanning ◽  
James Lambert-Smith ◽  
...  
Keyword(s):  
West Africa ◽  
Shear Zone ◽  
Thermal Gradient ◽  
Gold Mineralization ◽  
Regional Scale ◽  
Shear Zones ◽  
Gold Deposits ◽  
Hydrothermal Fluids ◽  
Western Margin ◽  
Form Part

Abstract Paleoproterozoic (Rhyacian) gold deposits of the Loulo district in western Mali contain >17 million ounces (Moz) Au and form part of the second most highly endowed region within West Africa. The deposits are located within siliciclastic, marble, and evaporitic rocks of the ca. 2110 Ma greenschist facies Kofi series, which were folded and inverted between ca. 2100 and 2070 Ma, prior to gold mineralization. Deposits at Yalea and Gounkoto are located along discontinuous, low-displacement, albite- and carbonate-altered shear zones, whereas Gara is confined to a tourmaline-altered quartz sandstone unit. Lodes typically plunge gently to moderately, reflecting the attitude of folds in the adjacent rocks and bends in the host shear zones, both of which influenced their location. Gold mineralization in the Loulo district was broadly synchronous with emplacement of the Falémé batholith and associated Fe skarn mineralization, which intrude and overprint the western margin of the Kofi series, respectively. However, hydrothermal fluids generated during metamorphic devolatilization of the Kofi series rocks appear responsible for gold mineralization, albeit within a district-wide thermal gradient associated with emplacement of the Falémé batholith. The regional-scale Senegal-Mali shear zone, commonly cited as an important control on the location of gold deposits in western Mali, is absent in the Loulo district.

Reaction between Cu-bearing minerals and hydrothermal fluids at 800 °C and 200 MPa: Constraints from synthetic fluid inclusions

2020 ◽  
Vol 105 (8) ◽  
pp. 1126-1139
Author(s):  
Dongmei Qi ◽  
Harald Behrens ◽  
Roman Botcharnikov ◽  
Insa Derrey ◽  
Francois Holtz ◽  
...  
Keyword(s):  
Fluid Inclusions ◽  
Pure Water ◽  
Metallic Copper ◽  
Pressure Vessels ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Silicate Melt ◽  
Fluid Composition ◽  
Nacl Solution ◽  
Synthetic Fluid Inclusions

Abstract Transport and deposition of copper in the Earth's crust are mainly controlled by the solubility of Cu-bearing phases and the speciation of Cu in magmatic-hydrothermal fluids. To improve our understanding of copper mobilization by hydrothermal fluids, we conducted an experimental study on the interaction between Cu-bearing phases (metallic copper, Cu2O, CuCl) and aqueous chloride solutions (H2O ± NaCl ± HCl; with Cl concentrations of 0 to 4.3 mol kg-1). The experiments were run in rapid heat/rapid quench cold-seal pressure vessels at 800 °C, 200 MPa, and logfO2 ~ NNO+2.3. Either Cu or Au capsules were used as containers. The reaction products were sampled in situ by the entrapment of synthetic fluid inclusions in quartz. Fluid composition was subsequently determined by analyzing individual fluid inclusions using a freezing cell and laser ablation inductively coupled plasma-mass spectrometry. Our results show that large isolated and isometric inclusions, free of late-stage modifications, can be preserved after the experiment even when using a high cooling rate of 25 K s-1. The obtained results demonstrate that: (1) reaction between native Cu, NaCl solution, and quartz (± silica gel) leads to the coexistence of fluid inclusions and Na-bearing silicate melt inclusions. Micrometer-to submicrometer-sized cuprite (Cu2O) crystals have been observed in both types of the inclusions, and they are formed most probably due to the dissociation of CuOH. (2) When Cu0 reacts with HCl and CuCl solutions, or Cu+ reacts with NaCl solution, nantokite (CuCl) formed due to oversaturation has been found in fluid inclusion. Copper concentration in the fluid shows a strong positive dependence on the initial chlorine content, with Cu/Cl molal ratios varying from 1:9 to 1:1 in case 1 and case 2, respectively. When Cl is fixed to 1.5 m, initial fluid acidity has a major control on the Cu content, i.e., 0.17 ± 0.09 and 1.29 ± 0.57 m Cu were measured in fluids of case 1 and case 2, respectively. Cu solubility in pure water and in 1.5 m NaCl solutions are 0.004 ± 0.002 and 0.16 ± 0.07 m, respectively. The main responsible Cu-bearing complexes are CuOH(H2O)x in water, NaCuCl2 in NaCl solutions and HCuCl2 in alkali-free solutions. These results provide quantitative constraints on the mobility of Cu in hydrothermal solutions and confirm that Cl is a very important ligand responsible for Cu transport. The first observation that silicate melt can be generated in the fluid-dominated and native-copper-bearing system implies that transitional thermosilicate liquids can coexist with metal-rich fluids and may enhance Cu mobility in magmatic-hydrothermal systems. This may have important implications for the formation of Cu deposits in the systems with low S activities.

scholarly journals Transition from hydrothermal vents to cold seeps records timing of carbon release in the Guaymas Basin, Gulf of California

2018 ◽  
Author(s):  
Sonja Geilert ◽  
Christian Hensen ◽  
Mark Schmidt ◽  
Volker Liebetrau ◽  
Florian Scholz ◽  
...  
Keyword(s):  
Hydrothermal Vent ◽  
Gulf Of California ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Fluid Composition ◽  
Cold Seeps ◽  
Pore Fluids ◽  
Guaymas Basin ◽  
Carbon Release ◽  
Magmatic Intrusions

Abstract. The Guaymas Basin in the Gulf of California is an ideal site to test the hypothesis that magmatic intrusions into organic-rich sediments can cause the release of large amounts of thermogenic methane and CO2 that may lead to climate warming. In this study pore fluids close (~ 500 m) to a hydrothermal vent field and at cold seeps up to 20 km away from the northern rift axis were studied to determine the influence of magmatic intrusions on pore fluid composition and gas migration. Pore fluids close to the hydrothermal vent area show predominantly seawater composition, indicating a shallow circulation system transporting seawater to the hydrothermal catchment area rather than being influenced by hydrothermal fluids themselves. Only in the deeper part of the sediment core, composed of hydrothermal vent debris, Sr isotopes indicate a mixture with hydrothermal fluids of ~ 3 %. Also cold seep pore fluids show mainly seawater composition. Most of the methane is of microbial origin and consumed by anaerobic oxidation in shallow sediments, whereas ethane has a clear thermogenic signature. Fluid and gas flow might have been active during sill emplacement in the Guaymas Basin, but ceased 28 to 7 thousand years ago, based on sediment thickness above extinct conduits. Our results indicate that carbon release depends on the longevity of sill-induced, hydrothermal systems which is a currently unconstrained factor.

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