Quartz-sulfide Veins Research Articles

The Xilaokou carbonate-sulfide vein type gold deposit: A distinct mineralization in the giant Jiaodong gold province, North China

The Xilaokou gold deposit with ca. 50 t of gold reserve @ 2.7 g/t represents a novel type (carbonate-sulfide vein type) of gold mineralization within the Jiaodong gold province. However, its mineralization age and metallogenic mechanism remain poorly constrained, hindering a comprehensive understanding of the ore-forming processes in the Jiaodong gold province. In this study, we employ syn-ore stage hydrothermal monazite in situ U-Pb geochronology to determine the ore-forming age of the Xilaokou gold deposit. Additionally, we conduct in situ LA-(MC)-ICP-MS elemental mapping and sulfur isotope analysis in ore-related pyrite to unravel the sulfur source(s) and provide new insights into the ore-forming processes of the Xilaokou gold deposit. Our findings reveal the following key points: (1) U-Pb dating of hydrothermal monazite in Au-bearing pyrite yields an ore-forming age of119.9 ± 3.0 Ma. This age is consistent with the mineralization ages (around 120 ± 5 Ma) of other gold deposits in the region, including Liaoshang-, Jiaojia-, and Linglong-type deposits. (2) Gold in pyrite primarily occurs as micro-grains (5–20 μm) within pyrite fissures associated with sphalerite and galena. (3) Elemental mapping and sulfur isotope analysis indicate that major Au mineralization is linked to elevated concentrations of As, Sb, and Tl, along with heavy sulfur isotope values (δ34S∼24.7 ‰). (4) Early-stage Au mineralization is characterized by enrichment of As, Cu, and Bi, with normal sulfur isotopic composition (δ34S∼8 ‰). We propose that the carbonate-sulfide vein type gold deposits represented by the Liaoshang and Xilaokou gold deposits in the Jiaodong gold province are genetically linked to quartz-sulfide vein and disseminated type deposits. The major ore-forming stage involved the addition of S and Au from a metamorphic massif at slightly lower temperatures. These findings highlight a new exploration direction within the North China Craton. In summary, the Xilaokou gold deposit provides valuable insights into gold mineralization processes in Jiaodong, emphasizing the importance of considering diverse deposit types and their genetic relationships in the region.

Metallogenic model of the Lykling ophiolite-hosted lode Au deposit, Scandinavian Caledonides: Insight from fluid inclusions, mineral chemistry and stable isotope geochemistry

The Lykling lode Au deposit represents a unique example of gold mineralization in the Upper Allochthone of the Scandinavian Caledonides. The mineralization is hosted by the Early Ordovician Lykling Ophiolite Complex and the intruding trondhjemite unit and spatially associated with two generations of mafic dykes that crosscut both the ophiolitic complex and trondhjemite. Field observations indicate that the mafic dykes did not play an active role in the emplacement of Au at Lykling, however their contacts with the immediate host rocks (i.e., gabbro and trondhjemite) may have focused ore-forming fluids.Three main stages in the evolution of the hydrothermal system in the Lykling area are documented by two generations of auriferous quartz veins: 1) older quartz-carbonate veins hosted by moderately angled brittle-ductile shear zones and 2) younger quartz-sulfide veins that fill steeply dipping brittle faults. Stage 1 resulted in deposition of barren quartz and gold-free pyrite from moderately saline NaCl-CaCl2-H2O ± CO2 fluids at temperatures between ∼310–330 °C and pressures in the range from 2.7 to 3.5 kbars. Under the given physicochemical conditions Au was mobile in the form of its chloride complexes. Stage 2 is associated with multiple episodes of ductile deformation punctuated by concomitant brecciation reflecting brittle-ductile transition processes. Fluid inclusion data reveals a decrease in temperature and pressure that may result in the formation of stable Au-bisulfide complexes and making the hydrothermal mobility of Au sensitive to changes in pressure. Consequently, the fluctuation in pressure controlled by the development of brittle-ductile structures likely resulted in the precipitation of native gold in quartz veins. Stage 3 represents a pure brittle event which is accompanied by a significant decrease in the fCO2/fS2 ratio. Mixing of higher-temperature and moderate-salinity fluids with cooler fluids has been recognized as the principal trigger for deposition of sulfides and a paragenetically late phase of native gold in the Lykling hydrothermal system.The Lykling ophiolite-hosted lode Au deposit shows numerous similarities with orogenic gold deposits elsewhere, including structural controls during mineralizing events, deposition from moderately to low salinity CO2-bearing aqueous solutions, deposition from a focused fluid flow along trans-crustal fault zones with a mixed brittle-ductile character and the spatial association with regionally metamorphosed terranes. In contrast to the great majority of the known orogenic gold deposits, the Lykling ophiolite-hosted lode Au deposit records a magmatic origin of volatiles. Therefore, taking into consideration field relationships and the regional setting of the Lykling deposit, we argue that its formation is concomitant with emplacement of the Sunnhordland Batholith during post-collisional thinning of the crust and associated localized uplift within the Lykling Ophiolite Complex.

Advanced soil-gas geochemical exploration methods for orogenic gold deposits: A case study of Chalapu deposit, Xizang

Orogenic gold deposits play a significant role in the world’s gold reserves, and their distinctive characteristics pose challenges for exploration. The low sulfide content and narrow, fault-controlled sulfide-quartz veins hinder the use of traditional mineral exploration methods to locate deeply buried ore bodies, particularly in regolith-covered areas. Enhanced methods are required to detect deposits at greater depths. Soil gas composition shows promising potential for mineral exploration by conveying information about sulfur-rich and carbon-rich gases related to deep-seated mineralization into surface soils. However, the prospects of this method for gold deposits remain uncertain. In this study, a novel method was introduced to perform an integrated H2S, SO2, CH4, and CO2 soil-gas geochemical survey on gold ore bodies of different scales at the Chalapu deposit in Tibet. The results unveiled notable gas geochemical anomalies of H2S, SO2, CH4, and CO2 above the multi-layered or thick gold ore bodies. For instance, on exploration line 16 at point A1607, H2S reached the regional maximum value of 1.064 ppm, coinciding with the surface exposure of the thickest gold ore body, measuring 19.81 m. While the presence of CH4 and CO2 anomalies alone may not signify potential mineralized zones, the combined presence of anomalous H2S and SO2 values along with CH4 and CO2 concentrations appears to be effective in identifying mineralization. These combinations of geochemical anomalies not only uncover concealed ore bodies, but also delineate the trend and extension direction in strike and dip of ore bodies. Gas intensity may provide insights into the scale of the ore bodies, with stronger gas anomalies observed in areas with thicker ore bodies at similar depths. Thus, the study reveals that soil-gas exploration shows great promise as an exploration technique for orogenic gold deposits, especially in areas with regolith cover hindering traditional methods from detecting mineralized zones for gold exploration.

Origin of the Dongga Au deposit in the giant Xiongcun porphyry Cu–Au district, Tibet, China: Constraints from multiple isotopes (Re, Os, He, Ar, H, O, S, Pb) and fluid inclusions

The Dongga Au deposit (9.55 t Au; average grade = 6.9 g/t [up to 61.6 g/t]) is located in the Xiongcun giant porphyry Cu–Au district of the Gangdese porphyry Cu belt, Tibet. Its mineralization age, ore-forming processes, and relationship to adjacent porphyry mineralization remain unclear. To address this, we conducted a geological, pyrite Re–Os dating, He–Ar–H–O–S–Pb isotopic, and fluid inclusion study of the Dongga deposit. Pyrite samples from ore-bearing chlorite–sulfide veins yielded a weighted-mean Re–Os age of 178.4 ± 2.6 Ma (MSWD=0.01), implying the deposit formed during the Early Jurassic. Fluid inclusion analyses yielded homogenization temperatures of 237–360 °C for quartz–sulfide veins and 125–201 °C for late quartz veins, with corresponding salinities of 2.7–43.8 and 0.9–9.9 wt% NaCleq, respectively. Fluid inclusion analyses of pyrite samples yielded 3He/4He and 40Ar/36Ar values of 0.50–1.08 Ra and 325.1–559.4, respectively, and δD and δ18Ofluid values of –86.2 ‰ to –72.1 ‰ and –5.6 ‰ to 3.9 ‰, respectively. The He–Ar–H–O isotopic data suggest the mineralizing fluids were derived mainly from a crustal source with a small mantle contribution, and also contained a mixture of magmatic and meteoric waters. The S (δ34S = –1.57 ‰ to –0.55 ‰) and Pb (206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb are 18.17–18.41 ‰, 15.55–15.63 ‰ and 38.15–38.37 ‰, respectively) isotopic compositions of pyrite suggest the ore-forming metals were derived from a magma source in the mantle containing minor amounts of subducted sediment. Based on the geology, and isotopic and fluid inclusion data, we infer that mixing between magmatic and meteoric waters was the main trigger of Au precipitation. In addition, based on the geochronological, spatial, and genetic relationships with the adjacent No.2 deposit in the Xiongcun ore district, we propose that the Dongga Au deposit is a sub-epithermal deposit, which represents the transition between porphyry and epithermal deposits. The two deposits constitute a porphyry system and record the continuous evolution of hydrothermal fluids transported outwards in a porphyry system.

Anomalous cobalt enrichment in pyrite from an altered mafic dike in the Linglong gold deposit, Jiaodong Peninsula, China: Mechanisms and implications

Traditionally, gold deposits in the Jiaodong gold province of China have been regarded as gold-only deposits lacking economic base metals. However, recent studies found some cobalt (Co) enrichment in those deposits. The mechanisms of this Co enrichment remain poorly understood. In this study, we identified a type of pyrite highly enriched in Co (concentrations up to 32800 ppm) at the Linglong gold deposit, Jiaodong gold province. The pyrite was collected from a hydrothermally altered mafic dike contacting with gold ore veins. To decipher the enrichment mechanisms of Co, in-situ textural, elemental and sulfur isotopic analyses were conducted on the pyrite. The pyrite typically exhibits core-mantle-rim textures. The cores (Py-m1) have high Co concentrations (up to 5950 ppm) with homogeneous texture and elemental distribution, which could be the primary pyrite formed by pyritization of the mafic dike. The mantles (Py-m2) have the highest Co concentrations (up to 32800 ppm) and contain abundant mineral inclusions (chalcopyrite, galena, and sphalerite) and pores, showing the formation through coupled dissolution-reprecipitation (CDR) reactions. The rims (Py-m3) have low concentrations of Co (0.14–559 ppm) and show cubic shapes, forming directly from hydrothermal fluids. The δ34S values increase from the cores (4.2 ‰ to 9.1 ‰, mean of 8.0 ‰) to the mantles (8.9 ‰ to 11.9 ‰), but vary between the above two in the rims (4.2 ‰ to 12.2 ‰, mean of 9.0 ‰). The sulfur isotopic compositions of the Py-m are similar to those of pyrite (4.8 ‰ to 9.5 ‰) from the neighboring auriferous quartz-sulfide veins at Linglong in previous study. Combined with the geological and textural features, it is inferred that hydrothermal fluids during gold mineralization extracted abundant Co from the mafic dikes, leading to the primary enrichment of Co in the Py-m1. The Py-m1 was dissolved and re-precipitated during subsequent hydrothermal activities, forming Py-m2 with enhanced re-enrichment of Co. Basically, the Co-rich mafic dike provided the initial enrichment of Co while the gold-bearing hydrothermal fluids contributed to concentrate Co further. Considering the widespread mafic rocks and extensive hydrothermal activities during gold mineralization throughout the Jiaodong gold province, there might be a considerable Co resource formed through the above processes.

Geochronological and sulfide geochemical evidence for gold mineralization related to post-collisional magmatism in the Wulonggou goldfield of the East Kunlun Orogen, northern Tibet

The relationships among magmatism, orogeny, and gold mineralization in lode gold deposits have been controversial for a long time. The East Kunlun Orogen in northern Tibet has experienced a complex Paleo-Tethyan tectono-magmatic evolution and hosts the largest Wulonggou lode gold deposits (>120 t). The Shuizhadonggou-Huanglonggou (SZDG-HLG) gold deposit is the largest in the Wulonggou goldfield and is an excellent candidate for solving the controversy through detailed field observations, magmatic and hydrothermal mineral in-situ U-Pb dating, and gold-bearing sulfide in-situ trace elements and sulfur-lead isotopes. Gold mineralization in the SZDG-HLG deposit includes sulfide disseminations and minor amounts of small quartz-sulfide veins in hydrothermal alteration assemblages along a ductile shear zone. Gold mineralization can be divided into four stages based on crosscutting relationships and associated alteration assemblages. U-Pb ages from magmatic zircon, hydrothermal rutile, and hydrothermal monazite support field relationships that gold mineralization was later than the ductile deformation but synchronous with the post-collisional porphyries. Gold mineralization evolved from high to low temperatures (560℃ to less than 300℃), accompanied by markedly decreased sulfur fugacities (–6.3 to –12.5) and oxygen fugacities (–20.7 to –40.5). The gradual increase of sulfur isotopes (δ34S) from stage 1 (–0.9 to 1.8 ‰ in Py1a) to stage 3 (up to 8 ‰) is ascribed to sulfide precipitation from a finite fluid reservoir, while the sharp decrease of δ34S values in stage 4 (down to –24 ‰) is caused by the fluid oxidation. The negative covariations of δ34S and Se/S values, positive correlations between Au and chalcophile elements (As, Sb, Te, and Bi) in most sulfides, and overlapping lead isotopes of sulfides and Late Triassic granodiorite-diorite confirm a post-collisional magmatic gold and sulfur source. This study demonstrates that lode gold deposits in Phanerozoic orogens having similar characteristics to their counterparts in Archean metamorphic terranes can be genetically related to post-collisional magmatism.

Ore-forming process of the Xiaoyuzan gold deposit in the Western Tianshan, Northwest China: Constraints from mineralogy and S isotopes of sulfides

The Xiaoyuzan deposit is a typical intermediate-sulfidation epithermal Au deposit in the Boluokenu metallogenetic belt. The orebodies are hosted by the Lower Carboniferous Dahalajunshan Formation volcanic rocks and controlled by the NW- and NNW-striking faults. The metal minerals present in the ores mainly include pyrite, sphalerite, galena, chalcopyrite, and tetrahedrite. The non-metallic minerals are primarily composed of quartz, calcite, and sericite. Three ore-forming stages are distinguished based on mineral assemblages, wall-rock alteration, and vein crosscutting relationships, including the quartz-pyrite stage (I) with silicification and propylitization, quartz-sulfide stage (II) with phyllic alteration, and quartz-carbonate stage (Ⅲ) with carbonatization. Three different types of pyrite are classified: coarse-grained PyI with cubic from the wall rock, fine-grained PyII with a crystal form of pentagonal dodecahedron in the quartz-sulfide veins, and coarse-grained cubic PyⅢ in the quartz-carbonate veins. The in-situ δ34S value range of sulfides from stage I, stage II and stage Ⅲ are 5.0 ‰ to 5.5 ‰, 4.3 ‰ to 6.5 ‰ and 5.7 ‰ to 6.2 ‰, respectively. The composition of S isotopes indicates that the source of the sulfur is magmatic in origin, with main contribution from the host rock. All the types of pyrite are relatively enriched with Sb, Cu, Ag, Pb, Bi, and As. The composition of pyrite suggests that the Au in the pyrite present as lattice gold (Au+1). The gradual decrease in Co contents from in PyⅠ, PyⅡ to PyⅢ indicates a gradual decrease in temperature during fluid evolution. The contents of trace elements in sphalerite are relatively low, with Fe, Mn, Cd, and Cu being relatively enriched. Using the sphalerite geothermometer (GGIMFis), the calculated temperature falls within the range of 303.0 to 334.3 °C. Pyrite II is characterized by the occurrence of oscillatory zones, suggesting rhythmic changes in fluid physicochemical conditions and compositions. Although coexisting of liquid-rich and vapor-rich aqueous inclusions were locally observed in stage II quartz according to previous studies, the absence of crustiform/colloidal/lattice bladed quartz in the main stage suggests that slight or gentle fluid boiling has occurred. In summary, it is proposed that fluid-rock reactions made great contribution for the precipitation of gold and sulfides in the Xiaoyuzan deposit.

Texture and Geochemistry of Multi‐stage Hydrothermal Scheelite in the Mamupu Cu‐Au‐Mo(‐W) Deposit, Eastern Tibet: Implications for Tungsten Mineralization in the Yulong Belt

AbstractMultistage tungsten mineralization was recently discovered in the Mamupu copper‐polymetallic deposit in the southern Yulong porphyry copper belt (YPCB), Tibet. This study reports the results of cathodoluminescence, trace element and Sr isotope analyses of Mamupu scheelite samples, undertaken in order to better constrain the mechanism of W mineralization and the sources of the ore‐forming fluids. Three different types of scheelite are identified in the Mamupu deposit: scheelite A (Sch A) mainly occurs in breccias during the prograde stage, scheelite B (Sch B) forms in the chlorite‐epidote alteration zone in the retrograde stage, while scheelite C (Sch C) occurs in distal quartz sulfide veins. The extremely high Mo content and negative Eu anomaly in Sch A represent high oxygen fugacity in the prograde stage. Compared with ore‐related porphyries, Sch A has a similar REE pattern, but with higher ΣREE, more depleted HREE and slightly lower (87Sr/86Sr)i ratios. These features suggest that Sch A is genetically related to ore‐related porphyries, but extensive interaction with carbonate surrounding rocks affects the final REE and Sr isotopic composition. Sch B shows dark (Sch B‐I) and light (Sch B‐II) domains under CL imaging. From Sch B‐I to Sch B‐II, LREEs are gradually depleted, with MREEs being gradually enriched. Sch C has the highest LREE/HREE ratio, which indicates that it inherited the geochemical characteristics of fluids after the precipitation of HREE‐rich minerals, such as diopside and garnet, in the early prograde stage. The Mo content in Sch B and Sch C gradually decreased, indicating that the oxygen fugacity of the fluids changed from oxidative in the early stages to reductive in the later, the turbulent Eu anomaly in Sch B and Sch C indicating that the Eu anomaly in the Mamupu scheelite is not solely controlled by oxygen fugacity. The extensive interaction of magmatic‐hydrothermal fluids and carbonate provides the necessary Ca2+ for the precipitation of scheelite in the Mamupu deposit.

Insights into fluid evolution and Re enrichment by mineral micro-analysis and fluid inclusion constraints: Evidence from the Maronia Cu-Mo ± Re ± Au porphyry system in NE Greece

Porphyry-epithermal veins hosting Re-rich molybdenite and rheniite (ReS2) from the Maronia Cu-Mo ± Re ± Au porphyry in Thrace, NE Greece, provide new insights into the hydrothermal processes causing extreme Re enrichment. Quartz trace element chemistry (Al/Ti, Ge/Ti), Ti-in-quartz thermometry, and cathodoluminescence imaging reveal multiple quartz generations in consecutive hydrothermal quartz-sulfide veins associated with potassic, sericitic, and argillic alteration. Fluid inclusions in different quartz generations indicate that phase separation and fluid cooling are the main ore-forming processes in the porphyry stage (~ 500 – 350 °C), whereas mixing of a vapor-rich fluid with metalliferous (e.g., Pb, Zn, Au) meteoric water forms the epithermal veins (~ 280 °C). These processes are recorded by trace element ratios in pyrite that are sensitive to changes in fluid temperature (Se/Te), fluid salinity (As/Sb, Co/As), and mixing between fluids of magmatic and meteoric origin (Se/Ge). Highly variable intra-grain δ34S values in pyrite record S isotope fractionation during SO2 disproportionation and phase separation, emphasizing the importance of in situ δ34S analysis to unravel ore-forming processes. High δ34S (~ 4.5‰) values of sulfides are indicative of low SO42−/H2S fluid ratios buffered by the local host rocks and mixing of the magma-derived fluid with meteoric water. The formation of Re-rich molybdenite (~ 6600 ppm) is favored by cooling and reduction of a magma-derived, high-temperature (~400 °C), oxidized, and Re-rich fluid triggering efficient Re precipitation in early veins in the potassic alteration zone. The systematic temporal fluid evolution therefore reveals that coeval cooling and reduction of oxidized Re-rich fluids cause extreme Re enrichment at the Maronia porphyry system.

Two episodes of mineralization in the Baolun high-grade lode gold deposit, Hainan Island, South China: Insight from LA-ICP-MS analysis of hydrothermal rutile

The Baolun is the largest gold deposit on Hainan Island, South China, with proven reserves of over 80 t Au at an average grade of 10.3 g/t. Two economic types of gold mineralization coexist in the long-lived fault system: 1) Au-bearing sulfide quartz veins (Va), dominated by pyrite, pyrrhotite, and arsenopyrite; and 2) Au-Bi assemblage quartz veins (Vb), dominated by bismuthinite, maldonite, and native bismuth. The Baolun district has a long history of tectonic reactivation, involving crustal compression and extension, magmatic activity, multiple episodes of fluid flow, and hydrothermal mineralization. Consequently, there exists no generally accepted model for the precise timing and source of the Baolun gold deposits. In this study, two different rutile grains (Rt-1 and Rt-2) were recognized separately in the Va veins and Vb veins based on paragenetic sequence. In situ U-Pb dating indicates that Rt-1 and Rt-2 yielded two group ages of 248.3 ± 2.8 Ma (MSWD = 0.8) and 78.2 ± 8.4 Ma (MSWD = 1.4), respectively. The Rt-1 contains 632.0–6051.2 ppm W, 459.1–2169.1 ppm Zr, 1215.0–8267.5 ppm Nb, 107.3–1229.6 ppm Ta, 19.0–79.2 ppm Hf, 160.2–311.8 ppm Sn, 1371.6–3500.7 ppm V, 325.3–3813.9 ppm Cr, 0.6–22.7 ppm Sb, 0.1–38.8 ppm Y, with Ca below the detection limit. The Rt-2 contains 704.9–4390.2 ppm W, 1.8–168.5 ppm Zr, 1264.6–4062.9 ppm Nb, 108.1–453.2 ppm Ta, 0.3–6.9 ppm Hf, 6.5–32.1 ppm Sn, 14.3–311.0 ppm V, 29.4–167.1 ppm Cr, 0.6–27.3 ppm Sb, 56.3–38.8 ppm Y, and 548.7–2750.3 ppm Ca. Obviously, LA-ICP-MS trace element analysis revealed significant discrepancies in composition between Rt-1 and Rt-2, suggesting that they precipitated from distinct fluid systems. Combining mineral studies, field observations, structural analysis, and geologic evolution, the results of this study indicate that the Baolun gold deposit formed during two episodes of mineralization. The Early Triassic gold mineralization is clearly classified as an orogenic type. The ore-forming materials were liberated by the deformation and metamorphism during the Indosinian orogeny of South China, which was triggered by the closure of the Paleotethys Ocean. The Late Cretaceous Au-Bi mineralization belongs to a magmatic-hydrothermal origin, which was deposited under an extension setting associated with the post-subduction of the paleo-Pacific plate. The new mineralization model proposed provides significant implications for future exploration strategies.

Gold source and deposition in the Sanakham gold deposit, SW Laos: Constrains from textures, trace element geochemistry and in-situ sulfur isotopes of pyrite

The Luang Prabang (Laos) – Loei (Thailand) metallogenetic belt is endowed with major porphyry-skarn, and epithermal gold deposits. The Sanakham gold deposit is a newly discovered hydrothermal vein-type orogenic gold deposits (10.6 t Au @ 3.05 g/t) in the belt, and consist of a series of quartz-sulfide veins that are controlled by secondary structures of the regional NNE-trending brittle-ductile shear zone. Its mineralization can be divided into four stages: (I) quartz–pyrite–arsenopyrite, (II) quartz–pyrite–pyrrhotite–chalcopyrite, (III) quartz–pyrite–base-metal sulfide, and (IV) quartz–carbonate. Three pyrite generations were identified: py1 (stage I) as disseminated euhedral to subhedral coarse grains; py2 (stage II) as subhedral to anhedral fine grains occur around the cataclastic and corrosion textures in py1; py3 (stage III) as subhedral to anhedral fine grains occurred in sulfide veins or veinlets that overprint the existing quartz-sulfides. All three generations of pyrite have low trace-element contents including very low lattice-bound gold (py1: 0.040 ppm; py2: 0.098 ppm; py3: 0.028 ppm) and arsenic (py1: 227 ppm; py2: 133 ppm; py3: 13.3 ppm) contents. Visible gold grains are sited in textures of pyrite grains that relate to brittle cataclastic deformation. Considering the relatively low contents of pyrite in the ores of Sanakham, it is impossible to derive the high-gold grade orebodies through local remobilization of originally lattice-bound gold in pyrite. The py2 might be formed during hydrothermal overprinting and dissolution of py1 led by continuous supply of ore fluids with relatively higher contents of Au, Ag, Cu, Sb, Te, Pb, and Bi. A reduction reaction related to reduced carbon species in wallrock is an assignable cause for gold deposition, even though the fluid-rock interaction and fluid immiscibility processes might be important. The Au- and As-poor pyrites have similar δ34S values (py1: –2.58 to –0.83 ‰; py2: –2.17 ‰ to + 0.25 ‰; py3: –1.24 to –0.60 ‰ ppm) that close to 0 ‰, indicating the sulfur may have been originated from magmatic or mantle sources. Therefore, we propose that the Sankham gold deposit is a member of the orogenic deposit class, but notably characterized by the low concentrations of invisible gold in the relatively As-poor pyrite lattice.

Conformities distribution contents gold and silver in ore bodies of the Berezovskoe deposit (Middle Urals)

The relevance of the work is due to the importance industrial meaning associated with beresits and listvenites gold ores deposit in the world production. Purpose of the work – study conformities of distribution gold and silver concentration in ore bodies of the Berezovskoe deposit. Methods of research included separation industrial types of ores for valuation quality gold chute, use probabilistic-statistic, geometric-statistic and geostatistic models for description amplitude and frequency changeability gold and silver content in ore bodies of Berezovskoe deposit. Results. It was established definite conformities in distribution contents gold and silver in primary types ores of Berezovskoe deposit. So in limits mineralized dikes granitoids on percentage correlation rich, ordinary and poor ores, meaning coefficients wealth and the gold-silver ratio the best quality distiquished sulphide-quartz ores in the strip veins in comparison with more poor impregnation ores in berezites near veins. In distribution parameters gold mineralization (contents gold and silver, linear productivity of ores) was established tier vertical zonality with separation 2–3 levels the largest foul prevalence mineralization on dip dikes granitoids in interval of depth 112–712 meters. In distribution contents gold and silver in ores registered lateral zonality on strike ore-bearing dikes granitoids. She expressed in conforming growth productivity of ores on horizons with moving off in direction with south to the north from the contact Shartash massif of granitoids. Distribution gold and silver content in mineralized dikes granitoids on amplitude variability changed from quite uneven to extremely uneven. Among colour sulphide-quartz veins of Berezovskoe deposit on content in their gold and silver, linear productivity of ores the best quality defined veins, formed on upper ore level (53–168 m). Quality ores conforming lowered with growth of depth bedding veins on middle ore level (201–262 m) and lower ore level (442–512 m) horizons.

The origin and evolution of the ore-forming fluids at the Manondo-Choma gold prospect, Kirk range, southern Malawi

Abstract This study provides an in-depth analysis of fluid inclusions (FIs) and stable isotopes from the Manondo-Choma gold prospect in southern Malawi to understand the ore-forming mechanisms, genesis, and evolution of the hydrothermal fluids responsible for gold mineralization at the Manondo-Choma gold prospect. FIs and microthermometry studies were carried out on mineralized quartz veins from the area. The Manondo-Choma gold prospect is located in the southern Malawi within the Kirk range. Gold is mostly found in quartz veins within metamorphic rocks, such as gneiss and schists, and is structurally controlled by the NE–SW ductile shear zones. Gold mineralization is linked to quartz sulfide veins. Mineralization occurs in the following three stages: early, middle, and late, of which the middle stage is more plorific. The following three FI types were recognized in the quartz veins: pure carbonic, aqueous carbonic (CO2–H2O) and aqueous (H2O–NaCl) inclusions. Gold and associated mineralization were likely precipitated due to the lowering of pressure and fluid immiscibility. Oxygen isotope data indicate that the source of ore-forming fluids at the Manondo-Choma gold prospect was largely metamorphic in origin with minor magmatic input.

Deposit-scale controls of hypozonal gold mineralization in amphibolite facies metaturbidites: 3D modelling of the Twin Hills deposit, Damara Belt, Namibia

The recently discovered Twin Hills deposit is a new resource in the Pan-African Damara Belt of central Namibia, described by a finely dispersed, low-grade and high tonnage disseminated and vein-style gold mineralization. The underlying assumption of the 3D implicit modelling followed in this study is that the integration of gold grades and ore shells with structural and lithological data from oriented core logging reflects the underlying controls of hydrothermal fluid flow and mineralization at Twin Hills. The deposit comprises distinct clusters of economic-grade gold mineralization, measuring several hundred meters along strike, separated by several kilometer-long intervals of only sporadic and sub-economic gold grades. Mineralization is developed on the subvertical southern limb of a regional-scale syncline hosted in highly-strained compositionally heterogeneous, amphibolite facies metaturbidites. Additionally, the stretch of the main mineralization in the central parts of the ∼12 km long east-northeast-trending mineralized Twin Hills corridor coincides with the change of the fold vergence direction. We suggest that the steep orientation of the wall-rock strata generated high-permeability fluid conduits for focusing regional fluid flow during flexural-slip folding and associated local dextral strike-slip component of D2/3 deformation. Disseminated sulfide mineralization is mostly developed in pelitic units, whereas networks of quartz-sulfide veins and veinlets with subordinate disseminated sulfides are present in rigid psammitic beds in interbedded pelite-psammite horizons. While the wide distribution of finely disseminated sulfides point to the rather pervasive fluid flow along grain-scale permeabilities during recrystallization of mineral fabrics, the formation of fractures and resultant dilatancy in psammitic units created hydraulic gradients and focused fluid flow into the psammite horizons. High-grade ore shoots are controlled by the combination and interplay of two main factors, namely lithological contacts and subtle deflections of bedding of the highly-strained, subvertical metaturbidites. The mineralized corridor of the Twin Hills deposit is largely confined to imbricated and/or tightly folded packages of interbedded pelites-psammites within the otherwise pelite-dominated sequence. It is these units that promoted fracturing, fluid flow and the development of fine-scale vein networks as a result of pronounced strain partitioning between pelitic units (ductile) and interbedded psammites (brittle) during regional deformation. Ore shoots of higher-grade mineralization (>1.5 g/t Au) follow these main lithological contacts, but are laterally confined to subtle (5–15°) clockwise deflections of bedding (dilational jogs) from its regional east-northeast trends. Outside these deflections, gold mineralization is patchy and only sub-economic. The structural and lithological controls of the Twin Hills mineralization closely resemble those of orogenic gold deposits, whereas the fine-grained and dispersed texture of gold and associated sulfide mineralization are more reminiscent of disseminated gold deposits. We suggest that the Twin Hills deposit is an example of a hypozonal orogenic gold deposit formed under peak metamorphic amphibolite conditions.

Genesis of the Taoguanping molybdenum deposit in the Northern Qinling Belt, Central China: Constraints from geology, fluid inclusions, and H–O–S isotopes

The Taoguanping molybdenum deposit is located in the west of the Mangling pluton in the Northern Qinling Belt, but its fluid characteristics and ore-forming process are unclear, hindering the understanding of its ore genesis and genetic model. The paragenetic sequence of the Taoguanping molybdenum deposit can be divided into: quartz–K-feldspar–sulfide stage (Stage I), quartz–polymetallic sulfide stage (Stage II), and quartz–calcite stage (Stage III). Stage I is characterized by disseminated molybdenite mineralization associated with siliceous and K-feldspar alteration in the medium- to fine-grained monzogranite, representing the early mineralization. Stage II is the main mineralization featured by coarse-grained quartz–sulfide veins, e.g., quartz–molybdenite and quartz–biotite–molybdenite ± pyrite ± chalcopyrite veins, crosscutting monzogranite and host rocks. Stage III is late hydrothermal veins to crosscut former minerals. Detailed fluid inclusion study shows that temperature and salinity of fluids decreased from Stage I (peaks at ca. 320–380 °C and 3.7–13.6 wt% NaCl eqv.), through Stage II (peaks at ca. 260–300 °C and 1.2–11.8 wt% NaCl eqv.) to Stage III (peaks at ca. 180–220 °C and 0.4–8.9 wt% NaCl eqv.), accompanied by fluid mixing and boiling. The H–O isotopes of quartz (δDfluid = –72‰ to –53‰ and δ18Ofluid = 9.1–10.9‰) suggest Stage II fluids are magmatic–hydrothermal origin mixed with minor meteoric water. The in-situ sulfur isotope of pyrite (–33.4‰ to –13.4‰ and 0‰ to 7.8‰) indicates Stage II fluids being mainly magmatic–hydrothermal origin, with participation of strata materials inferred by presence of Stage II euhedral to anhedral pyrite with inclusion-rich domains and CH4 in Stage II fluid inclusions during fluid–rock interaction. In combination of this study and regional tectonic setting, we propose that the Taoguanping molybdenum deposit underwent porphyry and hydrothermal vein-type mineralization, contributed by medium- and fine-grained monzogranite and possible granite porphyry, respectively, which should be ascribed to a porphyry mineralization system and formed in a post-collisional setting during the Late Mesozoic.

LA–ICP–MS U–Pb geochronology and geological significance of two types of monazite in the Xinjiazui gold deposit, northwestern margin of Yangtze Block, China

The newly discovered Xinjiazui gold deposit situates on the northwestern margin of the Yangtze Block, China. Previously, the absolute age of gold metallogenesis in this area has yet to be well defined due to the lack of suitable dating minerals, significantly hindering the study of ore genesis and metallogenesis of gold deposits. This study presents high precision in-situ laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS) U–Pb ages of monazite to address this issue. Two types of monazite have been found in this deposit, with Type 1 developed in the sedimentary diagenetic stage and Type 2 formed in the ore-forming stage. Type 1 monazite collected from carbonaceous slate is symbiotic with framboidal pyrite in a skeletal texture. It exhibits a high total amount of rare earth elements (REE) and low Y, Th, and U contents, indicating a low-grade metamorphic origin. In contrast, Type 2 monazite from the auriferous quartz vein is intergrown with hydrothermal mineral assemblages including free gold, Au-bearing pyrite and arsenopyrite, ankerite and sericite, suggesting a hydrothermal origin. The monazite (Type 1) LA–ICP–MS 206Pb/238U age is 460.8 ± 7.0 Ma, representing the sedimentary age of the host rock. A combination of lithologic associations and geochemical characteristics indicates that the Ordovician strata (O2ch) are important surrounding rocks in the Xinjiazui gold deposit. Additionally, the forming ages of monazite symbiotic with free gold in the auriferous quartz–sulfide veins range from 206.4 to 207.4 Ma, representing the gold mineralization age of the Xinjiazui deposit. Field geological observation shows that the vertical vein wall of columnar quartz crystals grows inward in the auriferous quartz–sulfide vein geodes and the euhedral granular sulfides develop in geodes. Therefore, this study proposes that the tectonic system changed from compression to extension in the late orogenic period with the closure of Paleo-Tethys and gold mineralization occurred in the Back-Longmenshan tectonic belt.

Scheelite composition fingerprints pulsed flow of magmatic fluid in the Fujiashan W skarn deposit, eastern China

Abstract Scheelite (CaWO4) is an economically important W mineral in skarns that form when magmatic fluids exsolved from a granitic intrusion react with carbonate wall rocks. In the Fujiashan W skarn deposit, scheelite formed during four stages of the hydrothermal skarn development. We present cathodoluminescence (CL) images and in situ trace element and Sr-O isotope data of scheelite from these four stages, i.e., scheelite in prograde and retrograde skarn, quartz-sulfide veins, and late calcite replacements. Scheelite from prograde skarn and quartz sulfide veins are homogeneous and show oscillatory zoning textures in CL images, whereas scheelite from retrograde skarn and late carbonate stages display dissolution-reprecipitation and patchy textures. The brightness of CL textures decreases with a higher substitution of Mo. Molybdenum-rich scheelite (up to 2.1 wt%) is characterized by relatively high contents of Nb and Ta (up to 156 and 0.9 ppm, respectively), positive Eu anomalies, high-δ18O values (5.2 to 5.9‰), and relatively low-87Sr/86Sr values (0.70661 to 0.70727), and has grown in a system with a continuous supply of magmatic fluid. Molybdenum-poor scheelite (0.2 wt%) has low contents of Nb and Ta, negative Eu anomalies, low-δ18O values (4.2 to 4.3‰), and relatively high-87Sr/86Sr ratios (0.70748 to 0.70804). This type of scheelite formed in a system with a restricted flow of magmatic fluid during scheelite precipitation became increasingly depleted in elements that substitute into scheelite. The continued reaction of the magmatic fluid with the wall rocks and the precipitation of minerals from the fluid resulted in a systematic change of the δ18O and 87Sr/86Sr ratios. Chemical and isotopic variations in scheelite may reflect the pulsed flow of a magmatic fluid and do not require the involvement of different fluids or contrasting redox conditions.

Localization patterns of gold mineralization in the Phuoc Son area, Central Vietnam

Background. In this paper, the authors aim to reveal the localization patterns of gold mineralization in the Phuok Son region of Central Vietnam, which formed a Proterozoic-Cambrian metamorphic complex in the zone of the Late Paleozoic Benzhang–Queshon granite block.Aim. To determine the localization patterns of gold mineralization in the Phuoc Son area, Central Vietnam.Materials and methods. The research was based on geological materials, as well as mine working and appraisal well data. The material composition of the materials was studied using 15 transparent sections and 18 polished sections. In total, 127 samples were subjected to atomic absorption spectroscopy.Results. Within the Phuoс Son gold ore field in Central Vietnam, the site of the Baidat and Baigo mines located in the zone of reverse-shear termination was investigated. Here, the gold ore bodies are represented by quartz-sulfide veins subparallel to schistosity. The ore-bearing zones are layered zones of tectonic faults, which formed at the end of the reverse-shear period and complicated the western limbs and locks of the anticlines. These zones were formed under regional sublatitudinal horizontal stresses. The horizons of carbonaceous quartz-sericite schists are of great importance in ore control. There are steeply dipping post-ore faults that displace ore bodies. Two gold mineralization stages can be distinguished. The early stage was characterized by a wide development of sphalerite and a smaller amount of gold. The later stage was associated with the main precipitation of gold and formation of galena. According to the geochronological data on the argon isotopy in biotite, the gold mineralization at Baidat and Baigo was probably formed in the Triassic (250–200 Ma ago), at the stage of extinction of the regional metamorphism of the Indosinian orogenyConclusion. The results obtained should be used when conducting local forecasting of gold deposits in Central Vietnam.

Genesis of the Heihaibei gold deposit in the East Kunlun Orogenic Belt, China: Evidence from in situ trace elements of gold-bearing sulfides and stable isotopes

The Heihaibei gold deposit, located in the south part of the East Kunlun orogenic belt (EKOB), is a newly discovered gold deposit, with similar tectonic setting and geological characteristics with typical orogenic gold deposits in the orogenic belt. The aim of this study is to enrich the understanding of metallogeny of the orogenic gold deposit in the EKOB by studying the genesis of the Heihaibei gold deposit. Pyrite and arsenopyrite, as the predominant Au-bearing sulfides, were investigated using a combination of laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) and laser ablation–multi-collector–inductivity coupled plasma–mass spectrometry (LA–MC–ICP–MS) for in situ trace elements and sulfur isotope. The analyses results provided significant information about genesis for gold mineralization. There are two types of smoky quartz–sulfide veins (barren and mineralized) in this deposit. Three types of pyrite based on host rock can be distinguished, including barren smoky quartz–sulfide vein- (Py0), mineralized altered monzogranite- (Py1) and mineralized smoky quartz–sulfide vein-hosted pyrite (Py2, including Py2a and Py2b). Py1 coexists with arsenopyrite. Py2a and Py2b occurs as disseminated crystals and veinlet assemblage, respectively. Petrographic observations and LA–ICP–MS analyses show that invisible gold in pyrite and arsenopyrite occurs dominantly as solid solution (Au+). Co/Ni ratios of pyrite and S–H–O isotopic compositions exhibit that pyrites (Co/Ni > 1, δ34SV-CDT = −5.28 to 5.08‰) hosted by barren smoky quartz–sulfide vein are consistent with a magmatic origin, whereas those (Co/Ni < 1, δ34SV-CDT = 7.37 to 9.48‰, δ18OH2O = 3.5 to 4.9‰; δDV-SMOW = −97.9‰ to −93.7‰) hosted by mineralized altered monzogranite and mineralized smoky quartz–sulfide vein were derived from a metamorphic source. Combined with regional tectonic evolution, the gold mineralization in the Heihaibei gold deposit may be related to the metamorphism of the regional strata, which was associated with closure of the Paleotethys Ocean during the early Mesozoic. In the following study, we will pay more attention to the metallogenic regularity of orogenic gold deposits in the EKOB.

Multi-stage metal enrichment and formation of gold mineralization in black shales: the role of high heat flow in a rift setting

Black shales may serve as an important source of metals such as Co, Ni, or As, largely due to anoxic to euxinic conditions in association with high concentrations of sulfur leading to efficient scavenging and transport of metals from seawater into the seafloor sediment. We report on an unusual type of Au mineralization newly discovered in Ediacaran trench-slope black shales in the Bohemian Massif, Czech Republic. The Au enrichment is related to the formation of a quartz–sulfide vein system and a progressive evolution of ore-forming fluids with decreasing temperature, from Sb- to As-rich to final precipitation of native gold from silica and Au-bearing low-temperature hydrothermal colloidal solutions. The hydrothermal nature of these solutions is also documented by Li contents and isotope compositions which differ markedly between barren black shales and those carrying significant late-stage quartz-rich veins. The structural relationships and orientation of the associated quartz veins point to a close connection between vein emplacement and high heat flow in response to Ordovician rifting, and breakup of the northern margin of Gondwana, and opening of the Rheic Ocean. This triggered metal and sulfur remobilization, including Au, from the associated Neoproterozoic–Cambrian volcanosedimentary successions. The documented Au mineralization and its association with the Ordovician rift-related magmatic activity is different from the widespread Variscan Au occurrences in the Bohemian Massif. Our study thus provides a new genetic model potentially important for future exploration of Au also in other terrains underlain by a rifted Cadomian basement.