Hydrothermal Evolution Research Articles

Crystallographic insights and crystal fractionation simulations of alkali- and water-bearing beryl: Implications for magmatic–hydrothermal evolution and Be enrichment mechanisms

Beryl, an economically significant mineral containing high concentrations of the critical metal Be, has been the subject of considerable characterization regarding its crystal structure and chemical composition. Despite this, discerning between alkali- and H2O-bearing beryls solely based on the alkali and water contents within the structural channels of beryl has remained a challenge. Additionally, the mechanisms that cause granitic melts to become enriched in Be remain ambiguous. Through comprehensive chemical and structural analyses of representative alkali-water-bearing beryl samples from Igla of East Egypt and Baishawo of South China, this contribution improves the beryl classification model and provides new perspectives on Be enrichment mechanisms. This analysis has demonstrated that a linear correlation exists between the water content and alkali content of hydrous beryls, and identified two distinct types of H2O molecules — Type I and II. Major elements are uniformly distributed throughout beryl grains, whereas trace elements exhibit core–rim zonation. Crystal–chemical characteristics of alkali- and water-bearing beryls provide valuable insights into pegmatite evolution, with implications for understanding mineralizing processes and formation conditions. The distributions of alkali metals, Mg, Mn and Fe in alkali-rich and H2O-rich (ARHR) beryl suggest that the pegmatite in the beryl-bearing zones is the product of magmatic metls. Low Fe/Mg ratios of alkali-poor and H2O-rich (APHR) beryl are associated with hydrothermal alkali-metasomatism. Using the Baishawo Be–Li–Nb–Ta pegmatite deposit as a case study, we utilize crystal fractionation simulations to demonstrate the alkali- and water-bearing beryls crystallized after high degrees of magma evolution. The study contributes to the classification of beryl varieties based on chemistry and structure, and provides new insights into Be enrichment mechanism in granitic melts and hydrothermal fluids.

Fluid evolution of the Nulasai Cu deposit, Xinjiang, NW China: Evidence from fluid inclusions and O-H-C isotopes

The Nulasai deposit is the earliest Cu mine in Xinjiang, NW China, and has been mined and smelted since the warring state period. Another striking characteristic of the deposit is the high-grade (ave. 1.34 % Cu) with bornite, chalcopyrite and chalcocite as main ore minerals. Through a field and petrographic investigation, three phases of hydrothermal evolution have been recognized at the Nulasai Cu deposit, including the stage I magnetite – quartz ± chalcopyrite ± bornite veins, the stage II calcite – barite ± chalcopyrite ± chalcocite ± pyrite ± bornite veins, and the stage III calcite – barite ± chalcopyrite ± sphalerite ± pyrite ± galena veins. Fluid inclusions of the stage I veins were captured under two-phase condition indicates that existence of both contemporaneous daughter mineral-bearing and liquid-rich fluid inclusions; they have an intermediate-high salinity (11.5 ∼ 38.5 wt% NaCl equiv) and homogenization temperature (266 ∼ 376 °C), with entrapment pressures from 47 to 167 bar (depth of approximately 0.5 to 1.7 km). The coexistence of vapor-rich and liquid-rich fluid inclusions was a defining feature of the stage II fluid inclusions, and they have an intermediate salinity (6.2 ∼ 10.7 wt.%NaCl equiv) and homogenization temperature (211 ∼ 287 °C), with entrapment pressures from 18 to 70 bar (depth of approximately 0.2 to 0.7 km). Fluid inclusions of the stage III veins were captured under two-phase condition, and intermediate-low salinity (3.2 ∼ 9.2 wt.%NaCl equiv) and homogenization temperature (155 ∼ 241 °C), with entrapment pressures of 6 to 32 bar (depth of 0.1 to 0.6 km). According to the stable isotope (O-H-C) data for the three mineralization phases, magmatic water containing organic carbon made up the majority of the early ore-forming fluids, whereas abundant meteoric water has been involved during the late stage of mineralization. Therefore, we suggest that fluid mixture between magmatic water and meteoric water may have led to simultaneous decrease of fluid temperature, salinity and their stable isotope values, and finally facilitates the Cu ore precipitation. This study emphasizes how high-grade Cu deposition in orogenic belts is initiated by fluid dilution.

Multi-stage magmatic–hydrothermal evolution of nepheline pegmatite: Insights from the mineralogy and geochronology of a zircon megacryst from the Yilanlike nepheline pegmatite, South Tianshan

Magmatic–hydrothermal evolution plays a key role in the formation of peralkaline rocks and associated zirconium and rare earth element (REE) mineralization. Zircon is a common mineral in peralkaline rocks and can record invaluable information about the magmatic–hydrothermal evolution of these systems. To help better constrain the magmatic–hydrothermal evolution of and Zr enrichment processes in peralkaline systems, we characterized the mineralogy and geochronology of a texturally complex zircon megacryst from the rare metal mineralized Yilanlike nepheline pegmatite in the South Tianshan. Here we present laser Raman spectra, in situ elemental data, and U–Pb geochronological data for the zircon megacryst to constrain the age and magmatic–hydrothermal evolution of this nepheline pegmatite. Three types of zircon domains (Zrn-I, Zrn-II, and Zrn-III) are distinguished based on their morphological and geochemical characteristics. Zrn-I has well-developed oscillatory zoning, REE patterns similar to magmatic zircon, high Th/U ratios (0.09–0.47), and concordant U–Pb ages, indicative of a magmatic origin. Zrn-II is characterized by weak oscillatory and patchy zoning, low full width at half maximum (FWHM) values (6.58–14.86 cm−1), and low trace-element contents (e.g., Nb = 0.16–0.92 ppm, Ta = 0.13–0.54 ppm, U = 195.77–812.92 ppm, Th = 15.85–158.95 ppm, and total REE = 13.00–187.75 ppm), indicative of a recrystallized origin as this process generates heterogeneous zoning, heals the zircon crystal lattice, and lowers trace-element contents. Concordant U–Pb ages and low Th/U ratios (0.05–0.26), combined with moderate Ce/Ce* and (Sm/La)N ratios (0.38–33.96 and 1.34–27.73, respectively), which are characteristic of the magmatic–hydrothermal transition, indicate that Zrn-II recrystallized in the presence of hydrothermal fluids. Zrn-III is characterized by “spongy” textures, thorite inclusions, high FWHM values (6.58–47.87), relatively high contents of total REE (14.79–962.05 ppm), and discordant U–Pb ages, suggestive of an origin related to the hydrothermal alteration of earlier zircons. Results of U–Pb dating of Zrn-I and -II yield weighted concordant ages of 286.9 ± 1.9 Ma (MSWD = 1.5, n = 23) and 279.3 ± 2.3 Ma (MSWD = 0.24, n = 20), respectively, whereas the U–Pb results for Zrn-III are largely discordant. Based on these textural, geochemical, and geochronological results, a multi-stage process for the formation of the zircon megacryst and nepheline pegmatite is proposed. First, the parent magma of the nepheline pegmatite was emplaced and the zircon megacryst crystallized at ca. 286.9 Ma (represented by Zrn-I). As the magma differentiated, hydrothermal fluids derived from the evolved magma recrystallized Zrn-I to Zrn-II at ca. 279.3 Ma. Finally, a second hydrothermal event altered Zrn-I and -II to form Zrn-III. Given the low concentrations of UO2, ThO2, and Y2O3 in Zrn-II, and the CHARAC behavior of Zr and Hf, the fluid that formed this zircon variety likely had relatively low F contents. This multi-stage magmatic–hydrothermal evolution likely played an essential role in concentrating Zr and generating the Zr mineralization. Zirconium is primarily enriched via magmatic crystallization, as illustrated by the high abundances of Zrn-I in the Yilanlike nepheline pegmatite. The presence of hydrothermal zircon (Zrn-II and Zrn-III) suggests that hydrothermal recrystallizatio nay have also facilitated the enrichment of Zr. It is, therefore, suggested that both magmatic and hydrothermal processes contributed to the enrichment of Zr in the Yilanlike nepheline pegmatite.

Understanding the extreme differentiation of granitic magmas through elemental geochemistry and Fe isotope signatures

The petrogenesis of extremely fractionated igneous rocks is closely linked to the evolution of the continental crust and the formation of rare metal mineralization. Extremely fractionated magmas evolve via fractional crystallization, hydrothermal evolution, and volatile-rich fluid–melt interaction, but the specific effects of these magmatic and magmatic–hydrothermal processes remain unclear. To understand the mechanisms by which extremely fractionated granitic magmas evolve, we characterized the geochemical and Fe isotope signatures of a suite of granites and pegmatites from the Baishitouquan (BST) granitic pluton in northwest China. The BST granitic system evolved from a high SiO2 and volatile-poor system to a low SiO2 and volatile-rich system as it transitioned from an evolutionary stage dominated by magmatic processes to one dominated by magmatic–hydrothermal processes. This transition is supported by changes in the degree of melt polymerization (NBO/T) and other geochemical indicators of fluid activity (e.g., TE1,3 (REE tetrad effect), Zr/Hf, Nb/Ta, and F/Cl ratios), suggesting that extremely fractionated granites form as a result of a combination of fractional crystallization and volatile-rich fluid–melt interactions. The bulk-rock samples of the BST pluton exhibit significant Fe isotope variability, with δ56Fe values ranging from 0.40 ± 0.02‰ in the least evolved leucogranite (Zone-a) to 0.65 ± 0.02‰ in the most evolved topaz albite granite (Zone-e). Notably, the increase in bulk-rock δ56Fe values during magma evolution is accompanied by a decrease in SiO2 contents, which is opposite to the general trend during granitic magma evolution. Given the correlations between δ56Fe values and indicators of magmatic differentiation (e.g., Fe2O3T, Rb, (Na + K)/(Mg + Ca), and (La/Lu)N), the variability in bulk-rock Fe isotope composition of granites is likely due to changes in magma composition, with garnet removal being the most likely mechanism fractionating Fe isotopes. Rhyolite-MELTS modeling, coupled with geochemical and petrographic characterization, indicate that the high concentrations of F and H2O in felsic magmas likely play critical roles in structurally modifying granitic melts by dramatically reducing their viscosity and enhancing fluid flow. The distinct geochemical–isotopic features of granites can, therefore, be used as tracers for identifying magmatic–hydrothermal processes and, potentially, rare metal mineralization.

Downward continued ocean bottom seismometer data show continued hydrothermal evolution of mature oceanic upper crust

Abstract Heat flow measurements indicate hydrothermal activity in oceanic crust continues at least for 65 m.y. after formation. Hydrothermal activity progressively fills cracks and pores with alteration products, which is expected to lead to a trend of increasing seismic velocities with age. Compilations of seismic-P-wave velocity models inverted from ocean bottom seismometer (OBS) data have failed to detect such an aging trend beyond crustal ages of ca. 10 Ma. However, in these models, the velocities of the uppermost crust, where fluid flow would be most concentrated, are poorly resolved. This is because as the oceanic crust matures, the first crustal arrivals on OBS records (which best resolve upper crustal velocities using tomographic inversion), become hidden in the coda of the water wave. This may lead to the masking of any aging trend in the seismic velocities. For the first time, we show how including downward continuation (DC) in the analysis of OBS data collected across 65 Ma seafloor significantly improves measurements of the P-wave velocities of the upper crust. Our new analysis reveals a highly heterogeneous upper crust, with ridge-parallel P-wave velocity variations of 25%, implying local porosity values that are up to double that of global averages. Our new results, combined with other most recent advanced seismic analyses, reveal that seismic velocities indeed evolve with age up to at least 70 Ma, confirming that hydrothermal activity continues in mature oceanic crust.

High‐resolution cathodoluminescence of calcites from the Cold Bokkeveld chondrite: New insights on carbonatation processes in CM parent bodies

AbstractCarbonates, as secondary minerals found in CM chondrites, have been widely employed for reconstructing the composition of the fluids from which they precipitated. They also offer valuable insights into the hydrothermal evolution of their parent bodies. In this study, we demonstrate that high‐resolution cathodoluminescence (HR‐CL) analyses of calcites derived from the brecciated Cold Bokkeveld CM2 chondrite can effectively reveal subtle compositional features and intricate zoning patterns. We have identified two distinct types of cathodoluminescence (CL) centers: a blue emission band (approximately 375–425 nm), associated with intrinsic structural defects, and a lower energy orange extrinsic emission (around 620 ± 10 nm), indicating the presence of Mn cations. These compositional variations enable discrimination between the calcite grain types previously designated as T1 and T2 in studies of CM chondrites. T1 calcites exhibit variable CL and peripheral Mn enrichments, consistently surrounded by a rim composed of Fe‐S‐rich serpentine–tochilinite assemblage. Conversely, T2 calcites display homogeneous CL and more abundant lattice defects. These polycrystalline aggregates of calcite grains, devoid of serpentine, contain Fe‐Ni sulfide inclusions and directly interface with the matrix. We propose that changes in the Mn content of calcite (indicated by the intensity of orange CL emission) are influenced by variations in redox potential (Eh) and pH of the fluid phase. This proposed hydrothermal evolution establishes a parallel between terrestrial serpentinization followed by carbonation processes and the aqueous alteration of CM chondrites, warranting further exploration and investigation of this intriguing similarity.

The Spatial and Temporal Evolution of the Sadisdorf Li-Sn-(W-Cu) Magmatic-Hydrothermal Greisen and Vein System, Eastern Erzgebirge, Germany

Abstract The Sadisdorf Li-Sn-(W-Cu) prospect in eastern Germany is characterized by vein- and greisen-style mineralization hosted in and around a small granite stock that intruded into a shallow crustal environment. The nature and origin of this mineral system are evaluated in this contribution by a combination of petrography and fluid inclusion studies, complemented by Raman spectroscopy and whole-rock geochemical analyses. The early magmatic-hydrothermal evolution is characterized by a single-phase low-salinity (7.0 ± 4 wt % NaCl equiv), high-temperature (>340°C), CO2-CH4–bearing aqueous fluid, which caused greisen alteration and mineralization within the apical portions of the microgranite porphyry. The bimodal distribution of brine and vapor fluid inclusions, and the formation of a magmatic-hydrothermal breccia associated with the proximal vein mineralization are interpreted to mark the transition from lithostatic to hydrostatic pressure. The vein- and stockwork-style mineralization (main stage) displays lateral zonation, with quartz-cassiterite-wolframite-molybdenite mineral assemblages grading outward into base-metal sulfide-dominated assemblages with increasing distance from the intrusion. Late fluorite-bearing veinlets represent the waning stage in the evolution of the mineral system. The similarity in the homogenization temperature (250°–418°C) of fluid inclusions in quartz, cassiterite, and sphalerite across the Sadisdorf deposit suggests that cooling was not a significant factor in the mineral zonation. Instead, fluid-rock interaction along the fluid path is considered to have controlled this zonation. In contrast to quartz-, cassiterite- and sphalerite-hosted fluid inclusions, which have a salinity of 0.0 to 10.0 wt % NaCl equiv, the fluid inclusions in late fluorite veins that overprint all previous assemblages have a salinity of 0.0 to 3.0 wt % NaCl equiv and homogenize at temperatures of 120° to 270°C, thus indicating cooling with or without admixture of meteoric fluids during the waning stage of the mineral system. The Sadisdorf deposit shares similar characteristics with other deposits in the Erzgebirge region, including a shallow level of emplacement, similar mineralization/alteration styles, and a hydrothermal evolution that includes early-boiling, fluid-rock interaction, and late cooling. In contrast to most systems in the region, both proximal and distal mineralization are well preserved at Sadisdorf. The recognition of such spatial zoning may be a useful criterion for targeting greisen-related Li and Sn resources.

Magmatic and hydrothermal evolution of the superlarge Dashui goldfield in the West Qinling Orogen, China

Gold (Au) is a precious metal that has played an important role in the development of the global economy. It is therefore important to better define the genesis of Au mineralisation as an aid to focus exploration as the consumption of Au increases. The Dashui goldfield contains a super large Au resource of over 120 t (tonnes) in the West Qinling Orogen, central China. Despite several studies have focused on the genesis of the Dashui goldfield, the original physico–chemical natures of magmatic and hydrothermal evolution remain unclear. Biotite and apatite in the mineralised diorite porphyry of the goldfield are sensitive to the changes in the physico–chemical conditions and the evolution of magmatic and hydrothermal fluids, and thus provide important keys to address these issues. Hence, we conducted detailed in–situ major and trace element studies of biotite and apatite from the ore–bearing diorite porphyry in the Dashui goldfield. Our aim is to elucidate the physico–chemical conditions, magma source, and magmatic and hydrothermal evolution processes during the deposition of the gold, and to enhance the understanding of the Au genesis in the West Qinling Au province. Using the geochemistry of magmatic apatite, and magmatic and hydrothermal biotite, we have found that the crystallisation temperature and pressure along with emplacement depth of diorite porphyry were constrained at ∼ 737–791 °C, 1.08–1.73 kbar, and 3.94–6.30 km. The diorite porphyry has the geochemical affinities with calcium alkaline orogenic suites derived from a mixed crustal and mantle source. During the early emplacement of diorite porphyry, the melt had a high oxygen fugacity and was highly enriched in Au. During the late magma crystallisation of diorite porphyry, the magma was enriched continuously in most elements with the Ba/Rb ratios in the biotite varying from 10 to 5, and most of the Au was hosted by pyrite. Additionally, elements were continuously dissolved into fluids generating Cl–rich hydrothermal fluids during the evolution of the magma. During hydrothermal evolution, Au is migrated with As and Sb in the vapour phases of fluids, whereas Au migrated with Cl in the liquid phase. When temperatures dropped to ∼ 200–400 °C, Au started to combine with S and Si in the liquid phase of fluids. Subsequently, hydrothermal fluids interacted with host carbonate to form the Dashui goldfield, Au during this stage was also transported and hosted in magnetite, hematite, and quartz within the carbonate rocks.

Evolution of impact-generated hydrothermal systems in basaltic targets on Earth and implications for habitats on Mars

Impact-generated hydrothermal systems are a potential habitat for life on Earth and other planetary bodies. The ubiquity of impact craters on Mars makes them of particular interest for the search for life on this planet although their viability as a habitat is not well understood. To better understand such systems, two analogue impact structures on Earth were investigated, as their dominantly basaltic target rock makes them similar to impact structures in the Martian crust: the Vista Alegre and Vargeão Dome impact structures in Brazil.The goals of this paper are to 1) better understand the Vista Alegre and Vargeão Dome impact structures, and 2) understand how impact-generated hydrothermal systems on Earth can be compared with similar systems on Mars. To enable comparison, the software HYDROTHERM is used to reconstruct the hydrothermal evolution of both impact systems on Earth. Permeability, porosity, thermal conductivity, and initial temperature distributions are varied to simulate slow--, medium-, and fast-cooling models. The medium cooling rate models are then adapted to Martian conditions and scaled to 1×, 2×, 4×, and 8× the size on Earth, also adapting the impact energy and initial heat distribution, to check the comparability using similar target rocks. Finally, target rocks are changed to a basaltic composition only, to check how a lower-permeability Martian surface composition would affect the hydrothermal system.The models indicate between 150 and 650 thousand years (ka) of hydrothermal activity for both the Vista Alegre and Vargeão Dome impact structures. Due to the limited availability of water in the initial, high-temperature situation in the crater centre, water flux first increases and then decreases, although after 650 kyr the water flux towards the crater centre remains active in Vargeão Dome only. This sustained water flux is likely related to the low relative pressure in the crater centre due to the lack of overlying rock in comparison to outside the crater, as well as the direct connection of an underlying sandstone aquifer with high-permeability, fractured basalt in the centre of the structure.The Martian models with the same lithologies as on Earth show overall lower water flux and contain permafrost, which prevents the water flux within the aquifer from outside the crater towards the crater centre as seen in Vargeão Dome. The cooling times increase with scaling from 1× to 8× the size to ∼0.2 and 5 Myr, respectively. With only basalts in the target, cooling times reach ∼0.2 to 9 Myr. However, in that case, the water flow only remains active for up to the first Myr, and a minimum crater diameter of approximately 40 km is needed to achieve surface water fluxes close to those in Vargeão Dome and Vista Alegre.Below the Martian surface, hydrothermal system activity can persist for millions of years, providing potential for supporting life. Unfortunately, these parts of the system are currently unreachable for both sampling and spectroscopic techniques, and the short lifetime and low water fluxes at the surface related to the permafrost layers do not favour impact-generated hydrothermal systems on present-day Mars as targets for the search for life. However, these systems are highly dependent on the rock types and related permeabilities and could have provided habitats before 3.5 Ga, when the planet was warmer and liquid water was present at the surface.

Oligocene to Miocene magmatic and hydrothermal evolution in the Maricunga belt (Región de Copiapó, Chile): A new look to a long known metallogenic belt

The Maricunga metallogenic belt, herein defined to encompass the region from 25° S to 28° S along the Cordillera Frontal of northern Chile, is known for hosting a series of gold-copper and lesser copper-molybdenum porphyries and gold-silver epithermal systems that are hosted in a segment of the late Oligocene-Miocene Andean calc-alkaline magmatic arc. Based on an up-to-date geochronological database, four episodes of magmatism and related hydrothermal deposits are proposed to characterize intensity and style of volcanism and hypabyssal intrusive rocks over time. The late Oligocene episode (26-21 Ma) is characterized by stratovolcanoes, dome complexes, pyroclastic sequences, and hypabyssal intrusives of andesitic to dacitic composition that host gold-rich porphyry systems such as Caspiche, Maricunga, and La Pepa. The early Miocene episode (21–17 Ma) has similar rock types but is volumetrically reduced, hosting epithermal and porphyry deposits like La Coipa and Caserones, respectively. A reinvigoration of volcanism occurred during the third stage between 17 and 11 Ma, giving rise to large volcanic complexes and intra-to extra-caldera ignimbritic deposits that host several gold-rich porphyry deposits such as Lobo-Marte, Luciano, and Cerro Casale; as well as epithermal deposits such as Fenix. Some of the 17 to 11 Ma and younger igneous rock belong to the high-K calc-alkaline series, showing a higher alkali content compared to previous periods. The last magmatic episode, from 11 to 5 Ma, coincides with the shallowing of the subduction angle and is characterized by an eastward migration of volcanism, and more heterogeneous rocks including trachytic compositions. During this period mineralization was emplaced at the Salares Norte epithermal deposit and El Volcan porphyry Au–Cu deposit.Porphyry and epithermal systems formed throughout the evolution of the Maricunga belt. Overprint of advanced argillic alteration on porphyry style alteration is widespread albeit commonly devoid of significant addition of epithermal Au–Ag mineralization. The Au-rich nature of the majority of the porphyry systems is attributed to the shallow crustal depths of emplacement compared to Cu- and Mo-rich porphyry systems. Conversely, high-sulfidation epithermal Au–Ag deposits such as La Coipa and Nueva Esperanza are not known to be telescoped on coeval porphyry gold deposits.The location of the mineralized centers was favored by crustal weaknesses expressed by intersection of oblique- and parallel-to arc structures, the former inherited from the construction of the continent before to the formation of the Andean range. The arc oblique structures also segment the Maricunga belt into domains with unique magmatic and hydrothermal styles.

Mineralization process of the Changjiang uranium orefield in South China: Constraints from pitchblende geochemistry

The Changjiang uranium (U) orefield in northern Guangdong (South China) contains several important granite-related uranium deposits, including the Mianhuakeng deposit. The hydrothermal evolution and mineralization mechanism of the deposit remain unclear, and hence in this study we analyzed the mineral compositional variations of pitchblende from different elevation (−300 to −50 m) in the orebody at Mianhuakeng deposit. The results indicate that with decreasing depth, the hydrothermal mineral assemblage changes from a reducing one (pitchblende, pyrite, and chlorite) to a moderately oxidizing one (pitchblende, coffinite, hematite, and goethite). The contents of U, Sr, ∑REE, U/Th, and LREE/HREE ratios in the pitchblende decrease (whereas the Cu-Pb-Zn-Ni-Co-Sc-Rb contents increase) progressively with decreasing depth. Also, Ce anomaly (Ce/Ce*) changes from positive to negative, and Eu anomaly (Eu/Eu*) becomes more negative with decreasing depth. We interpreted such vertical variations to be caused by the ascent of deep, mid-to-high temperature, highly-oxidizing ore-forming fluid, which was reduced by early-stage reducing minerals in the wallrock, a process that also formed the mineralization at Changjiang. In addition, the pitchblende REE distribution patterns and Eu/Eu* at depth (−300 m) resemble those of the Zhuguang pluton, indicating that the ore-forming materials were originated from the U-bearing granite wallrocks. Therefore, the Ce/Ce* and Eu/Eu* variations of pitchblende can be used to guide deep uranium ore exploration.

Unveiling the connection between lode gold mineralization and the metamorphic core complex evolution from the large Yangzhaiyu gold deposit, North China Craton

The Xiaoqinling gold province, located in the Neoarchean−Paleoproterozoic uplifted footwalls of the Xiaoqinling metamorphic core complex (XMCC), is one of China’s largest gold producers; however, achieving a consensus regarding their metallogenic model remains elusive. Scheelite is an indicator mineral that commonly occurs in lode gold deposits worldwide used to recognize deposit types and understand hydrothermal evolution and the origin of features. Xenotime, monazite, and rutile are common hydrothermal minerals in association with lode gold deposits worldwide. Here, we provide textual, in situ U-Pb geochronology of xenotime, monazite, and rutile, and in situ elemental and Sr-Nd isotopic compositions of scheelite within different stages from the large Yangzhaiyu lode gold deposit, aiming to elucidate its genesis and, for the first time, establish a holistic correlation between the lode gold mineralization and the evolution of the XMCC. Notably low εNd(t) values (−30.7 to −23.7), high 87Sr/86Sr ratios (0.72659−0.75914), and distinct rare earth elements, Sr, Mo, and As contents of scheelite confirm a metamorphic crustal source. Xenotime U-Pb dating and pre-ore (Stage I) scheelite reveal that ore-barren metamorphic fluids at ca. 140 Ma were oxidized with low Bi contents and buffered by greenschist facies metamorphism when the XMCC initiated. Monazite and rutile U-Pb dating combined with ore-stage scheelite geochemistry indicate a compositional shift in the more reduced auriferous metamorphic fluids, which dominated during major gold deposition periods (stages II and III) from 130 Ma to 120 Ma, characterized by significantly depleted Na and increased Bi contents. This resulted from the prograde greenschist-to-amphibolite metamorphism at mid-lower crustal depths as the result of the XMCC isostatic doming and the lithospheric mantle thinning after 130 Ma. This study highlights the crucial role of metamorphic core complexes in governing the timing, locations, and resources of the lode gold metallogenic system.

Reactive transport numerical modeling of intermediate sulfidation epithermal deposit: A case study of Haopinggou Ag-Au-Pb-Zn deposit, Henan province, China

The Haopinggou Ag-Au-Pb-Zn deposit is the only deposit that simultaneously contains Au and Ag-Pb-Zn vein-type ores at the Xianyu ore field in Xiong'ershan District, Henan Province, China. The early-stage gold-bearing pyrite-quartz veins are cut or surrounded by late-stage silver-bearing Pb-Zn-sulfide veins. However, there is controversy whether these two-stage veins were formed from distinct fluid systems associated with discrete mineralization events or via hydrothermal evolution processes of individual mineralization events. To study the metallogenic dynamics of how the Au and Ag-Zn-Pb veins were formed at the same depth in the Haopinggou deposit under these two distinct metallogenic models, we established a series of reactive transport numerical models. We studied the influence of the temperature of the hydrothermal fluid, fault permeability, and HS−, Au+, and Ag+ concentrations on the mineralization of Au, Ag, Pb, and Zn. Based on the model results, two distinct mechanisms causing Au and Ag to precipitate at the same depth has been established: (1) Under the assumption of the single hydrothermal fluid metallogenic model, the deep part of the early Au precipitation will be overlapped by the shallow part of the late Ag precipitation due to temperature and permeability decreases, causing Au and Ag to precipitate at the same deep depth; (2) Under the assumption of the distinct hydrothermal fluids metallogenic model, the shallow part of the early Au precipitation will be overlapped by the late Ag precipitation due to high concentration of HS−, causing Au and Ag to precipitate at the same shallow depth. The metallogenic mechanisms behind these two controversial understandings indicate that the deeper parts of the Haopinggou deposit have a high metallogenic potential for gold or silver.

Magmatic–Hydrothermal Evolution at the Barren Wushan Pluton, Southeast China: Insight into Controls on Mineralization Potential

Abstract A-type granites typically exhibit enrichment and mineralization of critical metals such as molybdenum and tin, essential for emerging technologies. However, the key factors influencing their mineralization potential remain elusive. The scarcity of studies on barren systems impedes the understanding of this question. Here, a detailed melt and fluid inclusion study was conducted on the barren Wushan pluton to reconstruct its magmatic evolution and magmatic–hydrothermal transition and explore the factors controlling the metallogenic potential of Mo and Sn in A-type granites. The Wushan pluton displays apparent lithological zoning consisting of two major phases, i.e., medium-grained seriate to porphyritic alkali feldspar granite and fine-grained porphyritic granite. Miarolitic cavities are widely developed in each lithofacies. The silicate melt inclusions from two granitic phases are rhyolitic, with moderate F contents (0.06–0.53 wt %) and depleted H2O contents (2.0–3.5 wt %). Melt inclusions show a wide range of incompatible element contents, such as Cs (9–1977 μg/g) and Rb (268–2601 μg/g), suggesting that Wushan has undergone a high degree of magma evolution. Mo behaves incompatibly in the magmatic evolution, and its content is enriched with the increasing degree of fractional crystallization, but remains constant after the Cs content exceeds 50 μg/g. Rayleigh fractionation model suggests that a large amount of Mo is extracted from fluid exsolution, which restrains Mo from further enrichment. In contrast, Sn behaves as a mildly incompatible element during the entire magmatic evolution history. The contents of Sn increase slowly compared to the trend of Mo, and the maximum contents reach ~30 μg/g in the highly evolved melts. The separation and crystallization of Sn-bearing minerals such as biotite, magnetite, and titanite inhibit the enrichment of Sn. Intermediate-density (ID-type) fluid inclusions hosted in the miarolitic quartz, representing the initial fluid exsolving from magma, display high Mo but low Sn concentrations. Constrained from two assemblages of coexisting ID-type fluid and melt inclusions, the fluid/melt partition coefficients of metals are obtained, with DMo, fluid/melt at 16–19, while DSn, fluid/melt is only about 1. The comparison between Mo-mineralized and barren intrusions worldwide shows that the metal contents in melts and fluids are not fundamentally different. The mineralized intrusions are characterized by the lower melt viscosity and the development of apophyses, both of which facilitate the extraction of metals and fluids from large magma chambers, followed by their concentration into a small rock volume. Consequently, it appears that physical and structural conditions rather than chemical compositions play a crucial role in the Mo mineralization process. Enrichment of Sn in melts is necessary but not decisive for Sn mineralization, whereas Sn enrichment in the initial exsolving fluid determines the Sn mineralization potential of a given granitic system. Compared to Sn enrichment in source melting and fractional crystallization which commonly enhance final Sn fertility in the highly evolved melts, the efficiency of Sn partitioning between melt and fluid plays a fundamental role in converting melt fertility into Sn-enriched fluids and thereby high mineralization potential of the magmatic–hydrothermal system. Our findings suggest a prospect for Mo exploration in the coastal A-type granite belt in South China, while the potential for Sn mineralization is expected to be limited.

Study of hydrothermal characteristics of large‐scale water conveyance trunk canals in seasonally frozen ground regions under the influence of different initial water contents

AbstractIn seasonal frozen soil, freezing and thawing can change the physical and mechanical properties and affect slope stability. There are complex moisture conditions in the main water transfer canal. A study of the hydrothermal evolution of canals with different initial water contents under the action of freezing and thawing is of great importance for the prevention and control of canal slope slides. Hydrothermal coupling models are the key to revealing the canal's hydrothermal evolution. As some of the modeling parameters in the current hydrothermal coupling model are based on empirical values, particularly those in the van Genuchten equation, which are not necessarily related to soil properties, they are not suitable for analyzing the hydrothermal evolution of canals. This paper determines the soil‐water characteristic curve from the cumulative curve of particle gradation in the subsoil, and then determines the hydraulic parameters of the subsoil using the VG model, which then corrects the hydrothermal coupling model. The method of modifying the hydrothermal coupling model is original, which makes the model more realistically reflect drainage soil characteristics. During freezing and thawing of channel slopes with different initial water contents (21%, 25%, 29%, 33%, 37%, and 41%), temperature field, water field, and ice content distributions were investigated. Using the V‐G model, the optimal parameters for canal subsoil were a = 0.06, n = 1.2, and m = 0.17, and temperature distribution trends between canals with different water contents were basically similar. Water will accumulate at the bottom as the liquid water content increases at the canal boundary.

In-Situ Geochemical and Rb–Sr Dating Analysis of Sulfides from a Gold Deposit Offshore of Northern Sanshandao, Jiaodong Peninsula, North China: Implications for Gold Mineralization

The gold deposit offshore of Northern Sanshandao is an ultra-large-scale gold deposit discovered in the Jiaodong ore area in recent years. This deposit is a fractured-zone altered-rock-type gold deposit; however, its ore genesis and precise mineralization processes are still highly controversial. Based on petrographical observation, the trace elements, sulfur isotopes, and rubidium–strontium isotopes of the gold-bearing pyrite were analyzed using LA-MC-ICP-MS to obtain the source of the ore-forming fluids and ore genesis. The results show that Au has a good positive correlation with Ag, As, and Cu. It is speculated that the As in the pyrite of the gold deposit offshore of Northern Sanshandao is in the form of As−, replacing S− and entering the pyrite, causing its lattice defects, and thus promoting the entry of Au+ into the gold-bearing pyrite. The Co/Ni ratios mainly range between 0.1 and 10, indicating that the mineralization process has experienced different forms of hydrothermal evolution and the mixing of different fluids. The results of the in-situ sulfur isotope analysis show that pyrite δ34S in the mineralization period is characterized by a high sulfur value. The authors of this study believe that the initial sulfur isotope composition has mantle-derived components. The large-scale, deep cutting, and high degree of fragmentation in the Sanshandao fault zone are conducive to the interaction between fluids and rocks, as well as the mixing and addition of seawater, resulting in the characteristic high δ34S value. The Sr isotopic compositions indicate a crust–mantle mixing attribute of the mineralized material source. The Rb–Sr isochron age of the pyrite is 118.5 ± 0.65 Ma, which represents the age of gold mineralization. According to the characteristics of the trace elements and sulfur isotopes, it is inferred that the gold deposit minerals offshore of Northern Sanshandao originated from deep magmatic-hydrothermal reservoirs, and the mixing of seawater and Au–As-rich hydrothermal fluids was the formation mechanism of huge amounts of gold precipitation.

Geology and ore fluids geochemistry of the Hamzeh–Gharanin orogenic gold deposit, NW Iran

The Hamzeh–Gharanin gold deposit (HGD) is located in the Qolqoleh–Kasnazan shear zone in the northwest of Sanandaj–Sirjan Zone (SSZ) and 40 km SW of Saqez. The main rock units are an assemblage of the Precambrian metasedimentary (pelitic) rocks and the Cretaceous phyllite associated with marble interlayers. The post–Cretaceous intrusive granitoids with NW–SE trends intruded within these two units. Mineralization occurs mainly within the NE–SW extensional veines and veinlets in proto–mylonitic, mylonitic and ultra–mylonitic rocks. Hydrothermal alterations consist of sericitization, carbonatization, silicification and chloritization. The main ore minerals include pyrite, chalcopyrite, arsenopyrite, pyrrhotite, sphalerite, galena, gold, magnetite and hematite. The fluid inclusions study from quartz minerals associated with the mineralization shows four different phases: single vapor phase (V; type I), single liquid phase (L; type II), liquid–vapor biphasic (LV; type III) and three phases (LLV; type IV). Microthermometric studies were performed on types III and IV of fluid inclusions. Homogenization temperatures (Th) for Types III and IV inclusions vary between 138 and 310 °C (mean 230 °C) and 250–335 °C (mean 300 °C) and their salinity varies between 0.52 and 13.87 and 4.79 to 9.58 (wt% NaCl), respectively. Moreover, the density of Types III and IV inclusions vary from 0.71 to 0.927 g/cm3 and 0.700–0.870 g/cm3, respectively. The oxygen (in quartz: 4.58–7.80 ‰; mean 5.82 ‰) and δ34S (in pyrite: 5.54–6.28 ‰; mean 5.91‰) isotope compositions of the mineralizing fluids indicate an insignificant meteoric water input during hydrothermal evolution and a magmatic origin of sulfur in the deposit which is broadly similar to those of orogenic gold deposits worldwide.

Fe–Cu mineralization of Tangal-e-Sefid; a magnetite rich massive sulfide deposit from Kuh-e-Sarhangi district, Central Iran

The Tangal-e-Sefid Fe–Cu mineralization forms syngenetic stratiform deposit in the Late Neoproterozoic volcano sedimentary sequence from the Central Iran. Early Cambrian metamorphic rocks are associated ore-bearing geologic units. The mineralization includes early oxide phase as a magnetite-rich bodies that are overprinted by a pyrite-chalcopyrite-rich sulfide phase. The most current alteration zone includes propylitic-carbonate, chlorite, sericite and silicic with a well-developed distribution of chloritization, especially in the layered part. Magnetite, pyrite and chalcopyrite comprise the primary main mineral assemblage, which is accompanied by malachite, covellite, hematite and goethite as the secondary minerals associated with epidote, chlorite, quartz and calcite minerals. Magnetite chemistry reveals the hydrothermal evolution of mineralization, and all the examined magnetite fall within fields of magnetite from VMS deposits. Fluid inclusion analysis of quartz and calcite coexisting with magnetite represent homogenization temperature range of 198 °C and 357 °C with a cooling trend from the massive toward the layered parts. The measured fluid salinity identifies two distinct medium-salinity fluids with mean values corresponding to 15 and 22 wt% NaCl. There is no significant difference in terms of temperature and salinity measured in calcite and quartz minerals. However, the average measured temperature values of fluids trapped in calcite (189–336 °C) are slightly lower than quartz (227–357 °C). Since the ore deposit distribution is spatially associated with actinolite schist, thermometric data of actinolite show temperature fluctuations of 310–315 °C and mineral formation pressures of 2.5–3 Kbar, which are correlated with the low-grade metamorphism.Primary hydrothermal fluids derived from submarine magmatism in an extensional system of seafloor were enriched in Fe and Cu (± Zn and possibly Pb) and it is the responsible for the first stage of magnetite formation and following the overprinting pyrite and chalcopyrite mineralization. The ore deposit geometries associated with magnetite mineralization and sulfide replacement styles; reveals that in the second stage of mineralization, hydrothermal fluid is mixed with oceanic water and eventually metal sulfides are deposited. The mineralizaton zone associated with the volcano-sedimentary sequence is affected by low-grade regional metamorphism related to Pan-African orogeny and represent the green schist territory as the VMS deposits related to Archean.

Geochronology and geochemistry of zircon and columbite–tantalite group minerals from the Weilasituo Sn–polymetallic deposit, northeastern China: Implications for the relationship between mineralization and the magmatic–hydrothermal transition

The Weilasituo Sn–polymetallic deposit, located in the southern portion of the Great Xing'an Range of Inner Mongolia, China, is a super-large Sn deposit associated with abundant Li, Rb, Nb, Ta, Zn, and Cu resources. Despite that previous studies have characterized the age, hydrothermal evolution, and genetic relationship between the alkali feldspar granite porphyry and associated Sn–polymetallic mineralization, the magmatic–hydrothermal evolution and ore–forming processes remain ambiguous. To address these ambiguities and bridge this knowledge gap, this contribution characterizes the texture, geochemistry, and U–Pb isotope composition of zircon and columbite–tantalite group minerals (CGMs) from amazonitized alkali feldspar granite (AMG) and albitized alkali feldspar granite (ABG) in the Weilasituo deposit. Type-I zircon (Zr1) is inclusion-poor, translucent, and is characterized by low light rare earth element (LREE) contents, high (Sm/La)N ratios (mean = 655.7), and low Th/U (mean = 0.21 < 0.3), Zr/Hf (mean = 5.46), and Y/Ho ratios (mean = 4.42), indicating that it formed during the magmatic–hydrothermal transition. Type-II zircon (Zr2) is inclusion-rich, porous, has a low CL response, and is characterized by low Th/U ratios (0.08–0.32, mean = 0.17), high LREE contents, weakly positive Ce anomalies, and low (Sm/La)N ratios (mean = 20.7), indicating that it formed via hydrothermal alteration of Zr1 (i.e., magmatic–hydrothermal zircon). Type-I CGM (CGM1) generally lacks oscillatory zoning, and has similar and positively correlated Ta/(Nb + Ta) and Mn/(Mn + Fe) values (AMG: R2 = 0.93; ABG: R2 = 0.75), indicative of a magmatic origin. Type-II CGMs (CGM2) occur as rims on CGM1 and are characterized by higher Ta/(Nb + Ta) and lower Nb/Ta ratios than CGM1, indicative of precipitation from a hydrosilicate liquid during the magmatic–hydrothermal transition. Based on the characteristics of CGMs, two stages are evident in the evolution of the Weilasituo granite porphyry: an earlier magmatic differentiation stage and a later magmatic–hydrothermal transition stage. Furthermore, the magmatic–hydrothermal transition stage can be subdivided into the AMG and ABG substages within the porphyry system based on petrological and mineralogical characteristics. The U–Pb ages for zircons and CGMs from the alkali feldspar granite porphyry range from 137.2 ± 2.0 Ma to 129.8 ± 1.4 Ma, without a notable age gap. The similarity in U–Pb ages between CGM1–CGM2 and Zr1–Zr2 indicates that the magmatic stage and the magmatic–hydrothermal transition at Weilasituo were continuous processes that occurred during the Early Cretaceous.

Mineralogy and a New Fertility Index of Alunite in the Fanshan Lithocap, Luzong Basin, Anhui Province, China

Alunite is used as a representative mineral for indicating deposits in lithocaps, and lithocaps are generally related to the porphyry–(high-sulfidation) epithermal mineralization system. The study of alunite is of theoretical and exploration significance for prospecting potential underlying porphyry and epithermal deposits. Studies on alunite geochemistry have made breakthroughs, but there is little research on alunite mineralogy, for example, using scanning electron microscopy (SEM) images, differential thermal analysis (DTA), and Fourier-transform infrared spectroscopy (FT-IR). This study mainly focuses on alunite micromorphological characteristics, weight loss changes with temperature, and ionic group structure, aiming to identify the relationship between these features and indications for prospecting. The Fanshan lithocap is located in the northwest part of the Luzong basin, Anhui province of China, and it can potentially be used for exploring porphyry and epithermal deposits. Fanshan alunite is formed in two stages with three types of alunite. IA alunite is formed in the early hydrothermal stage and replaces felsic minerals in the Zhuanqiao Formation, IB alunite is formed in the later hydrothermal stage and fills in open spaces with bladed particles, and II alunite is the product of pyrite oxidation and reaction with other minerals in the supergene stage. Alunite electron microprobe data and energy-dispersive spectroscopy data further confirm temperature decreases with hydrothermal evolution, and the presence of a high-sulfidation epithermal system in the Luzong basin. Aside from the forming environment, SWIR, and geochemistry of alunite, there are other indication indexes; for example, the larger peak values at 3480 cm−1 and smaller peak values at 1080 cm−1 in FT-IR spectra and the deeper exothermic valleys at 750 °C and steeper weight loss slopes in the DTA curve suggest a favorable formation environment for alunite and provide valuable indications for deposit exploration and assessments of mineralization potential.