Hydrothermal Mineralization Research Articles

Assessment of potential cobalt zones by modeling radiometric and ASTER data using the AHP method: A case of the Bou Azzer El Grara inlier, Central Anti-Atlas, Morocco

The Bou Azzer El Grara inlier belongs to the Central Anti-Atlas range, renowned for its mineral deposits. The study carried out on the inlier aims to identify potential areas of cobalt mineralization based on a multi-source methodology of radiometric and remote sensing data processing. The data used includes hydrothermal alteration minerals (argillic, phyllic, propylitic, iron oxides) mapped with Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery using band ratio and principal component analysis (PCA) techniques, potassium enrichment zones through K/eTh and K/eU ratios calculated from radiometric data, as well as geological data (serpentinite outcrops and geological faults). The analytic hierarchy process (AHP) was used to combine the various thematic layers. Validation was carried out through the field studies in several anomalous zones. The mineral prospectivity map generated highlights nine major zones that appear the most favorable for mineralization, some of which coincide with zones in production and others requiring further exploration.

San Albino, Nicaragua: A Low-Angle, Thrust-Controlled Orogenic Gold Deposit

Abstract The San Albino deposit is an orogenic gold occurrence hosted by a low-angle thrust that is the site of a new open-pit mine in northern Nicaragua. The deposit is hosted in greenschist facies rocks of the Jurassic metasedimentary Neuvo Segovia Formation. The schist was uplifted and exposed during arc accretion and Cretaceous thin-skin deformation, forming the NE-striking Colon fold-and-thrust belt. Deformation included emplacement of the 119 to 113 Ma NE-trending Dipilto batholith into the regionally metamorphosed clastic rocks about 5 km northwest of the San Albino deposit. Mineralization is dominated by three laminated quartz vein systems (i.e., San Albino, Naranjo, Arras) that broadly follow shallowly dipping (approx. 30°) carbonaceous shears roughly concordant to schistosity along the limbs of a doubly plunging antiform. The three main parallel shears are each separated by about 90 m and individually reach a maximum thickness of about 8 m. Maximum thickness of ore zones is where post-ore local folding and reverse motion along the shallow shears has duplicated the laminated low-angle gold-bearing veins (D2 and early D3). Additional gold was added to the veins, with abundant sulfides, during a subsequent brecciation event of the early formed quartz veins that accompanied progressive thrusting (late D3). This predated boudinage of the veins during continued compression and thrust loading (D4); high gold grades are particularly notable along pyrite- and arsenopyrite-bearing stylolites formed during D4 pressure solution. The D2 to D3 gold event is likely coeval with Albian uplift of the Dipilto batholith and with back thrusting in the schist aided by the stress inhomogeneities provided by the igneous complex. Low-angle thrust-controlled orogenic gold deposits may represent world-class exploration targets because of their large linear footprints, although they are traditionally looked at as less favorable exploration targets relative to gold systems developed more commonly along high-angle reverse faults. Our case study of the San Albino deposit shows that although low-angle deposits are not inherently misoriented for failure like the more common subvertical reverse fault-related deposits, they may be sites of significant pressure buildup due to hydrothermal mineral precipitation during initial water-rock interaction or slight temperature decreases along the low-angle flow path. Resulting fluid cycling may lead to thick laminated vein development, such as seen at San Albino, where especially high-grade zones may be associated with local steepening and/or dilational zones within the broader, low-angle vein-hosting shear system.

Mineralization processes of the Mount Garnet Zinc deposit, NE Queensland (Australia): Insights from garnet geochemistry and U-Pb geochronology

The Mount Garnet Zinc deposit in NE Queensland, Australia, is located in the region of voluminous magmatism associated with the formation of Palaeozoic continental arcs of Gondwana. Ore-forming events of this deposit are related to the intrusion of the Kennedy Igneous Association (KIA) – a large suite of igneous rocks spanning Late Carboniferous to Early Permian in age – into the Silurian limestone (Chillagoe Formation) in the Hodgkinson Province (Mossman Orogen). Petrographic observations and in situ major and trace element analysis reveal the sequence of garnet growth and fluid-rock interaction during skarn formation. Three types of garnets are identified, Grt I (including IA and IB) and Grt II. Grt IB is related to Zn-Pb mineralization. All garnets have elevated Sn and W and the highest levels of W and Sn are observed in Grt II. Garnet U-Pb ages of Grt IB provide the first direct geochronological result of hydrothermal minerals in the Mount Garnet region. New data argues that the base metal mineralization may take place during early Permian period and be sourced from the Claret Creek Supersuite. Sn-W mineralization may be associated with the O’Briens Creek Supersuite.

Giant Rare Earth Element Accumulation Related to Voluminous, Highly Evolved Carbonatite: A Microanalytical Study of Carbonate Minerals From the Bayan Obo Deposit, China

Abstract The giant Bayan Obo deposit in China represents the largest rare earth element (REE) resource in the world, but the mechanisms for its highly anomalous REE enrichment have long been controversial. The central debate concerns the nature and origin of the ore-hosting dolomite. In this study, a texturally constrained microanalytical study of carbonate minerals from the Bayan Obo ore-hosting dolomite is presented to resolve this controversy. The dolomite rocks contain two major components: the early-stage coarse-grained dolomite (CD) and the late-stage fine-grained dolomite (FD). The CD dolomite grains have C-O isotope ratios (δ13CVienna-PeeDee Belemnite (V-PDB): –4.8 to –3.3‰; δ18OVienna-standard mean ocean water (V-SMOW): 7.1 to 11.9‰) plotting in or adjacent to the primary igneous carbonatite field, with a narrow range of low 87Sr/86Sr ratios (0.70262–0.70327). The mantle-like C-O and Sr isotopes indicate that the coarse-grained dolomite rocks are magmatic in origin. Dolomite grains from the FD have experienced extensive hydrothermal alteration related to both REE mineralization and post-ore metamorphism of the Bayan Obo deposit. The domains of primary unaltered dolomite have high SrO and MnO contents that clearly distinguish them from sedimentary carbonates. The 87Sr/86Sr ratios of unaltered dolomite domains range from 0.70271 to 0.70473, with the majority lower than 0.7035, contrasting with higher 87Sr/86Sr ratios of Mesoproterozoic sedimentary carbonates globally. Thus, the primary unaltered fine-grained dolomite, the precursor to the FD, is also proposed to be a carbonatite. Compared with dolomite grains from the CD, most of the unaltered dolomite domains within the FD are more enriched in FeO and MnO and have higher δ13CV-PDB (-4.9 to 0.3 ‰) and δ18OV-SMOW (9.4 to 17.1 ‰) values. In addition, the FD contains abundant REE- and volatile-rich hydrothermal minerals and Fe-Mg carbonates, which are rare in the CD. The geochemical and mineralogical data in conjunction indicate that the melts forming the late-stage FD were much more evolved than those forming the early-stage CD. It is noteworthy that the unaltered dolomite domains within the FD have a wider range of 87Sr/86Sr ratios than those within the CD, which implies that the CD and FD, at least a proportion of them, are unlikely to have crystallized from the same progenitor magmas. Some FD was possibly the product of fractionation of less-evolved carbonatitic magma that generated the CD, whereas other FD crystallized from new pulses of magmas that were highly fractionated at depth. When compared with other carbonatite complexes, the Bayan Obo carbonatite suite is notable for having a large surface area (~48 km2 in outcrop) and containing an anomalously large proportion of highly evolved components. The voluminous evolved carbonatite clearly provided a basis for the accumulation of significant ore metals. Therefore, the giant-sized REE deposit is proposed to be associated with large-volume, highly evolved carbonatite at Bayan Obo.

Hydrothermal Plume Fallout, Mass Wasting, and Volcanic Eruptions Contribute to Sediments at Loki's Castle Vent Field, Mohns Ridge

AbstractSediments surrounding hydrothermal vents are important transition spaces between hydrothermal and pelagic environments. These sediments accumulate through diverse processes that include water column plume fallout, volcanic ash deposition, and mass wasting of hydrothermal chimneys and mounds superimposed upon background sedimentation which may originate from pelagic, terrestrial, and volcanic sources. In addition to being a sink for elements discharged from hydrothermal vents, elements may also be scavenged from seawater onto oxidized hydrothermal material. Preservation of these hydrothermal sediments may occur depending on the extent of oxidative and/or reductive dissolution processes after burial. Sediments remaining adjacent to active venting may also be hydrothermally altered after emplacement. To better understand these processes, here we evaluate sediment push cores collected from the Loki's Castle vent field at the intersection of the slow‐ultraslow spreading Mohns and Knipovich mid‐ocean ridges. All samples were collected within ∼225 m of current high‐temperature (299–316°C) “black smoker” fluid discharge. These sediment cores are highly heterogeneous and lack stratigraphic correlation, even for samples taken within meters of each other. Most sediment cores are dominated by either pelagic sediments or mass wasted hydrothermal material, with hydrothermal plume fallout contributing a low proportion of material, and only a single volcanic ash layer occurring in one of the 13 cores. Dominant hydrothermal minerals found include talc, goethite, pyrite, pyrrhotite, and sphalerite. We find that even after several thousand years, most mass wasted hydrothermal material remains minimally altered, with sedimentation rates indistinguishable from background rates within several hundred meters of the hydrothermal vent source.

Episodic hydrothermal alteration on Middle Permian carbonate reservoirs and its geological significance in southwestern Sichuan Basin, SW China

To analyze the episodic alteration of Middle Permian carbonate reservoirs by complex hydrothermal fluid in southwestern Sichuan Basin, petrology, geochemistry, fluid inclusion and U-Pb dating researches are conducted. The fractures and vugs of Middle Permian Qixia–Maokou formations are filled with multi-stage medium−coarse saddle dolomites and associated hydrothermal minerals, which indicates that the early limestone/dolomite episodic alteration was caused by the large-scale, high-temperature, deep magnesium-rich brine along flowing channels such as basement faults or associated fractures under the tectonic compression and napping during the Indosinian. The time of magnesium-rich hydrothermal activity was from the Middle Triassic to the Late Triassic. The siliceous and calcite fillings were triggered by hydrothermal alteration in the Middle and Late Yanshanian Movement and Himalayan Movement. Hydrothermal dolomitization is controlled by fault, hydrothermal property, flowing channel and surrounding rock lithology, which occur as equilibrium effect of porosity and permeability. The thick massive grainstone/dolomites were mainly altered by modification such as hydrothermal dolomitization/recrystallization, brecciation and fracture-vugs filling. Early thin–medium packstones were mainly altered by dissolution and infilling of fracturing, bedding dolomitization, dissolution and associated mineral fillings. The dissolved vugs and fractures are the main reservoir space under hydrothermal conditions, and the connection of dissolved vugs and network fractures is favorable for forming high-quality dolomite reservoir. Hydrothermal dolomite reservoirs are developed within a range of 1 km near faults, with a thickness of 30–60 m. Hydrothermal dolomite reservoirs with local connected pore/vugs and fractures have exploration potential.

Deep gold prospectivity modeling in the Jiaojia gold belt, Jiaodong Peninsula, eastern China using machine learning of geometric and geodynamic variables

Gold mineralization in the Jiaojia gold belt was formed in a structurally-dominant hydrothermal mineral system showing a close spatial association with the Jiaojia detachment fault. This study delves into the Jiaojia gold belt from the perspective of coupled spatial association and ore-forming processes by employing spatial analysis of three-dimensional (3D) models, 3D ore-forming numerical modeling, and 3D prospectivity modeling using machine learning techniques (random forest (RF) and multilayer perceptron (MLP)). The overarching goal is to gain insight into the structural-hydrothermal gold system and pinpoint potential areas of deep-seated gold deposits for future exploration endeavors. The spatial analysis of ore-controlling faults uncovers a close correlation between gold enrichment and specific fault geometrical attributes, including a dip angle ranging from 20° to 40°, minimal variations in dip angle (less than 5°), and convex topographical features. These attributes likely stem from the influence of fault morphology on the flow and pooling of fluids. In conjunction with this, 3D ore-forming numerical modeling of structural deformation and fluid flow reveals that gold mineralization is intertwined with moderate volumetric strain and shear strain of rock and fluid divergence. This interaction seems particularly pronounced in areas characterized by channel-like or gentle features. Consequently, it is plausible that gold distribution in the Jiaojia region is the outcome of a comprehensive coupling process involving strain localization, rock deformation, fluid flow, heat transfer and/or interaction. The deep gold prospectivity models of RF and MLP for the Jiaojia district jointly using the predictive variables of fault geometry features and ore-forming simulation data (volume strain, shear strain, temperature variation, and fluid flux) exhibit higher AUC (area under the curve) values compared to models employing individual predictor variable datasets. This improvement underscores their enhanced predictive capability. The prospectivity results thus were used for identifying gold potential within the Jiaojia region, where five promising gold targets at depth were ultimately determined.

Jurassic–cretaceous exhumation history of the Northern Qaidam Basin and its implications for Northeastern Qinghai–Tibet plateau tectonism: evidences from zircon fission track thermochronology

ABSTRACT Reconstructing the growth model of the Northeastern Qinghai–Tibet Plateau is of significant importance in understanding its tectonic evolution through time. We present 20 new zircon fission track data on samples collected from the Chakabeishan-Shaliuquan district in the North Qaidam Tectonic Belt (NQTB) to constrain its Mesozoic mineralization and exhumation history. Sample ages and characteristics are differentiated by regional thrust fault systems. The mineralized pegmatite ages with high U concentrations can be divided into two groups of 170–168 Ma and 149–137 Ma, recording exhumation and hydrothermal mineralization events, with average cooling and exhumation rates of 0.074 mm/y and 2.305°C/Ma, respectively. Two ZFT ages groups characterized by low U concentrations at the deposit periphery of 125–106 Ma and 99–80 Ma, respectively, are associated with accelerated cooling and exhumation, with mean values of 7.662°C/Ma and 0.245 mm/y. We suggest that the NQTB was positioned in the high background thermal field in the Triassic, and subsequent tectonic extension resulted in the unroofing, cooling and mineralization of the region. The transition from extensional to contractional deformation in the Cretaceous tectonic setting has reactivated regional thrust fault systems and reset the Jurassic ZFT ages, and this exhumation event was influenced by the closure of the Middle-Tethys and Mongol-Okhotsk Oceans, consistent with the double-sided subduction model.

A study of fluid overpressure microstructures from the creeping segment of the San Andreas fault

Evidence of episodic fluid overpressure events noted in samples from the San Andreas Fault Observatory at Depth (SAFOD) have remained largely uncorrelated in terms of their collective significance for seismic history of the fault zone. The compositional and microstructural correlations sought in this study could shed light on questions about potential for major seismic events in the creeping segment of the SAF in central California. We used quantitative energy dispersive spectroscopy (EDS), Cathodoluminescence (CL) and Scanning Electron Microscope (SEM) imaging, and electron backscatter diffraction (EBSD) analysis to acquire geochemical and microstructural data from a suite of twenty SAFOD core samples including the damage zone and the active core of the fault. The results indicate intermittent coseismic fluid overpressure events that overprint the background aseismic creep across the fault. Analysis of trace elements and deformation in the coseismic calcite vein generations and their associated hydrothermal mineral phases indicate progressive uplift and exhumation followed by an asymmetric incursion of meteoric water into the damage zone. The same analysis suggests that the actively creeping intervals act as permeability barriers. Our results are in overall agreement with recent studies of the SAF in central California that indicate large seismic events have occurred intermittent with aseismic creep in recent geological time or suggest future potential for such events.

Characteristics of Ore-Forming Fluids and Genesis of the First Mining Area and Eastern Ore Section of the Pulang Porphyry Copper Deposit, Southeastern China: A Comparative Study

The Pulang copper deposit, formed in the Late Triassic, is the largest porphyry Cu-Mo-Au deposit in the eastern Tethys, and its genetic type and mineralization potential have received widespread attention. Identifying the characteristics of ore-forming fluids and the sources of ore-forming materials in the deep and peripheral ore bodies of Pulang is particularly important for constructing a complete porphyry copper mineralization system. Based on detailed core logging and geological observations, this article provides extensive petrographic, fluid inclusion micro-thermometry, laser Raman spectroscopy, and H-O-S isotope data on the veins of the main mineralization stage (B veins) in the first mining area and eastern ore section of the Pulang porphyry copper deposit. The genetic correlation between the eastern ore section and the first mining area is clarified, and their mineralization potential is inferred. The results indicate that the deep vein bodies in the first mining area exhibit multi-stage characteristics, and the fluid in B veins exhibits both high-temperature and salinity characteristics. The magma-derived early ore-forming fluids underwent processes such as boiling and experienced immiscibility during meteoric water mixing, which could be the primary mechanism of the precipitation of Cu, Mo, Au, and other metals. The outer eastern ore section is located in a medium-to-low-temperature hydrothermal mineralization zone far from the mineralization center. This outer eastern ore section is a distant part of the magmatic–hydrothermal system of the first mining area.

Hydrothermal Mineralization and Mineral Chemistry of Arsenides and Sulfarsenides in the Fe-Co-Ni-As-S System and Introduction of Three Unique Minerals, Port Radium Deposit, Canada

The Port Radium U-Cu-Ni-Co-Ag deposit in northwestern Canada is hosted within a mineral system that has generated a variety of mineralization styles from iron oxide-copper-gold to iron oxide-apatite, porphyry, skarn, and epithermal. Their genesis is linked to an extensive subduction-related magmatism that formed widespread dacite-rhyodacite-andesite volcanic and volcanoclastic sequences (~1.87 Ga), which have been intruded by their equivalent intrusive plutons. Pervasive and intensive hydrothermal alterations, including albitic, magnetite-actinolite-apatite, potassic ± albitic, phyllic, and propylitic occurred before the main sulfide, sulfarsenide, and uraninite vein-type mineralization. Although scarce sulfide minerals formed at the beginning of the hydrothermal activity, the main polymetallic arsenide-sulfarsenide-sulfide ± uraninite vein-type mineralization occurred during the epithermal stage. In addition to the common arsenides and sulfarsenides including nickeline, cobaltite, rammelsbergite, safflorite, skutterudite, gersdorffite, and arsenopyrite, three unique sulfarsenides were also found: Co0.67Ni0.32Fe0.02S0.19As2.80, which could be a sulfur-rich skutterudite, Ni0.85Co0.15S0.39As1.60, and Ni0.69Co0.31S0.47As1.52, which are chemically comparable to the Port Radium rammelsbergite with substantial addition of S and Co; they could be the solid solution product of gersdorffite-cobaltite or safflorite-rammelsbergite.

Towards a Model-Based Interpretation of Measurements of Mineralogical and Chemical Compositions

We introduce a new methodology for inference of fluid composition from measurements of mineralogical or chemical compositions, expanding upon the use of reactive transport models to understand hydrothermal alteration processes. The reactive transport models are used to impute a latent variable explanatory mechanism in the formation of hydrothermal alteration zones and mineral deposits. An expectation maximisation algorithm is then employed to solve the joint problem of identifying alteration zones in the measured data and estimating the fluid composition, based on the fit between the mineral abundances in the measured and predicted alteration zones. Using the hydrothermal alteration of granite as a test case (greisenisation), a range of synthetic tests is presented to illustrate how the methodology enables objective inference of the mineralising fluid. For field data from the East Kemptville tin deposit in Nova Scotia, the technique generates inferences for the fluid composition which compare favourably with previous independent estimates, demonstrating the feasibility of the proposed calibration methodology.

Nature, source, and evolution of the ore-forming fluids in the Dunbasitao gold deposit, East Junggar, China: Constraints from geology, fluid inclusions, and C-H-O isotopes

The origin of CO2-dominated fluids in orogenic gold deposits is usually mired in controversy. The Dunbasitao gold deposit is the largest among several gold deposits along the Armantai suture zone, East Junggar, China. Orebodies are hosted in volcano-sedimentary rocks of the Lower Carboniferous Jiangbasitao Formation and porphyritic quartz diorite and are controlled by shear zones. Based on the cross-cutting relationship of veins, the hydrothermal process can be divided into the early, middle, and late stages and the gold only occurred in the middle stage. Seven types of fluid inclusions (FIs) were identified in the Dunbasitao deposit: Type-1 FIs (LH2O + LCO2 or LH2O + LCO2 + VCO2) that homogenized to H2O phase or show critical homogenization; Type-2 FIs (LH2O + LCO2 or LH2O + LCO2 + VCO2) that homogenized to CO2 phase; CO2-dominated Type-3 FIs (LCO2 or LCO2 + VCO2); Two-phase aqueous Type-4 FIs (LH2O + VH2O) that homogenized to liquid phase; Type-5 FIs are composed of three phases (LH2O + VH2O + Solid), which homogenized to liquid phase; Type-6 and Type-7 FIs refers to FIs composed of a single liquid or vapor H2O phase, respectively.Microthermometry and laser Raman spectroscopy (LRS) analyses show that the initial ore-forming fluids in the early stage were moderate-Th (326–342 °C), low salinity (2.4 to 4.7 wt% NaCl equiv), and homogenous H2O−CO2−NaCl liquid fluids, containing 13–33 mol% CO2 and a small amount of CH4, H2S, and N2. The calculated δ18OH2O (V-SMOW) values are 7.5–8.5 ‰, δ18DH2O (V-SMOW) values range from −100 to −96 ‰, and δ13Cfluid (PDB) range from −3.8 to −2.5 ‰. In the middle stage, two typical immiscible fluid inclusion assemblages (FIA.18 and FIA. 27) composed of both Type-1 and Type-2 FIs were measured. The salinity of FIA.18 is 3.3 wt% NaCl equiv. and Th is 320 °C. For FIA.27, the salinity is 2.2 wt% NaCl equiv. and Th is 298 °C. The salinities of Type-4 FIAs vary from 5.9 to 14.4 wt% NaCl equiv., significantly higher than Type-1 and Type-2 FIs (1.7 to 3.5 wt% NaCl equiv). The salinities of three isolated Type-5 FIs (halite-bearing) range from 30.3 to 32.9 wt% NaCl equiv. and Th vary from 257 to 277 °C. These facts indicate extreme unmixing between carbonic and aqueous fluids in the middle stage, which led to gold precipitation. The Type-3 FIs represent the salt-free, H2O-lost, CO2 end-member composition, whilst the Type-5 FIs and high-salinity Type-4 FIs represent the highly saline aqueous end-member composition. Late-stage fluids are initially liquid, very low-salinity (1.4 to 2.6 wt% NaCl equiv), and low-Th (176–233 °C) aqueous fluids.Two immiscible carbonic FIAs from the middle stage yield a trapping pressure (Pt) of 86.9–133.9 MPa. Considering the rapid pressure fluctuations during fluid immiscibility, using hydrostatic or lithostatic pressure alone cannot get the real mineralization depth, Therefore, we use the lithostatic pressure for the Pt maximum and hydrostatic pressure for the Pt minimum and calculated a mineralization depth of 5.3–8.9 km, which doesn't represent the change but uncertainty for depth. Combining the characteristics of ore-forming fluids with the hydrothermal alteration and mineral compositions of ores, the Dunbasitao gold deposit is determined as a mesozonal orogenic gold deposit and there is considered to be prospecting potential in the deep.

Mapping of surface hydrothermal mineral alterations and geological structures related to geothermal systems in the Songwe region, SW Tanzania

ABSTRACT Geothermal energy is one of the most valuable and preferable renewable energy sources, given that it produces sustainable, dependable, and clean energy. Understanding the geothermal systems, parameters such as heat, fluids, and structures help to identify potential geothermal systems. These parameters are manifested as hot springs, fumaroles, and alteration minerals. Hydrothermal alteration minerals are often used in geothermal system exploration to evaluate factors such as temperature, fluid, and structures. This study employed GIS and remote sensing in the investigation of hydrothermal mineral alterations and delineating geological structures which provided invaluable information for identifying prospective geothermal resource zones. ASTER was utilised to map phyllic, argillic, and propylitic minerals using SPCA, whereas ISO cluster classification was used to detect kaolinite, smectite, calcite, chlorite, and muscovite/illite-rich areas. DEM was used to extract and map geological lineaments. Results have revealed that the regions that were mapped with indicator hydrothermal alteration minerals were also associated with geological structures. The field work, XRD, and ASD laboratory analysis results indicated a good match with the findings from the remote sensing data. The approach applied in this study may be used along with other techniques during the early phases of geothermal exploration to define geothermal potential targets.

Short wavelength infrared (SWIR) reflectance spectroscopy of alteration minerals of Qibaoshan ore district, Shandong Province, China

Qibaoshan is a recently discovered ore district including a significant epithermal deposit; it has three different types of deposits that have been developed in the Qibaoshan subvolcanic complex, including Jinxiantou copper–gold deposit, Qibaoshan polymetallic epithermal deposit and Diaoyutai pyrite deposit.The characteristics of these deposits and geochronological studies indicate that they may belong to the same mineral system. To study the relationship between the deposits and to determine potential for deposits under cover, surface alteration mapping by short-wave infrared spectroscopy (SWIR) analyses was conducted on the ore field. The results showed that the Jinxiantou copper–gold deposit has illite ＋ chlorite alteration, and the Qibaoshan deposit has illite + chlorite alteration as vein halos and gradually transitions outwards to montmorillonite alteration. Illite alteration is widely developed in the Qibaoshan ore field.Study of the spectral characteristics of illite in the east of the ore district showed it has a lower wavelength Al-OH absorption peak position (Pos2200) and higher illite crystallinity (IC) value and shows a trend of gradually decreasing Pos2200 and increasing IC to the west, indicating that the inferred heat center in the eastern ore district may be the center of hydrothermal activity. The Qibaoshan ore district contains a porphyry-epithermal hydrothermal mineral system, and the east of the ore district may have potential for discovery of porphyry deposits.

Multiple mineralization events recorded in the Dahenglu Cu[sbnd]Co deposit, eastern North China Craton: Constraints from Re[sbnd]Os and U[sbnd]Pb geochronology

The formation of sediment-hosted CuCo deposits remains controversial, in part due to the lack of a precise age for CuCo mineralization. The Dahenglu deposit is located in the eastern part of the Jiao–Liao–Ji Belt (JLJB), one of the famous sedimentary–metamorphic-type CuCo deposits in China, that is mainly hosted within Palaeoproterozoic epimetamorphic rocks. The orebodies occur as stratoid, lenticular and veined forms in conformity with the carbonaceous sericite phyllite. In this study, we present new ReOs and monazite UPb geochronological data for carbonaceous sericite phyllite, and zircon UPb geochronological data for diorite porphyry associated with the deposit. The ReOs geochronology on carbonaceous rocks from the Dalizi Formation provides a direct and reliable depositional age of 1967 ± 23 Ma. The UPb analyses of metamorphic monazite intergrown with cobaltite yield an age of 1812 ± 8 Ma. Magmatic zircon UPb dating from ore-bearing diorite porphyry yields a weighted mean age of 121.8 ± 0.8 Ma. These results constrain three periods of mineralization in the Dahenglu deposit. Syngenetic sedimentary mineralization and metamorphic mineralization occurred during the Palaeoproterozoic, and magmatic–hydrothermal mineralization occurred during the Early Cretaceous. We suggest that ReOs and UPb geochronology on carbonaceous-bearing epimetamorphic rock and metamorphic monazite can serve as robust chronometers to establish the age and temporal evolution of sedimentary hosted CuCo mineralization.

Relationship of copper-molybdenum and gold minering with magmatism

In the investigated deposits, a combination of skarn and hydrothermal mineralization has been identified. Specific facies within intrusive complexes align with distinct postmagmatic formations. Skarn-magnetite formations are intricately linked with the granitoid complex of the initial phase, while hydrothermal mineralization has a genetic connection to the subsequent phase of magmatism, characterized by minor intrusions of granodiorite porphyry. A distinctive zonal structure of individual facies, such as quartz-sericite-chlorite metasomatites, is observed around these granodiorite porphyry intrusions. The manifestation of rock wall metasomatism, as well as copper-molybdenum and gold ore mineralization, closely corresponds to the extent of the granodiorite-porphyry occurrences. This correlation highlights the intimate relationship between the scale of mineralization and the manifestation of granodiorite-porphyry, emphasizing the role of specific magmatic phases in the formation of skarn and hydrothermal deposits. The findings contribute to our understanding of the geological processes governing the development of diverse mineralization types within these deposits.

MULTIPULSED MAGMATISM AND DURATION OF THE HYDROTHERMAL SYSTEM OF THE GIANT JIAMA PORPHYRY Cu SYSTEM, TIBET, CHINA

Abstract Jiama is the largest porphyry-skarn ore system in the Gangdese metallogenic belt, Tibet. It is composed of porphyry Cu-Mo, Cu-polymetallic skarn, Cu-Pb-Zn manto, and distal vein Au orebodies with associated Ag, W, and Bi. However, the precise timing of the magmatism and hydrothermal events at Jiama remains obscure. Here, using high-precision chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb zircon dating of ore-bearing and post-ore intrusions, we accurately constrain the lifespan of magmatism and hydrothermal mineralization. Monzogranite porphyry dikes are cut by Cu-Mo vein mineralization in the deeper part of the system, indicating that they were emplaced pre-ore, and yield a crystallization age of 15.534 ± 0.007 Ma (mean square of weighted deviates [MSWD] = 0.99, n = 6). A granodiorite porphyry that cuts the monzogranite porphyry and hosts vein and disseminated chalcopyrite and molybdenite is considered synchronous with ore and yields a crystallization age of 15.368 ± 0.007 Ma (MSWD = 1.01, n = 5). These two phases of intrusions are cut by quartz-diorite porphyry bodies, which yield a crystallization age of 15.076 ± 0.006 Ma (MSWD = 0.13, n = 6) and contain weak, subeconomic Cu and almost no molybdenum mineralization. A post-ore barren quartz monzonite porphyry yields a crystallization age of 14.925 ± 0.006 Ma (MSWD = 1.12, n = 6). The lifespan of magmatism at Jiama is thus about 0.61 m.y. The difference with previous molybdenite Re-Os isochron ages from the porphyry (14.7 ± 0.3 Ma), hornfel (14.7 ± 0.4 Ma), and skarn (15.4 ± 0.2 Ma) suggests that high-precision chronology is required to decipher accurate timing of mineralization in porphyry systems such as Jiama. The 40Ar/39Ar ages of hydrothermal biotite coexisting with molybdenite in monzogranite porphyry and hornfels are 15.25 ± 0.17 Ma (MSWD = 1.6) and 15.25 ± 0.24 Ma (MSWD = 0.14), respectively, slightly younger than the granodiorite porphyry and older than weakly mineralized quartz diorite porphyry, which represents the time of the ore-forming hydrothermal event. Thus, Jiama is the product of pulsed magmatism during which a short-lived hydrothermal event formed the giant Cu polymetallic system.

Discovery of the intrusive rocks hydrothermal altered clay-type lithium mineralization in southern Anhui Province and its geological significance

Discovery of the intrusive rocks hydrothermal altered clay-type lithium mineralization in southern Anhui Province and its geological significance

The Early Cretaceous hydrothermal sedimentation and its influence on sandstone-type uranium mineralization in the Xinniwusu Sag, Bayingobi Basin, NW China

The presence of Early Cretaceous hydrothermal sedimentation was initially observed in the Xinniwusu Sag, Eastern Bayingobi Basin, NW China. To gain deeper insights into the features of hydrothermal sedimentation in this region and its relationship with uranium mineralization, we conducted an analysis encompassing petrography, geochemistry, the electron microprobe, and low-temperature thermochronology of the hydrothermal sedimentary rocks. Petrographic analysis revealed that the predominant hydrothermal sedimentary rocks in the upper member of the Bayingobi Formation within the Xinniwusu Sag encompass dolomitic limestone and sinter, followed by clastic rocks mixing with hydrothermal sedimentation. Major and trace element analyses emphasized the enrichment of elements including Ca, Mg, P, U, REEs, Sr, Y, Mo, Sb, Cd, and Pb in the hydrothermal sedimentary rocks. Notably, a prominent positive correlation was identified between U and P, REEs, Sr, and Y. Electron microprobe analyses illuminated that uranium primarily exists within fluorapatite in the form of adsorption or isomorphism. Isotopic analyses, δ13CV-PDB and δ18OV-PDB, of carbonate cements in clastic rocks and limestone yielded values ranging from −3 to 2.1 ‰ and − 17 to −6.9 ‰, respectively. These findings suggest that the carbon in the hydrothermal fluids predominantly originates from marine strata, with some potential contribution from the mantle. The paleotemperatures based on the O isotope data range from 67 °C to 78 °C, with an average of 71 °C, implying that the hydrothermal sedimentation corresponds to the continental low temperature white smoker type. Furthermore, apatite fission-tracks of grayish-white gritstone within the upper member of the Bayingobi Formation were completely annealed at 116 ± 7 Ma, partially annealed at 112 ± 4 Ma, also indicating that there was a hydrothermal sedimentary environment for a long time. The hydrothermal sedimentation predominantly influenced the uranium preconcentration in the upper member of the Bayingobi Formation. The uranium source in the hydrothermal fluids is likely linked to the Mesoproterozoic Zhaertai Group within the southern basement of the basin. This revelation offers valuable insights into the distribution of uranium deposits and mineralization points in the Bayingobi Basin, primarily concentrated in the southern sector. Consequently, these areas characterized by well-developed faults connecting the basement and the Lower Cretaceous Formation in the south of Bayingobi Basin are favorable areas for uranium mineralization. This study bears immense significance in enhancing our understanding of the uranium metallogenic mechanisms in the Bayingobi Basin and hydrothermal sedimentation mineralization widely distributed in the world.