Magmatic-hydrothermal Mineralization Research Articles

Newly discovered Early Cretaceous Au mineralization overprinting Late Jurassic Pb-Zn-Ag mineralization in the Qin-Hang metallogenic belt (South China)

Magmatic and mineralizing events in South China were traditionally thought to be limited between 150 Ma and 130 Ma despite the numerous Mesozoic-aged magmatic-hydrothermal deposits in the region. This viewpoint is being reevaluated in light of new age data. Kangjiawan is a representative Pb-Zn-Ag-Au deposit in the Hengyang Basin in the Qin-Hang metallogenic belt of South China that contains 1.96 Mt of Pb-Zn resource with 4.70% Zn, 6.02% Pb; 2280.5 t of Ag resource with 108.23 g/t of Ag; and 58 t of Au resource with 3.25 g/t of Au. Its mineralization can be divided into four stages: (I) pre-ore quartz−pyrite, (II) quartz−pyrite−galena−sphalerite, (III) quartz−galena−sphalerite, and (IV) calcite−pyrite. Multiple generations of pyrite were identified at Kangjiawan. Generation I pyrite (Py1, formed in Stage I) is coarse-grained, texturally homogeneous, and contains abundant silicate inclusions (e.g., K-feldspar and titanite). Generation II pyrite (Py2, formed in Stage II) is generally fine-grained and exhibits a core-rim texture, with the porous, sphalerite−galena inclusion-bearing core (Py2a) having replaced Py1 and the rim (Py2b) being homogeneous. Generation III pyrite (Py3, formed in Stage IV) is subdivided into Py3a and Py3b, with the homogeneous Py3a often replaced by the porous Py3b. The low Co/Ni ratio of Py1, along with the abundant silicate inclusions, is suggestive of intense fluid-rock interaction during Stage I. Py2a is As-Cu-Pb-Ag-Au−rich, Co-depleted, and has elevated Ag/Co (average 3.24) and As/Co (average 10,217.14) ratios, which are suggestive of extensive fluid boiling during the formation of Py2a. This is also supported by the ubiquitous Py2-cemented hydrothermal breccia. In contrast, Py2b is depleted in As-Cu-Pb-Ag-Au but enriched in Co, which is indicative of non-boiling conditions. Subsequent sealing of fractures by veins may have caused the formation of coarse-grained sphalerite and galena in Stage III. The similar 207Pb/206Pb values among Py1 (average 0.849), Stage II galena (average 0.849), Stage III galena (average 0.849), and the nearby Shuikoushan granodiorite stock (corrected average 0.848) suggests that mineralization in stages I−III may represent distal skarn-type Pb-Zn-Ag mineralization genetically related to the Shuikoushan stock. This interpretation is supported by the similar ages of mineralization Stage I (apatite U-Pb: 159.4 ± 1.0 Ma) and Stage II (fuchsite 40Ar-39Ar: 158.1 ± 0.4 Ma) to the age of Shuikoushan stock (zircon U-Pb age: ca. 158 Ma). As the primary Au-hosting mineral at Kangjiawan, the As- and Au-rich Py3a occurs in sharp contact with porous Co-Ni-Se-Bi-Mo-As−poor Py3b, which commonly contains abundant fine-grained galena and sphalerite inclusions. This suggests that Py3b formed via coupled dissolution−re-precipitation of Py3a. This coupled dissolution−re-precipitation reaction favors the remobilization of Au from within the Py3a structure and its re-enrichment as Au inclusions in Py3b; this is supported by the anomalous Au peaks in time-resolved signal profiles from laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS) and the abundant outliers for Au concentrations in Py3b. The markedly distinct trace-element geochemistry of Py3 compared to those of Py1 and Py2, and the U-Pb age of Stage IV calcite (ca. 138 Ma), are indicative of an Early Cretaceous Au mineralization event. Published calcite C-O isotope data, coupled with the narrow range of δ34S values (0.6‰−2.2‰) of Py3, suggest that the Kangjiawan Au mineralization may be associated with a concealed Early Cretaceous pluton. We propose that the Kangjiawan deposit formed via the overprinting of Late Jurassic distal skarn Pb-Zn-Ag mineralization by Early Cretaceous magmatic-hydrothermal Au mineralization, which demonstrates that 150−135 Ma may also be an important period for the formation of the magmatic-hydrothermal mineralization belt.

Two-episode mineralization in the Haerdaban Pb–Zn deposit, NW China: Insights from sulfide trace elements, in situ S–Pb isotopes, and Rb–Sr geochronology

The Haerdaban Pb–Zn deposit, located in the eastern West Tianshan Orogen, hosts stratiform and vein-type mineralization within Precambrian carbonate rocks. However, there has been limited research on the distinctions and relationships between these two mineralization styles. In this study, we compared trace element distributions, fluid conditions, material sources, and mineralization ages between stratiform and vein-type mineralization and reconstructed a detailed genetic model. Two episodes and four stages of mineralization were identified, including five generations of pyrite and two generations of sphalerite. The sedimentary exhalative episode represents stratiform mineralization including Stage I pyrite–pyrrhotite layers (Py-1, Py-2a, Py-2b, and Py-3) and Stage II sphalerite–galena layers (Sph-1). The magmatic–hydrothermal episode represents vein-type mineralization including Stage III pyrite–quartz–calcite veins (Py-4) and Stage IV sphalerite–galena–quartz–calcite veins (Sph-2). LA–ICP–MS analysis of Se–Co–Ni–As–Ag–Sb–Bi contents in pyrite suggests that Py-1 to Py-3 formed under relatively low temperatures (280 ± 8 °C) and high ƒO2 sedimentary conditions. Py-4 formed under relatively high temperatures (339 ± 18 °C) and low ƒO2 hydrothermal conditions. Variations in Fe–Mn–In–Ga–Ge–Cd–Cu contents in sphalerite indicate that Sph-1 formed under relatively low temperature (211 ± 7 °C), intermediate ƒS2 (logƒS2 = −11.1 ± 0.5), and moderate pH sedimentary exhalative conditions. Sph-2 formed under relatively high temperature (292 ± 5 °C), high ƒS2 (logƒS2 = −7.4 ± 0.2), and low pH hydrothermal conditions. In situ analysis of sulfide S–Pb suggests that ore-forming materials for stratiform mineralization were primarily derived from marine sediments, while those for vein-type mineralization primarily originated from magmatic sources. Sph-1 from stratiform mineralization yielded an Rb–Sr isochron age of 719 ± 16 Ma, while Sph-2 from vein-type mineralization exhibited an Rb–Sr isochron age of 380.3 ± 7.7 Ma. Random Forest classification of trace elements in pyrite and sphalerite predicted that stratiform mineralization is of sedimentary genesis, whereas vein-type mineralization is of magmatic–hydrothermal genesis. Based on our results, we identified a two-episode mineralization history for the Haerdaban Pb–Zn deposit: Neoproterozoic syngenetic sedimentary exhalative mineralization overprinted by Devonian epigenetic magmatic–hydrothermal mineralization. The results of this study highlight the importance of considering multiple geological events in ore-forming processes and will facilitate the exploration of similar deposits in the West Tianshan Orogen.

Genesis of the Beizhan Iron Deposit in Western Tianshan, China: Insights from Trace Element and Fe-O Isotope Compositions of Magnetite

The Beizhan iron deposit (468 Mt at an average grade of 41% Fe) is the largest iron deposit in the Awulale iron metallogenic belt of Western Tianshan, northwest China. The high-grade magnetite ores are hosted in the Carboniferous volcanic rocks with extensive development of skarn alteration assemblages. While considerable progress has been made in understanding the characteristics of Beizhan and its genetic association with volcanic rocks, the genetic models for ore formation are poorly constrained and remain controversial. This study combines detailed petrographic investigations with in situ LA-ICP-MS analyses of trace elements and Fe-O isotope compositions of magnetite to elucidate the origin of magnetite and the conditions of ore formation. The trace element concentrations in magnetite unveil intricate origins for various ore types, implying the precipitation of magnetite from both magmatic and hydrothermal fluids. The application of the Mg-in magnetite thermometer (TMg-mag) reveals a notable temperature divergence across different magnetite varieties, spanning from relatively higher temperatures in magmatic brecciated magnetite (averaging ~641 and 612 °C) to comparatively lower temperatures in hydrothermal platy magnetite (averaging ~552 °C). The iron isotopic composition in massive and brecciated magnetite grains, characterized by lighter δ56Fe values (ranging from −0.078 to +0.005‰ and −0.178 to −0.015‰, respectively), suggest a magmatic or high-temperature hydrothermal origin. Conversely, the heavier δ56Fe values observed in platy magnetite (+0.177 to +0.200‰) are attributed to the influence of pyrrhotite, signifying late precipitation from low-temperature hydrothermal fluids. Additionally, the δ18O values of magnetite, ranging from +0.6 to +4.6‰, provide additional evidence supporting a magmatic–hydrothermal origin for the Beizhan iron deposit. Overall, the identified genetic associations among the three magnetite types at Beizhan provide valuable insights into the evolution of ore-forming conditions and the genesis of the deposit. These findings strongly support the conclusion that the Beizhan iron deposit underwent a process of magmatic–hydrothermal mineralization.

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.

Infrared microthermometry of fluid inclusion in sphalerite: A case study of the Xinqiao deposit in the Middle–Lower Yangtze metallogenic belt

Infrared microthermometry allows direct measurement of fluid inclusions hosted in opaque ore minerals and can provide direct constraints on the evolution of ore-forming fluids. This study presents infrared microthermometry of spherite-hosted fluid inclusions from the Xinqiao deposit in the Middle-Lower Yangtze Metallogenic Belt and sheds new light on the ore genesis of the deposit. Considering that infrared light may lead to non-negligible temperature deviations during microthermometry, some tests were first conducted to ensure the accuracy of the microthermometric measurements. The measurement results indicated that using the lowest light intensity of the microscope and inserting an optical filter were effective in minimizing the possible temperature deviations of infrared microthermometry. All sphalerite-hosted fluid inclusions from the Xinqiao deposit were aqueous. They show homogenization temperature ranging from ~200 to 350 °C, but have two separate salinity groups (1.0–10% and 15.1–19.2% NaCl equivalent). The low-salinity group represents sedimentary exhalative (SEDEX)-associated fluids, whereas the high-salinity group results from modification by later magmatic hydrothermal fluids. Combined with published fluid inclusion data, the four-stage fluid evolution of the Xinqiao deposit was depicted. Furthermore, our data suggest that the Xinqiao deposit was formed by two-stage metallogenic events including SEDEX and magmatic-hydrothermal mineralization.

Source and genesis of Chapai carbonate-hosted Zn-Pb deposit, South China: Constraints from in-situ S and Pb isotopes of sulfide and sulfate minerals

Chapai deposit is a special medium-sized carbonate-hosted Zn-Pb deposit (4.27Mt of sulfide ore with 8.15 % Zn, 3.44 % Pb, and 53.39 g/t Ag, as well as 0.82Mt of oxidized ore with 2.8 % Zn and 1.2 % Pb and 27.68 g/t Ag) with upper oxidized ore and lower sulfide ore of South China. Due to the shortage of detailed geological and geochemical constraints, the ore genesis of single stage magmatic hydrothermal mineralization or superposition of multi-stage mineralization remains unclear. Therefore, detailed geological and geochemical analyses of in-situ S isotopic compositions of sulfide and sulfate, trace elements of sphalerite, and ore Pb isotopic compositions were performed to decode the source and genesis of the Chapai deposit. Based on the investigation and microscopic observation, mineralization of the Chapai Zn–Pb deposit has obvious early hydrothermal alternation in the early hydrothermal sulfide stage (S1) and the late hydrothermal sulfide stage (S2) as well as the supergene oxidized mineralization stage (S3). The trace elements Cu, Ag, Ga, Sb, As and Ge are incorporated into S1 and S2 stages of sphalerite mainly through the following substitution mechanisms: Zn2+↔ (Fe2+, Cd2+),2Zn2+↔ (Ag+, Cu+) +(As3+, Ga3+, Sb3+), 3Zn2+↔ Ge4++2(Cu++Ag+), 4Zn2+↔(Cu++Ag+) + Sb3++Ge4++□(vacancy). In situ δ34S values of sulfides and sulfates are within a greater range (–3.0 to + 32.2 ‰), and are significantly higher in S2 compared to S1 stage, implying the mixing of two isotopically different end-members of hydrothermal fluids and wall rocks by sulfate reduction. The S isotope of sphalerite and galena crystallized in the early stage close to 0 ‰ may be controlled by magmatic-hydrothermal fluid source, while the increased S isotope in the late stage may be derived from the increased decomposition of organic matter and organic sulfate reduction (TSR). The Pb isotopic data (206Pb/204Pb = 18.355 ∼ 18.819, 207Pb/204Pb = 15.720 ∼ 15.778, and 208Pb/204Pb = 38.912 ∼ 39.222) indicate that the sources of metallogenic materials in the Chapai deposit are primarily upper crust basement rocks. The geothermometer studies of sphalerite in Chapai deposit show that it was generated from a medium–low temperature (142 ∼ 255 °C) condition. The low Zn/Cd ratios and high concentrations of Cd and Ge in sphalerite are in agreement with those of Mississippi Valley-type (MVT) deposits. Hence, the Chapai deposit was formed in a medium–low temperature magmatic- hydrothermal system and can be categorized as a MVT deposit within Nanling region (NR).

LA-ICP-MS U-Pb cassiterite age data of the Sadisdorf deposit link Sn-Li-(W-Cu) mineralization in the eastern Erzgebirge to the collapse of the Altenberg-Teplice Caldera

The Sadisdorf Sn-Li-(W-Cu) prospect in the eastern Erzgebirge (Germany) comprises two distinct styles of magmatic-hydrothermal mineralization, namely greisen-type mineralization at the Kupfergrube site, and stockwork-type mineralization at both the Kupfergrube and the Zinnklüfte sites. Previously, these two sites were regarded as expressions of two temporally distinct mineralization events. In this study, this temporal relation was tested by LA-ICP-MS U-Pb data obtained for 16 cassiterite samples, including samples from both sites and styles of mineralization. All 16 samples define a narrow range of ages between 315.1 ± 1.7 / 3.3 Ma and 311.0 ± 3.1 / 4.0 Ma. All ages overlap within uncertainty, suggesting that mineralization across the Sadisdorf prospect is likely related to the same magmatic-hydrothermal event.On the regional scale, the cassiterite ages suggest that Sn-Li mineralization is associated with late-stage felsic magmatism directly following the collapse (∼314–313 Ma) of the Altenberg-Teplice Caldera. The cassiterite ages also overlap with garnet U-Pb LA-ICP-MS ages of Sn-rich skarn occurrences in the western Erzgebirge (e.g., Breitenbrunn, Antonsthal and Hämmerlein). This observation provides direct evidence that greisen and skarn-hosted Sn mineralization are related to the same period of magmatism. The data indicate that the majority of Sn-mineralization in the Erzgebirge formed after 318 Ma (likely between 318 and 310 Ma), challenging previous models which invoked an older suite of granites (326–318 Ma) as causative source intrusions.

Ab-initio calculations and molecular dynamics simulations of In, Ag, and Cu replacing Zn in sphalerite: Implications for critical metal mineralization

Sphalerite has been recognized as the most important carrier mineral of the critical metal of indium (In), which mainly exists in sphalerite lattice through isomorphous substitution for Zn. It is widely reported that there are two significant coupled substitution schemes, namely Ag++In3+→2Zn2+ and Cu++In3+→2Zn2+, for In entering sphalerite in natural mineralization. However, there is still little known about physicochemical constrains on these two substitution reaction processes, which hinders the understanding of In mineralization. Thus, the current study uses ab-initio calculations and molecular dynamics simulations to investigate the replacement processes of Zn by In, Ag and Cu in sphalerite. The doped systems of Zn30InAgS32 and Zn30InCuS32, which correspondingly represent the products of the two substitution processes, were constructed by using 2 × 2 × 2 supercell model of sphalerite. Molecular dynamics method was employed to simulate the doped models, obtaining average configurations and formation energies at different temperatures. Then, ab-initio calculations were utilized to study the population values and electronic properties of the simulated configurations. In order to simulate a system close to natural mineralization conditions, a constant pressure of 30 MPa was set in molecular dynamics simulations, as this pressure level can represent the average metallogenic pressure observed in magmatic-hydrothermal deposits associated with In-bearing sphalerite. The temperature parameters were tested within the range of 175 °C to 400 °C, covering the known possible ore-forming temperatures. The simulation results show: (1) it is more stable for In to enter sphalerite via the coupled substitution scheme of Cu++In3+→2Zn2+ than that of Ag++In3+→2Zn2+; (2) the favorable temperatures for the two substitution processes are 225–250 °C and 325–350 °C; and (3) the changes in chemical reactivity caused by temperature fluctuations during the substitution processes of Zn by In, Ag and Cu may lead to the cyclic oscillation distribution that is commonly observed for In within sphalerite in magmatic-hydrothermal mineralization systems. This discovery not only shows the physicochemical properties of In-rich sphalerite formed by the two reaction processes of replacement of Zn, but more importantly, provides deep insights into the natural mineralising process of In at the atomic or/and molecular scale.

Metallogenic Setting and Temporal Evolution of Porphyry Cu-Mo Mineralization and Alteration in the Delamerian Orogen, South Australia: Insights From Zircon U-Pb, Molybdenite Re-Os, and In Situ White Mica Rb-Sr Geochronology

Abstract Paleozoic porphyry-style hydrothermal alteration and mineralization has previously been recognized within the Delamerian orogen, South Australia, where porphyry prospects include Anabama Hill, Netley Hill, and Bendigo. However, limited exploration due in part to thick postmineralization cover hinders the understanding of the temporal context, metallogenic setting, and mineral potential of the porphyry systems along the Proterozoic continental margin of Australia. In this study, we have characterized the hydrothermal alteration and mineralization of these porphyry occurrences. Zircon U-Pb, molybdenite Re-Os, and white mica Rb-Sr ages have been determined to constrain the timing for emplacement of magmatic intrusions, precipitation of metal-bearing sulfides, and duration of hydrothermal alteration in the Delamerian orogenic belt. Zircon U-Pb laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of nine granitoids reveal that the intrusive rocks were emplaced mostly between 485 and 465 Ma, whereas three intrusions at Bendigo have zircon U-Pb ages of 490 to 480 Ma. Molybdenite isotope dilution-negative thermal ion mass spectrometry (ID-NTIMS) Re-Os dating of the four prospects identifies two porphyry Cu-Mo mineralization events at 480 and 470 to 460 Ma, respectively. Nineteen white mica Rb-Sr LA-ICP-MS/MS (tandem mass spectrometers) analyses return an age range between 455 and 435 Ma for phyllic alteration at the Anabama Hill and Netley Hill prospects, whereas intense white mica-quartz-pyrite alteration at Bendigo prospect appears to have developed between 470 and 460 Ma. These geochronologic results indicate that the Delamerian porphyry systems postdated subduction-related magmatism in the region (514–490 Ma) but instead formed within an inverted back-arc regime, where mineralized magmas and fluids ascended along favorable lithospheric-scale structures, probably due to asthenospheric upwelling triggered by mafic delamination. Porphyritic stocks, dikes, and aplites with ages of 470 to 460 Ma are the most likely hosts to porphyry-style mineralization in the Delamerian orogen that appears to have formed simultaneously with the oldest known porphyry systems in the intraoceanic Macquarie arc (e.g., Marsden, E43, and Milly Milly; 467–455 Ma). These results emphasize the significance and potential of Early-Middle Ordovician intrusive systems to host such a type of magmatic-hydrothermal mineralization in the Delamerian orogen.

The genesis of acid alteration in the Luohe IOA-type deposit, Eastern China and its constraints on mineralization

Luohe is the largest IOA-type deposit in the Middle and Lower reaches of the Yangtze Metallogenic belt. The iron ore body is hosted in thick volcanic rocks, and widespread acidic alteration (secondary quartzite) developed at shallow depths, providing an excellent opportunity to study the genesis of acidic alteration rocks and the genetic links with the IOA mineralization. In this study, detailed mineralogy, in situ sulfur isotopes, and trace element analyses were performed on pyrite from a shallow drill hole in the Luohe deposit. The results indicate that the formation time of acidic alteration is between magnetite (stage II) and anhydrite-pyrite (stage IV), with pyrite sulfur isotopes ranging from −14 to 4‰, which is significantly different from those in stage IV (7-9‰). The anomaly negative sulfur isotope suggests the existence of SO2 disproportionation reaction, and the δ34S of pyrite increases with depth decrease, ultimately falling within the mantle sulfur range. This indicates that the sulfur origin of acidic alteration pyrite is a single magma sulfur source, which is significantly different from the deep iron mineralization system (magmatic + evaporite). The trace elements Co, Ni, As, Ti, Cu, Sb, Tl in pyrite indicate that the acidic alteration fluid has the characteristics of low temperature, low pH, and is rich in F and Cl. Combined with the sulfur isotope results, it is believed that pyrite in the acidic alteration rock of the Luohe was formed by the mixing of gaseous SO2 and shallow groundwater, which is a part of the Luohe magmatic-hydrothermal mineralization system and an important indication for regional exploration of similar deposits.

Multi-Isotopic Compositions of Ores from the Shizishan Cu–Au–Mo Orefield in the Tongling Region, Eastern China: Implications for Ore Genesis

The Middle–Lower Yangtze Metallogenic Belt (MLYMB) hosts abundant porphyry–skarn–stratabound-type Cu–Au–Mo deposits. Despite extensive research, the origin of the stratabound-type deposits, which developed at the unconformity interface between the Devonian and Carboniferous strata in the MLYMB, remains controversial. The primary debate centers on whether these deposits are the result of Carboniferous sedimentary exhalative mineralization or Mesozoic magmatic–hydrothermal mineralization. In this paper, we examine three representative deposits in the Shizishan orefield: the Chaoshan skarn-type Au deposit, the Hucun porphyry–skarn-type Cu–Mo deposit, and the Dongguashan Cu–(Au) deposit, which has a disputed genesis of its stratiform orebodies. Economically important ore minerals, such as chalcopyrite, molybdenite, and pyrrhotite, and their associated quartz and calcite, were focused on, rather than the extensively studied pyrite in the Tongling region. The ore genesis and sources of mineralized elements in the Shizishan orefield were investigated using H, O, C, S, Pb, and Cu isotopes. The H–O isotopic compositions of hydrothermal quartz from the Chaoshan, Dongguashan, and Hucun deposits indicate that the ore-forming fluids were mainly magmatic water with some meteoric water input. The C–O isotopic compositions of calcite show a large difference from the local sedimentary carbonates. The S isotopic compositions of sulfides reveal a magmatic sulfur signature. The Pb isotopic compositions in the three deposits are similar to those of the Shizishan intrusions, suggesting a magmatic source for Pb. The Cu isotopic compositions of chalcopyrite and pyrrhotite demonstrate that Cu, the primary ore-forming element, was mainly derived from magmatic–hydrothermal fluids. The stratiform orebodies display H–O–C–S–Pb–Cu isotopes consistent with the porphyry orebodies in the Dongguashan deposit, as well as in the Chaoshan and Hucun deposits, indicating a common ore genesis. From these, we conclude that the porphyry–skarn–stratabound-type Cu–Au–Mo deposits in the Shizishan orefield can be classified as a unified Mesozoic magmatic–hydrothermal metallogenic system. The stratabound-type copper sulfide deposits and the porphyry–skarn-type copper deposits in the MLYMB have a strong similarity in the source and genesis of their ore-forming elements.

In Situ LA-ICP-MS U-Pb Geochronology, Sr-Nd-Hf Isotope and Trace Element Analysis of Volcanic Rocks from the Gacun Volcanic-Hosted Massive Sulfide Deposit in Sichuan, China

The Gacun deposit is a typical Volcanic Hosted Massive Sulfide (VHMS) associated with Late Triassic seafloor calc-alkaline felsic volcanics. Studies of zircon ages, petrology, major and trace element geochemistry, and Sr-Nd-Hf isotope geochemistry of volcanic rocks from the Northern Yidun arc were undertaken in this paper. We reshaped the Gacun magmatic system activity time, defined the origin of magma evolution, and proposed a metallogenic model of the deposit. Whole-rock major element compositions of the magmatic rocks in the Northern Yidun island arc indicate that they are a complete basalt–andesite–dacite–rhyolite assemblage, showing three obvious stages of composition evolution. They are enriched in large-ion lithophile and light rare earth elements, but depleted in high field-strength and heavy rare earth elements, with weak-to-negligible Eu anomalies (obvious in rhyolite). These geochemical features indicate that the Northern Yidun island arc is a magmatic arc based on ancient continental crust. The Ganzi–Litang oceanic subduction induced mantle melting and produced calc-alkaline basaltic magma, while the MASH processes at the bottom of the crust produced andesitic magma. Part of the andesite magma erupted to form andesite lava. The remaining part was mixed with magma produced via anatexis of ancient crust (approximately 20%–40% of the ancient crustal component), forming the ore-bearing rhyolite. Zircon U-Pb age data defines Gacun magmatic–hydrothermal mineralization sequence of events: At 238 Ma, arc magmatism led to the formation of andesite in the eastern part of the deposit. At 233 Ma, in the arc zone (the western part of Gacun deposit), a large-scale bimodal magmatism formed the main ore-bearing rock series of Gacun deposit, rhyolitic volcanic rocks. At 221 Ma, volcanic eruptions tended to end and sub-volcanic intrusion occurred, forming a lava dome, which was located under the ore-bearing rhyolitic volcanic rocks. The lava dome acted as a thermal engine and promoted hydrothermal circulation. The hydrothermal activity reached a peak at 217 ± 1 Ma, and the Gacun VHMS deposit was formed.

The Genetic Link between Iron-Oxide–Apatite and Porphyry Cu–Au Mineralization: Insight from the Biotite–Pyroxene–Zircon Study of the Nihe Fe Deposit and the Shaxi Cu–Au Deposit in the Lower Yangtze Valley, SE China

Different ore deposit types may evolve from a common magmatic-hydrothermal system. Establishing a genetic link between different deposit types in an ore cluster can not only deepen the understanding of the magmatic-hydrothermal mineralization process but can also guide exploration. Both the Nihe iron-oxide–apatite (IOA) deposit and the Shaxi porphyry Cu–Au deposit in the Lower Yangtze Valley, Anhui, Southeast China, formed in the Luzong Cretaceous volcanic basin at ~130 Ma. We examined a temporal–spatial and potential genetic link between these deposits based on stratigraphic lithofacies sections, biotite and clinopyroxene mineralogical chemistry, zircon chronology, Hf isotopes, and trace elements. Stratigraphy, petrology, mineralogical chemistry, and available fluid inclusion results support that the emplacement depth of the Nihe ore-related porphyry is shallower than that of the Shaxi porphyry. The magmatic zircon and hydrothermal zircon from Nihe provided U–Pb ages of 130.6 ± 0.7 Ma and 130.7 ± 0.7 Ma, respectively. The magmatic zircon U–Pb age (130.0 ± 0.8 Ma) of Shaxi overlaps with its molybdenite Re–Os age (130.0 ± 1.0 Ma). The agreement between the mineralization and porphyry emplacement ages of Nihe and Shaxi indicates a temporal coincidence and supports a possible genetic link between the two deposits, considering their close spatial relationship (in the same ore district, 15 km). The zircon Hf isotopes and trace elements support the evolution of both deposits from an enriched lithospheric mantle, although the Shaxi deposit may have experienced contamination of the Jiangnan-type basement. Both deposits lie above the fayalite-magnetite-quartz buffer, but the Nihe magmatic zircons are of lower temperature and less oxidized than that of Shaxi. The much higher Eu/Eu* and Yb/Dy values of zircons from Shaxi are likely caused by the suppression of early plagioclase crystallization and the prevalence of amphibole fractionation, thus indicating more hydrous content of the Shaxi ore-related magma. Additionally, the Shaxi ore-related porphyry has higher zircon Hf concentrations, suggesting that the porphyry Cu–Au deposit has experienced a greater degree of magma fractionation. Our study highlights that the Nihe IOA deposit and the Shaxi porphyry Cu–Au deposit have a common magma source, while different extent of crust contamination, magma oxidation state, hydrous content, and degree of magma fractionation collectively result in the two distinct ore deposits. This possible genetic link suggests a great potential of porphyry Cu–Au-PGE mineralization in the Middle–Lower Yangtze River metallogenetic belt, especially in the deep part of the IOA district in the Luzong Cretaceous volcanic basin.

Characteristics of REEs and Trace Elements in Scheelite and Muscovite Ar–Ar Isotopic Dating of the Daping Tungsten Deposit

The recently discovered Daping tungsten deposit is located about 25 km north of Tongcheng County, Hubei Province, in the northern margin of the Sijiapu granite deposit of the Mufushan composite batholith. The ore body is produced in the northeast-oriented greisenization granite and quartz vein, and belongs to the greisen-vein-type scheelite deposit. The resources of the Daping W deposit have a value of 7935 t W and the average grade is 0.201% WO3. Based on mineralogical and petrographic studies, scheelite is classified into two types. A study of the geochemical characteristics of rare earth elements (REEs) and trace elements indicated that some scheelite specimens showed LREE depletion. Meanwhile, the total amount of scheelite rare earth elements (REEs) is low and the ratio of LREE/HREE ranges from 0.40~2.72 in the Daping W deposit. The contents of REEs and trace elements in the two types of scheelite differ significantly. Type I scheelite has an average ∑REE content of 195.65 ppm, an LREE/HREE value of 0.5, an Eu anomaly (δEu) of 0.78, Mo of 366.20 ppm, Sn of 22.62 ppm, and Sr of 264.80 ppm. However, type II scheelite features an average ∑REE of 111.28 ppm, an LREE/HREE ratio of 1.43, a δEu of 1.56, Mo of 188.48 ppm, Sn of 0.15 ppm, and Sr of 829.93 ppm. The content level of Mo in the two types of scheelite is not high, indicating that this whole metallogenic environment is a reduction environment. However, this is a complex process. The presence of type I scheelite with negative Eu anomalies and relatively high Mo content indicates that the ore-forming environment in the early period of the greisen stage was relatively oxidizing. In contrast, type II scheelite contains large amounts of Sr and large positive Eu anomalies, which are likely to be released from plagioclase in the granite during greisenization. The extremely low composition of Mo in type II scheelite is closely related to the reducing environment in the later period of the greisen stage. Because Mo probably exists in its Mo4+ state, it may be difficult for it to replace W6+ in the scheelite lattice. Additionally, comparing the contents of Sn and Sr in different types of scheelite shows that the metallogenic environment changes from relative oxidation to the reduction of scheelite. The variation in trace elements and REEs in scheelite over time reflects a complex magmatic–hydrothermal mineralization environment. Additionally, the Ar–Ar system dating results for muscovite that is closely associated with scheelite in the greisenization granite vein indicate that a muscovite 40Ar/39Ar plateau age of about 133 Ma represents the time of tungsten mineralization. This muscovite 40Ar/39Ar dating result is close to the previous zircon U-Pb age data of the biotite monzogranite (ca. 140–145 Ma), which is the largest intrusion in the orefield. Meanwhile, the new age data reported here confirm that the Daping tungsten deposit represents a Mesozoic magmatic–hydrothermal mineralization event with a setting of lithospheric extension in the Mufushan composite batholith.

Post-collisional magmatic-hydrothermal mineralization in the São Gabriel Terrane (southern Brazil): Insights from mineral chemistry, stable isotopes, and sulfide trace-elements of the Caçapava do Sul skarns

Prograde and retrograde magnesian skarns associated with the Caçapava do Sul Granitic Complex intrusion (central Dom Feliciano Belt, southern Brazil) host Cu–Fe (Mo–Au) mineralization. Vein and contact prograde skarns contain disseminated pyrite, pyrrhotite, molybdenite, and chalcopyrite formed from the interaction of mafic and felsic intrusions and dolomitic marbles at ca. 578 Ma. The prograde skarn mineralization is mainly localized in fold hinges and pinch-and-swell structures. Retrograde skarns host massive chalcopyrite and pyrite with chlorite and calcite associated with brittle structures at ca. 557 Ma. In this contribution, we provide mineral chemistry analyses of magmatic and skarn assemblages, calcite stable isotope analyses, and trace-element characterization of pyrite and chalcopyrite to assess ore-forming processes involved in the formation of the skarns. Amphibole-plagioclase geothermobarometry in granodiorite and monzonite apophyses of the Caçapava do Sul Granitic Complex yielded crystallization pressures between 4 and 5 kbar and temperatures from 680 to 750 °C. Biotite and amphibole composition of granodiorite, monzonite, and garnet-leucogranite apophyses suggest a trend of decreasing oxygen fugacity from early to late intrusions. Calcite-dolomite solvus thermometry in prograde skarns indicates temperatures between 580 and 630 °C whereas chlorite thermometry in retrograde skarn yields lower temperatures between 280 and 310 °C. Calcite from the retrograde skarns shows values of approximately −5.5‰ for δ13CVPDB and ∼9.0‰ for δ18OSMOW, indicating a major contribution of magmatic fluids during the retrograde stage whereas previous studies indicate a mixed igneous-sedimentary character of the calcite in prograde skarns. Our findings propose a multiphase magmatic-hydrothermal origin for the Cu–Fe (Mo–Au) skarn mineralization hosted by the Passo Feio Metamorphic Complex. The prograde and retrograde magnesian skarns of Caçapava do Sul were formed in the same age interval (578 - 557 Ma) as many other magmatic-hydrothermal base and precious metals mineralization in the São Gabriel Terrane. Hence, we suggest that the studied skarns belong to a multi-intrusive Cu-porphyry system in the São Gabriel Terrane formed during the post-collisional stage of the Dom Feliciano Belt.

Mineralogical, magnetic and geochemical data constrain the pathways and extent of weathering of mineralized sedimentary rocks

The oxidative weathering of sulfidic rock can profoundly impact watersheds through the resulting export of acidity and metals. Weathering leaves a record of mineral transformation, particularly involving minor redox-sensitive phases, that can inform the development of conceptual and quantitative models. In sulfidic sedimentary rocks, however, variations in depositional history, diagenesis and mineralization can change or overprint the distributions of these trace minerals, complicating the interpretation of weathering signatures. Here we show that a combination of bulk mineralogical and geochemical techniques, micrometer-resolution X-ray fluorescence microprobe analysis and rock magnetic measurements, applied to drill core samples and single weathered fractures, can provide data that enable the development of a geochemically consistent weathering model.This work focused on one watershed in the Upper Colorado River Basin sitting within the Mesaverde Formation, a sedimentary sandstone bedrock with disseminated sulfide minerals, including pyrite and sphalerite, that were introduced during diagenesis and subsequent magmatic-hydrothermal mineralization. Combined analytical methods revealed the pathways of iron (Fe), carbonate and silicate mineral weathering and showed how pH controls element retention or release from the actively weathering fractured sandstone. Drill core logging, whole rock X-ray diffraction, and geochemical measurements document the progression from unweathered rock at depth to weathered rock at the surface. X-ray microprobe analyses of a 1-cm size weathering profile along a fracture surface are consistent with the mobilization of Fe(II) and Fe(III) into acidic pore water from the dissolution of primary pyrite, Fe-sphalerite, chlorite, and minor siderite and pyrrhotite. These reactions are followed by the precipitation of secondary minerals such as of goethite and jarosite, a Fe-(oxyhydr)oxide and hydrous Fe(III) sulfate, respectively. Microscale analyses also helped explain the weathering reactions responsible for the mineralogical transformations observed in the top and most weathered section of the drill core. For example, dissolution of feldspar and chlorite neutralizes the acidity generated by Fe and sulfide mineral oxidation, oversaturating the solution in both Fe-oxides. The combination of X-ray spectromicroscopy and magnetic measurements show that the Fe(III) product is goethite, mainly present either as a coatings on fracture surfaces in the actively weathering region of the core or more homogeneously contained within the unconsolidated regolith at the top of the core. Low-temperature magnetic data reveal the presence of ferromagnetic Fe-sulfide pyrrhotite that, although it occurs at trace concentrations, could provide a qualitative proxy for unweathered sulfide minerals because the loss of pyrrhotite is associated with the onset of oxidative weathering. Pyrrhotite loss and goethite formation are detectable through room-temperature magnetic coercivity changes, suggesting that rock magnetic measurements can determine weathering intensity in rock samples at many scales. This work contributes evidence that the weathering of sulfidic sedimentary rocks follows a geochemical pattern in which the abundance of sulfide minerals controls the generation of acidity and dissolved elements, and the pH-dependent mobility of these elements controls their export to the ground- and surface-water.

Mapping hydrothermal alteration of the Au-Cu deposits in the Zhenghe magmatic-hydrothermal mineralization system, SE China, using Short Wavelength Infrared (SWIR) reflectance spectroscopy

Magmatic–hydrothermal mineralization developed in Zhenghe area, where a potential of blind porphyry Cu polymetallic deposits is expected. To explore alteration characteristics and their relationship with mineralization, alteration mineral mapping with the help of SWIR reflectance spectroscopy was carried out in the Dongji Au deposit, the Maluntou Au deposit, the Shizigang Cu polymetallic deposit, and the Dongkeng volcanic basin. The results suggest that illite ± chlorite assemblage predominates in the Dongji deposit, whereas phengitic illite ± chlorite ± epidote occurred in the Maluntou deposit. Chlorite ± epidote ± actinolite developed pervasively in the Shizigang deposit. The alteration feature and ore geology indicate the Dongji and Maluntou deposits formed in a low-intermediate sulfidation epithermal environment with moderate-low temperatures. Maluntou is more likely approached to a heat source. Four alteration zones including potassic–silicic zone, propylitic zone, phyllic zone, and surficial argillic zone are divided, and a heat center is roughly inferred in the Shizigang district, suggesting a proximal porphyry-hydrothermal alteration style.A model demonstrating mineralization and alteration is established, along with mineral spectral vectors to mineralization. Illite with Pos2200 (wavelength of sericite Al-OH absorption peak position) of about 2203 nm is correlative with Au mineralization in the Dongji deposit and phengitic illite with Pos2200 ranging from 2215 nm to 2219 nm is the product of metallogenesis in the Maluntou deposit. Illite with Pos2200 of approximately 2205 nm–2206 nm in the Nanyuan Formation and illite with Pos2200 of about 2207 nm in the Huangkeng Formation are formed in the non-mineralization stage or weathering. Muscovite with the Pos2200 of roughly 2206 nm has the potential to be an orebody vector in the Shizigang district. Pos2250 (wavelength of chlorite Fe-OH absorption peak position) variation in the Shizigang district indicates the location of drill hole ZK1-1 is approximal to the hydrothermal center.Shizigang Cu, Maluntou Au, Dongji Au, and other deposits in Zhenghe are probably part of an integrated metallogenic system with epithermal-porphyry features. High-intensity magmatic-hydrothermal activity indicates the potential for deep prospecting in the region.

The Chemical Characteristics and Metallogenic Mechanism of Beryl from Cuonadong Sn-W-Be Rare Polymetallic Deposit in Southern Tibet, China

The Cuonadong deposit is the first large scale Sn-W-Be rare polymetallic deposit located in southern Tibet, China, where beryl is the main beryllium-bearing mineral. In this paper, the beryl crystals in the pegmatitic and hydrothermal vein orebody from the Xianglin area of the Cuonadong deposit are the research objects, marked as Beryl-I and Beryl-II, and they are investigated by EPMA, LA-ICP-MS and in situ micro-X-ray diffraction (XRD). Data by EPMA and LA-ICP-MS reveal that beryls from this area are alkaline beryls, among which Beryl-I is composed of Li-Cs beryl, and Beryl-II is composed of Na beryl and Na-Li beryl, indicating that beryls have undergone noticeable alkali metasomatism during formation. The Cs/Na ratio in Beryl-I ranges from 0.10 to 0.44, and the Mg/Fe ratio is almost 0, showing that Beryl-I is formed under high-differentiation evolution conditions and is rarely affected by hydrothermal transformation, whereas the Mg/Fe ratio in Beryl-II ranges from 2.73 to 17.31, and the Cs/Na ratio is nearly 0, indicating that Beryl-II has been obviously affected by late hydrothermal metasomatism. In situ XRD analysis shows that both Beryl-I and Beryl-II are t-beryl, and the c/a ratio of Beryl-I (1.0010–1.0012) is slightly higher than that of Beryl-II (1.0005–1.0008), which may also reflect the transition from magmatism to hydrothermal metasomatism in the late stage of pegmatitic magmatism. Based on comprehensive analysis, we believe that the precipitation of Beryl-I is mainly caused by the emplacement of highly fractionated magma containing Be to the top of the rock mass or surrounding rock, the melt-fluid undercooling, and the crystallization of volatile-bearing minerals (such as tourmaline and fluorite). Moreover, the Be-bearing ore-forming fluid has further migrated upward along the near north–south faults formed in the middle Miocene (16–15 Ma), during which Beryl-II precipitates owing to the hydrothermal water mixing, the ore-forming fluid cooling, and large amounts of crystallization of volatile-bearing minerals (mainly fluorite). Therefore, it can be concluded that beryl mineralization largely reflects the process of magmatic–hydrothermal mineralization. Because of a large number of mineralized areas with the similar metallogenic backgrounds to the Cuonadong deposit in the Himalayan region, it has great potential to be a new globally significant rare metal metallogenic belt.

Multiple isotopic dating constrains the time framework (Age) of a porphyry system: A case study from the Sangri Cu-Mo deposit, Bangongco-Nujiang metallogenic belt, Tibet, China

Obtaining a precise time framework has been a key but difficult problem for the study of metallogenic porphyry systems. This is more complicated when there are several stages of intrusion emplacement, different alterations, and mineralization events. To solve this problem, the Sangri porphyry-skarn Cu-Mo deposit in the Bangongco-Nujiang metallogenic belt, Tibet, was used as a study site for multiple isotopic dating studies. Zircon U-Pb dating of different intrusions shows that the magmatism of intermediate-felsic intrusions dates from 83.2 ± 0.8 Ma to 81.7 ± 0.7 Ma. Garnet U-Pb dating places the skarn as being formed in 83.2 ± 2.3 Ma. Re-Os dating of molybdenite in quartz-molybdenite vein and Ar-Ar dating of K-feldspar indicate ore-forming and alteration periods of 82.6 ± 0.6 Ma and 80.3 ± 1.8 Ma, respectively. The Sangri deposit is a product of magmatic-hydrothermal mineralization between 84 and 80 Ma in the Late Cretaceous. The mineralization of the Sangri deposit and precise geochronology data indicate that there was a Late Cretaceous metallogenic event in the Central Bangongco-Nujiang metallogenic belt, which provides a new clue for regional exploration and metallogeny. Finally, multi-element isotopic dating is shown to be an important method for constructing the time framework of porphyry systems.

Ta-Nb mineralization in the shallow-level highly-evolved P-poor Shihuiyao granite, Northeast China

The Shihuiyao granite district in the southern Great Xing'an Range, Northeast China, is a newly discovered area of rare-metal-bearing granites (RMG). The latest Jurassic Shihuiyao granitic pluton, emplaced into the Lower Permian Linxi Formation, comprises porphyritic granite, leucogranite, and amazonite-bearing pegmatite, all enriched in rare metals (mainly Ta, Nb, Rb). The Shihuiyao granites are peraluminous (A/CNK = 1.02–1.27), characterized by high contents of SiO2 (69.4–78.0 wt%), Al2O3 (12.7–16.9 wt%) and total alkalis (6.8–12.8 wt%), enriched in Ta, Nb, Rb, Cs, and Sn, but depleted in Ba and Sr. They have strong negative Eu anomalies (Eu/Eu⁎ = 0.02–0.42) and show the M-type REE tetrad effect. Low Nb/Ta (<4) and Zr/Hf (<8) values indicate high degree of magmatic fractionation. Whole-rock and mineral compositions variations indicate that the Shihuiyao granites are a typical low pressure and P-poor RMG, which experienced intensive magmatic fractionation followed by intensive hydrothermal reworking. The narrow range of δ7Li values (−0.86‰ to 0.88‰) and Rayleigh distillation modeling suggest that the porphyritic granite and leucogranite represent products of the same magma source, but evolved independently at depth. LA-ICP-MS UPb dating of monazite from the porphyritic granite and leucogranite yield lower-intercept ages of 150.2 ± 0.6 Ma and 147.0 ± 1.7 Ma, respectively. The 40Ar39Ar plateau ages of mica from leucogranite (146.3 ± 1.1 Ma) and an ore-bearing quartz vein (145.6 ± 1.0 Ma), and the UPb age of columbite (146.7 ± 4.7 Ma) further identify this as a latest Jurassic magmatic-hydrothermal mineralization event in NE China. Rapid crystallization and chemical quenching of magma resulted in neutralization of the acid fluoride solution, and a loss of the fluoride ligand during fluid evolution. This further triggered the subsequent crystallization of NbTa oxides. As revealed from geochemical and textural characteristics of the columbite group minerals, the high-degree of fractional crystallization and Ta-rich hydrosilicate fluid metasomatism are the main factors leading to the enrichment of TaNb within Shihuiyao RMG. In general, we conclude that rare metal-hosted magmatism took place in two episodes in NE China, namely, (i) Latest Jurassic to Early Cretaceous (150–130 Ma) peraluminous to metaluminous Ta-Nb-Sn-W RMG, and (ii) Early Cretaceous (130–120 Ma) alkaline Nb-Ta-Be-REE-Zr RMG, which highlight the prospecting fertility for Nb-Ta-REE (SnW) mineralization in NE China.