Episodes Of Mineralization Research Articles

Long-lived Nb-Ta mineralization in Mufushan, NE Hunan, South China: Geological, geochemical, and geochronological constraints

The Mufushan Complex (MFSC), located in northeastern Hunan, is a significant producer of Nb-Ta-Li-Be rare metals in South China. The present study examines the genetic relationship, material provenance, fluid evolution, and metallogeny of the co-developed ore-free pegmatite (OFP) and ore-bearing pegmatite (OBP) in granite-related pegmatite-type Nb-Ta rare-metal deposits in MFSC. Three minerals (columbite-tantalite (coltan), zircon, and monazite) were chosen for analysis. The coltan grains display both primary crystallization structures (crystal homogeneity, oscillatory zonings, and primary growth rims) resulting from equilibrium and disequilibrium reactions due to localized changes in the physicochemical conditions and environment, as well as later replacement structures (alteration rims, patches, irregular zonations, and complex zonations) from metasomatic replacement processes related to hydrothermal fluid activity. The coltan yielded two weighted mean 206Pb/238U ages of 138.1 ± 2.1 Ma and 125.3 ± 2.0 Ma corresponding to magmatic and hydrothermal Nb-Ta mineralization ages. For the OFP, zircons also yielded two weighted mean 206Pb/238U ages of 138.4 ± 0.8 Ma and 131.5 ± 0.7 Ma, whereas monazite gave a weighted mean U-Pb age 142.9 ± 1.2 Ma. The ages of 142–138 Ma and 131 Ma represent the early and late stages of OFP crystallization and barren pegmatites in the MFSC, respectively. Zircon Lu-Hf isotopic compositions link rare-metal metallogenesis to the Lengjiaxi Group, which was the source material to the Mufushan composite batholith. Calculated εHf(t) values and TDM2 ages from the OFP (−7.6 to −3.6 and 1676–1418 Ma, respectively) and the OBP (−14.1 to +4.9 and 2976–1548 Ma, respectively) are akin to those of schists and metasandstones of the metasedimentary Lengjiaxi Group. We propose a long-lived (ca. 13-Myr) event involving two metallogenic episodes of Nb-Ta mineralization in the Mufushan region. This study demonstrates the potential of zircon, coltan, and monazite for fingerprinting minerals and classifying the mineralization potential of pegmatite veins.

A New Alpine Metallogenic Model for the Pb-Ag Orogenic Deposits of Macôt-la Plagne and Peisey-Nancroix (Western Alps, France)

Understanding mass transfer associated with fluids circulation and deformation in the Alpine orogeny is often complex due to common multistage crystallization. For example, in two emblematic and historic Pb-Ag deposits of the French Alps, Macôt-la Plagne (MP) and Peisey-Nancroix (PN), a sedimentary or orogenic origin is still debated. To discriminate between the metallogenic models of the two deposits, an integrative methodology combining field, microstructural, mineralogical, thermobarometrical, and geochronological data was here applied for establishing detailed Pressure–Temperature–Time–Deformation (P-T-t-d) mineralization conditions. Both deposits are located in Permo-Triassic quartzite of the External Briançonnais domain along the Internal Briançonnais Front (Internal Western Alps). The ore mainly occurs as veins and disseminated textures containing galena, pyrite, and variable content of tetrahedrite–tennantite and chalcopyrite. Quartz porphyroclasts and sulfide microstructures indicate a dynamic recrystallization of the quartzite during the main fluid mineralization episode. Chlorites and K-white micas (phengite) chemical analysis and thermodynamic modeling from compositional maps indicate an onset of the mineralization at 280 °C, with a main precipitation stage at 315 ± 35 °C and 6.25 ± 0.75 kbar. In situ U-Pb dating on monazite, cogenetic with sulfides, gives ages around 35 Ma for both deposits. The integrative dataset converges for a cogenetic MP-PN Alpine Pb-Ag mineralization during deformation in relation to the thrusting of the “Nappe des Gypses” and the Internal Briançonnais at the metamorphic peak.

Mesozoic magmatic and hydrothermal uranium mineralization in the Huayangchuan carbonatite-hosted U-Nb-polymetallic deposit, North Qinling Orogen (Central China): Evidence from uraninite chemical and isotopic compositions

The giant Huayangchuan deposit in the Qinling Orogen is a newly discovered U-Nb-polymetallic deposit mainly hosted in Triassic carbonatite. Petrographic, elemental, and isotopic composition analyses of uraninite were conducted to determine the formation and evolution of this deposit. At Huayangchuan, four types of uraninite are identified. Pristine Ur1 and Ur2 formed at 209 Ma and 131 Ma, representing two episodes of uranium mineralization. The early episode belongs to carbonatitic magmatic uranium mineralization. It was related to a mantle-derived, initially U-rich carbonatitic magma, which has been further enriched in U through a high degree of crystal fractionation. The late episode corresponds with a high-temperature hydrothermal U mineralization that is related to Early Cretaceous granitic intrusions in the region. This high-temperature fluid event was also responsible for the alteration of Ur1 into Ur1alt. The LREE/HREE ratio variation between Ur1 and Ur1alt indicates that this fluid may have been rich in F. The post ore alteration, characterized by the alteration of Ur2 into Ur2alt, was caused by a low-temperature F-free fluid. We propose that the early stage of U mineralization formed under a post-orogenic extensional environment following the collision between the Qinling and South China blocks, and the late stage of U mineralization corresponds to a long phase of lithospheric thinning due to westward subduction of the Paleo-Pacific Plate. Moreover, compared with other carbonatite-related uranium deposits in the world, the high U contents and low Th/U ratios inherited from the subducted oceanic crust may be critical factors that caused the formation of magmatic-origin uraninite in the Huayangchuan deposit.

Geology, C-H-O isotopes, and muscovite 40Ar-39Ar dating of the Qingbaishan gold deposit: Implications for tectonism and metallogenesis of early Devonian gold deposits in the Beishan orogen, NW China

The Beishan orogen is an economically important gold mineralization belt that hosts more than 20 gold deposits. Most Au orebodies occur within large-scale fault zones, indicating a correlation between structural evolution and gold mineralization. Previous studies have demonstrated that Au mineralization generally developed in the Permian–Triassic; however, pre-Permian gold mineralization and its temporal relationship with tectonic evolution remain poorly understood. The Qingbaishan deposit, located in the Beishan orogen, NW China, is hosted by the Sanjiashan shear zone. A detailed field-based structural analysis revealed that the Sanjiashan shear zone has thrust and sinistral strike-slip characteristics, such as asymmetrical folds and S-C fabrics. The muscovite 40Ar/39Ar age from auriferous quartz shows that the Qingbaishan gold system formed around 399.7 ± 1.6 Ma, consistent with the time of Sanjiashan sinistral ductile shearing in the Beishan orogen. The carbon and oxygen isotope compositions of auriferous quartz suggest that the host rocks within the Precambrian Gudongjin Group would have been a significant source of ore metals and that the low δ18O values in quartz resulted from fluid reactions with 18O-poor host rocks. The Qingbaishan Au deposit is concluded to be a strike-slip-dominated orogenic-type system related to continental collision between the Tarim and Kazakhstan–Ili plates.By integrating the age data obtained from this study with previous geochronological results, two episodes of gold mineralization in Beishan are distinguished: an early episode around 399 Ma, when sinistral strike-slip zone-related orogenic gold deposits formed in a syncollisional setting, and a late episode around 298–231 Ma, when dextral strike-slip deformation produced deposits in a postcollisional extensional setting.

Genesis of orogenic gold systems in the Daduhe belt: Evidence of long-lived fertile mantle lithosphere as a source of diverse metallogeny on the western margin of the Yangtze Craton, China

The poorly documented Daduhe gold belt on the western margin of the Yangtze Craton, an important metallogenic belt in southwest China, is characterized by typical orogenic gold systems against a highly anomalous geodynamic setting. A synthesis of regional and deposit geology, mineralization ages, and S-O isotopic compositions of 33 gold deposits from the Danba-Kangding-Shimian-Mianning area of the belt reveals regional metallogenic patterns, establishes a consistent genetic model, and demonstrates a source equivalent to other diverse mineral systems on the western margin of the Yangtze Craton. The Daduhe orogenic gold deposits are controlled by the lithosphere-scale Xianshuihe and Anninghe strike-slip faults in the northern and southern segments of the belt, respectively. The alteration and ore mineral assemblages of the Daduhe orogenic gold deposits define a wide range of hypozonal, mesozonal, and epizonal sub-types. They formed during two episodes: 1) Early Jurassic gold mineralization related to closure of the Paleo-Tethys Ocean, with a large hypozonal gold deposit on the margin of the Danba dome in the northern segment; 2) Cenozoic gold mineralization associated with continental collision on the Tibetan Plateau, with small mesozonal and epizonal gold deposits in shear zones in migmatite basement and at contacts with cover sequences in both the northern and southern segments. At the belt and deposit scales, the ore-controlling structures for both mineralization episodes are NNE-trending second-order extensional faults or their intersections with the dominant NW-trending compressional faults. The three deposit sub-types have overlapping δ34S of 0 ∼ 10‰, δ18Ofluid of 6 ∼ 11‰, and low He-Ar isotope ratios, all consistent with derivation of ore fluids from metasomatized mantle lithosphere. Importantly, the Daduhe orogenic gold deposits have similar S-O-He-Ar isotope compositions to the giant IOCG, Cu-Ni-PGE, Fe-V-Ti, anomalous porphyry Cu-Mo-Au, and carbonatite-related REE deposits in the Panxi region on the shared margin of the western Yangtze Craton. This suggests that these diverse mineral systems have a common source of ore fluids and metals derived from fertile mantle lithosphere during different geodynamic and metallogenic events. Such a widespread hydrous metal-rich deep source with lithosphere-scale faults as ore fluid pathways, and a depth continuum of orogenic gold deposits in the Daduhe belt suggest a high prospectivity and a higher future gold endowment for the belt. This study adds to an increasing awareness of the diversity of mineral systems on specific craton margins globally.

GEOCHRONOLOGY OF Sn MINERALIZATION IN MYANMAR: METALLOGENIC IMPLICATIONS

Abstract Myanmar, the third largest global tin supplier, is an important component of the Southeast Asian tin province. We have conducted laser ablation-inductively coupled plasma-mass spectrometry U-Pb dating of cassiterite, wolframite, and zircon and Re-Os dating of molybdenite from six primary and two placer Sn deposits in Myanmar. A combination of our geochronological data with previous studies revealed that three episodes of Sn mineralization in the Western tin belt of Southeast Asia formed during the closure of multiple Tethys oceans, namely the Late Triassic (~218 Ma) mineralization in a collisional setting after closure of the Paleo-Tethys, the Early Cretaceous (~124–107 Ma) mineralization during subduction of the Meso-Tethys, and the Late Cretaceous to Eocene (~90–42 Ma) mineralization related to the Neo-Tethys subduction. Recurrent Sn mineralization is recorded not only in the Western tin belt but also in the Central and Eastern tin belts in Southeast Asia. Compilation of currently available cassiterite U-Pb ages from all over the world revealed that durations of regional Sn mineralization events are typically in the range of ~5–30 m.y., whereas the Neo-Tethys subduction in Southeast Asia generated prolonged Sn mineralization lasting up to ~50 m.y. The Southeast Asian tin province, as a whole, has the longest cumulative episodes of mineralization, compared to other Sn provinces. The Sn mineralization ceased in the late Eocene when the tectonic setting changed from Neo-Tethys subduction to dextral motion along a series of strike-slip faults and extrusion of the Indochina block in Southeast Asia.

Mesozoic-Cenozoic exhumation history and its implications for the uranium mineralization in the southern Junggar Basin, North China

The phases of tectonic activity and exhumation of the southern margin of the Junggar Basin during the Cretaceous through Cenozoic shows significant relationships with the timing of uranium mineralization episodes. To clarify the succession of metallogenetic stages that were controlled by different phases of uplift and exhumation, apatite fission track (AFT) thermochronology was performed on the Jurassic through Cenozoic sediments from the Manas section in the southern Junggar Basin. The mean ages of the AFT suites range from 63 Ma to 133 Ma, and are younger than the host sediment for the Mesozoic samples and older than the host for the Cenozoic samples. The mean track lengths (MTLs) are between 10 and 11 μm. These results indicate that most of the apatite grain assemblages in these samples experienced complicated annealing histories. AFT ages were combined with thermal history modeling to unravel the timing of the multi-phase regional uplift and exhumation history and to reveal the tectonic constraints on the uranium mineralization. The populations of AFT single-grain ages display four peaks, which are interpreted as regional uplift and cooling episodes: mid-Early Jurassic (189–180 Ma), late Jurassic–early Cretaceous (157–116 Ma), late Cretaceous–early Paleocene (88–59 Ma) and late Eocene–early Oligocene (37–28 Ma). Thermal history modeling indicates two episodes of rapid cooling of the basin sediment deposits during the late Cretaceous–Paleocene (80–50 Ma) and the Pliocene (5 Ma)–Present. A synthesis of the temporal relationship between AFT age peaks, of the modeled time–temperature paths, of a compilation of age data and regional geologic events from the Tianshan mountain belt, suggests a close relationship between tectonic evolution and uranium mineralization. Uranium metallogenesis episodes occurred in conjunction with tectonic uplift and exhumation episodes along the southern margin of the Junggar Basin during the late Cretaceous–early Paleogene and during the latest Miocene-Present. The earlier episode was the primary mineralization stage, and the later episode was a partial transformation stage superimposed on the earlier one.

Mineralogy of Miocene Petrified Wood from Central Washington State, USA

Silicified wood occurs abundantly in Middle Miocene flows and sedimentary interbeds of the Columbia River Basalt Group (CRBG) in central Washington State, USA. These fossil localities are well-dated based on radiometric ages determined for the host lava. Paleoenvironments include wood transported by lahars (Ginkgo Petrified Forest State Park), fluvial and palludal environments (Saddle Mountain and Yakima Canyon fossil localities), and standing forests engulfed by advancing lava (Yakima Ridge fossil forest). At all of these localities, the mineralogy of fossil wood is diverse, with silica minerals that include opal-A, opal-CT, chalcedony, and macrocrystalline quartz. Some specimens are composed of only a single form of silica; more commonly, specimens contain multiple phases. Opal-A and Opal-CT often coexist. Some woods are mineralized only with chalcedony; however, chalcedony and macrocrystalline quartz are common as minor constituents in opal wood. In these specimens, crystalline silica filling fractures, rot pockets, and cell lumen may occur. These occurrences are evidence that silicification occurred as a sequential process, where changes in the geochemical environment or anatomical structures affected the precipitation of silica. Fossilization typically began with precipitation of amorphous silica within cell walls, leaving cell lumen and conductive vessels open. Diagenetic transformation of opal-A to opal-CT in fossil wood has long been a widely accepted hypothesis; however, in opaline CRBG specimens, the two silica polymorphs usually appear to have formed independently, e.g., woods in which cell walls are mineralized with opal-A but in which lumen contain opal-CT. Similarly, opal-CT has been inferred to sometimes transform to chalcedony; however, in CRBG, these mixed assemblages commonly resulted from multiple mineralization episodes.

Texture and morphology of veins and their relationship to gold mineralization in the Penjom deposit, Malaysia

AbstractPenjom deposit is an orogenic gold deposit located in the Central Belt of Peninsular Malaysia. Gold mineralization is associated with various styles and textures of quartz‐carbonate veins hosted within the metasedimentary as the main host rock and felsic igneous rock including minor volcanic rock. Vein textural features and morphologies have been investigated based on macroscopic and microscopic characteristics to understand the process of veins formation, and the relationship with gold mineralization. At the hand specimen scale, veins show a variety of textures that are either primary or superimposed. Primary textures are comb, massive anhedral buck quartz veins, and laminae veins or vein septa representing early vein introduction without vein modification. Extension veins that are normally concordant to maximum compressive stress direction show either a common comb texture within these veins or buck texture inside thick veins. Secondary textures are ribbon, stylolites, breccias, and late spider veinlets that overprint early veins formed during repeated structural episodes. Later stage deformation events superimposed on the existing veins texture results in intensely deformed veins. The interrelationship of structure, vein‐type and texture, gold and sulfide mineralogy have been correlated to constrain the episodes of gold mineralization in the Penjom deposit. Characteristics of vein textures indicate physio‐environment under confining lithostatic pressure where fluids filled the space through crack and sealing mechanism. Vein systems and gold mineralization events that have been correlated with the D2D3 (fold‐fault) deformation events and inferred to be temporally related to the late‐stage regional orogenic event dated Late Triassic‐Early Jurassic that affected Peninsular Malaysia.

A critical comparison between the Fungurume 8 and 88 Cu-Co deposits, Central African Copperbelt

The Fungurume 88 deposit located in the Tenke-Fungurume Mining (TFM) district is situated in the northern extent of the Central African Copperbelt (CACB). It is an unusual sedimentary stratiform copper (SSC) deposit of this area, since it contains high-grade hypogene carrollite mineralization in the SD-1b subunit of the lower Shales Dolomitique (SD) Formation of the Mines Subgroup. These lithologies are normally regarded as being barren to poorly mineralized, here however, they boast cobalt concentrations as high as 3 wt% along with Cu concentrations in excess of 4 wt%. Detailed logging of drill core revealed that the sediments of the Fungurume 88 deposit which host the anomalous SD-1b mineralisation differ in both grainsize and mineralogy to the well-recognised Long Facies sediments exhibited by the majority of deposits in the TFM district - including the overlying Fungurume 8 deposit. Petrographic studies have revealed several distinct sulphide textures including the dominant disseminated style, stratiform style, bedding parallel jack veins and crosscutting veins. These sulphides also exhibit distinct trace element compositions suggesting several episodes of mineralization and support a multiphase hypogene Cu-Co model. The specific timings of the mineralisation events are constrained to an early phase (probably contemporaneous with diagenesis and early lithification) as well as a later phase associated with quartz-carbonate-sulphide veining and possibly linked to the regional brecciation event, and thus, in support of existing literature, indicate the presence of at least two mineralizing fluids. Host rock geochemistry obtained from SEM analyses together with LA-ICP-MS analyses on sulphide phases have helped to constrain the mineralizing process in the Fungurume 88 deposit by corroborating fluid-rock interaction, sulphide mineral paragenesis and trace element variation. Drill core assay data has also revealed prominent zonation and segregation between Cu and Co and the latter’s local enrichment observed in the SD-1b subunit. Metal zonation of this kind has also been described in some deposits of the Zambian copperbelt and are therefore used as a proxy here. The detailed petrographic analyses on the host rock shows that the sediments of the Fungurume 88 deposit potentially belong to the Kalumbwe, Menda or a geochemically similar deep marine sedimentary facies rather than the usual Long Facies. This lithological variation was likely the key ingredient, providing an optimal reducing environment or “trap site” for the precipitation of carrollite and other copper sulphides in the SD-1b subunit. These geological and geochemical observations provide insights into the genesis for the Fungurume 88 deposit, understood in a context of the regional geology and Cu-Co mineralisation throughout the greater Copperbelt. Moreover, it highlights that the northern apex of the Lufilian arc and the broader CACB hold vast exploration potential for similar deeper-water sub-basins which may host significant, and yet-undiscovered metal (notably Co) resources.

The Changshagou gold deposit, Eastern Tianshan, NW China: orogenic gold mineralization overprinting a porphyry gold occurrence

Abstract The temporal–spatial relationships of porphyry and orogenic gold mineralization in the Eastern Tianshan Orogenic Belt are ambiguous. The newly discovered Changshagou deposit in this belt contains both porphyry and orogenic gold mineralization, which are characterized by polymetallic–sulfide veinlets and quartz–pyrite veins, respectively. Fluid inclusions in the porphyry mineralization episode were trapped at 290–340°C with salinities of 3.0–8.0 wt% NaCl equiv . The homogenization temperatures and salinities in the orogenic mineralization episode range from 240 to 300°C and from 1.0 to 5.0 wt% NaCl equiv . Coexisting V- and L-type fluid inclusions with similar homogenization temperatures are indicative of fluid immiscibility. The δ 18 O w and δ D w values are in the ranges 7.6–9.1 and −70.9 to −84.0‰ in the porphyry mineralization episode, and 6.4–7.1 and −65.7 to −72.1‰ in the orogenic mineralization episode, overlapping magmatic and metamorphic ranges, respectively. The pyrite δ 34 S values range from 3.5 to 4.9‰, falling into the magmatic range. Pyrite in porphyry and orogenic mineralization episodes yield Re–Os isotope ages of 269.1 ± 2.9 and 257.4 ± 2.4 Ma. The porphyry and orogenic gold mineralizations are genetically associated with the quartz syenite porphyry and Kanggur strike-slip shear activity, respectively.

Genetic Environments of the Eunjeok Au–Ag Deposit in the Yeongam District: Implications for Cretaceous Epithermal Au–Ag Mineralization in South Korea

Eunjeok Au–Ag deposits are situated in the Yeongam district, Cheollanamdo-province, South Korea. They are genetically related to the Bulgugsa magmatic event (ca. 110–60 Ma), caused by the transition in the subduction direction and style of the Izanagi Plate. Three gold- and silver-bearing hydrothermal veins filled the fractures of the Cretaceous rhyolitic tuff. The major ore minerals were arsenopyrite (31.47–32.20 at.% As), pyrite, chalcopyrite, sphalerite (8.58–10.71 FeS mole%) and galena with minor amounts of electrum (62.77–78.15 at.% Au), native silver, and argentite. Sericitization was dominant in the alteration zone. The various textures of quartz veins (i.e., breccia, crustiform, comb, and vuggy) may indicate the formation of an epithermal environment. The auriferous fluids with the H2O–NaCl system have homogenization temperatures and salinities of 204 °C to 314 °C, less than 10 wt.% equiv. NaCl, and experienced mixing (dilution and cooling) events during mineralization. Considering the characteristics of the geologic setting, major fault system, and host rock, the Eunjeok Au–Ag deposit within the Yeongam district tends to share the general geologic characteristics of Haenam–Jindo epithermal mineralization episodes. However, the age of gold–silver mineralization (86.0 Ma) is older than that of Haenam–Jindo epithermal mineralization episodes (<70.3 Ma), implying some differences exist in the genetic sequence of extensional characteristics caused by transcurrent Gwangju–Yeongdong faults.

Redox-controlled antimony isotope fractionation in the epithermal system: New insights from a multiple metal stable isotopic combination study of the Zhaxikang Sb–Pb–Zn–Ag deposit in Southern Tibet

Redox reactions, biological processes, evaporation and precipitation processes, adsorption, and Rayleigh distillation mechanisms have been proposed to account for the fractionation of antimony (Sb) isotopes in natural materials. However, only one paper was published to support and characterize the Rayleigh distillation induced Sb isotopic fractionation in a hydrothermal system. Therefore, the Sb isotopic fractionation mechanism research in the epithermal system is still negligible, which severely restricts future application. The Zhaxikang Sb–Pb–Zn–Ag deposit is the only super-large deposit within the North Himalayan Metallogenic Belt (NHMB), which comprises two episodes of mineralization (First episode: Pb–Zn mineralization, Stages 1 and 2; Second episode: Sb mineralization, Stages 3 to 6). Herein, we measured the δ123SbNIST 3102A values of stage 4 sulfosalt minerals and stage 5 stibnite from the Zhaxikang Sb–Pb–Zn–Ag deposit, to resolve the fractionation direction and relative magnitude of Sb isotopes caused by these aforesaid geologically prominent mechanisms in the epithermal systems with an auxiliary investigation of Fe–Cu isotopes. The second episode of Sb-containing hydrothermal fluid has leached metals (e.g., Pb, Ag, Fe, Cu) from pre-existing Pb–Zn orebodies, to initiate the formation of stage 4 sulfosalt minerals. According to XPS (X-ray Photoelectron Spectroscopy) analyses, the Cu isotopic variation of stage 4 bournonite (0.08‰ – 0.89‰) must be controlled primarily by the reduction reaction (Cu2+ + e− → Cu+) during leaching and precipitation. Keeping in mind a good linear correlation between δ123Sb and δ65Cu values (R2 = 0.99) for bournonite, the same mechanism was used to decipher the variation in δ123Sb values (0.10‰ – 0.48‰) of bournonite (Sb5+ + 2e− → Sb3+). Abundant native sulfur within the orefield allowed for the overall reaction equation of CuFeS2 + FeS2 + PbS + Sb5+(aq) = CuPbSbS3 + Fe2+(aq) + 2S to describe the bournonite formation. Accordingly, the Sb isotopic variations (−0.27‰ to 0.48‰) of Sb-bearing minerals (boulangerite, bournonite and stibnite) were empirically attributed to redox reactions. The Rayleigh distillation model indicated that the observed fractionation was most likely induced by redox reactions, while the related theoretical calculations revealed a great antimony exploration potential in deeper parts of the orefield. Overall, the Sb isotopes could be used to identify redox changes in the epithermal system, and exhibit great potential in tracing metal sources, monitoring fluid evolution and ore formation, and providing insights into mineral exploration.

Shallow Rupture Propagation of Pleistocene Earthquakes Along the Hurricane Fault, UT, Revealed by Hematite (U‐Th)/He Thermochronometry and Textures

AbstractThe material properties and distribution of faults above the seismogenic zone promote or inhibit earthquake rupture propagation. We document the depths and mechanics of fault slip along the seismically active Hurricane fault, UT, with scanning and transmission electron microscopy and hematite (U‐Th)/He thermochronometry. Hematite occurs as mm‐scale, striated patches on a >10 m2 thin, mirror‐like silica fault surface. Hematite textures include bulbous aggregates and cataclasite, overlain by crystalline Fe‐oxide nanorods and an amorphous silica layer at the slip interface. Textures reflect mechanical, fluid, and heat‐assisted amorphization of hematite and silica‐rich host rock that weaken the fault and promote rupture propagation. Hematite (U‐Th)/He dates document episodes of mineralization and fault slip between 0.65 and 0.36 Ma at ∼300 m depth. Data illustrate that some earthquake ruptures repeatedly propagate along localized slip surfaces in the shallow crust and provide structural and material property constraints for in models of fault slip.

Oligocene Nb-Ta-W-mineralization related to the Xiaruleucogranite in the Himalayan Orogen

<p indent=0mm>Himalayan leucogranites are abundant within a ~2000-km-long, E-W trending belt on the Tibetan Plateau. Recently, it has been shown that several leucogranites and pegmatites (including aplites) of the Himalayan leucogranitic belt are closely related to rare-metal mineralization. The leucogranites and pegmatites are commonly peraluminous to strongly peraluminous, classifying as highly-fractionated granites in terms of whole-rock geochemistry and characteristic mineral assemblage with phases such as garnet, mica, zircon and oxides. The leucogranites contain typical rare-metal-bearing minerals formed during the magmatic-hydrothermal stage, including spodumene, beryl, columbite-group minerals (CGMs), cassiterite, and wolframite, associated with Li-, Be-, Nb-Ta-, Sn- and W-mineralization. Multiple episodes of magmatism and mineralization (~25−12 Ma) have been identified for the leucogranites. Nevertheless, our understanding of the rare-metal mineralization in the Himalayan orogeny and its age range remains limited. The Xiaru Dome, which crops out in the central part of the northern Himalaya, is mainly composed of middle-high grade metasedimentary rocks and granitic gneiss. Intrusions of tourmaline-garnet-bearing leucogranite and Be-Nb-Ta pegmatite are relatively common. Beryl and CGMs have been previously observed within pegmatite with the total Nb₂O₅ and Ta₂O₅ contents of up to ~0.014wt%. During recent field work, Nb-Ta-W-bearing tourmaline granite/pegmatite was found for the first time. To further constrain the leucogranite evolution and related Nb-Ta-W mineralization, we have studied the rock-forming and ore-forming phases of the Nb-Ta-W-bearing leucogranite/pegmatite and country rock granitic gneiss. We have characterized whole-rock geochemical compositions, the textures and the chemical compositions of the Nb-Ta-W oxide minerals, and complemented these by U-(Th-)Pb dating of CGMs, zircon and monazite. Our work shows that the granitic samples are peraluminous (ACNK =1.06−1.26), with high silica (SiO₂ = 72.2wt%−75.5wt%) and alkali contents (Na₂O+ K₂O = 8.4wt%−9.4wt%). They contain high concentrations of B, Nb, Ta and W (780×10⁻⁶, 58×10⁻⁶, 17×10⁻⁶ and 67×10⁻⁶, respectively), which are hosted in schorl, CGMs, wolframoixiolite, qitianlingite, and wolframite. Zircon and monazite U-(Th-)Pb dating shows that the leucogranites formed at ~530−387, ~44, and ~36−35 Ma, indicating multiple episodes of magmatism for the Xiaru intrusions, while U-Pb dating of CGMs reveals that the Nb-Ta mineralization related to the Xiaru leucogranites occurred exclusively at ~34−33 Ma. The Oligocene Nb-Ta mineralization of the Xiaru district is thus the oldest (earliest) rare-metal mineralization related to Himalayan leucogranites ever discovered. We highlight that the ore-forming age is best determined by dating ore-minerals directly instead of associated zircon or monazite. We conclude that a high B concentration in the parental magma possibly permitted high fractionation of the magma and concentration of Nb and Ta. Magmatic columbite formed early, which was later metasomatically altered by Ca-W-F-rich fluids. At the hydrothermal stage, a characteristic mineral assemblage formed, including qitianlingite, wolframite, scheelite, and microlite. The enrichment of W in the local granitic gneiss, located adjacent to the Nb-Ta-W-bearing granite, is possibly related to the ingression of W-bearing fluids from the leucogranite. Compared with skarn-type W mineralization related to the Cuonadong pluton in the eastern Himalayan orogen, there are at least two types of W mineralization related to the Himalayan leucogranites: Skarn-type and granite-type. The discovery of Nb-Ta-W mineralization related to the leucogranite/pegmatite in the Xiaru gneiss dome deepens our understanding of Himalayan rare-metal mineralization and provides the basis for exploration of similar mineralization types elsewhere in the Himalayan Orogen.

Multiple Hydrothermal Iron-Formation Upgrading Events in Southeastern São Francisco Craton

Large-scale, hypogene iron mineralization systems developed recurrently in the São Francisco craton in association with two orogenies. During the ca. 2.1–2.0 Ga Trans-Amazonian orogeny, low-temperature and low-to-moderate-salinity metamorphic fluids resulted in carbonatization-related iron enrichment of the early Paleoproterozoic Cauê Iron Formation (IF) of the Minas Supergroup (MSG) as well as short-distance iron mobilization. Monazite from the iron-oxide veins yielded a SHRIMP 232Th/208Pb date corresponding to fluid circulation coeval with the migmatization of the Archean tonalite-trondhjemite-granodiorite crust. During the Ediacaran to Cambrian Brasiliano orogeny, when the São Francisco craton was consolidated in its present configuration, hydrothermal fluids repeatedly mineralized the Cauê IF and the younger IFs of the lower Espinhaço Supergroup. Far-field hydrothermal alteration associated with distinct Fe mineralization episodes widely affected Meso- to Neoproterozoic sequences as well as Archean to Paleoproterozoic terranes of the cratonic core. Circulation of hydrothermal fluids during the Brasiliano orogeny caused desilicification, iron mobilization, and widespread alteration of the rocks. The alteration events are dated with monazite and xenotime intergrown with hematite, anatase, and recrystallized rims of detrital zircons from interlayered quartzites and of igneous zircons from pegmatites, granites, acidic volcanic rocks, and orthogneisses, yielding U-Pb dates between 542 and 493 Ma. U-Pb dates point to five Cambrian hydrothermal events from the waning stages to the aftermath of the Brasiliano orogeny. These hydrothermal fluid circulation events correspond to the emplacement ages of four granite suites and pegmatites that lasted from the final stages of the collision to the collapse of the Araçuaí-West Congo orogen. Episodic circulation of fluids continued for approximately 2 billion years after IF deposition on the eastern São Francisco craton with the formation of high-grade iron ore deposits and resetting of the IF trace-element inventory.

Multiple episodes of hydrothermal alteration and uranium mineralization in the Singhbhum Shear Zone, eastern India: constraints from chemical and boron isotope composition of tourmaline

In this study, the chemical and B-isotope composition of tourmalines that coprecipitated with uraninite in schistose rocks of the Mohuldih and Bagjata uranium deposits along the Singhbhum Shear Zone are used to constrain the sources and the nature of the mineralizing fluids, along with the mechanism of primary uraninite precipitation. Three generations of tourmaline are identified, which can be correlated with three generations of uraninite in the host rocks. These correspond to three major episodes of hydrothermal alteration of the shear zone rocks at 1.8-1.9 Ga, 1.66-1.56 Ga, and ca. 1.0 Ga, synchronous with metamorphism/granitoid activity. The texturally earliest tourmaline with δ11B of 8.8 ± 0.3 ‰ precipitated together with primary uraninite from externally-sourced high saline fluids derived from subducting slab during the 1.8–1.9 Ga hydrothermal alteration event. The precipitation of uraninite can be linked to the decreasing salinity of the hydrothermal fluid as a consequence of fluid-rock interaction. Dissolution of chlorite/biotite and the precipitation of more Mg-rich tourmalines resulted in decrease of fluid salinity, which destabilized Fe-chloride and U-chloride complexes leading to the precipitation of Fe-rich tourmaline together with primary uraninite. The texturally later second and third generation tourmalines (δ11B = 2.5 to 6.3 ‰) and uraninites formed from mixed fluids derived from the slab and dehydration of pelitic assemblages during renewed episodes of hydrothermal alteration synchronous with metamorphism at 1.66-1.56 Ga and ca. 1.0 Ga. The δ11B of the tourmalines from the schists of the Singhbhum Shear Zone correspond to the range of values (–10.4 ‰ to +6.0 ‰) reported for IOCG-type deposits associated with metamorphic slab-derived fluid sources.

Control of basement on Paleozoic mineralizations in the Wuyi metallogenic belt

The Wuyi metallogenic belt can be divided into the South and the North Wuyi metallogenic belt by the ENE-trending Nanping–Ninghua–Ganzhou Tectonic Belt. In the Wuyi metallogenic belt, Paleozoic mineralization, which has caused typical deposits such as the Yongping, Fenglin, and Yushui Cu deposits and the Makeng Fe deposit, exhibits notable variations. However, systematic research on the controlling factors of these mineralization episodes is lacking. In order to understand the Paleozoic minerlization in the Wuyi metallogenic belt, we study the genesis of typical deposits in Wuyi metallogenic belt. The phenomenon of “basal ore control” was observed as different basement units control different ore types in the Wuyi metallogenic belt. We believed that Paleozoic mineralization in the Wuyi metallogenic belt includes siliceous–carbonate Jingshe, Lindi, and Chuanshan Formations, which are related to the Fe–Mn deposits such as the Makeng Fe deposit, Dapai Fe–Pb–Zn deposit, and Luoyang Fe deposit in the Southwest Fujian Province, carbonate formations of the Hutian Group related to Cu deposits such as the Yushui Cu deposit in the North Guangdong Province of the southern Wuyi region, and the Carboniferous Outangdi Formation related to the Yongping and Fenglin Cu deposits in the Northeast Jiangxi Province of the northern Wuyi region. Based on a systematic analysis on typical metallogenic deposits and basement characteristics in the Wuyi metallogenic belt, we proposed that the Paleozoic mineralization is not only controlled by Paleozoic strata and Mesozoic magmatism, but also by the basement. The basement controls Paleozoic Cu mineralizations in the southern and northern Wuyi regions. However, Fe–Mn mineralization is mostly related to Late Paleozoic sedimentation. The superposition and transformation of Mesozoic magmatism to the basement and Paleozoic strata is an indispensable factor in the Cu and Fe–Mn mineralizations in the Wuyi metallogenic belt.

Genesis of the Xinfang Gold Deposit, Liaodong Peninsula: Insights from Fluid Inclusions and S-Sr Isotopic Constraints

The North China Craton (NCC) has been continuously reactivated since the Mesozoic and this decratonization is responsible for its economically important gold mineralization in the Mesozoic. The Early Cretaceous (110–130 Ma) gold mineralization in the NCC has been well-studied due to its significance, but little attention has been given to other episodes of gold mineralization related to polyphased reactivation of the NCC. The Xinfang mesozonal gold deposit (143 Ma) in the Liaodong Peninsula is related to the one of the episodes of the Yanshanian orogeny. The orebodies of the Xinfang gold deposit were controlled by the low angle transpressive fault systems and hosted by the Neoarchean monzogranitic gneiss. Fluid inclusion microthermometry reveals that the mineralizing temperatures range from 220 to 280 °C, with salinities from 6 wt.% NaCl eqv. to 15 wt.% NaCl eqv., pressures from 199 to 321 Ma. The S isotopic characteristics of sulfides not only record a heterogeneous source including magmatic or gneissic sulfur but also record inter-mineral isotope fractionation. The initial 87Sr/86Sr values of pyrite (0.713 480–0.729 031) indicate a radiogenic crustal origin for the sources. The metamorphic dehydration of the underlying basement resulted in the genesis of the Xinfang gold deposit. We summarize three episodes of gold mineralization in the Liaodong Peninsula related to continuous reactivation of the NCC, which indicates a great exploration potential of this area.

A magmatic-hydrothermal indium-bearing polymetallic vein mineralization belt in the western Jiangnan Orogen: Evidence from zinc and cadmium isotopes of sphalerite

Polymetallic veins of Zn-Pb (Cu) deposits containing elevated levels of indium are hosted within the upper part of the Banxi Group in the western Jiangnan Orogen. The indium in the polymetallic vein deposits is hosted within sphalerite and chalcopyrite. Cu++In3+↔Zn2++Fe2+ is the most plausible indium substitution mechanism for ZnS in these deposits. Hydrothermal fluids were enriched in Cu, In, Co, Mn and Fe in the later mineralization stage. Ores, sphalerite and dolomite minerals displayed analogous Ce and Eu anomalies, and Zn/Cd ratios, while being noticeably different from its host rocks, that provided its mineralized metals were not derived from its host rock. Despite the Zn and Cd isotopic variations in sphalerite being relatively narrow (δ66ZnJMC = +0.01‰–+0.28‰; δ114CdSpex = −0.14‰–+0.11‰), they display increase during mineralization and are negatively correlated to Cd concentrations; the Rayleigh distillation might be the fractionation mechanism. Zn/Cd ratios and Zn-Cd isotopic variations suggest the magmatic-hydrothermal origin of the polymetallic vein-type deposits. These hydrothermal fluids might derive from the fractionation of Zn, Cd, Cu, In and Sn in the granitic magma. This is triggered by crust thickening and the detachment of the lower crust along the Jiangnan Orogen during the intracontinental orogenic events of the Guangxi orogeny. This period of granitic magmatism might be another important indium mineralization episode in South China.