Mineralium Deposita最新文献

We present coupled textural, elemental, and boron isotopic data of tourmaline from the large Zhunuo–Beimulang collision-related porphyry copper deposits (PCDs) located within the western Gangdese, Tibet. Based on morphology and high-resolution mapping, the tourmaline is classified into three paragenetic generations. The first generation of schorlitic Tur-1 occurs in the monzogranite porphyry as disseminations intergrown with porphyritic K-feldspar and plagioclase. It shows decreasing Fe and Ca and increasing Mg and Al contents from core to rim and has relatively homogeneous δ¹¹B values (− 9.9 to − 8.6‰); low Fe³⁺/(Fe²⁺ + Fe³⁺), Cu, F, H₂O, and Sr/Y ratios; and high rare earth elements. These features indicate Tur-1 formed in a low fO₂ and metal-poor granitic magma during the pre-mineralization stage. The second generation of porphyritic euhedral Tur-2 is hosted in diorite porphyry enclaves and dikes, where it is intergrown with plagioclase and biotite. It forms part of the schorl-dravite solid solution, with high Fe³⁺/(Fe²⁺ + Fe³⁺), Cu, F, H₂O, Sr/Y, and δ¹¹B (− 9.7 to − 5.1‰) values. These features indicate it crystallized from a hydrous, oxidized, metal-, and volatile-rich diorite magma. The third generation of Tur-3 is the most volumetrically important and occurs as veinlets and disseminations in the porphyry, or around Tur-1 and Tur-2. It shows radial and oscillatory zoning and is locally intergrown with chalcopyrite and pyrite within the main mineralization assemblage. It has δ¹¹B values (− 10.5 to − 6.0‰) that overlap with Tur-1 and Tur-2 values. Tur-3 also has variable Fe³⁺/(Fe²⁺ + Fe³⁺), Cu, and volatiles (F and H₂O), indicating it crystallized from oxidized to relatively reducing metal- and volatile-rich hydrothermal fluids. Overall, the three generations of tourmaline show a narrow range of δ¹¹B values between − 10.5 and − 5.1‰ that are indicative of a single magmatic source. The high Cu, ferric iron, volatiles, and δ¹¹B values in Tur-2 are interpreted to reflect injection of diorite magma into an open crustal magma storage system that led to the formation of an oxidizing and metal-volatile-rich porphyry system. The three stages of tourmaline formation reflect evolution of the magmatic–hydrothermal system from low fO₂ conditions towards more oxidizing, volatile-rich conditions and then a return to more reducing conditions that accompanied Cu precipitation. Overall, the injection of oxidized metal-rich magma into a long-lived magma reservoir is a critical driving force for the development of collision-related PCDs.

Abstract

Iron oxide–apatite (IOA or Kiruna-type) deposits typically consist of a magnetite-apatite-actinolite/diopside assemblage and are spatially associated with extensive Na-(Ca) alteration and brecciation. The origin of these deposits is highly controversial and has been ascribed to the separation of iron-oxide/sulfate-(carbonate) melts, magnetite emulsions, or metasomatic replacement by aqueous fluids from silicate magmas. Here, we propose a new model based on the findings from a cluster of IOA deposits located in the early Cretaceous Ningwu andesitic volcanic field, eastern China. In these deposits, magnetite coeval with apatite and actinolite occurs as coarse-grained veins, massive replacement, and fine-grained disseminations in the albitized, often brecciated, apical zones of diorite porphyry intrusions, the overlying andesites, and adjacent sedimentary rocks. The primary magnetite grains from ores with various textures contain similar and variable trace element compositions with up to 5 wt% Ti + V and show the characteristics of high-temperature hydrothermal magnetite in magmatic-hydrothermal systems. Diopside and garnet as well as magnetite contain fluid inclusions with multiple daughter minerals (vapor + halite + sylvite ± anhydrite ± iron chloride ± liquid ± hematite), which show extremely high salinities of more than ~ 90 wt% NaCl_equiv, homogenization temperatures of 745–846 °C, and Cl/Br mole ratios of 2000–6000. In combination with oxygen isotopes of the magnetite-apatite assemblage and the association with shallow-seated ore-hosting porphyry, available evidence suggests that these deposits formed from hydrosaline liquid exsolved from subvolcanic dioritic magmas with high Cl/H₂O at magmatic temperatures (~ 800 °C). Decompression from lithostatic to hydrostatic condition and the interaction with country rocks explain the abundance of breccia bodies and widespread sodic alteration in IOA deposits.

A peculiar type of stratabound tungsten mineralization in metacarbonate rocks was discovered and explored at Mallnock (Austria) during the late 1980s. It is the only tungsten occurrence in the Eastern Alps in which scheelite is associated with wolframite (96 mol% ferberite). The tungsten prospect is located in the Austroalpine Drauzug-Gurktal Nappe System recording polyphase low-grade regional metamorphism. Raman spectroscopy of carbonaceous material yield maximum metamorphic temperatures of 296 ± 27 °C and 258 ± 27 °C, which are assigned to Variscan and Eoalpine metamorphism, respectively. Scheelite and ferberite occur as polyphase stockwork-like mineralization in Fe-rich magnesite in the northern ore zone (Mallnock North), whereas in the western ore zone (Mallnock West), scheelite-quartz veinlets are exclusively hosted in dolomitic marbles. LA-ICP-MS analyses of scheelite and ferberite yield low contents of Mo, Nb, Ta, and rare earth elements, but high contents of Na and Sr. Uranium is particularly high in scheelite (up to 200 µg/g) and makes this mineral a suitable target for U–Pb dating. In situ U–Pb dating of scheelite yielded an early Permian age (294 ± 8 Ma) for Mallnock West and a Middle Triassic age (239 ± 3 Ma) for Mallnock North. A monzodioritic dike close to Mallnock yielded a U–Pb apatite date of 282 ± 9 Ma and supports the polyphase formation of this mineralization. The U–Pb scheelite ages indicate that a model for tungsten metallogeny in the Eastern Alps must also consider remobilization of tungsten by metamorphic fluids. In the Alps, the Permian to Triassic period (ca. 290–225 Ma) is characterized by an overall extensional geodynamic setting related to the breakup of Pangea. Lithospheric thinning caused higher heat flow, low-P metamorphism, and anatexis in the lower crust, which led to enhanced crustal fluid flow in the upper crust. These processes were not only responsible for the formation of metasomatic hydrothermal magnesite and siderite deposits in the Eastern Alps but also for this unique magnesite-ferberite-scheelite mineralization at Mallnock.

Chromitites or chromite mineralization of varying degrees has been discovered in the various ophiolites along the east–west trending Yarlung-Zangbo Suture Zone (YZSZ) in Tibet, China. The high-Cr variety dominates the Yarlung-Zangbo chromitites, with rare high-Al chromitites reported in the Zedang, Dongbo, and Purang ophiolites. Using empirical equations, the calculated parental magmas that formed the high-Cr YZSZ chromitites are similar to boninitic melts. ¹⁸⁷Os/¹⁸⁸Os ratios of chromites from the YZSZ chromitites range from 0.12525 to 0.12933, lower than the proposed present-day ¹⁸⁷Os/¹⁸⁸Os values for the primitive upper mantle. The T_RD age variation of the YZSZ chromitites from late Neo-Proterozoic to early Triassic thus reflects that their parental magmas are derived from depleted mantle sources mixed with diachronous ancient mantle domains. The light Zn isotopic compositions of the YZSZ chromitites indicate that subducted materials (e.g., serpentinites and sediments) have contributed to the parental magma of the YZSZ chromitites. By compiling previously published data on mantle peridotites of the YZSZ ophiolites, we concluded that the YZSZ ophiolites may either have formed initially in an ultraslow-slow mid-ocean ridge environment and were then trapped in a supra-subduction zone environment, or have formed in an ultraslow-slow forearc spreading center in a supra-subduction zone environment. The Luobusa ophiolite hosting the largest chromite deposits is discriminated from the other ophiolites in the YZSZ by a thick dunitic transition zone. Previous theoretical modeling indicates that relative to olivine, only a small amount of cumulus chromites crystallize in cotectic volume ratios of around 100:1 to 100:2 of olivine to chromite, which means that large chromite bodies should always be accompanied by a significantly larger mass of dunites. Therefore, we concluded that a thick dunite transition zone or large masses of dunite of boninitic affinity is an indicator for chromitite prospecting in the future.

The Cornubian Batholith (SW England) is an archetypal Variscan rare metal granite with potential for Li-mica mineralization. We present a petrographic, trace element and multivariate statistical study of micas from the Cornubian Batholith granite series and related hydrothermally altered units to assess the role of magmatic vs subsolidus processes and of fluxing elements (F and B) on the Li cycle during the evolution of the system. The mica types are as follows: (1) magmatic, which include Fe-biotite, protolithionite I and phengite-muscovite from the most primitive granites, and zinnwaldite I from more fractionated lithologies; (2) subsolidus, which encompass high-temperature autometasomatic Li-micas and low-temperature hydrothermal muscovite-phengite. Autometasomatic species include protolithionite II, zinnwaldite II and lepidolite, which were observed in the most fractionated and hydrothermally altered units, and occur as replacements of magmatic micas. Low-temperature hydrothermal Li-poor micas formed via alteration of magmatic and autometasomatic micas or as replacement of feldspars, and albeit occur in all studied lithologies they are best represented by the granite facies enriched in metasomatic tourmaline. The evolution of micas follows two major trends underlining a coupling and decoupling between the Li(F) and B fluxes. These include as follows: (1) a Li(F)-progressive trend explaining the formation of protolithionite I and zinnwaldite I, which fractionate Li along with Cs, Nb and Sn during the late-magmatic stages of crystallization, and of zinnwaldite II and lepidolite forming from the re-equilibration of primary micas with high-temperature Li-B-W-Tl-Cs-Mn-W-rich autometasomatic fluids; (2) a Li(F)-retrogressive trend explaining the low-temperature hydrothermal muscovitization, which represents the main Li depletion process. Trace element geochemistry and paragenesis of late muscovite-phengite support that muscovitization is a district-scale process that affected the upper parts of the granite cupolas through acidic and B(Fe-Sn)-saturated hydrothermal fluids associated with metasomatic tourmalinization, which were mixed with a low Eh meteoric component.

Abstract

The Val-d’Or vein field (VVF), located in the southern Abitibi subprovince (Québec, Canada), is host to ~ 47 Moz gold and is therefore an example of a greenstone-hosted orogenic gold district. Gold is contained in quartz-tourmaline-carbonate veins that cut As-poor intermediate to mafic volcanic and intrusive rocks, including dioritic, granodioritic and gabbroic sills, dikes, stocks, and plutons. Five investigated orebodies (Goldex, Triangle, Plug #4, Pascalis Gold Trend, Beaufor) host gold in vein- and wallrock-hosted pyrite-rich sulfide aggregates (> 95 vol%) that show a porous core domain (Py1), with abundant inclusions of carbonate, silicate, and Fe-oxides up to several tens of µm in size. A homogeneous pyrite rim domain (Py2) surrounds Py1 and contains most of the gold as native gold and polymetallic (Au-Ag-Te-Bi) inclusions, primarily calaverite and petzite. The two pyrites show different Au and As contents (Py1 = Au ≤ 30 ppm; As ≤ 67 ppm; Py2 = Au ≤ 1250 ppm; As ≤ 550 ppm). Pyrite shows a ubiquitous shift in δ³⁴S values of up to + 3.0‰ from Py1 (δ³⁴S = − 0.4‰ to 5.8‰, n = 32) to Py2 (δ³⁴S = 0.0‰ to 6.3‰, n = 59) and records a small, slightly negative Δ³³S signature between – 0.20‰ and 0.01‰. The δ³⁴S shift suggests that removal of reduced sulfur species from auriferous hydrothermal fluids causes the formation of inclusion-hosted gold in Py2 by a decrease in the fluid sulfur fugacity (fS₂) through wallrock sulfidation of Fe-oxides. The shift also correlates with locally enriched Co and Ni concentrations in Py1 (< 1 wt%), compared to lower, oscillatory zoned concentrations (< 0.1 wt%) in Py2, respectively, indicating an overall decrease in fluid oxygen fugacity (fO₂). Contemporaneously, a decrease in fluid tellurium fugacity (fTe₂) drives polymetallic inclusion-hosted gold formation in Py2, initially as calaverite followed by increasingly Ag-bearing petzite and hessite. The multiple sulfur isotopes and trace element compositions recorded in pyrite in the VVF indicate that a homogeneous fluid reservoir introduced gold-sulfide complexes. Even if considered a localized process at the ore-shoot scale, fluid-wallrock sulfidation reactions can lead to a coupled decrease in fS₂, fO₂, and fTe₂ of auriferous hydrothermal fluids in a greenstone-hosted As-poor gold district.

This study presents an investigation of the distribution of trace elements within base metal sulfides from magmatic Ni-Cu-Co deposits from the Proterozoic anorthositic Espedalen Complex, Norway. The mineralisation occurs both as primary, undeformed sulfides and as deformed sulfides hosted within shear zones. Distinct deposits yield Ni tenors ranging from 3 to 10%, allowing the assessment of whether the metal tenor of a deposit is reflected in its sulfide composition. The results allow constraining geological processes spanning from the compositional traits of the parental melts to late-magmatic fluid interactions. Notably, the sulfides exhibit a relatively low concentration of chalcophile elements compared to other Ni-Cu-Co deposits worldwide, particularly platinum-group elements (PGE). This is because these deposits formed from PGE-depleted magmas. Elements compatible with monosulfide solid solution (MSS; Co, Rh, Ru, Ir, Os and Se) are predominantly hosted by sulfides, whereas a smaller proportion of incompatible elements (Pb, Cd, Ag, Bi, Zn, In, Tl, As, Sn and Mo) is also accommodated by sulfides. Our findings for sulfide composition support for the first time a positive correlation between Se concentrations in pentlandite and whole-rock Ni tenors for both Espedalen and magmatic Ni-Cu-Co sulfide deposits worldwide. This is because of the more efficient collection of both Ni and Se by an immiscible sulfide liquid under high R-factor regimes, combined with the fact that Se concentrations in pentlandite remain largely undisturbed during post-cumulus processes as opposed to other trace elements. Consequently, Se concentrations in pentlandite may serve as a proxy for metal enrichment in magmatic sulfide deposits.

Abstract

The Zhazixi deposit hosted in sedimentary rocks is a major Sb-W deposit in South China. The mineral scheelite, which can be dated by the U-Pb method, commonly occurs in both tungsten (W)-dominated and antimony (Sb)-dominated ore veins of the deposit. Cathodoluminescence (CL) images reveal the presence of three distinct stages of scheelite (Sch-I, Sch-II and Sch-III) within the deposit. These three scheelites were dated using in-situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), yielding U-Pb ages of 158.1±5.4 Ma and 157.6 ± 4.9 Ma for Sch-I, 155 ± 11 Ma for Sch-II, and 151.3±6.1 Ma for Sch-III. These data suggest that the Zhazixi Sb-W deposit formed during the Late Jurassic (160–150 Ma) rather than the Late Triassic as previously suggested. Considering the temporal similarity with low-temperature hydrothermal Sb deposits in the Xiangzhong metallogenic province (XZMP), the formation of the Sb-W deposit may have followed a similar genetic model, where meteoric groundwater circulated to depth and extracted metals from fertile basement rocks through fluid-rock interaction, resulting in the generation of ore fluids. This study highlights that Late Jurassic low-temperature hydrothermal Sb-polymetallic mineralization in the XZMP is likely more extensive than previously perceived.

The origin of propylitic fluids in intermediate sulfidation mineralization has not been investigated in detail. Here, we present an extensive petrographic, geochemical, and isotopic (O-H-Sr) study of propylitic epidote, chlorite, and calcite from the Zhengguang intermediate sulfidation epithermal Au-Zn deposit, NE China. Propylitic minerals can be divided into three main types based on their different textural occurrences, namely interstitial cement of clasts of hydrothermal breccia, replacement of primary plagioclase or hornblende, and vein infill of cracks, with late, minor calcite as amygdules in vesicles of andesite representing a fourth textural occurrence. The H-O isotope compositions and mass balance calculations suggest that most propylitic epidote records a dominant (> 50%) contribution of magmatic fluids. The decrease of the average δ¹⁸({mathrm O}_{{mathrm H}_2mathrm O};)values equilibrated with different types of epidote (cement 6.8 ± 0.7‰, replacement 5.1 ± 1.1‰, vein 4.5 ± 1.4‰, 1 SD), and the decreasing content of high-temperature elements (e.g., Cu-Mo) from cement, through replacement to vein epidote and chlorite, collectively indicates a decreasing role of magmatic fluids. Replacement epidote and chlorite are enriched in Sr-Mn-Y-Sb, whereas replacement epidote and calcite record similar (⁸⁷Sr/⁸⁶Sr)_i values to the andesitic host rock, suggesting that replacement minerals inherit certain elements from plagioclase and hornblende, and the Sr isotope signature of the wall rocks. We highlight that propylitic alteration in epithermal deposits can involve significant proportions of magmatic fluids and texturally different alteration mineral types should be considered when using mineral isotopic or chemical compositions to track fluid sources or to vector towards the location of intrusive centers.

The world-class Huize deposit hosts significant germanium (Ge) resources in the Sichuan–Yunan–Guizhou (SYG) Mississippi Valley-type (MVT) Pb–Zn province of China. The distribution and enrichment mechanism of Ge is still poorly understood. In the main ore-forming stage of Huize, we identified six sphalerite colors from C1 (black) to C6 (white) in transmitted light. Two color sequences are confirmed, including C1 → C2 → C3 → C6 and C1 → C2 → C4 → C5 → C6. We used multiple analytical methods to reveal the Ge distribution and incorporation mechanism into sphalerite and the possible enrichment factors. Our results show that Ge occurs as argutite (GeO₂), and in the sphalerite crystal lattice, C1 and C3 sphalerite has up to 593 ppm Ge. Two substitution mechanisms, i.e., Ge⁴⁺ + □_(vacancy) → 2Zn²⁺ (e.g., C1 and C2) and Ge⁴⁺ + 2Cu⁺ → 3Zn²⁺ (e.g., C2, C3, C4, and C5), are inferred from the Huize sphalerite. They show different spatial structures of sphalerite and a weak shift of the white line observed by high-resolution X-ray absorption near-edge structure (XANES) spectroscopy. The trace-element composition of sphalerite suggests that reduced sulfur content of the ore-forming fluid contributes to Ge enrichment, followed by high temperature (> 300 °C).