δ18OSMOW Values Research Articles

Characteristics of antimony mineralization in the Yangla polymetallic deposit, northwestern Yunnan, SW China: Insights from calcite Sm-Nd dating and C-O-Sr isotopes

Calcite is the main gangue mineral in antimony (Sb) deposits, and its compositions can reflect the physicochemical conditions of Sb mineralization. The Yangla is the largest Sb deposit (10 kt Sb @ 14.87 %) in the Jinshajiang suture zone (SW China), and the lode-type Sb orebodies are stratabound or developed along NE-trending fracture zones in marble. To constrain the time of Sb mineralization and establish any genetic link with the local magmatism and wallrocks, we performed calcite Sm-Nd dating and bulk C-O and in-situ Sr isotope analyses. The results show that the Sb mineralization (∼155 Ma) was considerably younger than the Cu-Pb-Zn mineralization (∼230 Ma), skarn alteration (∼234 Ma), and granitoid emplacement (∼230 Ma) at Yangla, but much older than the local W mineralization (∼30 Ma). The initial 87Sr/86Sr ratio of calcite (0.71972–0.72208) is much higher than that of the Triassic granodiorite (0.71149– 0.71990) and Carboniferous basalt (0.70562–0.70995), suggesting mixed source of calcite from the ore fluids and Devonian wallrocks. The ore-related calcite has δ13CPDB (−4.53 to − 2.33 ‰) and δ18OSMOW (+14.98 to + 16.30 ‰) values that fall between the granite and marine carbonate isotopic fields. This suggests that the ore-forming fluid may be related to the low-temperature alteration of granites and marine carbonate dissolution. Simulated precipitation temperature calculation for the ore-related calcite yielded 200–150 °C, and the calcite C-O isotopes suggest that fluid mixing, fluid-rock interactions, and CO2 degassing may have precipitated the stibnite in the fracture zones under low-temperature conditions. Our new geochemical results and published data suggest that the Yangla polymetallic mineralization was multiphase, comprising the Indosinian Cu-Pb-Zn (∼230 Ma), Yanshanian Sb (∼155 Ma), and Himalayan W-Sb (∼30 Ma) metallogenic events.

Distribution and Enrichment Mechanisms of Selenium in Stibnite from the Xujiashan Sb Deposit, Hubei Province, China

The Xujiashan Sb deposit located at the Mufushan fold thrust belt of the Yangtze block is one of the most important Sb deposits in this district. Stibnite in this deposit contains high and various contents of Se, but research on the distribution and enrichment of Se in stibnite remains limited. This paper conducts geochemical composition, C-H-O isotopic composition, and scanning electron microscopy morphology of the Xujiashan deposit to discuss the sources of ore-forming materials and fluid, as well as the distribution and enrichment mechanisms of selenium in stibnite. The results showed that the ores have trace element compositions comparable with the wall rocks, and Sb and Se contents are significantly higher than the average carbonate rocks. The δ13CPDB values of calcite and quartz range from −12.8‰ to 5.5‰, the δ18OSMOW values range from 20.4‰ to 24‰, and the δDV-SMOW values range from −57.8‰ to −86.9‰. Trace element and isotope compositions indicate that the ore-forming materials were mainly derived from the wall rocks (sedimentary–metamorphic rocks) that S, Se, and Sb dissolved during fluid–rock interactions. The ore-forming fluids were metamorphic water produced by metamorphism, which had experienced multistage mixing with meteoric water and organic-rich fluids. Selenium substitutes for sulfur in the stibnite crystal lattice, causing rhythmically distributed Se contents in stibnite, which resulted from multistage physicochemical changes in ore-forming fluids during crystallization. The varied patterns of Se contents are the result of different cross-sections of the stibnite.

Temperatures of Vein Formation Associated With Plate Interface Deformation Constrained by Oxygen and Clumped Isotope Thermometry

AbstractTectonic mélanges, characterized by conditions reflective of modern subduction fault zones, preserve mineral veins formed through mass transfer, a mechanism influencing the slip behavior of subduction megathrusts. In this study, we apply secondary ion mass spectrometry quartz‐calcite oxygen isotope thermometry and clumped isotope thermometry to examine the temperatures of vein formations in six mélange units in the Cretaceous Shimanto belt and one mélange in the Kodiak accretionary prism. Calcite in the veins exhibits δ13CPDB values ranging from −17.2‰ to −6.8‰, indicative of a carbon source mixing with sedimentary carbonate and organic matter. δ18OSMOW values of calcite range from +11.1‰ to +17.2‰; quartz yields δ18OSMOW values of +14.9‰ to +21.7‰. Oxygen isotopic signatures in minerals reveal that most vein‐forming fluids are significantly affected by rock buffering, while some retain isotopic compositions of seawater and meteoric water. Temperature estimates, derived from both thermometers, fall within the range of 100–250°C. Notably, vein temperatures remain constant across diverse vein types and mélange units with distinct maximum temperatures. The combined temperature records and fluid isotopic compositions imply vein formations at shallower depths linked to the incorporation of seawater, meteoric water, and fluid released from early dehydration reactions. At greater depths, vein formations are associated with fluid released from clay dehydration and long‐distance fluid flow. Reduced vein formations between 250 and 350°C may correlate with a shift to fluid‐unsaturated conditions resulting from clay hydration reactions. Our study highlights potential mechanical and hydraulic variations within the thermal conditions of 100–350°C along the plate boundary driven by fluid‐mineral interactions.

Shallow mantle cycle of subducted sedimentary limestone indicated by carbonate xenoliths

In the subduction zone, carbon (C) release from the subducted plate into the mantle wedge takes place by various mechanisms, including metamorphic degassing, carbonate dissolution, and hydrous melting. Recent studies have highlighted the significant role of buoyant limestone diapirs in facilitating C recycling during subduction processes. Here, we report that the Hannuoba carbonate xenoliths of eastern China were introduced into the shallow mantle in the form of sedimentary limestone diapirs. We conducted a comprehensive study of the Hannuoba carbonate xenoliths using petrological analysis, major- and trace-element analysis, in situ zircon dating, and C-O isotopic analysis techniques. The whole-rock major and trace elements, along with high δ18OSMOW values (22.8‰−23.2‰), indicate that the protolith of Hannuoba carbonate xenoliths consists of sedimentary limestones. The spectral age peaks of detrital zircons (400−100 Ma, 500−450 Ma, 2.0−1.6 Ga, and 2.8−2.2 Ga) suggest that the primary source of the protolith is the North China Craton. When sedimentary limestone diapirs enter into the mantle wedge, they undergo partial melting under high-temperature conditions. This process results in the melting of low-melting point pelitic components, while leaving behind resistant minerals such as pure calcite. Due to its low density and viscosity, this pure limestone component will continue to migrate upward and assimilate with the mantle peridotite. In this process, the pure calcites are preserved in the shallow mantle in a solid-state form rather than as carbonatitic melts. The discovery of graphite and spinel in the Hannuoba carbonate xenoliths indicates that the depth of formation of the sedimentary limestone diapirs does not exceed 2.5 GPa (<70 km). The calcite in Hannuoba carbonate xenoliths exhibits extremely low δ13CVPDB (−11.8‰ to −11.0‰) and high δ18OSMOW (22.8‰−23.2‰) contents. This characteristic C-O isotopic signature can be explained by the Rayleigh decarbonation of sedimentary limestones under upper-mantle conditions (<3 GPa). Based on calculations, the Hannuoba carbonate xenoliths are a product of subducted sedimentary limestone experiencing 99% volume decarbonation. Through this metamorphic decarbonation process, limestone diapirs release a significant amount of CO2 into the arc magma system. During subduction processes, sedimentary carbonate rocks can be recycled to the mantle wedge of island arcs as solid limestone diapirs. The C flux released by this mechanism cannot be ignored.

Fingerprinting Pb-Zn mineralization events in the SW Yangtze Block, South China: A case from Yuanbaoshan deposit

The southwestern Yangtze Block represents one of the world’s largest lead–zinc provinces, comprises more than 400 known carbonate-hosted Pb-Zn deposits and contains over 30 million tons (Mt) of total Pb + Zn reserves. The Pb-Zn deposits in this area have been studied extensively by economic geologists, but the origin and mineralization processes of these deposits are still controversial. The Yuanbaoshan deposit is a typical carbonate-hosted Pb-Zn deposit of medium scale (0.19 Mt P + Zn reserves @ 0.7–26.31 wt%), which is in the northern part of the Pb-Zn mineral belt in the southwest margin of the Yangtze Block. In this study, we have conducted LA-ICP-MS sulfides trace elements, S isotope analyses, together with gangue carbonate C-O stable isotope analyses and pyrite Rb-Sr dating. We present Rb-Sr isotopic data on the pyrite that yields an isochron age of 196.4 ± 2.3 Ma. The mineralization temperature at Yuanbaoshan, as determined by the Ga, Ge, In, Mn and Fe (GGIMF) in sphalerite geothermometer, ranges from 161 to 264 ℃ (Sp1) and 141 to 246 ℃ (Sp2). The δ13CPDB values range from −0.66 to 0.61 ‰, δ18OSMOW values range from 15.6 to 17.3 ‰. In situ S isotopes show that the δ34S values of sulfides range from −1.4 to 17.73 ‰. The field, petrologic, geochemical and isotopic data from our study lead to the following salient findings. (1) The dissolved carbon and oxygen of ore forming-fluids of these Pb-Zn deposits were mainly derived from sedimentary carbonate dissolution. (2) The reduced S in the sulfide of the Yuanbaoshan Pb-Zn deposit is mainly derived from the thermochemical sulfate reduction (TRS) and the reduced S produced by the pyrolysis of S-containing organic matter in the carbonaceous mudstone of the Ebian Group. (3) The large-scale Pb-Zn mineralization in the southwest margin of the Yangtze Block was influenced by the post-collision extension between the Indosinian Block and the South China Block during ca. 200 Ma.

Distribution and Genesis of the Deep Buried, Fractured and Vuggy Dolostone Reservoir in the Lower Ordovician Succession, North Tarim Basin, Northwestern China

Recently, a series of prolific fracture-vug reservoirs have been discovered in the lower Ordovician dolostone successions of the northern Tarim Basin. However, the genesis of these reservoirs remains unclear. In this study, observations on drilling cores and thin sections identify the pore space characterized by dissolved fractures, fissures, and vugs. Petrology, cathodoluminescence, and homogenization temperatures of fluid inclusions aid in establishing the diagenetic paragenetic sequence. Dissolving enlargement occurred after chemical compaction of overlying limestone and before the Permian volcanic activity. Breccia pores containing unique fillings of terrestrial materials (quartz sand and allogenic kaolinite) and calcite cements with negative δ18OPDB values (−18.4‰) along with 87Sr/86Sr ratios (up to 0.71026) indicate that the dissolving fluid originated from meteoric freshwater at the surface. The δ18OSMOW values of the calcite precipitating fluid (−2.1‰ to −8.7‰) further suggest freshwater as the source of the dissolving fluid, buffered by the Ordovician wall rocks or formation water. As the distance from the unconformity surface increases, both the homogenization temperature and δ18OPDB values of the breccia pore-filling calcite in the southern study area gradually elevate and deplete, respectively, indicating a rise in temperature during the infiltration of meteoric freshwater with increasing subsurface temperatures. The abnormal reflection bodies identified as reservoirs in seismic profiles along deep-seated strike-slip faults delineate these faults as the channel for the infiltration of meteoric freshwater. The penetrating strata of these faults and the high 87Sr/86Sr values of breccia pore-filling calcite suggest that karstification occurred during the Devonian period. Accordingly, we establish a deep karst model in which the Devonian meteoric freshwater penetrated along the strike-slip faults and dissolved the Ordovician dolostones, resulting in the development of deep buried karstic fault reservoirs in the southern region of the northern Tarim Basin.

Lava–water–sediment interaction: Dolomite U[sbnd]Pb dating marks the Cenozoic Ocean–continent transformation in the southwestern Tianshan Mountains

The regression of the Neotethys Ocean from the southwestern Tianshan Mountains remains debatable because of notable sedimentary discontinuities and lack of fossil evidence. This study aimed to explain this problem by applying comprehensive carbonate UPb dating to newly recognised pyroclastic rock layers in the Tuoyun Basin, southwestern Tianshan Mountains. These rocks, referred to as peperite in the early literature, are not like typical pyroclastic rocks; rather, they are formed by the mixing of magma with wet sediment. Field observations have revealed that the pyroclastic rock layers are overlying Cenozoic pillow basalts and then covered by the later columnar jointing basalts, recording a transformation from marine to terrestrial environment. The dolomite-dominated mineralogy and major element analysis indicate that the pyroclastic rock is dolomitic in composition. The sedimentary origin is supported by the δ18OSMOW values (23.7‰ to 36‰) and δ13C values (−6.48‰ to −7.08‰) of the bulk-rock pyroclastic rock and the δ34S values (−20.79‰ to 23.86‰) of native sulfur. However, the relatively depleted initial ratios of 87Sr/86Sr (0.7048–0.7065) and εNd(t) values (−0.52 to +3.10) suggest the possibility of isotopic exchange with the conjugate basalts. For carbonate from Tuoyun pyroclastic rock, UPb isotope dating using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA–MC–ICP–MS) produced well-defined Lutetian ages of 46.1 ± 0.5–41.7 ± 0.6 Ma. This indicates that the Tuoyun region was in a marine environment during the Lutetian epoch and then transformed into a continental environment after the marine regression. In this study, we successfully applied the UPb technique by LA–MC–ICP–MS to constrain the timing of ocean–continent transformation through carbonate UPb dating. These findings explain the regression of the Neotethys Ocean from the southwestern Tianshan Mountains and offer novel insights into the geological evolution history of this region.

Study on the complex magmatic and hydrothermal metallogenic processes in the giant Huayangchuan uranium (U)-polymetallic ore district: Constraints from geochemical and geochronological evidences

The supergiant Huayangchuan uranium (U)-polymetallic deposit is situated in the west part of Lesser Qinling Orogen, Central China, which is renowned for its unique metallogenic type and complex mineralization processes. This newly-discovered deposit contains economic endowments of U, Nb, Pb, Se, Sr, Ba and REEs. The genesis of this deposit remains hugely controversial and the related magmatic and metallogenic framework have not been well established. In our study, we present newly obtained zircon U-Pb age data, whole-rock trace elements, detailed SEM observation, carbon and oxygen isotope determination and titanite U-Pb age result to provide geochemical and geochronological constraints on the magmatic and hydrothermal metallogenic processes in Huayangchuan ore district and give insight into the REE, Nb and U mineralization and remobilization mechanism. Carbonatite in Huayangchuan deposit is rich in Ba, Sr, Nb, U and REE and the δ18OSMOW and δ13CPDB (‰) values of carbonatite vary between + 7.30 ‰ to + 9.80 ‰ and − 6.00 ‰ to − 7.20 ‰, respectively, which is the unique characteristic of igneous carbonatite. The total REE contents of carbonatite range from 1319.5 to 2535.8 ppm, significantly higher than that of the granite pegmatite dykes and Taihua Group granitic gneiss. Two zircon grains from the Huayangchuan carbonatite yield the 206 Pb / 238 U age of 223 ± 5.6 Ma and 217 ± 8.6 Ma. Uranium and niobium are mainly hosted in the primary mineral of betafite, minorly in uraninite and fergusonite. REE are remained in various REE carbonates, phosphates and silicates, e.g. allanite, parite, monazite, apatite, yttrialite and xenotime. Betafite contains numerous mineral inclusions of calcite, allanite and apatite, which displays as vermicular relicts with metasomatic corrosion texture. The intimate relationship between betafite, calcite, apatite, allanite and REE carbonates implies that U and Nb mineralization occurred during carbonatite-related magmatic stage. Late Triassic carbonatite magmatism (∼220 Ma) was responsible for the world-class U-Nb-Mo-REE mineralization in the Qinling Orogen. Whereas, LA-ICP-MS U-Pb data of titanite collected from Huayangchuan carbonatite reveal two sets of ages in the Huayangchuan deposit: during the Late Triassic and the Early Cretaceous. LA-ICP-MS data of the Triassic titanite and Cretaceous titanite in Huayangchuan deposit yield the lower intercept age of 223.1 ± 9.4 Ma and 141.9 ± 4.7 Ma respectively in the Tera-Wasserburg (238U/206Pb - 207Pb/206Pb) diagram. Cretaceous hydrothermal titanites show enrichment in Y, HREEs and depletion in TiO2 and LREEs relative to the Triassic magmatic titanites. Primary betafite and titanite were subjected to later hydrothermal alteration. The close genetic relation between altered titanite and Ti-Fe-Nb-Pb-U mineral inclusions demonstrates that Early Cretaceous hydrothermal fluids contributed to the Nb, U and Ti remobilization. Early Cretaceous regional granitic magmatic activity brought hydrothermal fluids to alter the early carbonatite magmatic pyrochlore and titanite. U, Nb, Ti, Y, Pb and HREEs were transferred and subsequently re-precipitated into uraninite, and hydrothermal titanite.

Ore genesis of the Mengya'a distal Pb–Zn deposit in the Lhasa terrane, Tibet, China: Constraints from in situ garnet U–Pb dating and C–H–O–Sr isotopes

A large amount of distal skarn Pb–Zn deposits without any causative intrusions exposed have been discovered along the eastern Nyainqêntanglha metallogenic belt (NMB) in the Gangdese region, Tibet, China. As a typical distal skarn Pb–Zn deposit in the east of NMB, the Mengya'a deposit is adjacent to the Longmala Pb–Zn ± Cu ± Fe deposit. However, the linkage between these two deposits is not unclear due to the chaotic dating results. In situ Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA‐ICP‐MS) U–Pb dating of reddish‐brown and yellow‐green garnet from Mengya'a yielded lower intersect ages of 53.6 ± 3.1 and 52.4 ± 4.4 Ma, respectively, indicating that Pb–Zn mineralization took place during the main collision stage of the India–Asia plates. The δDSMOW values of garnet, quartz and calcite vary from −148.4‰ to −140.4‰, −123.5‰ to −115.3‰ and −127.9‰ to −121.3‰, with the δ18OH2O values ranging from 5.8‰ to 6.6‰, 0.4‰ to 3.7‰ and 1.0‰ to 1.7‰, respectively. The δ13CV‐PDB and δ18OSMOW values of calcite range from −8.2‰ to −4.7‰ and 9.8‰ to 18.6‰, respectively. These C–H–O isotopic compositions of hydrothermal minerals indicate that the ore‐forming fluids were initially derived from the magmatic water with progressive input of meteoric water from the prograde stage to the retrograde stage. The 87Sr/86Sr(53 Ma) ratios of sphalerite (0.72321–0.73474) are consistent with those of Ando gneiss in the Lhasa‐Golmud area, indicating that the basement gneiss makes a great contribution for the source of ore‐forming materials. The newly obtained garnet U–Pb ages at Mengya'a are consistent with those of mineralization and causative intrusion in the Longmala Pb–Zn ± Fe ± Cu deposit, suggesting that the Mengya'a and Longmala deposits constitute an integrated distal skarn‐type system. This proposed hypothesis suggests that the Fe–Cu ± Pb ± Zn mineralization within the contact zone should focus on the locations beneath the identified Pb–Zn orebodies at Longmala and Pb‐21 orebody at Mengya'a.

Geochemical and mineralogical evidence for the formation of siderite in Late Permian coal-bearing strata from western Guizhou, SW China

This paper presents the results of the geochemical and mineralogical investigation of siderite in the Late Permian coal-bearing strata from western Guizhou, SW China. Siderite occurs as fine-grained ooids, as recrystallized stellate-like forms, as ellipsoidal, rhombohedral, and oolitic aggregates, indicating their authigenic origin. In contrast, pore filling and veinlet siderite are of epigenetic origin. The low sulfur contents, absence of pyrite, and Sr/Ba ratios indicate that the siderite was deposited in a freshwater (non-marine) environment. The V/(V + Ni) values of studied samples, ranging from 0.68 to 0.86, indicate that the siderite developed under anoxic conditions. The presence of authigenic kaolinite and epigenetic siderite in the same samplesuggests that the chemical conditions changed from acidic to alkaline conditions during early diagenesis.Iron in the siderite was not only derived from silicate weathering of high-Ti basalts in the sediment source regions followed by transport as ions by ground and surface waters, but was also generated from in situ alteration of the Fe-bearing minerals within the peat itself. In addition, ascending hydrothermal solutions would also contribute some Fe, with the Fe probably sourced from the leaching of the basaltic basement. The presence of siderite-rich layers indicates enhanced chemical weathering rates in the sediment source regions. The δ13CPDB, δ18OPDB, and δ18OSMOW values of siderite in claystones and mudstones vary within the ranges of −7.7 to 5.8‰, −12.1 to −6.6‰, and 18.4 to 24.1‰, respectively, indicating that carbon and oxygen primarily originated from marine carbonate, dehydroxylation of organic matter, carbonate dissolution, and hydrothermal fluids. The released CO2 invoked the alteration of reactive silicate minerals in the sediments, and ultimately the formation of siderite. Circulating pore fluids dissolving iron, which is derived from the silicate weathering of high-Ti basalts in the sediment source regions and from in situ alteration of the Fe-bearing minerals within the peat, would transport some iron from the overlying peat into the underlying sediments, and the flow of fluids would be diminished or stopped at the base of the peat due to the mechanical barrier of the impervious claystone or mudstone layers. The ferrous iron was precipitated due to the alkaline environment conditions of the peat, by reaction with HCO3− dissolved in the waters to form siderite.

The Khajraha, oldest carbonatite from India: Implications on carbonated-eclogite source, multi-level emplacement and its petrogenetic link with orthomagmatic fluids

Age and petrogenesis of a Neoarchean calcio‑carbonatite dyke from the Khajraha, Bundelkhand craton (BC, India) is presented here. Zircon UPb age data show emplacement age of 2567 ± 8.0 Ma marking the discovery of the oldest Indian carbonatites. Dyke consists of coeval emplaced three litho variants, recording multi-level emplacement and concomitant exsolution of carbo-hydrothermal fluids in their micro-textures and geochemical composition. The first emplaced grey sovite (c1) grade to silico‑carbonatite (SiO2: 24–26 wt%) consist of abundant autolith-segregations set in groundmass of fine-size spinifex-habit calcite. Autolith-segregations are hydrothermally altered early-formed cumulate and their alteration products formed while deep-seated storage. The later emplaced magma batches, pink alvikite (c2) and white sovite (c3), are monomineralic of calcite and have pure calcio‑carbonatite composition represented to be residual melt formed after fractionation of silico‑carbonatite solid-residue (c1) as evident from Harker variations. During fractionation at depth, hydrous fluids exsolved are re-equilibrated with primary magmatic biotite and amphibole, forming chlorite with byproducts of titanite and K-feldspar at ~300 °C. This autometasomatism also witnessed precipitation of primary hydrothermal phases like spherulite-chlorite, epidote, titanite, K-feldspar, apatite and REE-phases. While emplacing to subvolcanic level they variably admixed, disaggregated and dispersed in calcio‑carbonatite magma defining micro- to meso-scale flow fabrics in c1. At subvolcanic level, undercooling led the calcio‑carbonatite to crystallize spinifex-habit calcite by wrapping autolith-segregations. Continuously increasing Y/Ho and Th/U ratios, negative Eu-anomaly and positive Y-anomaly in REE pattern of c1, c2 and c3 record that fractionation of carbonic fluids (Mn-rich) accompanied with this kinematic crystallization. In addition to undercooling, rate of retention and venting out of exsolved fluids in the dyke-conduit has regulated nucleation and growth rate of spinifex-habit calcite, particularly in c3, they grown to pegmatoidal size in hot CO2-rich fluid ambience as indicated the gradual lowering of δ18OSMOW values from 7.28 to 3.41 ‰ keeping δ13C values almost constant. Dyke contains low Ba (27–298 ppm), Sr (146–739 ppm) and total REE (7–696 ppm), representing to be a carbonatite of ‘trace-element depleted end-member’. The elevated δ13CPDB-1 values (−1.93 to −2.99 ‰) coupled with δ18OSMOW values (5.82–7.53 ‰, in c1 and c2) within the range of Primary Igneous Carbonatite (PIC), low Nb/Y (<1) and Nb/Ta (1.4–16.1) ratios and high Zr/Hf (40–48) and Zr/Nb (12–116) ratios similar to recycled slab component and zircons εHf(t) value ~ −4.0 with TDMC of ~3.0 Ga suggest that calcio‑carbonatite magma sourced from a Mesoarchean depleted mantle containing carbonated-eclogite.

Geology, geochemistry and genesis of the world-class Shizhushan wollastonite deposit, Mengshan area, South China

The recently discovered Shizhushan wollastonite deposit in the Mengshan district contains about 54 Mt of wollastonite, making it the world’s largest wollastonite deposit. Zircon U–Pb geochronological results indicate that the Mengshan composite pluton evolved during a prolonged magmatic history (ca. 230–218 Ma). The pluton and the surrounding carbonate units of the Maokou Formation have distinct initial 87Sr/86Sr ratios, with values of 0.7107–0.7162 and 0.7070–0.7075, respectively. Pure wollastonite crystals in the Maokou Formation are characterized by uniform 87Sr/86Sr values of 0.7070 that are indistinguishable from the carbonates, suggesting that the wollastonite was formed during contact metamorphism. Limestones of the Maokou Formation are characterized by variable δ13CV-PDB (−5.2 to 4.0‰) and δ18OSMOW (10.3 to 22.6‰) values. Carbonates with the lowest δ13CV-PDB and δ18OSMOW values (and elevated 87Sr/86Sr ratios) occur in the vicinity of a regional structure, suggesting that magmatic–hydrothermal fluids and CO2 were channeled along this fault.Based on new geological, geochronological and geochemical data, we propose that the world‐class wollastonite deposit formed as a result of several factors related to a relatively stable depositional environment during the Late Paleozoic as well as structural deformation and magmatic events during the Early Mesozoic. These features include: 1) juxtaposition of abundant sediment-hosted chert (SiO2) and limestone (CaCO3) units, 2) a prolonged heat source provided by multiple magmatic events, 3) CO2 degassing along the regional structure promoted wollastonite-forming reactions, and 4) the proximity of the Si- and Ca-rich sedimentary layers subparallel to the intrusion contact. Our study documents the important roles of Early Mesozoic deformation and magmatism in the genesis of non-metallic mineral deposits in south China.

Geochronology, Geochemistry, Fluid Inclusion and C, O Isotope Compositions of Calcite Veins in the Paleogene of the Jiangling Basin, South China: Implications for Fluid Evolution and Brine Potash Mineralization

AbstractDeep‐seated potassium‐rich brines were identified in the Jiangling Basin, South China. Although magmatic‐hydrothermal sources have been proposed, the relationship between brine‐type potash mineralization and volcanism remains unclear. In this study, U‐Pb geochronology, geochemistry, fluid inclusion and C‐O isotopic compositions of hydrothermal vein minerals in the Jiangling Basin are examined. Laser ablation U‐Pb dating of calcite veins indicates that the ages are slightly younger than the formation age of the Balingshan basalt. Fluid inclusions in hydrothermal minerals show medium–low homogenization temperatures (160–220°C) and low salinities (0.14 to 4.9 wt% NaCl eqv.) and densities (0.882–0.944 g/cm3). The liquid compositions of fluid inclusions in calcite veins from sedimentary strata have higher contents of potassium, compared with those from basalt. The coupled negative δ13CPDB (–10.3‰ to −8.0‰) and positive δ18OSMOW (17.4‰ to 20.7‰) values imply that calcite precipitation resulted from CO2 degassing of the basaltic magmatic fluids, as indicated by the gas composition of these inclusions in hydrothermal minerals. Rare earth element patterns indicate that water‐rock interaction between hydrothermal fluids and sedimentary wall rocks contributed to the calcite precipitation in sedimentary strata. It is proposed that high‐temperature water‐rock interaction between magmatic fluids and sedimentary strata resulted in the potassium enrichment in fluids, interpreted as one of the sources of potassium‐rich brines in the Jiangling Basin.

Origin of the Amensif Zn-Cu (Pb-Ag-Au) distal skarn deposit (Western High Atlas, Morocco): Constraints from C-O-S isotopes

The Amensif Zn-Cu (Pb-Ag-Au) ore deposit is located in the northern part of the western High Atlas. The deposit hosts 1 million tons (Mt) of Zn-Cu-Pb metal reserves at 3% Zn, 2% Cu, and 1% Pb. The lenticular sulfide ores are structurally controlled open-space fillings (fractures, faults) in the Lower Cambrian carbonates. The mineralogical paragenetic sequence consists of andradite-quartz-epidote-dolomite-calcite-sphalerite-chalcopyrite-pyrite-galena with subordinate amounts of barite. The pre-ore stage and ore stage I dolomite samples have δ13CPDB and δ18OSMOW values in the range of −10.2 to −2.6‰ and 17.4–26.8‰, respectively. The lower δ18O value of these dolomites suggests oxygen isotope exchange between the ore-forming fluids and the carbonate host rock whereas negative δ13CPDB values reveal the interaction between these hydrothermal fluids and black shales. The δ34S values of sulfides ore (sphalerite, chalcopyrite, and pyrite) are high, ranging from 6.4 to 14.4‰. These S isotopic values reveal that sulfur derived from the mixture of magmatic sulfur and lower Cambrian carbonate-derived sulfur in almost equal proportions. Sulfide ores precipitated from the mixing between the magmatic-hydrothermal fluids exsolved from a hidden magma or the nearby Azegour granite of Permian age and an external cooler fluid of unknown origin. Fluid-rock interactions with the carbonate host rock contributed in the precipitation of the ore. Mineralogical and geological features allow us to ascribe the Amensif Zn-Cu (Pb-Ag-Au) polymetallic ore as a distal skarn system which is spatially associated with the lower Permian granite intrusion.

Geology, geochemistry, fluid inclusions, and H–O–C–S–Pb isotope constraints on the genesis of the Atash-Anbar epithermal gold deposit, Urumieh–Dokhtar magmatic arc, central-northern Iran

The newly discovered Atash-Anbar gold deposit, with ∼2 Mt of ore grading 2.13 g/t Au (locally up to 14 g/t), is located in the Buin-Zahra Range, central-northern Iran. Hosted by Middle Eocene (ca. 39.0 Ma) volcanic-subvolcanic rocks, the Au-polymetallic orebodies occur as NW− and NE − trending quartz-sulfide veins that are structurally controlled by NW-trending faults. The Middle Eocene host rocks are characterized by high-K calc-alkaline, peraluminous signatures, and moderately Eu negative anomalies (Eu/Eu* = 0.2–0.6). Four primary paragenetic stages of veining have been recognized: (I) smoky-grey quartz-chalcopyrite stage, (II) grey-white quartz-polysulfide stage, (III) white-pinkish barite-sulfide stage, and (IV) late quartz-carbonate stage. Fluid inclusion investigations coupled with laser Raman analyses indicate that the ore-forming fluids were formed in a NaCl − H2O ± CO2 system with two types of FIs: two phase, liquid-rich inclusions (type I) and two phase, vapor-rich inclusions (type II). The primary coexisting types I and II inclusions are observed in gold-bearing ore-stage II, sharing similar homogenization temperatures in the range of 233–286 °C and 243–281 °C, but contrasting salinity values of 10.7–14.8 and 14.6–15.5 wt% NaCl equivalent, respectively. Fluid inclusion examinations show that fluid phase separation occurred concurrently with gold precipitation during the ore-stage II. The δ18Ofluid values calculated from the δ18OSMOW and δDSMOW values of the inclusions in quartz veins are 4.9–11.1 ‰ and −84.6 ‰ to −68.3 ‰, respectively. δ13CPDB and δ18OSMOW values of Fe-dolomite are −6.5 ‰ to −5.0 ‰ and 3.1 ‰–4.9 ‰, respectively. H–O–C isotope data indicate magmatic origin of initial ore-forming fluids with minor addition of meteoric water through time. The δ34S values (−3.1 ‰ to −1.2 ‰, avg. = −2.0 ‰) of the ore-stage II sulfides suggest that sulfur comes from a homogeneous magmatic source. The Pb isotopic compositions of sulfides (207Pb/204Pb = 15.420–15.525, 206Pb/204Pb = 18.423–18.536, 208Pb/204Pb = 37.135–38.208) indicate that the Pb in the Atash-Anbar gold deposit is a mixture of crust and mantle components. We conclude that (1) the Atash-Anbar is an IS epithermal system that (2) resulted from Eocene subduction of the NeoTethys Ocean plate beneath the central Iran plate and thus (3) ore-forming fluid and its metal components (i.e., Ag, Pb, and Zn) were emanated through crystallization of the final phase of a granite porphyry intrusion.

Constraints of C[sbnd]H[sbnd]O[sbnd]S[sbnd]Pb isotopes and fluid inclusions on the origin of the giant Zhugongtang carbonate-hosted Pb–Zn deposit in South China

The Sichuan–Yunnan–Guizhou (SYG) metallogenic province on the western margin of the Yangtze Block has long been a research focus and is an important region of Pb–Zn mineralization in China, but its genesis is poorly constrained. This study examines the Zhugongtang carbonate-hosted Pb–Zn deposit (>3.0 Mt, 0.09–35.04 wt% Pb + Zn), the largest discovery made in the past decade in the southeastern part of the SYG metallogenic province. Fluid inclusions from sphalerite and calcite, CHO–isotopes from calcite, and S–Pb isotopes from sulfide minerals in the Zhugongtang Pb–Zn deposit were analyzed to understand the sources and genesis of the metals and hydrothermal fluids. Fluid inclusions in sphalerite and calcite from the largest ore body indicate that the fluids of the main mineralization stage had low temperatures (105 °C–210 °C) and moderate salinities (0.35–12.89 wt% NaCl equiv.). The sulfides are characterized by narrow ranges of sulfur isotope compositions (δ34Spyrite = +14.27 ‰ to +15.89 ‰, δ34Ssphalerite = +14.31 ‰ to +15.53 ‰, and δ34Sgalena = +10.64 ‰ to +12.97 ‰), indicating that reduced sulfur was derived from sedimentary sulfate in the Devonian to Permian carbonate host rocks by thermochemical sulfate reduction with the addition of organic matter. The δ13CPDB and δ18OSMOW values of calcite range from − 8.6 ‰ to +0.82 ‰ and +15.45 ‰ to +19.41 ‰, respectively, which are similar to values for mantle, marine carbonate rocks, and sedimentary organic matter. The negative correlation between δ13CPDB and δ18OSMOW values indicates that CO2 in the hydrothermal fluids was sourced from marine carbonate rocks and sedimentary organic matter. Calculated δ18OH2O and δDH2O values range from +3.5 ‰ to +7.5 ‰, and −93 ‰ to −52 ‰, respectively, indicating that the ore-forming fluids were dominantly metamorphic, but diluted by meteoric water that had reacted with organic matter. The galena samples yield 206Pb/204Pb values of 18.52 to 18.82, 207Pb/204Pb of 15.68 to 15.93, and 208Pb/204Pb values of 38.97 to 39.96. The μ and ω values of the sulfides range from 9.61 to 10.07 and 38.84 to 43.67, respectively. These data plot on the upper crust Pb evolution curve, generally in the field of Devonian to lower Permian sedimentary rocks, although the value for one sample falls in the field of Proterozoic metamorphic rocks, pointing to a complex origin for the ore-forming materials. Overall, the fluid inclusion and isotope data, together with geological evidence, suggest that the ore-forming fluids of the Pb–Zn deposit were sourced from deep metamorphic water with the features of low temperatures and moderate salinities, and the ore-forming metals were sourced from Devonian to lower Permian sedimentary rocks and partly from basement rocks. The genesis of the Zhugongtang ore is typical of SYG-type deposits.

Zangalou Manto‐type deposit in the Sabzevar zone, northeast Iran: Evidence of mineralogy, geochemistry, U–Pb dating, fluid inclusion, and stable isotopes

The Zangalou Cu deposit lies in the Sabzevar volcanic‐plutonic zone, northeastern Iran. The deposit is hosted by the middle Eocene volcanic‐sedimentary sequences and it has been affected by propylitic, carbonate, sericitic, and minor argillic alterations. The volcanics have features typical of calc‐alkaline and metaluminous magmas and are plotted in the continental volcanic arc region. Zircon U–Pb dating of the andesite porphyry yield ages of 41.2 and 38.4 Ma (Bartonian). Ore mineralization occurs as stratabound with open‐space filling, dissemination, veinlet, and replacement textures in mineralized conglomerate, andesite porphyry, and trachyandesite host rocks. Cu content in Zangalou deposit vary from 1,234 g/t to 6.24% which mostly occurred as chalcocite mineral. Fluid inclusion data of mineralization‐related calcites indicate medium salinities (12.8–16.6 wt.% NaCl equivalents) and a wide range of temperatures (154–295°C) and show evidence of fluid cooling trend during the ore formation. The δ13C (between 19.3 and −2.8‰) and δ18OSMOW (between 24.8 and 25.34‰) values of ore‐related calcites suggests a contribution of sedimentary organic matter and marine carbonates as the source of carbon in the ore‐forming fluid. High positive δ34S values (27.8–33.47‰) suggest that the source of sulphur is related to sedimentary country rocks. Mineralization is lithologically and structurally controlled and it is epigenetic. According to geological, petrological, alteration, mineralization textures and geometry of deposit, fluid inclusion, and isotopic studies, the Zangalou deposit is similar to manto‐type deposits.

Metallogenesis of Ni–Co–Fe-arsenide type mineralization in the Purísima-Rumicruz deposit, Jujuy, Argentina

The Purísima-Rumicruz vein system is a Ni–Co–Fe-arsenide type or Five-Element deposit located in the Cordillera Oriental, northwestern Argentina. The host rocks are Ordovician black shales of the Acoite Formation. Three vein types, were identified (a) sulfides/sulfoarsenides + carbonates ± quartz; (b) barite; and (c) crystalline quartz veins. Sulfide-carbonate veins are narrow and exhibit multi-episode infill and are NW-SE and E-W oriented. Four successive stages of mineral precipitation were established. The first stage, sulfide-rich, comprises galena, pyrite, chalcopyrite, bornite, and Zn-rich tetrahedrite-tennantite. A second stage corresponds to native silver, arsenides, Ni-sulfarsenides and pitchblende, indicative of a rise in the As/S ratio in the hydrothermal fluids. The third stage evidences a decrease in the As/S ratio with sulfide precipitation of silver sulfides, chalcocite, chalcopyrite, tetrahedrite-tennantite, bornite and millerite. Finally, a supergene event with covellite, digenite, limonite and Cu-carbonates occurred. Microthermometric studies of Stage 1 quartz yield Th between 185 and 276 °C and 5.2–12 wt% eq. NaCl. Salinities. Stage 3 calcite yield Th 110-240 °C and salinities in two ranges, 1–11 and 16.8–24 %wt. NaCl eq. The δ34S values in chalcocite and galena range between +5.8 and + 7‰, and the δ18OSMOW values from quartz, are between +6.2 and + 9.0‰. δ18OSMOW and δ13CPDB values in calcite samples range between +10.9 and +14.7‰, and −3.05 to −4.07‰, respectively. Isotope data indicate a cortical source of the fluids, probably from connate waters. Early Cretaceous rifting produced a thermal anomaly and direct faults and fractures. Deep-seated brines mixed with connate fluids of the Acoite Formation led to the formation of the Purísima-Rumicruz veins.

Origin of the Bada porphyry Cu–Au deposit, eastern Tibet: Geology and isotope geochemistry (C–O–S–Pb) constraints

Bada is a newly discovered Cu–Au deposit located in the south part of the Yulong porphyry Cu (–Mo–Au) belt (YPCB), eastern Tibet. The Cu–Au mineralization, mainly hosted by the alkali-rich quartz monzonite porphyry (QMP), with minor by the fine-grained monzonitic porphyry (MP) and surrounding strata of the Nanxin Formation. The hydrothermal alteration assemblages recognized at Bada mainly include potassic, phyllic, propylitic, and argillic. The Cu–Au mineralization occurs within the potassic and phyllic alteration zones. Three main metallogenic stages have been identified: stage I ore-barren quartz ± dolomite ± K-feldspar ± pyrite veins, stage IIa dolomite ± quartz + pyrite veins, stage IIb dolomite ± quartz + polymetallic sulfide veins, and stage III dolomite ± calcite veins. The dolomite δ13CPDB values from stage I to III range from –2.2 – –1.8 ‰, –6.8 – –3.4 ‰, to –4.2 – 1.9 ‰. Their δ18OSMOW values vary from 7.7 – 9.8 ‰, 6.5 – 11.9 ‰, to 7.8 – 11.4 ‰, respectively. The corresponding calculated δ18Ofluid values ranging from 6.0 to 6.3 ‰ for stage I, and –1.1 to 4.3 ‰ for stage II, and –1.7 to 1.9 ‰ for stage III. The C–O isotopic compositions imply that the ore-forming fluids were dominated by magmatic water with the input of meteoric water. The narrow δ34S value range of sulfides (1.43 to 6.61 ‰, mean 4.64 ‰) reflects a predominantly magmatic origin for the sulfur. The Pb isotopic compositions of most sulfide samples coincide with the alkali-rich porphyries in the region, indicating that the alkalic porphyries provided the main source of Pb. Combined with the zircon U–Pb age of the ore-bearing porphyry (ca. 35.0 Ma), the Bada deposit is defined as a porphyry Cu–Au deposit in a late-collisional setting. The study of the genesis of Bada provides a better understanding of the Cu–Au mineralization potential of the southern YPCB.

Geology, C–O–S–Pb isotopes, and their implications for the ore genesis of the Xiaohe carbonate-hosted Zn–Pb deposit in northeastern Yunnan, China

The Xiaohe carbonate-hosted Zn–Pb deposit is located in the southwest Yangtze Block of the Tethyan Metallogenic belt, northeastern Yunnan, China. The accumulated Zn–Pb reserves account for approximately 2.19 million tons, with an average ore grade of Zn and Pb at 10 wt%. Zn–Pb mineralization occurs mainly in dense massive, stockwork, bedded and disseminated forms in the NW- and SN-trending faults and sedimentary dolostone of the Ediacaran Dengying Formation. The sulfide ore and gangue minerals mainly comprise pyrite, sphalerite, galena, and hydrothermal dolomite as well as calcite with a granular, filled, zonal and coedge texture. In order to reveal the nature and origin of ore-forming fluids and ore genesis of this deposit. In this paper, the large-scale tectonic-altered lithofacies mapping method in different mining levels is adopted, and C–O, S, Pb isotopes of different hydrothemal minerals have been analyzed. The results show that the paragenesis of sulfides, hydrothermal dolomite and quartz were found along NW-trending tenso-shear faults with obvious mineralization and alteration zoning patterns. The hydrothermal period can be subdivided into three stages: 1) dolomite–pyrite–quartz, 2) sphalerite–galena–pyrite and 3) calcite. The results of the C–O–S–Pb isotopic compositions showed that the ore-forming fluids of the deposit had the characteristics of multisource fluids mixing. The δ13CPDB and δ18OSMOW values of the carbonate rocks ranged from −4.4‰ to +0.9‰ and +16.6‰ to +24.5‰, respectively, suggesting that the carbon in the ore-forming fluids mainly originated from the dissolution of marine carbonates of the Ediacaran Dengying Formation and mixing with basement-source carbon. The δ34S values of sulfides from different stages ranged from +14.3‰ to +29.1‰, indicating a reduction in sulfur that was derived from marine sulfates of the host rocks by thermochemical sulfate reduction. Different sulfides had scattered Pb isotope compositions, and the data cluster resembled that of basement rocks (Kunyang and Huili groups). Moreover, some of the values were similar to those of the Ediacaran to Triassic carbonate rocks, indicating that the ore-forming metals had mixed sources but were mainly from basement rocks. Considering the above results, this work concluded that the genesis of the Xiaohe Zn–Pb deposit is a Huize-style (also be called as Mississippi Valley type-like) Zn–Pb deposit hosted by carbonate rocks and controlled by tenso-shear faults.