Rb-Sr Isochron Research Articles

Two-phase mineralization of Hongtaiping Cu polymetallic deposit in Yanbian area (NE China): Evidence from sulfide Rb–Sr dating and in-situ trace element analysis

The Hongtaiping Cu polymetallic deposit in Yanbian area (NE China) is located in the tectonic junction between the eastern Central Asian Orogenic Belt and the North China Craton. Two mineralization types are identified at the Hongtaiping deposit, i.e., stratiform mineralization hosted in the pyroclastic rocks of the Middle Permian Miaoling Formation (Fm.) and the quartz-sulfide vein-type mineralization controlled by fractures. To determine temporal and genetic relations between the two mineralization types, sulfide Rb–Sr dating and in-situ LA–ICP–MS trace element analysis were conducted. Seven sulfide samples from stratiform orebodies yielded a Rb–Sr isochron age of 268.3 ± 2.6 Ma, which is similar to the reported zircon U–Pb age of ore-hosting pyroclastic rocks of the Miaoling Fm., suggesting that the stratiform mineralization was syngenetic. The initial 87Sr/86Sr ratios of these sulfide samples show value of 0.7102–0.7103 (average of 0.7103), implying a major crustal origin, with certain mantle-derived input, for the ore-forming materials of the stratiform mineralization. Sulfides from the stratiform and vein-type ores have distinct trace elemental features. High Co/Ni ratio and low Se content in pyrite, and high Sn content and low Zn content in chalcopyrite reflect high temperature and vice versa. In the pyrite from stratiform and vein-type ores, average Se contents are 19.72 ppm and 9.70 ppm, and average Co/Ni ratios are 0.20 and 2.46, respectively. Whilst in the chalcopyrite from stratiform and vein-type ores, average Sn contents are 2.49 ppm and 60.31 ppm and average Zn contents are 346.55 ppm and 236.17 ppm, respectively, indicating that the temperature of the stratiform mineralization is lower than that of the vein-type mineralization. Integrating the geological and geochronological features of the two types of mineralization and wall rocks, as well as trace element compositions of the sulfides, we inferred that the stratiform mineralization at the Hongtaiping deposit can be classified as volcanogenic massive sulfide (VMS)-type, associated with the Middle Permian submarine volcanism caused by the subduction of the Paleo-Asian Ocean. The vein-type mineralization was likely related to the Late Triassic felsic magmatism. In a word, two-phase mineralization implies the VMS-hydrothermal reworking-type for the Hongtaiping deposit.

Superimposed mineralization in the deformed Yulekenhalasu porphyry Cu-Mo deposit (Northwest China): Rb-Sr geochronology, S isotope, and trace element analysis of chalcopyrite

The Yulekenhalasu porphyry Cu–Mo deposit is located ca. 40 km southwest of Qinghe, in the Chinese Altay-East Junggar section of the Central Asian Orogenic Belt, NW China. The belt preserves multistage tectonic-hydrothermal and porphyry Cu-Mo mineralization events associated with arc to syn- and post-collision environments over 87 m.y. The 359 Ma deformed granitic porphyries are characterized by positive εNd(t) (+0.62 to + 3.77) and (87Sr/86Sr)initial values (0.704304–0.705960), and old crustal model ages of 747 to 1216 Ma, whereas a 272 Ma sample from late chalcopyrite–molybdenite–pyrite–magnetite–feldspar–calcite–gypsum veins yielded (87Sr/86Sr)initial values of 0.704415 to 0.705764, high εNd(t) values (+5.81 to + 5.88) and young crustal model ages (715 to 614 Ma) suggesting an increasingly juvenile mantle source over time. Seven fragments of a single deformed chalcopyrite grain yielded an Rb-Sr isochron age of 358.6 ± 4.8 Ma (2σ, MSWD = 1.8), which is consistent with the 360 Ma recrystallized zircon grains in the deformed host granitic porphyries. Eight fragments of chalcopyrite from the chalcopyrite–molybdenite–pyrite–magnetite–feldspar–calcite–gypsum veins formed along cleavage planes yielded a younger Rb-Sr isochron age of 272.2 ± 2.6 Ma (2σ, MSWD = 1.8). The younger age is interpreted as the lower age limit for the Mo and Cu mineralization in the post-collisional stage. The heterogeneous initial Sr isotopic compositions of chalcopyrite in the Yulekenhalasu deposit are likely the result of phyllosilicate inclusions. Disseminated chalcopyrite crystals in the granitic porphyry have different trace elemental contents than chalcopyrite in the deformed granitic porphyry and late chalcopyrite veins. Our Rb-Sr and trace element data for chalcopyrite grains constrain the age and geochemistry of multistage mineralization in porphyry Cu-Mo deposits. In-situ S isotope data of chalcopyrite from the deformed granite porphyries and chalcopyrite-feldspar-quartz-muscovite veins display a similar mantle origin. The 272 Ma mineralization event at Yulekenhalasu is coeval with the formation age of the Cu-Ni-(PGE) sulfide deposit in the Chinese Altay, indicating that hydrothermal mineralization like that in porphyry deposits can form proximal to ultramafic–mafic rocks and potentially may have a genetic relationship with mantle-derived Cu-Ni-(PGE) sulfide deposits.

Geochronology and Isotope Geochemistry of the Yingfang Pb-Zn-Ag Deposit: Implications for Large-Scale Metallogeny along the Northern Flank of the North China Craton

The northern flank of the North China Craton (NCC) hosts a linear zone of gold, molybdenum, silver, lead, and zinc polymetallic ore deposits. Among these, the Yingfang Pb-Zn-Ag deposit is located in the central part of the Yanshan–Liaoxi metallogenic belt (YLMB) which extends for approximately 1000 km and forms part of the major mineralized zone. In this study, we characterize the mineralization and trace the ore genesis based on new sulfur and lead isotopic geochemistry and evaluate the timing of mineralization from Rb-Sr isotope dating of sulfides. The pyrite δ34S values range from +3.2‰ to +5.8‰ with a mean at +4.07‰, close to the values of mantle and meteorite sulfur. The 206Pb/204Pb values range from 16.833 to 18.956, 207Pb/204Pb from 15.374 to 15.522, and 208Pb/204Pb from 37.448 to 37.928. Five samples of sulfide, from the Yingfang deposit, yield a Rb-Sr isochron age of 135.7 ± 4.1 Ma. This age is close to the age of the adjacent Niujuan Ag-Au deposit and the associated Er’daogou granite, suggesting a close relationship between magmatism and metallogeny in this region. The S and Pb isotopes of the regional silver polymetallic deposits show similar sources of ore-forming materials. According to a compilation of the available age data on the Mesozoic ore deposits in the northern flank of the NCC, we divide the mineralization into the following four periods: 240–205 Ma, 190–160 Ma, 155–135 Ma, and 135–100 Ma. Mesozoic magmatism and mineralization in the Yingfang deposit mainly took place at 245 Ma and 145–135 Ma. We correlate the Pb-Zn-Ag mineralization to metallogeny associated with large-scale inhomogeneous lithosphere thinning beneath the NCC.

Metallogenic chronology and tectonic setting of the Erdaohe Pb–Zn–Ag deposit in Inner Mongolia, NE China: Constraints from sphalerite Rb–Sr dating, zircon U–Pb dating, and Hf isotope analysis

• The Erdaohe deposit is a large-scale Pb-Zn-Ag deposit in the Great Hinggan Range. • The granite porphyry and the sphalerite in the deposit formed at 133.6Ma and 130.5Ma. • The mineralization was affected by the Mongolia-Okhotsk and Paleo-Pacific Ocean. • The discovery of the Erdaohe deposit shows a good exploration prospect in the region. The Erdaohe deposit is a recently discovered large-scale Pb–Zn–Ag deposit in the northern section of the Great Hinggan Range, Inner Mongolia, China. The ore bodies are mainly located in the skarnized contact zone between the granite-porphyry and calcareous wall rock, and in the fissures of the wall rock of the outer contact zone. Several vein-type ore bodies are located in the fissures of the distal volcanic strata, with obvious magmatic–structural ore-control characteristics. In this study, seven sphalerite samples from ores in the quartz–sulfide metallogenic stage yielded an Rb–Sr isochron age of 130.5 ± 1.9 Ma (MSWD = 1.6), with initial 87 Sr/ 86 Sr ratios of 0.70967 to 0.70994. LA-ICP-MS zircon U–Pb dating of the granite-porphyry samples yielded a concordant age of 133.6 ± 0.46 Ma (MSWD = 1.2). Combined with the previous studies, dating results and the field relation between the granite-porphyry and the ore body, it is considered that the granite-porphyry is genetically related to the mineralization of the deposit. The zircon ε Hf (t) values of the granite-porphyry ranged from 6.8 to 8.5, and the two-stage Hf model age (t DM2 ) ranged from 575 to 668 Ma, revealing that the granite-porphyry originated from the partial melting of the juvenile crust accreted from the depleted mantle during the end of the Neoproterozoic. Extensive magmatism during the Early Cretaceous was caused by lithospheric delamination after the closure of the Mongolia–Okhotsk Ocean and the back-arc extension induced by the subduction of the Paleo-Pacific Plate towards Eurasia; thus, the Erdaohe deposit was formed under this favorable metallogenic structure and material system. By comparing the metallogenic age, tectonic setting, and ore-forming resources, we propose that the formation of Erdaohe Pb–Zn–Ag deposit belongs to the same regional metallogenic event as the Pb–Zn–Ag deposits in the southern segment of the Great Hinggan Range, potentially indicating further exploration prospects for Pb–Zn–Ag deposit in the middle segment of the Great Hinggan Range.

Genesis of the Hebaoshan gold deposit in Fujian Province of Southeast China: constraints from a combined fluid inclusion, H-O-C-S-Pb-He-Ar isotope and geochronological study

The large Hebaoshan gold deposit (41.5 t Au, average grade: 3.5 g/t) is located in a hitherto poorly documented gold province in the northeastern part of the South China Block. It is hosted by Precambrian metasedimentary rocks that experienced Triassic greenschist- to amphibolite-facies metamorphism. Three hydrothermal stages can be distinguished: quartz + sericite + pyrite + pyrrhotite (stage I), quartz + magnetite + sulfide (stage II), and quartz + carbonate + pyrite + hematite (stage III). Auriferous pyrite samples yielded a Rb-Sr isochron age of 234 ± 3 Ma (2σ, MSWD = 0.24), and ore-related hydrothermal sericite yielded a 40Ar-39Ar plateau age of 226.4 ± 2.0 Ma (2σ, MSWD = 1.01), which are distinctly younger than ca. 430 Ma granitic rocks in the mining district and older than 170–130 Ma granites in the region, ruling out any genetic link between granite emplacement and gold mineralization. The mineralizing fluid system can be described as carbonic-aqueous with low to moderate salinity (2.2–10.1 wt% NaCl equiv.) and medium temperature of 290 to 350 °C (stage I) and 230 to 280 °C (stage II). The δ18O quartz ranges from 13.3 to 15.4 ‰, and the δD values for fluid inclusions in quartz range from − 97 to − 60 ‰. The calcite has C-isotopes ranging from − 6.1 to − 3.8 ‰ and O-isotopes from 2.8 to 13.6 ‰. H-O-C isotope data are consistent with a metamorphic fluid derived from devolatilization of Neoproterozoic basement rocks during regional metamorphism in the Late Triassic Indosinian period. The δ34S values of sulfides for stages I, II, and III are 0.1 to 7.8 ‰, − 10.6 to 5.1 ‰, and − 18.9 to − 14.1 ‰, respectively, indicating an increase in oxygen fugacity during fluid ascent which resulted in more negative sulfur isotope values of sulfides and precipitation of gold. Pyrite separates have 206Pb/204Pb ratios of 17.340 to 17.687, 207Pb/204Pb ratios of 15.539 to 15.604, and 208Pb/204Pb ratios of 37.749 to 38.094. The S-Pb isotope data suggest derivation of S and Pb from the Precambrian metasedimentary country rocks. Auriferous pyrite yielded elevated 3He/4He ratios (0.78–1.46 Ra), which suggest a mantle component as can be expected from fluids derived from a subduction setting. It is concluded that Hebaoshan is an orogenic gold deposit that formed during Triassic flat-slab subduction of the paleo-Pacific plate beneath the South China Block and thus constitutes the first Triassic deposit of this type recognized in the coastal area of Southeast China.

The importance of sequential partial melting and fractional crystallization in the generation of syn-D3 Variscan two-mica granites from the Carrazeda de Ansiães area, northern Portugal

In the Carrazeda de Ansiães region, northern Portugal, a mesozonal granitic suite intruded Precambrian to Ordovician metasedimentary rocks during the late kinematic stages of the Variscan orogeny. In this multiphase granitic complex, consisting of ten granite types, the youngest group of two-mica granites (G7–G10) was emplaced between 318 ± 1 Ma and 316.2 ± 0.7 Ma, as determined by ID-TIMS U–Pb on zircon and monazite. Granite types G7–G9 were affected by the third phase of deformation (D3) before they were completely crystallized, as indicated by their internal NW–SE magmatic foliation concordant with the regional structures. The granite type G10 shows some distinctive textural features, showing a strong brittle deformation, probably due to its preferential emplacement in late NNE-SSW fault zones. Granites G7–G9 have equal or higher amounts of muscovite than biotite and contain surmicaceous enclaves, xenoliths, “schlieren”, and, more rarely, microgranular enclaves. The muscovite-dominant granite G10 does not contain enclaves. These Variscan granites are peraluminous, with ASI ranging between 1.22 and 1.39 and normative corundum of 2.79–4.39%, having the characteristics of S-type granites. In fact, the enrichment in LREE relatively to HREE, the negative Eu anomalies, and similar mean values of (87Sr/86Sr)i, εNdt and δ18O for G7 (0.7156 ± 0.0005; − 8.5; 11.49 ‰) and G8 (0.7155 ± 0.0007; − 8.4; 11.39 ‰) show that these two granite types resulted from sequential partial melting of the same metasedimentary material, where granite G8 would have derived from a higher degree of partial melting than G7. Granites G8–G10 and their minerals show a fractionation trend that is confirmed by modeling of major and trace elements. The subparallel REE patterns and the decreasing REE contents within the differentiation series, the Rb–Sr isochron for G8, G9 and G10 (315.5 ± 5.4 Ma; MSWD = 1.3) and the relatively uniform εNdt and δ18O data suggest that fractional crystallization was the main mechanism, which would have lasted less than 1 Ma. The tin-bearing granites G7 and G10 have ≥ 20 ppm Sn, but the main quartz veins containing cassiterite and wolframite cut granite G10, which contains 31 ppm Sn. Fractional crystallization was responsible for the increase in Sn content in granites from the G8–G10 series and their micas.

Constraints of S–Pb–Sr Isotope Compositions and Rb–Sr Isotopic Age on the Origin of the Laoyingqing Noncarbonate-Hosted Pb–Zn Deposit in the Kunyang Group, SW China

The Laoyingqing Pb–Zn deposit is located on the southwestern margin of the Yangtze block and on the east side of the Xiaojiang deep fault in the Sichuan–Yunnan–Guizhou Pb–Zn metallogenic triangle area (SYGT). This deposit was first discovered in the silty and carbonaceous slate of the Middle Proterozoic Kunyang Group that is structurally controlled by thrust faults and anticlines. This study is aimed at investigating whether the Laoyingqing deposit has the same ore-forming age and type as other Pb–Zn deposits related to the Pb–Zn metallogenic system and prospecting prediction of the deep and peripheral areas of the deposits in the SYGT. Based on the sphalerite Rb–Sr age dating and S–Sr–Pb isotopic composition analysis of the Laoyingqing Pb–Zn deposit, the following results were obtained. First, the Rb–Sr isochron age of sphalerite is 209.8 ± 5.2 million years (Ma), consistent with the ages of most Pb–Zn deposits in the SYGT (approximately 200Ma), thereby potentially indicating that these Pb–Zn deposits may have been formed synchronously during the late Indosinian orogeny. Second, the Pb isotopic compositions of sulfides show a linear trend on the average crustal Pb evolution curve in 207Pb/204Pb vs. 206Pb/204Pb plot. In addition, Pb isotopic ratios were consistent with the age-corrected Pb isotopic ratios of basement rocks, consequently suggesting that the source of mixed crustal Pb is mainly derived from basement rocks. Combined with the initial 87Sr/86Sr ratios of sphalerite between the (87Sr/86Sr)200Ma value of the basement rocks and that of the Upper Sinian–Permian carbonates, it can be concluded that the ore-forming metals were mainly derived from basement rocks. Third, sulfur isotopic composition of sphalerite from the Laoyingqing deposits shows δ34SCDT values that range mainly from -2.62‰ to 1.42‰, which is evidently lower than the δ34SCDT values of sulfides (8–20‰) from other Pb–Zn deposits in the SYGT. This can be interpreted as a result of mixing with reduced S that was mainly derived from the thermochemically reduced S in the overlying strata and a small amount of reduced S produced by the pyrolysis of S-containing organic matter. We conclude that the Laoyingqing deposit and most of the Pb–Zn deposits in the SYGT are Mississippi Valley-type deposits, thereby providing new ideas for investigating the deep and peripheral areas of Pb–Zn deposits.

Rb–Sr geochronology of metamorphic rocks from the Central Indonesian Accretionary Collision Complex: Additional age constraints for the Meratus and Luk Ulo complexes (South Kalimantan and Central Java)

Metamorphic rocks of the Central Indonesian Accretionary Collision Complex are exposed in widely scattered occurrences on the islands of Java, Sulawesi, and Kalimantan. Their relationship to one or more subduction zones is controversial which can partly be explained by insufficient geochronological investigation. Using Rb–Sr geochronology we have dated various schists from the Meratus Complex, South Kalimantan, and the Luk Ulo Complex, Central Java. The Meratus schists first experienced high-pressure/low-temperature (HP/LT) metamorphism and were later overprinted at medium pressure conditions. Due to the rarity and poor preservation of such rocks, isotopic ages for well-preserved HP/LT rocks could not be determined yet. Previously obtained K–Ar white mica dates (180–160 Ma) were attributed to the HP/LT event, however, this was speculative as the dated rocks only record greenschist- to amphibolite-facies P–T conditions. A newly dated partially overprinted but still glaucophane-rich sample yielded a well-defined Rb–Sr isochron age (phengite, epidote) of 112.9 ± 0.7 Ma (all uncertainties on Rb–Sr dates indicate 95% confidence level), providing a minimum age for the HP/LT stage. Internal mineral isochrons of more severely overprinted samples show poor linear fits between mica and associated phases indicating incomplete resetting of the Rb–Sr isotope system during the later lower pressure metamorphic event. Isochrons that are derived only from different grain-size fractions of white mica indicate dates between 115 and 110 Ma (± 3 to 6 Ma). In contrast to previous interpretations that linked high-grade rocks of the Meratus Complex to collision-induced crustal thickening it is here considered more likely that these rocks either represent exotic fragments from NW Australia or the metamorphic sole of the Meratus ophiolite. Differences in temperature estimates for HP/LT rocks from the Luk Ulo Complex probably indicate erroneous textural interpretation of equilibrium mineral assemblages and/or compositions. Neither petrological analysis nor geochronological dating has yet unambiguously confirmed different P–T–t paths for eclogites with and without tourmaline (Trm) from the Luk Ulo area. The newly dated Trm-bearing epidote blueschist from the serpentinitic Muncar River mélange yielded a well-defined Rb–Sr isochron of 119.0 ± 0.7 Ma (phengite, epidote, tourmaline) that perfectly matches with existing K–Ar and Rb–Sr data for Trm-free HP/LT rocks. Two samples of the more widespread garnet-phengite schists of the Luk Ulo area yielded Rb–Sr ages (phengite, feldspar) of 118.0 ± 0.8 Ma and 114.7 ± 1.3 Ma. A meter-sized epidote amphibolite block included in these clastic metasedimentary rocks provided a Rb–Sr isochron age of 116.8 ± 0.7 Ma (phengite, epidote, whole rock). These ages match existing K–Ar data for severely overprinted rocks from the Luk Ulo area and further corroborate the geological significance of Early Cretaceous metamorphism in Central Java. Petrological and geochronological data of the Meratus and Luk Ulo complexes are in accordance with a model suggesting that both occurrences belong to the same Cretaceous subduction system. The existence of an additional Cretaceous suture zone cutting through Sulawesi is considered likely.

Amazonite Li–F Granites with REE–Nb–Zr–Th–U Specialization: Geochemistry, Mineralogy, and Isotope Geochronology of the Turga Massif, Eastern Transbaikalia

The paper reports major relations and trends determined in the distributions of trace elements and the Sr and Nd isotope composition of leucogranites of the Turga massif in Eastern Transbaikalia. Three varieties of the leucogranites are distinguished: porphyritic biotite granites, equigranular granites with Li-siderophyllite, and amazonite granites that make up small stocks and dikes. All of the rocks define a single Rb–Sr isochron that corresponds to an age of 134 ± 1 Ma at IR(Sr) = 0.71768 ± 22 and MSWD = 1.2, i.e., all of these rocks crystallized within a narrow age span. The porphyritic biotite granites, which are thought to be parental for the leucogranites, crystallized at lower temperatures (710–740°C) than the younger granites with Li-siderophyllite (810–850°C). Moreover, the granites with Li-siderophyllite have elevated Fe concentrations, which is reflected in that their micas are Fe-rich. The leucogranites are enriched in HFSE (270 ± 59 ppm Zr, 337 ± 93 ppm REE, 72 ± 31 ppm Th, and 16 ± 6 ppm U), which is atypical of amazonite granites in the study area. Considered together with very low Sr and low Ti and P concentrations, these compositional features are distinguishing features of A-type granites. The rare-metal granites of the Turga massif are unique in composition: being similar to amazonite granites in mineralized massifs, these rocks carry accessory minerals typical of peralkaline rocks. They contain LREE fluorides and fluorcarbonates (fluocerite, bastnaesite, and parisite), minerals of the pyrochlore and samarskite groups, and minerals of the isostructural group of REE–Y–Zr–Th–U silicate-phosphates. Our data provide grounds for classifying the rare-metal granites of the Turga massif with an unusual transitional geochemical subtype: peraluminous columbite-bearing amazonite granites of elevated alkalinity with peralkaline REE–Nb–Zr–Th–U mineralization.

鄂西宜昌地区页岩气勘探发现对MVT铅锌矿成矿的指示意义

The coupling relationship between hydrocarbon accumulation and the involvement of organic matter in metal mineralization has been a frontier scientific question in recent years. On the basis of the petrography and Raman spectral analysis of fluid inclusions, high-density methane inclusions were discovered in the samples of quartz and calcite veins from Sinian Doushantuo shales, Lower Cambrian Niutitang shales, and MVT (Mississippi Valley type) lead-zinc deposit of Sinian Dengying Formation in Yichang area. The Raman scatter peak v of methane inclusions was applied to calculate the density of pure methane inclusions, and the ore-forming ages of MVT lead-zinc deposit were determined by using Rb-Sr and Sm-Nd isochron dating. The density of methane inclusions trapped in the quartz veins within the Doushantuo shales of well EYY 1 mainly ranges from 0.237 to 0.278 g/cm, and the density of methane inclusions trapped in the calcite veins within the Hejiaping MVT lead-zinc deposit mainly ranges from 0.213 to 0.271 g/cm, which signifies methane inclusions of high density. Paragenetic mineral association sphalerite and galena within the Hejiaping lead-zinc deposit have a Rb-Sr isochron age of 189.1±1.8 Ma, and calcite within the Hejiaping lead-zinc deposit yields a Sm-Nd isochron age of 189.9±2.0 Ma, which indicates is the mineralization of Hejiaping lead-zinc deposit was closely related to the Yanshanian tectonic compressions. The Sr/Sr values of the paragenetic mineral association (0.711 92) and calcite (0.712 03-0.712 27) indicate that the ore-forming fluids of the Hejiaping lead-zinc deposit were derived largely from shale sources. The high-density methane trapped in fluid inclusions within the Hejiaping lead-zinc deposit was most likely derived from the high-density overpressure methane generated by the Doushantuo shales and/or Niutitang shales. The discovery of high-density methane inclusion in the shale gas layer and MVT lead-zinc deposit, and the determination of ore-forming ages of MVT lead-zinc deposit provide new evidence for the study of organic matter participation in the mineralization of MVT lead-zinc deposit.

Genesis of the Nailenggele Mo-Cu-Pb-Zn polymetallic orefield in the Boluokenu Metallogenic Belt, Western Tianshan, China: Constraints from geochronology, fluid inclusions and isotope geochemistry

The Nailenggele orefield, located in the northwestern Chinese Tianshan Orogenic Belt, is composed of the Lailisigao’er Mo deposit, No. 3571 Cu prospect and Qixing Pb-Zn deposit. Lailisigao’er is a typical porphyry deposit with characteristic veinlet-disseminated ores and potassic, phyllic and propylitic alterations. No. 3571, situated in the peripheral of Lailisigao’er, is characterized by large amounts of oxidized ores at surface with limited intrusions outcropped. Qixing, about 3 km from Lailisigao’er, is characterized by quartz-sulfide veins controlled by fractures. This study aims to examine the genetic relationships between these deposits and/or occurrences, and discuss the significance for further exploration in the orefield and elsewhere in the region. LA-ICP-MS U-Pb dating on zircons from the ore-bearing porphyry in the Lailisigao’er deposit yielded an age of 367.5 ± 4.8 Ma. The molybdenite Re-Os and sphalerite Rb-Sr isochron ages recalculated from previously published data are 365.9 ± 2.1 Ma for Lailisigao’er and 362.0 ± 5.7 Ma for Qixing, respectively, suggesting that they are coeval and both related to the granodiorite porphyries. Three types of fluid inclusions occur in the Mo-bearing quartz from Lailisigao’er, including two-phase aqueous inclusions (Type I), solid mineral-bearing aqueous inclusions (Type II) and CO2-H2O inclusions (Type III). The total homogenization (Th) temperatures cluster from 260 to 320 °C (to liquid) for type I inclusions, 310 to 332 °C (to liquid) for type II inclusions, and 268 to 324 °C (to CO2 phase) for type III inclusions. The salinities are mainly in the ranges of 2.0–8.0, 32.9–42.0, and 1.4–5.5 wt% NaCleq for types I, II and III inclusions, respectively. By contrast, only type I inclusions were identified in the Pb-Zn-bearing quartz from Qixing, with Th values of 149–261 °C and salinities of 1.7–5.3 wt% NaCleq. The δ34SCDT values of hydrothermal sulfides from Lailisigao’er, No. 3571 and Qixing range from 2.8‰ to 4.0‰, 4.0‰ to 4.6‰ and 0.7‰ to 4.9‰, respectively. Sulfides from these three locations have uniform Pb isotopic compositions. The (87Sr/86Sr)0 ratios of fluid inclusions (average 0.70971) in Mo-bearing quartz at Lailisigao’er and sphalerite (average 0.71020) at Qixing are similar to those of Mo-mineralized porphyries (average of 0.70886) from Lailisigao’er. The δ18OH2O and δDH2O values of Pb-Zn-bearing quartz from Qixing are similar to those of Mo-bearing quartz from Lailisigao’er, both plotting close to the field of magmatic water but shifted toward the meteoric line. These geochronological, fluid inclusions and isotopic data suggest that the mineralization at different localities in the Nailenggele orefield constitutes part of an integrated magmatic-hydrothermal system centered on the Lailisigao’er porphyry Mo deposit, with the Qixing Pb-Zn polymetallic deposit representing a distal end-member. Both metals and sulfur were dominantly derived from porphyritic intrusions, whereas the ore-forming fluids were initially derived from the magmatic intrusions, with increasing involvement of meteoric water in time and distance from magmatic-hydrothermal center. Fluid immiscibility in the early stage and fluid mixing in the later stage, together with cooling, were responsible for ore precipitation. Based on this mineralization model, it is inferred that concealed porphyry Cu-Mo mineralization may be developed underneath the No. 3571 and Qixing.

Early Silurian Wuchuan–Sihui–Shaoguan exhalative sedimentary pyrite belt, South China: constraints from zircon dating for K-bentonite of the giant Dajiangping deposit

The Wuchuan–Sihui–Shaoguan (WSS) exhalative sedimentary pyrite belt in the southwestern part of the Qinzhou–Hangzhou (Qin–Hang) belt is the most important sulfur industry base in China. However, a wide range of metallogenetic ages spanning from Ediacaran to Devonian has been reported in the literature. This age range does not support the idea that the typical character of “coeval mineralization” in an exhalative sedimentary mineralization belt in China and worldwide. Therefore, the precise determination of mineralization ages of representative deposits is necessary to provide guides for exploration and metallogenetic models. The Dajiangping pyrite deposit is a typical example of this kind of deposits and is also the largest deposit with a proven reserve of 210 Mt. This deposit was thought to have formed in Ediacaran or Devonian. In this study, 2–3 layers of 10–25 cm thick 2M1-type microcrystalline muscovite slate abruptly embedded in the No. IV massive orebody of the deposit has been identified to be low-grade metamorphic K-bentonite. A Concordia zircon LA–ICP–MS U–Pb age of 432.5 ± 1.3 Ma (mean standard weighted deviation of concordance and equivalence = 1.2; N = 11) has been yielded for the low-grade metamorphic K-bentonite. This age is distinctly different from the Rb–Sr isochron age of 630.1 ± 7.3 Ma for siliceous rock at the top of the No. III banded orebody and the Re–Os isochron age of 389 ± 62 Ma for pyrites from a laminated orebody. Instead, it is close to the intercept age (429 Ma) of the youngest detrital zircons from sandstone interlayers of the No. III banded orebody. The Concordia age is also coincident with those of the Late Caledonian (400–460 Ma) magmatism-metamorphism events which are widely distributed in Cathaysia Block. Particularly, it agrees well with that of the Early Silurian extensional volcanism (434–444 Ma) which have been revealed in the Dabaoshan, Siqian–Hekou, and Nanjing volcanic basins in northern Guangdong Province and southern Jiangxi Province. Hence, the dating result in this study confirms that the sedimentary time of the ore-host Daganshan Formation is Early Silurian, and implies that the mineralization age of the Dajiangping pyrite deposit should also be Early Silurian. In combination with the Early Silurian age of Shezui pyrite deposit and the Dabaoshan volcanic basin along the WSS pyrite belt, it could be inferred that the WSS pyrite belt provides a record of the northern expanding of Qinzhou–Fangcheng trough in Early Silurian and that the exhalative pyrite mineralization was triggered by the post-collisional extension of the margin of Cathaysia Block after the intracontinental collision between Cathaysia Block and Yangtze Block during Late Caledonian stage.

Timing and characterization of multiple fluid flow events in the Beibuwan Basin, northern South China Sea: Implications for hydrocarbon maturation

The history of thermal and fluid flow events is of crucial importance to understand the mechanism of hydrocarbon maturation. The northern South China Sea (SCS) contains abundant hydrocarbon resources with high heat flow anomalies, but the mechanisms responsible for modification of thermal regimes are poorly understood. Here we conducted the first high-precision Rb-Sr isochron dating and geochemical analyses of authigenic illites separated from the Palaeogene sandstones in the Beibuwan Basin, northern SCS. Eight high-precision Rb-Sr isochron ages reveal three major thermal and fluid flow events in the Beibuwan Basin, northern SCS. The 34.5 ± 0.9 Ma and 23.6 ± 0.8 Ma events occurred in the western area are probably related to the Eocene-Oligocene transition characterised by a significant regional unconformity resulted from intensive uplift of Hainan Uplift and Oligocene-Miocene transition marked by a post-rift unconformity, respectively. By contrast, the 31.2 ± 0.6 Ma event affecting the eastern area appears to be closely associated with the igneous intrusion dated by zircon U/Pb to 32.3 ± 0.7 Ma. REE and stable isotope characteristics indicate that the illites from the western area formed within a meteoric-hydrothermal system, whilst those from the eastern area were likely precipitated from fluids heated by the large-scale igneous intrusion at higher water/rock ratios. Moreover, our data in conjunction with palaeo-temperature reconstructions show that the fluid flow events had profound effects on the rapid organic maturation in the northern SCS.

Sr–Nd–O isotopic evidence of variable sources of mantle metasomatism in the subcratonic lithospheric mantle beneath the Grib kimberlite, northwestern Russia

To provide new insights into the type and extent of mantle metasomatism in the subcratonic lithospheric mantle, we examined the Sr–Nd–O isotopic compositions of orthopyroxene, clinopyroxene, garnet, ilmenite and phlogopite from sheared garnet lherzolite, granular garnet harzburgites and lherzolites and clinopyroxene-phlogopite rocks from the Grib kimberlite in the Arkhangelsk diamond province in northwestern Russia.Clinopyroxene and orthopyroxene from sheared garnet lherzolite initially have a close value of 87Sr/86Sr(t) (~0.7034) and close weak positive εNd. Orthopyroxene and clinopyroxene are in oxygen isotope equilibrium with coexisting olivine. Clinopyroxene from a garnet harzburgite has a low 87Sr/86Sr(t) isotope ratio of 0.70266. Clinopyroxene from granular garnet lherzolites has a relatively narrow variation in 87Sr/86Sr(t) (0.70456–0.70582) and considerably larger variations in εNd (−4.3 − +1.0) isotope ratios. Garnet displays elevated initial 87Sr/86Sr(t) values (0.70540–0.70633). Ilmenite shows a narrow range in 87Sr/86Sr(t) (0.70497–0.70522) coupled with εNd values of +0.4 and +3.5. These isotopic data suggest granular garnet lherzolite of mantle metasomatism took place during the interaction of kimberlite melts with SCLM that contained mica-amphibole-rutile-ilmenite-diopside (MARID)-type metasomes. Clinopyroxenes from clinopyroxene-phlogopite (phlogopite wehrlite) xenoliths display a broader range in 87Sr/86Sr(t) (0.70486–0.70813) that is significantly higher than the kimberlite values and a circa-chondritic εNd (−0.1 − +1.3) with a restricted δ18O range (5.11‰–5.33‰). More radiogenic Sr isotopic composition decoupled from Nd isotopes could have been induced by metasomatic melt/fluid related to a subducted material.The isotopic compositions of mantle minerals preserve Sr–Nd isotopic evidence of pre-kimberlite metasomatic events that were probably due to incomplete reequilibration with ultramafic carbonated melt. Based on mineral pairs Rb–Sr isochrons and a clinopyroxene-based Sm–Nd errochron, these mantle metasomatic events correspond to ~550–600 Ma and ~1200 Ma episodes of magmatic–thermal activity.

Discovery of Late Triassic mineralization in the Gangdese Metallogenic Belt, Tibet: The Banduo Pb–Zn deposit, Somdo area

The newly discovered Banduo Pb–Zn deposit in the Somdo area of Tibet is hosted by a Late Triassic granodiorite. A combination of zircon U–Pb dating, Hf isotopic compositions, sulfide Rb–Sr dating, and whole-rock geochemistry was used to determine the age of the mineralization and characterize the metallogenesis of the deposit. The weighted-mean U–Pb ages of zircon from the granodiorite (203.8 ± 1.7 Ma, MSWD = 0.53; 206.1 ± 0.4 Ma, MSWD = 0.098) and the weighted-mean Rb–Sr isochron age of sulfides from the Pb–Zn mineralization (202.7 ± 2.3 Ma; MSWD = 1.3) suggest that the timing of mineralization was close to that of granodiorite crystallization during the Late Triassic. The average (87Sr/86Sr)i value of 0.71026 implies that the ore-forming metals were sourced from a mixture of mantle and crustal material. The weakly altered granodiorite of the deposit is characterized by SiO2 = 66.78–67.85 wt%, K2O = 2.57–3.37 wt%, Al2O3 = 13.53–15.15 wt%, and Mg# = 45.5–51.3. It is enriched in LREEs and LILEs and depleted in HREEs and HFSEs, and it exhibits a negative Eu anomaly. The granodiorite has positive and negative εHf(t) values (−2.5 to 1.7) and crustal model ages (TC DM) of 1.14–1.40 Ga. Hf isotopic analyses and whole-rock geochemistry indicate that the Late Triassic granodiorite was likely sourced from of a mixture of mantle and ancient lower-crust material that had undergone variable degrees of fractional crystallization. Based on regional data, the Banduo deposit is the oldest Pb–Zn deposit in the Gangdese belt and likely formed as a result of the northward subduction of the Neo-Tethys Ocean. The metallogenic epoch indicates that deposits related to the northward subduction of the Neo-Tethys oceanic crust exist in this area. The Late Triassic age of granitoid-hosted mineralization provides additional prospects for exploration in the Gangdese Metallogenic Belt.

Precambrian faulting episodes and insights into the tectonothermal history of north Australia: microstructural evidence and K–Ar, <sup>40</sup>Ar–<sup>39</sup>Ar, and Rb–Sr dating of syntectonic illite from the intracratonic Millungera Basin

Abstract. Australian terranes concealed beneath Mesozoic cover record complex Precambrian tectonic histories involving a successive development of several Proterozoic to Palaeozoic orogenic systems. This study presents an integrated approach combining K–Ar, 40Ar–39Ar, and Rb–Sr geochronologies of Precambrian authigenic illites from the recently discovered Millungera Basin in north-central Australia. Brittle deformation and repeated fault activity are evident from the sampled cores and their microstructures, probably associated with the large-scale faults inferred from interpretations of seismic surveys. Rb–Sr isochron, 40Ar–39Ar total gas, and K–Ar ages are largely consistent in indicating late Mesoproterozoic and early Proterozoic episodes (∼1115±26, ∼ 1070±25, ∼1040±24, ∼1000±23, and ∼905±21 Ma) of active tectonics in north-central Australia. K–Ar results show that illites from fault gouges and authigenic matrix illites in undeformed adjacent sandstones precipitated contemporaneously, indicating that advection of tectonically mobilized fluids extended into the undeformed wall rocks above or below the fracture and shear (fault gouge) zones. Isotopic age data clearly indicate a Mesoproterozoic minimum age for the Millungera Basin and thus previously unrecorded late Mesoproterozoic–early Neoproterozoic tectonic events in north-central Australia. This study provides insight into the enigmatic time–space distribution of Precambrian tectonic zones in central Australia, which are responsible for the formation of a number of sedimentary basins with significant energy and mineral resources.

Magmatism, geological setting, alteration, and metallogenic potential of Donghua area, Dehua County, Fujian Province, Southeast China: Insights from porphyry zircon U-Pb and pyrite Rb-Sr geochronology, geochemistry and remote sensing

Located in the southern section of the Wuyi Mountain metallogenic belt, the Dehua-Youxi-Yongtai (DYY) ore district is one of the potential areas of gold deposits in the Fujian province, Southeast China. Gold mineralization is widely distributed in this district, including Qiucun, Shuangqishan, Ancun, and Dongyang gold deposits. However, the DYY ore district is still at a low degree of exploration and research. This paper focuses on the Donghua area in the northwest of the DYY ore district as its typical and integrated volcano-magma mechanism revealed in this study. Combined approaches including zircon SHRIMP U-Pb geochronology, Rb-Sr isochron dating and mineral chemistry of pyrite, and hyperspectral remote sensing are employed, aiming to identify the magmatism, alteration, geological setting, and metallogenic potential of the Donghua area. The zircon SHRIMP U-Pb ages of the granite porphyritic dykes in Donghua are 154.6 ± 1.1 Ma and 153.2 ± 1.2 Ma, respectively, indicating that the dykes were formed in the late Jurassic. The Rb-Sr geochronological age of hydrothermal/epithermal pyrite in Donghua is 153.7 ± 2.4 Ma, which is almost coeval with that of the granite porphyritic dykes within error, and consistent with the regional volcanic-magmatic activity and the metallogenic age of the regional metallogenic event. The granitic dykes in Donghua exhibit the characteristics of both A-type and I-type granitoids, thus indicating the presence of transitional geochemical characteristics. As a result of the subduction of the Pacific Plate towards the Eurasia, the ca. 154–153 Ma magmatic event in the Donghua area occurred at the beginning of large-scale delamination of the continental crust. The zoning distribution of the mineral alteration of chlorite, dickite, kaolinite, and gypsum, the interpretation of volcanic activity from the annular structure of hyperspectral remote sensing, and the inferred deep-seated intrusion emplacing from northwest to southeast are in agreement, thus displaying the volcano-magma-alteration mechanism developed in the Donghua area. The magmatism, dykes, faults, and Neoproterozoic metamorphic rock provide favorable advantages for the mineralization in Donghua, suggesting metallogenic potential.

First Direct Dating of Alteration of Paleo-Oil Pools Using Rubidium-Strontium Pyrite Geochronology

Direct dating of petroleum systems by hydrocarbon or associated authigenic minerals is crucial for petroleum system analysis and hydrocarbon exploration. The precipitation of authigenic pyrite in petroliferous basins is commonly genetically associated with hydrocarbon generation, migration, accumulation, or destruction. Pyrite rubidium-strontium (Rb-Sr) isotope dilution thermal ionization mass spectrometry (ID-TIMS) is a well-developed technique, and its successful application for high-temperature ore systems suggests that this dating method has the potential to directly date key processes in the low-temperature petroleum systems. Rb-Sr data for pyrites in two Ordovician carbonate rock specimens collected from ~4952 m in the YD-2 well in the Yudong region, northern Tarim Basin (NW China), yield two identical isochron ages within analytical uncertainties: 206 ± 13 (2σ) and 224 ± 28 Ma (2σ). SEM investigations demonstrate that Rb and Sr atoms mainly reside in the crystal lattice of the pyrites due to the absence of fluid and mineral inclusions. The rigorous Rb-Sr isochron relations documented in the samples indicate that such residency can result in sufficient Rb/Sr fractionation and initial Sr isotopic homogenization for geochronology. In addition, the closure temperature (227–320 °C) for the Rb-Sr isotope system in pyrite is higher than the precipitation temperature for pyrite in petroleum-related environments (below 200 °C), suggesting that the Rb-Sr age of pyrite was not overprinted by post-precipitation alteration. Integrating the lead-strontium-sulfur isotopes of the pyrites with burial history analysis, the ages are interpreted as the timing of alteration of the paleo-oil pool by a hydrothermally-triggered thermochemical sulfate reduction process. This study, for the first time, demonstrates that Rb-Sr pyrite geochronology, combined with radiogenic and stable isotopic analyses, can be a useful tool to evaluate the temporal evolution of oil pools. This approach bears great potential for dating of petroleum systems anywhere else in the world.

Tungsten mineralization during slab subduction: A case study from the Huxingshan deposit in northeastern Hunan Province, South China

The Huxingshan tungsten deposit (~0.21 Mt at 0.3 wt% WO3) is located in the Jiangnan Massif tungsten ore belt, South China. Here, the W mineralization is restricted to quartz and muscovite-quartz veins intruding variable country rocks of the Lower Cambrian strata. Rb-Sr isochron ages derived from fluid inclusions trapped in muscovite-quartz veins (ca. 134 ± 2 Ma) agree with the zircon U–Pb crystallization age of the associated Huxingshan granite (137.8 ± 0.5 Ma) and may thus suggest a close petrogenetic relationship between both rock types. Zircon εHf (t) values of the Huxingshan granite (−16.2 to +6.6) overlap with those of the specially related metasedimentary Banxi and Lengjiaxi Groups, consistent with melting of Neoproterozoic Yangtze lower crustal materials with mantle melts input to the source. We suggest that the highly differentiated signatures of tungsten and beryllium granite might be inherited from the origin chemistry of source rocks and further modified by highly fractional crystallization rather than by fluid-rock interaction processes. During this process, tungsten and beryllium was enriched in the residual melts/fluids, which finally separated from the solidifying melt body and were introduced into the county rock to precipitate scheelite and beryl along skarn and greisen horizons by large-scale fluid movements. The outlined processes are likely to be coupled to large-scale melting of continental crust and associated granitic magmatism under a regime of subduction of the paleo-Pacific Plate beneath South China and subsequent tearing of the slab. The newly discovered Huxingshan deposit underlines the huge prospecting potential for the northwestern Jiangnan Massif.

Sulfide Rb-Sr, Re-Os and In Situ S Isotopic Constraints on Two Mineralization Events at the Large Hongnipo Cu Deposit, SW China

The Hongnipo deposit, a newly discovered large copper deposit in the Kangdian copper belt, SW China, is hosted in the Paleoproterozoic Hekou Group. This deposit contains ~4200 Mt of Cu ores, with an average grade of 1.42 wt.% Cu. Orebodies occur mainly as stratiform, stratoid and lenticular forms. Mineralization consists predominantly of high grade vein-type ores and low grade laminated ores. Field relationships indicate vein-type mineralization crosscuts laminated mineralization and host rocks, indicating that there were at least two mineralization events during the formation of the deposit. Pyrite separates from the laminated ores yield a Rb-Sr isochron age of 1552 ± 80 Ma, with a highly radiogenic initial 87Sr/86Sr ratio of 0.71214 ± 0.00081, indicating a major contribution from the ore-hosting rocks. Sulfides from the laminated ores have δ34S values ranging from −1.8‰ to 11.4‰, with the vast majority in the range of 5.3‰ to 11.4‰, suggesting the mixed derivation of sulfur from seawater sulfates and magmatic fluids. Chalcopyrite separates from the vein-type ores have a Re-Os isochron age of 794.8 ± 7.9 Ma. The initial 187Os/188Os (2.8 ± 1.2) and γOs (+2202) values are slightly lower than the average values of continental crust, indicating a major metal source of the Hekou Group with minor mantle input. Sulfides from the vein-type ores have δ34S values that range from −10.3‰ to 4.0‰ and cluster between 0‰ to 2.2‰, which implies a significant contribution of magmatic-sourced sulfur with minor biogenic sulfur. Two major mineralization events have been identified. The Rb-Sr age of the laminated ores likely records a VMS mineralization event at ~1.6 Ga. The much younger Re-Os age is considered to represent the timing of an important mineralization event, which is likely related to the Neoproterozoic magmatism and/or metamorphism and represents a newly documented mineralization event to be targeted by exploration.