Rb-Sr Isochron Age Research Articles

Formation of the Miaoan Au-Polymetallic Deposit in the Northern Taihang Mountain, North China Craton: Ore Geology, Geochronological and Geochemical Perspectives

Several gold ore-concentrated areas have been recognized in the destruction zone of the North China Craton (NCC). However, the deposits in the western part of the destruction zone have received less attention. Miaoan, a typical Au-polymetallic deposit in the northern Taihang Mountain, provides a good sample for deepening our understanding of the genesis of gold deposits in the western destruction zone. In this study, detailed ore geology, pyrite Rb-Sr age, trace element and S-C-O isotopes of Au-bearing ores were conducted to constrain the source of ore-forming materials and their tectonic setting. The pyrites obtain an Rb-Sr isochron age of 129.5 ± 2.5 Ma, consistent with those of magmatic rocks in this deposit, suggesting their genetic relationship. The δ34S values ranging from −5.5‰ to 1.6‰ and the high Co/Ni and Y/Ho ratios of pyrites indicate the mantle-crust mixing characteristics of ore-forming fluids. The δ13C (−6.3‰ to −2.0‰) and δ18O (9.3‰ to 17.6‰) values of Au-bearing ores and calcites suggest mixing characteristics as well. Geochronologically, the Miaoan Au-polymetallic deposit was formed during the destruction of the NCC. We propose that the Miaoan Au-polymetallic deposit is a decratonic gold deposit and that its ore-forming materials have a mixed source of mantle and crust.

The magmatic and tectono-metamorphic history of the Sistan suture zone, Iran: New insights into a key region for the convergence between the Lut and Afghan blocks

• Meta-plagiogranites of the Sistan mélange document Cretaceous igneous activity. • This adakitic magmatism is synchronous to or slightly earlier than the HP/LT event. • Felsic rocks and eclogites shared the same P–T evolution after tectonic mixing. • Melt formation can be reconciled with the subduction of a spreading ridge. • The youngest zircon age of a gabbro from the Birjand ophiolite is 104.2 ± 0.5 Ma. The Sistan suture zone, eastern Iran, exposes a well-preserved accretionary complex that formed by the closure of a Neotethyan ocean basin between the Central Iranian Lut block and the Afghan microcontinent. Mélange sequences include tectonic slices of adakitic plagiogranitic rocks and rare jadeitite. Adakitic whole rock characteristics, compositional zoning of phengites, and matching U–Pb zircon and Rb–Sr isochron ages ( c. 87–85 Ma) suggest that the plagiogranites formed before or during the high-pressure/low-temperature (HP/LT) metamorphism that affected other parts of the subduction zone complex. Meta-plagiogranites, eclogites, and blueschists only shared the same P–T evolution after blocks of the felsic intrusions had been tectonically incorporated into the mélange. The suture zone has also been intruded by felsic melts that have largely escaped metamorphic overprinting. The weighted mean U–Pb zircon age of 81.0 ± 1.2 Ma for a newly dated sample of this group is consistent with the 86–71 Ma range previously reported for such rocks. Melt formation is not limited to the forearc region and can be reconciled with a model suggesting subduction of a spreading ridge. A newly dated gabbro yielded a weighted mean U–Pb zircon age of 104.2 ± 0.5 Ma, which is interpreted to represent magmatic crystallization and the youngest protolith age reported so far for the Birjand ophiolite. The geological relevance of an even younger intercept age (91.0 ± 2.7 Ma) of a small zircon subset remains elusive.

Timing and ore genesis of the Ciweigou low-sulfidation epithermal gold deposit in the Yanbian Cu-Au district, NE China

The Ciweigou low-17 sulfidation epithermal Cu-Au mining district, NE China, is hosted by Early Cretaceous andesite of the Jingouling Formation. From bottom to top (not explored below the 100 m level), the ore bodies consist of gold-bearing quartz veins, gold-bearing quartz-calcite veins, and calcite veins and the sides are stockwork veins and hydrothermal breccia ore bodies. Five mineralization stages are distinguished: (I) pyrite-sericite, (II) quartz-calcite, (III) grey quartz, (IV) milky quartz-adularia and (V) late carbonate. Au-bearing minerals deposited in stages II and III. Hydrothermal alteration is composed of an inner silicic-pyritic zone, intermediate zone of quartz-sericite-adularia, outer zone of quartz-chlorite-epidote and upper zone of calcite. Systematic fluid inclusion petrography shows that two-phase vapour-rich and liquid-rich inclusions are the dominant fluid inclusions types in the quartz and calcite veins, suggesting that the ore-forming fluids belong to a moderate- to low-temperature (140 °C−320 °C) and low-salinity (0 wt%−14 wt% NaCl-eqv.) H2O-NaCl-CO2 system. HO isotopes (δ18OH2O = -14.0 ‰ to −4.9 ‰ and δD = −123.4 ‰ to −88.1 ‰) indicate that the ore-forming fluids likely originated from mixed fluids driven by residual andesitic magmatic fluid. The precipitation mechanisms are mixing and major fluid boiling. The comprehensive geological and isotopic characteristics show that the Ciweigou deposit is a low-sulfidation epithermal deposit. Six pyrite samples from stages I and II yielded a Rb-Sr isochron age of 102.6 ± 2.2 Ma (MSWD = 1.19), consistent with other low-sulfidation epithermal gold mineralization ages in the Yanbian district and Lesser Xing'an Range. The timing of the Ciweigou gold mineralization at ∼103 Ma postdates the eruption of andesitic magma (106.4 ± 2.1 Ma, zircon U–Pb) and granodiorite porphyry (106.6 ± 1.2 Ma, zircon U–Pb) and diorite porphyry (107.8 ± 1.8 Ma, zircon U–Pb) emplacement, suiting in an extensional environment attributed to the rollback of the subducting Paleo-Pacific Plate.

The mineralization of Daxiao carbonate-hosted Pb-Zn deposit, northeast Yunnan province, SW China: Constraints from Rb-Sr isotopic dating and H[sbnd]O[sbnd]S-Pb isotopes

The Sichuan-Yunnan-Guizhou (SYG) Pb-Zn metallogenic province located in western Yangtze Block contains more than 400 carbonate-hosted Pb-Zn deposits. Uncertain mineralization age and ore-forming material source causing debates on the genesis of these carbonate-hosted Pb-Zn deposits. To address this issue, the Daxiao Pb-Zn deposit was chosen as a case study. The orebodies of Daxiao deposit are hosted in Mesoproterozoic Heishan formation argillaceous dolomite interbedded with slate. Three main mineralization stages have been identified, including syn-sedimentary stage, hydrothermal stage and supergene stage. The ore minerals consist of galena, sphalerite, chalcopyrite, argentite, smithsonite, anglesite and cerussite in the deposit. The early hydrothermal stage sphalerite yielded a Rb-Sr isochron age of 223.5 ± 2.9 Ma, consistent with the spike of Pb-Zn mineralization in SYG metallogenic province. Quartz in hydrothermal stage yields δDSMOW values of −69.6 to −65.8 ‰ and calculated δ18OFluid values of + 3.4 – +5.6 ‰, showing an affinity of metamorphic water. While the quartz in supergene stage yields δDSMOW values of −68.3 to −65.8 ‰ and calculated δ18OFluid values of −4.1 to −1.7 ‰, indicating abundant basinal brine or meteoric water had mixed into ore-forming fluid during its evolution from hydrothermal stage to supergene stage. Sulfur isotopic composition (δ34S = +6.3 – +19.1 ‰) of different stage sulfides reveal that the ore-forming sulfur originated from sulfates within the wall rocks, and mainly reduced by Thermal-chemical reduction (TSR). Moreover, the 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of early hydrothermal stage sphalerite are 18.282 – 18.312, 15.603 – 15.681and 38.287 – 38.311, respectively. Those of late hydrothermal stage galena are 18.315 – 18.491, 15.676 – 15.721 and 38.314 – 38.326, respectively. All of them plot in the overlapping area of Emeishan flood basalts, Kunyang and Huili groups and Sinian to Triassic strata, indicating that these wall rocks jointly contributed the ore-forming metals for these Pb-Zn deposits in SYG metallogenic province. Hence, a metallogenic model for Daxiao and other carbonate-hosted Pb-Zn deposit in SYG metallogenic province was proposed: In the thrustfold systems caused by the subduction of Paleo-Pacific and the closure of Jinshajiang-Ailaoshan Paleo-Tethys ocean in Late Triassic to Early Jurassic. The fluids originated from metamorphic water migrated along deep faults and extracted ore-forming materials from wall rocks (including Proterozoic basement rocks, Sinian to Triassic sedimentary wall rocks and Permian Emeishan flood basalts), and then precipitated ores in the secondary thrust faults or interlayered fractures within these thrustfold systems.

Genesis of the Maoling gold deposit in the Liaodong Peninsula: Constraints from a combined fluid inclusion, C-H-O-S-Pb-He-Ar isotopic and geochronological studies

The large tonnage Maoling gold deposit (25 t @ 3.2 g/t) is located in the southwest Liaodong Peninsula, North China Craton. The deposit is hosted in the Paleoproterozoic metamorphic rocks. Four stages of mineralization were identified in the deposit: (stage I) quartz-arsenopyrite ± pyrite, (stage II) quartz-gold- arsenopyrite-pyrrhotite, (stage III) quartz-gold- polymetallic sulfide, and (stage IV) quartz-calcite-pyrrhotite. In this paper, we present fluid inclusion, C-H-O-S-Pb-He-Ar isotope data, zircon U-Pb, and gold-bearing sulfide (i.e. arsenopyrite and pyrrhotite) Rb-Sr age of the Maoling gold deposit to constrain its genesis and ore-forming mechanism. Three types of fluid inclusions were distinguished in quartz-bearing veins, including liquid-rich two-phase (WL type), gas-rich two-phase (GL type), and daughter mineral-bearing fluid inclusions (S type). Fluid inclusions data show that the homogenization at temperatures 197 to 372 °C for stage I, 126 to 319 °C for stage II, 119 to 189 °C for stage III, and 115 to 183 °C for stage IV, with corresponding salinities of 3.7 to 22.6 wt.%, 4.7 to 23.2 wt.%, 5.3 to 23.2 wt.%, and 1.7 to 14.9 wt.% NaCl equiv., respectively. Fluid boiling was the critical factor controlling the gold and associated sulfide precipitation at Maoling. Hydrogen and oxygen stable isotopic analyses for quartz yielded δ18O = −5.0‰ to 9.8‰ and δ D = −133.5‰ to −77.0‰. Carbon stable isotopic analyses for calcite and ankerite yielded δ13C = −2.3‰ to −1.2‰ and O = 7.9‰ to 14.1‰. The C-H-O isotope data show that the ore-forming fluids were originated from magmatic water with meteoric water input during mineralization. Hydrothermal inclusions in arsenopyrite have 3He/4He ratios of 0.002 Ra to 0.054 Ra, and 40Ar/36Ar rations of 1225 to 3930, indicating that the ore-forming fluids were dominantly derived from crustal sources almost no mantle input. Sulfur isotopic values of Maoling fine-grained granite range from 6.‰1 to 9.8‰, with a mean of 7.7‰, δ34S values of arsenopyrite from the mineralized phyllite (host rock) range from 8.9‰ to 10.6‰, with a mean of 10.0‰, by contrast, δ34S values of sulfides from ore vary between 4.3‰ and 10.6‰, with a mean of 6.8‰, suggesting that sulfur was mainly originated from both the host rock and magma. Lead radioactiveisotopic analyses for sulfides yielded 206Pb/204Pb = 15.830–17.103, 207Pb/204Pb = 13.397–15.548, 208Pb/204Pb = 35.478–36.683, and for Maoling fine-grained granite yielded 206Pb/204Pb = 18.757–19.053, 207Pb/204Pb = 15.596–15.612, and 208Pb/204Pb = 38.184–39.309, also suggesting that the ore-forming materials were mainly originated from the host rocks and magma. Zircon U-Pb dating demonstrates that the Maoling fine-grained granite was emplaced at 192.7 ± 1.8 Ma, and the host rock (mineralized phyllite) was emplaced at some time after 2065.0 ± 27.0 Ma. Arsenopyrite and pyrrhotite give Rb–Sr isochron age of 188.7 ± 4.5 Ma, indicating that both magmatism and mineralization occurred during the Early Jurassic. Geochronological and geochemical data, together with the regional geological history, indicate that Early Jurassic magmatism and mineralization of the Maoling gold deposit occurred during the subducting Paleo-Pacific Plate beneath Eurasia, and the Maoling gold deposit is of the intrusion-related gold deposit type.

Eocene fault-controlled fluid flow and mineralization in the Paradox Basin, United States

Abstract Sedimentary rocks of the Paradox Basin of the Colorado Plateau (southwestern USA) record widespread manifestations of paleo–fluid flow and fluid-rock reactions including Cu, U-V, and Fe-Mn mineral deposits, Si and Ca metasomatism, hydrocarbon accumulations, and bleached sandstones. Many of these are spatially associated with faults. Here we show evidence for a widespread phase of fault-related fluid migration and mineralization at 41–48 Ma in the Paradox Basin. We measured K-Ar dates of multiple size fractions of clay-rich fault gouge, yielding statistically overlapping dates of authigenic (1Md) illite for the Salt Valley (47.0 ± 3.0 Ma), Kane Springs (47.7 ± 3.8 Ma), Cliffdweller (43.4 ± 4.6 Ma), Courthouse (41.9 ± 2.3 Ma), Lisbon Valley (45.3 ± 0.9 Ma), and GTO (48.1 ± 2.6 Ma) faults. The latter two have an illite Rb-Sr isochron age of 50.9 ± 3.5 Ma, and fault-adjacent bornite has a Re-Os isochron age of 47.5 ± 1.5 Ma. Authigenic illite from a paleo–oil reservoir near the Courthouse fault formed from the interaction of reduced fluids with oxidized red-bed sandstones at 41.1 ± 2.5 Ma. The Moab and Keystone faults have older authigenic illite ages of 59.1 ± 5.7 Ma and 65.2 ± 1.0 Ma, respectively. Our results show a close temporal relationship between fault gouge formation, red-bed bleaching, and Cu mineralization during an enigmatic time interval, raising questions about drivers of Eocene fluid flow.

Superimposing porphyry Mo and vein-type Cu-Pb-Zn mineralization in the Panjiaduan deposit, Great Xing’an Range (NE China): Perspective from zircon U-Pb and sphalerite Rb-Sr dating, geochemistry and S-Pb isotopes

The southern Great Xing’an Range (SGXR) is located in the eastern Central Asian Orogenic Belt (CAOB), and represents the most important Cu-Mo-Pb-Zn polymetallic mineral province in NE China. The Panjiaduan deposit in the SGXR is characterized by superimposing mineralization: (1) porphyry Mo ore hosted by syenogranite, and (2) superimposing vein-type Cu-Pb-Zn ore, hosted by fracture zones in the Manitu Formation volcanics and granodiorite. Two zircon U-Pb ages of 233.9 ± 2.8 Ma and 236.1 ± 2.8 Ma for the syenogranite (porphyry) ore host indicate that the porphyry Mo mineralization occurred in the Late Triassic, coeval with the adjacent Laojiagou porphyry Mo deposit. Sphalerite from the Cu-Pb-Zn ore veins yielded a Rb-Sr isochron age of 138.5 ± 3.5 Ma, suggesting Early Cretaceous overprinting mineralization. The syenogranite is geochemically similar to the ore-causative monzogranite at Laojiagou. They are unfractionated I-type granites, LILE- and LREE-enriched, and HFSE- and HREE-depleted. In addition, their magma source was likely derived from partial melting of the juvenile lower crust. Major sulfides (pyrite, molybdenite, and galena) from the porphyry ores have slightly lower δ34S values (−2.8 to −0.3 ‰) than the vein-type ore sulfides (pyrite, chalcopyrite, sphalerite, and galena) (1.5 to 5.3 ‰), although they are all close to the mantle δ34S values and thus suggests a magmatic sulfur source. Meanwhile, the Pb isotope compositions of the two ore types suggest that the Pb for the porphyry mineralization was likely derived from an orogenic Pb reservoir, while the latter may have crust-mantle mixed Pb source. We suggested that both mineralization events were formed in an extensional setting, induced by the post-collision tectonics after the Paleo-Asian Ocean closure and the Paleo-Pacific subduction rollback, respectively.

An Early Cretaceous gold metallogenesis in the Wuhe area, Eastern Anhui province: Constraints from geology, fluid inclusion, H-O isotope and geochronology on the Hekou gold deposit

The Wuhe area in eastern Anhui province, hosting 23 metric tons of gold, has been recognized as a new gold ore cluster in the North China Craton (NCC) since the Hekou gold deposit was discovered in 2017. Its metallogenic setting and ore-forming process remain unclear. In this contribution, we perform a combined geology, cathodoluminescence, fluid inclusion, H-O isotope and pyrite Rb-Sr geochronologic studies on the Hekou gold deposit of the Wuhe area. In order to perform detailed fluid inclusion petrography study, we used scanning electron microscope-cathodoluminescence (SEM-CL) on a well preserved sulfides-bearing quartz grain from the auriferous quartz vein. In this quartz grain, generation A barren quartz in the core zone (QA, CL-white), minor sulfides bearing generation B (QB, CL-light gray) in intermediate zone and sulfides rich generation C (QC, CL-dark gray) in the distal zone and fractures were revealed. Only in QC, the higher carbonic proportion (50–80 vol%) inclusions (CC) coexist with the two-phase liquid-rich aqueous fluid inclusions (LC) and sulfides, meanwhile the CC and the LC show a similar Th of 258–313 °C and 249–308 °C, but different salinities of 1.4–5.3 wt% NaCl equivalent and 6.0–10.9 wt% NaCl equivalent, respectively. It suggests that dominating fluid immiscibility recorded in QC is responsible for the prime deposition of gold and sulfide minerals. The δ18O (-4.1 to −6.5‰) and δD (-67.1 to −81.3‰) values of fluid inclusions in quartz suggest that ore-forming fluids were mainly derived from magmatic water which could related to mantle source. Gold-bearing pyrites yield an Rb-Sr isochron age of 128.1 ± 2.7 Ma, which is 8 m.y. earlier than the peak value of gold mineralization ages (ca. 120 Ma) at Jiaodong in response to the Early Cretaceous lithospheric thinning of the NCC and the reactivation of the Tan-Lu Fault zone (TLFZ). The Wuhe area shares similar characteristics of geology, fluid inclusions, H-O isotopes, and ore-forming ages with the Jiaodong gold ore cluster, highlighting the exploration potential in this region.

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.

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.

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.

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.