Volcanic-intrusive Complex Research Articles

Genesis of the Supergiant Shuangjianzishan Ag–Pb–Zn Deposit in the Southern Great Xing’an Range, NE China: Constraints from Geochronology, Isotope Geochemistry, and Fluid Inclusion

The supergiant Shuangjianzishan (SJS) Ag–Pb–Zn deposit, located in the southern Great Xing’an Range (SGXR), is the largest Ag deposit in China. The SJS deposit can be divided into two ore blocks: the Shuangjianzishan ore block and the Xinglongshan ore block. Given the importance of the Xinglongshan ore block in the SJS deposit, our work is focused on the Xinglongshan ore block. The vein orebodies in the Xionglongshan ore block mainly occur in the NW-, NNW-, and NNE-trending fault zones, and its mineralization is mainly related to a deep concealed syenogranite. Here, we present new geochronology, isotope geochemistry, and fluid inclusion data for the Xinglongshan ore block and provide additional insights into the metallogenic mechanism of the deposit. The dating results show that the syenogranite related to the mineralization formed at approximately 137 Ma, which is coherent with some previous age determinations in sulfides from the ore deposit. The mineralization of the Xinglongshan ore block can be divided into four stages: sphalerite–arsenopyrite–pyrite–chalcopyrite–quartz stage (stage I), sphalerite–galena–pyrite–silver-bearing mineral–quartz stage (stage II), sphalerite–galena–silver-bearing mineral–quartz–calcite stage (stage III), and weakly mineralized quartz–calcite stage (stage IV). Four types of fluid inclusions (FIs) have been identified within quartz and calcite veins: liquid-rich, gas-rich, pure-liquid, and pure-gas FIs. The homogenization temperatures in the four stages exhibit a gradual decrease, with stage I ranging from 253 to 302 °C, stage II from 203 to 268 °C, stage III from 184 to 222 °C, and stage IV from 153 to 198 °C, respectively. The salinity for stages I, II, III, and IV falls within the ranges of 3.4–6.6 wt% NaCl eqv., 2.6–7.2 wt% NaCl eqv., 2.9–7.0 wt% NaCl eqv., and 1.2–4.8 wt% NaCl eqv., respectively, indicative of a low-salinity ore-forming fluid. The δ18Owater and δD values of the ore-forming fluid span from −13.9‰ to 7.4‰ and −145‰ to −65‰, with δ13CV-PDB values between −11.0‰ and −7.9‰. These values suggest that the ore-forming fluid predominantly originated from a mixture of magmatic and meteoric water. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of sulfides range from 18.278 to 18.361, 15.530 to 15.634, and 38.107 to 38.448, respectively. These ratios imply that the ore-forming material was primarily derived from the Early Cretaceous granitic magma, which resulted from the mixing of depleted mantle- and crustal-derived magmas. The fluid mixing was the dominant mechanism for mineral precipitation. The Xinglongshan ore block belongs to a magmatic-hydrothermal vein-type deposit related to the Early Cretaceous syenogranite, and the Shuangjianzishan ore block belongs to an intermediate sulfidation epithermal deposit related to coeval subvolcanic rocks. The Ag–Pb–Zn mineralization at Shuangjianzishan is genetically related to the Early Cretaceous volcanic–intrusive complex.

Barium isotope variations in highly-fractionated granites linked to tin mineralization: New insights into tin recycling and enrichment in the continental crust

Most primary tin deposits are intimately associated with highly-fractionated granites (HFGs), but the factors controlling the formation of tin mineralization; including source enrichment, partial melting, fractional crystallization, and fluid processes, are still subject to debate. The potassium-rich Yanbei volcanic-intrusive complex is part of the world-class Nanling WSn metallogenic belt in South China and contains both barren and Sn-rich igneous rocks. We report here Ba isotope compositions of these rocks in an effort to elucidate the relationship between HFGs and related Sn mineralization. Overall, the results show δ138/134Ba values ranging widely from −0.83 to +0.21‰. The δ138/134Ba of the barren volcanic rocks (−0.11 to +0.21‰) are correlated with SiO2, Sr, and Ba contents, and Eu/Eu* values in a manner indicating that fractional crystallization is the main control over their Ba isotope variation. The most fractionated volcanic rocks have the highest δ138/134Ba due to crystallization of alkali-feldspar rich in light Ba isotopes. In contrast, the highly-fractionated tin granites have low Ba contents and δ138/134Ba values of −0.83 to −0.23‰. These low values cannot be explained by either addition of mantle-sourced melts and magmatic fluids, or fractional crystallization and fluid circulation at the shallow emplacement level. Rather, these geochemical features are likely inherited from an isotopically lighter crustal source with enhanced tin contents related to the recycling of intensely chemically weathered sediments. When combined with bulk-rock chemical data, the Ba isotope data suggest that assimilation of this tin-enriched source played a key role in forming the tin granites and related tin deposits.

Miocene Volcanism in the Slovenský Raj Mountains: Magmatic, Space, and Time Relationships in the Western Carpathians

The Miocene volcanic-intrusive complex in the Slovenský Raj Mountains, middle Slovakia, comprises a swarm of subalkaline basalts and basaltic andesites with alkaline basalts, trachybasalts and basaltic trachyandesites. Basaltic to doleritic feeder dykes and sporadic hyaloclastite lavas are exposed in contact with the Triassic Bódvaszilas Formation of the Silica Nappe. The primary clinopyroxene, plagioclase, and Fe-Ti oxide assemblage also contains calcite spheroids inferred to represent carbonatitic melt. These spheroids are associated with subsolidus chlorite, actinolite, magnetite, titanite, calcite, and epidote. Micropoikilitic clinopyroxene, albite, and Ti-magnetite formed due to rapid quenching. There was an incorporation of host rock carbonate during the eruption. The erupted products are the result of magmatic differentiation of the parental basaltic tholeiitic magma with a redox of ∆QFM = +1 to +3, affected by varying degrees of 0%–50% fractionation and the assimilation of carbonate material in a shallow magmatic reservoir. REE geochemistry shows N-MORB-like type patterns with both LaN/YbN and LaN/SmN < 1 at near constant Eu/Eu* (~0.9). This is supported by εNd(t=13 Ma) values of +8.0 to +7.4 determined from the basaltic rocks. The REE values can be modeled by 1% fractional melting of garnet peridotite mixed with 7% melting of spinel peridotite of PM composition (1:9 proportions). SIMS and LA-ICP-MS U/Pb analysis of zircons yields a concordant age of 12.69 ± 0.24 Ma and a 13.3 ± 0.16 Ma intercept (Serravallian) age. The Middle Miocene volcanic activity was related to subduction-collision processes along the boundary of the Cenozoic ALCAPA (Alps–Carpathians–Pannonia) microplate and the southern margin of the European plate.

Hydrothermal beryllium mineralization in the Qingtian volcanic-intrusive complex, southeast China

Hydrothermal Be mineralization in igneous-related systems is controlled by magma composition, physical conditions (e.g., temperature and pressure), hydrothermal fluid properties, and the host rocks. However, the transport, concentration, and mineralization of Be in volcanic-intrusive complexes remain poorly understood. We report the petrography, mineralogy, and geochemistry of the Qingtian volcanic-intrusive complex (Zhejiang Province, southeast China), to investigate the concentration and mineralization of Be during the hydrothermal alteration of subvolcanic rocks. The granite porphyry dikes (subvolcanic rocks), granite, and the host tuff have similar chemical, mineralogical, and isotopic compositions, and comprise one volcanic-intrusive suite. The Be mineralization in the Qingtian volcanic-intrusive complex corresponds to variable hydrothermal alteration of the granite porphyry dikes, and extensive Be mineralization mainly occur in Shawan, Huangshanlong and Tuoliao. The formation of the Shawan Be ore is likely related to the F-rich metasomatism of the granite porphyry dike after albitization, the Huangshanlong Be ore was resulted from hydrothermal alterations between granite porphyry dike and host tuff by Be-rich fluids, and the Tuoliao Be ore was formed by the hydrothermal alteration of the granite porphyry dike by evolved F− and (CO3)2−-rich fluids. Fluorine plays a key role in hydrothermal Be mineralization in these Be ores, but (CO3)2− and S2− increase the diversity of Be mineralization. The chemical compositions of Be-bearing minerals (bertrandite, phenakite, and helvine-group minerals) reflect the metasomatic alterations of the granite porphyry dike by Al-poor hydrothermal fluids. Low Be contents of the granite porphyry dike and the surrounding granite, and widespread high Be contents of the altered tuffs in Qingtian area suggest that Be may have been derived from the later hydrothermal alteration of the surrounding tuff. These results not only provide an example of the exploration of Be resources in volcanic-intrusive complexes but also suggest the potential for significant Be resources in the volcanic rocks along the southeast coast of China.

A preliminary study on the volcanic intrusive complex type beryllium metallogenic belt from the southeast coast of China

A preliminary study on the volcanic intrusive complex type beryllium metallogenic belt from the southeast coast of China

Exploring volcanic-intrusive connections and chemical differentiation of high silica magmas in the Early Cretaceous Yanbei caldera complex hosting a giant tin deposit, Southeast China

Study of the origin and chemical differentiation of silicic magmas can provide important insights into crustal evolution and rare metal metallogeny. Tin mineralization always tends to form in relatively reduced, highly fractionated granite systems. Recognition of distinctions between fertile and barren magmas is of enormous benefit to mineral exploration. The Yanbei caldera complex (YCC), is a typical inland volcanic-intrusive complex that also hosts a giant porphyry-type tin ore deposit in Southeast China. To study the origin and chemical differentiation of the YCC and constrain its relationship with tin mineralization, a comprehensive petrological, whole-rock major and trace element geochemical data, along with zircon UPb ages, trace element and Hf isotopic data of the Yanbei caldera complex (YCC) and the Xiaoji granite (XG) near the YCC are carried out. LA-ICP-MS zircon UPb dating indicates that the generation and evolution of the YCC and the XG took place in a short time (4 M.y.) of between 142.4 and 138.4 Ma. Distinct zircon Hf isotopic compositions of the volcanic and intrusive units from the YCC suggest that they were derived from different magma sources. The volcanic rocks and the XG have consistent and low zircon Hf isotopic compositions (εHf(t) = −14.9 ~ −9.0), implying that they were almost exclusively derived from melting of Paleoproterozoic crustal rocks. But the magma source of the intrusive units (the granite porphyry, GP and the biotite granite, BG) (εHf(t) = −6.0 ~ −0.8) contains a significant mantle-derived component input. The whole-rock and zircon compositions suggest that the compositionally zoned volcano of the YCC can be interpreted in terms of the “crystal mush model”. The rhyolite has the geochemical characteristics of highly evolved magmas which undergo crystal fractionation, while the dacite displays a complementary geochemical signature implying that it represents the residual crystal mush after extraction of the rhyolitic melts. The XG displays similar chronological, compositional, and isotopic features to the rhyolite, suggesting that it is the intrusive equivalent of the rhyolite. The intrusive units (GP and BG) of the YCC are highly-evolved granites with elevated tin contents, responsible for tin mineralization. By comparison of fertile and barren systems in the YCC, we suggest that simple crystal fractionation for the high-evolved/extracted granitic melt does not necessarily lead to tin mineralization. A tin-bearing and volatile-rich melt originated under high-temperature partial melting of crustal source induced by underplating/input of a hot mantle magma is an essential precondition for some magmatic-hydrothermal tin mineralization systems.

Two-stage rollbacks of the paleo-Pacific plate beneath the Cathaysia block during Cretaceous: Insights from A-type granites and volcanic rocks

Petrogenesis and tectonic implications of the Cretaceous A-type rocks in the Cathaysia block remain controversial. We address this issue by the inland early Cretaceous (137–136 Ma) A-type Tiantangshan volcanic-intrusive complex and late Cretaceous A-type (96 Ma) Shihu-Huilong syenogranites, and integrating them with Cretaceous A-type rocks in the Cathaysia block. The Tiantangshan volcanics (trachyte-trachydacite-rhyolite) have εNd(t) (−3.5 to −2.6) and zircon εHf(t) (−3.0 to −1.3), suggesting their forming by partial melting of crust with significant addition of asthenosphere mantle-derived magma. The Tiantangshan granite, genetically connected with the volcanics, having higher εNd(t) (-1.2 to −0.8) and zircon εHf(t) (avg. 0.6) with more evolved composition, was likely formed by extensive fractional crystallization of the parental magma of the volcanics, recharged by asthenosphere-derived magma. The Shihu-Huilong syenogranites have initial 87Sr/86Sr (0.707987 to 0.708939), εNd(t) (−3.7 to −4.0) and zircon εHf(t) (avg. −1.6 to −0.6), suggesting a hybrid crustal and asthenospheric magma source. The early Cretaceous A-type rocks, distributed in the inland region with northeastward younging trend, mostly have A2 chemical features and inhomogeneous isotopic composition. However, the Tiantangshan and Baijuhuajian A-type rocks are distinct by A1 chemical subgroup and more depleted isotopic composition, likely reflective of intensified extensional back-arc environment due to slab rollback with high dipping angle. We propose an asynchronous and asymmetric rollback model during early Cretaceous that southern subducted paleo-Pacific plate started to retreat earlier than its northern part, and the rollback gradually developed northeastward. The late Cretaceous A-type granites in the coastal region, and Shihu-Huilong granites, are all characterized by A1 subgroup with relatively homogeneous isotopic composition, suggesting more involvement of asthenospheric materials in magma sources, and that the coastal region was entirely under an intensified extensional back-arc environment due to slab rollback with high dipping angle. The rollback of the subducted paleo-Pacific plate during Cretaceous likely occurred as two discrete stages.

Geochemistry, geochronology, and zircon Hf isotopic compositions of felsite porphyry in Xiangshan uranium orefield and its geological implication

Recently, a new kind of volcanic rock, felsite porphyry, has been revealed by drilling in Xiangshan area, Jiangxi Province, China. To better understand petrogenesis and magmatic evolution sequence of the Xiangshan volcanic-intrusive complex, we studied systematic petrology, geochemistry, LA-ICP-MS zircon U–Pb dating, and Hf isotope results of the felsite porphyry. Results show that the felsite porphyry has similar geochemical characteristics to the porphyroclastic rhyolite, which is the predominant lithology of Xiangshan uranium orefield. Felsite porphyry and porphyroclastic rhyolite have high SiO2, Al2O3, and K2O contents, low Na2O, and MgO contents, and slightly negative Eu anomalies. Moreover, these rocks are relatively depleted in large ion lithophile elements (K, Ba, and Sr) and are enriched in high field strength elements (Th, Zr, and Hf). LA-ICP-MS zircon U–Pb dating of the felsite porphyry yielded a crystallization age of 132.2 ± 0.9 Ma, which is coeval to that of the porphyroclastic rhyolite. These ages signified that Xiangshan volcanic-intrusive complex formed in the Early Cretaceous, during which the entire South China was in the back-arc extension tectonic setting related to the subduction of the Pacific Plate under the Euroasian Plate. In-situ zircon Hf isotope data on a felsite porphyry sample show eHf(t) values from − 8.82 to − 5.11, while the Hf isotope two-stage model age (TDM2-Hf) ranges from 1513 to 1747 Ma. Combined with petrological, mineralogical, geochemistry, and geochronology results of the felsite porphyry, it is concluded that the felsite porphyry in Xiangshan might be originated from the partial melting of the Mesoproterozoic ancient metamorphic rocks, with possible input of small amounts of mantle materials.

The Jurassic volcanic–intrusive complex in the Dehua gold orefield, coastal region of SE China: Implications for the tectonic setting and epithermal mineralization

The Dehua gold orefield is an important epithermal gold metallogenic district closely related to volcanic–subvolcanic rocks in the coastal region of the Cathaysia Block, southeastern China. This paper presents new LA-ICP-MS zircon U–Pb ages, elemental and Hf isotopic data for volcanic and intrusive rocks in the Dehua gold orefield. Our results show that the volcanic rocks were produced during the Middle Jurassic (ca. 169–164 Ma), whereas the intrusive rocks were formed in the Late Jurassic (ca. 163–157 Ma). Geochemically, these rocks are characterized by high-K calc-alkaline series and are commonly enriched in LILEs and LREE, depleted in HFSE with negative Nb, Ta, and Ti anomalies, and have lower Ta, Yb, Y and Rb contents, suggesting an arc magma geochemical affinities. Hence, this study firstly reports the Middle Jurassic high-K continental arc volcanic rocks in SE China, implying that the initial subduction of the paleo-Pacific plate began at least in the Middle Jurassic. Besides, in situ Hf isotopic analyses for dated zircon from the volcanic and intrusive rocks yield εHf(t) values range from −9.03 to +1.46 and the Paleo- to Mesoproterozoic two stage Hf model ages. The partial melting of the mixture of ancient continental crust materials and newly underplated potassic-rich mantle-derived mafic magmas likely explains the genesis of volcanic and intrusive rocks in the Dehua gold orefield. In addition, the exposed areas of the Jurassic volcanic rocks in the coastal region of SE China may have great potential to prospect the epithermal deposits.

Evolution of the uranium mineralisation in the Zoujiashan deposit, Xiangshan ore field: Implications for the genesis of volcanic-related hydrothermal U deposits in South China

Volcanic-related hydrothermal U deposits from the Xiangshan ore field are situated within the Gan-Hang Metallogenic Belt in South China. These deposits are dominantly hosted in late Yanshanian felsic volcanic rocks that were emplaced during the Yanashanian post-orogenic extension. The host volcanic rocks are moderately fractionated high-K calc-alkaline A2-type volcanic rocks and are one of the possible U sources for U ore genesis in the district. Porphyroclastic rhyolite is the main host facies and contains an average of 12 ppm U, which can be released through volcanic glass devitrification and mobilised by oxidised fluids for the formation of hydrothermal mineralisation. However, REE patterns of the U mineralisation suggest multiple U sources with U mobilised from additional felsic basement rocks subjacent to the Xiangshan caldera and/or from magmatic fluids related to a late peralkaline intrusion.At the Zoujiashan deposit in the Xiangshan ore field, structurally controlled albitised zones with brannerite-dominated U mineralisation are constrained by a maximum age of 116 ± 1 Ma on hydrothermal zircon and a minimum crystallisation age of 109 ± 1 Ma on pitchblende. This constitutes the early stage of mineralisation that occurred during the early Cretaceous (ca. 120–105 Ma). The Th-Mo-P-REE-Y-Ti-Zr whole-rock geochemical signature and disseminated Th-brannerite associated with a complex mineral assemblage including hydrothermal rutile, apatite, zircon, uranothorite, sphalerite, pyrite, xenotime and REE-carbonate indicated temperatures >250 °C for the hydrothermal system. The Th-REE-Y-Nb-Zr signature of the U mineralisation concomittent with the intrusion of alkaline mafic dykes suggest that a peralkaline intrusion located at depth, postdating the Xiangshan volcanic-intrusive complex by at least 10 Ma, provided the heat source and U-Th-REE-Y-Nb-Zr-rich fluids to the hydrothermal system for the formation of the early U mineralisation. In contrast, the structurally controlled disseminated- to vein-type pitchblende-dominated U mineralisation that yielded a minimum crystallisation age of 81 ± 4 Ma represents the main stage of mineralisation (ca. 100–80 Ma) and formed during the late Cretaceous crustal extension. The mineralisation occurred at low- to moderate-temperatures (150–250 °C) as Ti-Th-Zr-rich pitchblende associated with extensive illite and fluorite alteration. Here, pitchblende that overprinted the early mineralisation stage most likely inherited the primary chemical signature of this early mineralisation, especially the high Th contents. During this episode of crustal extension, uranium was leached from the host volcanic rocks and subjacent felsic basement rocks by surface-derived oxidised fluids and transported through basement faults as carbonate and/or fluoride complexes in solution. These U-bearing solutions mixed with deep-seated magmatic-derived fluids, and the resulting destabilisation of metal complexes in solution together with pressure decrease in opening fractures promoted U deposition. Therefore, the volcanic-related hydrothermal U mineralisation in the volcanic belt formed during two major stages related to different genetic conditions.

Petrogenesis and tectonic setting of the Cretaceous volcanic-intrusive complex in the Zijinshan ore district, Southeast China: Implications for different stages of mineralization

Volcanic–subvolcanic rocks and associated Cu-Au-Ag-Pb-Zn mineralization within the Zijinshan ore district, located in the southwestern part of Fujian Province, represent a large metallogenic district within the southeastern coastal volcanic belt of China. This study presents new whole-rock geochemical, Sr–Nd–Hf isotopic, and zircon trace element data for igneous rocks within the Zijinshan area. Combining these new data with previously published geochronological results allows to constrain the magmatic and hydrothermal history and to understand the ore-related geological setting. Our results provide evidence of multi-stage metallogenic events within the Zijinshan district that can be roughly divided into early stage Cu-dominant (ca. 105–102 Ma) and late-stage Pb-Zn-enriched Ag-polymetallic (ca. 95–92 Ma) mineralization. Igneous rocks associated with the early stage of mineralization are enriched in the large ion lithophile elements (LILEs), depleted in the high field strength elements (HFSEs) with negative Nb, Ta and Ti anomalies, and have relatively high Mg# (35.9–63.5), low initial 87Sr/86Sr (0.7065–0.7088), relatively depleted εNd(t) and εHf(t) values (-3.6 to −2.3 and −5.04 to 0.85, respectively), and younger two-stage Hf model ages (1.4–1.1 Ga), suggesting that the components from metasomatized mantle were incorporated. The zircons in these early stage rocks are with elevated Ce4+/Ce3+ values (358–1029) indicating the high oxygen fugacity. In comparison, the igneous rocks associated with the late stage of mineralization have high initial 87Sr/86Sr values (0.7071–0.7103), enriched εNd(t) and εHf(t) values (−6.6 to −5.5 and −8.92 to −4.15, respectively), and older two-stage Hf model ages (1.7–1.4 Ga), that are indicative of formation from magmas that incorporated ancient crustal material. The late-stage igneous rocks contain zircons with low Ce4+/Ce3+ values (20–387) that are indicative of low oxygen fugacity conditions. Besides, the late stage ore-related igneous rocks are of high silica contents with highly evolved chemical signatures, indicative of intensive fractionation processes. The diverse metal endowments may be attributed to different sources, oxygen fugacity and magmatic evolution levels of the ore-related magmas. The Cretaceous magmas in Zijinshan were likely generated under an extensional setting. The lithospheric extension triggered partial melting of the fertile metasomatized subcontinental mantle, incorporating a large amount of mantle-derived components and generated the early Cu-Au-Mo mineralization. Later, a local and temporary shift to the more compressional environment would weaken the contribution of mantle. More ancient crustal materials were incorporated in the late stage and the magmas underwent intensive fractional crystallization, leading to the generation of Ag-polymetallic mineralization in the Zijinshan ore district.

New Volcanic Complex Found Below the Southern Tyrrhenian Sea

Researchers have identified a previously unknown volcanic-intrusive complex that originated through the melting of mantle material at the northern edge of the Ionian slab.

Metallogeny of the Zoujiashan uranium deposit in the Mesozoic Xiangshan volcanic-intrusive complex, southeast China: Insights from chemical compositions of hydrothermal apatite and metal elements of individual fluid inclusions

The Zoujiashan U deposit in the Mesozoic Xiangshan volcanic-intrusive complex is one of the largest volcanic-related type U deposits in China. Chemical composition of hydrothermal apatite and metal contents in individual fluid inclusions of quartz and fluorite are investigated in order to understand the precipitation mechanism of U and to further constrain the origin of U and ore-forming fluids of the Zoujiashan deposit. Illitization, hematitization, and U mineralization successively occurred within rhyolite and porphyritic lava. Three types of hydrothermal apatite are identified. Apatite Type 1 (Ap1) and apatite Type 2 (Ap2) are both euhedral-subhedral crystals found in hematitization zone, while only Ap2 shows evident irregular chemical zoning along its rims. Apatite Type 3 (Ap3) occurs as anhedral aggregates closely associated with U-minerals in U ore veins, implying synchronous precipitation of Ap3 and U ores. Comparable chemical compositions of Ap1 and cores of Ap2, including similar high Cl content, indicate both of them were precipitated from a Cl-rich fluid that induced hematitization. The elevated F contents of Ap3 and rims of Ap2 implies that a F-rich fluid was involved and altered Ap2 during the main stage of U deposition. Ap1 and cores of Ap2 have lower Mn contents than Ap3 and rims of Ap2, indicating an oxidized character for the Cl-rich fluid and a reducing character for the F-rich fluid.Metal contents of fluid inclusions in fluorite and quartz occurring in U ores suggest that two end-members of fluids, including a U-rich and a U-poor, were involved in the main stage of U mineralization. Mixing between these two fluids led to the deposition of U- and Th-minerals through oxidation-reduction reactions and destabilization of Th-F complexes, respectively. The U-rich fluid is depleted in Th and Sr compared with the U-poor fluid. Based on comparison of chemical compositions of apatite and fluid inclusions, we suggest that the Cl-rich fluid precipitating Ap1 and Ap2 corresponds to the U-rich end-member fluid, while the F-rich fluid precipitating Ap3 represents a mixture between the two end-members. The high U (12.7–58.5 ppm) in the U-rich end-member fluid is in agreement with a relatively high oxygen fugacity and a surface-derived origin. The U-poor end-member fluid has lower Rb/Cs than the U-rich end-member and the unaltered host rocks, indicating the U-poor fluid was derived from a mantle wedge that experienced addition of Cs by fluids generated from the devolatilization of the subducted paleo-Pacific slab.

A-type volcanic–intrusive complex in the Huanggangshan Basin: Implications for early cretaceous crust–mantle interaction in the Gan-Hang Belt and adjacent areas, South China

The origin and petrogenesis of Early Cretaceous A-type volcanic–intrusive complexes in the Gan-Hang Belt and adjacent areas of South China remain controversial. An A-type volcanic–intrusive complex in the Huanggangshan Basin of North Wuyi Mountain comprises syenite porphyry, granite porphyry, granite, and tuffaceous volcanic and pyroclastic rocks. These rocks were subjected to geochronological, geochemical, and isotopic analyses in order to investigate their age and petrogenesis, and crust–mantle interactions in South China. Field observations reveal that this A-type volcanic–intrusive complex contains abundant mafic microgranular enclaves. Zircon UPb dating of the various rock types yielded ages between 136 and 128 Ma. Geochemically, the rocks have A-type affinities, including high large-ion lithophile and high-field-strength element contents, Ga/Al ratios, and zircon saturation temperatures. (87Sr/86Sr)i values vary from 0.702704 to 0.711298, and εNd(t) = −10.63 to −7.28 and εHf(t) = −13.26 to −7.70. Three stages of magmatism are proposed to explain the petrogenesis of the A-type volcanic–intrusive complex in the Huanggangshan Basin: (1) syenitic magmas formed by mingling of crustally derived silicic and mantle-derived mafic magmas; (2) fractional crystallization of anorthitic plagioclase + biotite + ilmenite from the syenitic magmas generated A-type igneous rocks with SiO2 < 71 wt%; and (3) fractional crystallization of plagioclase + K-feldspar + biotite + apatite + allanite + ilmenite then generated A-type igneous rocks with SiO2 > 71 wt%. Combined with previous studies, we suggest that the Early Cretaceous A-type igneous rocks in the Gan-Hang Belt and adjacent areas might have been generated by crust–mantle-derived magma mixing, and the crust–mantle interaction was more intense from southwest to northeast. This increased crust–mantle interaction may have been a response to the Early Cretaceous back-arc extensional environment, possibly as a result of the rollback of the Paleo-Pacific Plate.

Petrogenesis and Tectonic Implications of the Yuhuashan A-Type Volcanic-Intrusive Complex and Mafic Microgranular Enclaves in the Gan-Hang Volcanic Belt, Southeast China

AbstractEarly Cretaceous felsic volcanic-intrusive complexes are widespread in the Gan-Hang Volcanic Belt (GHVB) and accompany abundant uranium ore resources. However, the petrogenesis and tectonic...

Петролого-геохимические особенности рудовмещающих эффузивных и интрузивных пород Николаевского месторождения золото-порфирового типа (Южный Урал)

Object. The article considers the results of geochemical studies of ore-bearing effusive and intrusive rocks of the Nikolaevka gold deposit, located in the zone of the Main Uralian fault in the Southern Urals. The deposit belongs to the gold-porphyry type which unconventional for the Urals and poorly studied here. Methods. The rock composition was determined by chemical analysis (IG UFRC RAS), mass-spectrometry with inductively coupled plasma on the ELAH 9000 quadrupole mass-spectrometer (IGG UB RAS) and X-ray fluorescence analysis on the VRA 30 spectrometer (IG UFRC RAS). Results. It is established that gold-porphyry mineralization associated with an island-arc volcanic-intrusive complex that unites plagiophyric and pyroxene-plagiophyric basalts, their tuffs, gabbro intrusions and ore-bearing series of dikes plagiophyric dolerite-porphyrites and gabbro-diorite-porphyrites. The rocks of the complex, including ore-bearing dikes, have normal alkalinity, tholeitic and transition from tholeitic to calc-alkaline composition. Among the volcanogenic formations, faunistically dated in the zone of the Main Ural fault in the Southern Urals, by a number of geochemical parameters (for example, the ratios of Zr/Nb and Nb/Th) the effusive and intrusive rocks of the deposit are the closest to the volcanics of the pyrite-bearing Baymak-Buribay Formation (D 1 e 2 ), lying at the base of the section of the Magnitogorsk island arc, and, in all probability, are their age analog. At the same time, the gold-bearing complex differs from the Baymak-Buribay Formation by a general increased iron and titanium content, with a reduced magnesia of all rock types, as well as the absence of boninites and acid volcanics, the predominance of porphyry rock types, which can be due to the geodynamic conditions of its formation. Conclusion. Geodynamic analysis of geochemical data using diagrams (La/Sm)N-TiO 2 and V-Ti/1000 suggests that the Nikolaevka deposit was formed in the articulation zone of the island arc and the back-arc basin. Gold-porphyry mineralization associated with the Late Emsian volcanic processes was isolated in the Southern Urals for the first time.

Chemical composition and Sr isotopes of apatite in the Xiangshan A-type volcanic-intrusive complex, Southeast China: New insight into petrogenesis

A series of Late Mesozoic A-type granitoids, including the Xiangshan volcanic-intrusive complex, was recently identified along the Gan-Hang volcanic belt, which was close to the boundary of the Yangtze and Cathaysia blocks in South China. However, significant issues on the petrogenesis of the Xiangshan complex, especially how mantle-derived magma contributes, if any, still remain controversial. In this study, we focused on the apatite geochemistry of the Xiangshan complex to understand the characteristics and evolution of its primary magma. In the Xiangshan complex, mainly including rhyolite, porphyritic lava, granite porphyry, and quartz monzonite porphyry, apatites occur mostly as inclusions in plagioclase and biotite, and exhibit high Srap (Sr content in apatite)/Srhr (Sr content in host rock) (from 0.97 to 3.22, 1.85 on average), indicating these apatites crystalized before plagioclase in the melt. Therefore, the negative Eu anomalies (from 0.06 to 0.83) in apatites of the Xiangshan complex indicate that plagioclase is a remaining stable mineral phase in the source rocks during the partial melting. In addition, most of apatites in the Xiangshan complex with varied whole-rock ASI (aluminum saturation index) values (from 0.88 to 1.19) are characterized by high and relatively homogeneous F content (from 3.14 to 3.55). Therefore, F-rich mineral should be a primary phase in the source. Compared with apatites in three earlier rocks of the complex, apatites from quartz monzonite porphyry have higher Mn and Cl contents, stronger degree of negative Eu anomalies, and lower initial 87Sr/86Sr (0.70642–0.70714), suggesting that before apatites crystalized, the magma to form quartz monzonite porphyry had been mixed with a Cl-rich magma derived from a mantle source that received addition of Cl from subducting oceanic sediments of the Paleo-Pacific plate. The Sr isotope ratios and halogens contents of apatite from quenched dark enclaves found in granitic porphyry imply that the enclaves were formed from this Cl-rich mantle-derived magma through injecting part of this magma into the granitic magma and remaining as quenched enclaves without mechanic mixing and no significant chemical influence on the host granitic magma. Thorough mixing between this mantle-derived magma and the felsic crustal magma did not occur until the latest stage of the Xiangshan volcanism when quartz monzonite porphyry was forming.

Petrogenesis of Cretaceous volcanic-intrusive complex from the giant Yanbei tin deposit, South China: Implication for multiple magma sources, tin mineralization, and geodynamic setting

The giant Yanbei tin ore deposit is the largest porphyry-type tin deposit in South China. The orebodies are hosted by the granite porphyry in the central part of the Yanbei volcanic basin in southern Jiangxi Province. The Yanbei volcanic-intrusive complex mainly consists of dacitic-rhyolitic volcanic rocks, granite, granite porphyry and diabase dikes. In previous papers, the granite porphyry was considered as subvolcanic rocks, which came from the same single magma chamber with the volcanic rocks. In this study, zircon U-Pb ages and Hf isotope data, as well as whole-rock geochemical and Sr-Nd isotopic compositions of different magmatic units in the Yanbei complex are reported. Geochronologic results show that various magmatic units have different formation ages. The dacite yielded a zircon U-Pb age of 143±1Ma, and the granite porphyry has the emplacement age of 138±1Ma. Diabase dikes which represented the final stage of magmatism, yielded a zircon U-Pb age of 128±1Ma. Distinctive whole rock Sr-Nd and zircon Hf isotopic compositions suggest that these magmatic units were derived from different magma sources. The volcanic rocks were mainly derived from the partial melting of Paleoproterozoic metasedimentary rocks without additions of mantle-derived magma. The granite porphyry has an A-type geochemical affinity, and was derived from remelting of Paleo-Mesoproterozoic crustal source with involvement of a subordinate mantle-derived magma. The granite porphyry is also a typical stanniferous granite with high F (4070–6090ppm) and Sn (7–39ppm) contents. It underwent strongly crystal fractionation of plagioclase, K-feldspar, and accessory minerals (like apatite, Fe-Ti oxides), which may contribute to the tin mineralization. The diabase was derived by partial melting of enriched lithospheric mantle which had been metasomatised by slab-derived fluids. The change of magmatic sources reflected an increasing extensional tectonic environment, perhaps induced by slab rollback of subducted paleo-Pacific plate.

Basement components of the Xiangshan-Yuhuashan area, South China: Defining the boundary between the Yangtze and Cathaysia blocks

The exposed metamorphic rocks and xenolithic metamorphic rocks in the Xiangshan-Yuhuashan (XSYHS) area in central Jiangxi Province, South China, were studied in order to reveal the compositions of the basement rocks and their tectonic implications. Bulk geochemistry and zircon U-Pb-Hf isotopic compositions suggest that the basement metamorphic rocks in the XSYHS area are mainly composed of Neoproterozoic (after 822–683Ma) meta-sedimentary rocks. The exposed meta-sedimentary rocks show higher K2O/Na2O and Al2O3/(Na2O+CaO) and lower Eu/Eu∗ than those occurring as xenoliths in the Yuhuashan volcanic-intrusive complex, indicating relatively strong weathering and leaching in the provenance area. Geochemical data suggest that the detritus of the exposed metasedimentary rocks was derived mainly from felsic to intermediate igneous rocks, similar to Neoproterozoic sedimentary rocks in the southern Yangtze Block, whereas the xenolithic metasedimentary rocks contain more recycled material, similar to those in the Cathaysia Block. These xenoliths from the mid-lower crust also have significantly high U contents. Consequently they probably are an important source for uranium in the XSYHS volcanic rocks.U-Pb ages of detrital zircons show that the protoliths of the xenoliths are mainly composed of Neoproterozoic, Neoarchean and Paleoproterozoic detritus, similar to the components of the Wuyi terrane in the eastern Cathaysia Block. In contrast, the protoliths of the exposed metasedimentary rocks consist mainly of Neoproterozoic detritus with minor Neoarchean and Paleoproterozoic fragments, similar to those in the southern Yangtze Block. Both geochemistry and zircon U-Pb-Hf isotope compositions suggest that the deep basement metamorphic rocks in the XSYHS area belong to the Wuyi terrane, whereas the surface metamorphic rocks are derived from the southern Yangtze Block. Therefore, the real boundary between the Yangtze and Cathaysia blocks lies north of the study area. The exposed Yangtze-related metamorphic rocks were overthrust southward from the southern Yangtze Block, and onto the Cathaysia basement, during the Indosinian to Yanshanian Orogeny.

Petrogenesis and geodynamic setting of Early Cretaceous felsic rocks in the Gan-Hang Belt, Southeast China: Constraints from geochronology and geochemistry of the tuffs and trachyandesitic rocks in Shengyuan volcanic Basin

The Late Mesozoic geology of the Gan-Hang Belt is characterized by extensive magmatism forming a belt of volcanic-intrusive complex. The geochronology, petrogenesis, and geodynamic setting of the Late Mesozoic magmatic rocks in the Gan-Hang Belt are still controversial. The Shengyuan volcanic Basin is located in the NW region of the belt and mainly contains crystal tuff, welded tuff, and trachyandesitic rocks. We integrate geochronological and geochemical data for these tuffs and trachyandesitic rocks, to explore the origin of these rocks and improve our understanding of the Late Mesozoic magmatic and tectonic evolution of the region. Zircon U-Pb dating shows that these samples were formed in the Early Cretaceous (135–137Ma). All the tuffs have a pronounced A2-type geochemical signature and their chemical compositions are controlled by crystal fractionation. All trachyandesitic rocks exhibit high K2O contents and were attributed to the shoshonite series; they are characterized by arc-like trace element distribution patterns, with significant enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE) but depletion in high field-strength elements (HFSE). Moreover, all the tuffs and trachyandesitic rocks were characterized by negative whole rock εNd(t) and zircon εHf(t). An integrated interpretation of all these geochemical data leads to the conclusion that the Shengyuan trachyandesitic rocks were primarily derived from mantle materials and oceanic crust-derived melt. The Shengyuan tuffs were formed by the partial melting of the Proterozoic orthometamorphic and parametamorphic rocks. Our studies together with previous published data suggest that the Early Cretaceous A-type felsic rocks, with ages between 138Ma and 122Ma, occurred along the Gan-Hang Belt, indicating an important Late Mesozoic extensional event in the Belt. This event represents a back-arc tectonic setting due to the rollback of the Paleo-Pacific plate.