Early Cretaceous Intrusions Research Articles

Multi-stage early Cretaceous magmatism in the Tongling region, lower Yangtze metallogenic belt (E. China)

ABSTRACT A combined investigation of geochemistry and geochronology was carried out for Early Cretaceous magmatic rocks in Tongling, centre of the Middle and Lower Yangtze River. The magmatic activity can be divided into two stages, peaking at ~140 Ma and ~127 Ma. The previous show high Sr and Sr/Y, low Y, and the later have low Sr, Sr/Y and La/Yb. There are correlation patterns between Sr-Nd isotopes and SiO2, and samples show little variation of V and Cr with large variation of Rb, which suggest the effects of partial melting of the diverse source and magma mixing/crustal assimilation were more important than fractional crystallization. The broad variation of εNd(t) and εHf(t) values can be attributed to binary mixing of YC lower crust with slab-derived or enriched mantle melts. The TDM2 of Nd and Hf, Zr saturation temperature, and magma oxygen fugacity display increased trend from ~140 Ma to ~127 Ma. Based on these signatures, origin model of the Early Cretaceous intrusions in Tongling was proposed. Affected by Pacific Plate subduction, following metasomatism by slab-derived fluid/melts, basaltic magma derived from lithospheric mantle underplated the lower crust. Meanwhile, partial melting of the lower crust formed the intermediate-felsic rocks of the first stage. As subduction continued, roll-back of the subducted slab resulted in extension, causing lithospheric thinning and the upwelling of hot asthenosphere. The second stage intrusions were the result of the reworking of the Meso-Neoproterozoic crust in the extension tectonic setting.

Origin of the Early Cretaceous Be mineralization in the Tongbai-Dabie orogen, central China

The Niangniangding Be deposit is a Be-only deposit in the Tongbai-Dabie orogen. The Be mineralization is hosted in albitized granite in the contact zone between biotite monzogranite and metasedimentary rocks. Genthelvite, a Zn-rich helvine-group mineral, is the major carrier of Be. The Niangniangding biotite monzogranite and albitized granite were emplaced at 769–766 Ma and were derived from reworking of Paleoproterozoic crust in a Neoproterozoic continental-rift setting. Hydrothermal monazite coexisting with genthelvite yields an in situ U-Pb age of 126.7 ± 1.6 Ma, demonstrating that the Be mineralization is genetically unrelated with the Niangniangding granite that was albitized by Early Cretaceous ore-forming fluids. The albitization caused an increase of Al, Na, Mn, Fe, Zn, Be and Sr contents and a decrease of Si, K, Rb and Ba contents, reflecting in the formation of spessartite, albite, genthelvite and calcite and the consumption of quartz, K-feldspar and biotite. Petrographic and geochemical evidences hint that ore-forming fluids and metals (e.g., Be, Zn, Mn) may be sourced from non-exposed Cretaceous intrusions and metasedimentary wall rocks (the Huangmailing Formation). The Early Cretaceous intrusions are related to crustal extension due to the rollback of Paleo-Pacific plate. The close spatial relation between genthelvite, calcite, and albitization indicate that the fluid composition (the availability of Na+ and CO2– 3) may have crucially controlled the precipitation of Be. Our study indicates that the Tongbai-Dabie orogen has potential for Early Cretaceous extension-related Be deposits.

Grain-scale zircon Hf isotope heterogeneity inherited from sediment-metasomatized mantle: Geochemical and Nd-Hf-Pb-O isotopic constraints on Early Cretaceous intrusions in central Lhasa Terrane, Tibetan Plateau

AbstractClarifying the mechanism of recycling of pre-existing continental crustal materials into the source of mantle-derived magma is a challenging effort that can be of great value to improving our understanding of mantle processes and continental crust growth. This study presents an integrated investigation of whole-rock and mineral geochemical and Nd-Hf-O-Pb isotopic data for dolerites and diorites intruded in the central Lhasa Terrane of Tibetan Plateau at ca. 120 Ma (zircon U-Pb ages). These intrusions have similar distributions of trace elements that are characterized by depletion in Nb-Ta relative to Th, Ba, and U, and moderately negative whole-rock εNd(t) (–5.0 to –1.7) values. Magmatic zircon shows dramatically variable εHf(t) values (from –5.0 to +13.7 in the same rock, including up to 12 epsilon unit variability in single grains). On the other hand, the zircon δ18O values are relatively uniform (+6.0‰ to +7.7‰). The constant 208Pb/206Pb values of clinopyroxene crystallized at ca. 500–900 MPa suggest no contamination with lower continental crust. The lack of covariation between Hf and O isotopes from the same grains, and the lack of relationship between Hf isotopes and trace elements (e.g., Hf, Th/U, and Yb/Gd) in the magmatic zircons, together with the absence of ancient zircon xenocrysts, imply limited upper crustal contamination. In combination with high-whole-rock Th/La (>0.29) ratios, we interpret the zircon Hf isotope heterogeneity as inherited from a depleted asthenospheric mantle with the addition of 1–4% Hf from isotopically heterogeneous sediments. Our study therefore emphasizes the need for caution when using complex Hf isotopic zonation in zircon as an argument for intracrustal hybridization of two end-member magmas derived from distinct reservoirs. In addition, the high-Zr/Y ratios and no negative Zr-Hf anomalies of the Aruo intrusions imply a high surface temperature of the down going slab that was able to fully dissolve zircons in the subducted sediments. This requires a special geodynamic condition that was most likely related to the steepening of flatly subducted Neo-Tethyan lithosphere at ca. 120 Ma according to a synthesis of regional tectonic-magmatic-sedimentary records.

Late Jurassic and Early Cretaceous magmatism along the northeastern margin of the Inner Mongolia Plateau and its tectonic significance

The Inner Mongolia Plateau is located in the north of the Late Palaeozoic Hegenshan ophiolitic mélange belt, and its Mesozoic magmatism impacts our understanding of the tectonic evolution affected by the closing of the Mongol‐Okhotsk Ocean and Palaeo‐Pacific Ocean. Here, we present new U–Pb ages, whole‐rock geochemistry and Hf isotopes from the Late Mesozoic magmatic rocks in the Dalai area along the northeastern margin of the Inner Mongolia Plateau. The Late Jurassic rock types include medium‐fine‐grained phenocryst‐bearing and porphyritic monzogranites as well as medium‐fine‐grained monzogranites with the precise age range of 167.7–159.8 Ma. The Early Cretaceous rock types consist of fine‐grained biotite monzogranite and medium‐fine‐grained biotite monzogranite with the precise age range of 140.9–130.7 Ma. The geochemistry data show that the Late Jurassic and Early Cretaceous rocks are peraluminous granites and high‐K calc‐alkaline series and can be classified as A‐type granite. These granites are enriched in large‐ionlithophile elements such as Rb, Th and U, depleted in the high‐field‐strength elements such as Nb, Sr, P, and Ti. Rare earth elements have high total concentrations and present the light rare earth elements enriched with the heavy rare earth elements depleted. Zircon Hf isotopes show that εHf(t) ranges from +8.0 to +15.9 from the Late Jurassic rocks and +6.9 to +13.5 from the Early Cretaceous rocks. Our new results reveal that the Late Jurassic and the Early Cretaceous magmas were derived from partial melting of the younger lower crust, and the Early Cretaceous rocks are more strongly contaminated than the Jurassic intrusions. The Late Jurassic rocks in the Dalai area were formed from a post‐collisional setting related to the closure of the Mongol‐Okhotsk Ocean in the Early‐Middle Jurassic. The Early Cretaceous intrusions were formed from a transition setting from post‐collision to syn‐collision associated with the superposition of the Mongol‐Okhotsk Ocean and the Palaeo‐Pacific Ocean tectonic domain.

Spatial-temporal heterogeneity of magma emplacement process and its constraints on localization of associated orebody: A case study in the Shizishan orefield of the Tongling Ore Cluster, East China

We present a study on the Dongguashan quartz diorite stock which is the largest Early Cretaceous intrusion associated with skarn-porphyry polymetallic ore deposit in the Tongling Ore Cluster, Middle-Lower Yangtze Metallogenic Belt in East China. The Dongguashan quartz diorite show massive texture without obvious foliation, and intrusive contact was locally observed inside of the stock. The anisotropy of magnetic susceptibility (AMS) results of the stock show two distinct groups. The Group I (G-I) is dominated by NE-SW-striking magnetic foliation with variably oriented magnetic lineation. The Group II (G-II) that intruded into G-I is characterized by steep NW-SE-striking magnetic foliation and lineation, which are parallel to the vein-like orebody developed in the stock. The 3D geometrical modelling of the stock displays a triangular shape in plan-view with an eastward bulge and irregular stock boundary in the eastern side and the contact surface is steeper in the west than that in the east, denoting that the stock was constructed with an eastward magma accretion trend. Furthermore, the Dongguashan quartz diorite has a wide range of composition and geochronological data, suggesting a multiple magma pulses emplacement model. Accordingly, we propose that the Dongguashan stock was constructed by at least two stages magma pulses. The earlier stage magma pulses intruded along the NE-SW-striking pre-emplacement structures in the country rock and partly intruded into the lithological and mechanical discontinuous interfaces which yielded the stratabound skarn orebody. The eastward magma accretion produced a highly deformed and longer heated country rock on the eastern side of the stock, favoring the orebody development along the eastern stock-country rock contact interface. The late-stage magma pulse and the parallelism among the trend of magnetic foliation of G-II, extensional structure and vein-like orebody suggest that the vein-type orebodies may controlled by both magma emplacement and regional tectonics.

Petrogenesis and geodynamic significances of the early Late Cretaceous intrusion in the Langxian Complex, eastern Gangdese batholith of southern Tibet

Petrogenesis and geodynamic significances of the early Late Cretaceous intrusion in the Langxian Complex, eastern Gangdese batholith of southern Tibet

New data concerning the age and composition of intrusion complexes of the northern part of Balygychan-Sugoi rift depression (North-Eastern Russia)

The Balagychan-Sugoi (Omsukchan) riftogeneous depression is described by different authors both as a part of Okhotsk-Chukotka volcanic belt (OCVB) and as a separate structure. The unique Dukat gold and silver deposit and a lot of others ore deposits including rare-metal, such as Arylah, Lunnoe, Askold, Mechta, Tidid, Krasin, are associated with this structure. All mentioned objects are located in the south part of the depression and from this point of view are connected with OCVB structure. Evolution of the Balygychan-Sugoi depression is closely related to the stages of magmatic evolution of the region. In the article, these stages are characterized based on the data form intrusion bodies located in the northern part (Naygain depression). This part is the most outlying from the OCVB and less investigated. For the first time, the U-Pb zircon and baddeleyite dating and the description of petrographic and geochemical composition have been carried out for Mandychan gabbro-diorite and Nayahan gabbro leucogranite intrusion complexes from the northern part of the depression and for Omsukchan leucogranite complex. The Late Jurassic – Early Cretaceous intrusions of the Mandychansk complex dated as 143-139 Ma mark the beginning of the rift depression formation. Intrusion of granitoids of the Nayahan and Omsukchan complexes dated as 84-85 Ma and 81-82 Ma correspondently is related with new stage of magmatic activity, synchronous to OCVB formation. The petrographic and geochemical compositions of these granitoids indicate their belonging to the I-type granites, which are typical for extension environments, whereas leucogranites of the Omsukchan complex have some features corresponding to the A-type granites.

Petrogenesis of Cretaceous granitoids in the Bengbu–Wuhe area, southeastern North China Craton: Implications for gold mineralization

Sinistral slip along the Tancheng–Lujiang Fault Zone (TLFZ) during the Mesozoic resulted in an offset of approximately 400 km between the Dabie and Sulu orogens. The Bengbu–Wuhe gold belt (BWGB) represents an extension of the Zhaoyuan–Yexian gold belt to the west of the TLFZ. Early Cretaceous intrusions are widely distributed throughout the BWGB. Gold deposits in the BWGB are commonly associated with intermediate acid dykes that are roughly contemporaneous with mineralization, and some orebodies are hosted in granitoids. This paper investigates granitoids within the BWGB to constrain their petrogenesis, tectonic setting, and metallogenic significance using systematic whole-rock elemental geochemistry, apatite geochemistry, zircon U–Pb dating, zircon Lu–Hf isotopes, and whole-rock Sr, Nd, and Pb isotopes. The timing of Au mineralization (134–113 Ma) in the area is consistent with the age of intrusive adakite-like rocks (130–115 Ma) and normal calc-alkaline granitoids (114–109 Ma). The adakite-like samples are characterized by pronounced enrichment in light rare earth elements (REE), depletion in heavy REE ((La/Yb)N = 30.5–66.2), an absence of Eu anomalies, high Sr contents and Sr/Y ratios, low Y and Yb contents, and fractionated REE patterns ((Dy/Yb)N = 1.22–1.69). They have relatively low Mg# values (38–42) and variable Sr–Nd–Pb–Hf isotopic compositions (87Sr/86Sr(t) = 0.7083–0.7111; εNd(t) = −22.2 to −14.9; 206Pb/204Pb(t) = 17.219–18.010; zircon εHf(t) = −21.0 to −12.3). These features indicate that the parental magmas of the adakites were derived from partial melting of thickened lower crust of the South China Plate and/or the North China Craton. The normal calc-alkaline granitoids have low Sr/Y (6.0–40.5), La/YbN (6.8–24.7), and Dy/YbN (0.90–1.28) ratios, exhibit negative Eu anomalies, and have variable Sr–Nd–Pb–Hf isotopic compositions (87Sr/86Sr(t) = 0.7082–0.7085; εNd(t) = −22.7 to −17.7; 206Pb/204Pb(t) = 16.686–16.713; zircon εHf(t) = −24.9 to −19.0), indicating they were derived from the middle to lower crust of the North China Craton. Compared with the normal calc-alkaline granitoids, the adakite-like rocks have higher zircon Ce4+/Ce3+, higher apatite SO3 and lower apatite MnO contents, lower and more variable zircon crystallization temperatures, and higher apatite molar OH/F and Cl/F ratios, indicating that the adakitic magmas were more enriched in volatiles and more highly oxidized. Taken together, field observations and geochemical data suggest that the adakite-like rocks related to the subducted South China Block are the ore-causative rocks.

From 2D to 3D Modeling of Mineral Prospectivity Using Multi-source Geoscience Datasets, Wulong Gold District, China

The Wulong gold district (WGD) is located at the northeastern margin of the North China Carton (NCC) on the Liaodong Peninsula, China. The results of early mineral exploration, mining, and metallogenic modeling research show that gold deposition was associated with lithospheric thinning of the NCC and the emplacement of voluminous Early Cretaceous intrusions. In this study, multi-source information on the ore formation and geology (including geophysical, geochemical, and remote sensing data) was used to construct two-dimensional (2D) prospectivity maps at multiple levels (surface (0 m), − 500 m, − 1000 m, − 1500 m, − 2000 m, − 2500 m, and − 3000 m) for subsurface mineral exploration in the WGD. The methodology employed consists of four steps. Firstly, three-dimensional (3D) geological and geophysical models were constructed using UBC-GIF and SKUA-GOCAD software. 3D geophysical modeling included 3D gravity and magnetic inversions, and 3D resistivity models were based on 2D magnetotelluric (MT) inversion. Secondly, multi-source, ore-forming, and geoscientific data were integrated using radial basis function link net modeling technology within ArcGIS-SDM. Thirdly, multiple-level 2D prospectivity maps were integrated using the discrete smooth interpolation method within the SKUA-GOCAD software to produce 3D prospecting models. Finally, posterior probabilities were classified to delineate 3D exploration targets using the concentration–volume fractal method (GeoCube software, v. 2.0). The results suggest that: (1) the Early Cretaceous intrusions are key ore-forming and ore-controlling objects within the WGD, and a potential target is the western part of the Sanguliu intrusion at depths from 1000 to 3000 m, in the zone where the Wulong and Yangjia gold deposits cross; (2) there are potential targets within 2500 m of the Wulong gold deposit; however, (3) there are no potential targets from 1000 to 3000 m in the Sigdaogou gold deposit.

Early Cretaceous granodiorite and its mafic enclaves from the Shuiyu area (Southern North China Craton): implications for crust–mantle interaction

ABSTRACT The Early Cretaceous granitoids are widely distributed in the southern North China Craton (NCC), petrogenesis of these rocks is critical to understanding the implications for the Early Cretaceous geological evolution at the southern margin of the NCC. This paper presents detailed zircon LA-ICP-MS U-Pb ages, geochemistry, in-situ zircon Hf isotope for the granodiorite and its mafic microgranular enclaves (MMEs) from the Shuiyu area, southern NCC. The granodiorite and its MMEs have identical zircon U-Pb ages (~130 Ma). Field and petrological observations, such as ellipsoidal shapes, partly diffusive contact to the host rocks, erosion and resorption textures in amphibole, combined with their low SiO2 content, high Mg# values and negative εHf(t) values (−13 to −18), suggest the MMEs were derived from enriched lithospheric mantle. The host granodiorite displays moderate SiO2 contents, high Sr/Y (44 to 113) and La/Yb (25 to 38) ratios, and low zircon Hf isotopes (−10 to −23), suggesting they were from primary magmas generated by partial melting of the ancient thickened lower continental crust of the North China Craton. The petrogenesis of Early Cretaceous intrusions and its MMEs in southern NCC geodynamically interpreted as resulting from the break-off of the subducted Yangtze Craton slab, associated with the upwelling of asthenospheric mantle material, which provided the necessary heat and triggered the partial melting of the enriched lithospheric mantle beneath the southern NCC, producing primary mafic magma. Then, the mafic magma underplated and caused partial melting of a thickened region of the lower continental crust in the southern NCC.

Metallogenic model of the Wulong gold district, China, and associated assessment of exploration criteria based on multi-scale geoscience datasets

The combined use of geological and geophysical modeling is effective for delineating subsurface exploration criteria and conducting quantitative analyses to determine potential mineral targets. In this paper, total horizontal derivative, multi-scale edge detection (worms), and bi-dimensional empirical mode decomposition (BEMD) of district-scale gravity and magnetic data were applied to extract geophysical information reflecting deep-seated structures and concealed intrusions. In addition, deposit-scale 3D modeling and controlled-source audio-frequency magnetotelluric data were used to identify potential ore-controlling structures. The results of our integrated multi-scale geological and geophysical studies suggest that the Early Cretaceous intrusions and gold deposits in the Wulong gold district, which is located on the Liaodong Peninsula, China, at the NE margin of the North China Craton (NCC), are spatially and genetically associated with a network of NE- and NW- striking faults. Gravity and magnetic modeling effectively identified buried Early Cretaceous intrusions and NW- striking faults at depths from zero to five kilometers. In summary, the combined use of multiple-source and multi-scale geophysical information and multi-scale 3D geological modeling facilitated delineation of the metallogenic model and provided exploration criteria for determining potential exploration targets in the study area.

Petrogenesis of the Payangazu Complex in Southern Mandalay, Central Myanmar and Its Tectonic Implications

The Payangazu complex in the central Myanmar is composed mainly of quartz diorite, granodiorite, and some synplutonic mafic dikes. The quartz diorite and granodiorite have zircon U-Pb ages of 130.5±4.0 (MSWD=3.5) and 118.4±2.5 Ma (MSWD=2.4), respectively. Rock samples of the quartz diorite and granodiorite are metaluminous, enriched in large-ion lithophile elements like LREE, Rb, Th, and U, and depleted in high field-strength elements such as HREE, Nb, Ta, P, and Ti, indicative of arc-type magmatic affinities. Whole rock samples of the quartz diorite have eHf(t) value of +0.6, initial 87Sr/86Sr ratios of 0.708 6 to 0.710 0, and eNd(t) values of -4.8 to -4.9; whereas rocks of the granodiorite are relatively isotopically enriched, with eHf(t) values of -5.1 to -7.2, initial 87Sr/86Sr ratios of 0.711 7 to 0.711 8, and eNd(t) values of -8.7 to -8.8. The isotopic data together with the high Mg# (both the quartz diorite and granodiorite have Mg# values of >40) suggest a strong involvement of mantle materials in the genesis of the parent magmas. The possible petrogenetic process may be that the ascending of melts from partial melting of metasomatized mantle wedge triggered by dehydration of subducted slab resulted in partial melting of the lower crust and mixed with the latter. These Early Cretaceous intrusions from the complex are older than those found in the eastern Wuntho-Popa arc in western Myanmar, eastern Himalaya, and western Yunnan which are interpreted to be related to the Neo-Tethyan subduction, and have eNd(t), eHf(t) values lower than the latter. On the contrary, the ages and geochemical characteristics of the Payangazu complex are consistent with some of the intrusions in the northern magmatic belt in Tibet, eastern Himalaya, and western Yunnan which are believed to be associated with the subduction of the Bangong-Nujiang Ocean crust. Thus, we propose that the Early Cretaceous intrusions in the central Myanmar are most likely related to the southward subduction of an ocean slab that was possibly an extension of the Bangong-Nujiang Ocean.

The aeromagnetic expression of New Zealand’s Alpine Fault: regional displacement and entrainment of igneous rock

ABSTRACTThe Alpine Fault is very well delineated by recent high-resolution aeromagnetic data sets over much of its length in New Zealand’s South Island. Aeromagnetic data acquired over parts of the West Coast, Tasman and Marlborough regions for the New Zealand Government reveal different types of total magnetic intensity anomalies associated with the fault that can be characterised as truncated, step, ridge, trough and broad anomalies. Fault-terminated Permian ultramafic rocks, Late Cretaceous basalt and some Early Cretaceous intrusions are attributed to the more prominent truncated anomalies. The pre-eminent step anomaly is associated with relatively magnetic Alpine Schist juxtaposed against variable but generally less magnetic Western Province rocks. Strongly positive ridge anomalies occurring in the Alpine Fault zone are associated with Mesozoic mafic metavolcanic and ultramafic rocks. A trough anomaly associated with the Alpine Fault occurs in the southernmost survey and may reflect some hydrothermal demagnetisation. Broad, low-amplitude anomalies underlying the hanging wall are attributed in one instance to the extension of the magnetic Hohonu Range granitoids and dikes extending southeast in the footwall and in other places as magnetic schist rocks in the hanging wall. The apparent great-circle displacement of the Alpine Fault based on offset of magnetic anomalies associated with the Dun Mountain Ultramafics Group rocks is c. 461 km, in close agreement with the more precise 459 km inferred from geological map offset.

Petrogenesis of Early Cretaceous intermediate-felsic dikes in the Jiaodong Peninsula, south-eastern North China Craton: Constraints from geochronology, geochemistry and Sr-Nd-Pb-Hf isotopes

Early Cretaceous dike swarms are widely developed in the Jiaodong Peninsula, NE China. In this study, we newly investigated the spatial-temporal distribution, petrography, geochronology and whole-rock geochemistry of the intermediate-felsic dikes from the Jiaobei terrane and the Sulu orogenic belt in the Jiadong Peninsula. The zircon U-Pb dating has constrained the timing of the emplacement of intermediate-felsic dikes to 128–108 Ma. The quartz diorite dikes in Jiaobei show adakitic geochemical features, including high SiO2 (66.3–67.5 wt%) contents and high Sr/Y (76–149) and La/Yb (41–91) ratios. The combination of a series of isotopic data, including initial 87Sr/86Sr ratios (0.7098–0.7104) and negative εNd(t) (−20.1 to −14.7) and zircon εHf(t) values (−19.9 to −9.5), indicates that these quartz diorite dikes were likely derived from partial melting of thickened ancient lower crust with involvement of underplated mafic magmas. Additionally, the diorite dikes in Jiaobei and those in Sulu show similar chemical compositions, as both yield the high-Mg andesite (or andesitic rocks) (HMAs) characteristics with a high Mg# value (60–72), high MgO, Cr, and Ni contents, and low Na2O (average = 3.25 wt%) contents. They also exhibit crustal geochemical signatures, such as depletion in Nb, Ta, and Ti, but enrichment in Th and U; high initial 87Sr/86Sr ratios (0.7063–0.7094), and low εNd(t) (−16.7 to −9.6) and εHf(t) values (−29.4 to −9.8). The entire geochemical evidences imply that they derived from the partial melting of mantle wedge peridotite metasomatized by hydrous fluids from the subduction of the oceanic slab with marine sediments. In combination with the Early Cretaceous intrusions and mafic dikes at Jiaodong, the intermediate-felsic dikes represent a magmatic response to lithospheric thinning resulted from the prolonged thermo-mechanical-chemical erosion processes caused by slab rollback of the Paleo-Pacific plate.

Geochemistry and geochronology of Late Jurassic and Early Cretaceous intrusions related to some Au (Sb) deposits in southern Anhui: a case study and review

Some Au deposits in southern Anhui Province have recently been found to be closely associated with Late Mesozoic intrusions. Typical examples include the Huashan Au (Sb) deposit and Au deposits at Zhaojialing, Wuxi, and Liaojia. In order to understand the mechanisms that led the formation of these Au deposits, we make detailed reviews on the geological characteristics of these Au deposits. Specifically, we present new LA-ICP-MS zircon U–Pb dating, along with elemental and Hf isotopic data from the Huashan Au (Sb) deposit. Our data suggests that the Huashan ore-related intrusions were emplaced during the Late Jurassic and Early Cretaceous periods (144–148 Ma). They are characterized by arc-magma features and high oxygen fugacity and are rich in inherited zircons. Zircon U–Pb ages and Lu–Hf isotopes from intrusions suggest that Proterozoic juvenile lithosphere is the main source of these intrusions. The regional geological history implies that lithosphere beneath southern Anhui was produced during a Proterozoic subduction and was fertilized with Au (Cu) in the process. Integrated with the results of previous studies, we inferred that Late Mesozoic intrusions formed by the remelting of the lithosphere could provide the metal endowment for the Au-rich deposits in southern Anhui.

Revisiting Mesozoic felsic intrusions in eastern South China: spatial and temporal variations and tectonic significance

Whole-rock and mineral geochemical data are used to place new constraints on the petrogenesis and tectonic setting of Mesozoic granitoids (including syenites) in eastern South China. In the Early Mesozoic, granitoids of variable compositions were intruded in the Cathaysia Block which by this time had developed a thickened and highly differentiated Paleoproterozoic crust through the influence of subduction. Late Triassic (~225Ma) syenites are significantly different from Jurassic-Cretaceous syenites in South China and from most trachytes (GEOROC database) in terms of their high Th/U, La/Nb and Gd/Yb ratios. Their low Rb contents, coupled with their high K/Rb and Nb/Ta, and low 87Sr/86Sr and 206Pb/204Pb ratios suggest a source that had undergone granulite-facies metamorphism at the base of thickened (>45km thick) continental crust where garnet and rutile are stable. The Late Triassic alkaline intrusions thus appear not to be related to continental rifting. Compared with the Late Triassic syenites, contemporaneous syenogranites have higher Ga/Al and Rb/K ratios and ISr values. Their Ga/Al ratios are positively correlated with ISr values, and their higher Ga/Al ratios likewise do not appear to be related to a rift setting but reflect the composition of the source. New Pb isotopic data from Cretaceous magmatic rocks reveal that 120–100Ma I-type granitoids in Zhejiang Province were likely derived from mixing of three components: contemporaneous basaltic magma, an enriched crustal component and a depleted crustal component. Pb isotopes of both the I-type granitoids and the basalts become more radiogenic towards the coast, where the ca. 100Ma intrusions dominate. Furthermore, zircon-melt partition of Ce and hornblende oxygen barometries indicate that the Early Cretaceous intrusions also became more oxidized towards the coast. In addition, the ca. 100Ma granitoids have higher Gd/Yb and lower Fe/Mg ratios than those of the 120–110Ma suite, implying crustal thickening resulting from 120 to 100Ma basaltic underplating in the region.

Geochronology, geochemistry, Sr–Nd–Hf isotopic compositions, and petrogenetic and tectonic implications of Early Cretaceous intrusions associated with the Duolong porphyry–epithermal Cu–Au deposit, central Tibet

ABSTRACTThis article reports new zircon laser ablation-multicollector-inductively coupled plasma-mass spectrometry U–Pb and Hf isotope, whole-rock major and trace element, and Sr–Nd isotope data for mineralized and barren intrusions associated with the Duolong porphyry–epithermal copper–(gold) deposit (DPCD, a mining camp containing several individual deposits) in the western Qiangtang Terrane (QT), central Tibet. These data are used to further our understanding of the geological evolution of this region. The mineralized and barren DPCD intrusions are typical I-type granitoids that were synchronously emplaced at ca. 112.6–125.9 Ma. These igneous rocks show arc affinities that are characterized by enrichments in the light rare earth elements (LaN/YbN = 4.08–15.23) and the light ion lithophile elements (Rb, Th, U, K, and Pb), and depletions in the high field strength elements (Nb, Ta, and Ti). They have 87Sr/86Sr(i) values of 0.7046–0.7079, Nd(t) values of –6.0 to +1.1, and two-stage Nd model ages of ca. 823–1410 Ma. Zircons from these intrusive rocks have variable but generally positive εHf(t) values (–2.7 to +13.7) and relatively young zircon Hf crustal model ages of 335–1351 Ma. Combining these data with geochemical data reported in recent studies, we infer that the mineralized and barren DPCD intrusions formed in a continental marginal arc setting and likely originated from a common parental magma that was result of magma mixing of juvenile crust-derived basaltic melts and old lower crust-derived melts. The formation of the DPCD intrusions indicates that the Bangongco–Nujiang oceanic lithosphere was still undergoing northward subduction beneath the western QT at ca. 112.6–125.9 Ma, suggesting in turn that the oceanic basin have not closed completely during the Early Cretaceous. These new data also indicate that the processes that occur during the subduction of oceanic crust in continental marginal arc settings produce and preserve juvenile crustal material, leading to net continental crust vertical growth and thickening.

Early Cretaceous Na-rich granitoids and their enclaves in the Tengchong Block, SW China: Magmatism in relation to subduction of the Bangong–Nujiang Tethys ocean

The Na-rich intermediate-to-felsic granitic rocks provide insights into the generation of magmas in subduction zones. This paper presents zircon LA-ICP-MS U–Pb ages as well as whole-rock geochemical, mineral chemical, and in situ zircon Hf isotopic data on Na-rich granitic rocks from the Tengchong Block, SW China. The granodiorites and associated mafic magmatic enclaves (MMEs) from the Menglian batholith yield zircon U–Pb ages of 116.1±0.8 to 117.8±0.6Ma and 117.7±0.7Ma, respectively. Both host granodiorites and enclaves show calc-alkaline and sodium-rich nature, enrichment in large-ion lithophile elements (LILEs), and variable depletion in zircon Hf isotopic compositions. Euhedral amphiboles in both granodiorites and associated enclaves are magnesian-hornblende with high Mg and Ca and contain euhedral plagioclase inclusions of labradorite to andesine (An36–57) composition. The granodiorite was most likely derived through the mixing of partial melts derived from juvenile basaltic lower crust and a minor evolved component of ancient crustal sources. The quartz monzodiorite–granodiorites and associated MMEs from the Xiaotang-Mangdong batholith yield zircon U–Pb ages of 120.3±1.3 to 122.6±0.8Ma and 120.7±1.5Ma. These rocks are also sodium-rich and show calc-alkaline trend with negative zircon Hf isotopic compositions (−5.55 to +0.58). The MMEs in the host intrusions are monzogabbro with variable and depleted zircon Hf isotopic compositions. The amphiboles in the both host intrusions and the enclaves show Al-rich ferro-tschermakite composition. We infer that the quartz monzodiorite–granodiorites were derived from magmas generated by the melting of ancient basaltic rocks in the lower arc crust induced by the underplating of mantle-derived mafic magmas. The formation of the different types of Na-rich granitic rocks is correlated to the subduction of Bangong–Nujiang Tethyan ocean. A comparison with magmatism in the northern magmatic belt suggests that mantle-derived magmas played an important role in the genesis of Early Cretaceous intrusions from Tengchong to Lhasa Blocks, although crustal melting is the dominant contributor.

Origin of ore-forming fluids of the Haigou gold deposit in the eastern Central Asian Orogenic belt, NE China: Constraints from H-O-He-Ar isotopes

The Haigou lode deposit contains 40t of gold at an average grade of 3.5g/t, and is one of the largest deposits in the Jiapigou gold belt located along the eastern segment of the northern margin of the North China Craton. The deposit comprises 15gold-bearing quartz veins hosted in a Carboniferous monzonite–monzogranite stock. Cretaceous dikes consisting of diorite, diabase, and granodiorite porphyries are well developed in the deposit. The diorite porphyry dikes (130.4±6.3Ma) occur together with gold-bearing quartz veins in NNE- and NE-striking faults. Gold-bearing quartz veins crosscut the diorite porphyry dikes, and the veins are in turn crosscut by E–W-striking 124.6±2.2Ma granodiorite porphyry dikes. The mineralization mainly occurs as auriferous quartz veins with minor amounts of sulfide minerals, including pyrite, galena, chalcopyrite, and molybdenite. Gold occurs as either native gold or calaverite. Common gangue minerals in the deposit include quartz, sericite, and calcite. The deposit is characterized by various types of hydrothermal alteration, including silicification, sericitization, chloritization, potassic alteration, and carbonatization. Three stages of hydrothermal activity have been recognized in the deposit: (1) a barren quartz stage; (2) a polymetallic sulfide (gold) stage; (3) a calcite stage. Fluid inclusions in hydrothermal pyrites have 3He/4He ratios of 0.3 to 3.3 Ra and 40Ar/36Ar ratios of 351 to 1353, indicating mixing of fluids of mantle and crustal origin. Hydrothermal quartz yielded δ18O values of −1.3‰ to +7.2‰ and δD values of fluid inclusions in the quartz vary between −80‰ and −104‰. These stable isotope data also suggest mixing of magmatic and meteoric fluids. Noble gas and stable isotopic data suggest that the ore fluids have a predominant mantle source with a significant crustal component. Based on the spatial association of gold-bearing quartz veins with early Cretaceous intrusions, and the H–O–He–Ar isotopic data from the deposit and intrusions, we propose that gold mineralization in the Haigou deposit was formed in an extensional setting and was related to the early Cretaceous, mantle-derived intrusions.

The Mesozoic magmatic sources and tectonic setting of the Zijinshan mineral field, South China: Constraints from geochronology and geochemistry of igneous rocks in the Southeastern Ore Segment

The Zijinshan mineral field is a large porphyry-epithermal CuAuMoAg ore system located in the southwestern Fujian Province, China. The Southeast (CuMo) Ore Segment (SOE) is a newly discovered section located in the southeastern portion of the Zijinshan mineral field. Zircon UPb and molybdenite ReOs ages, as well as the geochemical compositions of intrusive and volcanic rocks and zircon Hf isotope data are used to constrain the timing, petrogenesis, tectonic setting and the relationship between magmatism and metallogenesis in the SOE and Zijinshan mineral field.Major and trace element geochemistry indicates that igneous rocks from SOE are mainly shoshonitic granitoids that are LILE enriched (Rb, Ba, Th, U) with HFSE depletion (Nb, Ta, Zr, Hf and Y), indicating a subduction related setting. New UPb zircon analyses yield weighted mean ages of ca. 160Ma for the Caixi pluton, ca. 110Ma for the Sifang granodiorite, ca. 107–105Ma for the Luoboling granodiorite porphyry, ca. 105Ma for the quartz diorite porphyry, ca. 108–105Ma for the dacite porphyry, ca. 98Ma for the rhyodacite, and 97Ma for the rhyolite in the SOE. These dates, integrated with previous geochronological data, indicate that there were two main magmatic events in this area: (1) a Middle to Late Jurassic event (165–150Ma), and (2) a Cretaceous event (110–95Ma) which can be further divided into two groups, i.e., the late Early Cretaceous event (110–105Ma) and the early Late Cretaceous event (100–95Ma). The late Early Cretaceous intrusions contain higher εHf (t) values (0.1 to −3.6), with TDM2 varying from 1.4 to 1.0Ga, which may come from mixing between crustal and subduction-related mantle derived melts in contrast to the Middle to late Jurassic intrusions that may come from the partial melting of the Cathaysia Block basement. The early Late Cretaceous intrusions display a broader range of εHf (t) values (−0.9 to −9.4), with TDM2 varying from 1.8 to 1.2Ga, suggesting a similar source to the late Early Cretaceous rocks but with more crustal material.The molybdenite ReOs ages for mineralization range from 110Ma to 105Ma, consistent with ages of the late Early Cretaceous rocks. Zircon trace elements analyses imply that the early Late Cretaceous rocks (Ce4+/Ce3+=113–1800) are characterized by higher oxygen fugacity with higher mineralization potential than the late Early Cretaceous (Ce4+/Ce3+=9–545) and the Middle to Late Jurassic rocks. Variability in ages, geochemistry and oxygen fugacity indicate that the Middle to Late Jurassic magmatic event represents pre-mineralization intrusions whereas the late Early Cretaceous is syn-mineralization and the early Late Cretaceous intrusions post-mineralization. We propose that both the Middle to Late Jurassic and the Cretaceous magmatic events may relate to the subduction of the Pacific slab, and the changing direction of the subducted slab may result in the different sources for the two magmatic events.