Abstract The southern Great Xing'an Range is the most critical Sn‐polymetallic metallogenic belt in northeast China. However, the tectonic setting of the Early Cretaceous magmatic‐metallogenic “flare‐up” event remains uncertain. This paper presents an integrated study on the occurrence, petrology, zircon U‐Pb ages, whole‐rock geochemistry, and in situ zircon Hf isotopes for Wenduerchagan granites of Xi Ujimqin Banner, central‐eastern Inner Mongolia. These granites consist primarily of granite porphyry (with ages of 137 ± 1 Ma and 138 ± 1 Ma) and (porphyritic) alkali feldspar granite (with an age of 141 ± 2 Ma), corresponding to the early Early Cretaceous. They are A‐type granites characterized by high silicon, alkali, and TFeO/MgO contents while being depleted of Ba, Nb, Ta, Sr, P, and Ti. They show right‐dipping trend rare‐earth element distribution characteristics with negative Eu anomalies (Eu/Eu* = 0.01–0.20) and weak heavy rare‐earth element fractionation ((Gd/Yb) N = 0.77–2.30). They demonstrate homogeneous zircon Hf isotopic compositions (positive ε Hf ( t ) values from +5.3 to +7.1 and young two‐stage Hf model ages of 851–742 Ma) and high zircon saturation temperatures (av. 810°C). These geochemical characteristics indicate that Wenduerchagan granites originated from the partial melting of juvenile crust under high‐temperature and low‐pressure conditions. Wenduerchagan granites most likely formed in a post‐collisional compression‐extension transition regime caused by the closure of the Mongol–Okhotsk Ocean, when combined with regional geology. Such a transition regime can probably be attributed to the upwelling of the asthenospheric mantle caused by the break‐off of a subducted Mongol–Okhotsk oceanic slab. Upwelling asthenospheric mantle provided sufficient energy and favorable tectonic conditions for magmatism and mineralization of the Early Cretaceous.
The Bailugou vein-type zinc-lead-silver deposit is located in the Eastern Qinling Orogen, China. There has been a long-standing debate about whether its formation is related to magmatism or metamorphism. To determine the origin of ore-forming materials and fluids, we conducted a geological and fluid inclusion investigation of the Bailugou. Field surveys show that the vein-type orebodies are controlled by faults in the dolomitic marbles of the Mesoproterozoic Guandaokou Group, and they are distal to the regional Yanshanian intrusions. Four ore stages, i.e., quartz–pyrite ± sphalerite (Stage 1), quartz–polymetallic sulfides (Stage 2), dolomite–polymetallic sulfides (Stage 3), and calcite (Stage 4), are identified through microscopic observation. The homogenization temperatures of measured fluid inclusions vary in the range of 100 °C to 400 °C, with the dominating concentration at 350 °C to 400 °C, displaying a descending trend from early to late stages. The estimated formation depth of the Bailugou deposit varies from 2 km to 12 km, which is deeper than the metallogenic limit of the epithermal hydrothermal deposit but conforms to the typical characteristics of a fault-controlled deposit. The ore-forming fluid in Stage 1 originates from a fluid mixture and experiences a phase separation (or fluid immiscibility) between the metamorphic-sourced fluid and the fluids associated with ore-bearing carbonate-shale-chert association (CSC) strata. This process results in the transition to metamorphic hydrothermal fluid due to water–rock interactions in Stage 2, culminating in gradual weakening and potential fluid boiling during the mineralization of Stage 3. Collectively, the Bailugou lead-zinc-silver mineralization resembles an orogenic-type deposit formed by metamorphic fluids in the Qinling Yanshanian intracontinental orogeny.
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The Tiantangshan tin‐polymetallic deposit, located in the Nanling Range of South China, is a medium‐sized polymetallic deposit found in the region in recent years. The deposit is hosted within volcanic rocks, and the orebodies occur in the cupola and outer contact zone of the concealed quartz porphyry, as well as the altered fracture zone of the volcanic rocks close to the intrusive contact. In light of field evidence and petrographic observations, the mineralization can be divided into four stages: greisenization stage (stage I), quartz–cassiterite–wolframite stage (stage II), quartz–fluorite–cassiterite–sulfides stage (stage III), and post‐ore stage (stage IV). Three types of fluid inclusions are present in the hydrothermal topaz, quartz, and fluorite, including H 2 O‐rich (W‐type, WL‐ and WV‐ subtypes), CO 2 ‐bearing (C‐type), and solid‐bearing (S‐type). Four stages of fluid evolution are observed by detailed fluid inclusion studies: (a) Stage I fluids are trapped under two‐phase immiscible condition, as evidenced by the coexistence of primary aqueous (W‐type) and aqueous‐carbonic (C‐type) fluid inclusions preserved in topaz and quartz; the fluid inclusions display homogenization temperatures of 378–448°C and salinities of 6.0–17.5 wt.% NaCl equiv. (b) Similarly, fluid inclusions in stage II quartz also record immiscible condition, as identified by the coexistence of W‐type and C‐type fluid inclusions with lower homogenization temperatures (308–400°C) and salinities (1.8–14.5 wt.% NaCl equiv.). (c) Stage III fluids are characterized by the coexistence of widespread WL‐subtype, minor S‐type, and rare WV‐subtype fluid inclusions, with similar homogenization temperatures (230–369°C) but contrasting salinities (0.5–39.5 wt.% NaCl equiv.), which indicates an episode of fluid boiling occurred in this stage. (d) Stage IV marks the end of the hydrothermal system characterized by the lower temperatures (175–298°C) and salinities (0.2–3.9 wt.% NaCl equiv.) W‐type fluid inclusions trapped. Microthermometry and H–O isotopes indicate that the early ore‐forming fluids (in stage I) exsolved from the granitic magma and underwent progressive mixing with meteoric water during subsequent ore‐forming process (in stages III and IV). The water–CO 2 fluid immiscibility is the main mechanism of cassiterite and wolframite precipitation, while fluid boiling and mixing are probably thought to be the dominant mechanisms for the deposition of sulfide at Tiantangshan. 40 Ar/ 39 Ar dating of hydrothermal biotite intergrown with cassiterite shows that tin‐polymetallic mineralization occurred at ~133 Ma which is coeval with the hidden intrusions. Taken together, these lines of evidence confirm that the Tiantangshan deposit is a magmatic hydrothermal greisen–quartz–vein type tin‐polymetallic deposit that formed in the lithospheric extension and thinning setting associated with the postsubduction Paleo‐Pacific Plate tectonic regime that influenced South China.
The newly discovered Tiantangshan tin polymetallic deposit is located in the southeast Nanling Range, Cathaysia block, Southeast China. The tin orebodies are mainly hosted in the greisen and the fractured alteration zones of the tufflava and trachydacite. However, the genetic relationship between the hidden alkali-feldspar granite and volcanic rocks and the tin mineralization remains poorly understood. This paper presents SHRIMP zircon U–Pb dating, whole-rock major and trace element analyses, as well as Nd isotopic data of the trachydacite and alkali-feldspar granite. The SHRIMP zircon U–Pb dating of the alkali-feldspar granite and trachydacite yields weight mean 206Pb/238U ages of 138.4 ± 1.2, and 136.2 ± 1.2 Ma, respectively. These granitic rocks have high levels of SiO2 (64.2–75.4 wt%, mostly > 68 wt%), alkalis (K2O + Na2O > 8.3 wt%), REE (except for Eu), HFSE (Zr + Nb + Ce + Y > 350 ppm) and Ga/Al ratios (10,000 × Ga/Al > 2.6), suggesting that they belong to the A-type granite. According to the high Y/Nb and Yb/Ta ratios, they can be further classified into A1 subtype. Their εNd (T) range from −3.8 to −6.5. They were likely generated by the assimilation-fractional crystallization (AFC) of the coeval oceanic island basalts -like basaltic magma. This study suggests that the A1 type granite is also a potential candidate for the exploration of tin deposits.
Abstract Adakitic rocks and related Cu–Au mineralization are widespread along eastern Jiangnan Orogen in South China. Previous studies have mainly concentrated on those in the Dexing area in northeastern Jiangxi Province, but information is lacking on the genesis and setting of those in northwestern Zhejiang Province. The Jiande copper deposit is located in the suture zone between the Yangtze and Cathaysia blocks of South China. This paper presents systematic LA–ICP–MS zircon U–Pb dating and element and Sr–Nd–Hf isotopic data of the Jiande granodiorite porphyry. Zircon dating showed that the Jiande granodiorite porphyry was produced during the Middle Jurassic ( ca. 161 Ma). The Jiande granodiorite porphyry is characterized by adakitic geochemical affinities with high Sr/Y and La N /Yb N ratios but low Y and Yb contents. The absence of a negative Eu anomaly, extreme depletion in Y and Yb, relatively low MgO contents, and relatively high 207 Pb/ 204 Pb ratios, indicated that the Jiande granodiorite porphyry was likely derived from partial melting of the thickened lower continental crust. In addition, the Jiande granodiorite porphyry shows arc magma geochemical features (e.g., Nb, Ta and Ti depletion), with bulk Earth‐like ε Nd (t) values (−2.89 to −1.92), ε Hf (t) values (−0.6 to +2.8), and initial 87 Sr/ 86 Sr (0.7078 to 0.7105). However, a non‐arc setting in the Middle Jurassic is indicated by the absence of arc rocks and the presence of rifting‐related igneous rock associations in the interior of South China. Combined with the regional Neoproterozoic Jiangnan Orogeny, it indicates that these arc magma geochemical features are possibly inherited from the Neoproterozoic juvenile continental crust formed by the ancient oceanic crust subduction along the Jiangnan Orogen. The geodynamic environment that is responsible for the development of the Middle Jurassic Jiande granodiorite porphyry is likely a localized intra‐continental extensional environment along the NE‐trending Jiangshan‐Shaoxing Deep Fault as a tectonic response to far‐field stress at the margins of the rigid South China Plate during the early stage of the paleo‐Pacific plate subduction. In terms of Cu mineralization, we suggest that the metal Cu was released from the subducted oceanic slab and reserved in the juvenile crust during Neoproterozoic subduction along the eastern Jiangnan Orogen region. Partial melting of the Cu rich Neoproterozoic juvenile crust during the Middle Jurassic time in the Jiande area caused the formation of adakitic rocks and the Cu deposit.
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