Search

[ Objective ] Carbonatites, as magmatic-origin rocks, are crucial source rocks for uranium, rare earth, and other minerals. They are widely distributed in the Xiaoqinling region of Shaanxi, giving rise to numerous large to super-large carbonatite deposits of uranium, molybdenum, and rare earth, represented by Huayangchuan and Dashigou, attracting attention from scholars in recent years. Previous studies on carbonatite deposits in the area focused on petrology, mineralogy, genesis, and mineralization chronology. However, they were often limited to individual deposits, needing more regional cross-sectional comparative studies. [ Methods ] This study employs field geological surveys, petrographic analysis, and geochemical characterization of typical rocks and ores to reclassify different types and stages of Xiaoqinling carbonatites. It analyzes the geochemical characteristics of various carbonatite types and explores the mineralization processes of uranium and rare earth elements associated with carbonatites. [ Results ] Xiaoqinling carbonatites exhibit a large vein, vein group, and vein network morphology, intruding into the Archean metamorphic basement, Xiong'er Group volcanic sedimentary rocks of the Changchengian System, and Gaoshanhe Group clastic rocks of the Jixianian System along fault structures. Based on field crosscutting relationships and primary mineral assemblage characteristics, Xiaoqinling carbonate rocks can be re-divided into five stages from old to new: aegirine syenite stage (I), aegirine carbonatite stage (II), potassium feldspar carbonatite stage (III), quartz carbonatite stage (IV) and zeolite-bearing carbonatite stage (V). Spatially, the division is roughly along the nearly EW-striking Xiaohe Fault, with northern carbonatite veins dominated by aegirine syenite and aegirine carbonatite, rich in aegirine, biotite and other dark minerals, distributed in the Archean gneiss basement. The southern part is mainly composed of light-colored potassic feldspar carbonatites and quartz carbonatites, almost devoid of dark minerals, with surrounding rocks consisting of Xiong'er Group volcanic sedimentary rocks and Gaoshanhe group clastic rocks. Zeolite-bearing carbonatites are distributed throughout the region. Temporally, the carbonatites formed in the Late Triassic, but distinct temporal differences exist among different sections. Previous data indicate a possible 30 Ma gap in the formation times of various carbonatite types in the Xiaoqinling area. The geochemical characteristics of Xiaoqinling carbonatites reveal an average SiO2 content of 30.43%, significantly higher than the global average for carbonatites. CaO is relatively low, with an average content of 28.71%, exhibiting a clear negative correlation with SiO2 content. Total alkali (Na2O+K2O) content is relatively high, averaging 2.25%, with a maximum value of 10.23%. The total alkali content decreases gradually from early to late stages, strongly correlating with CaO and Al2O3 content. The potassium-sodium ratio (w(K2O)/w(Na2O)) is exceptionally high, with an average of 4.625 and a maximum value of 36.55. Ferromagnesian content (TFe2O3+MgO) varies significantly, with early-stage carbonatites (Stages I, II, III) having higher ferromagnesian content (average 8.29%), while late-stage carbonatites (Stages IV, V) generally have lower ferromagnesian content (average 1.92%). Ferromagnesian content correlates positively with TiO2 content. MnO has an average content of 1.22%, reaching up to 4.49%, notably enriched in late-stage quartz carbonatites. REE content averages 0.26%, with a maximum value of 0.96%, exhibiting a positive correlation with MgO content. The ∑LREE/∑HREE ratio ranges from 0.47 to 27.72, with early-stage carbonatites (Stages I, II, III) showing strong heavy REE depletion. Late-stage quartz carbonatites have an average ∑LREE/∑HREE ratio of 2.15, indicating relatively heavy REE enrichment, especially in Tm, Yb, Lu, and Y. Heavy REE content correlates linearly with MnO content. The overall REE distribution pattern of carbonatites is a steep-left and gentle-right, relatively flat-right-trending model, showing continuous variations in REE distribution patterns throughout different stages. Ore-related element content characteristics of various carbonatite types reveal significant U and Nb enrichment in aegirine syenite, aegirine carbonatite, and potassium feldspar carbonatite. Mo-mineralization is closely associated with potassium feldspar carbonatite and quartz carbonatite, while Pb and Ba-Sr mineralization is evident in all carbonatite stages. [ Conclusions ] (1) Xiaoqinling carbonatites are categorized into aegirine syenites, aegirine carbonatites, potassium feldspar carbonatites, quartz carbonatites, and zeolite-bearing carbonatites in chronological order. (2) Xiaoqinling carbonatites exhibit notably high SiO2 and total alkali content, low MgO content, and exceptionally high potassium-sodium ratio. There is a gradual decrease in CaO, TiO2, Al2O3, ferromagnesian, and total alkali content from early to late stages, while MnO content shows an opposite trend. Carbonatites evolve from early ferrocarbonatite to late calciocarbonatite. (3) Different types of carbonatites show distinct ore-related characteristics, with early stages (aegirine syenite, aegirine carbonatite, and potassium feldspar carbonatite) mainly enriched in U (Nb), and Potassic Feldspar Carbonate additionally enriched in Mo. Late-stage quartz carbonatites are characterized by Mo and HREE enrichment. [ Significance ] The findings of this study provide valuable information for the exploration and research of carbonatite-type uranium, rare earth, and polymetallic deposits in the Xiaoqinling area, holding significant practical importance.

Objective The 509 Daobanxi deposit in the West Kunlun orogenic belt is a newly discovered large pegmatite-type lithium-polymetallic deposit in northwestern China. As a typical granite pegmatite lithium deposit in the region, the metallogenic characteristics and pegmatite evolution of the 509 Daobanxi deposits are of great significance for understanding the entire lithium-polymetallic mineralization process of the West Kunlun metallogenic belt. The granite pegmatites contain assemblages of plagioclase, spodumene, quartz, muscovite, etc., exhibiting strong mylonization and forming typical ductile deformation characteristics in the 509 Daobanxi deposit. Quartz, an essential mineral in granite pegmatite, is ideal for tracking pegmatite's mineralization process and studying the deformation behavior of continental rocks in long-term geological history. Methods To study the late-stage emplacement process of pegmatite evolution, comprehensive analyses were conducted on the quartz deformation structures measurements, fluid inclusion temperature, and quartz trace elements for the 509 Daobanxi granite pegmatites. Cathodoluminescence (CL) analysis of quartz in deformed granite pegmatite samples was performed to reveal the compositional zoning of Ti in quartz. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to analyze 64 points from samples Zk2707-9 and Zk1107-2. Results The minerals of spodumene and plagioclase in deformed pegmatites primarily show brittle fracturing characteristics, with the features of rigid body deformation and the muscovite presence of mica-fish. Meanwhile, the conspicuous feature is that quartz grains mainly develop dynamic recrystallization and contain subgranis. According to the microstructural characteristics of spodumene, plagioclase, and quartz, the deformation temperature of mylonitized granite pegmatite is 300~400℃. The CL images of quartz bands in the granite pegmatite samples have no apparent zoning, indicating that the Ti content reaches a relative equilibrium state in the quartz deformation stage. The LA-ICP-MS analysis shows quartz from the 509 Daobanxi granite pegmatites contains a lower concentration of Ti (1.03 ×10−6 to 7.67×10−6 and 1.04 ×10−6 to 6.75×10−6), suggesting relatively lower deformation temperatures. The Ti-in-quartz thermobarometry indicates quartz deformation temperatures ranging from 371 to 398°C and 351 to 377°C, respectively. The thermometric measurement shows that homogenization temperatures of the quartz fluid inclusions in pegmatite varied from 260℃ to 283℃, likely recording the temperature of the late stage of pegmatite evolution. Conclusion Comprehensive analysis shows that the 509 Daobanxi granite pegmatites underwent a period of intense ductile deformation during the emplacement process, with low temperature and high strain rate. The emplacement of pegmatite is a product of the rapid cooling process, and the grain size reduction caused by dynamic recrystallization (GBM) under high-stress and low-temperature conditions profoundly changed the rheological properties of pegmatite. The supercooling process from ~400℃ to ~260℃ (ΔT=140℃±), resulting in less rapid mineral crystalline new nuclei in pegmatites, is more conducive to the formation of coarse quartz and other mineral particles, forming the significant characteristics of granite pegmatites. [ Significance ]In fact, the emplacement process of granitic pegmatites remains a puzzle, and high-quality, accurate systematic work is needed to understand the evolution process and behavior of granite pegmatite. By studying the 509 Daobanxi granite pegmatites, we proposed that the pegmatite emplacement was a product of the rapid cooling process, and supercooling plays an essential role in pegmatite emplacement. Similar deformation characteristics are widely developed in the Tugeman lithium deposit in the Altyn Tagh area and the Jiajika lithium deposit in the western Sichuan. Although the current work is preliminary, our study provides some clues for exploring the emplacement process of granitic pegmatites.

Objective Rock fracturing and its subsequent activations are the most basic tectonic deformation modes. However, the classical fracturing criteria (Coulomb-Mohr criterion, Griffith criterion, and Byerlee sliding-friction law) have different limitations in practical applications. Methods Based on the classical fracturing criteria and the analysis of the physical nature of fracturing generation (extensional fracturing and shear fracturing), combined with the generalized shear activation criterion and long-term research practice, a "generalized fracturing activation criterion" is proposed through theoretical analysis in this paper. Conclusion This criterion can be used to quantitatively determine the possibility and types of fracturing of any medium, under any triaxial stress state, and at any orientation interface (including pre-existing weak surface and non-weakness surface). It unifies the Coulomb-Mohr criterion, Byerlee's law, and Griffith's criterion, and extends fracturing to fracturing activation. Significance The proposed criterion has broad application prospects in the fracturing activation-related resource (such as shale gas and hot, dry rock) exploration and development and prediction and prevention of natural disasters (such as earthquakes and landslides).

Xiazhuang uranium ore field, located in the southern part of the Nanling Metallogenic Belt, is considered one of the largest granite‐related U regions in South China. In this paper, we contribute new apatite fission track data and thermal history modeling to constrain the exhumation history and evaluate preservation potential of the Xiazhuang Uranium ore field. Nine Triassic outcrop granite samples collected from different locations of Xiazhuang Uranium ore field yield AFT ages ranging from 43 to 24 Ma with similar mean confined fission track lengths ranging from 11.8 ± 2.0 to 12.9 ± 1.9 μm and Dpar values between 1.01 and 1.51 μm. The robustness time‐temperature reconstructions of samples from the hanging wall of Huangpi fault show that the Xiazhuang Uranium ore field experienced a time of monotonous and slow cooling starting from middle Paleocene to middle Miocene (∼60–10 Ma), followed by relatively rapid exhumation in the late Miocene (∼10–5 Ma) and nearly thermal stability in the Pliocene–Quaternary (∼5–0 Ma). The amount of exhumation after U mineralization since the Middle Paleogene was estimated as ∼4.3 ± 1.8 km according to the integrated thermal history model. Previous studies indicate that the ore‐forming ages of U deposits in the Xiazhuang ore field are mainly before Middle Paleocene and the mineralization depths are more than 4.4 ± 1.2 km. Therefore, the exhumation history since middle Paleocene plays important roles in the preservation of the Xiazhuang Uranium ore field. [ABSTRACT FROM AUTHOR]

The Mesozoic to Cenozoic mountain uplift, exhumation, and deformation of the SW Tianshan Mountains (Kyrgyzstan and Northwest China) offer an important window to understand the intra-continental rejuvenation mechanism of the Central Asian Orogenic Belt (CAOB), as response to the far-field effects of the India-Asia collision. This article presents new observation and data for the planation surface and sedimentation and deformation features of the regional intermountain basins to rebuild the orogenic history in Mesozoic to Cenozoic. Three planation surfaces were recognized by field observation, showing that the mountain may have experienced lengthy erosion since the end Cretaceous, and a continuous planation surface may have formed at the Eocene to Oligocene. The filling sequences and deformation character revealed that the orogenic disintegrate and intermountain basin formation likely began in the end of Oligocene. Subsequently, the uniform planation surface in Western Tianshan may have begun to disintegrate, leading to the basin-and-range landform formation. Folds and nappes in the Cenozoic basins, large-scale thrusting of Palaeozoic rocks over Cenozoic sediments at the basin margin associated with the rapid mountain uplift may have occurred at the end of Early Pleistocene, suggesting a tectonic inversion. The Mesozoic-Cenozoic Tianshan uplift and deformation were likely induced by the collision/accretion along the southern margin of Eurasia. Both the northward propagation of the Parmir syntaxis to the SW Tianshan and the oblique dextral faulting of the Talas-Fergana fault have likely played an important role on the formation and deformation of the Cenozoic basins in the SW Tianshan. [ABSTRACT FROM AUTHOR]

The Atebayue Sb deposit is hosted in the Silurian clastics in the South Tianshan Orogen in Kyrgyzstan. The Sb ores appear as veins/veinlets and disseminations, with stibnite being the main ore mineral. Gangue minerals comprise quartz, calcite, and clay minerals. The quartz at Atebayue only contains aqueous fluid inclusions with low homogenization temperature (215–336 °C) and salinity (3.4–6.9 wt.% NaCl equiv.), supporting an epizonogenic hydrothermal origin. The minimum trapping pressures estimated from the NaCl─H2O inclusions are 9–14 MPa, suggesting that the Sb mineralization mainly occurred at a depth of 0.9–1.4 km. Sulphur isotopes (δ34S = −0.4 to 6.2‰) suggest that the host rocks within the Silurian system to be a significant source of ore metals. The ores contain average 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of 18.112, 15.547, and 38.064, respectively, and 2‐stage model ages of 337–381 Ma, indicating the ores were likely sourced from the Paleozoic strata. Integrating the data obtained from the studies including ore geology, fluid inclusion, and S─Pb isotope geochemistry, we conclude that that the Atebayue Sb deposit is best classified as epizonogenic type formed by the Tarim–Kazakhstan continent–continent collision. [ABSTRACT FROM AUTHOR]