Detailed geochronological, geochemical, and Sr-Nd-Hf isotopic data are presented for early Paleozoic volcanic rocks in the Karadaban area from the northern Altyn region, NW China, with the aim to constrain their petrogenesis and tectonic implications. The Karadaban volcanic rocks show a bimodal distribution in composition, with rhyolite and basalt. The LA-ICP-MS zircon U-Pb age indicates that the volcanic rocks were erupted at 512 Ma. The mafic rocks are calc-alkaline, enriched in light rare earth elements (LREE) and large-ion lithophile elements (LILE; Ba and U) and depleted in high-field strength elements (HFSE; Nb and Ta). These features together with their depleted isotopic signature (initial87Sr/86Sr=0.70413–0.70817,εNdt=2.7to 3.7) suggest that they were likely derived from a depleted mantle source but mixed with crustal components while upwelling. The felsic rocks show an A-type affinity, with high alkalis and Rb/Sr and Ga/Al ratios; enriched in LILE (e.g., Rb, K, Th, U, and REE) and depleted in Ba, Sr, Nb, P, and Ti; and with fractionated REE patterns with strong negative Eu anomalies. The combination of the decoupling ofεNdtvalues (−2.5 to −6.3) andεHftvalues (+5.5 to +14.7) in the setting of subduction indicates that the felsic rocks were generated by partial melting of the juvenile crustal as a result of magma upwelling. The geochemical and Sr-Nd-Hf isotopic characteristics, coupled with regional geology, indicate that the formation of the Karadaban bimodal volcanic rocks involves an extensional regime associated with a subduction-related environment. The rifting of the back arc in response to the retreat of the subducting northern Altyn oceanic lithosphere may account for the Karadaban bimodal volcanic rocks.
甘肃花牛山铅锌银矿床位于中亚造山带中段的甘肃北山地区。本文在详细的野外观察和室内鉴定的基础上，将花牛山铅锌银矿床成矿阶段划分为石英-毒砂-黄铁矿（第Ⅰ成矿阶段）和石英-多金属硫化物（第Ⅱ成矿阶段）两个阶段；进一步将黄铁矿划分为三种类型，分别为第一种类型的胶状黄铁矿（Py0）、第二种类型的热液叠加交代特征的黄铁矿（PyⅠ）及第三种类型的热液黄铁矿（PyⅡ）。黄铁矿、磁黄铁矿的原位硫同位素研究表明，成矿从早到晚硫化物δ34S值呈递增的规律，具有逐渐向岩浆硫演化的趋势；胶状黄铁矿δ34S值为-9.37‰~-8.10‰，具有沉积（生物成因）硫的特征；成矿第Ⅰ阶段硫化物δ34S值为-9.03‰~-7.03‰，成矿第Ⅱ阶段硫化物δ34S值为-5.77‰~-4.88‰，成矿阶段具有沉积硫与岩浆硫混合来源的特征。黄铁矿、磁黄铁矿的原位铅同位素研究表明，成矿期硫化物的206Pb/204Pb值、207Pb/204Pb值、208Pb/204Pb值以及μ、ω等铅同位素特征值组成范围较窄，铅源为与岩浆作用有关的壳幔混合来源，且与壳幔混合来源的晚三叠世花岗岩中长石铅及其控制的矽卡岩型金矿硫化物铅同位素组成类似。黄铁矿原位微量元素研究表明，胶状黄铁矿（Py0） Co/Ni和S/Se比值分别为0.004~0.34和3.43×104~34.84×104，Se含量为1.558×10-6~15.82×10-6，表现为沉积成因黄铁矿的特征。具有热液叠加交代特征PyⅠ的Co/Ni和S/Se比值分别为0.05~3.38、0.05×104~5.38×104，Se含量为10.09×10-6~1070×10-6，数值分布范围广，总体上有别于沉积成因黄铁矿，类似于热液成因黄铁矿的特征。热液黄铁矿（PyⅡ）的Co/Ni和S/Se比值分别为0.60~68.88、1.46×104~9.15×104，Se含量为5.938×10-6~35.91×10-6，表现为热液成因的特征。综上研究，认为花牛山矿床经历了南华纪-震旦纪沉积胶状黄铁矿形成期和晚三叠世岩浆热液成矿期，胶状黄铁矿在成矿过程中提供了部分硫，成矿金属物质主要来自晚三叠世岩浆成矿热液，并认为矿床成因为岩浆热液型矿床。;The Huaniushan Pb-Zn-Ag deposit in the Beishan area of Gansu Province is located in the middle segment of Central Asian Orogenic Belt. Based on detailed field observation and laboratory identification, the metallogenic stage of the Huniushan Pb-Zn-Ag deposit is divided into two stages: quartz-arsenopyrite-pyrrhotite (stage I) and quartz-polymetallic sulfide (stage II). The pyrite can be further divided into three types, namely colloidal pyrite of lst type (Py 0), pyrite of 2nd type with the characteristic of hydrothermal superimposition (Py I), and hydrothermal pyrite of the third type (Py II). The study of in-situ sulfur isotopes of pyrite and pyrrhotite indicates that the δ34S value of sulfide increases gradually in succession, and shows a characteristic trend of gradual evolution to magmatic sulfur. The δ34S values of colloidal pyrites vary within a range of -9.37‰~-8.10‰, with characteristics of sedimentary (biogenic) sulfur; the δ34S values of the sulfides in the first and second stages of mineralization are within -9.03‰~-7.03‰ and -5.77‰~-4.88‰, respectively. The metallogenic stage is characterized by the mixed source of sedimentary sulfur and magmatic sulfur. The study of in-situ lead isotope of pyrite and pyrrhotite indicates that the variation range of 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb and the characteristic values of lead isotopes such as μ and ω of sulfides during the mineralization period are narrow. The lead source is a crust-mantle mixed source related to magmatism. It is similar to the Late Triassic granite feldspar lead from the crust-mantle mixed source, and is also similar to the lead isotopic composition of the skarn-type gold sulfide ore controlled by the Late Triassic granite. The study of in-situ trace elements of pyrites indicates that the Co/Ni and S/Se ratios of Py0 are 0.004~0.34 and 3.43×104~34.84×104, respectively, and the mass fraction of Se is 1.558×10-6~15.82×10-6, showing the characteristics of sedimentary pyrite; The Co/Ni and S/Se ratios of Py I with the characteristic of hydrothermal superimposition are 0.052~3.38 and 0.05×104~5.38×104, and the mass fraction of Se is 10.09×10-6~1070×10-6. These values are widely distributed, which are different from those of sedimentary pyrites and similar to those of hydrothermal pyrites. The Co/Ni ratio of PyⅡ is within 0.60~68.88 with a mass fraction of Se varying within 5.938×10-6~35.91×10-6, and a S/Se ratio of 1.46×104~9.15×104, showing the characteristics of hydrothermal origin; PyI is a transitional type between Py0 and PyII, which exhibited the characteristic of hydrothermal superimposition. In conclusion, we inferred that the formation of Huaniushan deposit has experienced the pyrite depositional period of Nanhua-Sinian and the magmatic hydrothermal mineralization period of Late Triassic. Colloidal pyrite provide a few sulfur for mineralization, but the ore-forming metal materials mainly come from ore-forming hydrothermal fluid of the Late Triassic magmatic, and the origin of the deposit is considered to be magmatic hydrothermal deposit.
Abstract In recent years, there has been significant progress in shale oil exploration in the first member of the Qingshankou Formation (K 2 qn 1 ) in the Qijia‐Gulong Sag, Songliao Basin, Northeast China: It shows good prospects for shale oil. However, the recognized lack of the geochemical and hydrocarbon generation and expulsion characteristics of K 2 qn 1 source rocks limits an accurate evaluation of shale oil resource. This study systematically investigated the geological and geochemical characteristics, hydrocarbon generation and expulsion, and shale oil potential of the K 2 qn 1 source rocks. The results show that the K 2 qn 1 mudstones were mainly deposited in the semideep and deep lacustrine facies under reducing and weak reducing conditions. Compared with the southern Gulong Sag, the northern Qijia Sag has a higher salinity, more abundant prosperous aquatic organisms, and a greater paleoproductivity. The K 2 qn 1 source rocks are pervasive and continuous in the entire sag, with maximum thicknesses greater than 110 m. They have a higher organic matter (OM) abundance (2.40% of the average TOC), are dominated by type I and II 1 kerogen, and are mature (0.8%‐0.1.3% VR ), which indicate that they are good to excellent source rocks and have significant hydrocarbon generation potential. The source rocks in the Qijia Sag have a higher OM abundance, a better OM type, and a lower OM maturity than those in the Gulong Sag. The threshold and peak hydrocarbon expulsion values for marlstone source rocks are 0.85% VR and 0.95% VR , respectively. The volumes of hydrocarbons generated and expulsed from the K 2 qn 1 source rocks are 121.8 × 10 8 t and 46.9 × 10 8 t, respectively, with a retention efficiency of 61.5%. The in‐place and recoverable resources of shale oil are 74.9 × 10 8 t and (12.0‐13.5) × 10 8 t, respectively, indicating that the entire sag has a significant shale oil potential, especially the Qijia Sag.
This study examines the responses of soil organic carbon (SOC) pools and their components to agricultural water drainage in paddy fields, with a focus on the wetland–paddy field ecotone of Xingkai Lake, a transboundary lake shared by China and Russia. Field investigations targeted three representative wetland vegetation types: Glyceria spiculosa (G), Phragmites australis (P), and Typha orientalis (T), across drainage durations ranging from 0 to over 50 years. SOC fractions, including light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC), were systematically analyzed. The results revealed that SOC components in T and P wetlands steadily increased with drainage duration, whereas those in G wetlands exhibited a fluctuating pattern. SOC dynamics were primarily driven by LFOC, while MBC displayed species-specific variations. Correlation analyses and structural equation modeling (SEM) demonstrated that soil physicochemical properties, such as total nitrogen and moisture content, exerted a stronger influence on SOC fractions than microbial biomass. Overall, water drawdown significantly altered SOC dynamics, with distinct responses observed across vegetation types and wetland ages. This study provides critical data and theoretical insights for optimizing carbon sequestration and hydrological management in wetland–paddy field systems.
The Zhangquanzhuang gold deposit is a special deposit in the Zhangjiakou district, on the northern margin of the North China Craton. It is characterized by the enrichment of sulfides, the scarcity of tellurides and zero to positive sulfur isotope compositions compared with the famous Dongping and Xiaoyingpan Te-Au-Ag deposit types of the same district. In this paper, we use the in-situ LA-(MC)-ICP-MS and bulk trace element concentrations of pyrite, and in-situ sulfur isotope compositions of sulfides, to study physicochemical conditions and mechanisms of mineral deposition in the Zhangquanzhuang deposit. Pyrite from stage I (PyI) contains high Te contents, pyrite from stage II (PyII) has the highest Co and Ni contents, and pyrite from stage III (PyIII) contains high Cr, Zn, Pb, Ag, Cu, Sb, Bi and Au contents. The calculated in-situ δ34SH2S values range from 0.9‰ to 6.1‰, and the values for stages I and II are higher than those for stage III. The mineral assemblages and trace element contents in pyrite show that large amounts of metals precipitated during stage III, in which the pH and logfO2 were constrained within the range of 4.1 to 5.2 and −36.9 to −32.1, respectively. Sulfidation and boiling derived from decreasing pressure may be the main mechanisms leading to mineral deposition in stage III. The Zhangquanzhuang gold deposit was formed in a mineral system that was different from the one that formed the Dongping and Xiaoyingpan Te-Au-Ag deposits, and should thus be called the “Zhangquanzhuang−type” deposit and considered a third gold deposit type in the Zhangjiakou ore field.
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