Three-dimensional geologic structure of a Mesozoic granite pluton and related metallogeny in Northeast China: An integrated geophysical model

The Hanjialing pluton occurs within a Paleoproterozoic rift belt in the Liaodong Peninsula in Northeast China, a region endowed with rich polymetallic mineral deposits including gold, lead, and zinc. The genesis and distribution of these ores are closely related to the formation of the pluton. Here, we reconstruct the three-dimensional geological characteristics of the Hanjialing pluton in an attempt to constrain the relationship between intrusion and mineralization. Our high-precision gravity and magnetic measurements and magnetotelluric profiles trace the three-dimensional geometry of the pluton as an inflated balloon. We also demarcate its lateral and vertical extension and characterize the distribution of the associated ore mineralization. Our data suggest that more than 8 km of the upper part of the intrusion has been removed by erosion since the Cretaceous.

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Geological characteristics, deposit type, and metallogenic epoch of the Katebasu gold–copper deposit in western Tianshan

The Katebasu gold (Au)–copper (Cu) deposit is one of the extra large-scale Au–Cu deposits discovered in the western Tianshan Mountains in Xinjiang in the recent years. The geological characteristics of the deposit have not been systematically studied and summarized, and there is considerable debate about the deposit type and metallogenic epoch. In this paper, we studied the Katebasu Au–Cu deposit orebody production characteristics, ore mineral composition, structural tectonic, surrounding rock alteration, and metallogenic phases. We identified the deposit types, presented a new discussion on the metallogenic epoch combined with the study of garnet Sm–Nd chronology, and indicate that the deposit type is a skarn type–fracture zone alteration rock type. The skarn-type Cu–Au deposit is mainly distributed in the fault fracture zone and skarn in the contact zone between the rock mass and marble strata. The fracture zone alteration-type Au–Cu deposit is mainly distributed in the monzonite granite fracture zone. The mining area has two phases of metallogenesis, which are related to monzonite granite and diorite dykes, respectively, and have a certain degree of superposition in space. The early metallogenesis occurred at 334.3 ± 6.7 Ma. The above results provide direction for regional prospecting.

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Coupled U–Pb dating and Hf isotopic analysis of detrital zircons from Bayan Obo Group in Inner Mongolia: Constraints on the evolution of the Bayan Obo rift belt

The sedimentary record in the Late Palaeoproterozoic-Neoproterozoic Bayan Obo rift belt can provide critical insight into tectonic evolution of Columbia and the North China Craton. In this study, we present new U–Pb geochronology, Hf isotopic analyses from the Bayan Obo Group, the Mesoproterozoic kimberlite, and gabbro to constrain the depositional age and potential provenance information of the Bayan Obo Group. We show that the Dulahala-Jianshan, Bilute, and Baiyinbaolage formations were deposited at ca. 1.81–1.7 Ga, ca. 1.58–1.35 Ga, and ca. 1.25–1.0 Ga, respectively. Our data suggest the following potential provenance for sediments within the Bayan Obo Group: (a) The Khondalite Belt, Yinshan Block, and crystalline basement complex of the North China Craton to the south were the most potential provenance of the Dulahala and Jianshan formations during the initial deposition of Bayan Obo Group; (b) The Yinshan Block, and crystalline basement complex of the North China Craton, and local intermediate-acid igneous rocks were the most potential provenance of the Bilute Formation; and (c) the local gabbro and volcanic rocks were the most potential provenance of the Baiyinbaolage Formation. Based on regional geologic constraints and the sedimentary history, we propose that the Northern Marginal Rift System probably represented several distinct rifting events. Furthermore, the Bayan Obo and Huade rift belts were active more recently than 1.0 Ga, which suggests that these rift systems were not only related to the rifting of the Columbia supercontinent. We propose that the Bayan Obo rift belt also records the rifting related to the breakup of Rodinia with the deposition of Qingbaikou System (Tonian) strata.

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Geochemistry, geochronology, and petrogenesis of leucogranites in the Xiaogouli gold deposit in the West Qinling Orogen

Gold metallogenesis is closely related to orogeny. The Qinling–Dabie Orogen is the most important part of the Central China Orogen. The West Qinling Orogen was formed during the Indosinian period, the main period of amalgamation of the continent of China. The Xiaogouli gold deposit in the West Qinling Orogen has unique geological characteristics, with a unique albite–quartz-vein ore type and mineralization correlate well with the granites. The granites have relatively low concentrations of Sr and Yb (Sr < 400 ppm and Yb < 2 ppm) but relatively high Al content, with average Na2O/K2O of 1.86, indicating that they are Na-rich Himalayan type leucogranites. The minimum temperature of the initial magma was 804 °C; amphibolite-facies hornfelsization occurred in the contact zone, and there was micrographic texture widely developed in the potassium feldspar, indicating an initial high-temperature magma. The granites have low Mg# content (4.07–14.28) and are strongly enriched in light rare earth elements [(La/Yb)N = (101.57–355.49)], suggesting that they had experienced some fractional crystallization. The zircon SHRIMP U–Pb granite ages of 217.4 ± 1.5 Ma indicate that the granites were formed during the late stage of Indosinian magmatic activity in the area. The Xiaogouli leucogranites are believed to be products of partial melting of crust–mantle mixing rocks under the condition of high temperature, induced by asthenosphere upwelling during delamination and thinning of the lithosphere in the extensional environment in the late stage of orogenesis of the West Qinling Orogen. The magma formation depth was 30–50 km. Then, the magma experienced crystal differentiation, and the metallogenic materials and fluids were mainly from the crust–mantle magmas.

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Metasomatic alteration of volcanic-sedimentary terrane in the Early Devonian: Implication for the formation of the Mengxi porphyry copper deposit, eastern Junggar, Central Asian Orogenic Belt

The Mengxi porphyry copper deposit, situated in the eastern Junggar, Central Asian Orogenic Belt, is not a typical porphyry copper deposit, and the origin of the deposit has been a topical debate for a decade. The ore bodies of the Mengxi porphyry copper deposit mainly developed in the volcanic-sedimentary terrane (Huangcaopo Group) near a granite porphyry, with strong wall-rock alteration as well as vertical zonation and fracture-related vein fillings. The result of zircon U–Pb dating indicates that the granite porphyry was emplaced at 432.6 ± 6.7 Ma. The granite porphyry has relatively low initial 87Sr/86Sr ratios (0.70465–0.70537), high whole-rock ƐNd(t) values (−2.2 to 6.6), and similar geochemical affinities of adakites and Andean island arc volcanic rocks, indicating that the Mengxi granite porphyry was derived from the partial melting of the upper mantle modified by slab-derived fluids, with negligible assimilation of crust. Pyrites from the porphyry and volcanic-sedimentary terrane have a similar δ34S and Pb isotopic compositions, indicating that different pyrites may have similar source. Based on the detailed field investigation, observed mineral assemblages, and crosscutting relationships, massive fine anhedral chalcopyrite and bornite disseminated in the Huangcaopo Formation, chalcopyrite as inclusion in pyrite veins in the contact zone, and the amount of Cu-bearing minerals increased from terrane to veins have been recognized. All these observations reveal that the ore-forming materials of the Mengxi copper deposit were mainly derived from the metasomatic alteration of the Huangcaopo Group triggered by the extensive Early Devonian tectonic-magmatic events.

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