Chao Fu

Audio magnetotelluric (AMT) sounding is an essential tool for mineral exploration and subsurface electrical structure imaging. However, persistent cultural noise can severely degrade AMT data quality, particularly in mining areas with strong anthropogenic interference. In this study, we introduce an improved K-Singular Value Decomposition (K-SVD) dictionary learning method for time-domain AMT data denoising, incorporating three key innovations: (1) automatic identification of noise-contaminated segments using local kurtosis; (2) adaptive dictionary initialization combining principal component analysis with Gaussian perturbation, which accelerates convergence and avoids local minima; and (3) online atom screening and updating to maintain the noise specificity of the learned atoms. The proposed method learns noise morphology directly from raw AMT data without requiring reference stations or external training datasets. Synthetic experiments demonstrate that the method more effectively suppresses square-wave and charge-discharge noise compared with wavelet thresholding methods and conventional K-SVD, while better preserving signal morphology. Field applications further show that it significantly enhances the quality of observed data and apparent resistivity-phase curves compared with the widely used robust estimation method. The proposed method provides an efficient, reference-free solution for AMT data denoising in mining areas with strong cultural noise.

The Mongolian Ulaan Uul Tungsten Deposit is located in the southern segment of the Altai Cu-Pb-Zn-W-MoNi-Au-Ag-Sb-Co-Fe Metallogenic Belt. The metallogenic belt is situated in the border area of China, Russia, Mongolia, and Kazakhstan, where over 40 large-sized deposits have been discovered. Among these, only one large-sized deposit is found on the Mongolian side, while the others are medium or small in size. Therefore, strengthening the study of typical deposits and summarizing the metallogenic rules of this region is the best way to achieve a breakthrough in mineral exploration of Altai region in Mongolia. This study focuses on the Ulaan Uul W deposit, a newly identified deposit of Tungsten mineralization within the southern segment of the belt. We examine the deposit’s zircon U-Pb geochronology and Sm-Nd isotopic data. The LA-ICP-MS zircon U–Pb dating of the ore-bearing alkali feldspar granite indicates crystallization ages of 212.5±2.2 Ma, which closely align with the wolframite Sm-Nd isochron age of 211.2±1.5 Ma for the Ulaan Uul W deposit, suggesting an Late Triassic magmatic event marked by W-dominated mineralization coinciding with the extensional tectonic setting following the subduction-collision of the Tarim Craton and the Altai Orogenic Belt. Regional data indicate that the Altai metallogenic belt experienced concentrated W mineralization between 242 and 211 Ma. The formation of W- dominated deposits, such as Ulaan Uul in the southern segment of the belt, is at least 30Ma later, which underscores the presence of a significant W metallogenic event during this critical post-collision to extensional mineralization period.

The Ovor Bayan molybdenum deposit in Mongolia is located within the western segment of the Nukhetdavaa–Erlianhot–Dongwuzhumuqin–Aershan Mo–Pb–Zn–W–Cu–Sn–Cr–Fe metallogenic belt in the Mongolia–Daxing’anling Metallogenic Province. This metallogenic belt lies in the Sino-Mongolian border region, where over ten large-sized deposits have been discovered on the Chinese side in the past two decades. However, the discovered deposits in Mongolia side are relatively small in scale, primarily medium to small-sized, with no large deposits identified to date. Therefore, strengthening research on typical deposits and summarizing metallogenic patterns in this area are the optimal approaches to achieving breakthroughs in prospecting. This study focuses on the Ovor Bayan deposit, a newly identified deposit of molybdenum mineralization within the western segment of the belt. We examine the deposit’s zircon U-Pb geochronology and Re-Os isotopic data. The SHRIMP zircon U–Pb dating of the ore-bearing granite indicates crystallization ages of 183.3 ± 1.9 Ma, which closely align with the mean Re-Os age of 183.1 ± 2.3 MaMa for the Ovor Bayan molybdenum deposit, suggesting an Early Jurassic magmatic event marked by Mo-dominated mineralization coinciding with the extensional tectonic setting following the southeastward subduction-collision of the Mongol–Okhotsk Plate. Regional data indicate that the Nukhetdavaa–Erlian–Dongwuqi–Aershan metallogenic belt experienced concentrated Mo-W mineralization between 240 and 131 Ma. The formation of Mo-dominated deposits, such as Ovor Bayan and Aryn nuur in the western segment of the belt, is at least 50 Ma earlier, which underscores the presence of a significant Mo metallogenic event during this critical post-collision to extensional mineralization period. The molybdenite sample exhibits Re contents ranging from (969.2–1209) × 10⁻⁶, suggesting a mantle-derived source for the molybdenum mineralization.

The Khanbogd-Erdene region in southern Mongolia is a globally important copper–polymetallic metallogenic province, hosting large to super-large deposits, such as Oyu Tolgoi and Tsagaan Suvarga. The area experiences frequent tectonic–magmatic activity, particularly Late Paleozoic subduction-related magmatism, which controls the occurrence of large-scale copper–polymetallic mineralization. This study focuses on the Late Paleozoic granitic intrusive rocks in the Khanbogd-Erdene region of southern Mongolia. Using LA-ICP-MS and SHRIMP dating techniques, precise zircon U–Pb ages were obtained for 10 samples. A total of 209 zircon grains from these 10 intrusive rocks were analyzed, with most cathodoluminescence (CL) images of zircon grains showing distinct oscillatory zoning. Th/U ratios ranging from 0.11 to 2.92 indicate they are magmatic. The younger group of granitic rocks yielded ages between 260.2 ± 1.2 Ma and 286.6 ± 0.9 Ma, indicating an Early Permian geological age. The other seven samples yielded older ages between 315.9 ± 1.8 Ma and 340.9 ± 0.9 Ma, indicating a Carboniferous geological age. These large-scale Carboniferous to Early Permian intrusive rocks in the Khanbogd-Erdene region are products of tectonic–magmatic activity during specific stages of crustal evolution. The findings provide reliable chronological data for regional tectonic–magmatic activity and offer new evidence for constraining the timing of the Variscan orogeny in southern Mongolia.

The Jiaodong region ranks as the world’s third-largest gold metallogenic province, where Late Mesozoic gold mineralization exhibits close genetic connections with cratonic destruction and multi-stage plate tectonic interactions. This study systematically deciphers the deep-seated architecture and metallogenic controls through integrated analysis of gravity, aeromagnetic, and magnetotelluric datasets. The key findings demonstrate the following: (1) Bouguer gravity anomalies reveal a “two uplifts flanking a central depression” tectonic framework, reflecting superimposed effects from Yangtze Plate subduction and Pacific Plate rollback; (2) zoned aeromagnetic anomalies suggest that the Sanshandao–Jiaojia–Zhaoyuan–Pingdu Metallogenic Belt extends seaward with significant exploration potential; (3) magnetotelluric inversion identifies three lithosphere penetrating conductive zones, confirming the Jiaojia and Zhaoyuan–Pingdu faults as crust mantle fluid conduits, while the Taocun–Jimo fault marks the North China–Sulu Block boundary; and (4) metallogenic materials derive from hybrid sources of deep Yangtze Plate subduction and mantle upwelling, with gold enrichment controlled by intersections of NE-trending faults and EW-oriented basement folds. Integrated geophysical signatures indicate that the northwestern Jiaodong offshore area (north of Sanshandao) holds supergiant gold deposit potential. This research provides critical constraints for the craton destruction type gold mineralization model.

The Guodian Fe deposit is representative of the newly discovered Qihe–Yucheng high-grade Fe skarn ore cluster, Luxi Block, eastern North China Craton (NCC). The age of the Pandian Fe deposit remains elusive, which hinders the understanding of its metallogenic tectonic background. Phlogopites are recognized in syn-ore stages, and they are closely associated with magnetite in the Guodian skarn Fe deposit. Here, we carried out ⁴⁰Ar/³⁹Ar dating of phlogopite, which can place a tight constraint on the timing of Guodian iron mineralization and shed light on the geodynamic framework under which the Guodian Fe deposit formed. Ore-related phlogopite ⁴⁰Ar/³⁹Ar dating yielded ⁴⁰Ar/³⁹Ar plateau ages of 131.6 ± 1.7 Ma at 890–1400 °C, with the corresponding isochron age being 131.1 ± 2.6 Ma. These two ages are consistent within the error, indicating that they can represent the formation age of the Guodian iron deposit. The mineralization age overlaps the zircon U-Pb age of 124.4 Ma for ore-related Pandian pluton. This age consistency confirms that the iron skarn mineralization is temporally and likely genetically related to Pandian diorite. The present results, coupled with existing isotopic age data, indicate the Guodian skarn Fe deposit formed contemporaneously with large-scale skarn iron mineralization over the Luxi Block in the Late Mesozoic. The available data demonstrated that the eastern NCC was “destructed” in the Late Mesozoic, as marked by voluminous igneous rocks, faulted-basin formation, high crustal heat flow, and widespread metamorphic core complexes in the eastern part of the NCC. It is thus suggested that the Guodian Fe skarn deposits, together with other deposits of similar ages in the Luxi Block and even in the eastern NCC, were products of this craton destruction. Lithospheric extension and extensive magmatism related to the craton destruction may have provided sufficient heat energy, fluid, chlorine, and Fe for the formation of the Fe deposit.

The Daliuhang gold deposit in the Qipengfu (Qixia–Penglai–Fushan) ore concentration area is a typical gold deposit of medium-low temperature hydrothermal veins. Uncertainties regarding the primary sources of ore-forming fluids, as well as whether host rocks contribute materials to the mineralization of the gold deposits in the Jiaodong Peninsula, are still subject to intense debate. Hydrogen–oxygen isotope results show that atmospheric water is involved in ore-forming fluids. According to the results of the helium–argon isotopes of pyrite, it is hypothesized that the initial fluid source was located in the oceanic crust or upper mantle lithosphere above the Early Cretaceous Paleo-Pacific Plate, as it was subducted into the eastern part of the eastern North China Craton. In situ sulfur isotope results show that high δ³⁴S values characterize the pyrite in the main mineralization period. It is inferred that during the thinning and melting process of the lithospheric mantle, the volatile components enriched in pyrite contributed to the release of δ³⁴S. At the same time, when the fluids ascended to the weak zones, such as fissures of ore-endowed peripheral rocks, the δ³⁴S in the peripheral rocks were extracted, and the two processes acted together to cause high δ³⁴S values to occur. Similarly, the lead and strontium isotopic compositions indicate a crust–mantle mixing attribute of the mineralized material source. The zircon U–Pb age of the ore-hosting granodiorite was 130.35 ± 0.55 Ma, and the Rb–Sr isochron age of the pyrite from the main mineralization period was 117.60 ± 0.10 Ma, which represents the timing of felsic magmatism and gold mineralization, respectively, with at least 10 Ma between the magmatism and mineralization. The magma gradually cooled over time after its formation, and when the granodiorite cooled down to 300 ± 50 °C, the temperature and pressure conditions were most conducive to the precipitation of gold. It is inferred that gold-rich initial mantle fluids with volatile components, rising along tectonically weak zones, such as fractures, underwent fluid phase separation in the fractured position of the granite and extracted the gold from the granodiorite, forming gold deposits.