Tao Liu

Contamination of groundwater with the three forms of nitrogen (nitrate N, nitrite N, ammonium N) is a common environmental issue in agricultural, urban, industrial and animal production areas. The nitrogen species are highly mobile, stable, toxic, and redox-sensitive, but are also strongly coupled by biogeochemical reactions. This review systematically summarises the occurrence characteristics, migration behaviour, transformation mechanisms, and source analysis methods for three nitrogen pollutants in groundwater. Nitrate is highly soluble, poorly adsorbed, and the most mobile of the different forms in toxic aquifers. Although nitrite is normally transient, its presence may indicate incomplete nitrification, incomplete denitrification, or a lack of redox stability. Across the levels of ammonium, adsorption, ion exchange, organic nitrogen mineralization, dissimilatory nitrate reduction to ammonium (DNRA), and reducing environments are more strongly affected. The largest nitrogen sources are fertilizer application, manure, sewage leakage, septic systems, livestock wastewater, landfill leachate, industrial discharges, atmospheric deposition, soil organic nitrogen, and geological release of N. But the identification of sources is complicated by the transformation processes as groundwater moves. Thus, a combination of hydrochemical, stable isotopes, microbial functional genes, groundwater flow analysis, laboratory experiments and reactive transport modeling is crucial for the use of integrated approaches. This review emphasizes the importance of moving away from the traditional single-species approach towards a coupled source–migration–transformation approach and offers scientific guidance to support groundwater nitrogen pollution tracing, risk assessment, and remediation.

The northern part of the Great Xing’an Range in China hosts a prominent Au mineralization belt, where Mesozoic clastic rock-hosted Au deposits represent the mineralization type. A study of the Baoxinggou Au deposit in this region might provide new perspectives on the mineralization mechanisms of these Mesozoic clastic-rock-hosted Au deposits. This study investigated the age of mineralization, origins and evolution of the ore-forming fluids, and sources of the ore-forming materials in this deposit. Rubidium–Sr dating of sulfides yielded a mineralization age of 119 ± 2 Ma. Fluid inclusion analyses revealed that the ore precipitated from fluids with temperatures of 105–415 °C and salinities of 4.3–8.8 wt.% NaCl equivalent. Hydrogen and O isotopic data show that the ore-forming fluids were of magmatic origin and, during mineralization, the proportion of meteoric waters increased gradually and eventually dominated the late mineralization stage. Fluid mixing was the primary ore-forming mechanism. Sulfur isotopic data for pyrite and chalcopyrite (δ³⁴S_V–CDT = −4.35‰ to −0.91‰) and Pb isotopic ratios (²⁰⁶Pb/²⁰⁴Pb = 18.429–18.477; ²⁰⁷Pb/²⁰⁴Pb = 15.581–15.591) indicate the ore-forming materials were magmatic in origin, with a similar source as an Early Cretaceous diorite and mixed crust–mantle materials. The results indicate the Baoxinggou Au deposit is a magmatic–hydrothermal deposit.

The climate change and extension of human activities are shedding more stresses on ecosystems. Ecological zoning could help manage the ecosystem and deal with environmental problems more effectively. Geology and topography could affect the ecology primarily and are vital perspectives on ecological zoning. It is worth preliminarily understanding the spatial-temporal patterns of ecological-environmental attributes within various geological-topographical ecological zones (GTEZs). The objective of this study was to delineate GTEZs and present a spatial-temporal analysis on soil and land surface parameters within GTEZs. Firstly, Landsat imageries, high resolution satellite imagery products, digital elevation model, regional geological map, black soil thickness, soil bulk density, meteorological data, and ground survey were collected and conducted. Secondly, GTEZs in Hailun District were delineated according to geological and topographical background. Thirdly, soil composition, and monthly land surface temperature (LST), enhanced vegetation index (EVI), net primary productivity (NPP) were derived from ground survey and Landsat imageries. Finally, spatial-temporal patterns of various ecological-environmental attributes within different GTEZs were preliminarily revealed and analyzed. Results show that sand alluvial plain zone and silt-clay undulating plain zone mainly possess thick soil with fine-medium granule and higher bulk density, and are mainly covered by crops and grass, vegetation flourish the most in August with the highest monthly EVI and NPP. While the sand-conglomerate hill zone, sandstone hill zone, and granite hill zone possess relatively thin soil with medium-coarse granule and lower bulk density, and are mainly covered by forest, vegetation flourish the most in June and July, and has the highest yearly total NPP. With thinner soil thickness and higher NPP, hill zones tend to have more vulnerability to disturbance and more contribution to carbon neutrality target.

Water hazards in coal mines have always been the main geological hazard that restricts the safety of coal mine production. The traditional electromagnetic method is difficult to accurately detect the hydrogeological conditions of underground goafs due to accuracy and interference problems. The ground-to-air transient electromagnetic method is an electromagnetic detection technology with strong adaptability to various terrains, a large detection depth, a wide coverage, a high resolution, and fast speed. This paper mainly applies the ground-to-air transient electromagnetic method to conduct a hydrogeological engineering geological survey in a mine subsidence area. By using this method effectively, changes in hydrogeological and engineering geological conditions in the mine subsidence area are identified and water filling conditions below section 310 and section 250 of the roadway are determined. This study provides accurate and reliable basic data support for rescue operations and post-disaster reconstruction efforts, while also offering valuable insights for similar exploration projects.

As the need to discovers new mineral deposits and occurrences has intensified in recent years, it has become increasingly apparent that we need to map potentials via integrated information on the basis of metallogeny. Occurrences of mineralization such as tungsten (W), tin (Sn), columbium (Nb), tantalum (Ta), gold (Au), copper (Cu), lead (Pb), zinc (Zn), manganese (Mn) and monazite (Mnz) have been discovered in Rwanda. The objective of this study was to present a regional quantitative mineral prospectivity mapping (MPM) of W, Sn and Nb-Ta mineralization in Rwanda using the random forest (RF) method on the basis of open source data, such as geological maps, Bouguer gravity anomalies, magnetic anomalies, Landsat 8 images, ASTER GDEM, Globeland30, and OpenStreetMap. In addition, a newly introduced interpolation–density–delineation (IDD) process was applied to deal with the blank (masked) areas in remotely sensed mineral alteration extraction. Additionally, a k²-fold cross-validation method was also proposed to obtain more reasonable test errors. Firstly, the metallogenic regularity of W, Sn and Nb-Ta in Rwanda was summarized with the help of articles online. Secondly, original geological, geophysical, and remote sensing data were utilized to generate secondary data. Specifically, the IDD process was applied subsequent to the directed principal component analysis method (DPCA) to reconstruct the alteration anomaly map, and a relevant dataset was formed by the combination of original and secondary data. Thirdly, specific predictor layers for W, Sn and Nb-Ta were selected from relevant data via spatial correlation with known deposits, respectively, and the predictive models were established. Finally, near 26,000 squares were zoned in Rwanda, and RF was optimized and applied, the k²-fold cross-validation method was utilized to assess test errors, metallogenic belts and prospective areas for W, Sn, and Nb-Ta were delineated on the basis of total mineralization potential map and likelihoods map. Results proved that the open source data online were valid for drawing a preliminary mineralization potential map. Furthermore, it was also shown that the IDD method is suitable for the postprocessing of masked alteration anomaly maps. Belt IV-4 in the northwest and belt IV-2, IV-1 in the middle-east of Rwanda, containing a number of prospective areas, possess considerable likelihoods of deposits, and mining in Rwanda is at its dawn, with potential worth expecting.

The Qiyimuchang lead–zinc deposit is an important deposit in the Erguna Massif on the west slope of Daxinganling, for which the material source and age of mineralization remain unclear. The lead–zinc deposit in Qiyimuchang has been observed to occur in Jurassic volcanic strata as a vein-like orebody, and its strike is nearly perpendicular to that of the strata and the regional structures of the orogenic belt. The ore is mainly composed of sphalerite, galena, chalcopyrite, pyrite, and quartz, and hydrothermal alteration zones dominated by silicification, fluoritization, and pyritization are common within 1–5 m on both sides of the vein. The metasomatic lead–zinc mineralization is characterized by a massive vein structure. The mineralization process can be divided into three stages, pre-ore (mainly quartz, arsenopyrite and a small amount of pyrite), ore-formation (pyrite, chalcopyrite, sphalerite, galena, fluorite, and a small amount of tetrahedrite), and post-ore (quartz-calcite veinlets with a small amount of pyrite). Element and isotope geochemical studies show that the trace element compositions of the wall rocks (andesite, tuff, etc.) of Jurassic volcanic rocks in the ore bodies and surrounding rocks reflect affinity or similarity between them. The S isotopic composition of sulfide minerals in the metallogenic stage (δ ³⁴S_V-CDT = 1.6‰~4.8‰) indicate the sulfur isotopic composition of the magma. The Pb isotopic compositions of sulfide minerals (38.5–38.39, 15.55–15.62, and 18.33–18.41 for ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁶Pb/²⁰⁴Pb, respectively) in the metallogenic stage are relatively concentrated and close to the average Pb isotopic compositions of the mantle and average Pb isotopic composition of an orogenic belt, indicating that the ore-forming metals are likely to be a mixed source of crust and mantle. A new zircon U-Pb age of 150.8 ± 1.3 Ma (MSWD = 0.74) was obtained from andesitic tuff. Collectively considering the regional geology and ore deposit geological analysis, the lead–zinc mineralization in Qiyimuchang possibly occurred during the early Cretaceous. The ore-forming processes belong to Cretaceous magmatic-hydrothermal activity in extensional tectonic setting.