查看更多>>摘要：? 2022 Elsevier B.V.Radionuclides in the environment have been considered a health risk for many years owing to their contribution to the radiation dose to the human body. A great deal of field survey research has been conducted in this area. However, few researchers have studied the key sources of geological and geochemical substances that pose radioactive environmental problems from the perspective of airborne gamma-ray spectrometry. This study aims to determine the radiation variations in geological units caused by rocks containing radionuclides, evaluate the level of radiation, and analyze as well as identify the key radio-elements. The content of 40K, 238U, 232Th, and the total count (TC) in 15 different geological units were studied based on the concentration data. The gamma absorbed dose rate (D) of the whole region was calculated to identify and evaluate the main areas of high radiation. The quantitative statistical methods, the Pearson correlation analysis, principal component analysis (PCA), hierarchical cluster analysis (HCA), and geochemical mapping were used to analyze the selected high radiation areas and reveal potential key lithological factors. The results indicate that the Cretaceous intrusive rock, in the northeast of the study area, is a major source of natural radionuclides and continuous radiation. The high radiation in this area is strongly associated with the Yaocun rock mass containing K-feldspar granite, and the correlation coefficient of the 232Th with effective dose was the highest (0.91), whereas that of 238U was the lowest (0.49). The study has determined that 232Th is the key radio-element, causing high radiation by comparing the results of HCA of field gamma-ray measurement data. The findings from this study are valuable for determining the key factors causing high radiation levels in similar exposure conditions.
查看更多>>摘要：? 2022 Elsevier B.V.Whole-rock geochemical data and compositional balance analysis (CoBA), combined with a magnetic susceptibility model obtained from a high-precision magnetic survey, are useful exploration tools in the Jiama porphyry–skarn deposit, southern Tibet, China. In this paper, three innovative aspects of the model are described that have assisted exploration of the Jiama deposit: an improved geological understanding of a thrust–nappe structure, hydrothermal fluid pathways, and magma mixing; data- and knowledge-driven compositional balance analysis of whole-rock geochemistry; and a high-precision magnetic survey of the deposit. The local strata provided the materials and natural trap for skarn formation, and a site for fluid circulation and porphyry ore precipitation. An interlayer detachment zone, gliding nappe structure, and cylindrical fissure system provided channels for fluid migration, and the Niumatang Anticline provided the accommodation space for the porphyry system. Miocene magma mixing and crustal contamination led to the development of complex mineralization in the Jiama area. The geochemical signatures obtained from CoBA, and the spatial distribution of the strata, structures, igneous rocks, alteration, mineralization, and degree of erosion enable integration of the geochemical and geological data. The “demagnetization skylight” identified by magnetic anomalies and a magnetic susceptibility model obtained with UBCmag3D software revealed the location of a concealed porphyry system. A magnetic susceptibility of 0.014–0.016 was found to identify the location of an interlayer skarn. Our exploration indicators of the Jiama porphyry–skarn deposit can be used to guide ore exploration throughout the region.
查看更多>>摘要：? 2022 Elsevier B.V.The Dayingezhuang gold deposit is a giant gold deposit in the Jiaodong district, with explored gold reserves of 283 t. After decades of research, sources of ore-forming fluids remain controversial, resulting in continuous controversy on the origin of this deposit. In this study, trace elements of pyrite and C-O-S isotopic data are presented to provide constraints on the ore-forming fluids of the Dayingezhuang gold deposit. Two types of gold-related pyrite were identified. Py1, hosted in quartz-pyrite veins, has subhedral to anhedral textures with developed micro-fissures. Py2, hosted in quartz-polymetallic sulfide veins, is generally subhedral to anhedral and intergrown with polymetallic sulfides. Both Py1 and Py2 are characterized by Co/Ni <1, which supports that the ore-forming fluids are metamorphic fluids with the addition of sedimentary materials. The calcite C[sbnd]O isotope suggests a mantle-derived source mixed with sediments. Combined with the anomalously high δ34S values, the ore-forming fluids that generated the Dayingezhuang gold deposits were most likely originated from the mantle lithosphere which is metasomatized and fertilized by the subducted Paleo-Pacific Plate and its overlying marine sediments. This model is similar to the common genesis of worldwide orogenic type gold deposits which suggests that the Dayingezhuang gold deposit may be of orogenic origin.
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