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Geogas-carried metal prospecting, an integral part of deep-penetrating geochemistry, is potentially effective in the geochemical exploration of concealed ore deposits. However, its principles and applicability remain controversial. This study summarizes and discusses the progress in geogas-carried metal prospecting in China. The method comprises three constituents: geogas, nanoparticles, and their vertical transportation. Researchers have failed to determine the exact contributions of different sources of geogas. Studies on Pb isotopes, rare earth element patterns of geogas, the comparisons between metals in soil, geogas, and ore geochemistry, and characteristics of nanoscale metals in earthgas (NAMEG), confirmed the relationship between NAMEG and concealed ore deposits. A statistical analysis of field experiments and applications showed that geogas-carried metal prospecting is applicable for the geochemical exploration of magmatic and hydrothermal Cu, Au, Zn, Pb, U, Sn, and Ag deposits and is suitable for most geochemical landscapes except deserts and cold swamps. Finally, genetic models of NAMEG anomalies were constructed. High-permeability migration channels are critical in the formation of NAMEG anomalies over concealed ore deposits. Future work entails applying geogas-carried metal prospecting to certain types of ore deposits and geochemical landscapes and studying NAMEG to provide quantitative information for targeting concealed ore deposits. [ABSTRACT FROM AUTHOR]

The Baiyun deposit is a large gold deposit at the western end of the Liaoji rift zone in Liaoning Province, which has produced both auriferous quartz-vein type and altered-rock type mineralization. The ore bodies are mainly hosted in schist from the Gaixian Formation of the Liaohe Group. A detailed field geological survey showed that the quartz-vein type gold ore bodies are distributed in the near EW-trending and occur in the extensional tectonic space of schist in the Gaixian Formation, and the altered-rock type gold ore bodies are distributed in the near EW-trending structural belt and occur near in the Gaixian Formation of biotite schist, biotite granulite, marble and the upper footwall of dike. To further elucidate the source of ore-forming fluid and material in the Baiyun gold deposit, the H-O isotopes for quartz, S and Pb isotopes, in-situ trace elements for sulfides from quartz-vein and altered-rock type mineralization were studied. The H-O isotopic δDV-SMOW and δ18OH2O values of the auriferous quartz range were from −88.8‰ to −82.2‰ and −1.95‰ to 4.85‰, respectively, suggests that the ore-forming fluids were mainly magmatic water with minor meteoric water. The distribution ranges of in-situ S isotopic compositions of Au-bearing pyrite in the quartz-vein type and altered-rock type ores were −8.38‰–−10.47‰ (with average values of −7.89‰) and 11.38‰–17.52‰ (with average values of 11.55‰), respectively, indicating that the S isotopic compositions of the two ore types were clearly different. The in-situ Pb isotopic ratios changed almost uniformly, which showed that they had the same lead isotopic source. Based on the analysis of S and Pb isotopic compositions, the metallogenic materials in the Baiyun gold deposit were primarily from deep magma, and some wall rock materials may have been mixed in the metallogenic process. Co/Ni diagram shows that most Au-bearing pyrites have magmatic-hydrothermal or sedimentary alteration properties, and Au/As ratios were between 0.001 and 0.828 (the average value was 0.07), indicating that the ore-forming fluid in the Baiyun gold deposit may have been deep magma. Combining the geological, trace element, and isotopic data, as well as data from previous studies, we propose that the Baiyun gold deposit is a magmatic-hydrothermal ore deposit. [ABSTRACT FROM AUTHOR]

Reducing exploration risks and realizing scientific prospecting always have been frontier fields and research hotspots in the world of mineral exploration, the theory and method of ore prospecting prediction for exploration area is the valid channel to deal with this problem. Using this method, a geological model of ore prospecting can be established by combining the internal (geochemical behavior of elements) and external (types of geological processes) control factors for mineralization. The main components of the prospecting prediction model include geological bodies related to mineralization, metallogenetic structure planes and mineralization characteristics. Together with the results of special geological mapping, geophysical and geochemical exploration on large scale, orebodies have been located by synthetic information and explored by drilling. Case studies of the Lala copper deposit in Sichuan, Muhu-Maerkantu manganese ore deposit in Xinjiang and Aonaodaba tin-polymetallic deposit in Inner Mongolia, illustrate the effective application of this method in ore prospecting prediction. [ABSTRACT FROM AUTHOR]

Soil gases, particularly sulfur gases, have not been widely used in mineral exploration due to their high mobility and reactivity. However, our team developed a portable multi-component gas analyzer (PMGA) capable of on-site and real-time measurement of H 2 S, SO 2 , CH 4 , and CO 2 concentrations in soil gas. This study showcases the applicability and effectiveness of PMGA in the geochemical exploration of concealed ore deposits in the Qinjiaying Ag–Pb prospect in semi-arid steppes. Comparison tests between different analyzers and periods were conducted in the Qinjiaying Ag–Pb prospect. The results showed that PMGA has high stability, consistency, and reproducibility. Then, soil gas geochemical surveys were carried out by applying PMGA along eight prospecting lines, with three prospecting lines passing through the known mineralized zone and the remaining five prospecting lines focusing on the covered areas. Three composite anomalies of H 2 S, SO 2 , CH 4 , and CO 2 were identified. The No. 1 soil gas anomaly corresponds well to the known No. I mineralized zone. The No. 3 gas anomaly is characterized by large-scale and strong multi-gas anomalies, indicating the presence of great prospecting potentials. Finally, drilling verification revealed a medium-sized Ag–Pb–Zn deposit in the No. 3 gas anomaly. The results demonstrate that PMGA is a powerful tool for mineral exploration in the study area. This successful practice provides a paradigm for applying PMGA in mineral exploration in semi-arid steppes. • A portable multi-component gas analyzer (PMGA) was developed. • PMGA can detect H 2 S, SO 2 , CH 4 , and CO 2 in soil gases on site and in real time. • A new Ag–Pb–Zn deposit was discovered according to the No. 3 gas anomaly. [ABSTRACT FROM AUTHOR]

The Jiaodong Peninsula is one of the most important Au ore provinces in China. There is an ongoing debate on the correlation between ore formation and magmatism in this province, because few intrusive rocks exhibit a clear association with ore deposits. A mineralized biotite monzodiorite (BM) stock, with disseminated ore, pervasive phyllic alteration, and no deformation, was found in a borehole in the footwall of the Zhaoping fault within the Luanjiahe Au deposit, which may shed light on this debate. The biotite monzodiorite contains explosion breccias, miarolitic cavities, skeletal and dendritic quartz, and late-stage evolved aplite dikes, and the in-situ δ34S values of the disseminated pyrite which is associated with Au mineralization are −1.7‰ to 7.3‰ (mean=3.5‰), indicative of a magmatic-hydrothermal system. These findings, combined with the reported age of 123 Ma, show that the intrusion has close spatial, temporal, and geochemical relationships with Au mineralization in the area. The biotite monzodiorite is metaluminous, high-K calc-alkaline and shoshonitic, with enrichment in light rare earth elements (REEs) and large-ion lithophile elements (LILEs), depletion in high-field-strength elements (HFSEs), and enriched Sr-Nd isotopic compositions. The intrusion may be the product of partial melting of enriched lithospheric mantle with a small lower crustal component. The hydrous, Au-bearing, enriched mantle source, and the strongly oxidized magma that was generated, created favorable conditions for Au mineralization. [ABSTRACT FROM AUTHOR]

Regional-, national- and global-scale geochemical mapping projects have been carried out in China since the late 1970s. These geochemical mapping projects have provided high-quality data for both mineral resource investigations and environmental assessments. Four national-scale geochemical mapping projects in China are described here. (1) The Regional Geochemistry–National Reconnaissance (RGNR) project is China''s largest national-scale geochemical mapping project and has covered more than 6 million km2 of the country''s hilly and mountainous regions since 1978. Generally, stream-sediment samples were collected at a density of 1 sample per km2 and four samples were composited into one analytical sample for analysis of 39 elements. (2) The Deep-penetrating Geochemical Mapping (DEEPMAP) project has been conducted in covered terrains, including basins, at a density of 1 sample per 100 km2 with analysis of 30–70 elements since 1994. In the past ten years, an area of approximately 800 000 km2 has been covered. (3) The 76 Geochemical Element Mapping (76 GEM) project has been carried out since 1999. Approximately 1 million km2 has been completed at present. (4) Multi-purpose eco-geochemical mapping projects have been conducted in the Quaternary plains of eastern China to provide data for environmental regulation and for improvement of agricultural practices since 1999. The data generated continue to play an important role in finding mineralization targets and ore deposits. China is also playing a leadership role in international geochemical mapping projects by transferring its expertise in sampling, chemical analysis and map generation to the developing countries through bilateral and multilateral collaboration. China is a leader in two large projects on a global scale: (1) the Environmental Geochemical Monitoring Network (EGMON) Project aims not only to have a quick overview of the geochemistry in China, but also to provide a pilot study for choosing the optimum sampling medium for geochemical mapping projects at a global scale; (2) the Geochemical Mapping Project uses delta and floodplain sediments of large rivers at a global scale. [ABSTRACT FROM AUTHOR]

[Display omitted] • The block boundaries were identified. • The Mesozoic magmatic rocks were summarized. • Three kinds of ores were analyzed. To explore the macroscopic characteristics of geological block boundaries, Mesozoic magmatic rocks, and various ore deposit distributions in South China, we processed large-scale stream sediment geochemical data covering the entire South China region. Two unsupervised data mining algorithms, cluster analysis and correlation analysis, were used to identify the geochemical distribution patterns. The combined geochemical patterns of nine major elements show two gradient lines that divide the South China region into three blocks. These gradient lines reveal the eastern and western boundaries of the intracontinental orogenic belts between the Yangtze and Cathaysia blocks. We suggest that the Nanning-Pingxiang segment is located on the southern end of the Yangtze-Cathaysia block boundary, and the Jishou-Kaili segment is a part of the boundary between the Yangtze block and the eastern orogenic belt. In the Mesozoic, the distribution of magmatic rocks migrated from the inland to the southeast coast. Meanwhile, the mantle-derived compatible elements were gradually depleted, whereas the crust-derived incompatible elements were gradually enriched. The migration and enrichment of geochemical elements provide material sources for the formation of various ore deposits. High-temperature metallogenic deposits related to Mesozoic magmatic activity are widely developed in eastern South China, while low-temperature metallogenic, sedimentary, and metamorphic deposits are more developed in inland South China. The regional geochemical patterns indicate the distributions of deposits to varying degrees. [ABSTRACT FROM AUTHOR]

• Mesozoic orogenic gold mineralization occurred in the northern margin of North China Craton. • Gold mineralization largely post-dated regional metamorphism. • Gold deposit formed as a result of reactivation of metasomatized mantle. The genesis of orogenic gold deposits in the northern margin of the North China Craton (NCC) is still ambiguous, and this is addressed in this case study on the Zhangquanzhuang gold deposit. This deposit shows features typical of orogenic gold deposits, including quartz vein-type mineralization controlled by shear zones, sericite-quartz-pyrite-carbonate alteration along shear zones, absence of connection to any magmatic intrusion, and occurrence of native gold and electrum. The Zhangquanzhuang gold deposit, which is hosted in Archean high-grade metamorphic rocks, was formed in Mesozoic and largely later than the regional metamorphism. In this deposit, the Pb isotope compositions of sulfides in ores have low 206Pb/204Pb ratios of 16.874–17.007, 207Pb/204Pb ratios of 15.368–15.410, and 208Pb/204Pb ratios of 37.023–37.215, and these are much less radiogenic than those of regional metamorphic and magmatic rocks. This finding precludes the possible derivation of ore fluid from regional magmatism and metamorphism. In pyrite-hosted fluid inclusions in the ores, the 3He/4He and 40Ar/36Ar ratios are 1.26–1.75 Ra and 1622–2816, respectively, showing prominent signature of mantle sources. These geochemical features, together with the large temporal discrepancy between regional metamorphism and mineralization, suggest that ore fluid and metal had a subcrustal source similar to the gold deposits in the Jiaodong gold province in the southeastern margin of the NCC. The calculated δ 34S H2S values for the ore fluid are 2.31–4.48‰, which are heavier than the δ 34S of depleted mantle. The δ 18O of ore-related quartz mostly cluster around 11‰, implying high δ 18O of subcrust-derived ore fluid. The stable O and S isotope data indicate that the subcrustal source has been metasomatized by subducted crustal sediments. [ABSTRACT FROM AUTHOR]