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The Au value of stream sediments in swamp-forest areas in Northeast China is lower than in other areas, according to results from the Regional Geochemistry–National Reconnaissance Program. Two dissolution methods for measurement of Au levels were compared in this study. The Au values in samples dissolved by using four acids (HClO4 + HF + HNO3 + HCl) are larger than those dissolved by using aqua regia, especially when the Au content is greater than 1.25 ng/g. We found that a large amount of Au may be absorbed to or/and included in SiO2 colloids, apart from that occurring in organically bound forms in organic-rich sediments of swamp-forest areas. The Au absorbed to or/and included in SiO2 colloids is related to plant metabolism. This Au can migrate for long distances protected by high-concentration organic acids in water solution, but cannot be dissolved by aqua regia. The results of a pilot survey with an ultra-low sampling density in the Jiayin area, Heilongjiang Province, show that the Au anomalies obtained by using four-acid dissolution are not only larger in scale but also more coincident with corresponding metallogenic belts than those using aqua regia dissolution. [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]

[Display omitted] • Low density geochemical mapping is efficient of delineating potential prospecting areas of IAREDs. • Positive REE anomalies are mainly associated with granitic, basaltic and carbonate rocks. • More than 95% of the IAREDs are located in granitic REE anomalies. • Overall, a two-step strategy for prospecting of IAREDs is proposed. Ion-adsorption rare earth deposits (IAREDs) have received widespread attention as their indispensable supply of heavy rare earth elements (HREE), which have naturally paved the way for IAREDs exploration. However, studies on regional prospecting methods, especially geochemical methods, on IAREDs are very limited. Here, we aimed to study how to identify and delineate the potential prospecting areas of IAREDs based on 5244 sets of stream sediment geochemical data from the 76-element Geochemical Mapping (76- GEM) project in South China at the scale of 1:2,000,000. The results showed that stream sediments in South China had a higher average concentration of REE (212 mg/kg) than Chinese catchment sediments (187 mg/kg) and Chinese soils (190 mg/kg), which indicated a great prospecting potentiality of IAREDs. Geochemical and geological maps revealed that the positive REE anomalies were mainly associated with three types of parent rocks: granitic, mafic igneous and carbonate rocks. Almost all IAREDs were spatially distributed in the positive REE anomalies and more than 95 % of the IAREDs were located in granitic REE anomalies. The distinct geochemical characteristics of the parent rocks, such as δEu, δCe, Eu, Si, Ca, K, Ni, Cr and Ti content, could help to distinguish REE anomalies of granitic rocks from those of mafic and carbonate rocks. Accordingly, a two-step method was proposed to prospect for IAREDs with stream sediment geochemical mapping. Overall, this study corroborated the finding that low-sampling density stream sediment geochemical mapping is an efficient method of delineating potential target areas of IARED on a national scale. But it was difficult to distinguish between LREE deposits and HREE deposits. This method showed great potential in IARED prospecting, especially in areas with a low geological degree. To the future exploration of IAREDs, the targeted multi-scale approaches for different exploration stages are essential to be developed. [ABSTRACT FROM AUTHOR]

Continental-scale stream sediment geochemical data from the 76-element GEochemical Mapping (76-GEM) project covering southern China were analyzed in this contribution. 5244 composite stream sediment samples at the scale of ca. 1 sample per 500 km2 were used. The focus has been directly put on element associations of: (1) Light Rare Earth Elements (LREEs, i.e. La, Ce, Pr, Nd, Sm and Eu); (2) Heavy Rare Earth Elements (HREEs, i.e. Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y); (3) Iron Group Elements (IGEs, Ti, V, Cr, Mn, total Fe 2 O 3 (FeT), Co and Ni); (4) Platinum Group Elements (PGEs, i.e. Ru, Rh, Pd, Os, Ir and Pt) and (5) Mo, Sn, W and Bi. Given that geochemical data are typical of compositional (closed) data, the five associations were represented by the sum values of centered logratio ( clr ) transformed data of elements in the predefined groups. It presents the first-time the continental-scale patterns of representative element associations in southern China. Maps were compared to independent datasets of lithology, tectonics and topography to discover processes governing the distribution. The five element associations could reflect the processes of: (1) weathering of dominantly felsic intrusive rocks (LREEs and HREEs); (2) weathering of mafic/ultramafic rocks (IGEs and PGEs); (3) weathering of dominantly felsic intrusives and hosted mineralization (Mo-Sn-W-Bi) and (4) anthropogenic and possible geogenic additions (Mo-Sn-W-Bi and PGEs). A general good agreement was found between maps of element associations and maps of surface geology and tectonics. The clr patterns are interpretable geologically and respond reasonably well to the processes such as lithological control and secondary transportation. As indicated by the clr patterns, two prominent tectonic units with controversial boundary in southern China, i.e. the Yangtze and Cathaysia blocks can be geochemically demarcated by the spatial patterns of REEs, IGEs and PGEs at this scale. The distinct patterns across the Jiangshan-Shaoxing and Pingxiang-Chaling faults (or the Shi-Hang Belt) suggested a felsic end-member to the southeast and a mafic end-member to the northwest. The spatial patterns of IGEs, PGEs and Mo-Sn-W-Bi also reflected that lithology is in dominant control of the distribution rather than local mineralization at this scale. Future studies of this dataset regarding single elements and certain element associations of particular interests (e.g., Cd, Ni and REEs) are also needed, which may provide new insights into environmental issues, mineral resources and tectonic framework in southern China. • Continental-scale multi-element stream sediment geochemical data of southern China is studied. • Centered logratio ( clr ) transformation is conducted due to compositional nature. • The clr distribution patterns show agreement with lithology, weathering and transportation. • The boundary between the Cathaysia and Yangtze blocks is inferred by clr geochemical patterns. • Continental-scale geochemical mapping may provide insight into tectonic framework. [ABSTRACT FROM AUTHOR]