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The Xiangfan-Guangji fault zone(XGF) is a boundary fault separating the Dabie orogen and the foreland fold-thrust belt on the northern Yangtze cratonic margin. Its geometry, kinematics and structural evolution characteristics have recorded the collision, assembly and interaction between two tectonic units in the north and south. Based on field investigation, structural and geochronological analyses, and combined with published regional geological and geophysical data, we considered that the eastern XGF is characterized by a “crocodile mouth” offset structure of deep south-directed thrust and shallow north-directed thrust, which differs significantly from the structural deformation style and sequence of the western XGF. The eastern part of the middle Yang-tze block is controlled by the N-S-directed tectonic system. Subduction of the northern Yangtze cratonic margin beneath Dabie oregen may have extruded the orogen from north to south. The nappe structure may have affected the Ruichang area, and the shallow thrust nappe from south to north may have affected the vicinity of Meichuan. The two structures are likely connected in the Qichun-Wuxue-Xishui area in the eastern XGF. The XGF has undergone various structural deformation stages, including the N-S-directed thrust nappe ductile shearing (end T2), Early-Middle Yanshanian shallow bipolar offset detachment (J1-3), Late Yanshanian normal faulting (K1-2), and minor early Xishanian thrusting (E1) from north to south.
A suite of greenschist to lower-amphibolite-facies metasedimentary rocks is exposed at Guantianmen in the Mianlue tectonic belt, and is characterized by intense ductile deformation. The depositional ages and tectonic settings of these rocks have long been controversial, which limits our understanding on the regional tectonic evolution. To constrain their depositional ages and tectonic settings, we conducted petrology, petrogeochemistry, and LA-ICP-MS detrital zircon U-Pb dating on the metasedimentary rocks. The results show that protoliths of the Guantianmen metasedimentary rocks are a set of fine-grained clastic rocks with local carbonate interbeds. Our work indicates that the metasedimentary rocks have undergone low-degree chemical weathering and sedimentary recycling, and were mainly derived from felsic to intermediate igneous rocks with continental arc signature. Two samples yielded similar age distributions, displaying a dominant ca.880-800 Ma age group with a main age peak at ca.830 Ma. The youngest age group is 747-736 Ma(avg.742±6 Ma). Combined with previous work, we suggest that the main provenance region of the Guantianmen metasedimentary rocks is the Early-Middle Neopro-terozoic magmatic arc in the Bikou and Hannan-Micangshan microblocks. The depositional age of the Guantianmen metasedimentary rocks should be later than 720 Ma. The rocks were most likely deposited in an extensional rift system during the middle-Late Neoproterozoic, in response to the Rodinia supercontinent breakup.
The Dangjiasi granite complex is a larger pluton in the central-eastern part of the Indosinian Nanshan granite belt(Qinghai Province). The complex was emplaced in the Early Triassic (243.5±2.9 Ma,247.2±1.7 Ma)-Middle Triassic (240.1±2.1 Ma,241.0±2.6 Ma). There are many intermediate felsic dykes in the intrusion, comprising mainly diorite porphyry, quartz diorite porphyry, and granite porphyry, LA-MC-ICP-MS zircon U-Pb dating on the diorite porphyry dyke yielded early Late Triassic age (235.6±2.4 Ma), slightly younger than the minimum emplacement age limit of the Dangjiasi granite complex. As a shallow intrusive body, the dykes are similar to the Dangjiasi intrusion in structural setting, and their mineral and geochemical compositions have similar characteristics, indicating that the two rock types have similar genesis and tectonic background, and may have had the same crust-mantle mixed magma source region. Litho-geochemistry shows that the intermediate dykes have low SiO2(54.68%-64.75%), whilst the felsic dykes have high SiO2(66.00%-77.13%), and both have high Al2O3(12.24%-17.11%). The rocks are high-kcalc-alkaline metaluminous-weakly peraluminous (A/CNK=0.85-1.04), with typical island arc granite and collision granite affinities. The rocks are enriched in LREE, Rb, Th and K, but depleted in HREE, Nb, Ta, P, Ti and Ba with (La/Yb)N=5.05-17.61 and medium negative Eu anomaly. Comprehensive analysis suggests that the dykes were formed in the Late Triassic Gonghe rift-closure related collisional orogeny. The tectonic setting changed from compression to intraplate stability-extension, suggesting that the Gonghe Basin(and surroundings) had entered post-collision intracontinental environment in the early Late Triassic.
To deepen our understanding in the Carboniferous tectonic background in the western Central Asian Orogenic Belt, drill-core samples of andesite in Jinlong 10 well area of Zhongguai uplift (northwestern margin of Junggar basin) were studied via petrography, chronology and geochemistry. The results show that our andesite samples are low-K to medium-K calc-alkaline, with slightly right-inclining REE diagram and weakly negative Eu anomaly. In the primitive mantle-normalized spider diagram, the rocks have Pb and LILE (Rb, Ba) enrichments and HFSE (Nb, Ta, Zr) depletions, resembling those of typical subduction-related arc volcanic rocks. The Th/La, Th/Ce and Lu/Yb ratios of andesite are below those of the average continental crust, but similar to those of typical mantle-derived magmas. The andesite samples belong to the normal island arc volcanic rocks, which are derived from the water-rich mantle wedge and by partial melting of the fluid-metasomatized mantle wedge (produced by subducting-slab dehydration). LA-ICP-MS zircon U-Pb dating of the andesite yielded Middle Carboniferous age of (322.4±1.1) Ma. Combined with regional geological background and compared with coeval magmatism, we considered that the andesite in the Zhongguai uplift was formed in a continental arc setting, and was the subduction product of residual oceanic basin in West Junggar, which was not completely closed at (322.4±1.1) Ma.
Dyke swarms with complex lithology are distributed on the southern margin of the Alataw Mountains (some closely ore-related), providing a good window to understand the crustal growth process. Numerous intermediate-felsic dykes are exposed in the western section, which intruded the Upper Devonian Tuskuertau Formation. These dykes are dominated by diorite with minor granite porphyry and felsite. We carried out zircon U-Pb age and Sr-Nd dating on the granite porphyry dyke to reveal its formation age, magma source and tectonic setting. The zircon U-Pb dating yielded weighted average age of 310 Ma, indicating that the granite porphyry dykes were formed in the early Late Carboniferous. This age is very close to the eruption age (310 Ma) of the Shawan intraplate rhyolite formed under an extensional environment and the formation age of the Chahawusu batholith (313 Ma), which is the product of the latest magmatism in the western Alataw Mountains. The Sr-Nd isotopic compositions indicate that the dykes are featured by medium ISr (0.709,328-0.710,018) and negative εNd(t) (-3.92 to -2.33) values and older Nd model age (1,294-1,502 Ma), which are obviously different from those of coeval granitoids in the western Tianshan and northern Xinjiang. The latter has generally low ISr and highly positive εNd(t) values and younger Nd isotope model ages, and were likely derived from the mantle, and underwent magma underplating and ACF or magma mixing processes. After 310 Ma, the Alataw Mountains gradually entered a post-collision extension stage, which was in a vertical growth of continental crust. We conclude that the granite porphyry dykes were unlikely to be formed by mantle-derived magma underplating and evolution, and the magma source is the Precambrian basement rock with relatively high maturity. The dykes may have formed in a post-collision extensional setting.
Diorite porphyry has been widely studied due to its genesis and ore-bearing characteristics. Many diorite porphyry intrusions were found in the north of Abagaqi (Inner Mongolia), accompanied by high-background geochemical anomalies. Studies on petrology, zircon U-Pb geochronology, geochemistry and Lu-Hf isotopes have been conducted for the formation age and magma source of diorite porphyry samples from the Shazhangtu mining area in Inner Mongolia. The diorite porphyry was emplaced at (311.1±1.7) Ma, and is the product of the middle Hercynian (Late Carboniferous) tectonomagmatic activities. The rocks have SiO2=56.19%-60.45%, Na2O+K2O=4.81%-5.87%, and aluminum saturation index (A/CNK)=1.00-1.43. It belongs to high potassium calc-alkaline and peraluminous rocks. The LREE LILE (K, Rb) and HFSE (Zr,Th and U) are enriched, and the HFSE (Nb, Ta, P, Hf and Ti) are depleted, indicating that the geochemical characteristics of island are magmatic rocks in subduction zone. The total REE contents ranges from 139.62×10-6 to 150.67 ×10-6, showing a right-inclined pattern of light rare earth enrichment and heavy rare earth depletion with weak negtive Eu anomaly. The Hf isotopic data of zircons show that the single-stage and two-stage model ages range from 637 to 905 Ma and from 827 to 1,259 Ma, respectively, and the εHf(t) value of zircons varies from 1.10 to 7.80, indicating the characteristics of mantle-derived magma. It is probably the partial melting magma in the mantle wedge due to the dewatering of the subduction plate that underplated under the bottom of the lithosphere and the molten body rises to cause under-invasion, heated and induced the partial melting of the new formed juvenile basic lower crust, forming the crust-mantle sources mixed magma.
A number of rare metal deposits have been discovered in Narenwula area of Inner Mongolia, with high metallogenic potential. However, there are still many controversies about the chronology and genesis of Narenwula granite. LA-ICP-MS zircon U-Pb dating and geochemical analysis have been carried out to determine the age and genetic type of the Narenwula granite. The U-Pb dating results show that the medium-coarse biotite monzogranite and porphyritic monzogranite were emplaced in the Early Cretaceous, at (142.1±1.0)Ma and(142.3±1.2)Ma, respectively. Its diagenetic age is basically consistent with the ages of the extensive regional granite emlacement in the Late Jurassic-Early Cretaceous period. Whole-rock geochemistry shows that the granite is characterized by high silica(SiO2=73.69%-76.67%)and alkali(Na2O+K2O=8.40%-8.80%), but low P2O5, MgO, FeOT, CaO, and REE. The rocks have high LREE/HREE ratios(LREE/HREE=6.23-14.28) and marked negative Eu anomalies (δEu=0.20-0.36). They are obviously enriched in Zr, Hf, Rb, and Th, but strongly depleted in Ba, Sr, P, and Ti, and slightly depleted in Nb. The granite is high-K calc-alkaline and weakly peraluminous. Based on the characteristics of mineralogy, petrology and geochemistry, we concluded that the granite belongs to highly-fractionated I-type. Considering the structural features and regional geological background, we inferred that the Narenwula granite in the northern margin of the North China Plate was formed in the Early Cretaceous within-plate extensional setting.
To deepen our understanding on Caledonian magmatic rock evolution in northwest Guangdong, the petrology, petrography, isotope chronology, petrogeochemistry and Sm-Nd isotope geochemistry of the Daguishan pluton in northwest Guangdong is carried out.The result shows the Daguishan pluton is located in the northwest margin of the Fogang complex pluton in Guangdong Province, and the lithology is medium-/coarse-grained biotite syenogranite.LA-ICP-MS zircon U-Pb dating shows that its age to be (445.9±3.6) Ma, belonging to the Late Ordovician intrusive rock.The Daguishan pluton is rich in Si,K, high differentiation index and low Ca, Mg and Fe. The rocks show the total amount of REE is medium to low, the fractionation degree of LREE and HREE is low with negative Eu anomaly. The monzogranite is also enriched in LILEs(e.g., Rb,Th,U,K,La,Ce and Nd) and depleted in P,Sr,Ba and Ti. (87Sr/86Sr)i value is 0.025,3-0.100,2, and εNd(t) value is -3.15--5.26 with lower TDM2 value. Based on the geochronological and geochemical characteristics of the Daguishan pluton, it is inferred that the source area is the crust material with low maturity or the mixing of a certain proportion of crust mantle material. The crust gets extended due to the collapse of orogenic belt and the upwelling of asthenosphere. Due to mantle uplift, mantle-derived mafic magmatites and potassic-basalt magmatites were formed by upwelling or underplating.
The Qianchuiliu gold deposit was located in northeastern margin of Jiaolai Basin, Jiaodong Peninsula. Concealed gold orebodies with 13.5 tons of inferred gold reserve were discovered in the major ore-controlling structure-alteration belt in 2020. Two different granites were found adjoining to the major ore-controlling structure-alteration belt based on drilling. The hanging-wall comprises monzogranite of the Muniushan pluton and the Jingshan Group, whereas the footwall comprises mylonitized monzogranite of the Queshan pluton. The Muniu-shan pluton was conventionally considered as a part of the Queshan pluton, but we observed some differences in terms of metamorphic/deformation degree and mineral assemblages. Therefore, both kinds of granites were systematically analyzed by zircon U-Pb geochronology, lithogeochemistry, and zircon Hf isotope geochemistry to identify the differences and any gold metallogenic link. Zircon U-Pb age of the Muniushan monzogranite is 1,844.1±4.4 Ma, indicating a Paleoproterozoic (Orosirian) magmatic product. The monzogranite is characterized by relatively high SiO2 but low MgO contents. The monzogranite has low Sr content and Sr/Y ratio, high Y and Yb content, and obvious negative Eu anomaly (δEu=0.30-0.48). The Muniushan monzogranite is calc-alkaline and strongly peraluminous. The monzogranite has zircon εHf(t) values range from -9.5 to 3.0, most of them are negative with two positive values (0.2 and 3.0). The two-stage Hf model ages range from 2,492 to 3,083 Ma, indicating that they were mainly originated from partial melting of the Archaean lower crust. The Queshan mylonitized monzogranite yielded Late Jurassic zircon U-Pb age of 154.6±1.5 Ma, coeval with the well-known Linglong and Kunyushan granitic complexes in the region. The mylonitized monzogranite has high content of SiO2 and low content of MgO. Trace elements are characterized with high Sr and Sr/Y ratio, low Y and Yb content and significant positive Eu anomaly (δEu=1.61-2.20). The rocks are high-K calc-alkaline and peraluminous, showing adakite-like affinity. The mylonitized monzogranite has zircon εHf(t) values of -26.6 to -14.1. The two-stage Hf model ages range from 2,681 to 3,860 Ma, concentrated around 2,820 Ma, indicating that the granite was formed by melting of the Archaean thickened lower crust. All the above studies show the Muniushan monzogranite and the Queshan mylonitized monzogranite granite are two different granites with different zircon U-Pb ages, lithogeochemistry and tectonic setting. Both granites show close spatial link with the gold mineralization, but no temporal or direct genetic connection. Drill-cores of Qianchuiliu gold mine could be divided into three layers. This three-layer structure is geologically similar to the Queshan metamorphic core complex. The newly-discovered Qianchuiliu gold deposit implies great potential of gold prospecting in this area, especially the ductile shear zones and low-angle major detachment faults around the Queshanpluton.
The medium-sized Saibagou quartz vein-type gold deposit is located in the eastern part of the northern margin of Qaidam. The granite porphyry zircon U-Pb geochronology and geochemistry were analyzed in this study. The LA-ICP-MS zircon U-Pb dating yielded (372.4±4.1) Ma, indicating Late Devonian magmatism. The granite porphyry is characterized by high SiO2 and alkali-rich, with differentiation index (DI) of 81.40-84.54 and solidification index (SI) of 3.56-8.17, indicating substantial fractionation. The geochemical features show remarkable enrichments in La, Hf, Rb, and Th, but depletions in Nb, Ta, P, Ti, Ba, and Sr. The total rare-earth element (ΣREE) is 71.80×10-6-75.21×10-6, and the REE patterns are right-inclining with slightly negative Eu anomalies (δEu=0.77-0.96). Discriminant diagram shows that the granite porphyry is peraluminous calc-alkaline I-type, and was likely formed in a post-orogenic setting during the Middle-Late Devonian intracontinental extension in the northern margin of Qaidam. The granitic magmatism was likely syn-ore and occurred close to the orebodies and filled in structures. Therefore, the maximum age of the Saibagou gold mineralization can be set at 372.4 Ma, and future prospecting work should focus on the granitic porphyry dikes.
The northern sub-belt of Western Qinling Orogen is endowed with abundant polymetallic resource. To delineate mineral exploration targets, a 1:25,000 stream sediment geological survey was carried out in the Changjiashan district. Statistical analysis was performed from 1,141 samples for Kernal Density Estimation elements (Au, Ag, As, Sb, Bi, Cu, Pb, Zn, W, and Mo). Element concentrations are higher than the national and regional average, indicating metallogenic potential in the area. Element combinations of the four factors were obtained based on factor analysis, i.e., F1(Bi-Cu-Zn), F2(Au-As-Sb), F3(Ag-Pb), and F4(W-Mo). We obtained thresholds of geochemical elements and factor scores, and geochemical mapping via Concentration-Area (C-A) fractal modeling and Kriging interpolation, respectively. Combined with regional ore-controlling factors and anomaly spatial distributions, three polymetallic anomaly areas, i.e., Hz1, Hz2, and Hz3, were delineated. Geochemical halos comprise the supra-ore halo, near-ore hole, and sub-ore halo from northwest to southeast. Distribution of stream sediment geochemical anomalies indicates that all mineralization was fault-controlled, and the area close to the NW-trending Lixian-Lüjing fault at Changjiashan represents a favorable prospecting target.
The upper Yangtze River region is an important ecological security barrier for the Yangtze River Economic Belt. The river sediments collected from Daliangzi Pb-Zn mining area, Panxi in the upper reaches of the Yangtze River were investigated in this study. The spatial distribution, source, pH-dependent leaching characteristics, and ecological risk levels of heavy metals were evaluated. The results indicated that the concentration of heavy metals in the river sediments of Daqiaohe River in Panxi, whose spatial distribution of heavy metals was inhomogeneous extremely was significantly higher than in the Yangtze River. The comprehensive potential ecological risk index (RI) of heavy metals is very strong. Hg and Cd with high enrichment were severely polluted, Pb and Zn with moderate enrichment were moderately contaminated. The leaching tests showed that the concentrations of Pb, Zn and Cd in the leachate decreased rapidly and then stabilized under acidic and neutral conditions, and As decreased rapidly and then increased slowly. The source of As, Cd, Pb and Zn in the sediments of Daqiaohe River was the mining of Daliangzi Pb-Zn mining area. The source of Hg was rock weathering and pedogenesis. The source of Cu and Cr were agricultural and industrial activities. The soils in the Pb-Zn mining area of Panxi metallogenic belt were Cd-rich and Cr-poor. Cd, Pb, Zn and Hg with high ecological risks were the main potential contaminants.
In order to study the geochemical characteristics of selenium in surface soil of Qingzhou in Shandong Province, 8,132 surface soil samples were collected with the average density of 5.2 pieces/km2 in Qingzhou and the selenium content, organic matter, pH and other indicators were analyzed. The results showed that the selenium content in surface soil ranged from 0.02 to 2.77 mg/kg and the background value was 0.21 mg/kg (n=7,462). The area of selenium-abundant soil in the study area is 140.56 km2, accounting for 9.00% of the study area. The area of selenium-sufficient soil is 1,248.39 km2, accounting for 79.93% of the study area; the area of potential selenium-deficiency soil is 148.45 km2, accounting for 9.50% of the study area; the area of selenium-deficient soil is 24.52 km2, accounting for 1.57% of the study area. Selenium in surface soil has different characteristics in different geological units, soil types, landform types and land-use types. Selenium is relatively accumulated in the surface soil with Cambrian-Ordovician parent material, clay soil type, dissolution or moderate-cutting landform type, grassland and woodland land-use type. Correlation analysis showed that there was no correlation between pH and selenium content in surface soil of the study area, but there was a significant positive correlation between organic matter and selenium content.
To better understand the geochemical characteristics and influencing factors of the selenium-enriched soils of the arable land around the stone coal mine,144 topsoil samples were collected from the cultivated land around Huibu stone coal mine in Changshan County, Zhejiang Province, and 20 sugarcane samples, 6 soil vertical profile samples, 5 rock samples, 3 surface water samples were collected at the same time. The contents of Se, organic matter, As, Cd, Cu, Pb, Zn, Ni, Hg and Cr were determined to explore the geochemical characteristics of Se rich soil. The results showed that Se content mainly concentrated in the range of 0.47-1.34 mg/kg in surface soil, with an average content of 0.87 mg/kg, which was much higher than that average value of Zhejiang Province, and the high value area of Se content was consistent with the strike of stone coal mine in Huibu. Se content decreased with the increasing depth along the vertical profile of soil. 89.58% of the soil samples and 65% of the sugarcane samples reached the Se enrichment standard, but there was an ecological risk that the contents of Cd and other major heavy metals in soil and agricultural products exceeded the state standard. The average content of Se was the highest (1.31 mg/kg) in the $\epsilon$1h of soil stratum, and the lowest (0.64 mg/kg) in the O1-2. The average selenium content in dry field was slightly higher than that in paddy field without significant difference(p>0.05). The highest average selenium content was that of coarse bone soil, followed by that of limestone soil and paddy soil, and that of red soil was the lowest. The selenium content in soil had been affected by geological background, soil type and organic matter. The main factors for the formation of selenium rich soil had been regarded as the stone coal bed, black rock series and carbonate rocks, and a small part was related to human activities such as mining.
Selenium is one of the important life elements, which is of great significance to animal and human health. In this paper, we systematically summarized the geochemical characteristics of selenium in topsoil of cultivated land, and analyzed the distribution law of selenium in soil and the genetic relationship between selenium and black rock series. We also discussed the selenium enrichment mechanism in black rock series, and studied the selenium enrichment law in rice plants. We hope that these studies are helpful to reveal the source and ecological effect of selenium in soil of Jiande City. Our results show that the selenium content in topsoil of cultivated land in Jiande City ranges from 0.06 to 11.5 mg/kg, with an average of 0.35 mg/kg. The difference of selenium content in soil is very significant in different geological background, soil parent materials and soil types. In our study aera, 2,647 hectare of clean selenium-rich soils were delineated according to the content of selenium and heavy metals in the soil. Selenium-rich soils are mainly distributed in Cambrian limestone, carbonaceous shale, calcareous mudstone, indicating that the enrichment of selenium in the soil is closely related to the Cambrian “black rock series”. Paleosedimentology research shows that the black rock series were formed in the sedimentary environment of anoxic stagnant water. The organic-rich submarine sediments adsorbed a large amount of selenium from the mantle. After the consolidation and diagenesis, the black rock series which are rich in selenium and other elements were formed. The morphological characteristics of selenium in rice root soil in this study area show that the proportion of acetic acid soluble selenium is relatively small, while the proportion of residual selenium is relatively large, indicating that the availability of selenium in rice root soil is low. The selenium contents in rice, lotus seed and strawberry show that rice has the highest selenium enrichment coefficient, and the selenium content in rice plants was characterized by root > leaf > stem ≈ seed.
Based on geostatistics,GIS and traditional statistical analysis,spatial variability characteristics and influencing factors of available contents of 9 nutritive elements in the tillage layer soil of Ruian were studied. The results showed that alkali hydrolyzable nitrogen in the tillage layer of the study area with the distribution trend of high in the west and low in the east,while that of available contents of potassium,boron,manganese,molybdenum,copper and zinc were low in the west and high in the east,available phosphorus is high in both east and west but low in the middle,and available iron distributed uniformly; there is a lack of available boron in the tillage layer soil in the central and western parts of the study area,a lack of alkali-hydrolyzable nitrogen in the east,and a lack of available phosphorus in the central,except for these,the available contents of 9 nutritive elements in other parts of the study area are all above the medium standard; semi-variance function analysis showed that available contents of manganese and iron had strong spatial correlation,alkali-hydrolyzable nitrogen,available contents of potassium,phosphorus,molybdenum,copper and zinc had medium spatial correlation,and available contents of boron had weak spatial correlation. It is considered that the neutral or weakly alkaline soil environment with high salt content and active cations is beneficial to the enrichment of available contents of potassium and boron,and the acidic or weakly acidic soil with high organic matter content is beneficial to the enrichment of alkali hydrolyzable nitrogen and available contents of iron; the controlling factors of available contents of potassium,molybdenum,boron,copper and zinc are similar,which are mainly affected by structural factors such as soil parent material,soil type and topography,as well as random factors such as fertilization and tillage. Alkali-hydrolyzable nitrogen,available contents of iron,phosphorus and manganese are mainly affected by structural factors such as soil parent material,soil type and topography.
Mass geochemical data of surface soil have been obtained in recent years with the development of geochemical surveys of land quality. However, there is an obvious defect in the dataset of 1∶50 000 large-scale surface samples, i.e., the lack of ore-forming elements. In view of the important role of ore-forming elements in the prospecting of mineral resources, this article attempts to provide a supplementary plan based on existing data. Taking the rare metal rubidium as an example, 2,548 groups of 1∶250 000 small-scale surface soil data in the same area were divided into two groups randomly using the random forest algorithm according to the ratio of 8∶2, with 80% of the data for model training and 20% of the data for model verifying. The combination of variable importance metric ranking and learning curve construction was used to select 8 elements (K, B, Ni, V, Zn, As, Co, Cu) as predictors. The goodness of fitness(R2)of the model to the training data and test data reached 0.983 2 and 0.895 6, respectively, indicating that the optimal method of predictor variables is effective. Subsequently, the above-mentioned predictive variable data of 1∶50 000 surface soil was imported into the model as input variables, and the predicted Rb element content was obtained. The predicted results were in line with the actual characteristics. This study indicating that it is feasible to introduce the big data machine learning random forest algorithm into the spatial quantitative prediction of surface soil geochemical element content, and the service application dimension of land quality geochemical data can be further expanded.
