Ruidong Yang

Rare earth element geochemistry of Cambrian phosphorites from the Yangtze Region

Abstract Analysis on P2O5 and REE (rare earth elements) in basal Cambrian phosphorites from the Yangtze Region, showed that the phosphorites from Bailongtan in Yunnan Province, Zhijin, Jinsha, Xishui, Zunyi, Tianzhu and Tongren in Guizhou Province, Shangrao in Jiangxi Province, Jiangshan in Zhejiang Province and Nanjing in Jiangsu Province contained high REE contents in phosphorites, especially those from Tianzhu and Tongren in Guizhou Province, Shangrao in Jiangxi Province, Jiangshan in Zhejiang Province and Nanjing in Jiangsu Province. Among them, the highest REE contents reached up to 1361.59×10−6 and P2O5 contents up to 29.45%. In contrast, phosphorites from Kaiyang, Qingzhen and Zhenyuan in Guizhou Province had relatively low total REE contents and low P2O5 contents, with the lowest total REE content of 53.19×10−6, and the lowest P2O5 content of 0.07%. REE contents exhibited a positive correlation with phosphorous contents, indicating a close genetic relationship between REE and phosphorous element. The main reason was the difference of the sedimentary environments and the contents of phosphorous and REE in deep water mass formed in upwelling currents, at an upper slope facies (Slu) in reducing condition due to relatively closed sedimentary environment. It was very difficult for the upswelling phosphorous and REE to deposit, massive phosphorous deposits were hard to be formed. At a deep water ramp facies (DRa) in the ascending process of currents, phosphorus and REE underwent differentiation rather than sedimentation. Consequently, the contents of P2O5 sediments and REE were low. At a shallow water ramp facies (including shoals and tidal flats) (SRa), with active seawater circulation and phosphatic supplement, sunny weather, high nutrition and rapid growth of algae, were benefitial for the physical enrichment of carbonate sediments. Therefore, massive phosphorite deposits were easy to be formed with abundant REE minerals, and finally turned into high REE bearing phosphorous deposits.

Trace element and REE geochemistry of the Zhewang gold deposit, southeastern Guizhou Province, China

The Sanshenjiang gold deposit in southeastern Guizhou Province, China, is hosted by the Neoproterozoic metasedimentary rocks which experienced low-grade greenschist facies metamorphism. Gold mineralization occurs mainly in the ribbon chiltern slate of the first member of the Longli Formation and is controlled by both strata and faults. Ore bodies are characterized by abundant quartz-arsenopyrite-gold-pyrite-bedding veins, veinlets and small lenses within the shear zone. In this study, trace element and REE geochemistry was analyzed to constrain the origin and genesis of this deposit. The trace element signatures of wall rocks and veins display a basically similar tendency in the spider diagram, showing the genetic relationship. The values of Co/Ni, Y/Ho, Hf/Sm, Nb/La and Th/La reflect that the hydrothermal fluids of this deposit were derived from the mixture of multiple sources with marked enrichment of Cl and moderate to high temperature. There is a broad similarity in the chondrite-normalized patterns and REE fractionation between wall rocks and ore bodies, possibly reflecting their similar origin. Based on the difference in δCe and δEu, quartz veins and lenses can be subdivided into weakly negative Ce-anomalies (δCe=0.81 to 1.06) with slight Eu anomalies (δEu=0.81 to 1.06) type and the significant positive Ce-anomalies (δCe=1.13 to 1.97) with moderate negative Eu-anomalies type, probably suggesting physical-chemical changes in the evolution process of ore-forming fluids from the early to late stage. It can be concluded that the ore-forming process may have experienced three stages: formation of the original ore source bed, regional metamorphism and gold mineralization, on the basis of trace element and REE analysis and field observation.

Discovery of an abnormally high-δ 34 S barite deposit and a new understanding of global sulfur isotope variation during geological history

The evolution of the global sulfur isotope curve was plotted based on the δ34S values of evaporates resultant from oceanic evaporation. In the long period of geological history the δ34S values showed obvious peaks for three times during the process of ancient oceans’ sulfur isotope evolution, namely the Early Cambrian (+30‰), the Late Devonian (+25‰) and the Permian-Triassic transition interval (+17‰), but the causes of the abnormal rise of sulfur isotopic values during the geological period are still in question. In this paper, 18 samples collected from a large Devonian barite deposit from Zhenning County were analyzed to determine their δ34S values, revealing that the 18 samples have very high δ34S values (δ34S=41.88‰–+68.39‰), with an average close to 56.30‰, which are higher than the isotopic values of contemporary sulfates (+17‰–+25‰). A comparative analysis was conducted of the emerging of high δ34S barite deposits (from Cambrian and Devonian) and the δ34S variation curves of the ancient oceans. The results indicate that the time when the obvious peaks of δ34S values appeared and the time of massive sedimentation of high δ34S barite deposits are very close to each other, which, in our opinion, is not a coincidence. There may exist some correlations between the sulfur isotope evolution of ancient oceans during the diverse periods of geological history and the massive sedimentation of high δ34S barite deposits. Therefore, it is inferred that perhaps it was the massive sedimentation of high δ34S barites that caused the sharp rise of δ34S values in a short period of time.

Distribution and transfer of potentially toxic metal(loid)s in Juncus effusus from the indigenous zinc smelting area, northwest region of Guizhou Province, China

We collected samples (i.e., the aerial parts and roots of Juncus effusus and their growth media) in the indigenous zinc smelting area in the northwest region of Guizhou Province, China, and we measured and analyzed potentially toxic metal(loid)s (arsenic, As; cadmium, Cd; chromium, Cr; copper, Cu; mercury, Hg; lead, Pb and zinc, Zn) in these samples. The results include the following: First, there is a high concentration of one or more potentially toxic metal(loid)s in the slag and surrounding soil in the research area. This situation might be caused by metal(loid) damage or contamination due to the circumstances. Additionally, Juncus effusus in the indigenous zinc smelting area are contaminated by some potentially toxic metal(loid)s; since they are used for Chinese medical materials, it is especially significant that their As, Cd and Pb concentrations are greater than their limited standard values. Finally, both the bioconcentration factors and transfer factors for most potentially toxic metal(loid)s in Juncus effusus are less than 1 in the study area. Therefore, we suggest that Juncus effusus could be used for phytostabilization or as a pioneer plant for phytoremediation of potentially toxic metal(loid)s because it has a tolerance and exclusion mechanism for these metal(loid)s in the research district.

Evaluating the Factors Influencing Limestone-Dissolution Characteristics in the Karst Regions of Guizhou, China

Guizhou, China, is known for the abundance of subterranean drainage systems with sinkholes. Sinkholes may develop when acidic water starts to dissolve the surface of bedrock or bedding planes. The dissolution characteristics of limestone play a crucial role in the development of sinkholes. The main objective of this study was to develop a quantitative tool for evaluating the dissolution ability for sinkhole formations in the karst regions of Guizhou. The present study investigates a number of properties of limestone that may influence the dissolution in the karst regions of Guizhou. Over 200 rock samples were collected and tested to determine the CaO/MgO ratio, clast content, clastic/matrix ratio, primary porosity, permeability, and fracture density. A quantitative approach was developed to synthesize the influences of these multiple factors to establish the order of the limestone solubility in different regions of Guizhou via numerical modeling using the analytical hierarchy process (AHP) theory. It was found that the solubility of the karstic limestone from different geological formations was in the following descending order: Carboniferous Huanglong-Maping Formation, Permian Qixia-Maokou Formation, Cambrian Qingxudong Formation, and Triassic Yongningzhen Formation. As the water-bearing capacity of the geological formations in these regions is closely associated with underground cavern and sinkhole formations, the approach explored in the present study may have strong implications for the exploration and utilization of karst groundwater resources.

Distribution and controlling factors of selenium in weathered soil in Kaiyang County, Southwest China

Selenium is one of the life-related elements. Survey reveals that selenium enrichment in the studied strata from Kaiyang County is considered to be closely related to the following factors: regional black shale series in Niutitang Formation of Early Cambrian, strong adsorption of organic matter (OM), magmatic hydrothermal migrate along the deep fault, mixing and migration of hydrothermal brine, regional uranium mineralization and presence of a great deal sulfides. For selenium enrichment in its weathered soil and crops, the reason responsible is selenium-enriched bedrock, which provides material sources for weathering profile and is considered as the main controlling factor of selenium content in the soil profile. After leaching and migrates downwards, organic carbon (OC) adsorption, iron-manganese layer adsorption, geochemical barrier role, selenium content in different profiles, there are mainly three types of distribution features: bottom enrichment type, top enrichment type and no significant enrichment type. Comprehensive analyses find that selenium enrichment area is mainly distributed in the Machang, Gaoyun-Fengsan-Guanpo, Baimadong, Chuandong-Hefeng-Shaoshang and Longgang-Gaozhai region, etc. Besides, around the east part of the county, in Huali and Yongxing selenium are relatively scarce.

Risk assessment for potentially toxic metal(loid)s in potatoes in the indigenous zinc smelting area of northwestern Guizhou Province, China

We investigated potentially toxic metal (loid)s (arsenic, As; cadmium, Cd; chromium, Cr; copper, Cu; mercury, Hg; lead, Pb; selenium, Se; and zinc, Zn) in agricultural samples (i.e., Solanum tuberosum L. tubers (potatoes) and their planting media) in the indigenous zinc smelting area of northwestern Guizhou Province, China. Based on the pollution index values for As, Cd, Pb and Zn, the order of the samples was as follow: slag > planting soil with slag > planting soil without slag, and the order of the samples in terms of the bioconcentration factor was the opposite. Cr, Cu and Hg were present in the planting soil with and without slag at slight pollution levels, and the other potentially toxic metal (loid)s had different degrees of contamination. Additionally, the potentially toxic metal (loid) contents in potato were under their limit values except for Cd (all samples) and Pb and Se (some samples). All bioconcentration factors for potatoes were below 0.5, and no health risk index value for potatoes was higher than 0.1. Therefore, although no significant health risk associated with potentially toxic metal (loid)s via consuming potato exists for either adult men or women in the research area, the Cd concentration in this crop should be monitored.

Forming Mechanism Analysis of the Abnormally High δ34S Baryte Deposits: A Case Study from the Zhenning–Ziyun Large Devonian Baryte Deposits, Guizhou Province, China

ABSTRACT Stratiform baryte deposits are widespread in Cambrian and Devonian strata in China and around the world. In this article, the authors studied the sulfur isotopic features and forming mechanism of the stratiform baryte deposits occurring within the Upper Devonian cherts of the Zhenning-Ziyun county, Guizhou province, located in the Southwestern margin of the Yangtze Platform. The sulfur isotopic data from 18 baryte ore samples of the Leji section of Zhenning county are presented herein with values that range from +41.9‰ to +68.4‰ (AVG = +59.9‰). The δ34S values of the baryte ore from the Mohao section of Ziyun county are stable and show a narrow range from +41.3‰ to +47.0‰ (AVG = +44.0‰). In the Luocheng section of Ziyun county, the δ34S values of the baryte ore vary from +27.6‰ to +36.4‰ (AVG = +32.7‰). The δ34S values of all samples are higher than those of the coeval seawater sulfates (+25‰). The scanning electron microscope analysis indicates that spherical, dumbbell-shaped, clavate bacterial and bacteria-like fossils were observed, as well as the irregular schistose and framboid forms of Fe oxides that occur around the surfaces of baryte grains and inter-grains. Fe oxides take irregular schistose and framboid forms. These findings imply the significant concentration of heavy sulfur related to the seawater sulfates with the action of bacterial sulfate reduction in a closed basin. In addition, the trend of the δ34S value of baryte ores is gradually decreasing from the Leji to Mohao and Luocheng sections, which suggests that Leji area is located in the deepwater area of the restricted rift basin, and in a more closed depositional environment.

A study of dissolution and water-bearing characteristics of the restricted platform dolomite facies in the karst areas of Guizhou, China

The restricted platform facies dolomites are widely distributed in the northern and northeastern Guizhou, China, and they are the main lithology of karst groundwater and a primary target for locating drinking water resources in the province of Guizhou. The geological history and deposition environment of the restricted platform dolomite facies vary significantly across the province, making it more difficult to evaluate the dissolution and water-bearing capacity of karstic dolomites. This paper explores a quantitative approach to assessing the solubility of four typical geological strata using analytical hierarchy process (AHP) modeling. Properties including CaO/MgO, clast content, porosity, permeability and fracture density are investigated and used as the major criteria in the AHP analysis to render the rankings for solubility among the studied formations. Hydrogeological characteristics are also discussed. Overall the presented results demonstrate the feasibility of AHP as a modeling tool to provide a quantitative approach when a wide range of properties need to be considered. The explored approach can have strong implications for the exploitation and utilization of karst groundwater in Guizhou, China.

Geochemical characteristics of the giant Nibao Carlin-type gold deposit (Guizhou, China) and their geological implications

A large gold orebody controlled by Fault F1 was newly discovered in the giant Nibao Carlin-type gold deposit from southwestern Guizhou, China. Ore or rock samples were collected and studied to reveal the relationship among various orebodies which distributed in Fault F1 and its upper and lower plates, and to figure out the possible origin of ore-forming material. Tuff or tufaceous material was considered to be basic volcanic rocks in terms of their characteristic values of Al2O3/TiO2. Positive correlation was found between Au and As, and the correlation coefficient is particularly high within the fault fracture zone of the F1. Analysis shows that As can be regarded as a preferentially indicative element in gold prospection, while minerals of hydrothermal origin such as pyrite and arsenopyrite can be used as mineralogical indicative for gold prospection. Geochemical characteristics of trace elements and rare earth elements (REE) show that mantle source materials might have been involved in gold mineralization of different ore bodies. Large-scale Emei mantle plume eruption in the Early Permian resulted in thick volcanic sedimentary rock positioned between the karst unconformity surface at the top of the Maokou Formation and the bottom of the Longtan Formation. The Yanshanian tectonic activities played a significant role in driving gold-rich fluids to pressure-release spaces such as fault fracture zone and structure-controlling alteration zone (abbreviated to Sbt, according to Chinese). Those fluids reacted with ore-hosting rocks through water–rock interactions and resulted in the formation of gold-rich arsenian pyrite and arsenopyrite. Gold mineralization might have resulted from reactions between Fe-poor and gold-rich ore-forming fluids and tuffs which was relatively rich in iron, during which Fault F1 was considered to be the key to the formation of this giant gold orebody.