Xie Shuyun

Identification of Geochemical Anomaly by Multifractal Analysis

Abstract The separation of anomalies from geochemical background is an important part of data analysis because lack of such identifications might have profound influence on or even distort the final analysis results. In this article, 1 672 geochemical analytical data of 11 elements, including Cu, Mo, Ag, Sn, and others, from a region within Tibet, South China, are used as one example. Together with the traditional anomaly recognition method of using the iterative mean ±2σ, local multifractality theory has been utilized to delineate the ranges of geochemical anomalies of the elements. To different degrees, on the basis of original data mapping, C-A fractal analysis and singularity exponents, Sn differs from the other 10 elements. Moreover, geochemical mapping results based on values of the multifractal asymmetry index for all elements delineate the highly anomalous area. Similar to other 10 elements, the anomalous areas of Sn delineated by the asymmetry index distribute along the main structure orientations. According to the asymmetry indexes, the 11 elements could be classified into 3 groups: (1) Ag and Au, (2) As-Sb-Cu-Pb-Zn-Mo, and (3) Sn-Bi-W. This paragenetic association of elements can be used to interpret possible origins of mineralization, which is in agreement with petrological analysis and field survey results.

Magmatic-Hydrothermal Superlarge Metallogenic Systems—A Case Study of the Nannihu Ore Field

Abstract Located in the Qinling molybdenum metallogenic belt on the southern margin of North China craton, the Nannihu molybdenum (-tungsten) ore field, consisting of the Nannihu, Sandaozhuang, and Shangfang deposits, represents a superlarge skarn-porphyry molybdenum (-tungsten) accumulation. Outside the ore field, there are some hydrothermal lead-zinc-silver deposits found in recent years, for example, the Lengshuibeigou, Yindonggou, Yangshuwa, and Yinhegou deposits. Ore-forming fluid geochemistry indicates that these deposits belong to the same metallogenic system. The hydrothermal solutions were mainly derived from primary magmatic water in the early stage and from the mixture of the primary magmatic water and meteoric water in the later stage, with an obvious decreasing tendency in temperature, salinity and gas-liquid ratio of fluid inclusions. Sulfur and lead isotope data show that the ore-forming substances and related porphyries were mainly derived from the lower crust, and a hidden magmatic chamber is indicated by aeromagnetic anomaly and drill hole data indicate that the Nannihu granite body extends to being larger and larger with depth increasing. The large-scale mineralization was the consequence of lithospheric extension during the late stage of the tectonic regime when the main compressional stress changed from NS-trending to EW-trending.

Using Multivariate Statistical and Geostatistical Methods to Identify Spatial Variability of Trace Elements in Agricultural Soils in Dongguan City, Guangdong, China

Abstract Dongguan City, located in the Pearl River Delta, South China, is famous for its rapid industrialization in the past 30 years. A total of 90 topsoil samples have been collected from agricultural fields, including vegetable and orchard soils in the city, and eight heavy metals (As, Cu, Cd, Cr, Hg, Ni, Pb, and Zn) and other items (pH values and organic matter) have been analyzed, to evaluate the influence of anthropic activities on the environmental quality of agricultural soils and to identify the spatial distribution of trace elements and possible sources of trace elements. The elements Hg, Pb, and Cd have accumulated remarkably here, incomparison with the soil background content of elements in Guangdong Province. Pollution is more serious in the western plain and the central region, which are heavily distributed with industries and rivers. Multivariate and geostatistical methods have been applied to differentiate the influences of natural processes and human activities on the pollution of heavy metals in topsoils in the study area. The results of cluster analysis (CA) and factor analysis (FA) show that Ni, Cr, Cu, Zn, and As are grouped in factor F1, Pb in F2, and Cd and Hg in F3, respectively. The spatial pattern of the three factors may be well demonstrated by geostatistical analysis. It is shown that the first factor could be considered as a natural source controlled by parent rocks. The second factor could be referred to as “industrial and traffic pollution sources”. The source of the third factor is mainly controlled by long-term anthropic activities, as a consequence of agricultural activities, fossil fuel consumption, and atmospheric deposition.

Variation of the mid-latitude westerlies and Indian summer monsoon since the last deglaciation: Evidence from grain-size data from Linggo Co, central Tibet

The mid-latitude westerlies and Indian summer monsoon (ISM) have a significant impact on the water budget and general environment of the Tibetan Plateau (TP), and much work has been conducted in order to characterize variations in these two atmospheric circulation systems on various time scales. However, the nature of the interplay between the Asian summer monsoon and the westerlies during the last deglaciation remains controversial. In this study, a sediment core from Linggo Co, a closed lake in the central TP, was analyzed for grain size and ostracod content. The results suggest that environmental change in the Linggo Co basin during the past 17 ka can be divided into four stages: during Stage 1 (17–11.7 ka) Linggo Co was a shallow lake characterized by high amplitude hydrological fluctuations. Strong winds prevailed in winter, correlative with cold events in the North Atlantic region, and indicating the dominance of the westerlies. During Stage 2 (~11.7 ka), in the early Holocene, Linggo Co expanded rapidly and there was the disappearance of the shallow-water ostracod species Limnocythere inopinata together with a decrease in mean grain-size. These changes indicate that ISM was enhanced and that it was the dominant atmospheric circulation affecting TP rather than the westerlies. During Stage 3 (10–8 ka) Linggo Co experienced several intervals with a negative water budget, which may be attributed to a weakening of the weaken ISM or to the reduced influx of glacial meltwater as a result of the influence of cold climatic events. During Stage 4, after 8 ka, Linggo Co shrank progressively in parallel with a gradual weakening of the ISM and finally a transition to the present environment occurred at ~2.5 ka. A comparison of the record from Linggo Co and other records from the TP reveals that prior to 16.5 ka the mid-latitude westerlies was the dominant atmospheric circulation system controlling the entire TP. From 16.5 to 11.5 ka, the mid-latitude westerlies still controlled the central-northern TP; however, the ISM controlled the southern TP, which had a similar climatic pattern to the present day. During the early-middle Holocene, the ISM was the dominant system affecting the entire TP; however, its influence was considerably reduced during the late Holocene, which was probably accompanied by a strengthening of the westerlies.

A Grey Fuzzy Comprehensive Model for Evaluation of Geological Structure Complexity

Abstract Several structure sets (faults and folds) are characterized by their self-similarity properties. Herein, we discuss the degrees of complexity of fractures by introducing the box-counting fractal dimension of faults as a key criterion to be used in comprehensive fuzzy analysis model for evaluation of the complexity of structures. Totally, eight criteria including density, intensity, length of faults, types and box-counting fractal dimension of faults, the intersection angle between faults and coal beds, gradient coefficients, dip angles of the coal beds, and variation coefficients of dip angles of the coal seams, were used for the evaluation purpose. The grey fuzzy comprehensive assessment model was used to rank the relative importance of these criteria. Scores indicating the complexity of structure were calculated on the base of criteria values and their weights for each sub-area of the study area in the Pansan coal mine district in the southern Anhui Province, China. The result on the calculated complexity of structure is useful for mining planning in the study area.

Scaling Properties of Feldspar and Quartz in Micro-images of Ideal Granites

Abstract The properties of feldspar and quartze are studied in this article from a fractal point of view using gray-scale micro-images of granite samples collected at the Fangshan granite body in Hebei Province, China, which can be regarded as an ideal granite in the sense of Vistelius. We found that there exist power-law relationships between the eigenvalues of the gray-scale matrices and their ranks for the feldspar and quartz. The fractal model used here is a λ-R model similar to the N-λ model proposed by Qiuming Cheng in 2005. Meanwhile, we found that average variances for the gray-scale matrices of feldspar are larger than those of quartz on the same sections, and this may be useful for auto-identification of feldspar and quartz as well as other minerals.