Bao Zhengyu

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.

Geothermal and fluid flowing simulation of ore-forming antimony deposits in Xikuangshan

The Xikuangshan Antimony Deposit located in the Mid-Hunan Basin, China, is the largest antimony deposit in the world. Based on the hydrogeological and geochemical data collected from four sections, Xikuangshan-Dajienao (AO), Xikuangshan-Dashengshan (BO), Xikuangshan-Longshan (CO) and Dafengshan (DO) in the Basin, an advanced metallogenic model related to deep-cyclic meteoric water of Xikuangshan Antimony Deposit is put forward in this paper using a model of heat-gravity-driving fluid flow transportation. The simulation results show that the ore-forming fluid of the deposit mainly comes from the Dashengshan and Longshan areas where BO and CO sections are located if the overall basin keeps a constant atmospheric precipitation and infiltration rate during mineralization, and that the average transportation speed of the ore-forming fluids is about 0.2–0.4 m/a.

Ore zoning and dynamics of ore-forming processes of Yinshan polymetallic deposit in Dexing, Jiangxi

The Yinshan deposit, one of the large-scale Cu-Pb-Zn-Au-Ag polymetallic deposits, may be named a middle-low temperature subvolcanic hydrothermal deposit and referred to as the“transitional deposit” linking mineralization of the epithermal and porphyry copper types. In this paper, the characteristics and structures of ore zoning are briefly described. On the basis of the dynamics of ore-forming processes and applying computer numerical simulation technique, the mechanism of ore zoning is discussed and a concealed igneous body controlling ore deposition at depth of the Yinshan mine is predicted.

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.

Nonlinear instability and dynamic bifurcation of a plane interface during solidification

By taking average over the curvature, the temperature and its gradient, the solute concentration and its gradient at the flange of planar interface perturbed by sinusoidal ripple during solidification, the nonlinear dynamic equations of the sinusoidal perturbation wave have been set up. Analysis of the nonlinear instability and the behaviors of dynamic bifurcation of the solutions of these equations shows that (i) the way of dynamic bifurcation of the flat-to-cellular interface transition varies with different thermal gradients. The quasi-subcritical-lag bifurcation occurs in the small interface thermal gradient scope, the supercritical-lag bifurcation in the medium thermal gradient scope and the supercritical bifurcation in the large thermal gradient scope. (ii) The transition of cellular-to-flat interface is realized through supercritical inverse bifurcation in the rapid solidification area.By taking average over the curvature, the temperature and its gradient, the solute concentration and its gradient at the flange of planar interface perturbed by sinusoidal ripple during solidification, the nonlinear dynamic equations of the sinusoidal perturbation wave have been set up. Analysis of the nonlinear instability and the behaviors of dynamic bifurcation of the solutions of these equations shows that (i) the way of dynamic bifurcation of the flat-to-cellular interface transition varies with different thermal gradients. The quasi-subcritical-lag bifurcation occurs in the small interface thermal gradient scope, the supercritical-lag bifurcation in the medium thermal gradient scope and the supercritical bifurcation in the large thermal gradient scope. (ii) The transition of cellular-to-flat interface is realized through supercritical inverse bifurcation in the rapid solidification area.