Metallogenic mechanism of Pingguo bauxite deposit,western Guangxi,China:Constraints from REE geochemistry and multi-fractal characteristics of major elements in bauxite ore

Major and REE geochemistry and multi-fractal analysis of two types of bauxite(primary bauxite and accumulated bauxite) ores were studied in Pingguo bauxite orefield in western Guangxi,China.The results of geochemical data show that the accumulated bauxite has a feature of high Al_2O_3 whereas relative low Fe_2O_3 and SiO_2 contents compared to the primary bauxite.The similar chondrite-normalized rare earth element(REE) patterns illustrate that they have a cognate relationship.However,the negative Ce anomalies of primary bauxite and positive Ce anomalies of accumulated bauxite indicate that the ore-forming system changed from reducing environment to oxidation environment.The results of multi-fractal spectrum and parameters of Al_2O_3,Fe_2O_3 and SiO_2 between primary bauxite and accumulated bauxite show that the distinct multi-fractal spectrum parameters reflect the different grade distribution between accumulated and primary bauxite ores.Metallogenic process from primary bauxite to accumulated bauxite is accompanied by the loss of diffluent elements(e.g.,Si and S) and enrichment of stable elements(e.g.,Al and Fe) in the surface environment.Among the rest,the migration mechanism of iron during the evolutionary process from primary ore to accumulated ore can be described as combined leaching and chemical weathering action with participation of sulfur.

基于时域信号重构的广域电磁法高频有效数据提取方法

广域电磁法已经在油气、矿产及地质灾害勘探中得到了广泛应用,尤其在强干扰地区体现了很强的抗干扰能力,但在实际应用过程中,其高频成分,尤其是2048 Hz以上频率,对应广域视电阻率经常出现上翘现象,为地球物理反演和解释带来了诸多困难。本文研究发现,信号发送和采集对应的晶振时钟误差是造成该问题的主要原因。基于此,本文提出了一种基于时域信号重构的高频有效信息提取方法,其主要特点为记录完整发射电流时间序列和接收信号时间序列,并通过电流时间序列估计晶振误差,基于此误差对接收信号时间序列进行校正与重构,以获得校正后时域信号,进而提取数据中的高频有效信息。通过将该方法应用于实际数据,处理后的广域电磁归一化电场的高频部分不再上翘,获得了信号中准确的高频成分,表明该方法是提取广域电磁法高频信号有效方法。