【作者】 汪明启；

【导师】 沈镛立； 任天祥；

【作者基本信息】 中国地质大学（北京） ， 地球化学， 2003， 博士

【摘要】 随着勘查地球化学应用和理论研究的深入，常规的化探方法技术已走向成熟。自20世纪90年代以来，全球勘查地球化学转向覆盖区特别是运积物覆盖区方法技术研究上。地球化学弱信息提取技术作为可在覆盖区应用的重要方法之一，成为各国化探界的研究热点。本论文选择黄土覆盖区进行方法有效性实验研究，并通过各种实验手段，对某些问题进行必要的理论探索，试图为地球化学弱信息提取技术最终走向成熟打基础。 本文采用原子吸收法作为基本分析方法，并以ICP／MS为比较方法，通过选择性循序提取试验，研究了甘肃蛟龙掌多金属矿和河北张全庄金矿黄土覆盖条件下，地表黄土中地球化学弱信息特征。进一步证明弱信息提取在勘查隐伏矿方面的有效性。但与国外重点关注非晶质铁锰氧化物如酶、盐酸羟氨提取结果不同，在我国北方半干旱黄土覆盖景观区，粘土吸附和碳酸盐结合态金属元素的提取为最有效的提取步骤。而游离态、有机结合态的提取效果则受景观控制变化较大。铁锰氧化物态硅酸盐结合态金属元素在厚黄土覆盖区对矿带无指示意义。 吸附和解吸试验研究表明，黄土对金属离子具有很强的吸附能力：对于浓度较高的水—土体系，深部黄土和红土吸附能力大于地表黄土；而对于更接近自然界条件的低浓度水—土体系(ng级／ml)，地表黄土吸附效率高于深部黄土，使以离子形式迁移的一部分金属在地表黄土中得以被吸附固定而形成异常，这部分金属可被中性盐提取剂提取。 黄土覆盖区主要分布在干旱半干旱地区，次生碳酸盐在地表土壤中普遍存在，蒸发所产生的毛细作用、地气流的上升作用等所带入的各种形式金属元素，在地表土壤(黄土)与碳酸盐发生共沉淀或被吸持。实验表明，这部分金属可被醋酸有效提取。 不同浓度醋酸提取，黄土的结构、重量和矿物组成发生不同变化：黄土团粒界限变得模糊并出现孔洞，可能说明次生碳酸盐在黄土中主要成胶结物存在；随醋酸浓度增高，黄土重量逐渐降低，但当醋酸浓度大于3％后，重量变化明显变小；黄土中碳酸盐矿物含量逐渐降低，当醋酸浓度＞3％后，变化范围明显变小。 浓度提取试验结果表明，选择合适的提取剂浓度，可从根本上改善提取效果。与前人认识不同，进行可交换态(粘土吸附)和碳酸盐结合态弱信息提取时，不是提高提取剂浓度，而是降低浓度。在类似于蛟龙掌半干旱黄土覆盖景观区，醋酸提取剂浓度应小于或等于2％，氯化铵浓度小于或等于1％。因此，在覆盖区应用弱信息提取方法时，应结合景观和样品特征，采用实验方法确定合适的提取剂浓度。中国地质大学(北京)博士论文 弱信息铅同位素示踪发现，蛟龙掌矿区各地质母体铅同位素差异明显，利于进行同位素示踪。背景区土壤氯化氨和醋酸提取铅同位素组成与矿化区有所差异，但由于矿带上方铅元素异常弱，范围窄，因此，其同位素差异相对较小，比较而言，醋酸提取铅差异相对较大。不同地质母体对比分析发现，矿带上方土壤样品异常铅具双重来源特征:即来自黄土和多金属矿化体。证明同位素示踪覆盖区弱信息物质来源思路可行，但需要进行进一步探索。更多还原

【Abstract】 With the development of application and theory of Exploration Geochemistry, conventional geochemical techniques have gradually become mature. Since last decade of 20 centuries, global Exploration Geochemistry turns to study the methods and the techniques of geochemical exploration in overburdens. The techniques to extract the weak geochemical signals for exploring the concealed mineralizations have been a hit among global exploration geochemists.Choosing the atomic absorption spectrometry as a basic analytic method and ICP/ MS as a contrast method and Using the sequential selective extraction schedule, the characteristics of weak geochemical signals from deeply concealed deposits were studied in loess covered Jiaolongzhang polymetallic deposit and Zhangquanzhuang gold deposit. The results show that extracting the weak signal by selective dissolution of sample can be useful to explore the concealed mineralizations in overburden.Apart from geochemists from western countries, which paid a particular attention on amorphous iron-manganese oxides extracted by enzyme or 0.1 ~0.25M NH2OH ?HC1, our results show that the extraction of metals adsorbed by clay and bound to the carbonate in soil is most useful to identify the concealed mineralizations in the semiarid and loess covered terrains, northern China. Water soluble and organic-bound metals vary greatly with terrains and deposits. Other bound metals related to iron-manganese oxides and silicate indicate no change above the loess covered deposits.The tests of metal absorption and de-absorption on loess and red layer demonstrate that the loess soil is a very strong absorbent to metals. When metals in water-soil solution is high (>1 X 10-6), absorptive ability for loess in depth and red earth is higher than loess in surface soil. But when metals When metals in water-soil solution is low (>1 X 10-6), which is much closer to the natural conditions, absorptive ability for loess in surface soil is bigger than loess in depth and red earth. Therefore, metals moving upwards from mineralizations may be absorbed and form weak geochemical anomalies (weak signals) in surface loess. The metals can be effectively extracted by neutral salt.Loess-covered area in China is primarily distributed at the semiarid region, the secondary carbonates, which were formed after precipitation of ions through evaporation and capillary processes, are widespread in the surface soil. The metals transported in the various forms by the above processes can be co-consolidated with carbonate precipitation in the top soil, can easily be extracted by HO Ac.The structure, weight and mineral constituents of loess change with varies on concentration of HO Ac: the boundary between the grain become unclear after differentgradually, but when HOAc>3 %, the weight change become smaller. Also with increasing of HO Ac concentration, the carbonates in loess decreases gradually, while HOAc>3%, the change become smaller.The metal content of Extractants by different NH4C1 and HO Ac extraction shows that a reasonable selection of solvent concentration is key to improve the effects of response to mineralizations.Different from the existing cognition, the concentration of solvent should be much lower rather than higher when extracting the metals absorbed on clay minerals and bound to carbonates. To the terrain like Jiaolongzhang area, HOAc should be less than 2% to extract carbonates and NH4C1 should be less than 1%. Therefore, to use the weak signal extraction technique in overburden approportely, we should decide the extraction procedures after thoroughly test.The tracing of lead isotopes indicates different matrixes of lead isotopes have great difference, which makes an Pb isotope tracing is much easier to identify the sources of Pb. The Pb isotopes extracted by NH4C1 and HOAc in the background soil are slightly different from that in soil above the known ore bodies. But the different is quite small for the Pb anomalies extracted by both solvents is much weak. In contrast with different matri更多还原