Chemical alteration of volcanic glasses and related control by secondary minerals: Experimental studies

A detailed experimental mineralogical and geochemical study on hydrothermal alteration processes of volcanic glasses with a different chemical composition and leucites sampled in the Roman Comagmatic Region was carried out. 2g samples of different grain sizes and 50 ml of deionized water or seawater were sealed in bronze Teflon-lined autoclaves and placed in a rotating sample-holder at 200°C. The internal pressure was 16.2 bars. At arbitrary intervals, the pressure vessel was quenched to room temperature and both solids and solutions were separated by filtration. The solids were used to identify possible alteration products by means of X-ray powder diffraction, SEM and microprobe analyses. In all deionized water systems the contact solution reached pH basic values, but in the various systems the consumption of H⁺ ions occurred in different ways. This is probably linked to different concentrations of released cations. In seawater systems, however, pH values initially fell sharply but subsequently increased slightly. After 2 days, cation concentrations were clearly buffered by reaction products in all solutions. These were mainly zeolites and clay minerals. The following crystallization sequences in all glass/deionized water experiments were observed: the first reaction product was represented by phillipsite, followed by analcime and illite in the alkali-trachytic run; chabasite and analcime in the phonolitic-tephritic run; analcime and finally feldspar in shoshonitic and trachytic runs. Phillipsite and smectite crystallized together only in the basaltic run. In leucite/deionized water systems, however, the first reaction phase was illite, followed by analcime and then phillipsite. The reaction products in glass/seawater systems were smectite and anydrite. The chemical composition of synthetic zeolites was clearly controlled by the chemistry of initial glasses. These synthetic zeolites are like the natural ones in volcaniclastic products from central and southern Italy. This suggests that extensive zeolitization processes of these volcaniclastic rocks may occur through interaction of volcanic glasses with fluids at a very low salinity and a temperature close to 200°C.     

冀西北水晶屯金矿床剥蚀程度的判别方法

从冀西北水晶屯金矿近矿围岩蚀变的空间组合、金的指示元素的空间特征、黄铁矿标型特征等多方面地质数据资料入手，来判别矿床的剥蚀程度，认为该金矿床剥蚀程度正处在矿体的中上部。     

沉积成岩作用阶段划分的有关问题

本文将国内外众多沉积岩阶段划分方案归纳为５种类型，并认为最合理的划分方案同生成岩作用、再生成岩作用、表生成岩作用；还对目前理解不同、使用混乱的各种沉岩作用术语进行评述，提出了主要沉积成岩阶段划分方案的对比表。     

南平花岗伟晶岩中锂辉石的研究

锂辉石是南平稀有金属花岗伟晶岩中的重要标型和造岩矿物。本文论述了它的产状、物理性质、化学成分、Ｘ光粉晶衍射资料、红外光谱和差热分析结果，较详讨论了锂辉石转变成腐锂辉石的过程，最后分析了锂辉石在伟晶岩中的形成条件。     

冲绳海槽浮岩的蚀变作用原因

在冲绳海槽海底浮岩的蚀变中ＳｉＯ２和Ｎａ２Ｏ相对含量明显减少，而Ｆｅ２Ｏ３、ＴｉＯ２、ＣａＯ、ＭｇＯ、ＣＯ２、ＭｎＯ和Ｐ２Ｏ５含量则明显增加；Ａｌ２Ｏ３、Ｋ２Ｏ、ＦｅＯ含量基本保持不变。蚀变作用导致了赤铁矿、针铁矿和非晶质Ｆｅ、Ｍｎ氧化物和绿泥石等粘土矿物的生成。多数微量元素的含量在蚀变样品中增加，尤其是Ｃｒ、Ｃｏ、Ｘｃ、Ａｓ、Ｂｒ、Ｒｂ和Ｔｈ。除Ｎｄ外轻稀土元素含量增加，大部分重稀土元素含量减小     

吉林省汪清县金仓砂金矿地质特征及来源探讨

金仓砂金矿是吉林省延边地区著名的第四纪砂金矿床。其砂金含矿层中砾岩多呈棱角状,砂金粒度及形态沿河流流向分异现象不明显,砂金的连生矿物、伴生重砂矿物、成色、微量元素、稀土元素、铅及硫同位素、气液包裹体成分特征均可和矿区内原生金矿化对比。据此,初步从为金仓河砂金主要来源于金仓河谷中、上游底部基岩含金蚀变破碎带中的原生金。     

镇安盆地泥炭,软褐煤中的氯仿沥青“A”及其族组分的荧光特征

对滇西镇安盆地泥炭、软褐煤中的稳定组成进行荧光分析测试并未获得满意参数,又对其中抽提物—氯仿沥青“A”及其族组分进行荧光光度机测定,得到一些新的认识.     

烃类微渗漏的光谱遥感信息

烃类微渗漏的间接证据,包括一系列地球物理、地球化学、岩石矿物和地貌异常以及以后认识到的在土壤化学与植物生理方面引起的变异。所有这些现象均与烃类微渗漏密切相关。根据这种地表“蚀变体”的波谱特征,可利用遥感技术在特定波段内将其信息直接提取出来。     

Copper-bearing clay minerals of the oxidized zone of the Rakha-Chapri Block,Singhbhum Copper Belt,India

In the oxidized zone of Rakha-Chapri Block of the Singhbhum Copper Belt, alteration of biotite, chlorite and muscovite extends down to ∼ 60 m. Below this level, these minerals are not altered, implying a supergene origin for the clay alteration products. The altered host-rock profile consists of an upper, predominantly kaolinitic zone and a lower illite-chlorite rich zone, with the clay minerals showing an overall tendency to decrease with depth. Kaolinite is the dominant clay mineral, the proportion of which varies considerably with depth, and chlorite, illite and halloysite are the other clay minerals of the oxidized zone. Incipient removal of copper even from the cap rocks, in-situ transformation of sulphides to oxidized compounds, and the unusual mode of occurrence of copper in the oxidized zone are the characteristic features of the Rakha-Chapri Block. Insufficient localized hydrolysis of silicates is considered responsible for relatively low acidity in the oxidized zone as a whole. Copper forms a component of the clay minerals probably as surface adsorbed or/lattice-bound ions.