Hydrothermal alteration associated with rift zones at Fangataufa atoll (French Polynesia)

 The Mururoa and Fangataufa atoll basement consists of superimposed submarine and subaerial lava flows which have been intruded by late volcanics. The intrusions have developed large hydrothermal alteration haloes throughout the basaltic wall rock. The cuttings of the Natice-1 and Mitre-1 holes, drilled into the submarine volcanic pile at Fangataufa atoll, show a vertical zonation of clay minerals ranging from 270 to 850 m depth. The newly formed clay minerals occurring from top to bottom of the altered pile are: dioctahedral aluminous smectites, saponite, an intimate assemblage of saponite with two random chlorite/saponite mixed layers and an intimate assemblage of one random chlorite/saponite mixed-layer with one ordered chlorite/saponite mixed layer and one chlorite below 816 m depth. These clay mineral assemblages indicate a general increase in the chloritic component with depth. They are associated throughout the pile with secondary carbonates and quartz. The ∂¹⁸O and ∂¹³C of calcite and ∂¹⁸O of clay minerals, on the one hand, and the intimate mixtures of trioctahedral species, on the other, suggest a general cooling with the evolution of a paleogeothermal gradient from approximately 300  °C/km during the crystallization of chlorite to 150  °C/km for the late calcite precipitation. Received: 2 October 1995 / Accepted: 14 January 1997     

一种三八面体缘泥石／皂石1：1规则间层矿物（绿间皂石）的初步研究

在湖北恩施利川地区的三叠系中统巴东组钙质砂质粘土岩及砂质泥质岩中，产出一 种褐灰色粘土矿物。通过X射线粉末衍射、红外、热分析、化学分析及电镜观察等测试研究，各 项实验数据证明该粘土矿物是三八面体绿泥石与三八面体皂石1:1规则间层矿物(绿间皂石)。自 然风干样和各种化学处理样的OOl衍射数据，都具育良好的整数倍关系。风干样001衍射的标准偏 差δ=0.1007，波动系数υc= 0.347。d060=1.531A, b0=9.19A，cosinβ=29.05A。并计算出了 该矿物的化学结构式。     

矿物分散体系的触变性试验研究

目前尚没有国家标准来统一和规范触变性的测试方法,而轻工标准QB/T 1545—1992仍是应用于非金属矿物触变性测试的较为适用的方法之一,但该规范中的方法介绍较为简单,对触变性测试的影响因素(如电解质的添加)未有详细叙述和研究,实际指导性不强。本文依据QB/T 1545—1992,以膨润土和皂石为矿物样品,研究触变性测试方法及其影响因素,重点对电解质最佳用量和陈化时间进行条件试验。结果表明:添加电解质对触变性影响很大,不同矿种及同种矿物的样品在触变性试验中所需的电解质最佳添加量是不同的,测试具体矿物的触变性时,需先对电解质最佳添加量进行条件试验。样品悬浮物的陈化时间对其触变性的测试结果有很大影响。在测试触变性的过程中,应严格按照轻工标准QB/T 1545—1992规定的陈化时间10~12 h,以保证方法精密度要求;若陈化时间过长,其触变性明显增大,触变性已无法计算。本文通过对触变性测试方法中电解质用量和陈化时间两个重要影响因素的研究,可为现有触变性测试方法的改进提供一定的依据。     

一种三八面体绿泥石/皂石1:1规则间层矿物(绿间皂石)的初步研究

在湖北恩施利川地区的三叠系中统巴东组钙质砂质粘土岩及砂质泥质岩中,产出一种褐灰色粘土矿物。通过X射线粉末衍射、红外、热分析、化学分析及电镜观察等测试研究,各项实验数据证明该粘土矿物是三八面体绿泥石与三八面体皂石1:1规则间层矿物(绿间皂石)。自然风干样和各种化学处理样的00l衍射数据,都具有良好的整数倍关系。风干样00l衍射的标准偏差δ=0.1007,波动系数vc=0.347。d_(060)=1.531,b_0=9.19,c_0sinβ=29.05。并计算出了该矿物的化学结构式。     

固体核磁光谱法研究镁铝复合氧化物的水热转化机制

复合金属氧化物广泛分布于自然界,其中镁铝复合氧化物(简称MMO)则大量分布于基性-超基性岩浆岩、蒸发河湖相和海相沉积岩等之中。本研究以镁铝水滑石(HT)煅烧产物MMO为研究对象,采用水热合成方法,通过改变反应时长,考察并揭示MMO在富硅、碱性和160℃水热条件下的结构复原特性及其转化机制。X射线衍射结果显示,该条件下MMO首先复水形成水滑石相,进而水滑石相逐渐向皂石转化,并伴有钠霞石等杂相的形成与溶解。29Si和27Al魔角旋转核磁共振谱(MAS NMR)的结果证明,在皂石结晶过程中,Al3+优先占据四面体片层的四配位位置。该研究对揭示水滑石稳定性、水滑石与硅酸盐矿物异相成核与生长、热液类型的天然皂石矿床的形成过程等具有重要指示意义。     

不同粘土矿物对赖氨酸的吸附行为对比研究

以皂石、高岭石、绿泥石和伊利石为原材料,分别与赖氨酸进行反应,研究赖氨酸在上述粘土矿物上的吸附行为, 并运用粉末X-射线衍射技术（XRD）、傅里叶变换红外吸收光谱术（FTIR）和热重（TG）等分析方法,表征反应前后粘土 矿物的变化。实验结果表明,不同粘土矿物对赖氨酸的吸附等温线均符合Freundlich等温方程,且不同粘土矿物对赖氨酸的 饱和吸附量大小顺序为：皂石>蒙脱石>绿泥石>高岭石>伊利石;XRD结果表明皂石对赖氨酸的吸附发生在矿物层间,而绿 泥石、高岭石和伊利石对赖氨酸的吸附主要在矿物表面进行;FTIR和TG结果表明赖氨酸主要取代粘土矿物层间吸附水,以 氢键的形式与Si-O-Si(IVAl)键合。实验结果将有助于进一步探明环境中粘土矿物对有机质的吸附机理。     

Formation of magnesium‐smectite during lacustrine carbonates early diagenesis: Study case of the volcanic crater lake Dziani Dzaha (Mayotte – Indian Ocean)

The volcanic crater lake of Dziani Dzaha in Mayotte is studied to constrain the geochemical settings and the diagenetic processes at the origin of Mg‐phyllosilicates associated with carbonate rocks. The Dziani Dzaha is characterized by intense primary productivity, volcanic gases bubbling in three locations and a volcanic catchment of phonolitic/alkaline composition. The lake water has an alkalinity of ca 0·2 mol l^?1 and pH values of ca 9·3. Cores of the lake sediments reaching up to one metre in length were collected and studied by means of carbon–hydrogen–nitrogen elemental analyzer, X‐ray fluorescence spectrometry and X‐ray powder diffraction. In surface sediments, the content of total organic carbon reaches up to 20 weight %. The mineral content consists of aragonite and hydromagnesite with minor amounts of alkaline feldspar and clinopyroxene from the volcanic catchment. Below 30 cm depth, X‐ray diffraction analyses of the <2 μm clay fraction indicate the presence of a saponite‐like mineral, a Mg‐rich smectite. The saponite‐like mineral accumulates at depth to reach up to ca 30 weight %, concurrent with a decrease of the contents of hydromagnesite and organic matter. Thermodynamic considerations and mineral assemblages suggest that the evolution of the sediment composition resulted from early diagenetic reactions. The formation of the saponite‐like mineral instead of Al‐free Mg‐silicates resulted from high aluminum availability, which is favoured in restricted lacustrine environments hosted in alkaline volcanic terrains commonly emplaced during early stages of continental rifting. Supersaturation of the lake water relative to saponite is especially due to high pH values, themselves derived from high primary productivity. This suggests that a genetic link may exist between saponite and the development of organic‐rich carbonate rocks, which may be fuelled by the input of CO₂‐rich volcanic gases. This provides novel insights into the composition and formation of saponite‐rich deposits under a specific geodynamic context such as the Cretaceous South Atlantic carbonate reservoirs.