Système hydrogéologique d'un massif minier ultrabasique de Nouvelle-Calédonie

Ultramafic rocks outcrop over more than one third of New Caledonia's main island. Under tropical conditions, thick lateritic mantles with nickel concentrations developed on these rocks by geochemical weathering. Groundwater in ultramafic mined massifs represents a valuable resource, but also a severe constrain for mining engineering. Previous works describe several water tables in the various layers of the weathering mantle. From a hydrologic study of the Tiebaghi massif, the hydraulic continuity across the weathering layers down to the bedrock is proposed. To cite this article: J.-L. Join et al., C. R. Geoscience 337 (2005).     

Altérations dans la zone tropicale. Signification à travers les mécanismes anciens et/ou encore actuelsWeathering in tropical zone. Significance through ancient and still active mechanisms

The microscopic study of the organization of soils and alterites reveals the direction of evolution and the genetic and historical relationship between their constitutive minerals and how, subsequently, geochemical processes could be visualized. If certain soils and alterites may be considered to be the products of recent weathering, others span a much longer time interval. These different aspects of the weathering mantle coexist in the same landscape, and this situation makes them difficult to distinguish. In other words, the weathering mantle that extends over most continental areas is a real patchwork in search for an equilibrium never reached. So, in lateritic weathering mantles, most of genetic and evolutive modelling reveals the complexity of geochemical processes and time scale required to their differentiation ranges from one to several million years. The weathering rates and ages of weathering profiles are discussed as a function of processes that run at the top and at the bottom of weathering mantles. To cite this article: D. Nahon, C. R. Geoscience 335 (2003).     

The Bolcana Cu–Au ore deposit (Metaliferi Mountains,Romania): first data on the alteration and related mineralisation

The Bolcana ore deposit (Metaliferi Mountains, western Romania) is a porphyry ore deposit with associated epithermal veins. On the basis of different parageneses, four alteration types were distinguished: potassic, phyllic, argillic and propylitic. The mineralogical and geochemical data and estimated crystallisation temperatures of alteration minerals indicate an evolution of the system from an early period of porphyry type mineralisation (Cu+Au) to a late period of low-sulphidation epithermal mineralisation (Au+base metal). To cite this article: V. Milu et al., C. R. Geoscience 335 (2003).     

Apports des phyllosilicates dans la différenciation entre altération hypogène et altération supergène dans le basalte triasique du Moyen Atlas (Maroc)Contribution of phyllosilicates to distinguish between hypogene alteration and weathering in Triassic basalt from Middle Atlas (Morocco)

Triassic basalt of the Middle Atlas has been subject to metamorphic transformation then weathering. Occurrence in both metabasalt and saprolite of ubiquitous clay minerals, such as smectite and mixed layers chlorite–smectite, makes it difficult to distinguish between the two alteration facies and explains the interest of complementary sources of information. In the Bhallil weathering profile, petrographical and mineralogical analyses of primary igneous minerals and their alteration products coupled with Fe oxidation state determination in clay fractions allow to identify three alteration facies: (i) metamorphic basalt, where iron occurs mainly as the ferrous form; (ii) the lower part of saprolite, where iron is partially oxidized to its ferric form; (iii) the upper part of saprolite, where iron is completely oxidized. To cite this article: A. Dekayir et al., C. R. Geoscience 334 (2002) 877–884.     

Lithostratigraphie et histoire paléozoïque à paléocène des complexes métamorphiques de la région de Muteh, zone de Sanandaj–Sirjan (Iran méridional)Lithostratigraphy and Palaeozoic to Palaeocene history of some metamorphic complexes from Muteh area, Sanandaj–Sirjan zone (southern Iran)

A detailed analysis of metamorphic complexes outcropping in the Muteh area in central Iran leads to establish the regional stratigraphical column, and to propose a Palaeozoic age for the metamorphic protolith that mainly consists of volcano-sedimentary units. ⁴⁰K---⁴⁰Ar ages for minerals suggest the Mesozoic age of the metamorphic amphiboles and the Palaeocene ones for a late or even post metamorphic bimodal magmatism. To cite this article: N. Rachidnejad-Omran et al., C. R. Geoscience 334 (2002) 1185–1191.     

Pétrologie de l'intrusion alcaline mésozoïque de la région d'Anemzi, Haut Atlas Central, Maroc

The Mesozoic Anemzi intrusion belongs to the peri-Atlantic Mesozoic alkali magmatism. It is composed of gabbros (with or without olivine), monzodiorites and quartz-bearing syenites. Dolerite dykes of alcaline affinity occur nearby. The alkaline rocks are intrusive into mid-Jurassic limestones. Liquidus phases crystallised following the characteristic order of alkali magmas, i.e. olivine + spinel, plagioclase, clinopyroxene and amphibole. Clinopyroxene and amphibole compositions are governed by Ti-tschermakite substitutions. Clinopyroxene and amphibole in syenites are enriched in aegirine and richterite components, respectively. The mineralogical and chemical evolution in the Anemzi intrusion is consistent with low-pressure fractional crystallisation from an alkali lava under low to moderate fO₂ (MW + [1 − 2 log units]). However, the parental liquid shows some geochemical characteristics of transitional magma, such as a high SiO₂ content (48 wt%) and low La/Yb_N ratio (5). Silica activity decreased from the parental magma (0.56) to 0.08 after fractionation of the gabbros and then increased to 1.0 at the end of the magmatic differentiation. Compared with rocks of similar ages, belonging to the peri-Atlantic Cretaceous alkaline magmatism, the Anemzi intrusion is distinguished by low REE contents ([La/Yb]_N = 6) and transitional basalt(s) as parental magma. This magma was emplaced through reactivation of Palæozoic fault systems.     

A geological study of clayey laterite and clayey hydromorphic material of the region of Yaoundé (Cameroon): a prerequisite for local material promotion

A geological survey carried out in the Yaoundé (Cameroon) region has revealed the presence of homogeneous clayey laterite in the upper part of a laterite cover on interfluves, thickest on hills (780–800 m altitude) where ferricrete is absent, and clayey heterogeneous hydromorphic material in valleys. We present in this paper the physical, mineralogical and geochemical properties of these occurrences and discuss their potential as raw material for pottery, manufacture of bricks and tiles. These clayey raw materials are mostly made up of fine particles (ranging from 55 to 60% clay + silt in the clayey laterite, more than 70% clay + silt in the clayey hydromorphic material). Their chemical composition is characterized by silica (<60% SiO₂), alumina (<35% Al₂O₃) and iron (ranging from 3 to 14% Fe₂O₃). Their main clay minerals are disorganized and poorly crystallized kaolinites. The average limits of liquidity (44.56% versus 91.58%) and limits of plasticity (22.4 versus 45.93) revealed that clayey hydromorphic material has the greatest plasticity. The studied raw materials are suitable for making pottery as well as the manufacture of bricks and tiles. However, the high iron content in the clayey laterite (between 11 and 12% Fe₂O₃) prevents their efficient use in the manufacture of ceramics.     

青海省格尔木市那陵郭勒河西地区铁多金属矿工艺矿物学研究

青海省格尔木市那陵郭勒河西地区铁多金属矿规模大,具有铁铜金等多金属矿化,属于接触交代型铁多金属矿床。本文采用工艺矿物学研究方法,查明了矿石工艺矿物学特性。研究结果表明,矿石的组成矿物种类较为简单,金属硫化物主要是黄铜矿、磁黄铁矿、黄铁矿、闪锌矿;铁矿物主要是磁铁矿、赤铁矿。脉石矿物主要是石英、方解石、透闪石、透辉石;其次为石榴子石、白云母、蛇纹石。矿石中铁、铜锌矿物均具均匀细粒—微细粒嵌布特征;通过选矿可获得铜精矿、锌精矿、铁精矿。     

Behaviour of lead and zinc in calcrete-bearing soils around Bou Grine, Tunisia — its application to geochemical exploration

The behaviour of Pb and Zn was studied in soils containing calcrete to determine the effect of calcrete formation on the surface expression of mineralization. Earlier investigations had shown that: (1) calcrete develops epigenetically within the soil from other minerals present in the horizon that is being encrusted; and (2) this epigenetic replacement is isovolumetric.One consequence of this process for geochemical exploration is that the development of calcrete can be compared to installing a screen that weakens the contrast of the anomaly. Another geochemical consequence is that the metals that were initially associated with various mineralogical phases in the parent rock will associate mainly with HCl (1N) soluble components inthe calcrete horizons. In noncalcreted horizons, and in particular in the surficial layers, the metals are divided between carbonate and oxide phases, the latter being more or less well-crystallized.     

Mineralogy,geochemistry and origin of Mn in the high-Mn iron ores,Bahariya Oasis,Egypt

Although Mn is one of the major impurities in the economic iron ores from the Bahariya Oasis, information on its modes of occurrence and origin is lacking in previous studies. High-Mn iron ores from El Gedida and Ghorabi–Nasser iron mines were subjected to detailed mineralogical, geochemical, and petrographic investigations using X-ray diffraction (XRD), infrared absorption spectrometry (IR), Raman spectroscopy, X-ray fluorescence (XRF), scanning electron microscopy (SEM), and electron probe microanalyzer (EPMA) to clarify the modes of occurrence of Mn in these deposits and its origin. The results showed that the MnO₂ contents range between 0.03 and 13.9 wt.%. Three mineralogical types have been identified for the Mn in the high-Mn iron ores, including: (1) inclusions within the hematite and goethite and/or Mn accumulated on their active surfaces, (2) coarse-grained and crystalline pyrolusite, and (3) fine-grained cement-like Mn oxide and hydroxide minerals (bixbyite, cryptomelane, aurorite, romanechite, manjiroite, and pyrochroite) between the Fe-bearing minerals. The Mn carbonate mineral (rhodochrosite) was detected only in the Ghorabi–Nasser high-Mn iron ores. Since IR patterns of low-Mn and high-Mn samples are almost the same, a combination of XRD analysis using non-filtered Fe-Kα radiations and Raman spectroscopy could be the best way to identify and distinguish between different Mn minerals.Assuming that both Fe and Mn were derived from the same source, the occurrence of high-Mn iron ores at the base of the stratigraphic section of the deposits overlain by the low-Mn iron ores indicated a supergene origin of the studied ores by descending solutions. The predominance of Mn oxide and hydroxide minerals in botryoidal shapes supports this interpretation. The small grain size of Mn-bearing minerals as well as the features of microbial fossils such as spherical, elliptical, and filamentous shapes of the Fe-bearing minerals suggested a microbial origin of studied iron ores.Variations in the distribution and mineralogy types of Mn in the iron ores of the Bahariya Oasis demanded detailed mineralogical and petrographic characterizations of the deposits before the beneficiation of high-Mn iron ores from the Bahariya Oasis as feedstock for the ironmaking industries in Egypt by magnetizing reduction. High Mn contents, especially in the Ghorabi–Nasser iron ore and occurrence of Mn as inclusions and/or accumulated on the surface of the Fe-bearing minerals would suggest a possible utilization of the high-Mn iron ores to produce ferromanganese alloys.     

风化作用对铁陨石矿物学特征影响的探讨

本文对南丹IIICD铁陨石的矿物学特征进行了研究,并与同为铁陨石但化学分类不同的阿根廷IAB铁陨石和西伯利亚IIB铁陨石进行了对比,重点探讨了风化作用对铁陨石矿物学特征的影响.首先用偏光显微镜、静水称重、扫描电镜观察了样品的基本矿物学特征和微形貌特征,然后用振动式样品磁强计、X射线衍射与电子探针能谱半定量测试研究了样品的磁学性质、物相和化学组成.研究结果表明,南丹铁陨石在较强的自然风化作用下,光泽变弱为土状光泽,相对密度降低;风化产生的反铁磁性物质会使陨石的磁性下降;另外,样品表面物相组成也发生较大变化,以针铁矿(FeOOH)和磁铁矿(Fe₃O₄)等铁的次生矿物为主;但风化壳以下的矿物物相及化学成分均未发生明显变化,以Fe、Ni为主的铁纹石、镍纹石物相存在.     

Première approche pour l'étude des bassins hydrogéologiques profonds du Sud-Ouest tunisien

Due to their high cost, a small number of deep wells cannot give a satisfactory image of the architecture of deep geological formations and their continuity. However, it is very important at an early stage of research to recognize the relations that can exist between the different compartments of the underground formations. Generally speaking, we usually deduce that the hydrodynamic and geochemical parameters can be generated by geological discontinuity. In southwestern Tunisia, the seismic and diagraphic data make it possible to get a satisfactory insight into the underground layers so as to identify the hydrogeological basins and the extension of their parameters. To cite this article: M. Chalbaoui, C. R. Geoscience 337 (2005).     

论超高压变质的矿物学标志

近20多年来,对超高压变质的研究日益深入。超高压变质的矿物学标志,已远远超出柯石英一种,结合实验矿物学的成果,发现许多新的矿物标志。 可以归纳为以下3类：（1）矿物的多形转变, 如柯石英和金刚石;（2）超高压矿物的出溶,如K-单斜辉石、majorite-镁铝榴石和高硅榍石;（3）超高压(高压)变质矿物或矿物组合, 如多硅白云母、文石和菱镁矿等。文中介绍了这些矿物学标志的地质学和矿物学特征及应用前景。     

Modèle de formation du gisement d'argent d'Imiter (Anti-Atlas oriental,Maroc). Nouveaux apports de l'analyse structurale et minéralogique

Based on a combined geometrical and mineralogical analysis, a three-stage model of formation of the mineralized veins of the giant Imiter silver deposit (Anti-Atlas, Morocco) is herein proposed. A first episode is characterized by the development of quartz, pink dolomite and Ag-rich minerals veins formed during a dextral transpressive event. The second episode is associated with a normal left-lateral motion that re-opens previous structures, filled by pink dolomite gangue. Alteration stages contribute to a local Ag enrichment. To cite this article: J. Tuduri et al., C. R. Geoscience 338 (2005).     

马坑铁矿钻孔岩心红外光谱特征及蚀变分带特征研究

红外反射光谱技术可无损、快速、批量地识别出硅酸盐、硫酸盐、碳酸盐等矿物,近年来在矿物学研究、地质勘探与找矿、矿山选冶等方面取得了较显著进展。尤其是热红外波段（6000~14500nm）可识别出辉石、石榴子石、橄榄石等蚀变矿物以及长石、石英等造岩矿物,对于矽卡岩型、铜镍硫化物型以及石英脉型等矿床地质找矿、矿床成因研究等具有重要意义。本文通过对国家实物地质资料馆馆藏的马坑铁矿钻孔岩心进行短波-热红外反射光谱测量与分析,总结马坑铁矿各蚀变矿物光谱特征,并快速厘定了该矿床的蚀变矿物类型及组合特征。马坑铁矿蚀变矿物主要有石榴子石、辉石、碳酸盐、绿泥石、绢（白）云母、角闪石、绿帘石、蒙脱石、石膏等。石榴子石热红外光谱特征是在9199nm、9730nm、10500nm及11100nm处具有明显的反射特征,辉石热红外光谱特征主要是在11500nm和12150nm处具有明显的吸收特征。红外光谱分析表明蚀变矿物在空间上呈现出明显的分带性,蚀变矿物组合及分布严格受围岩岩性和热液交代的双重控制。通过红外反射光谱蚀变矿物组合特征研究,“石榴子石+辉石”可作为矽卡岩型矿床的标型矿物组合,蚀变分带特征也反映了主矿体从高温到低温的变化过程;结合矿床地质特征,推断出马坑铁矿为典型的层控矽卡岩型矿床。本研究可为矽卡岩型矿床的成矿规律认识和找矿勘探等方面提供科学支撑。     

Geochemical Characteristics of Apatite in Heavy REE‐rich Deep‐Sea Mud from Minami‐Torishima Area,Southeastern Japan

We have conducted geochemical and mineralogical investigations of the rare earth and yttrium (REY)‐rich mud from the Minami‐Torishima area in the Pacific in order to clarify the concentration of REY and their host‐phase in the mud. X‐ray diffraction analysis shows that the mud is mainly composed of phillipsite, fluorapatite, quartz, albite, illite and montmorillonite. Whole‐rock CaO, P₂O₅ and total REY contents of the mud are positively correlated. Relative abundance of apatite is also positively correlated to P₂O₅ and total REY contents. These correlations suggest that apatite is the main host of the P₂O₅ and REY in the mud. We make in situ compositional analyses of constituent minerals in the REY mud. The results show that the apatite is abundant in REY (9300–32,000 ppm) and is characterized by a negative Ce anomaly and enrichment in heavy rare‐earth elements. This abundance and composition of REY of the mud is similar those of fish debris apatites. In contrast, phillipsite is less abundant in REY (60–170 ppm). Therefore we conclude that the main REY host phase of the mud is apatite.     

Quantitative mineralogical and chemical assessment of the Nkout iron ore deposit,Southern Cameroon

The Nkout deposit is part of an emerging iron ore province in West and Central Africa. The deposit is an oxide facies iron formation comprising fresh magnetite banded iron formation (BIF) at depth, which weathers and oxidises towards the surface forming caps of high grade hematite/martite–goethite ores. The mineral species, compositions, mineral associations, and liberation have been studied using automated mineralogy (QEMSCAN^®) combined with whole rock geochemistry, mineral chemistry and mineralogical techniques. Drill cores (saprolitic, lateritic, BIF), grab and outcrop samples were studied and divided into 4 main groups based on whole rock Fe content and a weathering index. The groups are; enriched material (EM), weathered magnetite itabirite (WMI), transitional magnetite itabirite (TMI) and magnetite itabirite (MI). The main iron minerals are the iron oxides (magnetite, hematite, and goethite) and chamosite. The iron oxides are closely associated in the high grade cap and liberation of them individually is poor. Liberation increases when they are grouped together as iron oxides. Chamosite significantly lowers the liberation of the iron oxides. Automated mineralogy by QEMSCAN^® (or other similar techniques) can distinguish between Fe oxides if set up and calibrated carefully using the backscattered electron signal. Electron beam techniques have the advantage over other quantitative mineralogy techniques of being able to determine mineral chemical variants of ore and gangue minerals, although reflected light optical microscopy remains the most sensitive method of distinguishing closely related iron oxide minerals. Both optical and electron beam automated mineralogical methods have distinct advantages over quantitative XRD in that they can determine mineral associations, liberation, amorphous phases and trace phases.     

Long-term behaviour and mineralogical reactions in hazardous waste landfills: a comparison of observation and geochemical modelling

 Drill cores from a Bavarian hazardous waste landfill were investigated for their mineralogical composition. Because of the formation of many new minerals, geochemical equilibrium calculations were performed to find the most stable state of the waste body. A comparison of mineralogical observations and geochemical modelling was undertaken. The remaining solubilities of the newly formed secondary mineral assemblages were calculated. Newly formed minerals were shown using electron microscopy. Received: 26 November 1999 · Accepted: 15 May 2000     

The Processing Mineralogy for Lead and Zinc Oxide Ore in Sichuan

Using variety of modern testing methods, the processing mineralogical characteristics for a lead and zinc oxide ore in Sichuan were studied systematically. The chemical analysis result shows that the lead and zinc oxide content exceeding the minimum industrial grade and iron ore, total iron content reaches a minimum industrial grade and associated with gold and silver; The mineralogical analysis result shows that lead and zinc mineral composition and configuration are very complexity. The zinc minerals and zinciferous minerals are sphalerite, hemimorphite, Smithsonite, Hydrozincite, zinc chlorite, limonite, zinc dolomite and zincocalcite; lead minerals and plumbiferous minerals are mainly galena, cerussite, anglesite, limonite and Coronadite; The minerals disseminated grain size are very fine and mineral dissemination characteristics are very complex ; expected theoretical recoveries for lead and zinc were 72% and 67% respectively. The results of this study provide basic data and theoretical basis for ore dressing.     

Mineralogy of metamorphosed manganese deposits of the South Urals

A mineralogical investigation of metamorphosed manganese rocks was carried out at ore deposits related to the Devonian volcanic complexes of the Magnitogorsk paleovolcanic belt of the South Urals. The mineralogical appearance of these rocks is determined by three consecutively formed groups of mineral assemblages: (1) assemblages occupying the main volume of orebodies and formed during low-grade regional metamorphism (T = 200−250°C, P = 2–3 kbar); (2) assemblages of segregated and metasomatic veinlets that fill the systems of late tectonic fractures; and (3) assemblages of near-surface supergene minerals. Sixty-one minerals have been identified in orebodies and crosscutting hydrothermal veinlets. The major minerals are quartz, hematite, hausmannite, braunite, tephroite, andradite, epidote, rhodonite, caryopilite, calcite, and rhodochrosite. The mineral assemblages of metamorphosed manganese rocks (metamanganolites) are characterized. Chemical compositions of braunite, epidote-group minerals, piemontite, pyroxenes, rhodonite, pyroxmangite, and winchite are considered. The bibliography on geology and mineralogy of the South Ural manganese deposits is given.