Mineralogical and geochemical studies of brecciated ores in the Dalucao REE deposit,Sichuan Province,southwestern China

The Dalucao deposit, located in western Sichuan Province, southwestern China, in the western part of the Yangtze Craton, is one of the largest and most extensive rare earth element (REE) deposits in the Himalayan Mianning–Dechang REE belt. Moreover, the Dalucao deposit is the only deposit identified in the southern part of the belt. The Dalucao deposit contains the No. 1, 2, and 3 orebodies; the No. 1 and 3 orebodies are both hosted in two breccia pipes, located in syenite–carbonatite host rocks. Both pipes have elliptical cross-sections at the surface, with long-axis diameters of 200–400 m and short-axis diameters of 180–200 m; the pipes extend downwards for > 450 m. No. 1 and No. 3 have total thickness varying between 55 and 175 m and 14 to 58 m respectively. The REE mineralization is associated with four brecciation events, which are recorded in each of the pipes. The ore grades in the No. 1 and 3 orebodies are similar, and consist of 1.0%–4.5% rare earth oxides (REOs). The No. 1 orebody is characterized by a Type I mineral assemblage (fluorite + barite + celestite + bastnäsite), whereas the No. 3 orebody is characterized by a Type II assemblage (fluorite + celestite + pyrite + muscovite + bastnäsite + strontianite). Argon (⁴⁰Ar/³⁹Ar) dating of hydrothermal muscovite intergrown with REE minerals in typical ores from the No. 1 and 3 orebodies yielded similar ages of 12.69 ± 0.13 and 12.23 ± 0.21 Ma, respectively, which suggest that both mineral assemblages formed coevally, rather than in paragenetic stages. Both ages are also similar to the timing of intrusion of the syenite–carbonatite complex (12.13 ± 0.19 Ma). The ore-mineral assemblages occur in breccias, veinlets, and in narrow veins. The ore veinlets, which usually show a transition to mineralized breccia or brecciated ores, are commonly enveloped by narrow veins and stringer zones with comparable mineral assemblages. The brecciated ores form 95% of the volume of the deposit, whereas brecciated ores are only a minor constituent of other deposits in the Mianning–Dechang REE belt. The carbonatite in the syenite–carbonatite complexes contains high concentrations of S (0.07–2.32 wt.%), Sr (16,500–20,700 ppm), Ba (3600–8400 ppm), and light REEs (LREE) (2848–10,768 ppm), but is depleted in high-field-strength elements (HFSE) (Nb, Ta, P, Zr, Hf, and Ti). The syenite is moderately enriched in large-ion lithophile elements (LILE), Sr (155–277 ppm), and Ba (440–755 ppm). The mineralized, altered, and fresh syenites and carbonatites exhibit similar trace element compositions and REE patterns. Brecciation events, and the Dalucao Fault and its secondary faults around the deposit, contributed to the REE mineralization by facilitating the circulation of ore-forming fluids and providing space for REE precipitation. Some hydrothermal veins composed of coarse-grained fluorite and quartz are distributed in the syenite–carbonatite complex. The oxygen isotope compositions of ore-forming fluids in equilibrium with quartz at 215 °C are − 4.95‰ to − 7.45‰, and the hydrogen isotope compositions of fluid inclusions in coarse-grained quartz are − 88.4‰ to − 105.1‰. The syenite–carbonatite complex and carbonatite are main contributors to the mineralization in the geological occurrence. Thus, the main components of the ore-forming fluids were magmatic water, meteoric water, and CO₂ derived from the decarbonation of carbonatite. According to the petrographic studies, bastnäsite mineralization developed during later stages of hydrothermal evolution and overprinted the formation of the brecciated fluorite–quartz hydrothermal veins. As low-temperature isotope exchange between carbonates of the carbonatite and water-rich magmatic fluids will lead to positive shifts in δ¹⁸O values of the carbonates, C–O isotopic compositions from the bulk primary carbonatite to hydrothermal calcite and bastnäsite changed (δ¹⁸O_V-SMOW from 8.0‰ to 11.6‰, and δ¹³C _V-PDB from − 6.1 to − 8.7‰). According to the chemical composition of syenite and carbonatite, REE chloride species are the primary complexes for the transport of the REEs in the hydrothermal fluids, and the presence of bastnäsite and parisite means the REE were precipitated as fluorocarbonates. High contents of Sr, Ba and S in the syenite–carbonatite complex led to the deposition of large amount of barite and celestite.     

土壤重金属环境质量矿物学评价方法

利用环境矿物学理论和方法阐明了土壤矿物控制重金属活动状态,具体分析了重金属在矿物表面、层间域和孔道内可能的赋存位置。实验研究结果表明,矿物吸附重金属的作用受到介质pH值、介质离子强度等因素的影响。采用系统聚类分析方法,能定量地分析稳定的硫化物结合态微量有毒有害重金属元素的数量。利用粉晶X射线衍射分析方法,能定量地测定土壤矿物组成和含量。新提出土壤环境质量矿物学方法评价流程。该方法是在利用生态地球化学方法所完成的元素总量调查成果的基础上,开展单元性与剖面性土壤矿物组成与含量测定,查明表层土壤和深层土壤的矿物组成和分布,评价土壤中重金属的赋存状态及其对食物链的影响。旨在为农业地质环境评价提供新方法,切实提高农业地质环境调查质量与服务水平。     

Mineralogical studies of pyropes in kimberlites from China

Based on the measurements of refractive index,specific gravity,unit cell parameter,and mineral chemistry and infrared absorption spectrum analyses of pyropes in kimberlites from China,systematic studies of the Physical properties and compositional variations of pyropes of different colors and diverse paragenetic types,within and between kimberlite provinces have been undertaken,The origin of pyropes in the Kimberlites and the depth of their formation have been discussed.Pyropes of the purple series are different from those of the orange series in physical and chemical properties,for exaple,pyropes of the puple series are higher in α0,RI,SG,Cr2O3,MgO,Cr/(Cr Al),Mg/(Mg Fe),and Mg/(Mg Ca),and lower in Al2O3,Fe2O3 FeO than those of the orange series.The classification of garnets in kimberlites from china by the Dawson and Stephens‘ method(1975) has been undertaken and clearly demonstrates that pyropes of diamond-rich kimberlites contain much more groups than those of diamond-poor,especially diamond-free kimberlites.The higher in α0,RI,SG,Cr2O(3.Cr/(Cr Al),knorringite and Cr-component the pyropes are ,the richer in diamond the kimberlites will be.The infrared absorption spectrum patterns of pyropes change with their chemical composition regularly,as reflected in the shape and position of infrared absorption peaks.Two absortpion bands at 862-901 cm^-1 will grade into degeneration from splitting and the absorption band positions of pyropes shift toward lower frequency with increasing Cr2O3 content and Cr/(Cr Al) ratio of pyropes,LREE contents of orange pyrope megacrysts are similar to those of porple pyrope macrocrysts,but the former is higher in HREE than the latter,showing their different chondrite-normalized patterns.The formation pressures of pyropes calculated by Cr-component,Ca-component,knorringite molecules of pyropes show that some pyropes of the purple series in diamondiferous kimberlites fall into the diamond stability field.but all pyropes of diamond-free kimberlites lie outside the diamond stability field.The megacrysts were formed through early crystallization of kimberlites magma at high pressure condition,the majority of the purple pyrope macrocrysts have been derived from disaggregated xenoliths but the minoirty of them appear to be fragments of the discrete megacryst pyropes,or phenocrysts.     

Mineralogical and geochemical zoning and genesis of massive sulfide ores at the Oktyabr’sky deposit

Fractional crystallization and emanation differentiation of sulfide magma and related mineralogical and geochemical zoning are exemplified in massive sulfide ores of the Oktyabr’sky deposit, Noril’sk district. The mineralogical zoning is expressed in the change of mineral types of ore from pyrrhotite (Po) to chalcopyrite (Cp) (from the flanks to the center of the ore lode). In terms of geochemistry, the Cu content, Cu/(Cu + Ni) ratio, and contents of noble metals incompatible with Mss (Pt, Pd, and Au) increase in this direction, while the S and Fe contents decrease. The distribution of elements compatible with Mss (Ir, Os, Rh, and Ru) is more complex. Their contents decrease from Po to high-Cu Cp ore, although there is a second maximum for Cb-type ore. The distribution of ore elements in the vertical and horizontal sections of massive ores at the deposit is different. The upper outer contact zone and frontal parts of massive ore lodes are enriched in all ore elements and a light sulfur isotope. The succession of enrichment is correlated with the relative affinity for sulfur and remains independent of the affinity of these elements for Mss (Pd-Rh, Os-Au). The possible role of liquid immiscibility of sulfide magma in the development of the mineralogical and geochemical zoning of massive ore is discussed.     

乳腺炎症及增生症病灶中钙化的矿物学研究

选取9例乳腺炎症、7例乳腺增生的钙化样品,利用光学显微镜(OM)、环境扫描电镜(ESEM)、微区X射线衍射(μ-XRD)等矿物学分析方法对样品进行了原位形貌观察、分离后结构及成分的测试分析,探讨了病灶中钙化的矿物学特征及其组成成分和形成机制。研究结果表明,发生在炎症病灶中的钙化主要类型是脂肪坏死后的钙化,其发生和死亡的脂肪细胞和周围病变后期修复性Ⅲ型胶原有直接关系。增生症中的钙化主要有发生在扩张的导管内和在束状深度交联胶原中的坏死型钙化,扩张的导管边缘处Ⅳ型胶原和大片变性Ⅲ型胶原为钙化提供了成核位点,继而参与无机矿物的形成过程,最后形成较为致密的钙化。乳腺炎症和增生症中的钙化的主要成分均为碳羟磷灰石。     

Critical metals distribution in Tethyan karst bauxite: The cretaceous Italian ores

Bauxite is a residual rock, consisting mainly of a mixture of aluminium hydroxides, whose industrial significance is primarily due to its profitably exploitable alumina contents. In the last decades, bauxite, mainly karst bauxite, has been also considered as possible resource of a great number of economically interesting elements including some critical metals such as rare earth elements, Sc, Co, Ni, and Nb. In this study, we present results of univariate and multivariate (R-mode factor analysis) statistics performed on a large data set including chemical composition of the principal Cretaceous karst bauxites from central and southern Italy with the twofold aim to evaluate the inter-elemental relationship among major oxides and critical metals, and describe factors affecting their distribution. Univariate statistics reveal that some critical metals Co, Ni, and LREE, have a significant number of outliers. The Co-Ni relationship associated to the outliers dataset suggests that Co is likely hosted in Ni-rich phases whereas Ce accumulation in authigenic minerals, carbonate-fluoride and phosphate, is at the origin of LREE outliers. Multivariate R-mode statistics, applied to the outliers-devoid database, instead demonstrate that in absence of specific mineralization events, the distribution of most critical metals is controlled by Al-, Fe-, and Ti-oxi-hydroxides and, to a lesser extent, by detrital phases. Among the critical metals, Cr and Y are the exceptions. Their geochemical behaviour seems to be influenced primarily by their own chemical features that are responsible for the mobility of Cr during bauxitization and for the decoupling of Y from the REEs.     

我国首次发现的天然硅铋石的矿物学研究

硅铋石是一种极为罕见的铋的硅酸盐矿物,本次报道的天然硅铋石产于我国内蒙古自治区东乌旗朝不楞矽卡岩型铁多金属矿床中,附生在蔷薇辉石晶洞或裂隙中的透闪石纤维上。常见四面体{111}及三角三四面体晶形,一般粒径为0.07～0.15mm,颜色多为浅黄色,透明,玻璃光泽,性脆,条痕为无色,维氏硬度VHN_（100g）=487～583kg/mm²,平均535kg/mm²,摩氏硬度5,计算密度7.11g/cm³,计算折射率N=2.15。矿物化学分子式为Bi₄Si₃O₁₂。X射线衍射强线[d（Å）（I）]为4.26（85）、3.29（100）、2.77（79）、2.11（45）和1.67（33）,结构精修晶胞参数a=10.116（2）Å,V=1035.2（7）ų,空间群为I43d,Z=4。本文还对硅铋石的成因进行了初步探讨。     

Speciation of noble metals and conditions of their concentration in massive sulfide ores of the Urals

The distribution of noble metals has been studied in ores and sulfide concentrates from the Gai, Uchaly, Uzel’ga, Aleksandrinsky, Degtyarsk, and Saf’yanovka deposits. The ores, technological products, and hand-picked monofractions were analyzed with INAA; PGE were determined with kinetic and chromatographic methods after their preliminary chemical separation. The ultraheavy fractions from Au-rich samples were used for examining minerals of noble metals. Phase relations and compositions of ore minerals were studied with an X-ray microprobe and electron microscope equipped with an energy dispersive X-ray analyzer. Gold is associated largely with Fe and Cu minerals (pyrite, chalcopyrite, fahlore) and has been detected as an admixture in Pb, Bi, and Ag tellurides. Pyrite—the major mineral of massive sulfide ores—is the main gold concentrator (up to 20 ppm, ～1 ppm on average). As follows from the results of rational analysis, the concentration of finely dispersed gold in sulfide ores from the studied deposits ranges from 0.8 to 5.0 ppm, i.e., is less than the bulk Au content in the respective samples (0.93–21.2 ppm). Formation conditions of Au-enriched massive sulfide ores were estimated from the homogenization temperature of fluid inclusions in minerals and on the basis of the electrum-argentite-pyrite-sphalerite and electrum-hessite geothermometers, taking into account the sulfur and tellurium fugacities. The appearance of visible gold and tellurides in ores is caused by recrystallization of their fine-grained intergrowths with ore-forming minerals and, likely, by release of isomorphic admixtures contained in sulfides during epigenetic hydrothermal alteration.     

Noble metals in the insoluble carbonaceous substance of black shales and ores: Direct atomic emission data

The way of extraction of insoluble carbonaceous substance (ICS) from black shales and technique of determination of noble metals (NM) in it by direct arc atomic emission analysis (AEA) were developed. The first results are reported on the determination of mineral-bound noble metals in ICS concentrates, which were extracted from the rocks and ores of the Sukhoi Log, Vernyi, Vasil’evskoe, Kuranakh, Daugyztau, Bakyrchik, Kamennoe, El’dorado, and other deposits.     

Noble metals segregation and fractionation in magmatic ores from Ronda and Beni Bousera Lherzolite Massifs (Spain,Morocco)

Summary Three types of mineralization are found in high-temperature lherzolite massifs of Southern Spain and Northern Morocco: (Cr) chromite, (Cr-Ni) chromite-nickel arsenide, (S-G) sulphide-graphite. The ore veins are distributed in this order from the plagioclase-lherzolite core to the garnet-lherzolite border of the massifs. These hightemperature ore assemblages (1200-600°C) have cumulate textures including orthopyroxene and/or cordierite as main silicate minerals.High average PGE concentrations are present in the Cr-Ni ores (2000 ppb) in relation to the Ni-arsenide abundance. The Cr ores have only 900 ppb PGE, and the S-G ores are PGE-poor (350 ppb). Gold roughly follows the PGE distribution: 13,000 ppb in Cr-Ni ores, 570 ppb in Cr ores, and only 88 ppb in S-G ores. The chondrite normalized PGE patterns of the Cr-Ni ores are chondritic, whereas those of the Cr and S-G ores have respectively negative and positive slopes. The Pd/Ir ratio strongly increases from the Cr ores (0.39) to the Cr-Ni and the S-G ores (2.7 and 3.4)). There are some (Os, Ru)S₂ inclusions in the chromite of the Cr ores. In the Cr-Ni ores, some minute Au, Au-Cu, and Au-Bi-Te grains are observed. No PGM have been found, except in a weathered Cr-Ni ore sample where abundant PGM (PtAs₂, IrAsS) are present., suggesting that PGE may be hidden as solid solution in the Ni-arsenide.The ore-forming magma probably has a mantle source-rock. The earliest chromites (Cr ores) contain Os-Ir-Ru mineral inclusions, whereas most of the gold and the remaining PGE with higher Pd/Ir ratio were partitioned into an immiscible As-S-liquid, which fractionated later into an earliest PGE-Au-rich NiAs-phase (Cr-Ni ores) and then a PGE-Au-poor MSS-phase (S-G ores).

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Abtrennung und Fraktionierung von Edelmetallen in magmatischen Erzen der LherzolitMassive von Ronda und Beni Bousera (Spanien, Marokko)

Zusammenfassung In den Hochtemperatur-Lherzolit Massiven von Süd-Spanien und Nord-Marokko kommen drei Typen von Vererzung vor: (Cr) Chromit, (Cr-Ni) Chromit-Nickelarsenid, (S-G) Sulfid-Graphit. Die Erzgänge sind in dieser Abfolge vom Plagioklas-Lherzolit Kern zum Granat-Lherzolit Rand der Massive angeordnet. Diese Hochtemperaturparagenesen (1200°-600° C) haben Kumulattexturen mit Orthopyroxen und/oder Cordierit als Hauptsilikatminerale.Hohe Durchschnittsgehalte an PGE kommen in den Cr-Ni Erzen (2000 ppb) vor, und diese stehen in Beziehung zur Häufigkeit der Nickel-Arsenide. Die Cr-Erze führen nur 900 ppb PGE und die S-G Erze sind PGE-arm (350 ppb). Gold folgt in ungefähr der PGE-Verteilung: 13000 ppb in Cr-Ni Erzen, 570 ppb in Cr Erzen, und nur 88 ppb in S-G Erzen. Die Chondrit-normalisierten PGE Verteilungen der Chrom-Nickel Erze sind chondritisch, während jene der Cr- und S-G Erze negative, bzw. positive Neigungen zeigen. Das Pd/Ir Verhältnis nimmt von den Cr-Erzen (0, 39) zu den Cr-Ni und den S-G Erzen (2,7 und 3,4) deutlich zu. Es gibt einige (Os, Ru)S₂ Einschlüsse in den Chromiten der Cr Erze. In den Cr-Ni Erzen, kommen winzige Einschlüsse von Au, Au-Cu und AuBi-Te Körnern vor. Keine PGM konnten nachgewiesen werden, mit Ausnahme eines verwitterten Cr-Ni Erzes wo reichlich PGM (PtAs₂,1rAsS) vorliegen. Dies weist darauf hin, daß PGE in fester Lösung in den Nickel-Arseniden gebunden sein könnten.Das erzbildende Magma dürfte dem Mantel entstammen. Die am frühesten gebildeten Chromite (Cr-Erze) enthalten Einschlüsse von Os-Ir-Ru Mineralen, während ein Großteil des Goldes und der verbleibenden PGE mit höheren Pd/Ir Verhältnissen in eine nicht mischbare As-S fluide Phase gingen; die letztere fraktionierte später in eine frühe PGE-Au-reiche NiAs-Phase (Cr-Ni Erze) und dann in eine PGE-Au-arme MSS-Phase (S-G Erze).

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With 6 Figures     

Mineralogical siting and distribution of gold in quartz veins and sulfide ores of the Ashanti mine and other deposits in the Ashanti belt of Ghana: genetic implications

The Ashanti belt of Ghana constitutes a gold province which has produced a total of about 1500 t of gold historically. Gold mineralization is found in steep, NNE-SSW to NE-SW trending shear zones predominantly transecting metasediments of the Palaeoproterozoic Birimian Supergroup (2.2–2.1 Ga), disseminated in ca. 2.1 Ga granitoids, in paleo-conglomerates of the Tarkwaian Group (< 2135 Ma), and in recent placers. The distribution of gold, its chemistry, paragenesis and mineralogical siting in the mesothermal ores of the major mines in the Ashanti belt, namely Konongo, Ashanti, Bogosu and Prestea mine, are the subject of this study. At the localities studied, gold is present in two main types of ores: 1. Quartz veins with free-milling gold. The gold is relatively silver-rich (true fineness values from 730 to 954) and is accompanied by a distinct suite of Cu, Pb, Sb sulfides. 2. Sulfide ores, consisting of arsenopyrite, pyrite and rarer pyrrhotite and marcasite, with refractory gold. The ores have apparent fineness values larger than 910. Arsenopyrite and locally (at Bogosu) pyrite were identified as the hosts of submicroscopic gold. Mean concentrations of gold in arsenopyrite in various samples from the different mines, obtained by secondary ion mass spectrometry (SIMS), range from 67 to 314 ppm Au. Gold concentration mapping in individual arsenopyrite crystals from the different deposits revealed similar patterns of gold distribution: the grains possess a gold-poor core, and elevated gold contents are present along distinct crystal growth zones towards their rims. The outermost crystal layer is usually gold-poor. The well-preserved distribution patterns also indicate that remobilization of gold from the sulfides played an insignificant role in the ores of the Ashanti belt. Multiple quartz veining and growth zoning of the sulfides are interpreted as manifestations of multiple episodes of fluid infiltration, fluid flow and mineral deposition. The bimodal occurrence of gold in spatially closely associated quartz vein and sulfide ores indicates a genetic link between these ore types. A model implying a grossly coeval formation of the ores from mesothermal fluids is proposed. Received: 28 September 1995 / Accepted: 11 June 1996     

Isotope studies on the Rosebery,Mount Farrell and Mount Lyell ores,Tasmania

Preliminary studies have been made on the distributions of oxygen and sulphur isotopes in the Rosebery, Mount Farrell, and Mount Lyell ores. These ores lie in Cambrian geosynclinal volcanic rocks in West Tasmania. At each locality the sulphur of the sulphide minerals has a distinctive degree of enrichment in ³⁴S in relation to sulphur in meteorites and a narrow range of ³⁴S values. The dominant ore at Mount Lyell (mainly pyrite-chalcopyrite) has an average ³⁴S value of +7.0, the main lode at Rosebery (pyrite-sphalerite-galenachalcopyrite) averages +10.9, and the Mount Farrell ore (galena-sphalerite) averages +14.1. The degree of enrichment does not appear to be related to local, near-surface geological factors. Other ores of geosynclinal volcanic type with similar mineralogy also show narrow ranges in ³⁴S and varying enrichments in ³⁴S. Barite from a concordant sulphide-barite-carbonate lode at Rosebery has an average ³⁴S of +38.1 and an average ¹⁸O of +10.7. Barite from veins at Mount Lyell has an average ³⁴S of +25.3 and an average ¹⁸O of +10.6.

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Die Verteilung von Sauerstoff- und Schwefel-Isotopen in den Erzkörpern von Rosebery, Mount Farrell und Mount Lyell wurde untersucht. Die Erzkörper sind in kambrische, geosynklinale vulkanische Gesteine Westtasmaniens eingebettet. An jeder dieser Lagerstätten zeigt der Schwefel der Sulfiderze einen charakteristischen Anreicherungsgrad an ³⁴S im Verhältnis zum Meteoritenschwefel und einen eng begrenzten Bereich der ³⁴S-Werte. Die Erze des Mount Lyell-Lagers (hauptsächlich Pyrit-Chalkopyrit) zeigen überwiegend einen ³⁴S-Durchschnittswert von +7.0, das Hauptlager von Rosebery (Pyrit-Sphalerit-Galenit-Chalkopyrit) +10.9, und des Mount Farrell-Erz (Galenit-Sphalerit) +14.1. Der Anreicherungsgrad scheint nicht mit den lokalen geologischen Faktoren verbunden zu sein. Auch andere Erzkörper geosynklinaler vulkanischer Art von ähnlicher mineralogischer Struktur zeigen eng begrenzte ³⁴S-Werte und ³⁴S-Anreicherungsvariationen. Der Baryt des konkordant aufgebauten Sulfid-Baryt-Carbonat-Lagers bei Rosebery hat einen ³⁴S-Durchschnitt von +38.1 und einen ¹⁸O-Durchschnitt von +10.7. Der Baryt aus den Erzgängen von Mount Lyell ist durch einen ³⁴S-Durchschnitt von +25.3 und einen ¹⁸O-Durchschnitt von +10.6 charakterisiert.

     

Mineralogical and geochemical studies on Egyptian (U.A.R.) black sands

The economic mineral constituents of the black sand deposits occurring at the outpourings of the Nile Delta, Egypt, were studied from the mineralogical and geochemical point of view. These include magnetite, ilmenite, zircon, monazite, rutile und garnet. Microscopical, X-ray, chemical und spectrographic analyses are reported and discussed for each mineral.

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Zusammenfassung Die wirtschaftlich wichtigen Mineralkomponenten der Schwarzsand-Ablagerungen, die an den Mündungen des Nildeltas in Ägypten vorkommen, wurden in mineralogischer und geochemischer Hinsicht untersucht. Sie enthalten Magnetit, Ilmenit, Zirkon, Monazit, Rutil und Granat. Mikroskopische, röntgenographische, chemische und spektrographische Analysen werden für jedes Mineral angeführt und diskutiert.

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With 9 Figures in the Text     

Mineralogical and fluid inclusion studies of low-sulfidation epithermal veins at Osilo (Sardinia), Italy

Several precious metal-bearing, low sulfidation epithermal veins occur in the rolling topography of the Osilo area, northern Sardinia. The Sa Pala de Sa Fae and the Sa Pedra Bianca veins were subject to intense diamond drilling exploration in the mid 1990 s. The veins extend for 1–3 km, dip steeply, and range from 1 to 10 m in width. High K-calc-alkaline volcanic deposits containing plagioclase phenocrysts (along with lesser pyroxene, amphibole, magnetite, olivine and sanidine) form the main host rocks. Gold grades in drill intersections range from <0.1 to <20 ppm, with silver-gold ratios of around 4 to 7. Mineralogical studies show a systematic distribution of three hydrothermal mineral assemblages. At distances >50 m from the vein, the assemblage albite + Fe-chlorite + illite + pyrite (± montmorillonite ± calcite ± K-feldspar) prevails regionally, and its formation is attributed to minor metasomatism of the country rock involving the addition of water, carbon dioxide and hydrogen sulfide. At distances <10 m from the vein, the assemblage quartz + K-feldspar + pyrite ± illite dominates, forming an alteration envelope that cross cuts regional alteration. Quartz and K-feldspar increase in abundance towards the vein. Quartz is the main vein mineral, and it displays a range of morphologies and textures including crustiform colloform banding, quartz pseudomorphs of platy calcite, breccias and coarse euhedral crystals. Electrum and argentite which are the main gold and silver minerals deposited during the early stages of vein mineralization with rhomb-shaped crystals of K-feldspar (adularia). Pyrite, plus lesser marcasite, arsenopyrite, stibnite and sphalerite, are the other sulfide phases in veins. Kaolinite ± halloysite ± jarosite form a late assemblage overprinting earlier hydrothermal alteration. It is mostly restricted to shallow depths of a few meters, except near veins. Most of this assemblage likely formed from weathering and oxidation of sulfides. Microthermometric measurements were made on quartz-hosted, two-phase (liquid + vapor) inclusions, containing ∼75% liquid; mean homogenization temperatures (∼750 measurements) range from 220 to 250 °C, and ice-melting temperatures (∼550 measurements) range from 0.0 to −2.3 °C. The presence of co-existing vapor-rich and liquid rich inclusions, with quartz pseudomorphs of platy calcite, indicate that boiling conditions existed. Slight vapor-bubble expansion of a few fluid inclusions subjected to crushing experiments indicates inclusion fluids contained variable but low concentrations of dissolved gas. This study shows that gold-silver mineralization formed in subvertical channels from ascending solutions at 250 °C at around 300 to 450 m below the paleo-water table in a typical low-sulfidation epithermal environment. Hydrothermal solutions that produced vein mineralization and related alteration were dilute (<4.1 equivalent wt.% NaCl and <4 wt.% CO₂), near neutral pH, reduced and, at times, boiling. Received: 19 May 1998 / Accepted: 8 March 1999     

On Mineralogical Studies and the Use of Mineralogical Information in Solving Petro- and Ore Genesis Problems

Geology of Ore Deposits - The deep penetration of crystal chemistry and physics of minerals into mineralogy, as well as the introduction of modern physical methods, has advanced mineralogical...     

Effects of heavy metals on some soil biological parameters

The soils most polluted by heavy metals are probably alluvial soils. One of them is the alluvium of the Litavka River. The heavy metal content was much higher in some cases than the threshold values, allowed by the Czech standards. The effect of soil contamination on enzyme activity is presented. Generally, the values of enzymatic activities were highest in the soil above the source of contamination and they decrease as they approach the source of contamination. All measured parameters were affected by heavy metal concentrations. Our results demonstrate that several parameters of microbial activity could be used as good indicators of increasing concentrations of Cd, Pb and Zn in soil.     

Mineralogical and geochemical studies of boron-rich bauxite ore deposits in the Songqi region,SW Henan,China

The Songqi region, SW Henan, is an important bauxite province in China. The bauxite ore deposits occur unconformably on the top of Middle Ordovician argillaceous carbonates. The bauxite ores from the Songqi region are characterized by unusually high boron contents. In this paper, we report the mineralogical and chemical compositions of selected bauxite ores from the region. These new data, together with existing geochemical data of soils in the region, are used to evaluate the origin of boron enrichment in the bauxite ores. The compositional characteristics of tourmaline in the bauxite ores suggests that this mineral was likely derived from a meta-sedimentary protolith. Mass balance calculation reveals that tourmaline only accounts for a small portion of boron in the bauxite ores; the majority of boron in the ores must occur in other forms, possibly by ion absorption on the surfaces of diaspore and clay minerals. In the Songqi region, the Precambrian meta-sedimentary rocks are known to contain abundant tourmalines whereas the Cambrian–Ordovician argillaceous carbonates and the Upper Proterozoic shales are all enriched in boron in free ion state. We suggest that these rocks provided tourmaline and boron ion to the bauxite deposits in the region. Most known bauxite deposits in the Songqi region occur at the margins of boron-rich soil domains, suggesting that boron in soils is a potential exploration indicator for unknown bauxite deposits in this region.