Granitic dimensional stones in Uruguay: evaluation and assessment of potential resources

In Uruguay commercial granite varieties comprise mafic rocks, granitoids, and syenitoids. There is a long tradition in Uruguay, as well as worldwide, of using dimensional stones in architecture and art, specially granitic ones. Some of the present applications of these dimensional stones are as façade cladding, countertops, and outdoor and indoor floor slabs. The color spectrum of the Uruguayan granitic dimensional stones varies from black to light gray, covering a wide variety of red and pink and minor greenish-gray. The décor of these granitic dimensional stones is mainly determined by their fabric, fundamentally the grain size and the color distribution between the different minerals that compose the rocks. In the present research the most important commercial granites were sampled to analyze their petrography and petrophysical properties. A detailed structural analysis has been performed in several deposits, as well as the application of the software 3D Block Expert for modeling the possible raw block size distribution. Other factors controlling the mining viability of the deposits were also studied (e.g., homogeneity/heterogeneity of color and décor) and the possible reserves were calculated.     

Weathering of Fruchtschiefer building stones: mineral dissolution or rock disaggregation?

Building stones manufactured from contact metamorphic slates (Fruchtschiefer slate) from Theuma (Sachsen, Germany) were investigated for mineralogical alterations as well as for changes in porosity and surface roughness due to weathering. After weathering periods of several years to decades, the originally dark gray-colored slates show pale spots of several centimeters in size at the surface of building stones. The dark-colored and light-colored sections of the slate show no differences in mineralogy. Surface weathering did not result in newly precipitated minerals. It was also found that the observed differences in color are not caused by variations in sedimentary organic carbon concentration or in sulfide/sulfate concentrations. Obtained results instead indicate that dark surface sections may show a thin cover of recent organic matter (OM), e.g., living OM, soot, dirt, etc. Microscopic investigations suggested that this cover was exfoliated at light-colored surface sections. The observed disaggregation of the upper 2 mm of the building block material results in an increase in porosity. Porosity of black (unweathered) slate is <2 vol.%. Due to weathering, the slate’s pores with diameters >1 μm show a significant increase in frequency compared to the original pore size distribution. Porosity of weathered rock volumes increased to approx. 8 vol.%. Discolored surface sections show a higher surface roughness (root-mean-square roughness, Rq ~ 1 μm) compared to dark-colored slate surfaces (Rq ~ 200 nm), both data are for cleavage planes. Preferentially, the discolored surface sections are located close to the edges of cut stones. This and the alteration in porosity, pore size, and surface roughness indicate that color changes of the slate are largely influenced by rock disaggregation proceeding from the edges into the center rather than by mineral dissolution/precipitation processes.     

Ultraphyllonite origin for slate,mid-Atlantic Piedmont,USA

Structural, petrographic, and geochemical criteria are applied in combination to determine the petrologic origins of slaty rocks in polydeformed metasedimentary terranes. Multiple lines of evidence suggest that the Peach Bottom slate (PBs), mined over several centuries, is an ultraphyllonite. It occurs within an Alleghanian dextral retraining bend within the Appalachian Piedmont, as a segment of the Pleasant Grove-Huntington Valley shear zone system (>200 km long). The PBs differs markedly from other slates, in that, it contains abundant, micro-scale remnant porphyroclasts of higher-grade minerals. The PBs has major, trace and rare earth element geochemistry and ¹⁴⁷Sm/¹⁴³Nd ratios that are similar to the surrounding pelitic rocks. When compared to average slates, the geochemistry of the PBs exhibits depletion in alkali earth and alkali elements.     

南水北调西线工程板岩强度的各向异性特征

南水北调西线工程区域内岩体类型主要为砂岩、板岩,其中板岩强度特性具有明显的各向异性特征.研究复杂地质条件下板岩的强度特征及变形规律,确定合理的板岩强度参数,对于引水坝址的选取和深埋长隧洞的设计与施工都具有十分重要的意义.在南水北调西线工程选取钻孔采取的板岩岩样,通过单轴压缩变形试验和三轴压缩试验等室内试验方法,借助Ho...     

板岩遇水软化的微观结构及力学特性研究

通过偏光显微镜、电子扫描电镜、粉晶X射线衍射,测定板岩泡水过程中吸水率、润湿角的变化,不同浸泡时间下的矿物颗粒微观结构、孔隙度的变化,并通过三轴压缩实验,研究了板岩泡水后发生软化的过程与机理。研究表明：板岩在浸泡后吸水率受板岩内层理面的产状、密度等参数的影响而改变,随着泡水时间的增加,吸水率在最初两天内变化较大,后期变化不太明显;板岩内部矿物颗粒在浸泡过程中产生体积膨胀,胶结变得松散,颗粒膨胀的时间稍滞后于吸水率的变化过程;三轴压缩实验结果显示,板岩浸泡后发生软化,峰值抗压强度随着吸水率增加按负对数规律降低;微观结构分析及润湿角的降低趋势表明,随浸泡时间延长,矿物颗粒之间的毛细管力、表面张力降低,使得板岩内部黏结力降低,宏观上则体现为岩石发生软化;在垂直于层理面方向更易发生体积膨胀,因此岩石在浸泡后更易沿着层理面产生破坏。     

Mineralogical and geochemical alteration of low-grade metamorphic black slates due to oxidative weathering

Low-grade metamorphic black slates of Silurian and Lower Devonian ages (from the Thüringisches Schiefergebirge in Germany) were investigated to identify mineralogical and geochemical alterations that occur during the oxidative weathering black slates.The slates exhibit an intense total organic carbon decrease (>90 wt%) due to oxidative weathering. The organic matter in black slate consists mainly of non-pyrolysable material with only minor portions of pyrolysable material. In contrast to the non-pyrolysable organic matter, the concentration of pyrolysable organic matter is not decreased during weathering. Heating experiments have yielded information about a potential protection of pyrolysable organic matter against weathering, which is probably caused by a structural configuration or the intergrowth of organic matter and illite.The slates consist mainly of illite. Iron oxide (goethite) and phosphate encrustations were formed on slate surfaces as a result of oxidative and acid weathering of both iron sulfide and monazite. Kaolinite often occurs as an older encrustation beneath the iron oxide encrustations. Encrustations of iron oxide and phosphate are major sinks for trace elements, released during oxidative weathering.     

东昆仑造山带巴颜喀拉山群ASTER岩性信息提取!

巴颜喀拉山群在东昆仑地区分布广泛,岩性复杂,准确划分其岩性对巴颜喀拉山群的地层划分及构造属性的研究具有重要意义。对东昆仑造山带巴颜喀拉山群地区ASTER图像进行几何校正和大气校正后,通过主成分分析和矿物指数等岩性信息提取方法,获得主成分分析及比值图像;根据不同地质体的影像特征并结合野外地质调查,对研究区的巴颜喀拉山群进行了岩性段的划分。研究发现:分布于南部的上巴颜喀拉山群(T3by)岩性相对单一,主要为灰-深灰色粉砂质板岩和砂岩,在影像上特征不明显,所以仍将其划分为2个岩性段;而分布于研究区北部的原下巴颜喀拉山群(T1by),影像上色调纹理特征差异较大,由此将原来的2段细化分为4段,a段主要为深灰色粉砂岩和千枚岩,b段为灰绿色细砂岩,c段为黄褐色细砂岩,d段为深灰色细砂岩夹板岩。研究结果较好地体现了遥感技术在高原区域岩性划分中的优点,同时为巴颜喀拉山群地层的对比提供了参考。     

塔藏构造混杂岩带特征

运用大陆造山带构造岩片填图方法，首次对九寨沟塔藏构造带进行了系统研究。认为塔藏构造带为-构造混杂岩带。其南北边界断裂清楚，北界为牙扎沟断裂，呈北西-南东向展布；南界为荷叶断裂，也呈北西-南东向展布，边界断裂内部为塔藏构造混杂岩带，呈北西-南东向延伸长16-24km，宽7-8km，由上古生界与三叠系的多个大小不同，形态各异的构造岩片（或岩块）混杂堆积组成，与塔藏岩组砂板岩呈断层接触，总体表现为块体之间无序，块内有序，微观变形特征清楚，三维有限应变测量显示为北东-南西向，近南北向两个方向压缩，结合测区构造地质环境分析有4期变形。     

南岭东段龙头寨群南迳组的建立及其地质时代厘定

南岭带东段晚奥陶世广泛发育一套浅变质岩系,称为龙头寨群。以南迳乔子山剖面和中寨剖面为层型剖面建立南迳组,并置于龙头寨群顶部。用SHRIMP法测得南迳盆地南迳组安山岩样品14个锆石U-Pb年龄数据,其~(206)Pb/~(238)U年龄变化范围为460~425Ma,年龄加权平均值为442.1±3.9Ma(MSWD=0.75);英安岩15个锆石~(206)Pb/~(238)U年龄变化范围为450~420Ma,年龄加权平均值为439.9±3.7Ma(MSWD=0.50)。结合司前河口破火山口碎斑熔岩的SHRIMP锆石U-Pb年龄(443.6±5.4Ma(MSWD=1.3)),可将南迳组的地质时代归于晚奥陶世末期—早志留世初期。龙头寨群南迳组的建立和地质时代的厘定,不仅为龙头寨群的地质时代归入晚奥陶世—早志留世初期提供了可靠的依据,而且为南岭带东段晚奥陶世—早志留世浅变质岩系属含有火山岩的优地槽型沉积提供了证据。     

白云鄂博含矿碱性火山岩建造及其地球化学

白云鄂博矿床历经几十年的研究,主要集中在矿区H8岩性段矿化白云岩成因的认识,许多研究显示含矿白云岩是岩浆碳酸岩,本文主要从岩石学和地球化学方面进一步分析其属于火山喷发环境形成的火山碳酸熔岩。H8含矿白云岩段和H9板岩段作为一套含矿岩系主要由含矿白云岩、霓闪钠长岩、钾长板岩3类岩石组成,白云岩和霓闪钠长岩都具有的碎屑结构及角砾状构造、条带构造,显示为火山熔岩和火山碎屑岩特征,而钾长板岩则主要显示致密微晶火山熔岩特征。工业矿物主要是磁铁矿、赤铁矿、稀土矿物和铌铁矿物,其重要特征是出现大量原生赤铁矿,反映岩石氧化系数高,与火山喷发环境一致。霓闪钠长岩、钾长板岩岩石化学显示碱性特征,稀土元素与CaO、F相关系数在0.7以上,并与Fe2O3高氧化物相关,而与硅酸盐矿物组分反相关,表示碳酸岩与稀土成矿密切相关,并显示为表生氧化环境形成。稀土地球化学特征显示白云岩∑REE最高,钾长板岩∑REE最低,相应的岩脉∑REE低于喷发岩。各种岩石均表现为明显的轻重稀土分异,但是以白云岩LREE/HREE比值最大,霓闪钠长岩LREE/HREE比值最小,而纯钠长石岩脉和含稀土磁铁矿LREE/HREE明显高于其他岩石。白云岩和霓闪钠长岩均表现出不同的铕、铈负异常,但是碳酸岩脉和钾长板岩则显示弱正铈异常,霓闪钠长岩和钾长板岩铕异常不明显。矿化白云岩和碳酸岩脉的δ18O、δ13C值介于沉积灰岩与已知碳酸岩的δ18O、δ13C值之间,碳酸岩中白云石的δ18O低于方解石的δ18O,而δ13C高于方解石的δ13C,稀土矿物的δ13C、δ18O与碳酸岩脉δ13C、δ18O接近。归纳这些特征,含矿白云岩与霓闪钠长岩、钾长板岩是碱性火山岩组合,与一系列同期的碳酸岩、霓闪钠长岩碱性岩脉一起,构成一套完整碱性火山岩系。     

西秦岭寨上金矿区岩(矿)石孔隙度研究

寨上金矿区赋矿岩石主要为泥质、钙质、碳质板岩、粉砂岩等.通过对赋矿岩石的岩石学特征、孔隙类型进行研究,认为寨上矿区的赋矿岩石为低孔隙度.板岩相对粉砂岩的孔隙度高,究其原因,主要是板岩的层间孔隙、裂隙及微裂隙发育.     

Variable effects of labile carbon on the carbon use of different microbial groups in black slate degradation

Weathering of ancient organic matter contributes significantly to biogeochemical carbon cycles over geological times. The principle role of microorganisms in this process is well recognized. However, information is lacking on the contribution of individual groups of microorganisms and on the effect of labile carbon sources to the degradation process. Therefore, we investigated the contribution of fungi, Gram-positive and Gram-negative bacteria in the degradation process using a column experiment. Investigations were performed on low metamorphic black slates. All columns contained freshly crushed, sieved (0.63-2 mm), not autoclaved black slates. Two columns were inoculated with the lignite-degrading fungus Schizophyllum commune and received a culture medium containing ¹³C labeled glucose, two columns received only this culture medium and two control columns received only water.The total mass balance was calculated from all carbon added to the slate and the CO₂ and DOC losses. Phospholipid fatty acids (PLFA) were extracted to investigate microbial communities. We used both the compound specific ¹⁴C and ¹³C signal of the PLFA to quantify carbon uptake from black slates and the glucose of the culture medium, respectively.The total carbon loss in these columns exceeded the amount of added carbon by approximately 60%, indicating that black slate carbon has been used. PLFA associated with Gram-positive bacteria dominated the indigenous community and took up 22% of carbon from black slate carbon, whereas PLFA of Gram-negative bacteria used only 8% of carbon from the slates. PLFA of Gram-negative bacteria and fungi were both mostly activated by the glucose addition. The added Schizophyllum did not establish well in the columns and was overgrown by the indigenous microbial community. Our results suggest that especially Gram-positive bacteria are able to live on and degrade black slate material. They also benefit from easy degradable carbon from the nutrient broth. In natural environments priming due to root exudates might consequently enhance weathering.     

Do reduction spots predate finite strain? A magnetic diagnosis of Cambrian slates in North Wales

The purple Cambrian slates of North Wales contain green-colored, irregular patches drawn out along cleavage and the more familiar ellipsoidal reduction spots that are parallel to cleavage. Because parallelism of pre-strain ellipsoids could only be produced by extremely high strain, we reject the hypothesis that these are strain markers. Here, we use magnetic methods to resolve this argument. The magnetic analysis reveals that the magnetic fabric of purple slate differs from the green variety of the slate only in the oxidation state, and indicates that the reduction process postdates cleavage. This suggests that the shape of reduction spots reflects the anisotropy of diffusion during reduction, not finite strain and alignment of an initially ellipsoidal object in the slates.     

Determination of deterioration of the main facade of the Ferit Paşa Cistern by non-destructive techniques (Konya,Turkey)

Building stones have long been one of the most widely used construction materials in the world. Building stones used in historical monuments are deteriorated partly or completely depending on the environmental and atmospheric effects. In recent years, non-destructive test methods have been used to assess deterioration of building stones used in historical monuments. Gödene stone is one of the building stones being widely used in the historical buildings in the Konya region, Central Anatolia. The most deterioration effects are observed in the Ferit Pa?a Cistern among the historical structures built with Gödene stone in the region. The aim of this study is to assess the deteriorating effects in the street façade of the Ferit Pa?a Cistern via non-destructive testing methods (Schmidt hardness rebound value, P-wave velocity, humidity measurement and thermal imaging) and create maps of deteriorated features. Turkey’s historic places are integrated to Turkish culture, efforts are made to conserve heritage through rehabilitation. Therefore, this study will help developers and federal managers during the project planning stage by providing technical data.     

Modelling the physical and chemical changes in roofing slate caused by weathering processes

This research identifies the changes which takes place in roofing slate due to natural exposure and tries to replicate these changes experimentally. Traditional methods of testing, used by the British and other national standards, concentrate on the properties of unweathered samples and give no information on the relative durability of the different slates. Instead of concentrating on the initial properties, this research focuses on changes in the properties in order to assess durability. The effects of natural weathering were assessed by comparing old, used slates with new slates from the same or a similar source. The new slates were then weathered experimentally by repeated cycles of wetting and drying, and the increase in water absorbency compared with that observed in naturally weathering. Mineralogical differences due to both natural and experimental weathering were also measured using X-ray diffraction analysis. It was found that the effects of experimental weathering, using repeated cycles of wetting and drying, are similar to those observed in natural weathering. These include increased water absorbency and loss of crystallinity of the principal minerals. The greatest changes are found in those slates which are the most vulnerable to weathering, making it possible to identify poor quality slates.     

Reconnaissance geology in Upper Chitral,Baroghil and Karambar districts (northern Karakorum,Pakistan)

During the summer of 1992 a geological expedition crossed the northern Karakorum range in northern Pakistan, from the Chitral to Karambar valleys, from the villages of Mastuj to Imit. Some of the areas visited were geologically unknown. A number of structural units were crossed, belonging to the Karakorum block or to other crustal blocks north of it. They are: (a) the axial batholith, in which three plutonic bodies have been identified, and (b) the northern sedimentary belt (NSB), in which three major tectonostratigraphic units form thrust stacks dipping to the north. Their internal stratigraphy and structural style are partly different. The most complete contains a crystalline basement, transgressed by a marine succession during the Early Ordovician. The youngest strata are represented by the Reshun conglomerate, of inferred Cretaceous age. The northernmost unit of the NSB is tightly folded, whereas the central one forms a monocline. Vertical faults, mainly strike-slip, dissect the thrusted slabs. Metamorphic deformation is absent or reaches only the anchizone in the studied sector of the Karakorum NSB. To the north of the Karakorum proper there are several other tectonic units, separated by vertical faults. They are, from south to north: (a) the Taš Kupruk zone, with metavolcanics of basaltic to latibasaltic composition; (b) the Atark unit, mostly consisting of massive carbonate rocks of Mesozoic age; and (c) the Wakhan slates which consist of a thick widespread succession of dark slates, metasiltites and sandstones. The fine-grained elastic rocks are supposed to be Palaeozoic to Early Triassic in age. The Wakhan slates are intruded by plutons belonging to the East Hindu Kush batholith, from which a single K/Ar age on muscovite gave a Jurassic age.     

Magnetic susceptibility anisotropy in the Cambrian slate belt of North Wales and correlation with strain

The magnetic susceptibility anisotropy of 275 specimens comprising 38 sites from the Cambrian slate belt in North Wales was measured to determine the magnetic fabric of the slates. The susceptibility ellipsoid is oblate for all sites, and the maximum/intermediate susceptibility plane always coincides with the cleavage plane of the slates which has a Caledonian strike and is nearly vertical. The maximum axes align sub-vertically and the intermediate axes sub-horizontally, trending NE-SW. The minimum susceptibility axes are normal to this foliation plane and coincide with the poles to the slaty cleavage. The orientations of the principal susceptibility axes are found to be in excellent agreement with the orientations of the principal strain directions, determined by X-ray goniometry on one of the samples from almost all of the sites. Correlation of the magnetic susceptibility anisotropy with predicted March strains (March, 1932) shows that the principal magnitudes of susceptibility can be related to those of the strain by: (for i = 1, 2, 3. The orthogonal principal axes), where χ_f and χ₀ are the final and initial susceptibilities along a given axis i and l_f and l_i are final and initial axial dimensions in the same direction i of a principal strain axis. The exponent a for the North Wales slates was found to be 0.145 ± 0.005. Knowledge of such a relationship may permit rapid approximate determinations of a petrofabric in similar rocks from their magnetic fabrics. However, the exponent a will probably have to be recalibrated for each rock type.     

Magnesium sulphate salts on monuments in Saxony (Germany): regional geological and environmental causes

A record of mortar and salt analyses from the last 20 years on various monuments in Saxony demonstrates the close relation between the occurrence of magnesium sulphate salts and the use of dolomitic lime mortars in a regional frame. The regional distribution scheme of dolomitic lime in historic mortars depends on the geological setting of the territory, i.e. the natural occurrence of dolomite deposits. Sulphation of these mortars with the formation of magnesium sulphate and gypsum is mainly due to environmental pollution, as can be shown by sulphur stable isotope analyses. Exposure of the sulphated mortar surfaces to rain leads to the preferential dissolution and advective transport of the novel formed magnesium sulphate salts, which effloresce or subfloresce on the mortar surface or can be accumulated in the structure of adjoining porous building materials like natural stones. These processes may cause severe damages in mortars by the weakening of the binder and in porous stones by salt crystallisation of phases like epsomite and hexahydrite.     

皖南歙县砚石板岩矿床地质特征及安全性研究

通过详实的野外地质调查,查明了皖南歙县双河口地区砚石板岩矿床的赋矿地层及成矿地质条件。砚石矿是层控型浅变质沉积岩矿床,赋存于新元古代大谷运组上段黑色板岩中。通过系统的室内岩矿鉴定和分析测试,查明了砚石的矿物组成、结构构造及砚石板岩的化学组成。通过野外放射性测量,判定该天然矿石放射性辐射属于安全等级,为皖南地区砚石资源开发提供了科学依据。     

印度尼西亚塔里亚布岛锡铁多金属矿床的地质地球化学特征与成因

印尼塔里亚布岛新近发现大型锡铁多金属矿床,初步探明铁储量超过l亿吨,全铁品位可达50%.塔里亚布岛锡铁多金属矿床以矽卡岩型与矿浆型为主,兼具热液型,构成一个完整的成矿系统.印支期二长花岗岩源自地壳部分熔融产生的岩浆,是矿床的主要成矿物质来源与控矿因素;岩浆经过高度的演化分异过程,生成富铁矿浆贯入充填成矿,主要赋存于花岗...