The Whole‐Rock Geochemical Composition of the Wudaogou Group in Eastern Yanbian,NE China–New Clues to Its Relationship with the Gold and Tungsten Mineralization and the Evolution of the Paleo‐Asian Ocean

The late Paleozoic Wudaogou Group, one of the oldest metamorphic units in the eastern Yanbian area, has important tectonic and metallogenic significance. Here, we provide new insights into their protoliths, tectonic setting of the metamorphic rocks and their relationships with the gold and tungsten mineralization, using new petrographic and whole‐rock geochemical data for various lithologies within the Wudaogou Group. The protolith of the metamorphic rocks of the Wudaogou Group was intermediate–basic volcanic rocks (e.g. basaltic andesite, trachyandesite, and basalt) and sedimentary rocks including argillaceous rocks, quartz sandstone, arkose and clayish greywacke, as well as pyroclastic sedimentary rock, covering tuffaceous sandstone. Before undergoing late Paleozoic epidote–amphibolite facies regional metamorphism, these protoliths were formed during the middle–late Permian in an island arc setting within a continental margin collage zone. Combined with the regional tectonic evolution, it can be speculated that the formation and the subsequent metamorphism of the protoliths of the metamorphic rocks from the Wudaogou Group were influenced by the change from subduction to collision of the Paleo‐Asian Ocean. Similarities of the rare earth element (REE) patterns and parameters among the metamorphic rocks within the Wudaogou Group, auriferous ores from the Xiaoxi'nancha gold (copper) deposit, and scheelites from the Yangjingou tungsten deposit, together with the favorable metallogenic element contents within the metamorphic rock series, imply that the Wudaogou Group could provide parts of metallic material for the gold and tungsten mineralization in the eastern Yanbian area, as exemplified by the Yangjingou deposit and Xiaoxi'nancha deposit, respectively. Further, the metamorphic sedimentary rocks, especially the metamorphic sandstones, quartz schists and quartz mica schists within the Wudaogou Group, have closer genetic relationships with the Yangjingou tungsten mineralization. However, the specific lithologies within this group which control the gold mineralization are still uncertain, and need further research.     

四川石棉县大水沟岩片绿片岩锆石SHRIMP U-Pb年代学及其地质意义

大水沟岩片位于安宁河深大断裂带中段, 川西松潘甘孜造山带与扬子地台结合部位, 因其特殊的构造位置和赋存碲矿床而备受重视.运用SRHIMP U-Pb定年技术对大水沟绿片岩进行年龄测试, 来确定大水沟岩片的形成时代, 为大水沟周缘石棉-冕宁一带乃至川西扬子地台西缘的构造岩浆演化提供有益信息, 同时为大水沟碲铋矿床的形成时代提供线索.大水沟原岩恢复表明其应当有相当部分为沉积岩, 运用SHRIMP U-Pb定年从中获得的5种不同年龄段具有内部结构、外观特征的锆石差异.2467~2358Ma年龄的残留碎屑岩浆锆石说明扬子地台西缘存在太古代-古元古代的物源搬运; 790.5~762.5Ma的岩浆锆石与新元古代早期Rodinia超大陆裂解、地幔柱上涌时的岩浆事件有关; 696.8~642.9Ma锆石年龄反映了大水沟周缘碰撞造山和后造山期岩浆活动和变质作用; 伴随峨眉地裂大规模基性岩浆活动, 在大水沟近源很可能有262.0~220.0Ma碱性杂岩的侵入; 典型热液增生锆石216.5~167.1Ma年龄揭示了该区中侏罗世大规模的岩浆期后热液活动.大水沟岩片可能为异地推覆系统, 岩浆锆石年龄和热液增生锆石年龄限制了大水沟岩片总体定位于220.0~167.1Ma之间.      

可控源音频大地电磁法在探测铝土矿中的应用

河南洛阳某工区的铝土矿赋存层位为石炭系本溪组,属开阔平坦的近陆滨海侵蚀平原沉积,位于中奥陶统马家沟组之上,层理不发育。铝土矿与其围岩有较大的电性差异,特别是铝土矿与其标志层奥陶系灰岩侵蚀面的电阻率值相差较大,达数千欧姆米乃至数万欧姆米。在可控源音频大地电磁法测绘的视电阻率反演断面图,铝土矿发育处电阻率曲线横向表现为不连续,呈现一明显的低阻异常,通过实际地质资料验证,可控源音频大地电磁法提供的铝土矿探测资料可靠。     

http://www.sciencedirect.com/science/article/pii/S1674987110000095

<正>Bauxite deposits are studied because of their economic value and because they play an important role in the study of paleoclimate and paleogeography of continents.They provide a rare record of the weathering and evolution of continental surfaces.Geomicrobiological analysis makes it possible to verify that microorganisms have played a critical role during the formation of bauxite with the possibility already intimated in previous studies.Ambient temperature,abundance of water,organic carbon and bioavailable iron and other metal substrates provide a suitable environment for microbes to inhabit.Thio-bacillus, Leptospirilum,Thermophilic bacteria and Heterotrophs have been shown to be able to oxidize ferrous iron and to reduce sulfate-generating sulfuric acid,which can accelerate the weathering of alumi-nosilicates and precipitation of iron oxyhydroxides.Microorganisms referred to the genus Bacillus can mediate the release of alkaline metals.Although the dissimilatory iron-reducing and sulfate-reducing bacteria in bauxites have not yet been identified,some recorded authigenic carbonates and "bacteriopyrites" that appear to be unique in morphology and grain size might record microbial activity.Typical bauxite minerals such as gibbsite,kaolinite,covellite,galena,pyrite,zircon,calcium plagioclase,orthoclase, and albite have been investigated as part of an analysis of microbial mediation.The paleoecology of such bauxitic microorganisms inhabiting continental(sub) surfaces,revealed through geomicrobiolo-gical analysis,will add a further dimension to paleoclimatic and paleoenvironmental studies.     

滇东南铝土矿成矿物质来源探讨

滇东南含铝岩系为上二叠统吴家坪组（龙潭组）底部和第四系,铝土矿床类型分原生沉积型和第四系岩溶红土堆积型两大类,成矿物质分别来源于峨眉山大火成岩省的基性玄武岩的风化、剥蚀、淋沥所形成的含铝土矿碎屑-红土物质,以及邻近的原生沉积型铝土矿的风化残积、残坡积。     

Rapid analysis with energy-dispersive X-ray fluorescence spectrometry for bauxite investigation on the Mambilla Plateau, North Eastern Nigeria

Bauxite exploration involves routine analysis of a large number of samples for a wide range of elements. In Nigeria, though geological field exploration for bauxite started almost three decades ago very little has been achieved, mainly due to the non-availability of facilities for evaluating the dozens of suspected bauxite deposits scattered around the country. In this regard, a procedure for the rapid, accurate and precise measurement of a number of important elements in bauxite has been developed based on the newly acquired radioisotope based EDXRF spectrometer. Elements and oxides analyzed are Al₂O₃, SiO₂, TiO₂, Fe₂O₃, K₂O, Mn, Co, Cu, Zn, Ga, Rb, Sr, Y, Zr, Nb and Pb. The richest bauxite sample has concentrations of 48.08, 18.90, 1.26, 7.71 and 1.93 wt% for Al₂O₃, SiO₂, TiO₂, Fe₂O₃, and K₂O, respectively. The other values in ppm are Mn (3 0 2), Co (5 3 2), Cu (45), Zn (51), Ga (41), Rb (32), Sr (2 2 2), Y (32), Zr (8 4 9), Nb (89) and Pb (72). The measurement errors in terms of accuracy and precision are less than 5% and 10% and 5% and 15% for major and trace elements, respectively. Statistical correlation analysis carried out on the results shows the most significant relationships to be the negative correlations of alumina with silica, iron oxide and titanium. This is believed to be related to the processes of formation of bauxite, with the Si and Fe–Ti being removed as Al was being enriched.     

豫西偃师龙门地区上石炭统本溪组含铝岩系矿物学特征及其原岩分析

以华北陆块南部豫西偃师县龙门镇地区全取芯铝土矿钻孔ZK4704为主要研究对象,通过岩芯观察和垂向上连续取样,运用扫描电镜、能谱分析、X射线衍射分析、差热分析、红外光谱分析等手段对本溪组含铝岩系的矿物学特征及其垂向变化规律进行了分析。研究表明,偃龙地区本溪组含铝岩系的矿物均为自生矿物,除后期重结晶作用的影响外,主要以隐晶质或微晶存在,矿物成分在垂向上具有明显的变化规律:下部和上部泥岩以粘土矿物为主,但下部泥岩以伊利石为主,上部泥岩以高岭石为主。中部铝矿物含量较高,粘土矿物含量较少。在上述分析基础上,以化学风化作用的基本原理和产生的条件为联结本溪组含铝岩系矿物学特征和原岩的纽带,分析了铝土矿的原岩。认为,可以迅速水解的火山灰是最有可能的含铝岩系的原岩,而由弱碱性的海相环境逐渐转变为弱酸性沼泽环境的海退序列可以很好地解释水解过程中化学环境的变化,含铝岩系基底强烈的古岩溶作用,可以为硬水铝石的产生提供良好的泄水条件。偃龙地区本溪组铝土矿的火山灰物源可由华北陆块北缘和我国西部地区同时期强烈活动的火山作用提供。     

Origin and Metamorphism of Corundum‐Rich Metabauxites at Mt. Ismail in the Southern Menderes Massif,SW Turkey

The corundum‐rich metabauxites, found at the northwest limb of an NE–SW‐trending isoclinal recumbent fold at Mt. Ismail, are enclosed in thick‐bedded platform‐type marbles of Late Cretaceous age, surrounding the polymetamorphic core series in the southern part of the Menderes Massif (SW Turkey). The metabauxite horizons observed as typically boudine‐like structure, extend laterally over c. 3 km and are 1 to 5 m thick. These rocks have dominant mineral assemblages of corundum (～50 modal %), chloritoid (～30 modal %), white mica (margarite, muscovite), diaspore, Fe–Ti‐Oxides (ilmenite, ilmenohematite, rutile), and goethite, limonite, pyrite, tourmaline (uvite, schorl) as minor phases. Chemical analyses of whole rock samples and the mineral assemblage indicate that coexisting minerals of metabauxites are highly aluminous. A number of minerals (e.g. chloritoid and margarite) display a large compositional variation reflecting the initial chemical inhomogenetiy of the karstbauxites. The field observations, trace‐element accumulation coefficients, concentration of elements such as Cr, Zr, Ga and Ni and low amounts of immobile elements all suggest that the studied corundum‐rich metabauxites can be classified as karstbauxites, and are more likely to be a product of weathering of intermediate igneous or argillaceous parental rocks, similar to the karstic Tauric bauxites in the Central Taurides (Seydi ?ehir region) and probably are similar in age (Cenomanian–Turonian). In respect of tectono‐metamorphic evolution, the studied corundum‐rich metabauxites were regionally metamorphosed at ～5–6 kbar pressure and 500–600°C as a consequence of the Barrovian metamorphism referred to as the ‘Main Menderes Metamorphism’ related to the ophiolitic obduction onto the Menderes platform from the Izmir–Ankara Suture during the Middle Eocene.     

贵州省务正道地区沉积型铝土矿床合理勘探网度的探讨——以务川大竹园铝土矿床为例

本文以务川大竹园铝土矿床为例,用100× 100 m和200× 100 m钻探工程网度分别与200×200 m钻探工程网度进行对比,对其矿体厚度、矿体形态、主要化学成份含量及资源量变化进行分析对比,100× 100 m或200× 100 m工程网度都能更好地控制矿体形态、厚度、空间位置和矿石质量.勘探网度放稀圈定矿体更为合理,达到了事半功倍的效果.因此,对务正道地区沉积型的铝土矿床勘探,不能机械地套用勘探工程网度,应根据规范合理加密工程控制,从而满足矿山开采设计和生产的要求.     

文山铝土矿A12O3测试中半二甲酚橙的作用

一水硬铝石及含刚玉（A12O3）铝土矿的测试较困难。NaF置换滴定法以二甲酚橙及半二甲酚橙较敏锐。可用半二甲酚橙（变色酸度在PH=5～6）直接调节酸度,再用作滴定的指示剂,效果较好。