Geological,geochemical and mineralogical characteristics of REE-bearing Las Mercedes bauxite deposit,Dominican Republic

Bauxite deposits, traditionally the main source of aluminum, have been recently targeted for their remarkable contents in rare earth elements (REE). With ∑REE (lanthanoids + Sc + Y) concentrations systematically higher than ∼1400 ppm (av. = 1530 ppm), the Las Mercedes karstic bauxites in the Dominican Republic rank as one of the REE-richest deposits of its style.The bauxitic ore in the Las Mercedes deposit is mostly unlithified and has a homogeneous-massive lithostructure, with only local cross-stratification and graded bedding. The dominant arenaceous and round-grained texture is composed of bauxite particles and subordinate ooids, pisoids and carbonate clasts. Mineralogically, the bauxite ore is composed mostly of gibbsite and lesser amounts of kaolinite, hematite, boehmite, anatase, goethite, chromian spinel and zircon. Identified REE-minerals include cerianite and monazite-Ce, whose composition accounts for the steady enrichment in light- relative to medium- and heavy-REE of the studied bauxites.Considering the paleo-geomorphology of the study area, we propose that bauxites in the Las Mercedes deposit are the product of the erosion and deposition of lithified bauxites located at higher elevations in the Bahoruco ranges. Based on the available data, we suggest a mixed lithological source for the bauxite deposits at the district scale: bedrock carbonates and an igneous source of likely mafic composition.     

河南省新安县石寺-北冶地区铝土矿地球化学特征及成矿物质来源探讨

河南省新安县石寺-北冶地区铝土矿属典型的古风化壳沉积型铝土矿,矿体赋存于上石炭统本溪组.为研究该铝土矿及其基底碳酸盐岩及北秦岭伏牛山岩体的地球化学特征,对钻孔内3件铝土矿样品及3件含铝岩系基底碳酸盐岩样品进行了稀土元素测试,并结合碎屑锆石年代学研究成果,讨论铝土矿成矿物质来源.SiO2-Al2 O3-Fe2 O3三元图...     

黔北地区铝土矿找矿标志与找矿模式研究

在阐述了黔北务—正—道地区铝土矿成矿地质背景和成矿地质特征的基础上,总结了该区铝土矿的11个找矿标志：层位标志、底板岩性标志、含矿层标志、古侵蚀间断面标志、褶皱构造标志、地貌标志、植被标志、铝土矿标志、伴生矿产标志、脱硅、排铁标志、民采标志,进而初步建立了该区铝土矿的四个典型找矿模式：＂瓦厂坪模式＂、＂新木—晏溪模式＂、＂新民模式＂、＂三清庙模式＂。     

Sedimentation Patterns of Photosynthetic Bacteria Based on Pigment Markers in Meromictic Lake La Cruz (Spain): Paleolimnological Implications

Sedimentation fluxes of photosynthetic pigments and their derivatives, focused on the anoxygenic bacteria populations, were determined in meromictic Lake La Cruz over a three-year period using sediment traps. Bacterial settling occurs in pulses in response to lake dynamics. Two main annual events affect particle settling in Lake La Cruz: (1) Following an event of massive calcium precipitation in summer that caused water whiting, a maximum flux of chlorophyll a and derivatives towards the sediment was registered. Although whiting is accompanied by massive phytoplankton biomass sinking, it was not followed by concomitant photosynthetic bacterial sinking. (2) In contrast, the disruption of the chemocline and the contact of bacterial populations with oxygenated waters during autumn overturn provoked a destruction of the sulfur bacterial plate, causing mass mortality, registered in the settling material as photosynthetic pigments and their derivatives from phototrophic bacteria. Among the bacteriochlorophyll a oxidation products, bacterioviridin (bvir) was detected in high relative abundance in the settled material collected by sediment traps. The much increased flux of bvir after thermal overturn, associated with mass mortality of the purple sulfur bacterium, Amoebobacter purpureus, confirms the suitability of this molecule as a useful paleoindicator of the degree of oxygen exposure experienced by the purple sulfur bacteria population.     

Characterization of red mud derived from a combined Bayer Process and Calcining method for alumina refining

Red mud is the residue of bauxite processing for alumina. Red mud varies in physical, chemical and mineralogical properties due to differing mineral sources and refining processes adopted. In this project, red mud produced using a combined Bayer Process and Calcining （BPC） method was investigated. Red mud samples of varying ages were collected from the red mud storage facilities of the Zhenzhou Changcheng Aluminium Limited. The objective of this study is to （1） characterize the BPC red mud, and （2） examine the effects of this red mud on treating heavy metal-containing water and soil. Red mud samples were analyzed for pH, EC, water extractable salts and exchangeable basic cations, total element composition （by XRF）, mineral composition （by XRD）, micromorphological characteristics （by SEM） and thermogravimetric analysis （TGA）. The results show that the pH of the red mud decreased with increasing duration of storage time. The pH of the fresh, 5-year-old and 10-year-old red mud was 11.58, 10.56 and 9.61, respectively. Sodium dominated among the soluble cations, but the concentration of soluble Na decreased with increasing duration of storage time as a result of leaching. Cation exchange capacity as estimated from the sum of exchangeable cations also decreased with increasing duration of storage time, probably due to the decreasing pH which causes a reduction in negatively charged sites of the red mud. Calcium was the predominant exchangeable cation in the fresh red mud but the concentrations of exchangeable Ca markedly decreased in the old red mud which was dominated by exchangeable Na.XRF results showed that the red mud consists mainly of oxygen, calcium, iron, silicon, aluminium and titanium. Other important elements include sodium, carbon, magnesium and potassium. It is important to note that the red mud also contains elevated concentrations of radioactive elements, predominantly thorium （Th）, cerium （Ce） and rubidium （Rb）. XRD results showed that the major mineral types in the red mud were calcite, perovskite, illite, hematite and magnetite. There is a trend that the contents of magnetite decreased while the contents of hematite increased with increasing storage time, suggesting the conversion of magnetite to hematite. Observation using a SEM revealed that fresh red mud sample was amorphous while the 10-year-old red mud sample was fairly well crystallized. TGA results showed that the temperature at which the valley of weight loss occurred increased from 681.9℃ for fresh red mud to 722.9℃ for the 5-year-old red mud to 734.7℃ for the 10-year-old red mud. These results suggest that the contents of calcium carbonate increased with increasing storage time. Slow titration of the red mud samples with standardized acid solutions for two years indicated that the fresh red mud had an acid neutralizing capacity （ANC） of about 10 mol/kg while the ANC of old red mud samples was around 9 mol/kg. The ANC values obtained from the determination of BPC red mud here are much higher than those previously reported for red mud derived from the pure Bayer Process at the Queensland Alumina Limitd, Australia, and at the Pinggno Alumina Refinery, China.     

山东淄博铝土矿地质特征及成矿作用

山东淄博铝土矿,是一水硬铝石型沉积铝土矿.它在本区有两个层位,一个是中石炭世的浅海和滨海相地层,另一个是早二叠世的陆相湖沼沼沉积地层.通过分析该区铝土矿地质特征,探讨了本区的铝土矿的成矿作用,认为该区铝土矿经过红土风化成壳、密度流搬运沉积、矿质定位成矿、后生蚀变改造和表生氧化富集等五个成矿阶段.     

陕西铜川-韩城铝土矿带矿床地质特征及成矿规律

铜（川）-韩（城）铝土矿带位于陕西中部，已发现铝土矿床（点）数十处，探获铝土矿资源量1000多万t。笔者论述了矿带中主要矿区和矿体的地质特征，从控矿因素和成矿条件等方面分析了铝土矿成矿规律，提出进一步加强岩相古地理研究是该区扩大勘查成果的有效手段。     

云南红舍克铝土矿成矿地质特征和找矿前景研究

简述了云南红舍克铝土矿矿床的矿区地质概况,着重阐述了该矿区沉积型、堆积型铝土矿矿床地质特征、控矿因素及其作用。研究认为,在红舍克矿区外围的龙潭组含矿层及其附近的第四系堆积层分布范围内,是寻找沉积型、堆积型铝土矿的有利地段,并具有扩大铝土矿的找矿远景和资源量的潜力。     

小回线瞬变电磁测深勘查铝土矿试验

铝土矿含矿岩系与其基底灰岩存在明显的电性差异,是开展瞬变电磁测深工作的基本依据.利用小回线瞬变电磁设备在虎村等铝土矿区进行了剖面试验,分析了反演剖面的异常特征,认为高阻异常由铝土矿含矿岩系基底灰岩引起,其上界面与工程控制结果基本一致.