Relationships between major and trace elements during weathering processes in a sedimentary context: Implications for the nature of source rocks in Douala,Littoral Cameroon

In Douala (Littoral Cameroon), the Cretaceous to Quaternary formation composed of marine to continental sediments are covered by ferrallitic soils. These sediments and soils have high contents of SiO₂ (≥70.0 wt%), intermediate contents of Al₂O₃ (11.6–28.4 wt%), Fe₂O₃ (0.00–20.5 wt%) and TiO₂ (0.04–4.08 wt%), while K₂O (≤0.18 wt%), Na₂O (≤0.04 wt%), MgO (≤0.14 wt%) and CaO (≤0.02 wt%) are very low to extremely low. Apart from silica, major oxides and trace elements (REE included) are more concentrated in the fine fraction (<62.5 μm) whose proportions of phyllosilicates and heavy minerals are significant. The close co-associations between Zr, Hf, Th and ∑REE in this fraction suggest that REE distribution is controlled by monazite and zircon. CIA values indicate intense weathering. Weathering products are characterized by the association Al₂O₃ and Ga in kaolinite; the strong correlation between Fe₂O₃ and V in hematite and goethite; the affinity of TiO₂ with HFSE (Hf, Nb, Th, Y and Zr) in heavy minerals. The ICV values suggest mature sediments. The PCI indicates a well-drained environment whereas U/Th and V/Cr ratios imply oxic conditions. La/Sc, La/Co, Th/Cr, Th/Sc and Eu/Eu* elemental ratios suggest a source with felsic components. Discrimination diagrams are consistent with the felsic source. The REE patterns of some High-K granite and granodiorite of the Congo Craton resemble those of the samples, indicating that they derive from similar source rocks.     

造山带挤出构造与高压-超高压岩石剥露机制:以大别山为例

造山带挤出构造阐述了被边界断裂所围限的造山带深变质块体,在造山带内部垂向和(或)侧向应力的作用下折返变形的过程。研究主要集中在挤出块体的几何形态及其内部变形样式、边界断裂特征、挤出路径以及挤出动力来源等4个方面,其研究目的主要是为了解决造山带深变质岩石折返剥露的机制问题。依据挤出块体的挤出方向与造山带主体走向之间的关系,在三维球形坐标系Lx-Ly-Lz中,将造山带挤出构造大致分为7个端员类型(Ⅰ型～Ⅶ型)。其中Lx为造山带或俯冲带的主体走向;Ly呈水平方向并与Lx相垂直;Lz垂直于Lx和Ly所构成的平面。这些基本端员类型的组合及其之间的过渡类型可以详尽地诠释大别山印支期高压-超高压岩石的挤出过程。其中榴辉岩相挤出阶段介于Ⅳ型与Ⅶ型挤出构造之间,角闪岩相挤出阶段介于Ⅱ型与Ⅵ型挤出构造之间并可能具有渠道流挤出模式,而绿片岩相挤出阶段类似于Ⅴ型挤出构造。     

超基性岩中锆石年龄的特征和意义——以西南天山UHP蛇纹岩中锆石U-Pb年龄为例

超基性岩本身难以生长锆石的特性,使得研究其中的锆石需要特别谨慎。超基性岩中的锆石虽然具有多解性,但是锆石也携带了很多演化信息。产出不同地质背景的超基性岩,其中的锆石特征不同。本文总结现有的研究实例表明:(1)经历高温高压变质作用的石榴橄榄岩通常通过交代作用获得锆石,且锆石能够记录峰期变质时代,其中的继承锆石较少,可能在高温高压条件下,继承锆石发生分解重结晶;(2)大洋蛇绿岩型超基性岩和地幔岩捕掳体中通常具有年龄分布很广的锆石年龄特征,锆石年龄峰值通常与区域上构造事件相吻合,为捕掳晶锆石。接下来本文以西南天山超高压(UHP)蛇纹岩为例,对其锆石年龄进行解释。西南天山蛇纹岩为经历过超高压变质作用的大洋蛇绿岩型超基性岩,2个蛇纹岩样品中锆石的阴极发光图像分析和SIMS U-Pb定年分析结果显示,西南天山UHP蛇纹岩中的锆石包含捕掳晶锆石和变质锆石,捕掳晶锆石的年龄为2.1~1.0Ga,对应该区变泥质岩中碎屑锆石记录的年龄峰值。409~537Ma可能代表了蛇纹岩原岩结晶时代。区域上的变质压力峰期年龄(~320Ma)在蛇纹岩中没有记录,仅有1颗锆石记录了309±5Ma的近峰期时代。270~155Ma的退变质时代在西南天山蛇纹岩中出现较广,这与榴辉岩中出现的退变年龄相吻合,代表了折返过程中较为普遍的后期热液事件。基于对超基性岩中锆石特征的初步了解,结合西南天山蛇纹岩的研究实例,认为通过研究锆石的年代学,结合锆石矿物化学、包体矿物学、同位素地球化学等特征,不仅可以提供年代学信息,还可以对超基性岩的来源和演化过程进行解析。     

Petrogenesis and geotectonic setting of the PanAfrican basement rocks in Bamenda Massif, Obudu Plateau, southeastern Nigeria： Evidence from trace element geochemistry

1 IntroductionThe study area is part of the Obudu Plateau,which forms part of the Precambrian Pan-African tec-tonothermal belt, lying between the West African Cra-ton and the Gabon-Congo Craton ( Fig. 1). It isbounded by the Benue Trough, in the NE-SW axi…     

An investigation into strength and porous properties of metamorphic rocks in the Himalayas: A case study

If a rock is porous in nature, the genetic complexity associated with its petrofabric makes it difficult to predict its behavior. Here, a comprehensive study of the porous nature, physical and geotechnical responses of three varieties of schist, i.e. quartz mica schist, quartz mica schist with quartz veins and biotite schist of low grade metamorphism obtained from Nathapa-Jhakri hydroelectric project site in the foot hills of Himalayas, India, has been presented. The porous nature of the schists has been brought out through the Mercury Intrusion Porosimetry (MIP) testing and strength behavior through uniaxial testing. Through an experimental invesigation, the porous nature and pore size distribution parameters from MIP, which are closely related to the strength and performance of metamorphic schistose rocks, have been studied. The significance of the porous nature and its response for consideration in the design is emphasized.     

Accumulation and sources of heavy metals in urban topsoils: a case study from the city of Xuzhou, China

The knowledge of the variability, the anthropogenic versus natural origin and corresponding environmental risk for potentially harmful elements in urban topsoils is of importance to assess human impact. The aims of the present study were: (1) to assess the distribution of heavy metals (Sn, Li, Ga, Ba, Fe, Mn, Co, Be, Ti, Al, Hg, Cr, Sb, As, Bi, Pd, Pt, Au, Ni, Cd, Zn, Cu, Pb, Se, Mo, Sc and Ag) in urban environment; (2) to discriminate natural and anthropogenic contributions; and (3) to identify possible sources of pollution. Multivariate statistic approaches (principal component analysis and cluster analysis) were adopted for data treatment, allowing the identification of three main factors controlling the heavy metal variability in Xuzhou urban topsoils. Results demonstrate that Hg, Cr, Sb, As, Bi, Pd, Pt, Au, Ni, Cd, Br, Zn, Cu, S, Pb, Se, Mo, Sc and Ag could be inferred to be tracers of anthropogenic pollution, whereas Al, Ti, Ga, Li, V, Co, Pt, Mn and Be were interpreted to be mainly inherited from parent materials. Iron, Ba, Sn, Pd and Br were interpreted to be affected by mixed sources.     

Correlation between magnetic susceptibility and heavy metals in urban topsoil: a case study from the city of Xuzhou, China

Anthropogenic influence, mainly due to urban and industrial activities and traffic exhaust, may affect urban topsoil via atmospheric contamination and solid waste. Magnetic susceptibility measurements were conducted on 21 urban topsoil samples from the city of Xuzhou, China. High intensities of magnetic susceptibility were detected in the majority of the samples. SEM analysis shows that magnetic minerals are in the form of spherules and mainly due to anthropogenic inputs. The heavy metals Pb, Cu, Zn, Se, Sc, Mo, Fe, and Bi show strong correlations with magnetic susceptibility, and Ag, Ba, Cd, Ni, Cr, Sb, and Sn, on the other hand, show a weak correlation with magnetic susceptibility. Whereas, of these metals studied, only Hg has no significant correlation with the susceptibility. The Tomlinson pollution load index (PLI) also shows significant correlation with the susceptibility (χ). The present study shows that magnetic susceptibility is a fast, inexpensive, and non-destructive method for the detection and mapping of contaminated soils.     

Transport and sediment–water partitioning of trace metals in acid mine drainage: an example from the abandoned Kwangyang Au–Ag mine area, South Korea

Transport and sediment–water partitioning of trace metals (Cr, Co, Fe, Pb, Cu, Ni, Zn, Cd) in acid mine drainage were studied in two creeks in the Kwangyang Au–Ag mine area, southern part of Korea. Chemical analysis of stream waters and the weak acid (0.1 N HCl) extraction, strong acid (HF–HNO₃–HClO₄) extraction, and sequential extraction of stream sediments were performed. Heavy metal pollution of sediments was higher in Chonam-ri creek than in Sagok-ri creek, because there is a larger source of base metal sulfides in the ores and waste dump upstream of Chonam-ri creek. The sediment–water distribution coefficients (K _d) for metals in both creeks were dependent on the water pH and decreased in the order Pb ≈ Al > Cu > Mn > Zn > Co > Ni ≈ Cd. K _d values for Al, Cu and Zn were very sensitive to changes in pH. The results of sequential extraction indicated that among non-residual fractions, Fe–Mn oxides are most important for retaining trace metals in the sediments. Therefore, the precipitation of Fe(–Mn) oxides due to pH increase in downstream sites plays an important role in regulating the concentrations of dissolved trace metals in both creeks. For Al, Co, Cu, Mn, Pb and Zn, the metal concentrations determined by 0.1 N HCl extraction (Korean Standard Method for Soil Pollution) were almost identical to the cumulative concentrations determined for the first three weakly-bound fractions (exchangeable + bound to carbonates + bound to Fe–Mn oxides) in the sequential extraction procedure. This suggests that 0.1 N HCl extraction can be effectively used to assess the environmentally available and/or bioavailable forms of trace metals in natural stream sediments.     

Effects of fracture lineaments and in-situ rock stresses on groundwater flow in hard rocks: a case study from Sunnfjord, western Norway

Systematic field mapping of fracture lineaments observed on aerial photographs shows that almost all of these structures are positively correlated with zones of high macroscopic and mesoscopic fracture frequencies compared with the surroundings. The lineaments are subdivided into zones with different characteristics: (1) a central zone with fault rocks, high fracture frequency and connectivity but commonly with mineral sealed fractures, and (2) a damage zone divided into a proximal zone with a high fracture frequency of lineament parallel, non-mineralized and interconnected fractures, grading into a distal zone with lower fracture frequencies and which is transitional to the surrounding areas with general background fracturing. To examine the possible relations between lineament architecture and in-situ rock stress on groundwater flow, the geological fieldwork was followed up by in-situ stress measurements and test boreholes at selected sites. Geophysical well logging added valuable information about fracture distribution and fracture flow at depths. Based on the studies of in-situ stresses as well as the lineaments and associated fracture systems presented above, two working hypotheses for groundwater flow were formulated: (i) In areas with a general background fracturing and in the distal zone of lineaments, groundwater flow will mainly occur along fractures parallel with the largest in-situ rock stress, unless fractures are critically loaded or reactivated as shear fractures at angles around 30° to σ_H; (ii) In the influence area of lineaments, the largest potential for groundwater abstraction is in the proximal zone, where there is a high fracture frequency and connectivity with negligible fracture fillings. The testing of the two hypotheses does not give a clear and unequivocal answer in support of the two assumptions about groundwater flow in the study area. But most of the observed data are in agreement with the predictions from the models, and can be explained by the action of the present stress field on pre-existing fractures.     

滇东北麻栗坪铅锌矿床微量元素分布与赋存状态:LA-ICPMS研究

位于扬子板块西南缘的"川滇黔接壤铅锌矿集区"是我国西南大面积低温成矿域的重要组成部分,麻栗坪铅锌矿床位于该矿集区昭通-曲靖成矿带中段,是近年来滇东北地区新发现的铅锌矿床。本文以麻栗坪铅锌矿不同硫化物为研究对象,通过LA-ICPMS原位点测试和元素Mapping分析,尝试揭示该矿床中Ge、Cd和In等微量元素在不同硫化物中分布规律与赋存状态。本次研究发现,麻栗坪矿床不同硫化物中富集的微量元素明显不同,闪锌矿主要富集Mn、Cu、Sn、Cd、In和Ge,而方铅矿主要富集Ag、Sb和Se,黄铁矿则富集As、Co和Ni。闪锌矿是分散元素Ge、In和Cd的主要载体矿物,且Cd、Ge、In、Mn、As、Sb和Ag以类质同象形式赋存于闪锌矿中;而Cu则主要以类质同象形式存在,部分Cu以黄铜矿的显微包裹体形式赋存于闪锌矿中,其中以类质同象赋存于闪锌矿中Cu和Ge呈现明显的相关性,可能暗示其与Zn的置换方式为:3Zn2+Ge4++2Cu+。总体上,该矿床闪锌矿以富集Cd、Ge,贫Fe、Mn、Co、Sn为特征,这些微量元素组成与典型MVT型矿床基本一致,明显有别于喷流沉积和岩浆热液型矿床,而与中低温条件下形成的闪锌矿微量元素组成相似。结合该矿床后生成矿特征明显等地质地球化学研究成果,我们认为该矿床应属于MVT型铅锌矿床。值得注意的是,该矿床闪锌矿相对富集In,可能暗示其形成具有特殊性,这可能与其成矿流体在长距离运移过程中所流经地层有关,该类流体活化萃取了基底地层的中-酸性岩浆岩或火山碎屑岩中的In,致使矿床中闪锌矿相对富集In。     

Ecological environment response of benthic foraminifera to heavy metals and human engineering: A case study from Jiaozhou Bay,China

The estuary and coastal zone are the key areas for socio-economic development,and they are also the important channels for pollutants transported to the sea.The construction of the Jiaozhou Bay Bridge changed the hydrodynamic condition of the bay,which made the self-purification capacity of the bay weakened and the pollution in the estuary and adjacent coastal zone become more serious.In this study,55 surface sediment samples were collected from the three seriously polluted estuaries and the adjacent coastal zone of Jiaozhou Bay to comprehensively study how the benthic foraminifera response to heavy metal pollution and human engineering,and to assess the ecological risks of the bay.A total of 80 species,belonging to 42 genera,were identified in this study.The results showed that Cu,Pb,Cr,Hg,Zn,and As had low to median ecological risks in the study area which would definitely affect the ecological system.The construction of the Jiaozhou Bay Bridge has resulted in pollutants accumulated at the river mouth of Loushan River,which has adverse effects on the survival and growth of benthic foraminifera.The lowest population density and diversity as well as the highest FAI(Foraminiferal Abnormality Index)and FMI(Foraminiferal Monitoring Index)occurred at Loushan River Estuary which indicated that the ecological environment of the northeastern part of Jiaozhou Bay(Loushan River Estuary)had been seriously damaged.Licun River and Haipo River estuaries and the adjacent coastal zone were slightly polluted and had low ecological risk.As a consequence,it suggested that the supervision of industrial and domestic waste discharge and the protection of the ecological environment in northeast Jiaozhou Bay should be paid more attention.     

典型内陆湖泊沉积物氮、磷和重金属分布特征及生态风险评价——以武汉市武湖为例

城市内陆型湖泊湿地对城市生态系统具有重要的作用。以武汉市武湖为例,采用数理统计、营养盐指数、地累积指数和潜在生态风险指数等方法,对武湖表层沉积物中的氮、磷、有机质和重金属的平面分布特征、影响因素、富集污染程度、生态风险进行评价。结果表明: 武湖西北部表层沉积物中总氮、总磷和有机质的含量明显高于东南部,武湖周边地表径流和农田是营养元素的主要来源,旱地较水田有利于沉积物中总磷的富集; 武湖沉积物中有机质为内源水生植物和外源陆生植物的混合来源,与总氮具显著正相关关系; 沉积物中重金属含量总体较低,局部呈现高镉,平面上总体北部高于南部; 沉积物中重金属富集程度和潜在风险较低,局部地区镉和铅为轻微富集,镉和汞具中等潜在风险; 沉积物的潜在生态风险为低至中等,潜在生态风险与沉积物中镉的分布高度一致。     

贫Cd碳酸盐岩发育土壤Cd的富集与超常富集现象——以贵州岩溶区为例

通过对贵州岩溶区19条风化剖面Cd分布特征的研究, 初步揭示了贫Cd碳酸盐岩发育的土壤中Cd的富集机制及Cd含量的约束因素。①贫Cd基岩发育的土壤同样可以导致Cd的明显富集, 甚至超常富集, 且含量峰值通常位于土壤层底部(T1)。②Cd在基岩中通常优先赋存在酸不溶相, 另一方面, 由于基岩酸不溶物含量一般极低, 酸溶相的Cd占全岩Cd的比例仍处于绝对优势。在富Cd的基岩酸不溶物基础上, 叠加了来自酸溶相中Cd的贡献, 是岩溶区土壤Cd普遍富集的原因。③土壤中Cd的含量与其在基岩或基岩酸不溶物中的含量均不相关。T1中Cd的含量受制于Cd在基岩酸不溶物中的含量、基岩酸溶相Cd占全岩中Cd的质量百分数、T1中Cd的亏损率的共同约束。有利于Cd在T1中超常富集的最佳条件是: Cd在基岩酸不溶物中含量高、基岩酸溶相Cd占全岩中Cd的比例大、T1中Cd的亏损率小。另外, 对于由基岩酸不溶物残余累积形成的土壤层, T1为其发育起点, Cd在T1中含量高, 通常在土壤层中也高, 反映出一般风化剖面的发育特征。研究结果可以深化对岩溶环境Cd地球化学行为的认识, 为区域上基于地质成因开展Cd污染风险评价及建立其清洁水平提供参考。     

花岗质岩浆岩土壤重金属地球化学特征及生态风险评价——以云南盈江旧城—姐冒地区为例

基于云南盈江旧城—姐冒地区238件岩石样品和4 931件土壤样品,与其他地质单元对比,重点研究花岗质岩浆岩岩石和土壤中重金属地球化学特征和来源,并进行土壤重金属生态风险评价。结果表明:花岗质岩浆岩和高黎贡山岩群(Pt1GL.)具有相似的物源或继承性,二者岩石中Pb含量相对上地壳偏高,而其他重金属含量较低;第四系(Qa)、芒棒组(N2m)和高黎贡山岩群(Pt1GL.)土壤重金属含量和变化特征与花岗质岩浆岩基本一致,且土壤重金属含量明显低于第四系(Qb)和关上组(D1g)地层;结合岩性组分看,成土母质可能均以花岗质岩浆岩为主;花岗质岩浆岩和关上组(D1g)土壤重金属含量主要受自然源影响,人为活动影响相对较小;地累积指数和潜在生态风险指数表明花岗质岩浆岩土壤重金属生态风险小,为清洁土壤;德宏州地区具有粮、糖、蔬菜等生产功能的农田土壤成土母质以花岗质岩浆岩为主,但相关工作程度低。通过对比研究认为,德宏州地区具有发展绿色、无公害食品产地的巨大潜力。     

基于生物可利用性与宽浓度范围的Hakanson潜在生态风险指数法的创建——以小秦岭金矿区农田土壤为例

Hakanson潜在生态风险指数法是土壤重金属潜在生态风险评价的一种常用方法,研究与实践证明其有效性的同时,也发现了其不足之处:忽略了土壤重金属不同形态之间潜在生态风险的差异,且只重视重金属含量高于参考值时的生态风险,而对低于参考值时的情况没有给予考虑,以致特定情况下的评价结果不能很好地反映实际生态风险,因而有必要创建适用性更广的Hakanson潜在生态风险指数法。为此,基于全过程控制优化的思想,引入了生物可利用性毒性系数,并将修正浓度与参考值差值引入计算公式,创建了基于生物可利用性与宽浓度范围的Hakanson潜在生态风险指数法,实现了对重金属不同形态风险贡献的差异及重金属浓度低于参考值情况下潜在生态风险的准确把握。以小秦岭金矿区为典型区域,辅以对采集土样重金属总量及5种形态含量的分析,开展案例研究。结果表明,基于生物可利用性与宽浓度范围的Hakanson潜在生态风险指数法能客观地揭示土壤重金属的潜在生态风险,具有更大的适应性,是一种有效的潜在生态风险评价方法。     

Controls of oil family distribution and composition in nonmarine petroleum systems: A case study from Inner Mongolia Erlian basin,Northern China

The Erlian basin is a continental rift basin located in Inner Mongolia, Northern China. It is a typical representative of Cretaceous Northeast Asian Rift System, which includes many small petroliferous basins in Mongolia Republic and Northern China. Although Lower Cretaceous source rocks are understood to be most important in the Erlian petroleum systems, the precise identification of these source rock intervals and their determination on oil families distribution and composition are poorly understood in this tectonically complicated, nonmarine basin. New bulk data have been gathered from source rock intervals, oil sands and crude oil samples in eight main oil-producing subbasins. Geochemical analyses indicate that Lower Cretaceous Aershan formation (K₁ba) and Tengger 1 formation (K₁bt₁) are two main source intervals in the Erlian basin and their source rock facies vary from profundal lacustrine to marginal lacustrine according to biomarker and trace elements calibration, the profundal lacustrine facies is characterised by brackish water and anoxic environment, which is similar to their correlative oils (Family 1 oils). The marginal lacustrine facies is characterised by freshwater and suboxic environment, which sourced the most common Family 2 oils. Meanwhile, different maturation processes exercise the second control on oil groups and their compositions, the profundal lacustrine source rocks characterised by their sulphur-rich kerogens lead to two oil groups (group 1 and group 2 oils), whose maturity range from low to normal; while, the marginal lacustrine source rock only lead to normal-maturity oils. At last, biodegradation affected the composition of a certain oils and formed group 4 heavy oils. In addition, short migration distance in small subbasins made the contamination or fractionation less notable in the Erlian basin.     

过程响应理论及其在湖相碳酸盐岩中的应用——以辽河西部凹陷中北部地区Es_4为例

过程响应理论是在地球系统科学基础上提出的一种盆地沉积学研究方法,主要包括过程研究和响应研究两个方面,强调盆地演化过程对其沉积过程的控制意义。论文运用过程响应理论对辽河坳陷西部凹陷中北部地区Es4碳酸盐岩进行了研究,取得了很好的效果。研究表明,湖相碳酸盐岩的形成和分布在时间和空间上受湖盆演化过程控制明显,有利的地形和水动力条件、有利的气候和水介质条件、有利的物源和白云岩化条件,这三个关键要素,共同铸就了辽河坳陷西部凹陷中北部地区Es4湖相碳酸盐岩的沉积环境。运用过程响应理论,综合考虑碳酸盐岩沉积作用关键三要素,是建立更具指导作用和更具参考价值的湖相碳酸盐岩综合沉积模式的基础。     

重金属高背景区水稻镉积累与健康安全风险评价：以云南省会泽县娜姑镇为例

调查发现,重金属高背景区存在土壤中的镉含量超标,而农作物中的镉含量并未超标的现象,但对其原因知之甚少。开展区内农作物镉积累研究并探寻制约农作物镉吸收的因素,对土壤环境质量评价和污染土地生态修复都具有重要意义。以云南省会泽县娜姑镇娜姑坝子为研究区,采集了水稻籽实和配套土壤样品各41件,采用ICP-MS方法检测了Cd含量。通过偏相关、R型聚类、逐步线性回归等分析了水稻镉与土壤元素（指标）之间的相关关系。结果显示,水田土壤镉（Cd）含量为 0.467~1.87 mg/kg,平均为 0.78 mg/kg,是全国土壤背景值的 5.69 倍,58.5% 的样品超过农用地土壤污染风险筛选值。水稻（糙米）镉含量为 0.007~0.062 mg/kg,平均 0.016 mg/kg,均低于食品安全国家标准限值。水稻镉与土壤铀（U）、钼（Mo）等呈显著正相关,与土壤有机碳（TOC）、硫（S）等呈显著负相关,与土壤 Cd 总量和酸碱度（pH）无显著相关性。土壤镉超标而水稻镉不超标的现象可能与土壤富含有机碳有关,该地区土壤有机碳（TOC）含量达全国背景值的5.57倍。当 TOC > 3% 时,水稻镉含量迅速下降。据此提出土壤镉环境等级的有机碳修正方法,将研究区3.42 km2（5129 亩）Ⅱ等水田修正为Ⅰ等。此外,还提出了一些土壤养护和修复的建议。     

新疆阿尔泰可可托海矿区伟晶岩成因与矿化潜力研究：来自石英SEM-CL和微量元素的指示

新疆阿尔泰可可托海3号脉矿床是世界瞩目的伟晶岩型稀有金属Li-Be-Nb-Ta-Rb-Cs-Hf矿床。尽管前人对3号脉伟晶岩矿床已经进行了大量的研究工作, 然而在伟晶岩稀有金属成矿潜力以及伟晶岩成因问题上仍存在一些争议。本文以发育在可可托海矿区不同规模的伟晶岩脉以及淡色花岗岩为研究对象, 利用石英SEM-CL和原位微量元素技术手段, 查明各伟晶岩脉和花岗岩的稀有金属禀赋差异及成因联系。研究结果表明, 石英的Li和Al含量可以用来指示伟晶岩的矿化潜力。与1号和2号伟晶岩脉相比, 3号伟晶岩脉具有更宽的分异范围, 以石英中Ge/Ti变化于1.83×10^-6~159×10^-6范围为特征, 更高的Li含量, 其中外侧带平均Li含量为39×10^-6, 因而成矿潜力最大。此外, 证实了白云母钠长花岗岩为矿化花岗岩, 其微量元素组成和演化程度与3号脉伟晶岩外侧带相当, 而白云母碱长花岗岩为贫矿花岗岩。更重要的是, 本文利用各伟晶岩结构分带内的石英中Ge/Ti-Ge以及Ge/Ti-Al/Ti图解, 确定了各伟晶岩脉具有相似的演化趋势, 指示它们可能源于相同的花岗岩母岩。与世界上典型的RMG(花岗岩浆演化后残余熔浆结晶)和DPA(直接深部地壳熔融)成因的伟晶岩相比, 可可托海矿区含矿伟晶岩和花岗岩中石英微量元素与RMG成因伟晶岩存在地球化学亲和性, 这指示它们来源于花岗质岩浆的残留熔浆。

     

隐伏斑岩铜矿区微细粒土壤地球化学特征及其找矿指示意义-以福建罗卜岭铜钼矿为例

在风化壳覆盖区应用传统化探方法和矿物地球化学找矿方法开展斑岩型矿床深部找矿存在一定制约。土壤微细粒分离测量技术是一种可应用于覆盖区找矿的穿透性地球化学勘查技术,在干旱地区已取得良好的应用效果,亟需开展多景观、多矿种应用试验。基于此,本文选择为红土风化壳覆盖的福建省罗卜岭斑岩铜钼矿为研究区,开展风化壳土壤微细粒分离测量技术有效性实验。结果显示,与不含矿酸性岩体风化壳相比,研究区明显富集铜钼矿成矿及伴生元素,尤其是Mo、Cu、Au显著富集,与此同时,含矿岩体风化壳中元素变异系数较低,符合斑岩型矿床元素含量富集系数高、变异系数低的典型特征。元素空间分布特征与矿化蚀变、断裂构造、地形演化密切相关。Cu-Mo异常可以圈定矿化中心蚀变带,V、Hg则在外蚀变带富集。Cu与Mo在研究区西北部的分异指示了紫金山矿田由SE向NW主成矿作用由Cu-Mo演变为Cu-Au。元素剖面分布特征进一步验证了成矿蚀变、地形演化对元素分布的控制作用。地形演化决定了蚀变带在地表的分布,进而控制元素的分布。罗卜岭铜钼矿体呈马鞍状分布于古背斜两翼,在后期风化剥蚀作用下,背斜核部演化为负地形,使得中心蚀变带接近出露地表,表现为Cu的正异常;古背斜两翼现今为正地形,矿体埋深较大,前缘晕元素Hg表现为正异常。因子分析结果很好地展示了元素的组合与分异特征。总体上,可以根据Cu-Mo异常判断矿体中心位置,根据Hg判断矿体埋深,根据Sn、V、Cr等识别花岗闪长斑岩体边界。本研究系统证明微细粒土壤测量在风化壳覆盖区探测隐伏斑岩铜钼矿的有效性。