Surface-water quality for the Salí River watershed in NW Argentina

Spatial and temporal variations of Na, Mg, Si, K, Ca, SO₄^2-, Cl^-, HCO₃^-, Ag, Al, As, Au, B, Ba, Be, Bi, Br, Ce, Cd, Co, Cr, Cs, Cu, Dy, Er, Eu, F, Fe, Ga, Ge, Gd, Hf, Hg, Ho, I, La, Li, Mn, Mo, Nb, Nd, Ni, P, Pb, Pr, Rb, Sb, Sm, Sn, Sr, Ta, Tb, Te, Th, Ti, Tl, U, V, W, Y, Yb, Zn, and Zr were monitored through 37 sampling stations to determine the main aspects influencing the surface-water quality in the Salí River watershed (Tucumán Province, NW Argentina). The influence of the regional geological setting on water chemistry allows to distinguish three sub-basins. The interaction with sedimentary rocks was found to be dominant in the northern and central-eastern sub-basin as well as in the southern sub-basin, whereas the metamorphic-granitic basement of the Pampean Ranges was noted in the central sub-basin. In addition, anthropogenic activities affect the spatial variation of K, P, Mn, Rb, and Pb as well as dissolved oxygen concentrations and Eh. Temporal water-quality variation is related to the spatial distribution of precipitation and to the seasonal character of the main local industries (sugar cane, alcohol, citrus), increasing P and K concentrations and decreasing dissolved oxygen concentration and Eh in winter. Cl^-, Na, SO₄^2-, Al, As, B, Fe, Mn, Se and U concentrations exceed the regulated drinking-water thresholds at several sampling stations.     

STRUCTURAL CHARACTERISTICS OF THE NIUSHOU MOUNTAIN AND ITS GEOLOGICAL SIGNIFICANCE IN CENTRAL NINGXIA

There are many thrust-related structures occurring in the Paleozoic strata of the Niushou Mountain in the central part of Ningxia Hui Autonomous Region. The fault-related folds are the typical structures in this area. Based on the analysis about these structures and their relationships, the processes by which these structures of the Miboshan Formation were formed are reconstructed, and the strata underwent about three stages of deformation: (1) horizontal shortening, (2) folding, and (3) thrusting. And the fact that the Niushou Mountain is the leading edge of an old thrust sheet was proved, the Niushou Mountain, the Daluo Mountain and the Xiaoluo Mountain together constitute the front part of this old thrust zone, so the Niushou Mountain and the Ordovician strata in the central and southern parts of Ningxia now are likely allochthons. In the period from middle Ordovician to Devonian, the areas of the central and southern Ningxia belonged to the back-arc foreland basin of North Qilianshan orogen, which was adjacent to the continent in the north. In the later part of the early Paleozoic period, the Niushou Mountain was formed after the closure of the back-arc foreland basin.     

科尔沁沙地巴克窑地区近150年的环境演变*

在沉积和花粉分析的基础上,对科尔沁沙地东南部巴克窑地区过去150年的植被和环境演变进行了重建。巴克窑等湖泡的诞生时间是在上个世纪前期,约1837年前后。这个时间也正是科尔沁沙地东南部地区首次大规模人口移入和垦荒年代。突然增加的人类活动导致了沙丘植被的迅速破坏,而植被减少和沙丘活化引起区域水文循环的重新调整,即原来通过植物蒸腾作用输出的水量明显减弱,致使地下潜水位上升,形成一系列湖泡。以后,沙地系统的演化主要是在人类活动、气候和系统内部反馈机制的共同作用下完成的。     

综合物探在鄱阳湖铁路特大桥勘察中的应用

鄱阳湖铁路特大桥桥址位于鄱阳湖入长江的交汇处。该区地质情况复杂,断裂构造十分发育,因此地质勘探对桥址方案的比选显得尤为重要。此次有效地利用了综合物探,采用多种方法查明了岩性分区和地质构造格局,取得了良好的地质效果。充分显示了综合勘探、综合物探的优势。     

煤中黄铁矿的成因研究

本文在系统地研究四川晚二叠世高硫煤中黄铁矿矿物学的基础上，运用微区电子探针、中子活化、Ｘ光电子能谱和硫同位素等多 种方法综合地研究煤中黄铁矿的结构、成分、价态及同位素等成因标型特征，对黄铁矿标型特征进行了成因探讨，有效地判别了成岩期形成的Ｉ型脉状黄铁矿及后生热液Ⅱ型脉状黄铁矿。同时提出直接沉淀系列（自形晶→集合→聚晶）和复杂成因（微粒、莓粒→圆球→结核→团块）等两大类成因演化模式。它不仅对不同类型     

开发利用地理信息系统(GIS)综合分析地学信息进行矿产预测

众所周知,矿产资源预测是综合地学信息,进行优选靶区的有效手段之一。随着地学工作的深入和勘探技术的发展,已获取了大量的多源地学信息,如地质、地球物理、地球化学和遥感等资料。怎样从这众多的资料中提取有用信息进行综合分析,达到矿产资源预测的目的,一直是地学界探索的课题。过去,应用人工的方法来进行此项工作,不但费力、投资大,而且难以达到预期的效果,方法技术也不利于推广。如今,高速、高质量的计算机已趋于普及,使应用计算机技术高效地处理堆积如山的资料成为可能,尤其是近些年发展起来的地理信息系统(GIS),为综合处理地学资料的矿产资源预测的方法技术,开拓了广阔的前景。地理信息系统是一种计算机系统的应用软件,它集数据库管理和图像分析技术为一体,以空间数据迭加分析为重要特征。地学工作者进行矿产资源预测时,通常是从多源地学资料中提取有用信息,再应用专家知识,结合数学方法,如逻辑运算、贝叶斯(Bayes)规则等,建立预测模型,以模型的推理网格为线索,利用地理信息系统有效的空间分析手段,把各种证据图层综合迭加,最终产生以概率为指标的矿产资源预测图,高概率指示有利的矿产资源远景区,可作为勘探者和决策者进行勘查规划的依据。     

460铀矿床成矿构造背景

４６０矿床为一个大型斑岩型铀－钼矿床。晚侏罗世近东西向分布的火山岩系为铀元素的预富集打下了基础。白垩纪流纹斑岩为其主要的成矿母岩，可能为ＮＥ向展布。早第三纪末期的热液活动使铀进一步富集成矿，在区域应力场作用下，矿体呈ＮＷ走向。晚第三纪的表生淋积作用，使矿体上部近地表处形成次生富集带。基于上述研究，可以进一步明确此类矿床的找矿方向。     

The replacement of anthophyllite by jimthompsonite: a model for hydration reactions in biopyriboles

Anthophyllite crystals found in ultramafic lenses of the Lepontine Alps (Switzerland) contain coherent, submicroscopic intergrowths of ordered and disordered biopyribole polysomes. The chain width distributions of disordered polysomes were analyzed using high resolution transmission electron microscopy (HRTEM). Chains wider than triple were interpreted as intermediate products in the transformation of anthophyllite to the triple chain silicate jimthompsonite. The concentration of individual chain types is strongly correlated with the reaction progress. Based on observed zipper terminations and the transformation rules given by Veblen and Buseck (1980) a scheme of possible reaction paths leading from anthophyllite to jimthomp sonite is proposed. The reaction scheme and a simple kinetic model for elementary reactions allow modeling of the observed chain width distributions. The model suggests that the complex reaction paths involving steps with increasing and decreasing chain width are more important in the formation of jimthompsonite than the direct transformation from anthophyllite. The wide chains (>triple) occurring as intermediate products of the multi-step paths are structurally closer to talc than jimthompsonite. The back-transformation of these wide chains to triple chains is, therefore, a strong argument that jimthompsonite is a stable phase and not only a metastable intermediate product in the transformation of anthophyllite to talc. Received: 8 July 1996 / Accepted: 13 December 1996     

Geochronology, geochemistry and tectonic implications of Xiongshan diabasic dike swarm, northern Fujian

Sm/Nd isotopic age determination showed that Xiongshan dike swarm was at 585.7 Ma ± 30 Ma. The trace element geochemistry and Sr/Nd/Pb isotope gemhemistry studies indicate that the dike swarm was products of back-arc basin spreading ridge and the magma originated from the depleted mantle region which was metasomatized by LILE-rich liquids/melts derived from subduction slab. Project supported by the National Natural Science Foundation of China.