Causes of Land Subsidence in the Kingdom of Saudi Arabia

The occurrence of land subsidence in the Kingdom Saudi Arabia is either natural or man-made. Natural land subsidence occurs due to the development of subterranean voids by a solution of host rocks in carbonate and evaporite terrains, over many areas of Saudi Arabia. Man-induced land subsidence is either due to the removal of groundwater in the agricultural areas or to wetting of unstable soils. Therefore, earth fissures and a lowering of the ground surface in unconsolidated sediments took place in alluvial plains and volcanic vent terrains. Unstable soils include Sabkha soils and loess sediments. These types of soils occur in coastal plains, desert areas and volcanic terrains. When this soil is wetted either during agricultural activities, waste disposal or even during a rain storm, subsidence takes place due to either the removal of salts from the Sabkha soil or the rearrangement of soil particles in loess sediments.     

热液矿床石英铅同位素组成及其地质意义

作者以若尔盖铀矿床为例，研究了含矿热液形成的石英脉石英的铅同位素组成，并将其作为联系母源铅同位素组成的桥梁，判别铀的来源。结果表明，矿床中石英铅同位素组成与含矿黄铁矿和中酸性构造－岩浆成因的花岗岩铅同位素组成具线性演化关系。由此提出含矿热液中的铀来自中酸性构造－岩浆岩而不是地层岩石的新见解，同时提出利用热液石英铅同位素组成判别非放射性矿床成矿元素来源的可能性。     

内蒙古镁铁质-超镁铁质岩型铜镍矿床成矿条件与找矿远景分析

按构造环境控岩控矿特点,划分区内铜镍型矿成矿(岩)带,分析成矿条件,研究了与该类矿床成矿有关的镁铁质岩、超镁铁质岩分布规律及铜镍硫化物成矿特征,提出了找矿方向和建议.     

“Three-Component” Digital Prospecting Method：A New Approach for Mineral Resources Quantitative Prediction and Assessment

“Three-component” method consists of three clase-connected aspects: geological anomaly,diversity of mineralization and mineral deposit spectrum. All these three concepts are not new separately, but it is a new approach to combine these three aspects in one single concept for quantitative mineral resources prediction and assessment and it is also the first time to conduct a more detailed study in each aspect. Investigation and clarification of geological anomalies, diversity of mineralization and spectrum of mineral deposits are realized by digitization and quantification of ore forming controlling factors, oreexisting symbols or marks, characteristics of mineralization and regulation of ore-genesis and laws of distribution. These procedures lead to construction of a “digital model“ for mineral resources prediction andassessment.     

Diagenetic paths in the margin of a Triassic Basin: NW zone of the Iberian Chain, Spain

Buntsandstein deposits generated in a slowly subsiding basin on the western margin of the Iberian Chain are represented by a stratigraphic succession of fluvial deposits less than 100 m thick (conglomerates, sandstones, and shales). Diagenetic processes in sandstones can be grouped as eodiagenetic, mesodiagenetic, and telodiagenetic. Eodiagenesis can be associated with Muschelkalk, Keuper, and probably early Jurassic times. Mesodiagenesis is probably related to Jurassic times. Diagenetic chemical reactions suggest a maximum burial less than 1.5 km and low temperatures (<120°C). Patterns of porosity reduction by compaction and cementation suggest four diagenetic stages: (1) Loss of primary porosity by early mechanical compaction; (2) early cementation (K-feldspar and dolomite); (3) dissolution of cements; and (4) framework collapse by re-compaction. These stages are manifested by the presence of two types of sandstone. Type I sandstones present high intergranular volume (mean, 30%). Type II sandstones are characterized by high compactional porosity loss and exhibit low values of intergranular volume (mean, 16.9%). Type II sandstones are associated with the dissolution of cement and later re-compaction of type I sandstones. An intermediate telodiagenetic phase is deduced and related to the sharp unconformity between Lower Cretaceous sediments and the underlying sediments. This suggests that a mechanically unstable framework collapsed during the Cretaceous, generating type II sandstones. The analyzed diagenetic paths have a wide applicability on similar marginal areas of rift basins.     

粘粒含量对甘肃黄土抗液化性能的影响

甘肃黄土是介于砂土与粘土之间的一种过渡性土壤,它具有砂土的某些特性,又具有粘土的某些特性,存在一定的粘塑性。通过对含粘粒黄土所做的实验研究,包括：粘粒含量不同的原状土样所做室内的动三轴试验、激光粒度分析试验、化学分析和电镜扫描,试验结果分析对比后,得出了含粘粒黄土抗液化性能的特性。并得出以下结论：（1）粘粒颗粒级配不同,也引起黄土动力稳定性的变化;（2）液化强度与粘粒含量并非呈单调增加关系,无论固结压力如何,粘粒含量Pc=15％左右时抗液化性能最低;（3）粘粒含量为一定值时,液化孔压比偏大,偏离这一值时,液化孔压比偏小。     

广西红土型金矿基本类型及找矿前景分析

广西红土型金矿是90年代初发现的一种新型金矿.文章通过对广西红色风化壳及红土型金矿分布的研究,依据含金红土类型及金矿源体矿化特征将全区红土型金矿划分为7 种基本类型;并结合其成矿环境和控矿条件的剖析,认为广西红土型金矿具有较好的找矿前景,提出碳酸盐岩类、火山岩类及蚀变构造岩类红土型金矿是广西红土型金矿的主攻类型,主攻地区为桂西百色-平果、桂中横县-贵港、桂西南凭祥-崇左等地.     

西藏甲玛-卡军果推-滑覆构造系特征

通过矿区填图和路线调查,结合室内研究,指出:①甲玛-卡军果推-滑覆构造系由印度-欧亚板块碰撞引发,具有递进变形、自盆地中心向边部推覆、新盖老等特点,强变形于50Ma±。②推覆体下盘为叶巴组构造岩系;推覆体由上侏罗统和下白垩统碳酸盐-碎屑沉积岩系构成,主体为轴面北倾的复式褶皱,自南而北分为前部带、中部带和后部带。滑覆构造系推覆形成的复背斜轴部高位岩块失稳向北滑覆形成,自南而北分为后部带、中部带和前部带。③导致矿区蚀变的主要岩浆活动发生于推覆强变形后的松弛期,上侵受近南北向基底断裂和推覆断裂联合控制,就位受控于前部带推-滑覆褶断系,其后发生多次构造-岩浆-成矿液叠加,造就甲玛铜多金属矿床。     

四川省巴塘县措普一带多金属成矿条件分析

义敦印支岛弧褶皱带地质构造演化复杂,岩浆活动十分活跃,成矿地质地球化学条件优越,金、银、铜、铅、锌、锡等金属矿产资源丰富。西南三江为有色、贵金属资源富集区,义敦为花岗岩型锡-银多金属矿集区。根据区域成矿环境及研究区成矿条件分析,找矿潜力巨大,有望取得找矿突破。     

山东地区黄土研究综述

山东地区黄土开始堆积时期普遍较晚,目前已见的剖面中,以青州傅家庄剖面堆积厚度最大(30 m以上),起始堆积时间最早,出露的最老层位为L9,TL测年时间约为0.8 Ma B.P.。山东地区黄土成因类型多样,物质来源广泛,其岩性特征与其他地区的黄土有明显的差别;在本地区内部,黄土的差异也比较明显,大体可分为两大成因分布区:渤海湾滨海与岛屿区和鲁中山前区。前者黄土粒度较粗,且普遍含有海相微体化石,其物质来源主要为末次冰期时期出露的渤海陆架物质,西北气流携带而来的内陆远源物质占次要地位。而后者黄土类型成因多样,东部的潍坊、青州黄土分布区,受到末次冰期时强劲冬季风的影响,物质来源主要为北部出露的渤海湾,向西至淄博、济南地区则已逐渐过渡为西北内陆风尘物质成分占据主导。