Types and distribution of silver ore deposits in China

Silver is generally recovered as a by- and co-product along with Au, Pb, Zn, Cu, Sb, Bi, Hg, Sn and W from polymetallic and gold mines in China. Chinese silver deposits can be classified into five principal types according to host rocks. These types and their host rocks are: (1) marine volcanic-sedimentary rocks hosting (la) massive sulfide Pb-Zn-(Cu)-Ag ores and (1b) stratiform Ag-(Au) ores; (2) continental volcanic-sedimentary rocks containing (2a) various polymetallic-silver veins and/or stockworks, and (2b) Ag-(Au) veins in pyroclastic rocks; (3) rocks affected by metasomatic processes including (3a) complex Sn-polymetallic-Ag ores, (3b) Pb-Zn-(Cu)-Ag skarns, (3c) associated W-Ag quartz veins and/or skarns, and (3d) Ag-(Au) zones and veins in altered carbonate rocks; (4) metamorphic-intrusive rocks, principally Ag-(Au) veins in sheared and brecciated metamorphic rocks; and (5) sedimentary rocks including (5a) stratiform Pb-Zn-Ag ores in carbonate rocks, (5b) Ag-V mantos in black shales, and (5c) Cu-(Ag) layers in red sandstones. A sixth grouping includes gossans. The tectonic settings, geological features, and temporal and spatial distribution of these different types of silver occurrences indicate that silver mineralization reflects to a great extent the evolution of tectonic environments in China throughout geological time. Type 1 is generally developed in association with several fold belts from the Caledonian to Yanshanian orogens, while types 2, 3 and 4 correlate with rejuvenation of the eastern China continent during the Mesozoic period. The three subgroups of type 5 are recognized in different stages and various sedimentry and diagenetic environments during the development of paraplatforms and fold belts. Type 6 results from recent weathering of existing sulfide ores or protores. Editorial handling: DR     

滇西昌宁─孟连带南部地层地质问题

滇西孟连以南，整合于南段组浊积岩之上的拉巴群硅质岩含晚二叠世早期放射虫化石，南段组时代不仅限于石炭纪，可能延入二叠纪。二者为晚古生代思茅地块的外陆坡沉积。其西面的南基河杂岩（新名）由层序混乱的晚古生代硅质岩、泥岩和少量砂岩、玄武岩构成。放射虫化石证据表明，硅质岩时代不仅限于晚泥盆世－早二叠世，还延入晚二叠世，而有的砂岩时代为早石炭世，它们是经过强烈构造变动的古特提斯洋的沉积记录。昌宁－孟连带向南可能延至泰国北部的清迈带，而非东北部的难河带。     

周期性潮积岩及其研究意义

回顾了最近十余年来国外对周期性潮汐沉积物，特别是潮汐韵律层的研究进展，系统介绍了几种从古代沉积物中识别出来的潮汐周期，包括基本潮汐（半日潮，全日潮和混合潮），大一小潮周期以及一些长周期波动等。最后，对潮汐韵律层在推测地史时期地－月系的演化历史及计算短期沉积速率中的意义作了评述。     

内蒙古白银都西群变质火山岩的钕、锶同位素研究

白银都西群主要由斜长角闪岩、变粒岩、长英片岩和条带状混合岩组成,是白银都西-白乃庙地体的重要组成部分,主要分布在内蒙古白乃庙铜(金)矿床东北白银都西一带。长期以来,由于缺乏可信的同位素年龄数据,该套岩层的归属,构造性质和形成机理尚不清楚。笔者首次对白银都西群斜长角闪岩的Nd和Sr同位素组成进行了测定,所获Sm-Nd同位素等时年龄为1394±46Ma(23),Nd初始比值为0.511 243±8(23)和εNd(T)=+7.9±2.1(23)。~(87)Sr/~(86)Sr和~(87)Rb/~(86)Sr比值分别为0.705 79—0.709 12和0.17—0.34,两者之间不存在任何相关关系。结合野外地质证据和岩相学特征,我们认为:白银都西群基性火山活动发生在中元古代,成岩物质来自亏损地幔源,成岩以后构造变动和变质热液活动致使Rb-Sr同位素体系受到严重干扰破坏。     

衡阳盆地红层的磁性地层学研究

本文用磁性地层学方法研究衡阳盆地白垩纪－第三忆地层，建立了该地层的磁极性序列。以地磁极性年代表为时间标尺，并辅之岩石的＾３９Ａｒ－＾４０Ａｒ同位素年代测定值，研究了各地层单元的生成年代，为地层时代的确定提供了依据。研究认为，衡阳盆地东北组时代属早白垩世；神皇山时代为早白垩世－晚白垩世；载家坪组时代为晚白垩世；东塘组和霞流市组时代属古新世。     

Structural Styles of the Longmenshan Thrust Belt and Evolution of the Foreland Basin in Western Sichuan Province, China

The Longmenshan thrust system consists of two major groups of structural styles according to the depth of their involvement: basement thrusts-compressional fault blocks; fold-thrust system in the cover. In cross-section, the Longmenshan structural belt is divided into 5 zones. The propagation of the Longmenshan thrust system is piggy-back due to pushing at the early stage and overstep due to gravity sliding at the late stage. Balanced cross-sections and palinspastic reconstruction reveal that the total sliding displacement of the thrust system amounts to 120 km. The tectonic evolution of the Tethys domain in western Sichuan has experienced 5 stages: continental break-up; ocean-continent subduction ; continent-arc collision; orogenic thrusting; uplift of western Sichuan.     

Application of the weighted residual method to diffraction by 2-D canyons of arbitrary shape: I. Incident SH waves

A solution for the two-dimensional scattering and diffraction of plane SH waves by canyons of arbitrary shape in an elastic half space is presented. The wave field for arbitrary geometry in this paper is computed numerically by the method of weighted residues (moment method). The wave displacement field computed by the present residual method for the case of a semi-circular canyon was shown to agree analytically and numerically with that computed by the exact closed form series solution. The same observations about ground amplifications, their dependence on frequencies and orientations of the incident waves, can be stated here for canyons of arbitrary shape as previously made for circular canyons.     

太谷凤凰山饮用天然矿泉水水质特征及开发前景

太谷凤凰山矿泉水位于在建的太谷酎泉寺避暑山在，是锶－重碳酸－钙钠型低矿化度优质饮用天然矿泉水。泉水环境优越，开发利用前景良好。     

平江万古金矿床地球化学研究

平江万古金矿床，成矿物质来源于容矿地层中元古界冷家溪群坪原组，矿床继承了容矿地层富Ａｓ、Ｓｂ、Ｗ等微量元素的特点，成矿流体为与区域浅变质作用有关的ＨＣＯ＿３－－Ｃｌ－－Ｎａ￣＋－Ｃａ￣（２＋）型建造水热液，成矿过程中Ａｕ主要以ＡｕＡｓＳ＿２、ＡｕＡｓＳ＿３￣（２－）络合物形式迁移，矿床形成于中一低温，弱碱性、还原环境。     

北祁连块状硫化物矿床中矿石和主要矿石矿物地球化学特征

对北祁连山白银矿田和郭密寺矿田中主要矿床的矿石和矿石矿物组分特征研究表明，由于各矿田的成矿条件和地球化学背景存在差异，造成不同矿床的矿石和矿石矿物元素组合各具特色。但作为同一类型矿床，它们之间又有很多共性，特别是同一矿田内各矿床的地球化学特征具有相似性和过渡性，反映了成矿条件变化的趋势。