Taming the killer lakes of Cameroon

A chain of volcanoes, some of them still active, extends from the Atlantic Ocean into the highlands of Cameroon. Mount Cameroon, located at the edge of the continent, erupted in 1999 and 2000 and spewed lava part-way down its flanks, cutting off a coastal road. A number of the now extinct (or dormant) volcanic craters on the continental part of the line are filled with water, forming crater lakes. These lakes have achieved mythical status in local tribal lore. Lacking a written history, prior to the arrival of the colonial powers, much of our understanding of past natural phenomena relating to the lakes is based on these myths.     

Cyclical salt efflorescence weathering: an invisible threat to the recovery of underground mine environment for tourist exploitation

Enhancing the value of an underground mine environment for tourist exploitation involves altering the physico-chemical balance of stone materials whose original mechanical properties guaranteed the structural stability of the site’s galleries and chambers. Humidity and temperature changes caused by the public exhibition of this kind of assets are the main causes of such disorders. After the intervention in the Agrupa-Vicenta mine in La Union (Spain) there were still runoff-water leaks into the mine. These water runoffs through the fault and schistosity planes of the enclosing rock mass give rise to salt precipitation over time. Adapting this mine and turning it into a museum have meant a decrease in relative indoors humidity and an increase in temperature. These variations have caused rocks, which were stable in the original conditions, to increase their rate of physico-chemical weathering due to the polycyclic supergene alteration of the metal sulfides they contain. The resulting release of sulfates into the solution and their subsequent precipitation as single and double salt efflorescence causes haloclasty, deteriorating the rock’s mechanical properties and diminishing the structural stability of the operation. This paper presents the results of characterizing the supergene mineral phases of salt efflorescence in the rock bed enclosing an underground sulfide mine value enhanced for tourist exploitation. Dangers for the structural stability of this type of architectural intervention, associated to the formation of efflorescences, are also identified; these efflorescences are caused by the weathering of rocks that make up its supporting structure.     

氡-居室中的杀手

居室环境的质量已越来越引起人们的关注与重视。近年来,由于居室环境的污染,导致人体健康出现问题的报道屡见不鲜。通常的室内环境污染如烟雾、一氧化碳、二氧化碳、有害金属等较易被人们发现并加以治理,而居室中对人体健康有极大危害的氡污染却常常被人们忽略。1　氡的化学特征及环境存在趋势1 1　氡的一般化学特征氡是天然产生的一种放射性气体,原子序数为86,是最重的气体元素,在化学元素周期表中列第六周期零族,是惰性气体族(He、Ne、Ar、Kr、Xe、Rn、)的最后一个元素。氡是由放射性铀、镭放射衰变的中间产物,即放射性惰性气体。当氡…     

深海采矿对大洋生态系统的影响

本文扼要介绍了深海采矿的环境效应,重点研究了深海采矿对大洋生态系统特别是对底栖生物,浮游生物,食物链结构等的影响,最后探讨了对试采矿监测结果等的有效性评价以及国外最新的研究动态。     

钻孔水力开采工艺：开采地下矿产的新方法

介绍了国外新兴的采矿技术－钻孔水力开采工艺,指出其工艺特点,影响因素,使用条件和在我国推广的技术经济意义。     

Merapi (Java,Indonesia): anatomy of a killer volcano

Merapi is Indonesia's most dangerous volcano with a history of deadly eruptions. Over the past two centuries, the volcanic activity has been dominated by prolonged periods of lava dome growth and intermittent gravitational or explosive dome failures to produce pyroclastic flows every few years. Explosive eruptions, such as in 2010, have occurred occasionally during this period, but were more common in pre‐historical time, during which a collapse of the western sector of the volcano occurred at least once. Variations in magma supply from depth, magma ascent rates and the degassing behaviour during ascent are thought to be important factors that control whether Merapi erupts effusively or explosively. A combination of sub‐surface processes operating at relatively shallow depth inside the volcano, including complex conduit processes and the release of carbon dioxide into the magmatic system through assimilation of carbonate crustal rocks, may result in unpredictable explosive behaviour during periods of dome growth. Pyroclastic flows generated by gravitational or explosive lava dome collapses and subsequent lahars remain the most likely immediate hazards near the volcano, although the possibility of more violent eruptions that affect areas farther away from the volcano cannot be fully discounted. In order to improve hazard assessment during future volcanic crises at Merapi, we consider it crucial to improve our understanding of the processes operating in the volcano's plumbing system and their surface manifestations, to generate accurate hazard zonation maps that make use of numerical mass flow models on a realistic digital terrain model, and to utilize probabilistic information on eruption recurrence and inundation areas.     

多年冻土区矿山开采研究现状及展望

多年冻土区蕴藏着丰富的矿产资源,矿业开发已成为多年冻土区经济发展的主要产业之一.但是,在其开采过程将不可避免地受到冻土的影响,也造成多年冻土区生态环境恶化的影响.在西部大开发的进程中,能源需求量逐渐增加,而多年冻土区矿山露天开采量逐渐减少,开展多年冻土区矿山地下开采相关的研究工作显得尤为迫切.在分析和总结前人研究成果的...     

Multi-stage growth and invisible gold distribution in pyrite from the Kundarkocha sediment-hosted gold deposit,eastern India

Gold mineralization at Kundarkocha, India, is hosted in sheared gray quartz veins that were emplaced in carbonaceous pyritic phyllite. Gold occurs as enclosed grains within sulfides and free grains in quartz. Based on characteristic textural and chemical features, documented by X-ray element imaging, electron probe microanalysis and laser-ablation inductively-coupled plasma mass spectrometry analyses, four pyrite types were identified in carbonaceous phyllites and auriferous veins. Rock-hosted fine-grained syn-sedimentary to early diagenetic pyrite framboids (PyI) have lower contents of Co and As but consistently high gold values. Pyrite of the next generation (PyII) has numerous silicate and rare sulfide inclusions; lower contents of Co and Ni, moderate As values; the highest mean value of invisible gold and maximum concentrations of trace elements such as Li, Ti, Zn, Rb, Sr, Y, Zr, Nb, La, Ce, Ta, Th, U and Cr. Pyrite of the third generation (PyIII) shows evidence of overgrowth over PyII, contains both silicate and sulfide inclusions, and are characterized by moderate contents of Co, high Ni and low Au values and higher concentrations of large ion lithophile elements, but lesser amount of high field strength elements. Pyrites of the latest type (PyIV) occur as polycrystalline aggregates that contain inclusions of gold, sulfides and rare silicates, show oscillatory zoning of Co and As and the lowest concentrations of all other trace elements. Successive decrease in contents of majority of trace elements from PyII to PyIV is attributed to fluid-assisted recrystallization during diagenesis and low grade metamorphism.Later generation pyrites (PyII through PyIV) exhibit higher Au contents regardless of their As values, indicating occurrence of invisible gold mostly as nanoparticles, at times reaching up to 500 ppm. Unlike the majority of trace elements that underwent large-scale remobilizations, gold was somehow locked up in pyrite resulting in a rather lean deposit at Kundarkocha.     

Mining subsidence and its effect on the environment: some differing examples

 The impact of mining subsidence on the environment can occasionally be very catastrophic, destroying property and even leading to the loss of life. Usually, however, such subsidence gives rise to varying degrees of structural damage that can range from slight to very severe. Different types of mineral deposits have been mined in different ways and this determines the nature of the associated subsidence. Some mining methods result in contemporaneous subsidence whereas, with others, subsidence may occur long after the mine workings have been abandoned. In the latter instance, it is more or less impossible to predict the effects or timing of subsidence. A number of different mineral deposits have been chosen to illustrate the different types of associated subsidence that result and the problems that arise. The examples provided are gold mining in the Johannesburg area; bord and pillar mining of coal in the Witbank Coalfield, South Africa; longwall mining of coal in the Ruhr district; mining of chalk and limestone in Suffolk and the West Midlands, respectively; and solution mining of salt in Cheshire. These mineral deposits have often been worked for more than 100 years and, therefore, a major problem results from abandoned mines, especially those at shallow depth, the presence of which is unrecorded. Abandoned mines at shallow depth can represent a serious problem in areas that are being developed or redeveloped. Abstraction of natural brine has given rise to subsidence with its own particular problems and cannot be predicted. Although such abstraction is now inconsequential in Cheshire, dereliction associated with past subsidence still remains. Received: 21 October 1999 · Accepted: 14 February 2000     

浅析规范开采在矿山开采生产过程中的重要性--以某石灰岩矿山开采为例

规范开采应贯穿于地质勘探、矿山开采乃至矿区关闭整个过程,使矿山的人、财、物得到最优配置,并可充分体现矿山效益与安全的协和关系.通过对某石灰岩矿规范开采与矿山生产过程中安全、经济合理性的简要分析,进一步说明了规范开采是保障矿山效益与安全的一种有效手段.     

矿山开发对地质环境的影响及保护研究

黑龙江省是矿产资源大省，在开采诸如煤、金、石油、砖用粘土等矿产资源时破坏了地质环境，诱发了崩塌、滑坡、泥石流、矿坑塌陷等突变性地质灾害及土地沙化、盐渍化、地面沉降等缓变性地质灾害。它们对生命财产构成严重威胁。因此，合理开发和利用矿产资源，减轻地质环境破坏程度是建设和保护地质环境的基础，是国民经济持续发展的先决条件。     

Mining for the lowest grade ore: Traditional iron production in northern Malawi

Two contrasting, well preserved Iron Age mines are described from the Nyika Plateau of Malawi. At the first, Ncherenje, about 1600 m³ of material was mined over a linear distance of about 3 km from numerous shallow pits, several large excavations, and a number of underground shafts and horizontal tunnels. Here, low grade ore, ranging from 6.6 to 21.3 wt % Fe₂O₃ with small quantities of Fe-ennched ironstone averaging about 36%, was excavated from the regolith which had developed upon gneissic bedrock. The second mine at Mbiri, is a single excavation where about 15.5 m³ of magnetite-rich, partially weathered gneiss averaging 58% Fe₂O₃ was mined. Ethnographic studies as well as evidence from the mines themselves indicate that the low grade ore from Ncherenje was preferred by the smelters. The Mbiri ore contains insufficient silica to make a fayalite slag, a problem which can be overcome by adding old slag and lower grade material to the charge. Their two stage smelting technology, however, employs a primary natural draft furnace which essentially cannot produce high enough temperatures to melt high grade magnetite; it was apparently designed to process only low grade ore.     

MORB数据挖掘:玄武岩判别图反思

板块构造学说推动了玄武岩理论的完善和进步,从20世纪70年代兴起的玄武岩构造环境判别方法成为学术界关注的热点,虽然现在逐渐降温了,但在国内仍然倍受青睐。大洋中脊玄武岩(MORB)是拥有数据最多、数据质量最好、研究得最详细的玄武岩类,是构建玄武岩理论的基石。本文利用Pet DB数据库资料(http://www.earthchem.org/petdb/search),对全球MORB数据进行了初步的挖掘,发现早先的玄武岩构造环境判别方法的理论、思路需要进一步的完善。早先研究认为,N-MORB是强烈亏损的。但本文研究却显示,MORB成分具有较宽的变化范围,包含了从MORB到OIB及IAB的组分,即部分MORB并不是亏损的,而是相对富集的。因此,玄武岩构造环境判别理论及方法有待进一步的完善。     

青海聚乎更矿区三露天井田中侏罗统沉积环境

青海聚乎更矿区是全球陆域中纬度地区天然气水合物的首要发现地,水合物储存层位主要为该矿区三露天井田的中侏罗世含煤岩系。依据钻孔岩心及测井曲线,对该矿区三露天井田含煤岩系进行沉 积环境分析,在单孔沉积相及沉积相断面图分析的基础上,重建研究区的岩相古地理格局。木里组下段岩性主要为细砾岩、含砾粗砂岩及粗砂岩等粗粒岩石,以辫状河为主的沉积环境;木里 组上段岩性以厚层砂岩与厚层煤层互层为特征,反映了水体逐渐加深的过程中发育三角洲为主的沉积环境;江仓组下段以细粒砂岩及泥岩互层夹薄煤层为特征,反映水体进一步加深过程中的三角洲前缘和滨浅湖环境;江仓组上段以油页岩、暗色泥岩为主,含有瓣鳃类化石,反映湖泊为主的沉积环境。     

基于历史航卫片的城市“隐形”活动断层精确定位——以大同盆地水峪断裂为例

活动断层是城市地震灾害的重要风险源，准确厘定活动断层的空间几何展布是有效降低城市地震灾害和开展活动断层避让的基础。而城市化建设对原始地貌的严重改造使得原先出露地表的活动断层成为"隐形"断层，难以准确确定断层的几何展布。大同盆地中部的水峪断裂北段位于马铺山东缘，断错地貌明显，但南段进入大同市御东新区被城市建筑物覆盖，成为"隐形"断层。研究基于大同地区1965年历史航片影像资料，结合1∶10000地形图，运用航片像对和航空立体摄影的方法重建了该地区的数字高程模型（DEM）和正射影像（DOM），重点对水峪断裂"隐形"段进行识别和定位，厘定了水峪断裂断层陡坎的几何展布特征。研究结果表明，水峪断裂北段山前陡坎线性特征明显，由影像可以准确解译出断层几何展布位置；水峪断裂南段可基于2000年之前的Keyhole历史遥感影像、DOM与DEM资料，根据断层两侧的颜色差异及陡坎高度差异，精确厘定该段的断层几何展布位置；DEM提取的地形剖面表明"隐形"段陡坎高度在19 m左右。同时，基于野外调查的断层剖面与浅层人工地震剖面证明该陡坎就是水峪断裂的位置，这也表明利用历史航卫片对城市"隐形"活动断层进行精确定位的方法是可行的。该研究不仅为大同地区的地震危险性评估提供了重要依据，而且为城市"隐形"活动断层探测提供了一个新的思路和途径。