西非被动大陆边缘Walvis Ridge以南纳米比亚盆地的地质特征及油气意义——兼与Walvis Ridge以北盆地比较

西非被动大陆边缘近海盆地区是世界关注的油气产区和投资热点地区之一,但目前为止的油气产出主要集中在Walvis Ridge以北的盆地区(北部盆地区),而以南的纳米比亚盆地区只发现了一个Kudu气田。从西非被动边缘的构造演化历史、边缘结构特征等方面,通过纳米比亚盆地与北部产油气盆地间的比较,对纳米比亚近海盆地区的油气勘探前景进行了有益的探讨。综合分析后认为,纳米比亚近海盆地区油气勘探没有大的突破的主要原因是受政治影响、勘探程度低及公布资料较少、研究程度低。从边缘演化特征来看,纳米比亚盆地区裂谷作用及海底扩张方式、边缘结构等与北部盆地区十分相似,只不过时间上略早。南、北盆地区都经历了前裂谷期、同裂谷期、过渡期和后裂谷期等几个发育时期,形成了类似的构造—沉积组合,发育类似的烃源岩层(除与北部盆地区类似的烃源岩层外,纳米比亚边缘Karoo期前裂谷期沉积可能也是潜在烃源岩)。成熟度和热史模拟认为,纳米比亚边缘离开海岸线一定距离内油气成熟度达到中、高度,具备了油气生成条件,而储盖层及对西非产油意义较大的蒸发岩也较发育,漂移期地层中发育的重力滑动构造可形成大型构造圈闭并对漂移期浊积岩分布有控制作用。综合分析后认为,纳米比亚盆地区与北部盆地区具十分相似的地质背景,具备了形成油气的条件,应加强勘探与研究工作,而纳米比亚近海盆地离开岸线一定范围是油气勘探的优选目标区。     

纳米比亚铜矿铜地表富集成因及意义

通过对纳米比亚北部、中部和南部的热水喷流沉积型铜矿、夕卡岩型铜矿和斑岩型铜矿的观察,发现这些不同类型的铜矿有一个共同的特征:即铜在地表以碳酸盐(主要是孔雀石)的形式富集.研究认为,产生这种富集的原因是由于纳米比亚的气候干旱.干旱的气候使地表腐殖质缺乏,地表呈现碱性环境,因而不仅形成了遍布纳米比亚地表的钙结砾岩,也导致了地表铜的富集和氧化带铜的变贫.这种上移的水成异常呈现高值而局限、异常迁移少的特点.这种铜的地表富集与纳米比亚的土壤型铀矿的成因一致.     

纳米比亚不同类型铀矿床成因初探

纳米比亚的铀矿床主要有3种类型:侵入岩(白岗岩、伟晶岩)型、表生型(钙结岩型)、砂岩型(层控型)。矿床成因主要有两种类型,产于侵入岩中的白岗岩及伟晶岩型铀矿床,主要形成于岩浆的结晶分异与后期的热液叠加改造;产于钙结岩及沉积岩中的铀矿床,主要形成于新近纪富铀岩体中铀的活化转移,由于气候变化等原因铀富集成矿,后期的氧化作用形成次生铀矿物。     

International Rivers as Boundaries

Abstract

International rivers serve a number of purposes, the most obvious are the navigational and non-navigational uses. Less noticed is the fact that international rivers are also used to delimit boundaries between nations. The immediate question that would arise is: Where are such boundaries actually drawn across the river? Boundaries, however, are established by treaties and the answer to this question is often included in the interpretation of treaties delimiting such water boundaries, taking into account the special characteristics of the international river. Indeed, this has been the case regarding the boundaries across the Chobe river between Botswana and Namibia. Determining where such boundaries lie would result in deciding to whom a disputed Island, the Kasikili/Sedudu, belongs. In a praiseworthy step, the two countries agreed to take their dispute over the Island, after failure to resolve it through negotiations, to the International Court of Justice. This paper discusses the uses of international rivers as boundaries, and reviews the dispute between Botswana and Namibia, and the decision of the Court thereon.     

Natural hydrogen emanations in Namibia: Field acquisition and vegetation indexes from multispectral satellite image analysis

Natural hydrogen exploration is now active in various places of the world. Onshore, correlation between natural H₂ generation and the presence of iron rich rocks especially from Archean and Neoproterozoic cratons have been observed. Emanations and accumulations of H₂ have already been confirmed in such geological settings in Australia, South Africa and Brazil. The geological similitude and the presence of numerous sub circular depressions that are a good proxy for hydrogen emanations suggest that hydrogen resources may also exist in Namibia. We present here the results of a data acquisition campaign which allowed us to confirm the presence of natural hydrogen in this country in the vicinity of Neoproterozoic Banded Iron Formation. The H₂ content in the soil, as in Brazil, is variable within the depressions in time and space and is particularly time sensitive across the day. Comparison of the H₂ signal versus time within these two regions shows a similar behavior of the soils with an increase of the H₂ flow at the middle of the day. In addition, these new data allow us to better constrain the morphological characteristics of such H₂-emiting depressions. By using satellite images and digital elevation model we propose a new proxy to differentiate potentially H₂-emiting features from other type of depressions such as Salt Pan. The Landsat multispectral images and their processing through NDVI and SAVI indexes, that highlight a ring of healthy vegetation around the sub circular area with scarce vegetation already observed appear able to discriminate between H₂ emitting structures and other soft depressions.     

A methodology for reviewing the quality of strategic environmental assessments in development cooperation

A methodology is described for reviewing the quality of strategic environmental assessments (SEAs) and identifying problems associated with them. It was developed to support the work of the OECD DAC SEA Task Team and designed for application to SEAs undertaken in the context of development cooperation. The methodology is based on internationally accepted principles and elements of good practice and is question-based. Three modules separately address three core attributes of SEA: compliance with requirements, technical quality, and utility and benefits of the SEA. The methodology is applicable in various ways from a relatively quick desk exercise taking one or two days and conducted by an individual, to a longer review involving a team with fieldwork, ground-truthing and stakeholder engagement (e.g. for a multi-country SEA). A range of factors that need to be addressed in reviewing SEAs are considered. Independent and trial applications of the methodology to SEAs for development cooperation in Ukraine, the Caribbean and Namibia have shown that it can be usefully and successfully applied in this context.     

Groundwater Recharge Assessment for the Kalahari Catchment of North-eastern Namibia and North-western Botswana with a Regional-scale Water Balance Model

Groundwater is the only source of drinking water for the inhabitants of the Kalahari. Thus understanding spatial and temporal variations in groundwater recharge is very important and a regional-scale water balance model has therefore been set up for a 209,149 km² catchment in north-eastern Namibia and north-western Botswana. The model has a spatial resolution of 1.5 × 1.5 km, daily model time-steps, and climatic input parameters for 19 years are used. The distributed, GIS-based, process-oriented, physical water balance model (MODBIL) used in this study considers the major water balance components: precipitation, evapotranspiration, groundwater recharge, and surface runoff/interflow. Mean precipitation for the study area is 409 mm a⁻¹, while mean actual evapotranspiration is 402 mm a⁻¹ and mean groundwater recharge is 8 mm a⁻¹ (2% of mean annual precipitation). The recharge pattern is mainly influenced by the distribution of soil and vegetation units. Groundwater recharge shows a high inter- and intra-annual variability, but not only the sum of annual precipitation is important for the development of groundwater recharge; a large amount of precipitation in a relatively short period is more important. Published independent data from the Kalahari in Namibia, Botswana and the Southern African region under similar climatic conditions are used to verify the modelling results.     

纳米比亚西北部朝斯组铁矿地质特征研究与初步经济评价

纳米比亚西北部地区朝斯组中赋存大规模铁矿,该铁矿形成于新元古代约730 Ma时期,由于雪球地球的影响,全球在这一时期形成很多大的铁矿。本文通过对朝斯组铁矿岩芯的观察和对岩芯主量元素特征的分析可知朝斯组铁矿主要由Fe_2O_3和SiO_2组成,铁矿中SiO_2含量较高。微量元素特征表明铁矿中富集Co,相对亏损Rb。稀土元素特征表明铁矿中稀土总量均较低,具有相似的REE配分模式,轻稀土相对重稀土亏损,轻微的Eu正异常和明显的Ce负异常。地球化学分析表明铁矿的物质来源兼具陆源沉积物和海相沉积物的特征,Ce的轻微负异常反映了成矿时海水为低氧化环境,而Eu的轻微正异常说明海底低温热液参与了铁矿的成矿过程。朝斯组铁矿石资源量为20亿t,平均品位30%,潜在经济价值为700亿美元。纳米比亚对环境保护严格,采矿的征地成本很高,铁矿所在地区的基础设施非常差,从开采到铁矿运输的成本投入很高,这些都导致纳米比亚铁矿价格优势并不明显。本文认为,如果该地区未来不能发现其他价值更高的共伴生矿产,这些铁矿在目前技术经济条件下开采盈利的前景不明朗。     

我国矿业企业在纳米比亚投资面临的风险和对策

中国矿业企业在纳米比亚投资面临诸多风险。这些风险包括能否找到有价值的矿产资源、找到的矿产资源如何开采、采矿过程中对的环境破坏、矿产品价格波动、人才短缺和安全事故等。本文针对这些风险提出相应的对策。企业应该加强理论研究、重视地质专家在找矿中的作用和优化找矿方法降低勘探风险;引入其他公司参股、政府投资共同分担开发风险;通过严格的环保措施加强对环境的保护;通过超前市场预测避免矿产品价格波动风险;通过利用和培养当地人才并提高员工待遇解决人才缺乏风险;通过正规化管理降低安全事故发生频率。中国企业在纳米比亚矿业投资面临的风险客观存在,只能采取相应对策消除风险因素或降低风险发生后的损失,以实现盈利的最大化。     

纳米比亚地质概况及矿产资源特征（增刊）

纳米比亚共和国位于非洲西南部,地处南非以北,安哥拉和赞比亚以南,东与博茨瓦纳相邻,西濒大西洋。纳米比亚成矿地质背景较好,有着丰富的自然资源,在数百种矿藏中,已探明的有60余种。各种矿藏探明储量和产量均居非洲前5名,铀和钻石的开采在开采业中占据重要位置,整个采矿业的现在及未来都是纳米比亚国家经济中最主要的组成部分。纳米比亚是以下矿产品的重要生产国：钻石、铀、铜、铅、锌、金、石油、天然气等。本文通过搜集资料对纳米比亚的基本地质特征和矿产资源概况进行概述,供有意赴纳米比亚投资矿业者参考。