１∶５０万地质图数据库的研建

全国150万地质图数据库以国产软件MAPGIS作为基础平台,以各省(区)区域地质志附图和香港特别行政区120万地质图为基础资料,采用现代地质学、地层学、岩石学等的新理论和新的表示方法,按岩石地层单位、花岗岩谱系单位,侵入岩按时代加岩性编制而成.该库由数字地质图库和地理底图库构成,可按任意空间范围、不同比例尺、不同投影方式和不同地质、地理内容等单项或多项任意检索;通过检索能自动形成具有图例、图外整饰的完整的地质图.     

碳酸岩岩浆与地壳反应综述

碳酸岩是地表出露较少的地幔来源的岩石,其地幔交代作用已被广泛研究,而碳酸岩岩浆与地壳的反应过程却研究较少,目前已在中国草滩和丰镇地区、德国Kaiserstuhl地区、俄罗斯Petyayan-Vara地区和澳大利亚Nolans Bore矿床等各地被报道。碳酸岩岩浆与地壳反应的特征是可能形成大量富铁云母、辉石、榍石、钡冰长石等硅酸盐矿物并造成C-O和Sr-Nd同位素体系的扰动。实验岩石学研究发现碳酸岩岩浆在地幔与橄榄岩反应形成异剥橄榄岩,对应的在中下地壳反应形成反夕卡岩。碳酸岩岩浆与围岩的反应会造成局部Si的富集促使REE在早期岩浆阶段进入磷灰石,从而抑制稀土成矿。深部地壳的碳酸岩-硅酸岩反应在相同构造背景下通常不像浅部热液系统容易出露地表,并且其反应产物容易被误认为是夕卡岩矿物组合。因此,更多的高温高压实验研究以及对硅酸盐流体来源不是很清楚的高温夕卡岩矿物组合进行重新评估,将是揭示地壳深部反夕卡岩过程,特别是相关成矿作用的关键。     

Emerald deposits and occurrences: A review

Emerald, the green gem variety of beryl, is the third most valuable gemstone (after diamond and ruby). Although it is difficult to obtain accurate statistics, Colombia supplies most (an estimated 60%, worth more than $500,000,000 per year) of the world's emeralds. However there is speculation that the emerald mines in Colombia are becoming depleted. Brazil currently accounts for approximately 10% of world emerald production. Emeralds have also been mined in Afghanistan, Australia, Austria, Bulgaria, China, India, Madagascar, Namibia, Nigeria, Pakistan, South Africa, Spain, Tanzania, the United States, and Zimbabwe.Because it is difficult to obtain accurate analyses of beryllium, most published analyses of beryl are renormalized on the basis of 18 oxygen and 3 Be atoms per formula unit. The color of emerald is due to trace amounts of chromium and/or vanadium replacing aluminum at the Y site; in most cases the Cr content is much greater than that of V. To achieve charge balance, the substitution of divalent cations at the Y site is coupled with the substitution of a monovalent cation for a vacancy at a channel site.Beryl is relatively rare because there is very little Be in the upper continental crust. Unusual geologic and geochemical conditions are required for Be and Cr and/or V to meet. In the classic model, Be-bearing pegmatites interact with Cr-bearing ultramafic or mafic rocks. However in the Colombian deposits there is no evidence of magmatic activity and it has been demonstrated that circulation processes within the host black shales were sufficient to form emerald. In addition, researchers are recognizing that regional metamorphism and tectonometamorphic processes such as shear zone formation may play a significant role in certain emerald deposits.A number of genetic classification schemes have been proposed for emerald deposits. Most are ambiguous when it comes to understanding the mechanisms and conditions that lead to the formation of an emerald deposit. Studies of individual emerald deposits show that in most cases a combination of mechanisms (magmatic, hydrothermal, and metamorphic) were needed to bring Be into contact with the chromophores. This suggests the need for a more flexible classification scheme based on mode of formation. Stable isotopes can be used to estimate the contribution of each mechanism in the formation of a particular deposit. Such estimates could perhaps be more precisely defined using trace element data, which should reflect the mode of formation.Emerald may be identified in the field by color, hardness, and form. It will tend to show up in stream sediment samples but because its specific gravity is relatively low, it will not concentrate in the heavy mineral fraction. In Colombia, structural geology, the sodium content of stream sediment samples, and the lithium, sodium, and lead contents of soil samples have all been used to find emerald occurrences. Exploration for gem beryl could result in the discovery of new occurrences of non-gem beryl or other Be minerals that could become new sources of Be and Be oxide.Future efforts should go towards creating a comprehensive data base of emerald compositions (including trace elements), determination of the role of metamorphism in the formation of some emerald deposits, improved classification schemes, and more effective exploration guidelines.     

世界地下水资源图介绍

世界地下水资源图由联合国教科文组织、世界地质图委员会、国际水文地质学家协会、国际原子能机构和德国地球科学及自然资源研究院共同组织编制,其目标是利用地理信息系统在全球尺度上汇总地下水资源,以比例尺1:25M的图件为基础,为国际社会了解世界地下水系统提供基础。2004年3月在法国巴黎召开了世界地下水资源图指导委员会工作会议,8月将在第32届国际地质大会上展示1:50M世界地下水资源图。最终的成果将于2006年国际水文地质学家协会成立50周年之际出版。     

The Gronnedal-Ika Carbonatite-Syenite Complex, South Greenland: Carbonatite Formation by Liquid Immiscibility

The Grønnedal-Ika complex is dominated by layered nephelinesyenites which were intruded by a xenolithic syenite and a centralplug of calcite to calcite–siderite carbonatite. Aegirine–augite,alkali feldspar and nepheline are the major mineral phases inthe syenites, along with rare calcite. Temperatures of 680–910°Cand silica activities of 0·28–0·43 weredetermined for the crystallization of the syenites on the basisof mineral equilibria. Oxygen fugacities, estimated using titanomagnetitecompositions, were between 2 and 5 log units above the fayalite–magnetite–quartzbuffer during the magmatic stage. Chondrite-normalized REE patternsof magmatic calcite in both carbonatites and syenites are characterizedby REE enrichment (La_CN–Yb_CN = 10–70). Calcite fromthe carbonatites has higher Ba (5490 ppm) and lower HREE concentrationsthan calcite from the syenites (54–106 ppm Ba). This isconsistent with the behavior of these elements during separationof immiscible silicate–carbonate liquid pairs. _Nd(T =1·30 Ga) values of clinopyroxenes from the syenites varybetween +1·8 and +2·8, and _Nd(T) values of whole-rockcarbonatites range from +2·4 to +2·8. Calcitefrom the carbonatites has ¹⁸O values of 7·8 to 8·6and ¹³C values of –3·9 to –4·6. ¹⁸Ovalues of clinopyroxene separates from the nepheline syenitesrange between 4·2 and 4·9. The average oxygenisotopic composition of the nepheline syenitic melt was calculatedbased on known rock–water and mineral–water isotopefractionation to be 5·7 ± 0·4. Nd and C–Oisotope compositions are typical for mantle-derived rocks anddo not indicate significant crustal assimilation for eithersyenite or carbonatite magmas. The difference in ¹⁸O betweencalculated syenitic melts and carbonatites, and the overlapin _Nd values between carbonatites and syenites, are consistentwith derivation of the carbonatites from the syenites via liquidimmiscibility. KEY WORDS: alkaline magmatism; carbonatite; Gardar Province; liquid immiscibility; nepheline syenite     

国际地质编图现状及发展趋势

随着经济社会的发展和科学技术的进步,以及地质工作服务领域的空前扩展,地质图件作为地质工作成果的集中体现和地质工作服务于经济社会发展的主要工具,受到各国政府及国际地质组织的高度重视,并出现一些明显的特点和发展趋势,主要表现为:由专业性地质图件向更多实用性图件发展;由单一地质类图件向多学科系列图件发展;由地区性、国家级图件向洲际性及全球性图件扩展;由地表地质图件向反映深部地壳结构构造图件发展;并在图面结构、表现形式上进行了诸多改革,提供了更多地质信息。     

世界地下水资源图编制情况简介

世界地下水资源图由联合国教科文组织、世界地质图委员会、国际水文地质学家协会、国际原子能机构和德国地球科学及自然资源研究院共同组织编制,其目标是利用地理信息系统在全球尺度上汇总地下水资源数据,以比例尺1∶25M的图件为基础,为国际社会了解世界地下水系统提供基础资料。2004年3月在法国巴黎召开了世界地下水资源图指导委员会工作会议,8月将在第32届国际地质大会上展示1∶50M世界地下水资源图。最终的成果将于2006年国际水文地质学家协会成立50周年之际出版。     

Carbonatite in the tuffs of the West Eifel,Germany

Newly-discovered carbonatitic fragments from the West Eifel are described in terms of their petrography and trace-element content.     

Carbonatite diversity in the Central Andes: the Ayopaya alkaline province,Bolivia

The Ayopaya province in the eastern Andes of Bolivia, 100 km NW of Cochabamba, hosts a Cretaceous alkaline rock series within a Palaeozoic sedimentary sequence. The alkaline rock association comprises nepheline-syenitic/foyaitic to ijolitic intrusions, carbonatite, kimberlite, melilititic, nephelinitic to basanitic dykes and diatremes, and a variety of alkaline dykes. The carbonatites display a wide petrographic and geochemical spectrum. The Cerro Sapo area hosts a small calciocarbonatite intrusion and a multitude of ferrocarbonatitic dykes and lenses in association with a nepheline-syenitic stock. The stock is crosscut by a spectacular REE-Sr-Th-rich sodalite-ankerite-baryte dyke system. The nearby Chiaracke complex represents a magnesiocarbonatite intrusion with no evidence for a relationship to igneous silicate rocks. The magnesiocarbonatite ( REE up to 1.3 wt%) shows strong HREE depletion, i.e. unusually high La/Yb ratios (520–1,500). Calciocarbonatites ( REE up to 0.5 wt%) have a flatter REE distribution pattern (La/Yb 95–160) and higher Nb and Zr contents. The sodalite-ankerite-baryte dyke system shows geochemical enrichment features, particularly in Na, Ba, Cl, Sr, REE, which are similar to the unusual natrocarbonatitic lavas of the recent volcano of Oldoinyo Lengai, Tanzania. The Cerro Sapo complex may be regarded as an intrusive equivalent of natrocarbonatitic volcanism, and provides an example for carbonatite genesis by late-stage crystal fractionation and liquid immiscibility. The magnesiocarbonatite intrusion of Chiaracke, on the other hand, appears to result from a primary carbonatitic mantle melt. Deep seated mantle magmatism/metasomatism is also expressed by the occurrence of a kimberlite dyke. Neodymium and strontium isotope data (_Nd 1.4–5.4, ⁸⁷Sr/⁸⁶ Sr<Bulk Earth) indicate a depleted mantle source for the alkaline magmatism. The magmatism of the Ayopaya region is attributed to failed rifting of western South America during the Mesozoic and represents the only occurrence of carbonatite and kimberlite rocks in the Andes.