北武夷地区逆冲推覆构造的特征及其控矿作用

北武夷地区成矿地质条件优越,矿产资源分布广泛,而广泛发育的推覆构造深刻影响着矿床的成生与保存。区域性推覆构造是成矿前、成矿期还是成矿后的构造,其精细结构特征如何,是否具有控岩控矿作用,如果是破矿作用,是否造成矿体重复增大或者隐伏、缺失等问题,严重影响着地质找矿的效果。建议开展面积性、追索性的路线地质调查,查明逆冲推覆构造的区域分布、不同单元的产状、构造样式,分别采用40Ar-39Ar和Re-Os定年技术测定推覆构造和矿体的形成时代,结合定量化分析及精细构造解析,研究构造与矿床的成生联系,预测隐伏矿体可能的位置,进而为北武夷地区寻找隐伏矿床和扩大矿床远景提供参考。     

Radiocarbon redating of contaminated samples from a tropical volcano: the Mansion ‘Series’ of St Kitts,West Indies

Heavy rainfall and dense vegetation on tropical volcanoes produce abundant carbonized wood in pyroclastic deposits, in addition to easy contamination of this wood by root systems and soluble humic material. Because the physical nature of the charcoal varies, some samples are more prone to contamination. Two independent studies of the same volcano, Mt Liamuiga on St Kitts in the Lesser Antilles, sometimes using samples from the same carbonized tree, yielded a systematic difference in radiocarbon ages. An exchange of samples and a re-investigation of three physically distinct types of charcoal yielded the following results. Rare, hard, dense charcoal, lacking contamination, which had yielded a spurious age of 2860 years bp, was redated at 1845±58 years bp. Common soft, friable charcoal with good cellular structure proved to be susceptible to contamination. A field decontamination technique utilized by one group seems significant as it yields older ages than when only routine laboratory pre-treatment was used, indicating that the latter technique only partly removes the dried and hard residue produced by the decomposition of modern plant rootlets. A previous date of 24870 years bp obtained from powdery charcoal in a horizon beneath the Mansion Series contradicted ages older than 41000 years bp from common friable charcoal in the lower Mansion Series. The soft powdery charcoal was re-investigated using a sample collected a few centimeters from the original, although field decontamination of this sample was not possible, more extensive laboratory treatment yielded an age of ca. 43000 years bp, again proving that routine laboratory pretreatments are inadequate. A revised geochronology for the Mansion Series is described and a cautionary discussion is presented for the benefit of investigators using radiocarbon ages to date volcanic deposits.     

大别地块东南缘逆冲滑脱构造体系及其对金矿的控制作用

大别地块自晚元古代以来主要经受了自北而南的推挤,并且发生了两次较强烈的南移运动,造成了地块前线逆冲滑脱构造体系。特别是中生代的推挤和滑移,不仅构造变形强烈,而且还伴有热事件,大别地块东南缘郯－庐断裂南延部分和广济－宿松平移－推覆型韧性剪切带均是＂热线构造＂,它们提供了深层次岩浆活动的通道。本区岩石以绿片岩－角闪岩相变质岩为主,含金背景值高,逆冲滑脱构造和韧性剪切带的活动与金元素的活化、迁移和富集创造了良好的条件。     

新疆第四纪盐类矿产的形成和控制因素——兼论“高山深盆”成盐模式

根据袁见齐教授“高山深盆”成盐模式,探讨新疆天山对第四纪盐类矿床的形成和控制作用,阐述了天山地貌、气候、水文特征与盐类矿产的分布规律和特征。认为“高山深盆”并非一定是四周环山的深盆,可以是某一高山与其间深盆或两侧盆地的有机组合。高山的屏障作用造成了垂直的气候分带,在潮湿多雨的山区利于成盐组份的析出并迁移到干旱少雨的闭流深盆中,形成盐类矿床。     

稀土矿床：基本特点与全球分布规律

本文介绍了全球稀土资源供需历史、现状和对未来的展望。从矿床成因视角切入，将稀土矿床分为内生和外生两大类型，其中内生稀土矿床包括碳酸岩型、碱性岩型、碱性岩型- 碳酸岩型、氧化铁铜金型、热液脉型，外生稀土矿床包括风化壳离子吸附型、沉积岩型、沉积矿产(煤矿、铝土矿和沉积磷矿)伴生型、砂矿和现代海洋底部含稀土的锰结核、结壳和软泥型。归纳总结了主要类型矿床的基本特点和时空分布；认为内生稀土矿床产出于四类构造环境，包括裂谷环境、碰撞后伸展环境、大陆碰撞环境和后俯冲伸展环境；从构造演化入手，探讨了在外生与内生地质过程中稀土元素的迁移和富集规律，建立了涵盖主要矿床类型的构造- 成矿模型。     

中国南方离子吸附型稀土矿床成矿类型及其母岩控矿因素探讨

传统认为中国南方的离子吸附型稀土矿床可划分为以“足洞式”为代表的重稀土型和以“河岭式”(或“花山式”)为代表的轻稀土型两种矿化类型。然而，近年来发现的许多矿床(如清溪、寨背和馒头山等)的赋矿风化壳中出现了轻稀土矿与重稀土矿并存现象，表现出特殊的“上轻下重”双层矿体结构。这指示了除重稀土型和轻稀土型之外，还存在着轻重稀土共生型的过渡类型。本研究通过对三种不同成矿类型的若干典型矿床系统对比，指出成矿类型的多样性与母岩性质密切相关，尤其是母岩的稀土元素地球化学和稀土载体矿物属性是制约成矿类型变化的关键因素。统计数据表明，从重稀土型→轻重稀土共生型→轻稀土型，成矿母岩的全岩稀土总量变化不大(ΣREY: 200×10-6~450×10-6→200×10-6~500×10-6→200×10-6~800×10-6)，但轻重稀土配分值出现较显著的区间性差异(ΣLREE/ΣHREY: 02~1→1~5→2~10)。与之同时，母岩中能为离子相稀土提供物源且具有重稀土配分属性的稀土副矿物类型和数量明显减少，这与全岩稀土元素地球化学特征中重稀土分量占比的降低趋势也互相匹配。该结果指示，以往认为重稀土配分母岩形成重稀土矿床、轻稀土配分母岩形成轻稀土矿床的传统观点需要外延，即一部分具有低度轻稀土配分属性(1＜ΣLREE/ΣHREY＜5)且含有丰富易风化稀土副矿物的母岩还可能形成轻重稀土共生型矿床，该认识可为今后离子吸附型稀土矿床勘查工作提供新的找矿依据。     

High-resolution sequence stratigraphy of the Lower Triassic ‘Buntsandstein’ in the Netherlands and northwestern Germany

Detailed log correlations of the largely fluvio-lacustrine Lower Triassic Buntsandstein (Late Permian-Early Anisian), carried out on 80 wells in the Dutch onshore and offshore areas, can be linked to northwest-German high-resolution sequence stratigraphy. The correlations show that cyclic sedimentation occurred in large parts of the basin. Seven 1st-order sequences are recognised, namely the Main Claystone, Rogenstein, Volpriehausen, Detfurth, Hardegsen, Solling and Lower Röt Sequences. They are overlain by the lower part of the Upper Röt–Lower Muschelkalk Sequence. Distinct sequence boundaries have been identified at the bases of four sequences: Volpriehausen, Detfurth, Solling and Upper Röt. The higher-order sequences consist of fining-upwards cycles with a thickness of up to tens of metres. The sequences are laterally persistent and have a characteristic expression on gamma-ray and sonic logs. In the Lower Buntsandstein, they display a uniform character throughout most of the area, with only minor differences in thickness or lithology. NNE-oriented lows and swells were formed during deposition of the Volpriehausen, Detfurth and Hardegsen Sequences. Uplift prior to the deposition of the Solling Sequence caused deep erosion on the swells in the basin and minor erosion in the lows. The high-resolution sequences probably represent alternating, relatively wet and dry climatic periods, with a periodicity of about 100 000 years. An analysis of the sequences suggests that their reduced thickness on the swells is mainly the effect of erosion. This is supported by analyses of the accumulation patterns and rates.     

四川木里耳泽岩溶型金矿床形成条件和成矿机制

四川本里耳泽金-菱铁矿建造矿床,赋存于上二叠统海相碳酸盐岩层中,矿化受古岩溶的严格控制,组成矿石的基本矿物为菱铁矿,金不均匀地分布于菱铁矿矿体内。成矿溶液来自加热的循环地下水。成矿过程分为早阶段和中-晚阶段。成矿温度为156-210℃,成矿深度小于1km.成矿物质主要来自地层。成矿热液呈碱性和弱还原性,贫硫,含中等盐度。矿床形成时的地质构造环境较稳定。这是我国仅见的一种特殊金矿类型。     

Sector collapse,sedimentation and clast population evolution at an active island-arc volcano: Stromboli,Italy

Sciara del Fuoco is the subaerial part of a partially filled sector-collapse scar that extends to 700 m below sea level on Stromboli volcano. The collapse occurred <5000 years ago, involved 1.81 km³ of rock and is the latest of a series of major collapses on the north-west flank of Stromboli. A north-east trending arc-axial fault system channels magmas into the volcano and has caused tilting and/or downthrow to the north-west. The slope of the partial cone constructed between the lateral walls of the collapse scar acts as a channelway to the sea for most eruptive products. From 700 m below sea level and extending to >2200 m and >10 km from the shore to the NNW, a fan-shaped mounded feature comprises debris avalanche deposits (>4 km³) from two or more sector collapses. Volcaniclastic density currents originating from Sciara del Fuoco follow the topographic margin of the debris avalanche deposits, although overbank currents and other unconfined currents widely cover the mounded feature with turbidites. Historical (recorded) eruptive activity in Sciara del Fuoco is considerably less than that which occurred earlier, and much of the partial fill may have formed from eruptions soon after the sector collapse. It is possible that a mass of eruptive products similar to that in the collapse scar is dispersed as volcanogenic sediment in deep water of the Tyrhennian basin. Evidence that the early post-collapse eruptive discharge was greater than the apparent recent flux (2kg/s) counters suggestions that a substantial part of Stromboli's growth has been endogenous. The partial fill of Sciaria del Fuoco is dominated by lava and spatter layers, rather than by the scoria and ash layers classically regarded as main constituents of Strombolian (cinder) cones. Much of the volcanic slope beneath the vents is steeper than the angle of repose of loose tephra, which is therefore rapidly transported to the sea. Delicate pyroclasts that record the magmatic explosivity are selectively destroyed and diluted during sedimentary transport, mainly in avalanches and by shoreline wave reworking, and thus the submarine deposits do not record well the extent and diversity of explosive activity and associated clast-forming processes. Considerable amounts of dense (non-vesicular) fine sand and silt grains are produced by breakage and rounding of fragments of lava and agglutinate. The submarine extension of the collapse scar, and the continuing topographic depression to >2200 m below sea level, are zones of considerable by-passing of fine sand and silt, which are transported in turbidity currents. Evidently, volcanogenic sediments dispersed around island volcanoes by density currents are unlikely to record well the true spectrum and relative importance of clast-forming processes that occurred during an eruption. Marine sedimentary evidence of magmatic explosivity is particularly susceptible to partial or complete obliteration, unless there is a high rate of discharge of pyroclastic material into the sea.     

A multivariate statistical and geostatistical study on the geochemistry of allochtonous karst bauxite deposits in Hungary

A geochemical evaluation of the Szc-Halimba-Kisld area, Hungary, covering an area of more than 200 km² is presented using different statistical and geostatistical methods. The study area is a representative example of allochtonous karst bauxite accumulation. The three groups of deposits studied here have been explored and mined since 1950. Several thousand boreholes have been drilled, and bauxite cores were analyzed for the five main chemical components. A total of 80,000 pleces of analytical data were processed, followed by a geological examination of borehole logs and of mining excavations.The quantitative geochemical evaluation of the data set led to both geochemical and practical results: The geochemical behavior of the allochtonous, clastic karst bauxite deposits differs essentially from that of the autochtonous and parautochtonous ones, as well as that of the lateritic bauxite deposits. The deposits of the study area can be split into several subsequent geochemical-sedimentological units, each representing an event of bauxite transport and accumulation. Clear regional patterns can be revealed in the composition of these units. The geostatistically measured chemical variability of the geochemical units is rather different, the lowest units showing the smallest variability. The interrelations of the main chemical components are weaker and more irregular in the studied deposits than in the autochtonous lateritic bauxite deposits. Additional local genetic features, such as transport routes, can be delineated by the methods applied. Within each deposit, local changes of chemical composition and of its variability can be determined more precisely. These results can be used in bauxite prospecting and exploration, because areas of high or low bauxite quality can be predicted.