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961.
962.
963.
This paper summarizes advances since 1987 in the application of glacial sediment sampling to mineral exploration (drift prospecting) in areas affected by continental or alpine glaciation. In these exploration programs, clastic glacial sediments are tested by geochemical or mineralogical methods to detect dispersal trains of mineral deposit indicators that have been glacially transported from source by mechanical processes. In glaciated terrain the key sampling medium, till, is produced by abrasion, crushing and blending of rock debris and recycled sediment followed by down-ice dispersal ranging from a few metres to many kilometres. As a consequence of the mid-1980s boom in gold exploration, the majority of case studies and regional till geochemical surveys published in the past decade deal with this commodity. Approximately 30% of Canada and virtually all of Fennoscandia have been covered by regional till geochemical surveys that aid mineral exploration and provide baseline data for environmental, agricultural, and landuse planning. The most profound event in drift prospecting in the last decade, however, has been the early-1990s explosion in diamond exploration which has dramatically increased the profile of glacial geology and glacial sediment sampling and stimulated changes in sampling and analytical methods. 相似文献
964.
965.
金矿物统计研究中容易忽略的问题 总被引:4,自引:2,他引:2
当前的金矿物统计工作大多局限于颗粒数百分比计算,而且常常把粒比简单地等同于重量比,这在理论上的实践上均是错误的。金矿物配分的本质是重量上的配分。根据物质的三维尺度特性,在光片中可以用面积比代替重量比;而在重砂分析中应尽量直接测定金矿物的质量,否则只能用体积比代重量比。 相似文献
966.
Abstract The Wakino Subgroup is a lower stratigraphic unit of the Lower Cretaceous Kanmon Group. Previous studies on provenance of Wakino sediments have mainly concentrated on either petrography of major framework grains or bulk rock geochemistry of shales. This study addresses the provenance of the Wakino sandstones by integrating the petrographic, bulk rock geochemistry, and mineral chemistry approaches. The proportions of framework grains of the Wakino sandstones suggest derivation from either a single geologically heterogeneous source terrane or multiple source areas. Major source lithologies are granitic rocks and high‐grade metamorphic rocks but notable amounts of detritus were also derived from felsic, intermediate and mafic volcanic rocks, older sedimentary rocks, and ophiolitic rocks. The heavy mineral assemblage include, in order of decreasing abundance: opaque minerals (ilmenite and magnetite with minor rutile), zircon, garnet, chromian spinel, aluminum silicate mineral (probably andalusite), rutile, epidote, tourmaline and pyroxene. Zircon morphology suggests its derivation from granitic rocks. Chemistry of chromian spinel indicates that the chromian spinel grains were derived from the ultramafic cumulate member of an ophiolite suite. Garnet and ilmenite chemistry suggests their derivation from metamorphic rocks of the epidote‐amphibolite to upper amphibolite facies though other source rocks cannot be discounted entirely. Major and trace element data for the Wakino sediments suggest their derivation from igneous and/or metamorphic rocks of felsic composition. The major element compositions suggest that the type of tectonic environment was of an active continental margin. The trace element data indicate that the sediments were derived from crustal rocks with a minor contribution from mantle‐derived rocks. The trace element data further suggest that recycled sedimentary rocks are not major contributors of detritus. It appears that the granitic and metamorphic rocks of the Precambrian Ryongnam Massif in South Korea were the major contributors of detritus to the Wakino basin. A minor but significant amount of detritus was derived from the basement rocks of the Akiyoshi and Sangun Terrane. The chromian spinel appears to have been derived from a missing terrane though the ultramafic rocks in the Ogcheon Belt cannot be discounted. 相似文献
967.
Per-Einar Trften 《Sedimentary Geology》2000,130(3-4):167-181
Geological structures suggest that the Fennoscandian Shield was subjected to a higher seismicity at the end of the last glaciation than today. This article demonstrates the use of varved clay chronology for dating paleoseismic events. It is argued that the deposited annually layered glacial varves were sensitive to past ground movements. In the Stockholm area, the Erstavik varved clay chronology suggests four paleoseismic events: a first (I) dating from varve year 10,473 to 10,468 BP; a second (II) 10,451 to 10,445 BP; a third (III) 10,429 to 10,425 BP; and a fourth (IV) 10,409 to 10,404 BP. In De Geer's ‘old' (1940) chronology the first (I) dating corresponds with −1117 to −1112, the second (II) with −1095 to −1089, the third (III) with −1073 to −1069, and the fourth (IV) with −1053 to −1048. The most pronounced event was the one at around varve year 10,429 BP (varve −1073 in De Geer's ‘old' chronology). The recurrence time of about 20 years suggests a totally different seismic regime at the time of deglaciation than what exists today. It coincided with the period of maximum isostatic uplift. The complexity of the varved clay response to seismic events is also discussed. 相似文献
968.
969.
红粘土序列由7个古土壤组合和与之相间的红色黄土组合组成,它们是建议的地层划 分和对比的一级单位。系统的古地磁研究表明,黄土高原风尘沉积开始的年龄约为7.2MaB.P.,它标志着晚新生代亚洲内陆干旱化的开始,可能意味着青藏高原在此时达到了有意义的高度,东亚古季风环流基本建立。风尘沉积速率与夏季风强度在长时间尺度上的耦合揭示了它们与青藏高原高度的共同联系,也意味着青藏高原可能经历了多次隆升和夷平过程;第四纪黄土-古土壤序列是2.6~2.8MaB.P.全球冰期-间冰期气候旋回建立的证据。 相似文献
970.
充分认识元素和同位素在不同环境条件下的地球化学行为,是运用元素和同位素示踪环境变化的前提。对来自于黄土高原的黄土、古土壤和红粘土样品的宇宙成因核素10Be测量和化学成分分析,以及各种化学淋溶实验表明:10Be主要以吸附状态赋存于粉尘沉积物粘粒矿物的表面,部分已结合进自生的粘土矿物中;在粉尘沉积物风化过程中10BC与9Be和Al的活动性相似,基本没有发生迁移,其原因是连续沉积的粉尘含有大量的碱性物质,阻止了10Be的解吸附和淋滤;沉积和风化作用导致了10Be浓度与化学指标在黄土-古土壤和红粘土剖面中的协同变化。 相似文献