有机质在中国东北部森林沼泽区化探异常追踪和查证中的应用

在东北森林沼泽区的几个矿区(点)上,通过以泥炭、腐殖层土壤为采样介质的区域化探异常追踪查证方法技术试验研究,发现Au、Ag、Cu、Pb、Zn等主要成矿元素的测量结果与水系碎屑沉积物、残坡积物的基本一致,对矿体均有良好的反映.研究结果表明在这类景观区化探找矿工作中有机质是可以利用的.     

钾-氩和氩-氩定年样品的送样要求及预处理

介绍了K-Ar和Ar-Ar法定年样品的送样要求及实验室预处理程序，样品粒度以250～180μm为宜；用量则视样品的K含量和年龄情况而定，K含量越高、年龄越老，所需样品量越少，多数样品的用量在几十至几百毫克；对于年龄情况不清楚的样品，10～20g手标本或者1～2g合适粒度的样品可以保证用量。全岩样品常受蚀变和捕虏晶的影响，有效的预处理可以在很大程度上消除这些干扰因素。文章还介绍了用稀HNO3消除碳酸盐、1．7mol／L HF消除轻微蚀变的影响以及电磁选剔除捕虏晶的实验过程。     

分形理论与灰色系统理论在南岭地区地质异常圈定和金矿资源预测中的应用

应用分形理论研究了南岭地区地质弄常及其圈定方法，结合灰色系统理论对该区的金矿资源进行了预测。通过研究，圈定了10个地质异常区和7个金成矿远景区，为南岭地区金矿地质勘查提供了依据。     

The Glueckstadt Graben of the North-German Basin: new insights into the structure from 3D and 2D gravity analyses

The structure of the Glueckstadt Graben has been investigated by use of 3D gravity backstripping technique and by 2D gravity and magnetic modelling. Subtracting the gravity effects of the Meso-Cenozoic sediments together with Permian salt reveals a positive residual anomaly within the Glueckstadt Graben. This anomaly includes two local maxima over the Westholstein and Eastholstein Troughs. The 2D gravity models point to the presence of a high-density body within the lower crust of the Glueckstadt Graben. In addition, the results of 2D magnetic modelling indicate that the central part of the high-density body is overlain by an area with high susceptibility. Most probable, the formation of this high-density body is a result of complex poly-phase tectonic history of the study area. Finally, the results of gravity modelling indicate that Permian salt is not homogeneous. 3D gravity analysis and, especially, 2D gravity modelling have distinguished the differences in degree of salt saturation in salt-rich bodies, and elucidate the proportion of Rotliegend salt.     

Regional Tectonic Transformation in East Kunlun Orogenic Belt in Early Paleozoic: Constraints from the Geochronology and Geochemistry of Helegangnaren Alkali-feldspar Granite

The Helegangnaren feldspar granite exposed in the eastern part of East Kunlun, is characterized by high concentrations of SiO2 and alkaline, low abundances of Fe, Mg and Ca, metaluminous-weak peraluminous. Trace elements analysis shows that the granite is depleted extremely in Ba, Sr and Eu, and rich in some large-ion lithophile elements and high field strength elements. Besides, the granite has high Ga contents, the values of 104(Ga/Al) vary from 2.50 to 2.77, which is mainly greater than the lower limit of A-type granites (2.6), and is higher than the I- and S-type granites’ average (2.1 and 2.28, respectively). Rare earth element (REE) is characterized by relatively high fractionations of light REE (LREE) and heavy REE (HREE) (LREE/HREE=9.3–13.60, (La/Yb)N=10.92–18.02), pronounced negative Eu anomalies (δEu=0.08–0.13), and exhibits right-dipping gull pattern. Major elements, rare elements and trace elements features show the granite is ascribed to A-type granite and A2 subtype in tectonic genetic type. They are plotted into post-collision or within-plate area in a variety of tectonic discriminations. Geological and geochemical data comprehensively suggest that the granite is formed in a post-collision extensive tectonic setting. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating yields a weighted mean age of 425?Ma, belonging to Middle Silurian, which is similar to the age of the post-collision geological events in the region. The differences of magmatic rocks in formation age, rocks assemblage and rocks series systematically indicate that the regional tectonic stress regime in the East Kunlun orogenic belt experienced a major transformation from compress to extension in Middle Silurianin, and the Helegangnaren feldspar granite intruded in the early stage of tectonic transformation.     

Geochemical, Sr–Nd and zircon U–Pb–Hf isotopic studies of Late Carboniferous magmatism in the West Junggar, Xinjiang: Implications for ridge subduction?

Voluminous granitic intrusions are distributed in the West Junggar, NW China, and they can be classified as the dioritic rocks, charnockite and alkali-feldspar granite groups. The dioritic rocks (SiO₂ = 50.4–63.8 wt.%) are calc-alkaline and Mg enriched (average MgO = 4.54 wt.%, Mg^# = 0.39–0.64), with high Sr/Y ratios (average = 21.2), weak negative Eu (average Eu/Eu = 0.80) and pronounced negative Nb–Ta anomalies. Their Sr–Nd and zircon Hf isotopic compositions ((⁸⁷Sr/⁸⁶Sr)_i = 0.7035–0.7042, ε_Nd(t) = 4.5–7.9, ε_Hf(t) = 14.1–14.5) show a depleted mantle-like signature. These features are compatible with adakites derived from partial melting of subducted oceanic crust that interacted with mantle materials. The charnockites (SiO₂ = 60.0–65.3 wt.%) show transitional geochemical characteristics from calc-alkaline to alkaline, with weak negative Eu (average Eu/Eu = 0.75) but pronounced negative Nb–Ta anomalies. Sr–Nd and zircon Hf isotopic compositions ((⁸⁷Sr/⁸⁶Sr)_i = 0.7037–0.7039, ε_Nd(t) = 5.2–8.0, ε_Hf(t) = 13.9–14.7) also indicate a depleted source, suggesting melts from a hot, juvenile lower crust. Alkali-feldspar granites (SiO₂ = 70.0–78.4 wt.%) are alkali and Fe-enriched, and have distinct negative Eu and Nb–Ta anomalies (average Eu/Eu = 0.26), low Sr/Y ratios (average = 2.11), and depleted Sr–Nd and zircon Hf isotopic compositions ((⁸⁷Sr/⁸⁶Sr)_i = 0.7024–0.7045, ε_Nd(t) = 5.1–8.9, ε_Hf(t) = 13.7–14.2). These characteristics are also comparable with those of rocks derived from juvenile lower crust. Despite of the differences in petrology, geochemistry and possibly different origins, zircon ages indicate that these three groups of rocks were coevally emplaced at ~ 305 Ma.A ridge subduction model can account for the geochemical characteristics of these granitoids and coeval mafic rocks. As the “slab window” opened, upwelling asthenosphere provided enhanced heat flux and triggered voluminous magmatisms: partial melting of the subducting slab formed the dioritic rocks; partial melting of the hot juvenile lower crust produced charnockite and alkali-feldspar granite, and partial melting in the mantle wedge generated mafic rocks in the region. These results suggest that subduction was ongoing in the Late Carboniferous and, thus support that the accretion and collision in the Central Asian Orogenic Belt took place in North Xinjiang after 305 Ma, and possibly in the Permian.     

青海东昆仑东段金矿区地层含矿性分析

近年来勘查成果表明,青海东昆仑东段是一个以金为主的成矿聚集区,各矿区含矿层位不尽相同。通过对不同的含矿地层和岩体地球化学微量元素分析,认为地层并不能提供金矿成矿物质的来源。区域变质作用造成了金的活化迁移,后期的岩浆热液作用对金的富集具有重要的作用。     

青藏高原中部北北东向深部负磁异常带的成因及其意义

根据最新测量获得的青藏高原中西部航磁异常图 ,经不同高度向上延拓后 ,发现在测区东部 ,即青藏高原中部自柴达木向西南延伸的广大地区 ,出现一条极为明显的北北东向负磁异常带。从对航磁区域场的分析 ,并结合人工地震、重力计算莫霍面深度、热水活动、最新火山岩活动、地貌特征和天然地震活动等多种资料的解释 ,认为负异常带是由于深部热流沿北北东向上升引起局部岩浆熔融 ,使上地壳下部具有较高的地温 ,导致磁性层底部消磁作用的结果。与此同时也加快了青藏高原隆升的幅度 ,为高原形成和演化的研究提供了新的证据     

内蒙古额济纳旗黑大山锑矿化带化探异常特征及其找矿潜力评价

1∶20万区域化探工作在黑大山地区发现了规模较大的Sb、As为主的化探异常,经过异常查证工作,找到了2个锑矿化带。本区处于北山地区的锑矿成矿远景区,成矿地质条件十分有利,具有较大的找矿潜力。