Geochemical constraints on the distribution of trace elements and volatiles in fluorapatite from the Panasqueira tin-tungsten deposit (Portugal)     

《Chemie der Erde / Geochemistry》2021,81(2):125765

A large, euhedral crystal of fluorapatite (ca. 19.5 × 20.0 mm) from the Panasqueira tin-tungsten deposit (Portugal) was investigated in terms of the distribution of trace elements by using several microanalytical techniques. The studied material represents almost pure fluorapatite with minor amounts of other cations (mainly Sr, Mn, REE and Fe), OH and Cl. Particular interest was given to the distribution of rare earth elements with respect to the crystallographic orientation. A broad range of analytical techniques were used, including optical microscopy coupled with cathodoluminescence imaging, electron probe microanalysis (EPMA), laser ablation – inductively coupled plasma mass spectrometry (LA-ICPMS), Raman microspectroscopy, and simultaneous thermal analysis coupled with mass spectrometry. The investigated crystal consists of the main crystal with a distinct core and rim (Ap_2core and Ap_2rim, respectively), which grew on a previous, euhedral crystal (Ap₁). The fluorapatite demonstrates various types of zoning: regular oscillatory, irregular, and internal sectoring, which is also reflected in trace elements concentrations. The rim Ap_2rim has lower concentrations of Mn, Sr and Fe, and significantly higher concentrations of REE compared to the core Ap_2core and older crystal Ap₁. Furthermore, the rim Ap_2rim is strongly depleted in Th, U and Pb. The entire crystal shows elevated Eu contents, expressed as a strong positive anomaly in chondrite-normalized REE patterns. With regards to the volatiles, F concentrations are constant in Ap₁, Ap_2core and Ap_2rim, whereas Cl is below the EPMA detection limit. The Ap_2rim was the only part of the investigated material containing OH and CO₃, which were observed in the Raman spectra. Furthermore, part of the crystal Ap_2core is extensively altered, likely due to fluid-induced metasomatic processes. LA-ICPMS U-Pb dating yielded highly discordant dates due to common Pb content. A lower intercept age of 297 ± 13 Ma (MSWD = 0.13) indicates the age of the fluorapatite crystallization. The overall analytical data constrain growth and post-growth processes, including crystallization of Ap₁ and Ap_2core, which both have typical hydrothermal Sn-W deposit characteristics, whereas Ap_2rim is related to a carbonate stage of the mineralization in the Panasqueira deposit.  相似文献   

Orogenic Gold Mineralization in the Qolqoleh Deposit, Northwestern Iran   总被引：1，自引：1，他引：1  

Farhang Aliyari    Ebrahim Rastad  Hou Zengqian 《Resource Geology》2007,57(3):269-282

The Qolqoleh gold deposit is located in the northwestern part of the Sanandai‐Sirjan Zone, northwest of Iran. Gold mineralization in the Qolqoleh deposit is almost entirely confined to a series of steeply dipping ductile–brittle shear zones generated during Late Cretaceous–Tertiary continental collision between the Afro‐Arabian and the Iranian microcontinent. The host rocks are Mesozoic volcano‐sedimentary sequences consisting of felsic to mafic metavolcanics, which are metamorphosed to greenschist facies, sericite and chlorite schists. The gold orebodies were found within strong ductile deformation to late brittle deformation. Ore‐controlling structure is NE–SW‐trending oblique thrust with vergence toward south ductile–brittle shear zone. The highly strained host rocks show a combination of mylonitic and cataclastic microstructures, including crystal–plastic deformation and grain size reduction by recrystalization of quartz and mica. The gold orebodies are composed of Au‐bearing highly deformed and altered mylonitic host rocks and cross‐cutting Au‐ and sulfide‐bearing quartz veins. Approximately half of the mineralization is in the form of dissemination in the mylonite and the remainder was clearly emplaced as a result of brittle deformation in quartz–sulfide microfractures, microveins and veins. Only low volumes of gold concentration was introduced during ductile deformation, whereas, during the evident brittle deformation phase, competence contrasts allowed fracturing to focus on the quartz–sericite domain boundaries of the mylonitic foliation, thus permitting the introduction of auriferous fluid to create disseminated and cross‐cutting Au‐quartz veins. According to mineral assemblages and alteration intensity, hydrothermal alteration could be divided into three zones: silicification and sulfidation zone (major ore body); sericite and carbonate alteration zone; and sericite–chlorite alteration zone that may be taken to imply wall‐rock interaction with near neutral fluids (pH 5–6). Silicified and sulfide alteration zone is observed in the inner parts of alteration zones. High gold grades belong to silicified highly deformed mylonitic and ultramylonitic domains and silicified sulfide‐bearing microveins. Based on paragenetic relationships, three main stages of mineralization are recognized in the Qolqoleh gold deposit. Stage I encompasses deposition of large volumes of milky quartz and pyrite. Stage II includes gray and buck quartz, pyrite and minor calcite, sphalerite, subordinate chalcopyrite and gold ores. Stage III consists of comb quartz and calcite, magnetite, sphalerite, chalcopyrite, arsenopyrite, pyrrhotite and gold ores. Studies on regional geology, ore geology and ore‐forming stages have proved that the Qolqoleh deposit was formed in the compression–extension stage during the Late Cretaceous–Tertiary continental collision in a ductile–brittle shear zone, and is characterized by orogenic gold deposits.  相似文献   

湘西合仁坪钠长石-石英脉型金矿床围岩蚀变及质量平衡   总被引：2，自引：0，他引：2  

张婷  彭建堂 《地球科学与环境学报》2014,(4)

湘西柳林汊一带钠长石-石英脉型金矿十分发育。为了揭示该区金矿的成矿物质来源、成矿过程及成矿流体信息,对该区最典型的合仁坪钠长石-石英脉型金矿床围岩蚀变特征进行研究,并利用标准化Isocon图解法,对围岩蚀变过程中物质带入、带出进行质量平衡计算。结果表明:合仁坪金矿床的围岩蚀变主要包括绢云母化(褪色化)、黄铁矿化和绿泥石化,其中褪色化分布最为广泛,是该区金矿床最重要的蚀变类型;在合仁坪金矿床形成过程中,围岩中的Al2O3为惰性组分,Na2O、Sr、V、Cr、W、Nb、Th及部分挥发分(S、CO2和H2O)等组分被带入围岩中,而SiO2、Fe2O3、K2O、CaO、MgO、Cu、As、Pb、Zn、Ni、Co、Sb、Li、Rb、Ba等组分从围岩中迁出;轻稀土元素的迁出程度远远大于重稀土元素,围岩蚀变过程中轻、重稀土元素发生强烈的分异;矿脉中钠长石的钠质并非来自赋矿围岩,而是由成矿流体从外界带入的;矿脉石英中硅质则部分来自赋矿围岩。  相似文献   

卢氏西虎岭黄铁矿床围岩蚀变特征及其找矿意义     

阎五成 《河南国土资源》1996,(2)

文章通过对西虎岭黄铁矿床围岩蚀变的研究认为，围岩蚀变大致可分为６种基本蚀变类型，５个蚀变阶段，３个蚀变带。各蚀变带以矿体为中心对称分布，各带之间呈渐变过渡关系。同时认为矿床成因类型属中低温热液充填型，并指出围岩蚀变的找矿意义。  相似文献   

洛宁铁炉坪银铅矿床围岩蚀变分带特征     

郭时然 《河南国土资源》1995,(1)

本文通过对铁炉坪银、铅矿床围岩蚀变的研究，划分出６种基本蚀变类型，３种蚀变带。各蚀变带以矿体为中心对称分布，各带之间呈渐变过渡关系。并指出由蚀变作用引起围岩化学成分及微量元素含量的变化，岩石化学成分与矿物成分变化相一致，成矿与围岩蚀变相辅相成。还指出了围岩蚀变的找矿意义。  相似文献   

Geomorphology of coal seam fires     

Claudia Kuenzer  Glenn B. Stracher 《Geomorphology》2012,138(1):209-222

Coal fires occur in underground natural coal seams, in exposed surface seams, and in coal storage or waste piles. The fires ignite through spontaneous combustion or natural or anthropogenic causes. They are reported from China, India, USA, South Africa, Australia, and Russia, as well as many other countries. Coal fires lead to loss of a valuable resource (coal), the emission of greenhouse-relevant and toxic gases, and vegetation deterioration. A dangerous aspect of the fires is the threat to local mines, industries, and settlements through the volume loss underground. Surface collapse in coal fire areas is common. Thus, coal fires are significantly affecting the evolution of the landscape. Based on more than a decade of experience with in situ mapping of coal fire areas worldwide, a general classification system for coal fires is presented. Furthermore, coal seam fire geomorphology is explained in detail. The major landforms associated with, and induced by, these fires are presented. The landforms include manifestations resulting from bedrock surface fracturing, such as fissures, cracks, funnels, vents, and sponges. Further manifestations resulting from surface bedrock subsidence include sinkholes, trenches, depressions, partial surface subsidence, large surface subsidence, and slides. Additional geomorphologic coal fire manifestations include exposed ash layers, pyrometamorphic rocks, and fumarolic minerals. The origin, evolution, and possible future development of these features are explained, and examples from in situ surveys, as well as from high-resolution satellite data analyses, are presented. The geomorphology of coal fires has not been presented in a systematic manner. Knowledge of coal fire geomorphology enables the detection of underground coal fires based on distinct surface manifestations. Furthermore, it allows judgments about the safety of coal fire-affected terrain. Additionally, geomorphologic features are indicators of the burning stage of fires. Finally, coal fire geomorphology helps to explain landscape features whose occurrence would otherwise not be understood. Although coal fire-induced thermal anomalies and gas release are also indications of coal fire activity, as addressed by many investigators, no assessment is complete without sound geomorphologic mapping of the fire-induced geomorphologic features.  相似文献   

Quantification of human and climate contributions to multi-dimensional hydrological alterations: A case study in the Upper Minjiang River,China     

ZHANG Yuhang  YE Aizhong  YOU Jinjun  JING Xiangyang 《地理学报(英文版)》2021,31(8):1102-1122

Dual factors of climate and human on the hydrological process are reflected not only in changes in the spatiotemporal distribution of water resource amounts but also in the various characteristics of river flow regimes. Isolating and quantifying their contributions to these hydrological alterations helps us to comprehensively understand the response mechanism and patterns of hydrological process to the two kinds of factors. Here we develop a general framework using hydrological model and 33 indicators to describe hydrological process and quantify the impact from climate and human. And we select the Upper Minjiang River(UMR) as a case to explore its feasibility. The results indicate that our approach successfully recognizes the characteristics of river flow regimes in different scenarios and quantitatively separates the climate and human contributions to multi-dimensional hydrological alterations. Among these indicators, 26 of 33 indicators decrease over the past half-century(1961–2012) in the UMR, with change rates ranging from 1.3% to 33.2%, and the human impacts are the dominant factor affecting hydrological processes, with an average relative contribution rate of 58.6%. Climate change causes an increase in most indicators, with an average relative contribution rate of 41.4%. Specifically, changes in precipitation and reservoir operation may play a considerable role in inducing these alterations. The findings in this study help us better understand the response mechanism of hydrological process under changing environment and is conducive to climate change adaptation, water resource planning and ecological construction.  相似文献   

西准噶尔白杨河铍铀矿床中铍与铀成生关系初探——来自围岩蚀变和矿石矿物接触关系的证据     

刘畅 《地质与勘探》2020,56(3):465-477

与高硅富氟火成岩(流纹岩或花岗斑岩)有关的铍矿床中常伴有铀矿化,其成矿特色明显,是认识岩浆-岩浆热液-热液演化过程中铍与铀地球化学行为异同的理想对象,但其中铍与铀成矿的时空关系及成因关系尚不清楚。为了理解该类矿床中铍与铀的成生关系,并为区域内铍与铀的找矿勘查提供理论支撑,本文选取该类矿床的典型代表—西准噶尔白杨河铍铀矿床为研究对象,通过镜下观察、扫描电镜能谱和激光拉曼光谱分析,对矿区内单铍矿石、单铀矿石和铍铀矿石开展了系统的岩相和矿相学研究。结果显示,与铍矿化相关的围岩蚀变为钠长石化、电气石化、白云母化、萤石化、碳酸盐化和绿泥石化,与铀矿化相关的围岩蚀变为硅化、赤铁矿化、萤石化、伊利石化和锰矿化(含少量铅),且铍铀矿石中可见沥青铀矿切穿羟硅铍石的现象。结合铍与铀的地球化学行为和前人研究成果,认为白杨河铍铀矿床中铍矿化与铀矿化应是不同期热液作用的结果:铍矿化可能是花岗斑岩深部岩浆房分异的岩浆热液在不断演化过程中形成的,而铀矿化可能与后期流体(如幔源流体、加热循环的大气降水等)的淋滤作用有关。  相似文献   

黄河流域气候与农业种植面积变化对径流的影响     

李华贞  张强  顾西辉  史培军 《湖泊科学》2018,30(4):1138-1151

根据黄河流域1960—2005年5个水文站逐日流量、77个气象站1959—2013年逐日降水数据,结合流域内主要农作物种植面积及大型水库资料,全面探讨气候与农业面积变化及人类活动对黄河流域径流变化的影响.研究表明:黄河流域所有流量分位数总体呈下降趋势,并于1980s中后期到1990s中期发生突变.降水变化是黄河流域径流变化的主要影响因素.在考虑不同流量分位数情况下,农作物种植面积变化对不同分位数径流变化的影响也有差异性.花园口站农作物种植面积变化对径流量量级和可变性均有显著影响;其余4站各项气候变化与农作物种植指标参数较大,虽均未达到10%的显著性水平,但仍会对径流的量级变化产生影响.对唐乃亥站,农作物耕作面积的下降减少了灌溉用水,在0.5流量分位数时有高达60%增加径流量的间接作用.对于头道拐站,农作物耕作面积的增加使得流域总蒸发量增加,灌溉用水增加,在0.3流量分位数时有高达40%减少径流量的间接作用.该研究为气候变化与人类活动影响下黄河流域水资源优化配置提供重要理论依据.  相似文献   

中国微细浸染型金矿床围岩蚀变地质特征   总被引：3，自引：0，他引：3       下载免费PDF全文

吴烈善  彭省临 《地质找矿论丛》2005,20(3):151-155,160

微细浸染型金矿的围岩蚀变一般较弱,主要蚀变类型以硅化、碳酸盐化、粘土化、绢云母化为主;围岩蚀变与容矿岩石类型及其岩性组合密切相关,化学组分的变化因围岩的性质而异;金矿化强度与围岩蚀变强度和蚀变组合复杂程度成正比,金矿体出现在蚀变中心部位或蚀变分带的内带.  相似文献