Epigenetic hydrothermal origin of native copper and supergene enrichment in the Vista Alegre district,Paraná basaltic province,southernmost Brazil     

《International Geology Review》2012,54(10):1163-1179

Native copper is widespread in the Lower Cretaceous Paraná basaltic province, southern Brazil, both as films in fractures and as massive balls in amygdules. The focus of this investigation is on the large concentration of occurrences (n = 85) that forms the Vista Alegre district in the border region of Rio Grande do Sul and Santa Catarina states. The high average of 220 ppm Cu content of the basalts resulted in ore of native copper, Cu oxides, abundant chrysocolla in the top of mineralizations, and minor malachite and azurite. Native copper is associated with dioctahedral and trioctahedral smectites, zeolites (heulandite and clinoptilonite), quartz, and calcite, typical of a low-T (100–150°C) hydrothermal alteration assembly. The PGE distribution shows enrichment in Pd in relation to Pt both in basalts and in native copper, supporting the hypothesis of hydrothermal origin of the mineralization. No evidence was found of direct precipitation of copper from the lava; based on field and petrographic evidence, integrated with BSE images, EPMA analyses, EGP contents of native copper, and bulk rock analyses, this is an epigenetic hydrothermal copper mineralization, followed by supergene enrichment.  相似文献   

雅鲁藏布江西段东波超镁铁岩体经历了俯冲带流体的改造：来自铂族元素的证据          下载免费PDF全文

牛晓露杨经绥  陈松永刘 飞 熊发挥 刘 钊 郭国林 《中国地质》2013,40(3):756-766

提要：东波超镁铁岩体位于雅鲁藏布江缝合带的西段,在中国是一个不多见的面积超过400 km2的大型超镁铁岩体。已有的岩石学和矿物学特征表明,该岩体与同一带中含有大型铬铁矿的罗布莎岩体可以对比,是一个寻找铬铁矿床的远景区。本文开展了东波超镁铁岩的主要组成岩石类型——方辉橄榄岩的铂族元素（PGE）研究,并结合主量和稀土元素（REE）组成,探讨岩体的成因。东波超镁铁岩中方辉橄榄岩具有相当高的Os含量（3.52×10-9~4.36×10-9）,亏损的主量元素组成和低于原始地幔的稀土元素含量（0.89×10-6~1.37×10-6）,指示东波超镁铁岩为经历过部分熔融和熔体抽取的亏损残余地幔岩石。东波超镁铁岩的PGE总含量为23.97×10-9~31.98×10-9,高于原始地幔的含量;PGE配分型式为左倾的正斜率型,相对Ir亚组铂族元素（IPGE）亏损钯亚组铂族元素（PPGE）,Pd/Ir=1.49~2.65;REE配分型式为中稀土亏损的“V”型或“U”型,原始地幔标准化元素比值（La/Sm）m 为 1.05~3.37,（Gd/Yb）m=0.28~0.64;这些数据揭示东波超镁铁岩经历过交代作用,交代物质应富集不相容元素,高PGE含量,相对IPGE富集PPGE;较低的Cu/Pd比值（1226~3448）要求交代物质还应富含硫化物;推测交代物质可能来源于俯冲带构造环境下所产生岩浆熔离出的富硫化物熔体/流体。  相似文献   

铂族元素矿床热液流体成矿模型探讨   总被引：1，自引：0，他引：1       下载免费PDF全文

李瑞鹏  颜建东 《地质找矿论丛》2013,28(3):335-343

世界上所有的铂族金属矿床都有热液流体活动的迹象。影响铂族元素(PGE)成矿的流体主要有两类:堆晶体后期流体(>500℃)和岩浆后期流体(<500℃)。低温热液(<500℃)中,PGE可能主要以氯络合物及氢硫基络合物的形式运移;高温热液(>500℃)中,PGE可能主要以氯络合物的形式运移。在详细论述不同温度、压力条件下的热液流体中PGE溶解性质的基础上,分析了PGE在流体中的溶解、迁移、富集及可能的沉淀机制,为探寻PGE矿床的成因提供一个突破口。  相似文献   

中国大陆科学钻100～850 m深度岩心的贵金属地球化学   总被引：2，自引：1，他引：1  

王登红  陈毓川  徐珏  余金杰  李纯杰 《地球学报》2005,26(6):535-540

本文对CCSD超深钻中首次获得的铂族元素及金、银的地球化学特点进行了分析和研究,结果表明各类样品的铂族元素含量均偏低,100～850 m深度平均Ir小于0.1×10-9,Os小于0.3×10-9,Pd小于0.5×10-9,Pt小于0.4×10-9,Rh小于0.1×10-9,Ru小于0.4×10-9,只有个别橄榄岩样品的铂族元素含量接近于地壳丰度,但远远低于超基性岩的一般含量.这种极低的铂族元素含量,属于"负异常",表明在变质作用过程中铂族元素发生了活化转移.榴辉岩和橄榄岩的铂族元素含量都偏低,但其球粒陨石标准化配分明显具有明显不同的特点,利用铂族元素仍然可以帮助对变质岩进行分类或恢复原岩.前人在蒋庄超基性岩岩体的人工重砂中发现有铂族矿物,其中包括有铱铂矿.可见,铂族元素是可以活化转移的,其活化转移的原因还需要探讨,是在结晶分异过程中转移的、还是在折返过程中活化的、或者是在造山运动结束之后由于其他原因而造成的,尚需要深入研究.  相似文献   

长江口及邻近陆架沉积物中Pt、Pd分异的物源示踪     

张霄宇  张富元  高爱根  章伟艳 《地球科学》2009,34(4):604-612

Pt/Pd比值在研究区分布呈显著的区域特征.南黄海沿岸流输送物质以Pt/Pd > 1为特征, 为古黄河三角洲来源; 长江流域来源物质以Pt/Pd≤1为特征.长江物源组分的影响范围广, 在125°E、33°N沉积物中还能发现受长江物质的明显影响.除了源岩中Pt、Pd分配因素外, 黄河和长江流域不同类型和程度的风化作用对沉积物中Pt、Pd分异起着关键的控制作用.虽然沉积物中氯含量、粒度效应在一定程度上影响着Pt、Pd分布, 但是没有造成显著的Pt、Pd分馏.Pt/Pd≤1区域中元素组成和长江沉积物的组成特征一致, 呈现比较强的硅质风化作用; Pt/Pd > 1区域沉积物中的元素组成和黄河沉积物一致, K/Na-Rb/Sr图解显示古黄河物质在再侵蚀、搬运和沉积过程中化学成分进一步分异.   相似文献   

铜、镍、铂族元素地球化学性质及其在幔源岩浆起源、演化和岩浆硫化物矿床研究中的意义          下载免费PDF全文

宋谢炎胡瑞忠  陈列锰 《地学前缘》2009,16(4):287-305

Ni、Cu和PGE具有不同于其他微量元素的特殊的地球化学性质,这些特殊的性质使得它们在幔源岩浆起源和演化以及岩浆硫化物矿床的成因研究中具有不可替代的作用。在S不饱和的条件下,Ni、Os、Ir和Ru具有相容元素的特性,而Cu和Pd是强不相容元素,因此,它们在玄武岩浆分离结晶过程中常常发生分异。一旦体系达到S饱和,这些元素则会强烈地进入硫化物熔浆,特别是PGE具有极高的硫化物熔浆/硅酸盐熔浆分配系数,极微量的硫化物熔离便可导致残余岩浆中PGE的显著亏损,因此,PGE是玄武岩浆硫化物熔离作用最敏感的示踪元素。硫化物熔离和成矿实质上是幔源岩浆特殊演化过程的结果,所以,Ni,Cu和PGE的特殊性质可用来探讨岩浆硫化物成矿的关键控制因素。Ni、Cu和PGE具有不同的单硫化物固溶体/硫化物熔浆分配系数,因此,它们也是硫化物熔浆结晶分异的重要示踪元素。本文试图从Ni、Cu和PGE地球化学性质和行为入手,并借助一些研究实例,对它们在幔源岩浆起源和演化以及岩浆硫化物矿床成因研究中的示踪意义进行系统介绍。  相似文献   

Chromite and PGE deposits of mesoarchaean ultramafic-mafic suites within the greenstone belts of the Singhbhum craton,India: Implications for mantle heterogeneity and tectonic setting     

Sisir K. Mondal 《Journal of the Geological Society of India》2009,73(1):36-51

The Archaean cratonic nuclei of the continents are important as they contain the most significant evidences for the evolution of Earth e.g. the greenstone sequences. In the Indian Shield, one of the important cratons is the Singhbhum craton, where nearly 95% of the Indian chromite deposits and only PGE deposits are located which are hosted within Mesoarchaean ultramafic-mafic rock sequences. The ultramafic units occur as sill like intrusions within the Iron Ore Group (IOG) greenstone belts and often associated with gabbroic intrusions. In the Nuasahi and Sukinda mining districts of these occurrences, detailed petrological, geochemical and isotopic studies have been carried out in the last decades. Petrological and geochemical studies indicate a supra-subduction zone (SSZ) tectonic settings in Archaean for the origin of these ultramafic-mafic sequences. The Os isotopic and platinum group element (PGE) geochemical studies of chromites from the two mining districts indicate presence of a subchondritic source mantle domain beneath and within the Singhbhum craton similar to the Zimbabwean craton of southern African continent. The Os model age calculation indicates melt extraction from a subcontinental lithospheric mantle (SCLM) before 3.7 Ga which is similar to the other ancient cratons. As a whole the study supports the premise that India was part of the African continent in pre-Gondwana times and even in early Archaean and suggest possible amalgamation and building up of a supercontinent during late Archaean. However, in comparison with other occurrences, the Singhbhum craton of the Indian Shield and the Zimbabwean craton in southern Africa are characterized by the presence of subchondritic lithospheric mantle domains within the SCLM, which were developed prior to 3.7 Ga.  相似文献   

Tausonite and aluminum-fluorine titanite from the metamorphosed metalliferous sediments of the Triassic chert formation of the Sikhote Alin     

E. V. Perevoznikova  N. V. Miroshnichenko 《Russian Journal of Pacific Geology》2009,3(3):294-297

Rare strontium mineral tausonite and a peculiar Al- and F-rich titanite variety were found in the metamorphosed metalliferous sediments of the Triassic chert formation of the Sikhote Alin, which are distinguished by the abundance of native elements, intermetallic compounds, and metal solid solutions, as well as the presence of diverse Au, Ag, and PGE minerals. Tausonite was documented in the manganese (metamorphosed siliceous-rhodochrosite) rocks of the Ol’ga mining district and in the “brown cherts” (siliceous rocks with manganese garnet and spessartine) of the Dal’nerechensk district, Primorye. It forms rather numerous grains 2–10 μm across usually occurring as inclusions in quartz or rhodonite. According to the electron microprobe analysis, in addition to Sr, Ti, and O, the mineral contains only Fe³⁺ (up to 0.20 a.f.u.). Aluminum-fluorine titanite was found in the “brown cherts” of the Dal’nerechensk district of Primorye (upper reaches of the Gornaya River). Its crystals are up to 200 × 200 μm in size. The recalculation of the microprobe analyses to crystal chemical formulas indicated that up to half of the Ti sites in the structure of this mineral may be occupied by Al. The decrease of the total positive charge owing to the Al³⁺ substitution for tetravalent Ti⁴⁺ is compensated for by a decrease in the total negative charge owing to F^? substitution for O^2? via the scheme Al³⁺F^? → Ti⁴⁺O^2?. The occurrence of considerable amounts of F substituting for oxygen in the titanite structure and, as a consequence (owing to the crystal chemical features of the mineral), the high Al content were related to the reduced character of the metamorphism of the metalliferous deposits.  相似文献   

Hydrothermal Alteration, Fluid Inclusion and Stable Isotope Studies of the North Roby Zone, Lac des Iles PGE Mine, Ontario, Canada     

Alireza Karimzadeh Somarin  Stephen A. Kissin    Donald D. Heerema    Daniel J. Bihari 《Resource Geology》2009,59(2):107-120

The Archean mafic–ultramafic complex of Lac des Iles, Ontario, Canada, hosts economic platinum group elements (PGE)-Au-Cu-Ni mineralization in the Roby Zone. All lithologies in the North Roby Zone have been affected by hydrothermal alteration. The alteration products include talc (the most dominant mineral), anthophyllite, serpentine, actinolite, tremolite, chlorite, hornblende, zoisite, clinozoisite, epidote and sericite. In the altered rocks, light rare earth elements (La, Ce, Nd, Sm), Pb, Rb, Ba, Cs, S and possibly Y have been added by hydrothermal solution whereas Eu and heavy rare earth elements (Yb, Gd, Dy, Er) remained immobile. There are five types of fluid inclusions in the pegmatitic plagioclase with homogenization temperature and salinity ranging from 240°C to 445°C and 15.37 to 48.52 wt% equivalent NaCl, respectively. The δ¹⁸O and δD of talc range form 6.2‰ to 6.9‰ and −28‰ to −48‰, respectively. δ¹⁸O and δD water in equilibrium with talc during the hydrothermal alteration suggest a modified source for the hydrothermal solution. Microthermometry and stable isotope studies suggest that high temperature–high salinity fluid was diluted by, and mixed with, low temperature–low salinity meteoric solution. This mechanism precipitated the hydrothermal assemblage and redistributed trace elements during and after pegmatite formation in the North Ruby Zone.  相似文献   

岩浆铜-镍-铂族元素硫化矿床“深部熔离-贯入”成矿作用与模式——加拿大伏伊希湾和中国金川矿床地质特征对比     

高辉  曹殿华  范世家 《地质通报》2009,28(6):794-803

通过对金川铜镍矿床地质、矿化特征与加拿大伏伊希湾（Voisey’s Bay）铜-镍-铂族元素硫化物矿床进行系统对比分析,总结出这2个世界级铜镍硫化物矿床形成演化方面的相似性、可比性及其共同特点,即深部岩浆房含矿岩浆沿通道脉动式上侵,到上部表现为“小岩体,成大矿”。成矿作用过程和模式表现为：①含矿岩浆的有序侵位显示岩浆在深部岩浆房停歇过程中曾发生熔离分异,形成岩浆、含矿岩浆、富矿岩浆和矿浆分层结构;②成矿作用是在富有动力的岩浆环境下岩浆不连续（脉动式）上侵过程中发生的,岩浆熔融体富含挥发组分,上侵活动剧烈,围岩角砾化;③含矿岩浆沿相同的通道或越位上侵,在先期侵入岩体下侧或上方不同空间成矿;④岩浆运移过程中与围岩发生相互作用、组分交换和成矿物质的富集。深入阐明了含矿岩浆不连续（脉动式）上侵、后续岩浆补给和混合是镁铁—超镁铁岩体中硫化物被聚集在岩浆流动的通道内形成超大型铜镍硫化物型铂族元素矿床的重要机制。  相似文献