Lost City低温热液场——一种新的海底热液活动类型   总被引：3，自引：1，他引：3  

钱江初  于刚  刘春秋  雷吉江  初凤友 《海洋学研究》2006,24(1):43-49

综述了新近发现的海底热液活动的新类型——Lost C ity低温热液场。该低温热液场坐落于距洋中脊15 km远的轴外洋底上,下伏的橄榄石经蛇纹石化反应所产生的热能是驱动该热液场的热源。低温热液场烟囱结构的矿物组分主要为方解石、文石和水镁石,热液流的温度为40~75℃,并以高pH值以及高氢、高甲烷含量为特征。Lost C ity低温热液场,为研究者们了解早期地球热液过程与它们所支撑的生命系统关系,探讨蛇纹石化、碳酸盐沉淀、微生物活动之间关系提供了天然实验室。  相似文献   

Platinum-Group Elements in Sulphide Minerals, Platinum-Group Minerals, and Whole-Rocks of the Merensky Reef (Bushveld Complex, South Africa): Implications for the Formation of the Reef   总被引：4，自引：0，他引：4  

Godel  Belinda; Barnes  Sarah-Jane; Maier  Wolfgang D. 《Journal of Petrology》2007,48(8):1569-1604

The concentrations of platinum-group elements (PGE), Co, Re,Au and Ag have been determined in the base-metal sulphide (BMS)of a section of the Merensky Reef. In addition we performeddetailed image analysis of the platinum-group minerals (PGM).The aims of the study were to establish: (1) whether the BMSare the principal host of these elements; (2) whether individualelements preferentially partition into a specific BMS; (3) whetherthe concentration of the elements varies with stratigraphy orlithology; (4) what is the proportion of PGE hosted by PGM;(5) whether the PGM and the PGE found in BMS could account forthe complete PGE budget of the whole-rocks. In all lithologies,most of the PGE (65 up to 85%) are hosted by PGM (essentiallyPt–Fe alloy, Pt–Pd sulphide, Pt–Pd bismuthotelluride).Lesser amounts of PGE occur in solid solution within the BMS.In most cases, the PGM occur at the contact between the BMSand silicates or oxides, or are included within the BMS. Pentlanditeis the principal BMS host of all of the PGE, except Pt, andcontains up to 600 ppm combined PGE. It is preferentially enrichedin Pd, Rh and Co. Pyrrhotite contains, Rh, Os, Ir and Ru, butexcludes both Pt and Pd. Chalcopyrite contains very little ofthe PGE, but does concentrate Ag and Cd. Platinum and Au donot partition into any of the BMS. Instead, they occur in theform of PGM and electrum. In the chromitite layers the whole-rockconcentrations of all the PGE except Pd are enriched by a factorof five relative to S, Ni, Cu and Au. This enrichment couldbe attributed to BMS in these layers being richer in PGE thanthe BMS in the silicate layers. However, the PGE content inthe BMS varies only slightly as a function of the stratigraphy.The BMS in the chromitites contain twice as much PGE as theBMS in the silicate rocks, but this is not sufficient to explainthe strong enrichment of PGE in the chromitites. In the lightof our results, we propose that the collection of the PGE occurredin two steps in the chromitites: some PGM formed before sulphidesaturation during chromitite layer formation. The remainingPGE were collected by an immiscible sulphide liquid that percolateddownward until it encountered the chromitite layers. In thesilicate rocks, PGE were collected by only the sulphide liquid. KEY WORDS: Merensky Reef; Rustenburg Platinum Mine; sulphide; platinum-group elements; image analysis; laser ablation ICP-MS  相似文献   

Draa Sfar, Morocco: A Visean (331 Ma) pyrrhotite-rich, polymetallic volcanogenic massive sulphide deposit in a Hercynian sediment-dominant terrane     

Eric Marcoux  Abdelhay Belkabir  Harold L. Gibson  David Lentz  Gilles Ruffet 《Ore Geology Reviews》2008,33(3-4):307-328

Draa Sfar is a Visean, stratabound, volcanogenic massive sulphide ore deposit hosted by a Hercynian carbonaceous, black shale-rich succession of the Jebilet terrane, Morocco. The ore deposit contains 10 Mt grading 5.3 wt.% Zn, 2 wt.% Pb, and 0.3 wt.% Cu within two main massive sulphides orebodies, Tazakourt (Zn-rich) and Sidi M'Barek (Zn–Cu rich). Pyrrhotite is by far the dominant sulphide (70 to 95% of total sulphides), sphalerite is fairly abundant, chalcopyrite and galena are accessory, pyrite, arsenopyrite and bismuth minerals are rare. Pyrrhotite is monoclinic and mineralogical criteria indicate that it is of primary origin and not formed during metamorphism. Its composition is very homogeneous, close to Fe₇S₈, and its absolute magnetic susceptibility is 2.10^− 3 SI/g. Ar–Ar dating of hydrothermal sericites from a coherent rhyolite flow or dome within the immediate deposit footwall indicates an age of 331.7 ± 7.9 Ma for the Draa Sfar deposit and rhyolite volcanism.The Draa Sfar deposit has undergone a low-grade regional metamorphic event that caused pervasive recrystallization, followed by a ductile–brittle deformation event that has locally imparted a mylonitic texture to the sulphides and, in part, is responsible for the elongated and sheet-like morphology of the sulphide orebodies. Lead isotope data fall into two compositional end-members. The least radiogenic end-member, (²⁰⁶Pb/²⁰⁴Pb = 18.28), is characteristic of the Tazakourt orebody, whereas the more radiogenic end-member (²⁰⁶Pb/²⁰⁴Pb  18.80) is associated with the Sidi M'Barek orebody, giving a mixing trend between the two end-members. Lead isotope compositions at Draa Sfar testify to a significant continental crust source for the base metals, but are different than those of the Hajar and South Iberian Pyrite Belt VMS deposits.The abundance of pyrrhotite versus pyrite in the orebodies is attributed to low fO₂ conditions and neither a high temperature nor a low aH₂S (below 10^− 3) is required. The highly anoxic conditions required to stabilize pyrrhotite over pyrite are consistent with formation of the deposit within a restricted, sediment-starved, anoxic basin characterized by the deposition of carbonaceous, pelagic sediments along the flank of a rhyolitic flow-dome complex that was buried by pelitic sediments. Deposition of sulphides likely occurred at and below the seafloor within anoxic and carbonaceous muds.Draa Sfar and other Moroccan volcanogenic massive sulphide deposits occur in an epicontinental volcanic domain within the outer zone of the Hercynian belt and formed within a sedimentary environment that has a high pelagic component. In spite of the diachronous emplacement between the IPB deposits (late Devonian to Visean) and Moroccan deposits (Dinantian), all were formed around 340 ± 10 Ma following a major phase of the Devonian compression.  相似文献   

Magnetic mineral diagenesis in the post-glacial muddy sediments from the southeastern South Yellow Sea: Response to marine environmental changes   总被引：2，自引：1，他引：1  

Jeong-Hae Chang 《中国科学D辑(英文版)》2005,48(1):134-144

Core YSDP103 was retrieved in the muddy deposit under the cold eddy of the southeastern South Yellow Sea, and the uppermost 29.79 m core represents the muddy sediments formed in the shelf since about 13 ka BP. The lower part from 29.79 to 13.35 m, called Unit A2, was deposited during the period from the post-glacial transgression to the middle Holocene (at about 6 14C ka BP) when the rising sea level reached its maximum, while the upper part above 13.35 m (called Unit A1) was deposited in a cold eddy associated with the formation of the Yellow Sea Warm Current just after the peak of post-glacial sea level rise. Rock-magnetic properties of the uppermost 29.79 m core were investigated in detail. The experimental results indicate that the magnetic mineralogy of the core is dominated by magnetite, maghemite and hematite and that, except for the uppermost 2.35 m, the magnetic minerals were subject to reductive diagene-sis leading to significant decline of magnetic mineral content and the proportion of low-coe  相似文献   

昆盖山北坡火山岩型块状硫化物铜矿床成矿条件分析及找矿预测     

张佩民  孙海田  李纯杰  李长江 《地质与勘探》2006,42(6):5-9

在西昆仑盖山北坡恰尔隆-库尔浪-塔木铜多金属-金成矿带内,对产于下石炭统基性火山岩中的块状硫化物铜矿床和产于上石炭统酸性火山岩中的块状硫化物铜矿床的成矿条件,通过代表性矿床进行了对比分析.认为两者形成的地质构造环境相同,形成时间相近,空间上毗邻,矿化特征又极其相似,具有密切的内在成因联系数.结合成矿地质环境,铜金矿化蚀变信息提取图像上显示的色晕异常带与已知铜、金矿床和矿点的叠合程度,以及水系沉积物地球化学异常条件,进行铜矿成矿预测,认为该成矿带内的阿属河-木孜塔格-带是铜矿找矿的有望地区.  相似文献   

锍镍试金富集-等离子体质谱法测定西太平洋富钴结壳中的铂族元素   总被引：6，自引：9，他引：6  

石贵勇  孙晓明  屈文俊  薛婷  张美  熊德信  王生伟 《岩矿测试》2007,26(2):113-116

根据西太平洋麦哲伦海山富钴板状结壳样品的成分特征，对常规的锍镍试金配方作了改进；酌情减少捕集剂羰基镍的加入量，可显著降低铂族元素的空白值。富集后的样品，采用电感耦合等离子体质谱测定铂族元素（PGE）。其中，Ru、Rh、Pd、Ir和Pt用常规外标法测定，^175Lu作内标；Os用同位素稀释法测定。用国家一级标准物质GBW07290和GBW07291作监控分析质量的参考样，结果满足要求。  相似文献   

铅锌矿床中铅锌硫化物真的是从酸性溶液中析出?--以云南会泽铅锌矿床为例     

张振亮  黄智龙  饶冰  管涛  严再飞 《矿物学报》2006,26(1):53-58

流体是不是呈酸性,不是简单地由其pH值是否小于7确定,而应该根据其pH值是否大于一定温度下纯水的pH值确定。以会泽铅锌矿床为例,根据不同成矿阶段矿物相之间的平衡条件,讨论了成矿流体pH值随温度变化的情况。结果表明,会泽铅锌矿床成矿时流体呈中性—弱碱性,金属矿物(包括金属硫化物)是从中性—弱碱性溶液(而不是酸性溶液)中析出,这与前人的观点有着很大的不同。  相似文献   

The influence of bedrock‐derived acidity in the development of surface and underground karst: evidence from the Precambrian carbonates of semi‐arid northeastern Brazil     

Augusto S. Auler  Peter L. Smart 《地球表面变化过程与地形》2003,28(2):157-168

Very extensive cave systems are developed in Precambrian Una Group carbonates in the Campo Formoso area, eastern Brazil. In contrast, the area is largely devoid of significant surface karst landforms, as would be expected given its semi‐arid climate. The caves in the area display many morphological features characteristic of deep‐seated hypogenic caves, such as lack of relationship with the surface, ramiform/network pattern, abrupt variations of passage cross‐sections and absence of fluvial sediments, but do not show evidence of vertical passages marking the ascending path of acidic water nor present extensive gypsum or acid clay mineral deposits. Hydrochemical analyses of present‐day ground water indicate that oxidation of bedrock sulphide is an active process, and sulphuric acid may be the main agent driving carbonate dissolution in the area. A shallow mode of speleogenesis is thus proposed, in which sulphuric acid produced through the oxidation of sulphide beds within the carbonates controls cave initiation and development. Moreover, the geological situation of the area in an ancient stable passive margin precludes the possibility of deep‐seated sources of acidity. Under dry climate, due to the absence of recharge, solutional landforms will be largely subdued in the surface. Hypogenic processes, if present, are likely to predominate, producing a landscape characterized by a marked disparity in the comparative degree of development between surface and underground landforms. Rates of karst landform development have traditionally been analysed through a climatic perspective, runoff being the main controlling factor in promoting karst development. This view needs to be reassessed in the light of the growing awareness of the importance of climate‐independent processes related to hypogenic sources of acidity. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

安徽铜陵冬瓜山铜、金矿床两阶段成矿模式   总被引：21，自引：0，他引：21  

陆建军  华仁民  徐兆文  高剑峰  李娟 《高校地质学报》2003,9(4):678-690

冬瓜山铜金矿床包括层状硫化物矿体、矽卡岩型和斑岩型矿体。层状硫化物矿体具层状形态和层控特征，矿石具块状、层纹状和揉皱状构造。燕山期岩浆岩及其岩浆流体对层状矿体进行了叠加和改造，改变了其结构构造、矿物组合和矿石成分，并在其上叠加蚀变和矿化。层状矿体中的铜是由含铜流体交代块状硫化物矿石形成的。冬瓜山铜金矿床经历了两次成矿作用：第一成矿阶段．在石炭纪中期，海底喷流作用形成了块状硫化物矿床，矿石成分以硫、铁矿为主；第二成矿阶段。燕山期岩浆侵人，一方面岩浆热液与围岩相互作用发生矽卡岩化、硅化、钾长石化、石英绢云母化和青磐岩化，形成矽卡岩型和斑岩型矿体，另一方面岩浆流体对块状硫化物矿体进行叠加改造，致使块状硫化物矿体富集铜等成矿物质。  相似文献   

Oxidation of sulphur compounds in the atmosphere: I. Rate constants of OH radical reactions with sulphur dioxide,hydrogen sulphide,aliphatic thiols and thiophenol     

Barnes  I.  Bastian  V.  Becker  K. H.  Fink  E. H.  Nelsen  W. 《Journal of Atmospheric Chemistry》1986,4(4):445-466

The reactions of OH radicals with SO₂, H₂S, thiophenol, and a series of aliphatic thiols (1–5 C-atoms) have been investigated in 201 and 381 reaction chambers at 1 atm total pressure and 300 K using a competitive kinetic technique. Initially, OH radicals were produced by photolysis of CH₃ONO/NO mixtures in air. Applying this OH source rate constants for OH with SO₂, H₂S, and thiophenol in synthetic air were determined to be (1.1±0.2)×10^-12, (5.5±0.8)×10^-12 and (1.1±0.2)×10^-11 cm³ s^-1, respectively. However, when this method was applied to the aliphatic thiols the rate constants obtained were found to be dependent on the partial pressures of O₂ and NO. These effects have been attributed to the built-up of a radical species, not yet identified, which leads to uncontrolled chain reactions in the system. Using the photolysis of H₂O₂ at wavelengths greater than 260 nm as the OH source in 1 atm N₂, rate constants for the 1–5 aliphatic thiols in the range 2.9 to 5.6×10^-11 cm³ s^-1 were obtained. The rate constants obtained in the present study are compared with recent literature values.  相似文献