辽西火山岩型金矿地质特征及成因讨论

辽西火山岩型金矿分布在中生代陆相火山盆地边缘活动带内,受辽西弧形构造带控制,为火山期后热液矿床,可初步划分为3种成因类型:次火山(斑岩)热液型(二道沟式),火山—次火山热液型(红石砬子式)和爆发角砾岩型(水泉式),成矿作用与中酸性火山—次火山岩关系密切,成矿时代为燕山期(90—110Ma)。稳定同位素研究结果表明,含矿热液为富含挥发组份和多金属成矿元素的富金水溶液,来源于地壳深部或上地幔,即高温热卤水对镁铁质、超镁铁质岩石长期侵蚀、淋滤和溶解,获取大量的金属成矿元素,在不透水层之下形成深部液态矿源层。     

Metal-residence sites in lavas and tuffs from Volcán Popocatépetl, Mexico: implications for metal mobility in the environment

 Volcan Popocatépetl is a Quaternary stratovolcano located 60 km southeast of Mexico City. The summit crater is the site of recent ash eruptions, excess degassing, and dacite dome growth. The modern cone comprises mainly pyroclastic flow deposits, airfall tephras, debris flows, and reworked deposits of andesitic composition; it is flanked by more mafic monogenetic vents. In least-degassed fallout tuffs and mafic scoria, transition metals are concentrated in phases formed before eruption, during eruption, and after eruption. Preeruptive minerals occur in both lavas and tephra, and include oxides and sulfides in glass and phenocrysts. The magmatic oxides consist of magnetite, ilmenite, and chromite; the sulfides consist of both (Fe,Ni)_1-xS (MSS) and Cu–Fe sulfide (ISS). Syn- and posteruptive phases occur in vesicles in both lavas and tephra, and on surfaces of ash and along fractures. The mineral assemblages in lavas include Cu–Fe sulfide and Fe–Ti oxide in vesicles, and Fe sulfide and Cu–Fe sulfide in segregation vesicles. Assemblages in vesicles in scoria include Fe–Ti oxide and rare Fe–Cu–Sn sulfide. Vesicle fillings of Fe–Ti oxide, Ni-rich chromite, Fe sulfide, Cu sulfide, and barite are common to two pumice samples. The most coarse-grained of the vesicle fillings are Cu–Fe sulfide and Cu sulfide, which are as large as 50 μ in diameter. The youngest Plinian pumice also contains Zn(Fe) sulfide, as well as rare Ag–Cu sulfide, Ag–Fe sulfide, Ag bromide, Ag chloride, and Au–Cu telluride. The assemblage is similar to those typically observed in high-sulfidation epithermal mineralization. The fine-grained nature and abundance of syn- and/or posteruptive phases in porous rocks makes metals susceptible to mobilization by percolating fluids. The abundance of metal compounds in vesicles indicates that volatile exsolution prior to and/or during eruption played an important role in releasing metals to the atmosphere. Received: March 1997 · Accepted: 27 May 1997     

Zircon U-Pb geochronology of Early Jurassic-Late cretaceous volcanic rocks in North Yellow Sea BasinEI北大核心CSCD

The X-drilling cores of the North Yellow Sea basin reveal two sets of Mesozoic clastic rocks, which are the dark rocks in lower part and the red rocks in upper part, respectively. There are two layers of volcanic rocks at the bottom and the upper part of the dark rock unit. The volcanic rocks at the bottom part are trachytic dacite while rocks at the upper part are clastic dacite. The zircon grains from the upper and lower units of volcanic rocks are euhedral-subhedral columnar crystals and show oscillatory zoning on cathodoluminescence images. 22 tests of zircons in the trachytic dacite from the bottom part yield an age of 141-151 Ma, with weighted mean 206Pb/238U age of 145±2 Ma. Whereas 18 tests of zircons from the sample at the upper part give 206Pb/238U ages around 139-149 Ma with weighted mean 206Pb/238U age of 141±2 Ma, which implies that the X well volcanic rocks belong to Late Jurassic-Early Cretaceous. Comparing with the age and geochemical characteristics of the Mesozoic igneous rocks in Shandong peninsula, we suggest that the igneous rocks from both the North Yellow Sea basin and Jiaolai basin were formed under same dynamic setting, i.e., the subduction related volcano arc and back-arc extension. ©, 2015, Science Press. All right reserved.     

Biodiversity and abundance patterns of rock encrusting fauna in a temperate fjord

Fjords are semi-enclosed systems often with usually strong physical and chemical gradients. These gradients provide the opportunity to test the influence of various physical and chemical factors on biodiversity. However study area of this investigation, Trondheimsfjord, is a large water body where especially salinity gradient along the fjord is not well pronounced. The goal of this study was to establish within a temperate fjord a baseline identifying encrusting fauna on rocks and determine the factors driving changes along the length of the fjord and changing depths. There was no trend in species composition change and increase or decrease in number of species, diversity and number of individuals along the fjord. This was likely due to the relative homogeneity of both substrate (rocks) and environmental parameters. Nevertheless, the influence of fresh water inflow in the vicinity of the river mouth was apparent by the presence of characteristic brackish-water species at these locations. Multidimensional scaling analysis revealed three separate assemblages: intertidal, shallow and deep subtidal (below 50 m). Intertidal assemblages were species poor (one to 11 species) but relatively abundant (six to 2374 indiv./m² of rocks). Number of individuals and biomass was highest in the shallow subtidal (2059–13,587 indiv./m² of rocks). Overall the highest species number (45) was recorded at 50 m depth which is probably result of low competition pressure yet still relatively high nutrient concentration in comparison to shallower locations. Environmental parameters (i.e., tidal currents, wave action, salinity) change more drastically with depth than along the fjord and these changes are the major driving forces in shaping encrusting assemblages in Trondheimsfjord.     

Volcanic hazard communication using maps: an evaluation of their effectiveness

Hazard maps are considered essential tools in the communication of volcanic risk between scientists, the local authorities and the public. This study investigates the efficacy of such maps for the volcanic island of Montserrat in the West Indies using both quantitative and qualitative research techniques. Normal plan view maps, which have been used on the island over the last 10 years of the crisis, are evaluated against specially produced three-dimensional (3D) maps and perspective photographs. Thirty-two demographically representative respondents of mixed backgrounds, sex, education and location were interviewed and asked to complete a range of tasks and identification on the maps and photographs. The overall results show that ordinary people have problems interpreting their environment as a mapped representation. We found respondents’ ability to locate and orientate themselves as well as convey information relating to volcanic hazards was improved when using aerial photographs rather than traditional plan view contour maps. There was a slight improvement in the use of the 3D maps, especially in terms of topographic recognition. However, the most striking increase in effectiveness was found with the perspective photographs, which enabled people to identify features and their orientation much more readily. For Montserrat it appears that well labelled aerial and perspective photographs are the most effective geo-spatial method of communicating volcanic risks.

云南景东县卜勺磁铁矿矿床地质

磁铁矿矿体似层状、透镜状赋存于淇海岩组中上一中部的钠长绿泥片岩、钠长绿泥绿岩、钠长绿帘绿泥片岩中,严格受层位、岩性和构造的控制。     

浙江青田石平川钼矿控矿条件分析

石平川钼矿由燕山晚期第四次侵入碱性长石花岗岩体提供物源和热动力,火山机构、断裂和西山头组第二岩性段为成矿提供了导矿通道和容矿场所。     

关于南天山碰撞造山时代的讨论

南天山是天山山脉的一支,是中亚型造山带的典型代表,它经历了复杂的增生—碰撞过程。关于古南天山洋最终闭合—碰撞造山(碰撞事件)发生的时间一直存在不同的认识,争论由来已久。综合分析南天山造山带的构造、地层、古生物、岩石、地球化学和同位素年代学等方面的资料,特别是对放射虫、蛇绿岩、蓝片岩、火山弧及前陆盆地沉积等地质事实的研究,我们认为,南天山碰撞造山作用起始于二叠纪末—三叠纪初。     

陆上、水下喷发成因火山岩储层发育特征和成藏控制因素对比分析

火山岩油气藏的研究一般以陆上喷发沉积的火山岩体为主,事实上全世界四分之三的火山活动是在水下发生的,只是水下喷发沉积的火山岩在各个方面的研究还比较少,在勘探中尚未引起注意。本文以三塘湖盆地石炭系火山岩油藏为例,对比分析了陆上与水下喷发沉积形成的火山岩在岩性、颜色、结构构造以及储集空间特征和地震反射特征等方面的差异,指出了三塘湖盆地石炭系哈尔加乌组火山岩为水下喷发环境形成。通过对研究区两种类型的火山岩油藏系统的研究,总结出了水下喷发沉积的火山岩储层的形成机理以及其形成规模油气藏的条件,为今后的火山岩油气藏的勘探指出了新的方向。     

试论火山岩油气藏成藏机理

全球100多个国家/地区在火山岩内或其周围发现了油气藏或油气显示,展示了火山岩油气藏勘探的广阔前景。火山岩已从油气勘探的"禁区"转变为了"靶区",成为油气勘探的新目标。火山岩储集物性较好,其本身可直接作为储层,各类侵入体与围岩相互作用还可形成与火成岩有关的圈闭。火山岩油气藏的烃源包括有机成因和无机成因两种。火山作用可以明显提高烃源岩内有机质的成熟度,加快烃的产生,促进油气运移,并为无机成因烃提供合成原料(CO_2和H_2等)和运移通道。虽然火山岩在盆地早期尤为发育,约占盆地充填体积的1/4,但是目前火山岩油气储量仅占世界油气探明储量的1%左右,勘探潜力巨大。中国沉积盆地内发育不同时代火山岩,火山岩储层与烃源岩匹配较好,无机成因气来源丰富,火山岩油气藏正在成为我国油气勘探的重要领域之一。