Zebra dolomitization as a result of focused fluid flow in the Rocky Mountains Fold and Thrust Belt, Canada   总被引：4，自引：0，他引：4  

VEERLE VANDEGINSTE  RUDY SWENNEN  SARAH A. GLEESON†  ROB M. ELLAM‡  KIRK OSADETZ§  FRANÇOIS ROURE¶ 《Sedimentology》2005,52(5):1067-1095

Discordant zebra dolomite bodies occur locally in the Middle Cambrian Cathedral and Eldon Formations of the Main Ranges of the Canadian Rocky Mountains Fold and Thrust Belt. They are characterized by alternating dark grey (a) and white (b) bands, forming an ‘abba’ diagenetic cyclicity. These bands developed parallel to both bedding and cleavage. Dark grey (a) bands consist of fine (< 300 μm) non-planar crystalline impure dolomite. The white (b) bands are composed of coarse (up to several millimetres) milky-white pure saddle dolomites (b1) which are often covered by pore-lining zoned dolomite (b2). The b phases often possess a saddle-shaped morphology. In contrast to the replacement origin of the a dolomite, the zoned b2 dolomite rims are interpreted as a cement formed in open cavities. The b1 dolomite is interpreted as the result of recrystallization with diagenetic leaching of non-carbonate components. All the zebra dolomites studied are (nearly) stoichiometric and are characterized by enriched Na and depleted Sr concentrations. Fe and Mn concentrations in these dolomites differ depending on the sample locality. Fluid inclusion data indicate that the dolomites formed from relatively hot (T_H = 130–200 °C), saline (20–23 wt% CaCl₂ eq.) fluids. A diagenetic high temperature origin is also supported by depleted δ¹⁸O values (−20 to −14‰ VPDB). A contribution of ⁸⁷Sr-enriched fluids is reflected in the ⁸⁷Sr/⁸⁶Sr values (0·7091–0·7123). Zebra dolomite development is explained by focused fluid flow, which exploited areas of structural weaknesses (e.g. basin-platform, rim areas, faults, etc.). Expulsion of hot basinal brines in a tectonically active regime generated overpressures, which explains the development of secondary porosity during zebra dolomitization as well as the intra-zebra fracturing at decimetre to micrometre scale.  相似文献   

Magma evolution and the formation of porphyry Cu–Au ore fluids: evidence from silicate and sulfide melt inclusions     

Werner E. Halter  Christoph A. Heinrich  Thomas Pettke 《Mineralium Deposita》2005,39(8):845-863

Silicate and sulfide melt inclusions from the andesitic Farallón Negro Volcanic Complex in NW Argentina were analyzed by laser ablation ICPMS to track the behavior of Cu and Au during magma evolution, and to identify the processes in the source of fluids responsible for porphyry-Cu-Au mineralization at the 600 Mt Bajo de la Alumbrera deposit. The combination of silicate and sulfide melt inclusion data with previously published geological and geochemical information indicates that the source of ore metals and water was a mantle-derived mafic magma that contained approximately 6 wt.% H₂O and 200 ppm Cu. This magma and a rhyodacitic magma mixed in an upper-crustal magma chamber, feeding the volcanic systems and associated subvolcanic intrusions over 2.6 million years. Generation of the ore fluid from this magma occurred towards the end of this protracted evolution and probably involved six important steps: (1) Generation of a sulfide melt upon magma mixing in some parts of the magma chamber. (2) Partitioning of Cu and Au into the sulfide melt (enrichment factor of 10,000 for Cu) leading to Cu and Au concentrations of several wt.% or ppm, respectively. (3) A change in the tectonic regime from local extension to compression at the end of protracted volcanism. (4) Intrusion of a dacitic magma stock from the upper part of the layered magma chamber. (5) Volatile exsolution and resorption of the sulfide melt from the lower and more mafic parts of the magma chamber, generating a fluid with a Cu/Au ratio equal to that of the precursor sulfide. (6) Focused fluid transport and precipitation of the two metals in the porphyry, yielding an ore body containing Au and Cu in the proportions dictated by the magmatic fluid source. The Cu/S ratio in the sulfide melt inclusions requires that approximately 4,000 ppm sulfur is extracted from the andesitic magma upon mixing. This exceeds the solubility of sulfide or sulfate in either of the silicate melts and implies an additional source for S. The extra sulfur could be added in the form of anhydrite phenocrysts present in the rhyodacitic magma. It appears, thus, that unusually sulfur-rich, not Cu-rich magmas are the key to the formation of porphyry-type ore deposits. Our observations imply that dacitic intrusions hosting the porphyry–Cu–Au mineralization are not representative of the magma from which the ore-fluid exsolved. The source of the ore fluid is the underlying more mafic magma, and unaltered andesitic dikes emplaced immediately after ore formation are more likely to represent the magma from which the fluids were generated. At Alumbrera, these andesitic dikes carry relicts of the sulfide melt as inclusions in amphibole. Sulfide inclusions in similar dykes of other, less explored magmatic complexes may be used to predict the Au/Cu ratio of potential ore-forming fluids and the expected metal ratio in any undiscovered porphyry deposit.Editorial handling: B. Lehmann  相似文献   

浙江省绍兴市平水金矿体流体包裹体研究 与矿床成因     

陈辉  倪培  陈仁义  吕志成  耿林  张志辉  贾儒雅 《地质论评》2016,62(S1):95-96

浙江平水铜矿位于钦杭成矿带北东段浙西北地区,是浙江省最大的铜矿床,前人研究表明其为典型的火山成因块状硫化物矿床（Chen 等, 2015）。平水铜矿体在新元古代形成之后,该地区经历了加里东的变质变形作用,在铜矿体的下盘普遍发育千糜岩带（韧性剪切带）,本项目组在研究过程中认为千糜岩带与铜矿无关,但明确提出本区可能存在造山型金矿,继而老矿山接替资源勘查在平水铜矿布置了10个坑内钻孔,其中9个见矿,成功的在平水深部发现两层金矿体和一层铜矿体。金矿体严格的受韧性剪切带的控制;金矿石有明显的宏观和微观韧性变形结构;矿石矿物主要是自然金和少量的黄铁矿,脉石矿物主要有石英、绢云母、绿泥石、碳酸盐和白云石。本文主要对平水金矿体开展流体包裹体研究,结合矿床地质特征,最终确定金矿体成因类型,为平水地区下一轮深边部找矿勘查提供依据。  相似文献   

Origin and evolution of geothermal fluids from Las Tres Vírgenes and Cerro Prieto fields,Mexico – Co-genetic volcanic activity and paleoclimatic constraints     

《Applied Geochemistry》2016

Major and trace elements, noble gases, and stable (δD, δ¹⁸O) and cosmogenic (³H, ¹⁴C) isotopes were measured from geothermal fluids in two adjacent geothermal areas in NW-Mexico, Las Tres Vírgenes (LTV) and Cerro Prieto (CP). The goal is to trace the origin of reservoir fluids and to place paleoclimate and structural-volcanic constraints in the region. Measured ³He/⁴He (R) ratios normalized to the atmospheric value (R_a = 1.386 × 10⁻⁶) vary between 2.73 and 4.77 and are compatible with mixing between a mantle component varying between 42 and 77% of mantle helium and a crustal, radiogenic He component with contributions varying between 23% and 58%. Apparent U–Th/⁴He ages for CP fluids (0.7–7 Ma) suggest the presence of a sustained ⁴He flux from a granitic basement or from mixing with connate brines, deposited during the Colorado River delta formation (1.5–3 Ma). Radiogenic in situ ⁴He production age modeling at LTV, combined with the presence of radiogenic carbon (1.89 ± 0.11 pmC – 35.61 ± 0.28 pmC) and the absence of tritium strongly suggest the Quaternary infiltration of meteoric water into the LTV geothermal reservoir, ranging between 4 and 31 ka BP. The present geochemical heterogeneity of LTV fluids can be reconstructed by mixing Late Pleistocene – Early Holocene meteoric water (58–75%) with a fossil seawater component (25–42%), as evidenced by Br/Cl and stable isotope trends. CP geothermal water is composed of infiltrated Colorado River water with a minor impact by halite dissolution, whereas a vapor-dominated sample is composed of Colorado River water and vapor from deeper levels. δD values for the LTV meteoric end-member, which are 20‰–44‰ depleted with respect to present-day precipitation, as well as calculated annual paleotemperatures 6.9–13.6 °C lower than present average temperatures in Baja California point to the presence of humid and cooler climatic conditions in the Baja California peninsula during the final stage of the Last Glacial Pluvial period. Quaternary recharge of the LTV geothermal reservoir is related to elevated precipitation rates during cooler-humid climate intervals in the Late Pleistocene and Early Holocene. The probable replacement of connate water or pore fluids by infiltrating surface water might have been triggered by enhanced fracture and fault permeability through contemporaneous tectonic–volcanic activity in the Las Tres Vírgenes region. Fast hydrothermal alteration processes caused a secondary, positive δ¹⁸O-shift from 4‰ to 6‰ for LTV and from 2‰ to 4‰ for CP geothermal fluids since the Late Glacial infiltration.  相似文献   

Logs Fluid Typing Methods and Adaptive Analysis of Tight Sandstone Reservoir of Yingcheng Formation in Lishu Fault     

Mao Keyu 《地球科学进展》2016,31(10):1056-1066

Tight clastic reservoirs are characterized with low porosity and low permeability, which reduce contributions of reservoir fluids to geophysical logging responses, and it is more difficult to identify fluids of the reservoir. Therefore, it is necessary to study log interpretation and comprehensive evaluation methods for such clastic reservoirs. This study focused on geological characteristics of tight clastic reservoir of Yingcheng formation in Lishu Fault. Based on logs sensitivity to fluids, some fluid typing methods were discussed in detail, which included log curve overlap method, acoustic time overlapping method from density and neutron logs, porosity difference and ratio method, porosity-resistivity crossplot, normal distribution method, and other methods, and some effective fluid evaluation method were established and optimized. These above-mentioned methods were verified, which could achieve layer qualitative identification of tight sandstone in the study area. By contrast, two logs overlapping methods, porosity difference and ratio method, resistivity-porosity crossplot are more suitable for natural gas reservoirs, while porosity difference and ratio method, porosity-resistivity chart, normal distribution method are more suitable for oil and water reservoirs. The case study suggests that these methods be combined to archive more correct log interpretation in the study area, which provides important decision-making reference for oilfield exploration and development.  相似文献   

WFSD-4S孔流体地球化学特征   总被引：1，自引：0，他引：1       下载免费PDF全文

劳昌玲  唐力君  罗立强  夏瑜  龚正 《中国地质》2016,(5):1721-1728

本文开展汶川地震断裂带科学钻探现场流体研究,探讨了泥浆添加剂产生的化学反应以及钻孔中岩性变化引起的流体异常特征,并在排除这些影响因素的情况下,讨论地震期间流体的异常。研究表明在WFSD-4S钻进期间发生的两次较大地震前均伴有Rn、Ar、N2和O2等气体异常现象,其中氡的日均值均超出背景值的2.5倍。根据岩心观察得到WFSD-4S钻井地区主断层约在1084 m,而在断层之上931 m处开始出现了大量气体的高值异常,该异常可能是由于地震孕育过程中地下气体的运移通道被打开造成气体向上迁移,使断层气体的响应特征提前发生。  相似文献   

滇东南安那金矿床成矿流体地球化学研究   总被引：1，自引：1，他引：0  

董文斗  沈能平  苏文超  蔡佳丽 《岩石学报》2016,32(11):3321-3330

云南安那金矿床位于右江盆地南缘,产于二叠纪辉绿岩侵入体之中,广泛发育乳白色石英网脉,蚀变辉绿岩体即为金矿体。与右江盆地以沉积岩为容矿岩石的卡林型金矿床类似,具有硅化、粘土化、碳酸盐化和硫化物化等热液蚀变特征。本文对安那金矿床石英中的流体包裹体岩相学、显微测温学、激光拉曼光谱以及氢氧同位素组成进行了分析,发现成矿期石英中的流体包裹体主要为富含CO_2气-液两相或三相流体包裹体,其均一温度范围为208~312℃(平均254℃),盐度很低,变化范围为0~2%Na Cleqv,成矿溶液的密度为0.88~0.98g/cm~3,表明形成安那金矿床的成矿流体属于中温、低盐度、中-低密度的流体。激光拉曼光谱分析显示,石英中包裹体的气相成分富含CO_2、N_2以及微量CH_4等挥发分。成矿流体的氢氧同位素组成显示变质流体成因,结合矿石显微岩相学结构,认为流体溶蚀交代辉绿岩中的含Ti-Fe辉石或者钛铁矿,溶解Fe的硫化作用过程是含Au黄铁矿和毒砂沉淀富集的重要机制。成矿作用可能与右江盆地南缘印支期造山事件有关。  相似文献   

流体包裹体和C-H-O同位素对湘中古台山金矿床成因制约   总被引：6，自引：2，他引：4  

李伟  谢桂青  张志远  张兴康 《岩石学报》2016,32(11):3489-3506

古台山金矿是湘中盆地最典型的高品位石英脉型金矿床,主要赋存于新元古界和震旦系板岩-千枚岩中。为了探明古台山金矿的成矿物质和成矿流体来源,本次工作对其开展了详细的野外地质考察,对不同阶段石英进行了系统的包裹体岩相学观察、显微测温、激光拉曼探针及H-O同位素分析,对与金矿化密切相关的铁白云石进行了C-O同位素分析。包裹体岩相学及测温结果显示,不同阶段石英主要发育CO_2三相和水溶液两相包裹体,金沉淀阶段CO_2三相包裹体丰度最高,包裹体均一温度集中在180~320℃之间,盐度集中在0~13%NaCleqv之间。激光拉曼显示不同阶段石英包裹体成分主要为H_2O、CO12及少量的CH_4和N_2。不同阶段石英的δ~(18)O_(V-SMOW)变化范围为15.6‰~17.9‰,对应的δ8OH_2O变化范围为4.5‰~8.3‰,δD_(V-SMOW)变化范围-78‰~-49‰,显示成矿过程中有岩浆水参与。铁白云石的δ~(13)C_(PDB)集中在-10.3‰~-8.6‰,δ~(18)O_(V-SMOW)分布在13.9‰~15.7‰之间,暗示成矿流体中的碳主要来自深部岩浆。流体不混溶、CH_4气体存在、围岩及脉体发生硫化-碳酸盐化等因素是导致古台山矿床Au沉淀富集的重要机制。综合上述分析,推测古台山金矿可能是一个非典型的造山型金矿床。  相似文献   

Hydrocarbon alteration in the bituminous salt of the Kłodawa Salt Dome (Central Poland)     

《Marine and Petroleum Geology》2016

The so called bituminous salts occurring in the Kłodawa dome, located in Central Poland, differ from the surrounding salts by their colour change from light to dark brown. This colour is associated with an extremely large amount of hydrocarbon, mainly located in the inclusions. The presence of numerous fluid inclusions has been documented in previous petrologic studies, distinguishing seven main types of fluid inclusion assemblages (FIA) in terms of size, shape as well as the ratio of filling material. However, four types of inclusions were selected in the current investigations according to their unusual optical behaviour. Raman micro-spectroscopy a modern, non-destructive method was used for investigating a single inclusion being a part of FIA. Presented in this paper Raman spectra revealed a unique pattern of bands characterizing the content of the inclusions. The hydrocarbons show a very complex character reflected in the appearance of a strong fluorescence background. A well-marked heterogeneity characterized the inclusions, by diversity in the intensity of the background and in the pattern of the bands characterizing the presence of certain components. One can distinguish the presence of carbonaceous matter showing the different degrees of order. The depth profile and the analysis of the various points of the inclusions indicate that the carbonaceous matter is not evenly distributed in the inclusions but forms a thin, disorganized film on their walls. This film was also found in sites where the inclusions are filled with brine. The certain characteristics associated with the presence of the incipient phase transformation of the organic matter, or slightly transformed organic matter and the lack of light hydrocarbons as well as a number of petrologic features of inclusions indicate that these salt rocks have been subdivided into thermal transformations, accompanied by the recrystallization of the halite and the escape of the more volatile compounds such as methane, ethane, etc.  相似文献   

Three dimensional seismic studies of deep-water hazard-related features on the northern slope of South China Sea     

《Marine and Petroleum Geology》2016

Mass transport deposits and geological features related to fluid flow such as gas chimneys, mud diapirs and volcanos, pockmarks and gas hydrates are pervasive on the canyon dominated northern slope of the Pearl River Mouth basin of the South China Sea. These deposits and structures are linked to serious geohazards and are considered risk factors for seabed installations. Based on high resolution three dimensional seismic surveys, seismic characteristics, distributions and origins of these features are analyzed. A distribution map is presented and geometrical parameters and spatial distribution patterns are summarized. Results show that various groups of the mapped features are closely tied to local or regional tectonism and sedimentary processes. Mass transport complexes are classified as slides near the shelf break, initially deformed slumps on the flanks of canyons and highly deformed slumps on the lower slope downslope of the mouth of canyons. We propose them to be preconditioned by pore pressure changes related to sea level fluctuations, steep topography, and fluid and fault activities. Gas chimneys are mainly located in the vicinity of gas reservoirs, while bottom-simulating reflectors are observed within the gas chimney regions, suggesting gas chimneys serve as conduits for thermogenic gas. Mud diapirs/volcanos and pockmarks are observed in small numbers and the formation of pockmarks is related to underlying gas chimneys and faults. This study aims at reducing risks for deep-water engineering on the northern slope of South China Sea.  相似文献