New style of honeycomb structures revealed on 3D seismic data indicate widespread diagenesis offshore Great South Basin,New Zealand     

《Marine and Petroleum Geology》2017

In the Great South Basin, within the Eocene section, at time-depths around 700–900 ms two way time below the seafloor, unusual features are observed on 3D seismic data closely associated with polygonal faults. The features, referred to as honeycomb structures (HS), cover an area of ∼600 km², are packed circular, oval, to polygonal depressions 150–400 m across in plan view and several to 10 + m in amplitude. Polygonal faults rapidly die out at the Marshall Paraconformity, which is overlain by the Oligocene Penrod Formation. Hence the polygonal faults are inferred to have formed prior to the Marshall Paraconformity, and they cross-cut HS features. Consequently the top of the HS probably formed at burial depths of around 375–500 m, which is their decompacted depth below the paraconformity. The interval containing HS is about 125 m vertical thick. There are several possible origins for the HS. The most probable is related to bulk contraction of the sediment volume accompanied by fluid expulsion, which suggests a diagenetic origin, in particular the opal-A/CT transition. There are actually two polygonal fault systems (PFS) present in the area. The Southern Tier 1 PFS lies laterally to the HS and overlaps with it. The Northern PFS (Tier 2) lies above the HS, appears to be independent of the HS, and formed in the upper 200–300 m of the sediment column. The Tier 1 PFS probably formed by shear failure related to the same diagenetic effects that caused the HS.  相似文献   

Pressure significance of gas chimneys     

《Marine and Petroleum Geology》2017

Analysis was carried out of part of the northern North Sea to test what the presence and style of gas chimneys indicate about fluid pressure (P_f) within hydrocarbon reservoirs. Previous results suggest that broad chimneys above a trap and thin chimneys on the flanks indicate the presence of hydrocarbons, whilst thin chimneys in the crest suggest the hydrocarbons have escaped. Each type of gas chimney is usually associated with overpressure within Mesozoic reservoirs, but the water leg is hydrostatically-pressured in most Cenozoic reservoirs. This indicates: (a) gas leaking from a trap does not necessarily cause P_f to become hydrostatic; (b) overpressure may not be necessary for the expulsion of gasses through seal units to create the chimneys; (c) although gas chimneys indicate the existence of an active hydrocarbon system, their presence does not appear to indicate anything significant about present-day P_f.  相似文献   

福建政和东际金-银矿床的热液蚀变特征及其勘探指示意义   总被引：2，自引：0，他引：2  

卢燕 《地质与勘探》2017,53(6):1039-1050

福建东际金-银矿床产于中生代东坑火山岩盆地西缘的流纹质凝灰岩中,矿区及周边火山-沉积岩系遭受了广泛且强度不等的热液蚀变。本文工作采用红外反射光谱技术在东际矿区三个勘探剖面上对钻孔岩心进行系统性高密度采样分析,结果显示蚀变矿物组合及分带的大框架样式主要受原岩成分控制,具体表现为绢云母化趋向于发育于流纹质火山岩中,而绿泥石化则富集在安山质和英安质火山岩中。在更小的矿区局部空间范围内或单一岩性中,热液作用的物化条件作为次级控制因素决定着特定蚀变矿物的成分变化和蚀变类型的强度差异。从层状硅酸盐组合考虑,东际矿区热液蚀变以绢云母化和绿泥石化为最主要类型,而缺失发育良好的蒙脱石带,金-银矿化赋存在以伊利石为主的绢云母化带中,表明成矿环境属于低硫到中硫之间的浅成热液系统。含矿火山岩的热液蚀变组合和强度变化,以及金-银矿化的似层状特点,均指示成矿时流体是沿着南园组凝灰岩层内侧向流动,而蚀变分带细节显示在凝灰岩层中存在着二至三条流体主通道,金-银矿化则赋存在主通道中。流体主通道的热液蚀变标志是富铝绢云母,其与主通道之外的相对贫铝绢云母在红外光谱特征上反差明显。因此,采用红外光谱技术圈定整体热液蚀变系统的空间构型、解译成矿环境的物化条件及变化、并确定绢云母的铝含量变化用以判断成矿流体主通道位置,可以有效地缩小勘探目标和提高找矿工作的预测性。  相似文献   

The oldest Mo porphyry mineralization in the Yangtze Valley Metallogenic Belt of eastern China: Constraints on its origin from geochemistry,geochronology and fluid inclusion studies at Matou     

《Ore Geology Reviews》2017

The Matou Mo(-Cu) deposit, located in the Yangtze Valley Metallogenic Belt of central-eastern China, is a typical porphyry-type Mo deposit. The orebodies at the deposit are hosted by Matou porphyritic granodiorite, which is the largest intrusive in the area. Quartz vein-type and disseminated sulfide mineralization are well developed in the porphyry and near its contact with Silurian sandstone. Crosscutting relationships indicate that porphyritic granodiorite is the oldest phase in the pluton, which is crosscut by a porphyritic diorite containing traces of chalcopyrite, and later dolerite dykes. These phases have U-Pb zircon dates of 147 ± 3, 140 ± 1 and 135 ± 1 Ma, which confirms the cross-cutting relationships observed in the field. A Re-Os molybdenite isochron age of 147 ± 4 Ma indicates that the porphyritic granodiorite is the source of the oldest Mo mineralization in the metallogenic belt and was formed during a change of the tectonic setting in the area, from an intracontinental orogeny to extensional tectonics. From 147 to 135 Ma, crust-mantle interaction played an important role in the formation of magmatic rocks at Matou. Systematic petrological and geochemistry investigations reveal that the three phases have a crust source with minor input from the mantle. Investigation of ore-forming fluid, H-O isotopes, S isotopes, and the Re content of molybdenite indicate that the ore-forming fluid and metals were derived from the lower crust. During the evolution of fluid from initial magmatic fluids (stage I) to ore-forming fluids (stage II), fluid boiling accompanied by the input of relatively cooler meteoric water led to the deposition of the Mo mineralization.  相似文献   

Re–Os and U–Pb geochronology of the Shazigou Mo polymetallic ore field,Inner Mongolia: Implications for Permian–Triassic mineralization at the northern margin of the North China Craton     

《Ore Geology Reviews》2017

The recently discovered polymetallic Shazigou Mo–W–Pb–Zn ore field is located at the northern margin of the North China Craton. This integrated metallogenic system is comprised of quartz vein mineralization in three deposits: Shazigou Mo–W, Jindouzishan Pb–Zn and Mantougou Pb–Zn. The total reserves are estimated to be 50 kt Mo, 626 t WO₃, 244 kt Pb and 150 kt Zn. Molybdenite Re–Os dating of five quartz vein-type ores yielded a mean model age of 243.8 ± 1.6 Ma (MSWD = 0.81) and hydrothermal zircons yielded a concordant U–Pb age of 245 ± 2.6 Ma (MSWD = 0.65). These results suggest that the mineralization was formed in the early Triassic and could be related to Paleo-Asian Ocean subduction. Microthermometry and quartz fluid inclusion compositions indicate that fluids related to the Mo–W mineralization were mainly derived from magmatic sources and precipitated under relatively high temperature (280–340 °C) and salinity conditions (6–9 wt% NaCl equiv.), whereas subsequent Pb–Zn mineralization-related fluids may have been modified by metamorphic and meteoric waters. The discovery of the Shazigou ore field suggests conditions may be favourable for more extensive mineralization in the western Xilamulun Mo metallogenic belt at the northern margin of the North China Craton.  相似文献   

Geology,geochronology and fluid characteristics of the Pingqiu gold deposit,Southeastern Guizhou Province,China     

《Ore Geology Reviews》2017

The junction of the southeastern Guizhou, the southwestern Hunan, and the northern Guangxi regions is located within the southwestern Jiangnan orogen and forms a NE-trending ∼250 km gold belt containing more than 100 gold deposits and occurrences. The Pingqiu gold deposit is one of the numerous lode gold deposits in the southeastern Guizhou district. Gold mineralization is hosted in Neoproterozoic lower greenschist facies metamorphic rocks and controlled by fold-related structures. Vein types present at Pingqiu include bedding-parallel and discordant types, with saddle-reefs and their down limb extensions dominating but with lesser discordant types. The major sulfide minerals are arsenopyrite and pyrite, with minor sphalerite, galena, chalcopyrite, and rare pyrrhotite, marcasite, and tetrahedrite. Much of the gold is μm- to mm-sized grains, and occurs as fracture-controlled isolated grains or filaments in quartz, galena, sphalerite, pyrite, and wallrock.Three types of fluid inclusions are distinguished in hydrothermal minerals. Type 1 aqueous inclusions have homogenization temperatures of 171–396 °C and salinities of 1.4–9.8 wt% NaCl equiv. Type 2 aqueous-carbonic inclusions yield final homogenization temperatures of 187–350 °C, with salinities of 0.2–7.7 wt% NaCl equiv. Type 3 inclusions are carbonic inclusions with variable relative content of CO₂ and CH₄, and minor amounts of N₂ and H₂O. The close association of CO₂-rich inclusions and H₂O-rich inclusions in groups and along the same trail suggests the presence of fluid immiscibility. The calculated δ¹⁸O_H2O values range from 4.3‰ to 8.3‰ and δD_H2O values of fluid inclusions vary from −55.8‰ to −46.9‰. A metamorphic origin is preferred on the basis of geological background and analogies with other similar deposit types.Two ore-related sericite samples yield well-defined ⁴⁰Ar/³⁹Ar plateau ages of 425.7 ± 1.7 Ma and 425.2 ± 1.3 Ma, respectively. These data overlap the duration of the Caledonian gold mineralization along the Jiangnan orogen, and suggest that gold mineralization was post-peak regional metamorphism and occurred during the later stages of the Caledonian orogeny.Overall, the Pingqiu gold deposit displays many of the principal characteristics of the Bendigo gold mines in the western Lachlan Orogen (SE Australia) and the Dufferin gold deposit in the Meguma Terrane (Nova Scotia, Canada) but also some important differences, which may lead to the disparity in gold endowment. However, the structural make-up at deposit scale, and the shallow mining depth at present indicate that the Pingqiu gold deposit may have considerable gold potential at depth.  相似文献   

Metallogenic age and hydrothermal evolution of the Jidetun Mo deposit in central Jilin Province,northeast China: Evidence from fluid inclusions,isotope systematics,and geochronology     

《Ore Geology Reviews》2017

The Jidetun deposit is a large porphyry Mo deposit that is located in central Jilin Province, northeast China. The Mo mineralization occurs mainly at the edge of porphyritic granodiorite, as well as the adjacent monzogranite. Field investigations, cross-cutting relationships, and mineral paragenetic associations indicate four stages of hydrothermal activity. To determine the relationships between mineralization and associated magmatism, and better understand the metallogenic processes in ore district, we have undertaken a series of studies incluiding molybdenite Re–Os and zircon U–Pb geochronology, fluid inclusions microthermometry, and C–H–O–S–Pb isotope compositions. The molybdenite Re–Os dating yielded a well-defined isochron age of 168.9 ± 1.9 Ma (MSWD = 0.34) that is similar to the weighted mean ²⁰⁶Pb/²³⁸U age of 173.5 ± 1.5 Ma (MSWD = 1.8) obtained from zircons from the porphyritic granodiorite. The results lead to the conclusion that Mo mineralization, occurred in the Middle Jurassic (168.9 ± 1.9 Ma), was spatially, temporally, and genetically related to the porphyritic granodiorite (173.5 ± 1.5 Ma) rather than the older monzogranite (180.1 ± 0.6 Ma). Fluid inclusion and stable (C–H–O) isotope data indicate that the initial H₂O–NaCl fluids of mineralization stage I were of high-temperature and high-salinity affinity and exsolved from the granodiorite magma as a result of cooling and fractional crystallization. The fluids then evolved during mineralization stage II into immiscible H₂O–CO₂–NaCl fluids that facilitated the transport of metals (Mo, Cu, and Fe) and their separation from the ore-bearing magmas due to the influx of abundant external CO₂ and heated meteoric water. Subsequently, during mineralization stage III and IV, increase of pH in residual ore-forming fluids on account of CO₂ escape, and continuous decrease of ore-forming temperatures caused by the large accession of the meteoric water into the fluid system, reduced solubility and stability of metal clathrates, thus facilitating the deposition of polymetallic sulfides.  相似文献   

A comparison of Jiaojia- and Linglong-type gold deposit ore-forming fluids: Do they differ?     

《Ore Geology Reviews》2017

The Jiaodong peninsula contains the most important concentration of gold deposits in China, which can be divided into Jiaojia-type and Linglong-type deposits based on mineralization style. The former is characterized by disseminated- and stockwork-style mineralization hosted in first-order regional faults, with relatively larger tonnages and lower gold grades. The latter is characterized by massive auriferous quartz veins commonly hosted in subsidiary second- or third-order faults, with smaller tonnage but higher grade orebodies. Despite these differences, both groups of deposits have the same alteration assemblages, mineral paragenesis, element concentrations, and ore-forming ages.The mainly Jiaojia-type Luoshan gold deposit and the mainly Linglong-type Fushan gold deposit are characterized by H-O-S-Pb isotope data that indicate the ore-forming fluids have a dominantly metamorphic source. The fluids were derived during the Yanshanian orogenic event, and were most likely associated with dehydration and decarbonization processes near the top of the subducting paleo-Pacific plate. The Linglong-type ores have relatively lighter calculated δ¹⁸O compositions (−3.9 to −2.3‰) than the Jiaojia-type ores (0.3–8.0‰), possibly because of a greater degree of mixing with meteoric water. Petrographic, cathodoluminescence, microthermometric, and laser Raman spectroscopic analyses of fluid-inclusion assemblages in quartz from the two types of ores indicate fluids were similar, in both cases characterized by medium–high homogenization temperatures (211–393 °C), significant CO₂ (∼15% mol), minor CH₄ (⩽18% in the carbonic phase), and low salinity (⩽11.2 wt% NaCl eq.). The Linglong-type ores, however, have a wider range of CO₂ and CH₄ concentration and salinity than the Jiaojia-type ores. Fluid immiscibility, occurred in main ore stage of both ore types, with the trapping conditions of 77–185 MPa and 284–328 °C, although the unmixing is more intense and widespread in the Linglong-type ores. Both fluid-wallrock interaction and fluid immiscibility are important gold-deposition processes in the two types, but immiscibility is more important in the Linglong-type ores and that has led to the typical higher gold grade.In general, there is little geochemical differences between the ore-forming fluids for Jiaojia- and Linglong-type gold deposits. Both Jiaojia- and Linglong-type ores can exist in a single deposit and form in the same metallogenic event. The Linglong-type ores developed as more massive veins, because of their location in zones of more extensive extension and they lack significant post-ore cataclastic deformation.  相似文献   

Magmatic–hydrothermal processes in Sangdong W–Mo deposit,Korea: Study of fluid inclusions and 39Ar–40Ar geochronology     

《Ore Geology Reviews》2017

The Sangdong scheelite–molybdenite deposit in northeast South Korea consists of strata-bound orebodies in intercalated carbonate-rich layers in the Cambrian Myobong slate formation. Among them, the M1 layer hosts the main orebody below which lie layers of F1–F4 host footwall orebodies. Each layer was first skarnized with the formation of a wollastonite + garnet + pyroxene assemblage hosting minor disseminated scheelite. The central parts of the layers were subsequently crosscut by two series of quartz veining events hosting minor scheelite and major scheelite–molybdenite ores, respectively. The former veins associate amphibole–magnetite (amphibole) alteration, whereas the latter veins host quartz–biotite–muscovite (mica) alteration. Deep quartz veins with molybdenite mineralization are hosted in the Cambrian Jangsan quartzite formation beneath the Myobong formation. In the Sunbawi area, which is in close proximity to the Sangdong deposit, quartz veins with scheelite mineralization are hosted in Precambrian metamorphic basement. Three muscovite ³⁹Ar–⁴⁰Ar ages between 86.6 ± 0.2 and 87.2 ± 0.3 Ma were obtained from M1 and F2 orebodies from the Sangdong deposit and Sunbawi quartz veins. The Upper Cretaceous age of the orebodies is concordant with the published ages of the hidden Sangdong granite, 87.5 ± 4.5 Ma. This strongly suggests that the intrusion is causative for the Sangdong W–Mo ores and Sunbawi veins.Fluid inclusions in the quartz veins from the M1 and F2 orebodies, the deep quartz-molybdenite veins, and the Sunbawi veins are commonly liquid-rich aqueous inclusions having bubble sizes of 10–30 vol%, apparent salinities of 2–8 wt% NaCl eqv., and homogenization temperatures of 180–350 °C. The densities of the aqueous inclusions are 0.70–0.94 g/cm³. No indication of fluid phase separation was observed in the vein. To constrain the formation depth in the Sangdong deposit, fluid isochores are combined with Ti–in–quartz geothermometry, which suggests that the M1 and F2 orebodies were formed at depths of 1–3 km and 5–6 km below the paleosurface, respectively. The similarity of the Cs (cesium) concentrations and Rb/Sr ratios in the fluid inclusions of the respective orebodies indicate an origin from source magmas having similar degrees of fractionation and enrichment of incompatible elements such as W and Mo. High S concentrations in the fluids and possibly organic C in the sedimentary source likely promoted molybdenite precipitation in the Sangdong orebodies, whereas the scheelite deposition in the deep quartz–molybdenite veins hosted in the quartzite is limited by a lack of Ca and Fe in the hydrothermal fluids. The molybdenite deposition in the Sunbawi quartz–molybdenite veins hosted in the Precambrian metamorphic basement rocks was possibly limited by a lack of reducing agents such as organic C.  相似文献   

利用交会图法识别国外M油田岩性与流体类型的研究   总被引：1，自引：0，他引：1  

徐德龙  李涛  黄宝华  李娜 《地球物理学进展》2012,27(3):1123-1132

利用测井曲线进行岩性与流体类型的识别是测井解释的重要内容之一,可为油田油气藏的综合评价提供重要的基础依据.基于交会图法和岩心资料,本文分析研究了国外M油田的常规测井曲线特征与岩性和流体类型的关系.首先以岩心资料为基础,选取对岩性和孔隙流体敏感的物理量进行交会图分析识别,在现有测井资料的前提下,综合这些物理量建立了GR-BK、GR-NGR、NGR-BK、PHIE-SW交会图版,然后利用这些图版进行了岩性和流体的识别.其中:岩性主要依据自然伽马、中子伽马、电阻率交会图版来识别,流体类型主要依据饱和度和电阻率交会图版进行识别.在上面工作的基础上确定了该油田不同类型的岩性和流体的识别标准值范围:1)碳酸岩识别标准为GR<70API,NGR>2.5CU,BK<5Ω.m;砂岩识别标准为,70API162API.2)油气层有效孔隙度PHIE>20%,SW<55%,BK>2Ω.m;水层的有效孔隙度PHIE>20%,但是SW>55%,BK<2Ω.m.从上面的结果可看出,在该研究区域,该方法不仅可以区分砂岩和泥岩这样不太复杂的岩性,甚至可以区分砂岩、石灰岩和白云岩这样易混淆的岩性.最后,通过待测试数据对建立的交会图版进行检验,岩性和流体识别的准确率达到了94%和100%.本文的研究结果对中亚地区油田的岩性识别和储层预测具有重要的应用价值.  相似文献