The sediment properties of glacial diamicts from the Jutulsessen area of Gjelsvikfjella,East Antarctica: A reflection of source materials and regional climate     

《Polar Science》2014,8(3):264-282

The glacial diamicts deposited in the Jutulsessen area of Gjelsvikfjella, Dronning Maud Land, East Antarctica show the effects of localized meltwater channels and wind processes, as well as of the dominant glacial processes. These glacial sediments are characterized by poor sorting and a variable mean particle size, and the localized meltwater channels have removed silt- and clay-sized sediments, resulting in the relative enrichment of coarser sediments. The X-ray diffraction (XRD) patterns of clay minerals in samples collected across the study area show very similar characteristics. Biotite is the dominant mica mineral in the clay together with chlorite and K-feldspar. The presence of illite, and small amounts of smectite, demonstrates the limited extent of chemical weathering due to the cold and arid conditions. The samples from the glacial fan area contain mixed-layer clays, suggesting the effects of localized meltwater and limited chemical activity which has altered the crystal structure of biotite at lower topographic level. Scanning electron microscopy (SEM) analysis of surface microtextures from representative quartz grains suggest the dominance of glacial and glaciofluvial processes. The low rates of biogenic activity in this area are indicated by the low total organic carbon (TOC) content of the sediments.  相似文献   

Quartz cement and its origin in tight sandstone reservoirs of the Cretaceous Quantou formation in the southern Songliao basin,China     

《Marine and Petroleum Geology》2015

The tight sandstones of the Cretaceous Quantou formation are the main exploration target for hydrocarbons in the southern Songliao basin. Authigenic quartz is a significant cementing material in these sandstones, significantly reducing porosity and permeability. For efficient predicting and extrapolating the petrophysical properties within these tight sandstones, the quartz cement and its origin need to be better understood. The tight sandstones have been examined by a variety of methods. The sandstones are mostly lithic arkoses and feldspathic litharenites, compositionally immature with an average framework composition of Q₄₃F₂₆L₃₁, which are characterized by abundant volcanic rock fragments. Mixed-layer illite/smectite (I/S) ordered interstratified with R = 1 and R = 3 is the dominating clay mineral in the studied sandstone reservoirs. Two different types of quartz cementation modes, namely quartz grain overgrowth and pore-filling authigenic quartz, have been identified through petrographic observations, CL and SEM analysis. Homogenization temperatures of the aqueous fluid inclusions indicate that both quartz overgrowths and pore-filling authigenic quartz formed with a continuous process from about 70 °C to 130 °C. Sources for quartz cement produced are the conversion of volcanic fragments, smectite to illite reaction and pressure solution at micro stylolites. Potassium for the illitization of smectite has been sourced from K-feldspar dissolution and albitization. Silica sourced from K-feldspars dissolution and kaolinite to illite conversion is probably only minor amount and volumetrically insignificant. The internal supplied silica precipitate within a closed system where the transport mechanism is diffusion. The quartz cementation can destroy both porosity and permeability, but strengthen the rock framework and increase the rock brittleness effectively at the same time.  相似文献   

四川康定四家寨金矿地质特征及找矿标志     

和玉红 《云南地质》2014,33(3):384-386

四家寨金矿是康定杂岩内典型的石英脉-蚀变岩型金矿床,金矿（化）石英脉呈似层状,透镜状充填于构造破碎带中,硅化、黄铁矿化与金矿关系密切,脆-韧性剪切带是本区重要的找矿标志.  相似文献   

Clay coating preserving high porosities in deeply buried intervals of the Stø Formation     

《Marine and Petroleum Geology》2017

The Stø Formation is the most important reservoir interval in the Norwegian Barents Sea, however the reservoir quality can be highly affected by the detrimental effects of quartz cement where there have been extensive post depositional burial. Core plug data from well 7219/8-2 in the Southwestern Barents Sea shows abnormally high porosity and permeability values in certain units of the deeply buried and otherwise highly quartz cemented Stø Formation. The amount of quartz cement in the samples is inversely proportional to the porosity. Samples with high and low porosities are similar texturally and mineralogically, but the high porosity samples have a layer of illitic clay coating the majority of the detrital quartz grains. Illitic clay coating present at grain contacts can result in a lowered IGV given they aid in the dissolution of quartz at interfaces, also creating a source of dissolved silica. Clay induced dissolution means that silica saturation is not a limiting factor in quartz cementation in these samples. The results show that the illitic clay coating is capable of limiting the amount of authigenic quartz overgrowth from 20 to 23% in samples with negligible grain coating to 5–11% in the intervals with high coating coverage. The illitic clay coating inhibits quartz overgrowth by limiting the surface area available for nucleation on detrital grains. The Stø Formation comprises mainly shallow marine deposits of highly reworked clean sandstone. Abnormally high porosities appear to be linked to settings where sediments of a more proximal location are preserved without extensive reworking. The grain coating clay is illitic and most likely originates from clay infiltration processes prior to final deposition. The difference in extent of clay coating in similar facies can mostly be correlated with varying amount of post depositional reworking. This study suggests that there is a potential for considerable porosity and permeability to be preserved in deeply buried sandstones in the Barents Sea. This study could be important in the future exploration activity of deeply buried structures in the area.  相似文献   

山东省莱芜市北江水地区铜矿床地质特征及找矿方向          下载免费PDF全文

郭中  王海涛  付厚起  张宪尧  王铮  侯卫华  亓锦 《山东国土资源》2017,33(10)

北江水铜矿床位于鲁西重要的铜多金属成矿带内,在分析区域成矿地质背景和矿床地质特征的基础上,着重从构造、地层、岩浆岩等方面分析了控矿因素和找矿标志。利用矿区内最新施工的钻孔资料及物化探资料,对区内矿体的成矿规律、分布特征进行了全面、系统的分析,认为矿床成因类型属于中低温热液型,铜矿体呈脉状严格受北江水断裂控制。区内铜矿体赋存岩性为黄铜矿化石英脉,矿体侧伏方向为NW 300°,矿体沿侧伏方向富集明显,且深部未封闭。区内NW向断裂是重要的导矿、控矿构造,受断裂构造控制的热液型铜矿床,一般具有延深大于延长的特点。认为该区具有良好的找矿前景,指出了找矿方向为研究区西北部及矿体深部。  相似文献   

秦岭商丹糜棱岩带石英组构特征变化及成因分析          下载免费PDF全文

周建勋 《地质科学》1999,34(1):10-17

商丹糜棱岩带岩湾、沙沟和商南等3个区段石英C-轴组构和显微构造特征表明,该带自西向东石英C-轴组构形式由单一环带型转为Y-轴方向的点极密型,然后变为Ⅰ型交叉环带型,构造变形环境从低绿片岩相过渡到中-高绿片岩相,然后变为高绿片岩相-低角闪岩相。构造变形环境差异是造成石英组构形式变化的主要因素。随着温压条件的升高,石英滑移系从以底面〈a〉滑移系和柱面〈a〉滑移系的共同作用为主转向以单一柱面〈a〉滑移系为主,进而底面〈a〉滑移系和柱面〈a〉滑移系又重新变得活跃,且菱面滑移系的作用也变得十分重要。  相似文献   

FINE SEDIMENT OF THE UPPER MISSISSIPPI AND ILLINOIS RIVERS AND THE DISASTROUS CONSEQUENCES     

TaWei SOONG 《国际泥沙研究》1999,(2)

IINTRODUCTIONLanddevelopmentandlandusepatternsinthewatershedcaninduceincreasedsedimentloadsinriversandstreams.AGREATIllstudy(1982)illustratedthatsedimentyieldsfromagriculturallandcouldbeseveralfoldsmorethanothertypeoflandusesanderosionsources.ThesamestudyalsodemonstratedthatfinesedimentsweretheheaviestportionoftotalsoillossesfromeachtypeoflandusesinthetwelvehydrologicareasitinvestigatedintheUMRS.Thesamecouldbetrueforotheruplandareasalso.Howeverfinesediments,formthewashloadofthestream…  相似文献   

Discovery and exploration of the Gosowong epithermal gold deposit, Halmahera, Indonesia   总被引：1，自引：0，他引：1  

J. C. Carlile  G. R. Davey  I. Kadir  R. P. Langmead  W. J. Rafferty 《Journal of Geochemical Exploration》1998,60(3):207-227

The Gosowong epithermal gold deposit, on the island of Halmahera in eastern Indonesia, is located in an area of primary tropical rain forest with no previous history of gold mining or record of gold mineralisation. The deposit occurs in a newly recognised mineral district which contains a number of epithermal vein systems and at least two centres of low-grade porphyry style Cu–Au mineralisation. Several zones of argillic and advanced argillic alteration have been noted which may be related to additional centres of mineralisation. Gosowong is classified as a low-sulphidation epithermal quartz vein. Bonanza-grade gold–silver mineralisation is developed in shoots over a 400-m strike section of the vein system. Three types of veining are recognized; quartz–adularia veins and breccias; quartz–chlorite–illite veins and breccias; and crystalline or chalcedonic quartz vein stockworks. The area was targetted using a simple geological concept and the deposit was discovered and tested using basic exploration techniques commonly applied in the rugged tropical terrains of Indonesia. Sequential exploration methods comprised reconnaissance drainage sampling of stream sediment, BLEG and float media, ridge and spur soil sampling, prospect scale grid soil sampling, hand trenching and diamond drilling. Lapse time from identification of the initial reconnaissance anomaly to an inferred resource estimate of almost 1 million ounces of gold was less than 3.5 years. This case history illustrates that very detailed exploration is necessary to locate high-grade vein-type gold deposits in a tropical environment, but demonstrates that such resources still remain to be discovered in the relatively under-explored Neogene magmatic arcs of Indonesia.  相似文献   

Luminescence dating of glaciolacustrine silt in overdeepened basin fills beyond the last interglacial     

《Quaternary Geochronology》2017

OSL and IRSL dating are applied to samples from a 152 m-long drill core to constrain the timing of three glaciolacustrine depositional periods within the infill of an overdeepened bedrock trough in the Lower Glatt valley, N Switzerland. The characterisation of the dose-response suggests that the polymineral IRSL₅₀ and pIRIR_180/225 signals are close to saturation, while quartz OSL ages are within the range of reliable dating. The demarcation of the upper quartz OSL dating limit, however, remains challenging. Dose-recovery tests performed with long storage periods were used to investigate the reliability of the high region of the dose-response curve. They suggest an upper limit for reliable dating of ∼400 Gy for these samples, which was considerably lower than the commonly used 2D₀ criterion. Lifetimes were calculated for the quartz OSL and the thermal stability of the signal is not considered as problematic for the determined ages. Allowing for a contribution from inherited dose due to partial bleaching, places the infill of the overdeepened valley within the penultimate glacial cycle (MIS6).  相似文献   

数字重力仪高精度恒温测温系统设计与测试研究          下载免费PDF全文

秦佩  梁连仲  陶照明  黄涛  刘雨 《地球物理学报》2019,62(10):3665-3674

高精度数字重力仪广泛应用于矿产资源勘探领域,由石英弹性系统组成的重力传感器是高精度数字重力仪的核心部件,其对外界环境温度非常敏感,由环境温度变化引起的重力输出变化远远大于仪器本身精度指标,而且不同的数字重力仪具有不同的温度影响特性.若重力传感器的恒温环境得不到保障,或环境温度的微弱变化无法得到准确的测量和补偿,将严重影响重力仪器的测量精度和一致性.本文针对该问题,研究了高精度恒温测温系统的设计方法及关键技术,考虑到数字重力仪器精度高、体积小、功耗低和便携式的特点,对高精度恒温测温系统中的关键器件选型、热结构设计、电路设计、软件设计等进行深入研究,并给出具体的解决措施.并设计了静态试验、高低温试验和石英弹性系统温度系数测定试验三个部分验证高精度恒温测温系统的有效性.试验结果表明：高精度测温系统最小分辨率达到10 μ℃;静态常温时,高精度恒温系统温度变化约为70 μ℃;在-20℃~+45℃的环境温度冲击中高精度恒温系统温度变化小于1 m℃;恒温点微调装置可实现石英弹性系统温度系数的精确测定.该研究为高精度重力测量仪器研制中消除环境温度变化影响提供了一种有效解决方案.  相似文献