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青海省都兰县洪利铅锌矿床地处华南板块与柴达木盆地南缘的接合部,位于东昆中断裂带内,总体构造线走向为NW-SE向,构造形迹以断裂、褶皱为主,矿区断裂构造发育,按其走向可划分为2组,即NW,NE向断裂。其中NW向断裂为区内主干断裂,略具规模,控矿明显,为区内主要的导、控矿构造,洪利铅锌矿床即受其控制。次为NE向断裂,但规模不大,且对矿体具错断和破坏作用。区内岩浆活动多集中于晋宁期和华力西期,成矿地质条件较好。受后期构造活动影响,造成了该矿床由于矽卡岩化与热液蚀变在空间上的叠加而使其矿化特征的复杂多变。通过详细的野外观察和室内分析共圈出锌多金属矿体2个,磁铁矿体6个,金矿体2个,铁矾帽9个。根据围岩蚀变、矿体走向、分布特征及其与岩性、构造的关系,可分为南、北2个矿段,初步划分了Ⅰ,Ⅱ,Ⅲ条矿化带。研究认为铁矾帽、磁异常、地球化学、矽卡岩化、热液蚀变及角岩化是该区的主要找矿标志,其中铁矾帽系该矿区找矿的直接标志。 相似文献
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The role of endolithic cyanobacteria in the formation of lithified laminae in Bahamian stromatolites 总被引：5，自引：0，他引：5
The microboring activity of endolithic cyanobacteria plays a major role in the formation of the dominant lithified laminae in modern marine stromatolites in the Exuma Cays, Bahamas. These stromatolites are composed primarily of fine-grained carbonate sand that is trapped and bound by the filamentous cyanobacteria Schizothrix sp.. Periodic introduction of coccoid endolithic cyanobacteria Solentia sp. during hiatuses in stromatolite growth associated with very low rates of sedimentation results in the formation of lithified horizons, 200–1000 μm thick. These layers consist of micritized grains that are welded together at point contacts. The micritization is caused by extensive microboring and carbonate precipitation within boreholes concurrent with endolithic activity. Grain welding occurs when boreholes cross from one grain to another at point contacts. Thus, microboring destroys original grain textures but, at the same time, plays a constructional role in stromatolite growth by forming lithified layers of welded grains. These lateral bands of fused carbonate grains help to stabilize and preserve the stromatolite deposits. 相似文献
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CEES VAN der LAND FURU MIENIS HENK DE HAAS NORBERT FRANK RUDY SWENNEN TJEERD C. E. VAN WEERING 《Sedimentology》2010,57(3):912-931
Cold water coral covered carbonate mounds at the south‐west margin of the Rockall Trough form ridges several kilometres long and up to 380 m high. Piston cores obtained at three mound crests reveal the complex internal structure of the mound build up, with alternating unlithified coral‐dominated intervals and lithified intervals. The most recent lithified interval is covered by corals embedded in a fine‐grained matrix, comprising ca 11 000 years of continuous mound evolution. Before this time 230Th/U dating shows the presence of several hiatuses in mound build‐up. Aragonitic coral material is absent or only present as mouldic porosity in the lithified intervals and coccoliths display widespread overgrowth. Downcore X‐ray fluorescence scanning, computer tomography scan images and petrographic observations indicate different degrees of diagenetic alteration. The upper boundary of the most recent lithified interval shows some erosional features, but petrographic observations indicate that initial lithification of the sediments is not related to this erosive event or to long‐term non‐sedimentation, but to earlier sub‐surface diagenesis. Organic matter oxidation and the subsequent lowering of the saturation state of the carbonate system drives dissolution of the unstable aragonitic coral skeletons. Depending on the openness of the system, this can lead to precipitation of a more stable low‐magnesium carbonate. A model is presented describing the sedimentary and diagenetic processes leading to the formation of lithified intervals. 相似文献
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青海省都兰县洪利铅锌矿床地处华南板块与柴达木盆地南缘的接合部,位于东昆中断裂带内,总体构造线走向为NW-SE向,构造形迹以断裂、褶皱为主,矿区断裂构造发育,按其走向可划分为2组,即NW,NE向断裂。其中NW向断裂为区内主干断裂,略具规模,控矿明显,为区内主要的导、控矿构造,洪利铅锌矿床即受其控制。次为NE向断裂,但规模不大,且对矿体具错断和破坏作用。区内岩浆活动多集中于晋宁期和华力西期,成矿地质条件较好。受后期构造活动影响,造成了该矿床由于矽卡岩化与热液蚀变在空间上的叠加而使其矿化特征的复杂多变。通过详细的野外观察和室内分析共圈出锌多金属矿体2个,磁铁矿体6个,金矿体2个,铁矾帽9个。根据围岩蚀变、矿体走向、分布特征及其与岩性、构造的关系,可分为南、北2个矿段,初步划分了Ⅰ,Ⅱ,Ⅲ条矿化带。研究认为铁矾帽、磁异常、地球化学、矽卡岩化、热液蚀变及角岩化是该区的主要找矿标志,其中铁矾帽系该矿区找矿的直接标志。 相似文献
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