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震旦系陡山沱组沉积期形成的黔中开阳、瓮安富磷矿沉积区,矿石产量大、品位高,是国内外重要的磷矿资源产区。黔中磷矿主要分布于黔中古陆周缘的滨浅海环境中,矿石类型以碎屑状磷块岩为主,间夹原生泥晶磷块岩、生物结构磷块岩和次生土状结构磷块岩。开阳式高品位磷块岩的动态沉积成矿过程通常为“三阶段成矿”: 第一阶段为初始成磷作用阶段,在新元古代大规模成磷背景下,上升洋流携带深部富磷海水进入滨浅海地区,并通过生物化学作用使磷质聚集并形成原生磷块岩沉积;第二阶段为簸选成矿作用阶段,高能波浪、风暴水流对原生磷块岩持续的破碎、磨蚀、搬运和再沉积过程中,簸选去除了原生沉积物中的陆源细碎屑、砂泥质成分,保留并聚集磷质碎屑颗粒,形成品位较高的碎屑状矿石;第三阶段为淋滤作用阶段,海平面升降变化使之前形成矿石受暴露事件影响,遭受强烈的风化淋滤作用,碎屑状磷矿石内的碳酸盐岩胶结物和白云石条带被淋滤运移,导致矿层发育大量溶蚀孔洞,甚至形成土状磷块岩,矿石品位再次得到大幅度提升。三阶段成矿作用随古地理条件和海平面变化在沉积成岩过程中多期次、动态进行,最终形成工业价值极高的磷矿石。 相似文献
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云南省永善县务基磷矿赋存于下寒武统梅树村组中谊村段地层中,矿石矿物以胶磷灰石为主,具砂屑、砾屑及鲕粒结构,薄-中层状、块状及条纹条带状构造,矿石自然类型为砾屑状磷块岩、条纹状白云质磷块岩、条带状白云质磷块岩、硅质磷块岩。通过分析矿区所处古构造、古地理特征和矿石结构特征,认为务基矿区磷矿为浅海相沉积磷块岩矿床。 相似文献
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一、概述长期来广大岩矿工作者习惯把无一定外形、具有胶状裂纹,正低偏中突起,全消光显微晶质的磷酸盐称为胶磷矿,它是磷块岩的主要矿物成分。1912年前认为胶磷矿是一种非晶质的磷酸盐矿物。1912年劳埃采用伦琴射线研究矿物内部结构,发现胶磷矿是结晶的非均质体,内部质点排列遵循晶体所共有的空间格子规律。随着多种先进测试手段综合运用于这种结晶质磷酸盐矿物的研究中,对其认识日趋统一。目前普遍认为胶磷矿主要是由超微粒状碳氟磷灰石组成,我们研究了贵州福泉震旦纪磷质迭层石、四川峨嵋震旦纪砂屑磷块岩和安微凤台寒武纪砾屑磷块岩中的胶磷矿,得到了相同结论。 相似文献
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朝阳磷矿的磷块岩有五种类型,即泥晶磷块岩、球粒磷块岩、鲕粒磷块岩、内碎屑磷块岩和细晶磷块岩。其中内碎屑磷块岩占优势。磷酸盐岩沉积在海退旋回中,是处于深水向浅水过渡的层位。磷块岩的沉积环境主要是隆起附近的浅水带。 相似文献
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震旦纪陡山沱组的碎屑磷块岩 总被引：2，自引：0，他引：2
碎屑磷块岩主要由磷酸盐沉积物的碎屑组成。由于碎屑形成并再沉积在盆地内部,所以由它组成的磷块岩又叫做“内碎屑磷块岩“(intraclastic phosphorite)。我国许多磷块岩矿床都有这种矿石,是磷块岩的主要类型之一。本文主要是论述陡山沱组碎屑磷块岩的分布、物质组成、结构构造和生成特点。一、碎屑磷块岩的分布根据碎屑粒径大小的不同,碎屑磷块岩可分为大于2毫米的砾屑磷块岩和小于2毫米的砂屑磷块岩。由于成因上的联系和差别,这两种碎屑磷块岩在分布上既有共同特点又有特殊情况。 相似文献
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黔中陡山沱期磷块岩成因的系统研究 总被引：1，自引：0，他引：1
黔中成磷区是中国南方陡山沱成磷期磷块岩矿床的重要组成部分。包括瓮福、开阳两个大型磷块岩矿床和若干中小型磷矿床。本文从磷的来源、沉积和富集3个方面系统地揭示了该区磷块岩的成因。稀土元素分析表明,磷可能来自同期海底火山喷发物。海洋地球化学、生物化学及磷块岩的组构研究证明,藻类生物的吸收和固定作用是磷质沉积的主要途径。磷的富集的多阶段、多因素的,经历不同的富集阶段(或方式)形成不同的磷块岩类型。 相似文献
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Morphology, microstructure, and chemical composition of the nodular fraction of phosphatic sand from the outer Namibia shelf are considered. The nodules are divided into three varieties: concretions, phosphatic casts of shells pelecipod and gastropod, and phosphatized sea lion coprolites. A part of nodules shows massive homogeneous structure, whereas other nodules contain sand-size phosphatic grains derived from the host phosphatic sand. All nodules display the same spectrum of microstructures, including colloform, granular-globular, and crystallomorphic ones. The crystallomorphic nodules are composed of scattered and aggregated crystallites of isometric, rod-shaped, and dumbbell-shaped forms, as well as crystallized shells on grains incorporated into nodules. Phosphatized remains of diatoms, foraminifers, and embryonic gastropods, as well as vermicular and filamentous bacterial forms occur among biogenic components of the nodules. Framboidal pyrite is present in all nodules. In terms of phosphate microstructure, character of organic remains, and chemical composition, the nodules are similar to phosphate grains of the host sand, recent phosphorites from the inner Namibia shelf, and some ancient phosphorites. 相似文献
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鲕粒,豆粒磷块岩的显微结构和生成特点 总被引：4，自引：0，他引：4
晚震旦世陡山沱组和早寒武世渔户村组、辛集组磷矿中有各种鮞粒、豆粒磷块岩。豆粒、鮞粒内核的成分和结构复杂,有来自陆地的各种岩石砂屑、细砾,也有盆内沉积物破碎成的各种内碎屑。鮞粒、豆粒的壳层是同心纹层状磷灰石,它是内核在富磷海水扰动中逐层淀积而成。大部分豆粒、鮞粒在滨海高能浅水中与陆源砂、砾和岔内碎屑沉积在一起,少量鮞粒则沉积在滨外深水低能环境巾。豆粒、鮞粒和碎屑等沉积后又被不同物质胶结。 相似文献
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BAIOUM．H．M． 《中国地球化学学报》2002,21(3):215-226
The Campanian-Maastrichtian phosphatic deposits in Egypt,called the Duwi Forma-tion,comprise a part of the extensive Middle East to North African phosphogenic province of Late Cretaceous to Paleogene age.The province holds the greatest accumulation of phosphorites in the geological history,possibly in excess of 70 billion metric tons.The phosphate resources in Egypt alone exceed 3 billion metric tons.Two-third of these three billions occur only in the Abu-Tartur area.Among the phosphorite deposits in Egypt,the phosphorites of the Abu-Tartur area are characterized by high contents of iron ranging from 3% to 7% with an average of 5%.The detailed mineralogical and geochemical studies on the Abu-Tartur phosphorites revealed that iron is found in the form of pyrite,ankerite,clay minerals,microinclusions,and iron oxide.Pyrite,which is the major fraction,occurs as filling cement and partial to complete teplacement of phosphatic grains and confined to the fresh phosphorites while iron oxide occurs as cryp-tocrystalline aggregates of red to brown particles and is confined to the weathered outcrops.Ex-clusive relations between pyrite in the fresh phosphorite samples inside the Abu-Tartur mine and iron oxide in the equivalent horizon of the weathered exposure indicated that iron oxide was formed by the oxidation of pyrite as a result of weathering.All of these forms harm the quality of ore,manufacturing processes,and the produced phosphoric acid and fertilizers. 相似文献
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Microbial processes in the Negev phosphorites (southern Israel) 总被引：3，自引：0，他引：3
ABSTRACT Microscopic and SEM observations indicate that cyanobacterial activity was important during the formation of the Campanian Negev phosphorites. One aspect of such activity is the development of phosphorites through the binding of phosphate particles. These sediments often demonstrate a conspicuous smooth cryptalgal lamination. The algal binder was fossilized as intertwined phosphatic sheaths that coat and seal off the phosphate grains. Different types of sheaths representing the remnants of an algal community were found. Thick apatite overgrowth commonly deforms the microbial fossils converting them into barely recognizable forms. Fabrication of phosphate particles is another aspect of the microbial activity. Phosphate algal coated grains are a common constituent of the Negev phosphorites. The algal coating consists of stacked phosphatic tubes and colonies of coccoid unicells with an apatite infilling. Fragmented phosphatic sheath bundles form another type of phosphate particle produced by algae. Obliteration of algal structures is common, resulting in undifferentiated groundmasses of cryptocrystalline apatite. The extremely close connection between microbial structures and phosphatization processes suggests cyanobacterial participation in phosphorus enrichment. 相似文献
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《International Geology Review》2012,54(1):65-72
Chert-plus-pyrite pebbles have been known for some time in a number of Witwatersrand conglomerates, but their distribution is highly variable. A wide variety of textures in chert-plus pyrite pebbles are documented here, and these textures place constraints on the origin of such pebbles. Replacement of chert pebbles by pyrite is indicated (pyrite grains and aggregates continue across many pebble boundaries), and both distributional and textural evidence favors a post-burial timing for this process. Significant mobility of sulfur after burial is indicated. Whether this replacement was diagenetic or metamorphic is not certain. 相似文献
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Hassan M. BAIOUMY 《Resource Geology》2002,52(3):231-238
Abstract: Phosphorite deposits in Egypt, known as the Duwi Formation, are a part of the Middle East to North Africa phospho‐genic province of late Cretaceous to Paleogene age. Based on the petrographical observation, the phosphatic grains in the phosphorites are classified into phosphatic mudclasts and phosphatic bioclasts. Both of them are composed of francolite. The structural CO2 contents in the francolite range from 3.3 to 7.2 % with an average of 5.3 %. Results indicated that the substitution with CO32‐ of PO43‐ in the francolite decreases the unit cell volume and a‐cell dimension, and increases the c/a ratio. Effect is more obvious in the a‐cell dimension; therefore, it is more significant in distinction between the different apatite species. Lack of covariance between structural CO2 contents in the francolite and the carbonate minerals contents may render the supposition that the phosphorites formed as a result of replacement of preexisting calcareous sediments is doubtful. Similarity in CO2 content in both weathered and fresh samples indicates that the structural CO2 content in the phosphorites is not affected by weathering, and reflects the conditions and CO2 concentration of the depositional environment. Similarity in mineralogy and CO2 contents in the different phosphatic grains and higher CO2 content in the Egyptian phosphorites compared with the authigenic phosphates of Peru margin, which formed by the same mechanism as the Duwi phosphorites, suggest that the phosphatic grains in the Duwi Formation were francolitized during diagenesis by introducing CO2 from the surrounding pore water and diagenesis took place at an elevated temperature. Scattered values of structural CO2 contents suggest the reworking origin of the phosphatic grains in the late Cretaceous phosphorites in Egypt. 相似文献
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V. Purnachandra Rao Pratima M. Kessarkar R. Nagendra E. V. S. S. K. Babu 《Journal of Earth System Science》2007,116(6):525-536
Cretaceous phosphorites from the onshore of Tamil Nadu have been investigated for their origin and compared with those in
the offshore. Cretaceous phosphorites occur as light brown to yellowish brown or white nodules in Karai Shale of the Uttatur
Group in the onshore Cauvery basin. Nodules exhibit phosphatic nucleus encrusted by a chalky shell of carbonate. The nucleus
of the nodules consists of light and dark coloured laminae, phosphate peloids/coated grains and detrital particles interspersed
between the laminae. Scanning electron microscope (SEM) studies reveal trapping and binding activity of microbial filaments.
A mat structure with linearly arranged microbial filaments and hollow, cell-based coccoid cyanobacterial mat are present.
Nodules contain abundant carbonate fluorapatite, followed by minor calcite, quartz and feldspar. The P2O5 content of the phosphorites ranges from 18 to 26%. The CaO/P2O5, Sr and F contents are higher than that of pure carbonate fluorapatite. Concentrations of Si, Al, K, Fe, and Ti are low.
We suggest that the nuclei of the nodules represent phosphate clasts related to phosphate stromatolites formed at intertidal
conditions. At high energy levels the microbial mats were disintegrated into phosphate clasts, coated with carbonate and then
reworked into Karai Shale. On the other hand, Quaternary phosphorites occur as irregular to rounded, grey coloured phosphate
clasts at water depths between 180 and 320m on the continental shelf of Tamil Nadu. They exhibit grain-supported texture.
Despite Quaternary in age, they also resemble phosphate stromatolites of intertidal origin and reworked as phosphate clasts
onto the shelf margin depressions. Benthic microbial mats probably supplied high phosphorus to the sediments. Availability
of excess phosphorus seems to be a pre-requisite for the formation of phosphate stromatolites. 相似文献
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滇东下寒武统生物磷块岩的形成机制 总被引：3，自引：0，他引：3
显微结构研究表明,广泛分布于滇东地区下寒武统的磷块岩,除少量生物介壳磷块岩外,其它类型的磷块岩(包括菌藻生物磷块岩、内碎屑磷块岩和次生(风化)磷块岩等的颗粒均由磷质菌藻生物组成。从而揭示了菌藻生物磷块岩是磷块岩的基本类型。本文重点论述了生物磷块岩的结构成因分类、时空展布规律,以及滇东磷块岩的菌藻生物成磷—富磷作用,并探讨了菌藻生物磷块岩的形成机制。 相似文献
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In early calcite carbonatites of the Kovdor ore deposit four morphological types of dolomite are represented. In the first type, dolomite microcrystals occur as lamellae enclosed by optically continuous calcite. In the second, dolomite microcrystals occur as segmented rods, plates and xenomorphic grains, enclosed by optically discontinuous calcite, and in the third, dolomite is represented by grains of various morphologies, situated along calcite grain boundaries. The fourth type of dolomite occurs as a fine-grained aggregate, which develops along grain boundaries and cleavage cracks of calcite. From microscopic, scanning electron microscope and microprobe studies of these different types of dolomite microcrystals, as well as the calcite associated with them, it can be concluded that the first type of dolomite was exsolved from magnesian calcite during cooling. The second, and the third types of dolomite microcrystals were formed by recrystallization. The fourth type of dolomite was formed by metasomatic dolomitization. As the result of these two processes-recrystallization and metasomatic dolomitization-early dolomite microcrystals seldom occur. The composition of the early-formed primary magnesian calcite yielded temperatures of exsolution of dolomite from magnesian calcite between 665 and 700°C. 相似文献