研究生知识库

Phosphorus-bearing stratigraphies of the Central Guizhou deposited during Doushantuo Period, Sinian, and Meishucun Period, early Cambrian，gathering large phosphorus deposits and make the Central Guizhou important areas prospecting phosphate resource. Among them, Weng’an, Kaiyang and Wenquan phosphorites mainly hosted in Doushantuo Formation, In order to illuminate the ore-forming mechanism and ore-controlling factors of the phosphorus deposit, some typical deposits including Baidou, Chuangdong, Jinzhong, Yingping and Xifeng phosphorus deposits in the Central Guizhou were selected for the research. A detailed study was undertaken that involved field observations, major element and trace element, microbean analysis. The major findings are as follow：1．Through regional survey, the transition of paleogeographic environment was analyzed. The phosphorus deposits of the Central Guizhou formed in Doushantuo Period, and the progress was devided into three stages. In the first and third stages, large-scale transgressions caused phosphorus sediment, in the second stage, the regression led to dolomite interlayer.2. The major element of phosphorite are mainly P2O5、MgO、CaO、F, in which P shows positive correlation with CaO and F, but shows negative correlation with MgO, LOI. The trace element shows enrichment of As、Rb、Sr、Ba、Co、Pb relate to PAAS(Post Archean Australian Shal), the U/Th value of phosphorite range from 2.6 to 27 with an average of 17.5, and the date of Weng’an, Kaiyang phosphorite belong to hydrothermal area in Lg(U)-Lg(Th) diagram. The PAAS-normalized rare earth distribution patterns of phosphorite are characterized by pronounced enrichment of HREE (heavy rare earth element) compared to LREE (light rare earth element) resulting a “left-inclined” REE polt. ∑REE of phosphorite ranges from 28.29 to 507.58ppm with an average of 158.08ppm, and the concentration coefficient of LREE and HREE are 0.53, 1.23. The (Ce/Ce*)SN of phosphorite ranges from 0.54 to 1.08 with an average of 0.83, showing positive anomalies. The (Eu/Eu*)SN varies from 0.94~1.81 with an average of 1.11, showing negative anomalies. These characteristics of trace elements and PAAS-normalized rare earth distribution patterns of phosphorite suggest there was hydrothermal during phosphorite metallogenesis. What’s more, the upwelling caused by transgressions brought material source, participating in metallogenesis.3. Redox condition was analyzed used multiple discriminant indicators including Ce anomlies, V/Cr, V/(V+Ni), Th/U and δU. V/(V+Ni) of phosphorite range from 0.28 to 1.30, with an average of 0.61, and V/Cr of phosphorite range from 0.75 to 5.46, with an average of 2.40. Th/U of phosphorite range from 0.75 to 5.46, with an average of 2.40; δU of phosphorite range from 1.70 to 1.99, with an average of 1.89. All these trace element indicated that metallogenetic environment was anoxic-suboxic. 4. The mineral composition of phosphorite and microstructure characteristics of apites were found out. The mineral types and paragenetic assemblages of phosphorite are simple, EPMA shows that ore mineral is fluorapatite with element composition：Ca：38.31%、P ：17.692%、F：3.487% and gangue minerals consist mainly of dolomite, quartz, feldspar, clay minerals and pyrite followly. Under the observation of microscope, apatite diameters range from 100 to 600, with mutual stripes consist of dolomite stripes and apatite stripes. The micromorphologies of apatite were devided into three types： globular apatite, microbial apatite and amorphous apatite, among them, microbial apatite shows different morphologies including globular, petaloid, concentric ring, irregular cyclic, pistil and aggregation.5. The formation of apatite was discussed through scanning electron microscope (SEM). (1) The sedimentation process of globular apatite was related to sustaining mechanical dynamic of seawater, which caused fine sphericity. (2)The formation of microbial apatite was closely related to microbial growth, which was devided into four stages：algae microorganisms blooms and massive production of EPS, formation of granules by accretionary growth, slow precipitation, formation of isopachous apatite cement. (3) The amorphous apatites are main microcrystalline apatites relate to microorganisms, whose formation is more difficult.6. According to paleogeographic environment and indicators for deposit, prospect forecast of Dousahntuo Formation phosphorite was conducted. Therefore, two prospective areas were delineated: the first prospective area around Kaiyang is mixed flat along Caotang-Pingxi-Longdongin the east of Weng’an-Pingding. The second area is phase field between Gravel beach/ sand beach along Datianba-Wenggong and mixed flat along Xiaobazhai-Wengqing-Dianzishang.In conclusion, the origins of phosphorite may derive from hydrothermal processes. Seawater infiltrated into underground along the deep faults, and then was heated in deep rock. Finally the fluids enriched metallogenic materials upwelled into sedimentary basins by hydrothermal vents or volcanic activities. What’s more, ascending currents resulted by transgression may bring metallogenic materials participated in the mineralization. PO43+ was broght to anoxic water-sediment interface by FeOOH or microorganisms in upper oxic seawater. The pore water enriched in metallogenic materials and these materials was phosphatizationed in sediment, and then enduring broken- carried- rounded- resedimented procees. In diagenetic stages, phosphate was compressed, dehydrated, and cemented by dolomite and other detrital material, and finally formed phosphorite. 

贵州省中部地区含磷岩系主要沉积于震旦纪陡山沱期和早寒武世梅树村期，大中型矿床集中分布，储量巨大，是我国磷矿资源的重要分布区之一，其中瓮安、开阳、温泉磷矿主要赋存于陡山沱组地层。为了阐明黔中地区陡山沱期磷矿成矿作用和控矿因素，本文以瓮安、开阳磷矿为例，选取了瓮安白斗、瓮安穿洞、开阳金中、瓮福英坪、息烽温泉磷矿为研究对象，开展矿床地质、地球化学和矿物学研究，针对矿床地球化学特征、成矿古地理环境、成矿物质来源、成矿作用展开研究。获得的主要认识如下：1. 通过区域调查，分析总结了古地理环境的变迁，认为矿床位于陡山沱期黔中古陆北部边缘浅海并形成于潮坪环境，其成矿过程可划分为三个阶段，第一阶段和第三阶段经历了两次大规模的海侵作用分别形成下矿层和上矿层磷矿，第二阶段为海退阶段，形成白云岩夹层。2. 磷块岩主微量元素分析表明成矿物质可能来源于海相热水，其主量元素以P2O5、MgO、CaO、F为主，P与CaO、F呈正相关关系，R（相关系数）分别为0.9、0.94；与MgO、LOI呈负相关关系，R均为-0.84, 表明P与硅铝质可能不具同源特征，指示陆源碎屑物质提供物源的可能性较小。磷块岩相对澳大利亚后太古代页岩富集As、Rb、Sr、Ba、Co、Pb等元素，磷块岩U/Th比值为2.6~27，平均17.5，且在Lg(U)-Lg(Th)图解上，瓮安、开阳磷块岩的数据全部落在热水沉积作用区域；稀土元素PAAS配分模式为轻稀土亏损，重稀土富集的“左倾型”配分，∑REE为28.29~507.58ppm，平均值为158.08ppm，轻、重稀土元素富集系数分别为0.53、1.23；磷块岩Ce/Ce* 为0.54~1.08，平均为0.83，Eu/Eu* 值为0.94~1.81，平均为1.11，显示轻微的正异常。这些微量元素和稀土元素配分特征指示磷块岩形成过程中可能发生了海相热水作用，指示海相热水为沉积区带来了成矿物质，由于海侵作用导致的上升洋流带来大量成矿物质也参与成矿。3.采取多种判别指标对成磷过程的氧化还原条件进行分析，磷块岩V/（V+Ni）比值为0.28~1.30，平均0.61；V/Cr比值为0.76~5.46，平均2.40；Th/U极低，为0.01~0.93，平均0.18；δU> 1为1.70~1.99，平均1.89。以上微量元素及Ce负异常指示成矿环境为缺氧-次氧化环境。4. 查明了磷块岩的矿物成分及磷灰石的显微结构特征。磷块岩矿物共生组合简单，矿石矿物为氟磷灰石，电子探针显示，氟磷灰石元素组成为Ca：38.31%、P：17.692%、F：3.487%，脉石矿物以白云石为主，次为石英、长石、粘土矿物、黄铁矿等。磷灰石粒径100~600 μm，显微镜下可见明显的白云石条带和磷灰石条带互层，层厚约0.1-2 mm。磷灰石微观形态有三种：球状/似球状磷灰石、生物碎屑磷灰石、无定型磷酸盐组分，生物碎屑磷灰石具有球粒状、花瓣状、同心环状、不规则环带状、花蕊状、胶团状、球状集合体等不同的形态。5. 探讨了磷灰石的形成作用过程。对微观球状/似球状磷灰石、生物碎屑磷灰石、无定型磷酸盐组分的分析表明：（1）球状/似球状磷灰石的形成主要与持续的海水动力有关，海水的持续动力使早期形成的磷酸盐沉积物经历破碎-搬运-磨圆-再沉积过程，形成磷灰石颗粒具有较高的球度；（2）生物碎屑磷灰石的形成与微生物的生长密切相关，其形成主要经历四个阶段：藻类微生物爆发和胞外聚合物（EPS）产生阶段、颗粒生长阶段、缓慢沉积阶段、等厚磷灰石壳形成阶段；（3）无定型磷酸盐组分主要是与微生物有关的微晶磷灰石集合体。6. 根据古地理环境及找矿标志，进行了成矿预测。根据黔中地区陡山沱期古地理环境，认为混合坪和沙坪是成磷的有利相区。据此，将瓮安-平定东侧的草塘-平溪-龙洞一带混合坪相区、开阳大田坝-翁共一带的沙坪相区至小寨坝-翁庆-店子上一带的砾沙滩相区作为成磷的有利地区。综上，黔中地区陡山沱期的磷块岩成矿物质来源可能为海相热水，海水沿着深大断裂下渗，在深部被加热，随着热水喷流或者火山活动被带入沉积盆地的海水中，海相热水为主要的来源，另外，海侵作用带来的上升洋流也可能携带了成矿物质参与成矿。在氧化的上部水体中，PO43+被FeOOH或者微生物两种介质携带至还原的水岩沉积界面进入沉积物，孔隙水富含的成矿物质在沉积物中发生磷酸盐化作用形成磷酸盐，未完全固结的经历海水机械动力破碎-搬运-磨圆-再沉积等作用，在成岩阶段经过压实、脱水、被白云石或其他碎屑物质胶结，最终形成磷块岩。