陕南天台山、茶店一带磷块岩的时代和成因特征

陕西南部汉中天台山、勉县茶店和略阳何家岩、金家河一带磷块岩的时代,目前有三种看法,即:泥盆纪、震旦纪和寒武纪。这一带磷块岩的成因也比较复杂。在磷酸盐沉积、成岩以后,又受到变质、褶皱、断裂和水溶液活动影响。本文对天台山、茶店一带的磷块岩的成矿时代和生成特点提出一些初步意见。     

The incorporation of uranium into diagenetic phosphorite

The behavior of U during the diagenetic formation of marine phosphorite has been modelled. The model examines a dissolution-reprecipitation replacement of skeletal hydroxyapatite, calcium carbonate and earlier generated francolite by francolite. The amount of organic matter consumed relative to the mass of francolite formed, the replacement reaction progress, and the concentration of U in the replaced phases are the important parameters which dictate the concentration of U in the phosphate rock.A partition coefficient between apatite and interstitial solution was calculated, and is $\text{λ}{}_{\mathrm{U}}{}^{\mathrm{F}}\text{= 0.57}$.Natural phosphorites have been examined and are discussed in the light of the proposed model. The U mass-balance in a Recent phosphorite is in good accord with theoretical predictions. Differences in U concentrations between sea-floor phosphorites are explained either by the (original) variation in the organic matter distribution in the corresponding sediments and/or by mineralogical differences (CaCO₃vs. hydroxyapatite) therein.Senonian phosphate rocks which were formed via the francolite → francolite transformation, demonstrate that during that process the organic matter content in the sediment was approximately 50%.The model supports the idea that phosphorite rock formation is a multistage process.     

震旦纪陡山沱组的泥晶磷块岩

泥晶磷块岩(micritic phosphorite)是磷块岩的主要类型之一。我国的磷块岩矿床也多有这种矿石。过去往往把组成泥晶磷块岩的磷酸盐矿物叫做胶磷矿(collophane)。扫描电镜、X-射线衍射等观察结果表明,胶磷矿实际上也是结晶质磷灰石,只是由于颗粒极其微小而已。由这种泥晶磷灰石组成的泥晶磷块岩也同样不像过去描述的那样单调,而是具有比较复杂的结构、构造。     

A comparative study of Pleistocene phosphorites from the continental slope off western India

Two types of phosphorite recovered from the continental slope off western India are described. The first type, phosphorite 1, comprises a hard, grey nodule composed of carbonate fluorapatite (CFA) and calcite as major minerals. The phosphorite consists of light‐brown microcrystalline apatite containing a few skeletal fragments and planktonic foraminifera. Scanning electron microscope (SEM) studies show evidence of dissolution of skeletal calcite and filling of the resulting cavities by phosphate composed of ovoid to rod‐shaped apatite microparticles. Apatite also occurs as coatings on these particles. The P₂O₅ content of the phosphorite is 29%, and the CO₂ content of the CFA is about 4·5%. The rare‐earth element (REE) abundance (ΣREE=2·02 μg g^–1) is lower than in other modern phosphorites. The ⁸⁷Sr/⁸⁶Sr ratio and ?Nd value of this sample are 0·70921 and –9·9 respectively. The ¹⁴C age found through accelerator mass spectrometry (AMS) dating (18 720 ± 120 years BP) is much younger than that determined by the U‐series method (100 ka). The second type, phosphorite 2, comprises a friable, light‐brown nodule consisting of CFA as the only major mineral, with a CO₂ content of the CFA of 4·5%. In thin section, the phosphate is light brown and homogeneous, and a few bone fragments are present. The P₂O₅ content is 33%, and REE contents (ΣREE = 0·18 μg g^–1) are lower than in phosphorite 1. The age of phosphorite 2 is >300 ka. Phosphorite 1 appears to have formed during the late Pleistocene through replacement of carbonate by phosphate; phosphorite 2 is also of Pleistocene age but is much older than phosphorite 1. The initial substrate for phosphorite 2 was a fish coprolite, which was subsequently phosphatized during slow sedimentation under low‐energy conditions. Microbial mediation is evident in both phosphorites. The colour, density and P₂O₅ content of the phosphorites are found to be dependent on the nature of the initial substrates and physico‐chemical conditions during phosphatization. The CO₂ content of the CFA is not related to the precursor carbonate phase. The nature of sediments, rates of sedimentation and the time spent undergoing phosphogenesis at the sediment–water interface may control REE concentrations in phosphorites.     

荆襄地区陡山沱组磷块岩的类型、成因和沉积环境

本文根据野外调查和室内初步研究成果并结合有关地质资料,分析、讨论了荆襄陡山沱组含磷岩系的磷块岩类型、成因和沉积环境。通过分析可知,组成磷块岩的磷灰石有不同的形成方式;磷块岩沉积在海退旋回中粘土和硅质沉积向碳酸盐沉积的转变阶段;磷块岩矿床形成在陆缘海内与深水有联系的浅水地带。 矿区含磷岩系特征综合于图1。     

Alterations in guano phosphates and mio-pliocene carbonates of table mountain Santa Barbara,Curacao

The Table Mountain Santa Barbara, consisting of the Mio-Pliocene Seroe Domi Limestone Formation, was probably covered with a guano layer in the Pleistocene (?). Solutions, carrying guano-derived phosphate, percolated downwards, resulting in partial phosphatization of the underlying limestones. Only two phosphate minerals are present in the Table Mountain: apatite, and whitlockite.Phosphatization includes both replacement of the original carbonate or (pre-phosphate) dolomite, and cementation in primary- as well as secondary porosity (cryptocrystalline, isotropic phosphate cement, (micro)crystalline apatite, isopachous apatite fringe cement, multiple-zoned apatite crusts, rhombic whitlockite cements). Two factors controlled the final distribution of the phosphate within the Table Mountain. Firstly, changing positions of the sea level (and, therefore, of the diagenetic environments) determined the overall distribution of the phosphatized interval, a horizontal layer (98–128 m above sea level) sandwiched between two non-phosphatized limestone units.Original carbonate facies and -mineralogy was the second controlling factor causing the final variations in degree of phosphatization. The limestones comprise two lithofacies: (a) coralliferous limestone lenses erratically distributed amidst; and (b) micritic limestones. These coralliferous limestones are phosphatized preferentially forming so-called “phosphate pockets”, sharply outlined within a non-phosphatized micritic limestone “host”. These pockets are characteristically organized into five zones which are described in detail. Higher original porosity/permeability of the coralliferous limestone lenses as compared to the micrites, additionally enhanced by a phase of pre-phosphate dolomitization, determined preferential phosphatization of this facies type.A second controlling factor was the original carbonate mineralogy and resulting dia-     

Association of phosphate with rhyolite glass in marine Neogene tuffs from Patagonia,Argentina

The precipitation/replacement of Ca‐phosphate is a complex process that commonly takes place during the early diagenesis in marine sediments. The unusual occurrence of shallow marine, early diagenetic phosphatic deposits associated with glassy tuffs in the Neogene Gaiman Formation, in the Chubut Province, Patagonia, Argentina, constitutes a good case example for the study of replacement and precipitation of Ca‐phosphate on an unstable substrate. Isocon diagrams illustrate that chemical changes during glass diagenesis include gains in loss on ignition and Ca, and losses of K. These changes are the result of glass hydration during sea water–glass interaction, together with adsorption and diffusion of ions into the bulk shard; combined, these represent an incipient process of volcanic glass replacement by Ca‐phosphate. Subsequent early diagenetic P enrichment in the pore solutions led to phosphate precipitation, associated with pitting on the glass shards and pumice. The associated development of a reactive surface promoted the incorporation of P and Ca into their margins. Lastly, precipitation of calcium phosphate filled the vesicles and other open cavities, inhibiting further glass dissolution. The high porosity and reactivity of the volcanic glass provided an appropriate substrate for phosphate precipitation, leading to the development of authigenic apatite concretions in the volcanic‐glass bearing strata of the Gaiman Formation. This research is of significance for those concerned with marine phosphatic deposits and sheds light on the processes of early diagenetic phosphate precipitation by replacement of an atypical, unstable substrate like hydrated volcanic glass.     

磷块岩的胶结作用

磷块岩胶结物有泥质、硅质、磷质和碳酸盐质4种,共形成19种胶结结构,其中尤以磷泥晶环边结构、等厚纤状环边结构、似重力式结构、磷质纤状环边叠加云质亮晶充填结构特征突出,具有指示沉积成岩环境的意义。4种类型的胶结物在剖面和平面上的演变与水体深度和沉积成岩环境有关,而胶结作用的地球化学特征,既是磷块岩的环境指示,又反映微生物的影响状况。     

Microbial processes in the Negev phosphorites (southern Israel)

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.     

朝阳磷矿磷块岩的类型和成因特征

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。     

Pb-Pb age of sedimentary phosphorite reworking in Lower Riphean carbonate sediments,the Satka Formation of Southern Urals

The mineral composition and U-Pb and Rb-Sr systematics of phosphorites from the Satka Formation of Lower Riphean carbonates, the Burzyan Group of Southern Urals, are studied. Phosphorites occurring as small lenses between stromatolite layers are composed largely of fluorapatite with admixture of detrital quartz, feldspars, illite, and chlorite. Phosphorite samples have been subjected to stepwise dissolution in 1 N (fraction L-1) and 2 N (fraction L-2) HCl. As is established, the maximum apatite content is characteristic of fraction L-1, while fraction L-2 is enriched in products of dolomite and sulfide dissolution and in elements leached from siliciclastic components. The Sr content in the Satka apatites (280–560 ppm) is substantially lower as compared with that in unaltered marine apatite. The ⁸⁷Sr/⁸⁶Sr “initial ratio in the phosphorites studied (0.71705–0.72484) and host dolomites from the lower part of the Satka Formation is significantly higher than in the Early Riphean seawater that indicates a reset of the Rb-Sr original systems in sediments. The Pb-Pb age of 1340 ± 30 Ma (MSWD = 6.4) estimated based on 7 data points characterizing fractions L-1 and L-2 is younger than the formation time of overlying Burzyan sediments, being consistent, within the error range, with date of the Mashak rifting event recorded at the Early-Middle Riphean boundary. The comparative U-Pb characteristics of two soluble fractions (L-1 and L-2) and silicate residue of phosphorites show that epigenetic redistribution of Pb and U was characteristic of the phosphorite horizon only. The initial Pb isotope composition and μ (²³⁸U/²⁰⁴Pb) estimated according to model by Stacey and Kramers for the early diagenetic fluids in carbonate and phosphate sediments of the Satka Formation suggest that they were in isotopic equilibrium with erosion products of the Taratash crystalline complex.     

震旦纪灯影组磷块岩及其生成特点

灯影组磷块岩有四种类型,即泥晶磷块岩、内碎屑磷块岩、藻磷块岩和细晶磷块岩。组成磷块岩的主要矿物是磷灰石、白云石、石英和少量伊利石等。磷块岩主要沉积在陆缘海内,它的沉积环境是与深水有联系的浅水地区。深水和浅水环境的地质背景分别为构造拗陷和碳酸盐岩台地。前者提供成矿物质,后者提供有利于磷质成矿的沉积环境。     

Origin of Cretaceous phosphorites from the onshore of Tamil Nadu,India

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.     

贵州瓮安震旦纪陡山沱期磷酸盐化球状化石的新观察

我国贵州瓮安陡山沱期磷块岩中的磷酸盐化球状化石是近年来受到广泛关注的一类微体化石。对于它们的生物亲缘认识，长期以来存在着动植物之争，特别是近年来一些学者发现，部分磷酸盐化球状化石内部保存了2、4、8、16等几何级数增长的细胞特征，根据化石的大小、细胞排列方式和表面纹饰可与现生甲壳类动物的胚胎比较，认为它们很可能是运动胚胎化石，但另一些学者却持截然不同的观点，认为它们不是动物胚胎化石的观察与研究，同时结合相同层位岩石薄片所发现的大量同类化石微细结构的对比。特别是把磷块岩中的化石与燧石中发现的化石详细比较，对一些磷酸盐化球状化石的归属和亲缘关系进行探讨，研究表明贵州瓮安陡山沱期燧石中发现的化石详细比较，对一些磷酸盐化球状化石的归属和亲缘关系进行探讨。研究表明贵州瓮安陡山沱期磷酸盐化微体化石群具有多样性特征，包含不同门类，是迄今为止全球保存最好的晚新元古代磷酸盐化的化石库。     

沉积磷块岩结构类型、成因及成矿阶段

磷块岩的岩石类型和成矿阶段划分是磷块岩研究的一项基础性工作,早在50年代后期,叶连俊等人就对磷块岩及其分类进行过研究[1],随着沉积学的发展,尤其是近年来碳酸盐岩研究的进展,磷块岩岩石学研究也有了一些新的突破。磷块岩分类从矿体形态(层状、透镜状、结核状)、大地构造(地台型、地槽型)等分类走向了结构成因分类。在这方面,工作较多,较系统的有美国的S.R.Riggs和法国的M.S1ansky[9][10]。我国的孙枢、陈其英、赵东旭[2][3]及孟祥化[4]、周茂基[5]、东野[6]等人也先后对磷块岩的结构成因类型进行过研究。这些研究给磷块岩的分类奠定了一个很好的基础。     

中国南方新元古代可能后生动物成因的硅化和磷酸盐化球状微化石Tianzhushania

对中国南方贵州瓮安地区上新元古界陡山沱组两种类型沉积：燧石夹层(切片法研究)和磷灰岩／含磷碳酸盐岩(切片法和浸解法研究)中微化石的比较研究表明,磷酸盐化的Megasphaera ornata与燧石中保存的Tianzhushania tuberifera可能代表由不同矿化过程保存下来的同一生物分类。磷酸盐化标本的外层壁经常脱落,而暴露其具纹饰的中问壁。在一些孤立于围岩基质的磷酸盐化标本和在磷灰岩薄片所见到的标本上显现部分带刺的外壳保存,它们可以同燧石夹层薄片中发现的化石进行比较。磷酸盐化标本的中间壁瘤突表面上普遍见到的凹坑,相当于外层壁刺饰所遗留下的附着点。而具有刺饰的外层壁形态是Tianzhushania Yin and Li,1978属的典型特征,因此建议Tianzhushania arnate(xiao等,2000)Yin et al．,2004为该种的有效名称。而主要依据其中间壁的纹饰形态所得出的该种为后生动物休眠卵的认识与目前结果并不矛盾。但是,外层壁具刺饰的形态说明该种为浮游性的,而不是底栖性的生态类型。     

富钴结壳中的磷酸盐岩及其古环境指示意义

磷酸盐岩是富钴结壳老壳层的主要组分之一。本文对来自中太平洋海山的三块富钴结壳样品中的磷酸盐岩进行了研究,以期对富钻结壳形成环境的变化有所了解。通过扫描电镜发现结壳中磷酸盐岩的形态有六种,磷酸盐岩主要分布在老壳层,新壳层中偶见。结壳中的磷酸盐岩为碳氟磷灰石(CFA),经成分分析及电镜中反射色的差异可以区分出两种成因的CFA：一种为交代碳酸盐岩型的,相对富Si、Al、Fe;另一种为从结壳孔隙水中直接沉淀而成的,基本不含Si、Al、Fe。对CB12样品中磷酸盐岩脉进行生物地层学鉴定,得出其老壳层下部火焰状磷酸盐岩的形成年代为晚渐新世一早中新世(23.2-29．9Ma),而其上部充填脉状磷酸盐岩的形成年代为中中新世(10.8-16Ma)。老壳层中富集磷酸盐岩说明在结壳形成早期,结壳形成环境条件尚不够稳定,底部存在富磷深层储库,当底流突然增强时,可携带磷在海山上交代结壳中的碳酸盐岩或在结壳内部合适条件下直接沉淀形成磷酸盐岩充填脉。新壳层形成时底流已相对髂定,富磷深层储库已消失,不再有广泛磷酸盐化形成。     

Experimentally-controlled carbon and oxygen isotope exchange between bioapatites and water under inorganic and microbially-mediated conditions

Modern bone and enamel powders have reacted at 301 K with ¹³C- and ¹⁸O-labelled waters under inorganic and microbial conditions. The aim of the study is to investigate the resistance of stable isotope compositions of bioapatite carbonate (δ¹³C, δ¹⁸Oc) and phosphate (δ¹⁸Op) to isotopic alteration during early diagenesis. Rapid and significant carbon and oxygen isotope changes were observed in the carbonate and phosphate fractions of bone apatite before any detectable change occurred in the crystallinity or organic matter content. These observations indicate that chemical alterations of bone apatite are likely to start within days of death. Enamel crystallites are much more resistant than bone crystallites, but are not exempt of alteration. Non removable carbon and oxygen isotope enrichments were measured in the carbonate phase of bone (50-90%) and enamel (40%) after the acetic acid treatment. This result indicates that a significant part of ¹³C and ¹⁸O-labelled coming from the aqueous fluid has been durably incorporated into the apatite structure, probably through isotopic exchange or secondary carbonate apatite precipitation. As a result, acetic acid pre-treatments that are currently used to remove exogenous material by selective dissolution, are not adequate to restore pristine δ¹³C and δ¹⁸Oc values of fossil apatites. Under inorganic conditions, kinetics of oxygen isotope exchange are 10 times faster in carbonate than in phosphate. On the opposite, during biologically-mediated reactions, the kinetics of oxygen isotope exchange between phosphate and water is, at least, from 2 to 15 times faster than between carbonate and water. Enamel is a more suitable material than bone for paleoenvironmental or paleoclimatical reconstructions, but interpretations of δ¹⁸Op or δ¹³C values must be restricted to specimens for which no or very limited trace of microbial activity can be detected.     

Geochemistry of phosphate bearing sedimentary rocks in parts of Sonrai block,Lalitpur District,Uttar Pradesh,India

Major, trace and rare earth elements of phosphatic rocks around Sonrai block of Paleo-Mesoproterozoic age having phosphatic breccia, quartzite, shale, sandstone, limestone and ironstone, have been determined to evaluate their correlation, relationship with the phosphorus content, the nature of possible substitution of various elements and regional distribution pattern over the area. The study indicates that the number of elements is substituted in the apatite structures; few of them are associated with phosphate and carbonate minerals. The variable concentration of major, trace and rare earth elements in the phosphatic rocks has been influenced by various physico-chemical processes involved during weathering and leaching of the source rocks. The distribution of the major, trace and rare earth elements is controlled by the environmental variations in the sediment water interface. The majority of trace elements were mainly influenced by the principle adsorbents like the phosphate minerals in addition to clay, iron oxides and silicate minerals. The PAAS normalized REE patterns of Sonrai block of phosphorites are characterized by negative Ce anomalies and Positive Eu anomalies. It is inferred from the distribution and interrelationship of major, trace and rare earth elements that the deposition of phosphate minerals might have occurred in highly oxidizing to slightly reducing conditions in supratidal to intertidal continental margins and shallow marine environment. The deposition was controlled by marine upwelling leading to excess charge of phosphate in certain zones of phosphogenic basins, lithologic facies variations in restricted circulations of basinal waters and electrochemical factors such as negative Eh, pH and other factors, which influenced the deposition of phosphates. The replacement, precipitation in voids and fissures and diagenesis were also important mechanisms of phosphate generation in Sonrai basin. The main source for various elements may be the minerals of cratonic mass of Bundelkhand Granitic Complex, a basement of Bijawar Basin, which also provided land derived phosphorus through weathering of the terrestrial cover.     

Origin of PhosphoriteNodules of Lebedinsky Iron Deposit in Kursk Magnetic Anomaly （KMA） of the Russian Platform

INTRODUCTION TheKurskmagneticanomaly(KMA)coversnear ly120000km2andhasalengthof600kminSE NW direction,withawidthrangingfrom150kmto250 km.TheKMAbasinislimitedbytheDoneskPaleozoic massifinthesouthandthePrecambrianAzovsk podol skupliftinthesouth westanditsnorthernborderis markedbythecrystallinemassifupliftofVaronesh.0 c s TheLebedinskycomplexdepositislocatedinthecentral partoftheRussianplatformbetweenlatitude50°00′and50° 20′north,andlongitude34°00′and39°00′east,inthefron ti…