Composition and Formation Conditions of Neoproterozoic Phosphorites in the Middle Urals

IF 0.7 4区 地球科学 Q4 GEOCHEMISTRY & GEOPHYSICS Lithology and Mineral Resources Pub Date : 2023-04-18 DOI:10.1134/S0024490222700067
M. T. Krupenin, A. B. Kuznetsov, D. A. Zamyatin, E. A. Pankrushina, S. V. Lepekha
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Abstract

Phosphorite breccias compose a 6-m-thick member in the Vendian terrigenous Kernos Formation in the basin of the Mezhevaya Utka and Sylvitsa rivers (Middle Urals). Phosphorite pebbles and gravelites are accumulations of the fragments of redeposited crusts, originally formed during early diagenesis near the surface of sandy–clayey rocks below the water–sediment boundary. Phosphorite is represented by fluorocarbonate apatite with the following parameters: unit cell a ranging from 0.9359 to 0.9363 nm, spectral mode parameters in Raman spectra (ν1 FWHM = 1–2 cm–1 and peak position from 963 to 966 cm–1), and a band at 1095 cm–1 in FTIR spectra. The bands at ~1430 cm–1 and 1453 cm–1 in the FTIR spectra correspond to substitution of the orthophosphorus group by the carbonate ion (B type). According to the thermal analysis data, the CO2 content in apatite is 0.04–0.8%, and the admixture of dispersed organic matter as aliphatic compounds is 0.3–0.8%. Apatite is represented by two generations: primary (basal structureless fine-crystalline cement) and secondary (euhedral crystals up to 10 µm in size). Both generations corrode the detrital quartz grains. Relative to the primary apatite, the secondary variety is enriched in P2O5, CaO, and F, but depleted in SiO2, Fe2O3, Al2O3, MgO, and K2O. The PAAS-normalized REE distribution in the enriched phosphorites has a smoothed profile with a La/Yb ratio of about 2 and positive Ce and Eu anomalies. The average F/P2O5 value (0.09) corresponds to that in typical fluorocarbonate apatites subjected to catagenesis. High 87Sr/86Sr values (0.7130–0.7253) in detrital phosphorites of the Kernos Formation suggest their deposition in a desalinated wave-dominated shallow-marine paleobasin near a significant inflow of continental water (delta) or catagenetic recrystallization.

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中乌拉尔地区新元古代磷质岩组成及形成条件
中乌拉尔地区Mezhevaya Utka河和Sylvitsa河盆地的Vendian陆源Kernos组中有一段厚6 m的磷质角砾岩。磷质砾石和砾石是早期成岩作用时在水-沉积物边界以下的砂-粘土岩表面附近形成的再沉积地壳碎片的聚集体。磷矿以氟碳酸盐磷灰石为代表,其参数为:晶胞直径为0.9359 ~ 0.9363 nm,拉曼光谱模式参数为(ν1 FWHM = 1-2 cm-1,峰位为963 ~ 966 cm-1), FTIR光谱波段为1095 cm-1。FTIR光谱中~1430 cm-1和1453 cm-1的波段对应于正磷基团被碳酸盐离子(B型)取代。根据热分析数据,磷灰石中CO2含量为0.04-0.8%,分散的有机物质作为脂肪族化合物的混合物含量为0.3-0.8%。磷灰石分为两代:原生(基底无结构的细晶胶结物)和次生(自面体晶体,大小可达10微米)。两代碎屑都腐蚀石英颗粒。与原生磷灰石相比,次生磷灰石中P2O5、CaO、F含量较丰富,而SiO2、Fe2O3、Al2O3、MgO、K2O含量较低。富磷岩中稀土元素的paas归一化分布曲线较为平缓,La/Yb比值约为2,Ce和Eu呈正异常。平均F/P2O5值(0.09)对应于典型的氟碳酸盐磷灰石的变质作用。Kernos组碎屑磷岩87Sr/86Sr值较高(0.7130 ~ 0.7253),表明其沉积于陆相大量流入(三角洲)附近的淡化波主导的浅海古盆地或变质重结晶沉积。
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来源期刊
Lithology and Mineral Resources
Lithology and Mineral Resources 地学-地球化学与地球物理
CiteScore
1.30
自引率
37.50%
发文量
29
审稿时长
>12 weeks
期刊介绍: Lithology and Mineral Resources is an international peer reviewed journal that publishes articles on a wide range of problems related to the formation of sedimentary rocks and ores. Special attention is given to comparison of ancient sedimentary rock and ore formation with present-day processes. The major part of the journal is devoted to comparative analysis of sedimentary processes on the continents and in oceans, as well as the genetic aspects of the formation of sedimentary and hydrothermal–sedimentary mineral resources. The journal welcomes manuscripts from all countries in the English or Russian language.
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