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1.
Steffen Popp Innokenty Belolyubsky Frank Lehmkuhl Andrei Prokopiev Christine Siegert Valentin Spektor Georg Stauch Bernhard Diekmann 《Geological Journal》2007,42(5):477-497
A provenance analysis of late Quaternary deposits from tributaries of the Aldan and Lena rivers in Central Yakutia (eastern Siberia) was carried out using analysis of heavy minerals and clay mineralogy. Cluster analysis revealed one assemblage that is characterized by relatively high proportions of amphibole, orthopyroxene and garnet as well as pedogenic clay minerals, reflecting a sediment provenance from the wide catchment area of the Lena and Aldan rivers. In contrast, the three other clusters are dominated by stable heavy minerals with varying amounts of clinopyroxene, apatite and garnet, as well as high percentages of illite and chlorite that are indicative of source rocks of the Verkhoyansk Mountains. Glacial moraines reveal the local mountain source signal that is overprinted by the Lena‐Aldan signal in the oldest moraines by reworking processes. Alluvial sediments in the Verkhoyansk Foreland show a clear Lena source signal through intervals of the middle and late Pleistocene, related to a stream course closer to the mountains at that time. Loess‐like cover sediments are characterized by the dominant Lena provenance with increasing proportions of local mountain sources towards the mountain valleys. Aeolian sands in an alluvial terrace section at the mountain margin covering the time between 30 ka and 10 ka BP reflect temporarily dominant inputs of aeolian materials from the Lena Plains. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
2.
Trace levels of chalcophile elements that form volatile sulfide minerals are determined in stream sediments and in the nonmagnetic fraction of a heavy-mineral concentrate of stream sediments by a carrier distillation emission spectrographic method. Photographically recorded spectra of samples are visually compared with those of synthetic standards for the two sample types. Rock and soil samples may also be analyzed by comparison with the stream-sediment standards. A gallium oxide spectrochemical carrier/buffer enhances the early emission of the volatile elements.Detection limits in parts per million attained are: Sb 5, As 20, Bi 0.1, Cd 1, Cu 1, Pb 2, Ag 0.1, Zn 2, and Sn 0.1. A comparison with other methods of analysis, total-burn emission and atomic absorption spectroscopy, shows good correlation for standard reference for materials and samples from a variety of geologic terranes. 相似文献
3.
Bo Peng Adam Piestrzynski Jadwiga Pieczonka Meilian Xiao Yaozhu Wang Shurong Xie Xiaoyan Tang Changxun Yu Zhi Song 《Environmental Geology》2007,52(7):1277-1296
The mineralogy and geochemistry of the waste rocks distributed at Taojiang Mn-ore deposit, central Hunan province, China,
were studied using X-ray powder diffraction (XRD), electron microprobe analysis (EMPA) fitted with energy dispersive spectrometer
(EDS) and inductively coupled plasma mass spectrum (atomic emission spectra) ICP-MS (AES), with the aim of predicting the
environmental impacts of weathering of the waste rocks. The mineralogical results from microscope observation and XRD and
EMPA studies show that the waste rock is composed of black shale and minor Mn carbonates. The oxidation of sulfide minerals
such as galena, pyrite and chalcopyrite is accompanied by decomposition of Mn carbonates and K-feldspar during exposure to
atmospheric O2. The geochemical characteristics of major, rare earth elements (REE) and trace elements of the waste rocks also show that
the waste rock can be divided into black shale and Mn carbonate, and both of them are currently under chemical weathering.
The major alkalies and alkaline elements (Ca, Mg, Na, K, Rb, Sr and Cs) and major elements (Fe, S and P) and heavy metals
(Sc, V, Cr, Th, U, Sn, Co, Ni, Cu, Zn, Pb, Mo, Cd, Sb, an Tl) are being released during weathering. The mobility of alkalis
and alkaline elements Ca, Mg, Na, K, Rb, Sr and Cs is controlled by decomposition of Mn carbonates. The dispersion of Cr,
Sc and Th (U) might be related to weathering of K-feldspar, and the release of the heavy metals Co, Ni, Cu, Zn, Pb, Mo, Cd
Sb and Tl is dominated by the breaking of sulfide minerals. The REE of the waste rocks and surrounding soils and the spidery
distribution patterns of heavy metals in the waste rocks, the surrounding soils and the surface waters show that weathering
of the waste rocks and bedrock might be the sources of heavy metal contamination for the surrounding soils and surface water
system for the mining area. This is predicted by the mass-balance calculation by using Zr as an immobile element. Therefore,
it is urgently necessary take measures to treat the waste rocks distributed throughout the area for the local environmental
protection. 相似文献
4.
第四纪红色粘土在我国南方分布很广,最典型的分布在华中岗地上,土层较厚,上部土质均匀,下部具有红白网纹并含砾石,大都是中更新世的洪积-冲积或残积-坡积物,笔者认为可能是间冰期比较暖热气候条件下的产物。熊毅早就指出:各地环境殊异,地形复杂,母岩不同,其理化特征将随之而异。第四纪红色粘土来自不同的堆积相,和经受不同的风化和成土过程,这将在矿物组成方面反映出来。土壤普查的结果表明,第四纪红色粘土按其分布的地形部位,成因和物质来源,可分成两类:一类是残积坡积相，为中更新世较早的暗红色沉积物，即Q2另一类是冲积相，为中更新世较晚的红化程度较轻的淡红色沉积物。它们都经历了中更新世至今的成土过程1)”。为了查明它们的差异，并有助于第四纪沉积物的研究，笔者用部分标本进行矿物分析，并对初步结果进行讨论。 相似文献
5.
Roger M. Key Christopher C. Johnson Matthew S.A. Horstwood Dan J. Lapworth Katherine V. Knights Simon J. Kemp Michael Watts Martin Gillespie Michael Adekanmi Tunde Arisekola 《Applied Geochemistry》2012
Sixteen hundred stream sediments (<150 μm fraction) collected during regional geochemical surveys in central and SW Nigeria have high median and maximum concentrations of Zr that exceed corresponding Zr concentrations found in stream sediments collected from elsewhere in the World with similar bedrock geology. X-ray diffraction studies on a sub-set of the analysed stream sediments showed that Zr is predominantly found in detrital zircon grains. However, the main proximal source rocks (Pan-African ‘Older Granites’ of Nigeria and their Proterozoic migmatitic gneiss country rocks) are not enriched in zircon (or Zr). Nevertheless, U–Pb LA-ICP-MS dating with cathodoluminescence imaging on detrital zircons, both from stream sediment samples and underlying Pan-African ‘Older Granites’ confirms a local bedrock source for the stream sediment zircons. A combination of tropical/chemical weathering and continuous physical weathering, both by ‘wet season’ flash flooding and ‘dry season’ unidirectional winds are interpreted to have effectively broken down bedrock silicate minerals and removed much of the resultant clay phases, thereby increasing the Zr contents in stream sediments. The strong correlation between winnowing index (Th/Al) and Zr concentration across the study area support this interpretation. Therefore, ‘anomalous’ high values of Zr, as well as other elements concentrated in resistant ‘heavy’ minerals in Nigeria’s streams may not reflect proximal bedrock concentrations of these elements. This conclusion has important implications for using stream sediment chemistry as an exploration tool in Nigeria for primary metal deposits associated with heavy minerals. 相似文献
6.
RON GOLDBERY 《Sedimentology》1982,29(5):669-690
The Lower Jurassic sequence exposed at Makhtesh Ramon, in the south-western Negev of Israel, comprises cyclic fluviatile sediments derived almost exclusively from the reworking of an older laterite terrain. A succession of palaeosols, having the characteristics of modern, red-brown earths, has developed during periods of sub-aerial exposure upon the fine grained overbank sediments. A marked seasonal palaeoclimate with accompanying poor sub-surface drainage conditions, and some stagnation of ground water, is reflected by the distribution and mottling patterns of the iron minerals (with varying degrees of hydration), precipitation of illuviated carbonate and sulphate minerals and the development of soil microrelief. A complex history of pedogenesis and ground water alteration is shown by the rapid lateral facies change within this sequence, into one dominated by high-alumina flint clay and bauxite. Relict pedogenetic and sedimentological textural features of the combined palaeosol/fluviatile sequence, have been identified and mapped within the flint clay/bauxite lithologies. These features include irregular voids, produced by solution of pedogenic sulphate nodules, slickensided curviplanar surfaces of soil microrelief, and depositional bedding. The field relationships of these relicts indicate the overprinting of a younger, chemical weathering event giving rise to the high-alumina flint clay and bauxites. The geometric shape of the upper bounding surface of the ‘bauxite’ alteration zone, is irregular and has an ‘intrusive’ character with respect to the younger, overlying, unaltered sediments. This, together with abrupt changes in mottling patterns near the contact zone and subtle changes in mineralogy from a bauxitic assemblage at depth to one containing mixed-layer clay minerals and carbonates nearer the contact, leads to the conclusion that the later stages of chemical weathering occurred within a confined system, where ground water movements were induced by intake of underlying aquifers. 相似文献
7.
Kananathan Amalan Amila Sandaruwan Ratnayake Nalin Prasanna Ratnayake Shanaka Maduranga Weththasinghe Nimila Dushyantha Nalika Lakmali Ranjith Premasiri 《Environmental Earth Sciences》2018,77(21):737
Beach sediments in Sri Lanka contain industrial-grade heavy mineral occurrences. Samples of both offshore and onshore sediments were collected to examine the provenance, mineralogy and geochemical compositions of the heavy mineral occurrences. Coastal morphodynamic changes along the coastline of Sri Lanka were analyzed using the time-series satellite images. These coastal morphodynamic changes were used to identify the prominent directions of monsoon-influenced longshore currents, coastal sediment accretion and depositional trends and their relationships to the provenance of the heavy minerals. Results show the concentrations of detrital ilmenite, zircon, garnet, monazite, and rutile vary in the onshore and offshore sediments. The heavy mineral potential of the northeastern coast is high (average contents of about 45–50% in the Verugal deposit, 70–85% in the Pulmoddai deposit, and 3.5–5.0% in offshore samples stretching from Nilaveli to Kokkilai), compared to sediments in southwest (average content about 10% in onshore sediments and 2% in offshore sediments from the mouth of the Gin River). Therefore, no economic-grade heavy mineral placers were identified in the offshore environments. The high concentrations of heavy minerals in beach sediments and low concentrations in offshore sediments suggest operation of a panning system in the surf zone to form enriched placer deposits. Major and trace element compositions of beach sediments show marked enrichments of TiO2, Fe2O3, La, Ce, Zr, Cr, Nb, Th and V compared to average Upper Continental Crust (UCC) values. Analysis of prominent coastal longshore transport patterns identifies bidirectional sediment transport in the northeast coast of Sri Lanka. In the southwestern coast, two transport directions occur with anti-clockwise transport from Galle to Hambantota, and clockwise transport from Hikkaduwa to Wadduwa. The heavy minerals in the placers were mainly derived from Precambrian metamorphic rocks, and transported to the coast through the river systems of Sri Lanka. 相似文献
8.
沉积物中重矿物分布受物源区、构造抬升与剥蚀作用、古地貌以及沉积古气候、古环境等多种因素影响,因此沉积重砂矿物的研究可应用于物源区、沉积环境的分析,阐明构造旋回与沉积作用的响应关系。本文通过对塔中地区中1井等6口探井上泥盆统东河砂岩和志留系柯坪塔格组砂岩中重砂矿物分析,提出了塔中东河砂岩重砂矿物主要来自稳定的基底再沉积及花岗岩来源,但受近源的基性火山岩及岩浆期后热液作用影响较大;志留系下砂岩重砂矿物主要来自下覆碳酸盐岩、花岗岩和搬运再沉积物,总体形成于稳定的、多物源的构造-沉积环境,物源方向可能是东南至西北方向。 相似文献
9.
Proposed engineering of gypsiferous soil classification is given. This classification depends on soil texture, mineralogy, geochemistry and engineering properties. Study areas are located within the Mesopotamian plain and include four locations, namely, Najaf, Karbala, Falluja and Samarra which are located between latitudes 32° and 35° and longitudes 43° and 44° 30??. The study performed includes analyses of soil samples for their mineralogy and physical and engineering properties as well as the chemical analyses of soil water extracts. The results suggest that these soils consist of different percentages of sand, silt, clay and some gravel. Analysis also detected secondary gypsum, quartz, calcite, feldspar, different types of rock fragments and different types of heavy minerals in trace amount. Clay minerals are dominated by palygorskite. Hydrochemical analysis results of soil water extracts show that the calcium and sulphate ions are most common, followed by sodium, bicarbonate, chloride, magnesium and potassium. Bicarbonate and chloride show increased values in Karbala and Najaf areas. The highest gypsum content reached 67.5% in the Samarra area, while the lowest is in Karbala, which reached 28.9%.The physical and engineering properties of the studied soils were determined. Samples which were allowed to soak in water show a sudden drop in unconfined compressive strength, compression and shear values immediately after soaking and then decreased gradually. This classification of gypsiferous soils is composed of two classes: gypsiferous soil and highly gypsiferous soil, according to their gypsum content and initial void ratio, coefficient of curvature, coefficient of uniformity, the collapse potential, the compressive strength, cohesion, plasticity index, content of fines and the total dissolve solids of the soil water extracts. It is believed that this newly proposed classification for gypsiferous soils can be applied to other locations and therefore will be useful for other soil scientists and engineers as well because this classification depends on soil texture, mineralogy, geochemistry and engineering properties, while the other existing classifications deal with only one of these variables. 相似文献
10.
Geochemical signature of provenance in sand-size material in soils and stream sediments near the Tobacco Root batholith, Montana, U.S.A. 总被引：1，自引：0，他引：1
Trace-element geochemistry of sandstones are being used to determine provenance. We have conducted preliminary and limited experiments to determine to what extent daughter sands retain the geochemical signature of parent rocks. Six sets of first-order stream sediments, soils from adjacent slopes, and a variety of parent rocks were collected from southwestern Montana, U.S.A. Sampling in a low-relief area ensured that climate and residence time of soils on slopes could be eliminated as variables. Sand-size fractions of stream sediments and soils, and the corresponding parent rocks (granodiorite, quartz monzonite, granite gneiss, biotite-tonalite gneiss and amphibolite) were analyzed for most major elements and selected trace elements. Petrologic modal analysis of the parent rocks and the 0.25–0.50-mm fraction of each sand was done to monitor major mineralogic control, if any, on chemical compositions of the samples.
Our data show that the abundances of the Si and Al in sediments do not discriminate provenance. Abundances of Ca, Mg, Fe and Ti may broadly distinguish between sands derived from metamorphic and igneous source rocks, at least in the area studied. Differences in abundances of the Ba and Th, and the ratio of La/Lu between granitic, tonalitic and amphibolitic parent rocks are preserved in the daughter sediments that we studied. However, the size of the Eu anomaly in the REE patterns of different daughter sediments is not diagnostic of parent rocks. Abundances of Co and Sc distinguish between sediments derived from felsic and mafic rocks. A better provenance discrimination is obtained if the ratios La/Sc, Th/Sc, La/Co, Ba/Sc and Ba/Co are used.
Petrologic modal data show that mineral contents and chemical compositions of parent rocks are compatible with each other. The chemical composition of the sands may be roughly correlated to the petrological modal data but the abundances of some minor and trace elements of sediments cannot be inferred from modal mineralogy. This is expected because these elements may concentrate in accessory minerals and/or may weather out into aqueous or clay mineral fractions; it is also compatible with conclusions of previous studies that some of these elements do not reside in sand-size fractions of siliciclastic sediments. 相似文献
11.
12.
Anthropogenic influence, mainly due to urban and industrial activities, may affect fluvial environments and soils, via atmospheric contamination and liquid and solid waste.Continuing previous works on stream sediments and soils, the Gran La Plata area was chosen. In this area, located in the Northeast of Buenos Aires Province (Argentina), several streams and soils were sampled. The streams have similar characteristics, although some of them have a higher input of pollutants (fluvial effluents, fly ashes, solid wastes, etc.). The studied soils have different pedological development.Magnetic and chemical studies were carried out in the laboratory. Analyses of the results indicated that the behavior of magnetic parameters can be related to the variations of heavy metal contents in stream sediments but there is not a good correlation in soils. The comparison between both environments (stream-sediment and soils) reveals a different impact of pollutants. Magnetite, especially PSD grains, seems to be the main carrier for both environments. 相似文献
13.
M. J. Duane 《Mineralium Deposita》1988,23(1):50-57
The Gortdrum Cu-Ag-As-Sb-Hg-U orebody occurs in Lower Carboniferous strata on the downthrown side of an ENE transcurrent fault system in Southern County Tipperary, Republic of Ireland. The deposit comprises a linear discordant zone of brecciated carbonates and country rocks that are altered and mineralised. Research has indicated anomalous radioelement concentrations associated with the main copper orebody and in particular with the altered breccias within this zone. The metal association (Cu-Ag-As-Sb-Hg-U) is considered unique for Irish Carboniferous carbonate-hosted copper deposits. However, the low temperature mineral assemblage of early uranium-bearing minerals with later sulphide stages is reminiscent of many vein-type hydrothermal ore deposits. The geochemistry of uranium-enriched rocks indicates that the alteration of the basic dykes was a most significant event in the trapping of uranium within the limestones. Propylitization of the early basic dykes by CO2-bearing fluids produced the alteration which led to the development of hematite, leucoxene and clay minerals. The reducing environments attendant with such mineralogy created a favourable environment for uranium precipitation. The reduction of U+6 to U+4 by oxidation of reduced Fe in dolomitized brecciated limestone occurred prior to the main sulphide mineral sequences. The genesis of uranium in the deposit is linked to radioelement remobilization from uranium-bearing heavy minerals in sediments of upper Devonian-Lower Carboniferous age. The uranium became available to low temperature hydrothermal fluids which carried then deposited the uranium along a transcurrent fault system. The source of the heavy minerals is considered to be the Leinster Granite to the east, by which time in the Carboniferous, unroofing of the main pluton had commenced.Previous address: Department of Geology, Trinity College, Dublin 2, Ireland 相似文献
14.
《Journal of Geochemical Exploration》2004,84(1):3-20
The Chinkuashih is a group of dacite-related hydrothermal enargite-gold deposits of the Quaternary age, which produced 94 tons of gold and 119,101 tons of copper from 1895 to 1987. It has remaining reserves of 656 tons of gold with an average grade range of 1.5–3.5 g/ton of Au for all orebodies discovered.Mercury content in different media such as stream sediments, heavy minerals in stream sediments, soils, rocks/ores, and pyrite samples was analyzed by a gold–film mercury detector to evaluate whether mercury is a good pathfinder for these types of deposits at Chinkuashih. The gold film technique is more rapid and cheaper than the traditional fire assay or fire assay/ICP-MS gold and trace element analyses.Mercury in stream sediments and soils indicated the border zone of gold mineralization 12 km away from the center of mineralization at Chinkuashih. Mercury in heavy minerals of the stream sediments distinguished the intermediate zone with gold veins and gold/gold–copper breccia pipes from the core or inner zone with the gold–copper zone. It has been found that contours of 1000 or 500 ppb Hg of soil samples can delineate the outcropping gold orebodies. The gold ores generally contain 1000 ppb or more Hg. 相似文献
15.
《Applied Geochemistry》2004,19(2):257-260
Over the past 30 a, regional and national solid-phase geochemical surveys have been conducted by the United States Geological Survey and the Geological Survey of Canada. In the present paper the authors have examined the distribution of As in stream-sediment and soil samples of the US and Canada in terms of geologic and anthropogenic components. The results of the compilations indicate that the distribution of As in stream sediments, lake sediments, and soils in Canada and the US shows that most of the variability is controlled by the bed rock characteristics. 相似文献
16.
土壤重金属环境质量矿物学评价方法 总被引：10，自引：2，他引：10
利用环境矿物学理论和方法阐明了土壤矿物控制重金属活动状态，具体分析了重金属在矿物表面、层间域和孔道内可能的赋存位置。实验研究结果表明，矿物吸附重金属的作用受到介质pH值、介质离子强度等因素的影响。采用系统聚类分析方法，能定量地分析稳定的硫化物结合态微量有毒有害重金属元素的数量。利用粉晶X射线衍射分析方法，能定量地测定土壤矿物组成和含量。新提出土壤环境质量矿物学方法评价流程。该方法是在利用生态地球化学方法所完成的元素总量调查成果的基础上，开展单元性与剖面性土壤矿物组成与含量测定，查明表层土壤和深层土壤的矿物组成和分布，评价土壤中重金属的赋存状态及其对食物链的影响。旨在为农业地质环境评价提供新方法，切实提高农业地质环境调查质量与服务水平。 相似文献
17.
Shilpa Vuba Sadia Farnaaz Netramani Sagar S. Masood Ahmad 《Journal of the Geological Society of India》2013,82(3):217-226
The major, trace and rare earth elements geochemistry and clay mineral compositions in the river bed sediments from lower reaches of Godavari river suggest that they are derived from weathering of felsic rocks. Trace and rare earth elemental compositions indicate evidence of sedimentary sorting during transportation and deposition. Lower concentrations of transition elements, such as V, Ni and Cr imply enrichment of felsic minerals in these bed sediments. The REE pattern in lower Godavari sediments is influenced by the degree of source rock weathering. The light rare earth elements (LREE) content are indicating greater fractionation compared to the heavy rare earth elements (HREE). A striking relationship is observed between TiO2 and gZREE content suggesting a strong control by LREE-enriched titaniferous minerals on REE chemistry. Shale-normalized REE pattern demonstrate a positive Eu anomaly, suggesting weathering of feldspar and their secondary products, which are enriched in Eu. Chondrite-normalised REE pattern is characteristic of felsic volcanic, granites and gnessic source rocks. Trace elemental compositions in sediments located near urban areas suggest influence of anthropogenic activity. Chemical Index of Alteration (CIA) is high (avg. 65.76), suggesting a moderate chemical weathering environment. X-ray diffraction analysis of clay fraction shows predominance of clay minerals that are formed because of the chemical weathering of felsic rocks. 相似文献
18.
《Applied Geochemistry》2001,16(3):339-350
This study on the application of multi-element relationships in stream sediments to mineral exploration in the Walawe Ganga Basin presents one of the first of its kind in Sri Lanka. In order to determine the nature of these sediments, multi-element analysis of selected grain size (<63 μm, 63–125 μm, 125–177 μm and 177–250 μm) fractions was undertaken. The chemical composition of these fractions were compared with those of the upper continental crust.Some elements, notably Zr, Hf, Th, U, Ce and La, show very high enrichment factors (e.g. 54 for Zr) as compared to the upper crustal abundance. These are presumably associated with heavy minerals such as zircon, rutile and monazite found in abundance in the stream sediments of the Walawe Ganga Basin.Principal Component Analysis (PCA) of the geochemical data show that multi-element relationships could be effectively used to delineate target areas for mineral exploration. With the use of PCA, this study reveals that areas with associations of calc-silicate/marble and charnockitic rocks are probable source regions for mineral occurrences, particularly in the axial regions of anticlines. 相似文献
19.
Environmental Geochemistry of Heavy Metal Contaminants in Soil and Stream Sediment in Panzhihua Mining and Smelting Area,Southwestern China 总被引：4，自引：0，他引：4
Mining and smelting activities are the main causes for the increasing pollution of heavy metals in soil, Water body and stream sediment. An environmental geochemical investiga-tion was carried out in and around the Panzhihua mining and smelting area to determine the ex-tent of chemical contamination in soil and sediment. The main objective of this study was to in-vestigate the environmental geochemistry of Ti, V, Cr, Mn, Cu, Pb, Zn and As in soil andsediment and to assess the degree of pollution in the study area. The data of heavy metal con-centrations reveal that soils and sediments in the area have been slightly contaminated. Geo-chemical maps of Igeo of each heavy metal show that the contaminated sites are located in V-Ti-magnetite sloping and smelting, gangues dam. The pollution sources of the selected elementscome mainly from dusts resultant from mining activities and other three-waste-effluents. The areaneeds to be monitored regularly for trace metal, especially heavy metal enrichment. 相似文献
20.
《Russian Geology and Geophysics》2015,56(10):1437-1450
We studied recent sedimentation in small saline and brackish lakes located in the Ol’khon region (western Baikal area) with arid and semiarid climate. The lakes belong to the Tazheran system; it is a series of compactly located closed shallow lakes, with a limited catchment area and different mineralization, under the same landscape, climatic, geologic, and geochemical conditions. Two complementary approaches are applied in the research: (1) a detailed study of individual lake and (2) a comparison of the entire series of lakes, which can be considered a natural model for studying the relationship between endogenic mineral formation and the geochemistry of lake waters. The lake waters and bottom sediments were studied by a set of modern methods of geochemistry, mineralogy, and crystal chemistry. The mineral component of the bottom sediments was analyzed by powder X-ray diffraction (XRD), IR spectroscopy, and electron microscopy. The lakes are characterized by predominant carbonate sedimentation; authigenic pyrite, smectite, chlorite, and illite are detected in assemblage with carbonate minerals in the bottom sediments. Carbonate phases have been identified, and their proportions have been determined in the samples by decomposition of the complex XRD profiles of carbonate minerals into peaks using the Pearson VII function. Mathematical modeling of the XRD profiles of carbonates has revealed that predominantly Mg-calcites with variable Mg content and excess-Ca dolomite accumulate in lake bottom sediments influenced by biogenic processes. Aragonite, monohydrocalcite, and rhodochrosite form in some lakes along with carbonates of the calcite-dolomite series. We show a dependence of the composition of the assemblages of the newly formed endogenic carbonate minerals and their crystallochemical characteristics on the chemical composition of lake waters. 相似文献