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Benefication of low-grade chromite ores of abandoned mine at Topraktepe, Beysehir, SW Turkey
(BERG FAC TECHNICAL UNIV KOSICE, 2007) Ağaçayak, Tevfik; Zedef, Veysel; Aydoğan, Salih
Optimum enriching possibilities of chromite ores from the abandoned Topraktepe mine were investigated. To obtain the best enriching method(s), shaking table, multi gravity separator, humprey spiral and jigging tests were tested. The best grades for Cr2O3 are 55.65% by shaking table, 57.52% by multigravity separator, 54.58% by humprey spiral test and 50.68% by jigging. To provide these results, the particle sizes of the ore are -0.3 to 0.212 mm for shaking table, -0.106 to 0.075 mm for multi gravity separator, -0.3 to 0.212 mm for humprey spiral and -2 to 1 mm for jigging. Regarding the best grades obtained, the recoveries for shaking table, multi gravity separator, humprey spiral and jigging methods are 85.38%, 79.83%, 94.89% and 87.58% respectively. The results of these tests show that a further recovery of remaining 500 000 tons of ore could be possible from the abandoned Topraktepe chromite deposit.
Beneficiation of Topraktepe chromite ore by multi gravity separator, (Beysehir, Turkey)
(2007) Ağaçayak, Tevfik; Zedef, Veysel
In this study, enrichment probabilities of Topraktepe (Yesildag- Beysehir) chromites by Multi Gravity Separator were investigated. Multi Gravity Separator tests were carried out using -106-75 ?m particle size and 2500 g specimen. The results of beneficiation studies showed that concentrate containing 57.52% Cr2O3 was obtainable with a 79.83% rate of recovery. The results of Multi Gravity Separator test demonstrated that high recovery and high grade concentrates have been obtained for 3 drum speed. The best result has been obtained at 150 rpm drum speed.
Causes of Darkening of the Pamukkale Travertines, Denizli, South-West Turkey
(Parlar Scientific Publications (P S P), 2003) Zedef, Veysel; Matsuda, Yusuke; Tanaka, Yuji; Harada, Hisashi; Öncel, Mehmet Salim; Doyen, Adnan; Söğüt, Ali Rıza; Şensöğüt, Cem
Since the beginning of the 1990's, the travertines at Pamukkale, south-west Turkey, have faced a serious environmental pollution problem. The travertines were originally snow-white in colour, but this colour has been turning into pale grey. In addition to other features, the snow-white colour and the huge mass of rocks on the edge of Pamukkale plateau make the travertines unique and attractive to visitors. Living bacteria exist 1-2 mm beneath the surface of the travertines in both terrace and water channel types. The thickness of the bacterial lamina is 1-2 mm in the water channel type, whilst it is approximately 1 cm for other types. Absorbance Spectral (AS) data shows that the living bacteria are cyanobacteria, which are responsible for the green colour in certain areas of the travertines. Our investigations show that the major force responsible for the change of colour in the area is the increasing level of excess organic matter, which also causes a shift in the metal content of the travertines. While the greyish polluted samples have 584 ppm of Total Organic Carbon (TOC), the unpolluted snow-white samples have only 177 ppm of TOC. On the other hand, the Al, Fe and Mn contents of the polluted samples are respectively 144, 62, 6 ppm higher than the unpolluted samples. As the TOC is the main cause of the pollution, decreasing the organic matter in the pools would be the first step to protecting the area. This requires limiting, or even banning, people who enter the pools for swimming. Sources of Al, Fe, Mn and other hazardous metals should be reduced in the region.
Characteristics of the amphibolites from Nigde metamorphics (Central Turkey), deduced from whole rock and mineral chemistry
(GEOCHEMICAL SOC JAPAN, 2007) Kocak, Kerim; Kurt, Huseyin; Zedef, Veysel; Ferre, Eric C.
Whole rock and mineral chemistry of amphibolites are presented for the lower (Gumusler Formation) and higher parts (Kaleboynu Formation) of the Nigde Massif with the aim to constrain protolith genesis and metamorphic P-T-conditions. The amphibolites, associated with a series of supracrustal metasediments, as thin layers and discontinuous pod/small lenses, are of igneous origin with composition of subalkaline and tholefitic basalts. Based on immobile elements content and ratios, amphibolites from both formations are thought to have formed mostly by fractional crystallisation of pyroxene +/- spinel, amphibole, plagioclase as well as apatite and titanite; coupled with minor crustal contamination. Contamination is particularly clear for the Gumusler Formation formed in a back-arc basin (Paleothetys) during magmatic ascent through the thickened Central Anatolian crust. The basic rocks could have been metamorphosed later at 7.5-3 +/- 0.6 kb and 850-420 degrees C, with the temperature gradient ranging from 35 to 122 degrees C/km at different depths in the Neo-Tethyan subduction zone, and exhumed from depths of approximately 20 km via regional extension.
Chemical and physical properties of the Kizildag olivines. A giant olivine deposit, Antalya, SW Turkey
(OFIOLITI, 2004) Zedef, Veysel; Doyen, A.; Öncel, M. S.; Söğüt, A. R.; Köseleli, T; Koçak, K.
The Kizildag olivine deposit is found within the Kizildag ultramafics. The main source of the olivine are the dunites, which are located in the ultramafics. The chemical and mineralogical composition and the physical properties of the studied samples are relatively uniform. The main component of the dunites is forsteritic olivine (Mg2SiO4), which consists of 48.75% MgO, 42.31% silica and 7.21% Fe2O3, The average expansion rate and ignition loss is 1.18% and 0.96% respectively. These percentages satisfy the requirements of the iron and steel industry, as well as meeting acceptable refractory standards. The reserve of the Kizildag olivine deposits is estimated to be 9 billion (9,000,000,000) tons, which is comparable to the largest known olivine deposits of Aheim (Norway). The olivine of Kizildag can be exported to international markets, for the port of Antalya is situated 120 km from the deposits. The main disadvantage is the failure of the domestic market to recognize the olivine as a valuable resource.
Chromite occurrences in the Meram-Çayırbağı ophiolites (Konya, Turkey): geological and geochemical outline
(Selçuk Üniversitesi Mühendislik-Mimarlık Fakültesi, 2005) Zedef, Veysel
Two chromite occurrences have been found within the Meram-Çayırbağı (Konya) Ophiolitic Complex. The occurrences are located at Helvacıbaba and Bacağınkoyak Tepe, and the complex is promising for large chromite orebodies. The chromites are formed in dunitic rocks of the Meram-Çayırbağı Ophiolites. Chromite mineralization of >18.62 % (in weight) occurs in Helvacıbaba while the Bacağınkoyak Tepe have a minimum 35 % of Cr2O3. The major and trace element data of both occurrences indicate that the chemical composition of the chromite samples is mainly controlled by the Cr2O3 concentration.
Çimencik-Yellice (Ereğli-Konya) Yöresinin Stratigrafisi
(2000) Söğüt, Ali Rıza; Özkan, A. Müjdat; Zedef, Veysel
İnceleme alanında en altta Bolkar grubuna ait Dedeköy (Üst Permiyen) ve Gerdekesyayla (Alt-Orta Triyas) formasyonları yer alır. Dedeköy formasyonu; dolomitik kireçtaşı ve mermerlerden oluşur ve taban dokanağı inceleme alanında gözlenmez. Dedeköy formasyonu üzerine uyumlu dokanakla fillit, dolomitik kireçtaşı ile kalkşist ardalanmasından oluşan ve kireçtaşı olistolitleri kapsayan Gerdekesyayla formasyonu gelmektedir. Bolkar grubu üzerine uyumsuz olarak konglomera ve kumtaşıyla başlayan, kumlu kireçtaşı, killi kireçtaşı ara tabakaları kapsayan kumtaşı-şeyl ardalanmasından oluşan Halkapınar formasyonu (Üst Paleosen-Orta Eosen) gelmektedir. Halkapınar formasyonu içinde andezit, bazalt ve diyabaz daykları ile bunlara ait bloklar da yer almaktadır. Halkapınar formasyonu üzerine uyumsuz olarak konglomera ve kireçtaşlarından oluşan Kepeztepe formasyonu (Üst Miyosen-Alt Pliyosen) gelir. Bu birimdeki kireçtaşları genellikle stromatolitik olup stromatolitlerin gelişiminde Schizothrix sp., Phormidium sp ve/veya Scytonema sp. gibi alg cinsleri etkili olmuştur. Tüm bu birimler üzerinde ise Kuvaterner yaşlı akarsu çökelleri, yamaç molozları ve alüvyonlardan ibaret genç oluşuklar açılı uyumsuz olarak yer almaktadır.
DETERMINATION OF LEACH CONDITIONS OF KARACAM LATERITIC NICKEL ORES WITH SULFURIC ACID UNDER EFFECT OF SODIUM FLUORIDE
(INT SCIENTIFIC CONFERENCE SGEM, 2011) Ağaçayak, Tevfik; Zedef, Veysel
In this work, dissolution of Ni and Fe in sulfuric acid medium under the influence of sodium fluoride was studied. The samples of the nickeliferous lateritic ore were taken from Eskisehir (Karacam) region of Turkey. The effects on the nickel and iron dissolution rates of stirring speed, sulfuric acid concentration, sodium fluoride concentration, reaction temperature were investigated. In order to investigate the effects of leaching temperature range of 30-50 degrees C the shrinking core model was applied by using the results of experiments. Kinetics analysis showed that the nickel and iron dissolution from lateritic ore could be described by the "diffusion" for nickel and "surface chemical reaction" for iron, respectively. The activation energies (Ea) and Arrhenius constants for the dissolution reactions were calculated.
Determination of radon concentration levels in well water in Konya, Turkey
(OXFORD UNIV PRESS, 2013) Erdoğan, M.; Eren, N.; Demirel, S.; Zedef, Veysel
Radon (Rn-222) measurements were undertaken in 16 samples of well water representing different depths and different types of aquifers found at the city centre of Konya, Central Turkey. The radon activity concentrations of the well water samples collected in the spring and summer seasons of 2012 were measured by using the radon gas analyser (AlphaGUARD PQ 2000PRO). The radon concentrations for spring and summer seasons are 2.290.17 to 27.251.07 and 1.440.18 to 27.451.25 Bq l(1), respectively. The results at hand revealed that the radon concentration levels of the waters strictly depend on the seasons and are slightly variable with depth. Eleven of the 16 well water samples had radon concentration levels below the safe limit of 11.11 Bq l(1) recommended by the United States Environmental Protection Agency. However, all measured radon concentration levels are well below the 100 Bq l(1) safe limit declared by the World Health Organisation. The doses resulting from the consumption of these waters were calculated. The calculated minimum and maximum effective doses are 0.29 and 5.49 Sv a(1), respectively.
Dimension stones used in central Anatolia: Some of their geological and mechanical properties
(2011) Zedef, Veysel; Ağaçayak, Tevfik; Söğüt, Ali Rıza; Koçak, Kerim
It is aimed to study physical and chemical features of the samples from dacite-andesite quarries and travertine quarries of Konya and its surroundings. The dacites and andesites are the main products of the Neogene volcanism observed in Konya while the travertines are well exposed as chemical-sedimentary rocks where the young sediments were exposed at the outskirts of Konya plain. These rocks (dacite, andesite and travertines) have been extensively used as dimension stones in and around the city of Konya, Turkey. In terms of dry weight loss (dwl- an experiment assessing the resistance of the rocks against salt) values, the weakest rocks were created from a dacite quarry at Sa?lik. On the other hand, the andesites from Gölcük are probably the most suitable dimension stones for external uses (for example outdoor stairs and pavements), as indicated by having the highest uniaxial compressive strength (UCS) value (mean 90.7 Mpa). The travertines from the Mut region are the most fragile rocks with their 26.1 Mpa values indicating that preventing the uses of outdoor purposes. ©2011 Academic Journals.
Dissolution kinetics of a lateritic nickel ore in sulphuric acid medium
(BERG FAC TECHNICAL UNIV KOSICE, 2012) Ağaçayak, Tevfik; Zedef, Veysel
The dissolution kinetics of a lateritic nickel ore in the sulphuric acid solution were investigated. The shrinking core model was applied to the results of experiments. The effects of stirring speed (100-600 rpm), H2SO4 concentration (0.1-2 mol l(-1)), leaching temperature (40-96 degrees C) and the particle size of the ore were studied on the nickel dissolution rate. The correlation coefficients for each different parameters were calculated. The results indicated that the dissolution rate of Ni is controlled by diffusion. The activation energy (Ea) for the dissolution reaction was determined to be 68.66 kJ mol(-1). The Arrhenius constant was calculated to be 8.2578 s(-1). The order of reaction for the H2SO4 concentration and the particle size were also obtained. It was found that the stirring speed had no effect on the rate of nickel dissolution.
DISSOLUTION KINETICS OF LATERITIC IRON ORE IN SULPHURIC ACID MEDIUM
(INT SCIENTIFIC CONFERENCE SGEM, 2009) Ağaçayak, Tevfik; Zedef, Veysel
In this study, dissolution kinetics of iron leaching by sulphuric acid under atmospheric pressure from Karacam (Eskisehir-Turkey) lateritic ore was studied. The effects on the iron reaching rate of stirring speed, sulphuric acid concentration, temperature, particle size, and solid/liquid ratio were investigated. In order to investigate the effects of leaching temperature range of 40-90 degrees C the shrinking core model was applied by using the results of experiments. Kinetics analysis showed that the iron dissolution from lateritic ore could be described by "surface chemical reaction". The activation energy (Ea) for the dissolution reaction and Arrhenius constant was calculated.
DISSOLUTION OF LATERITIC NICKEL ORE IN SULPHURIC ACID MEDIUM WITH POTASSIUM DICHROMATE
(INT SCIENTIFIC CONFERENCE SGEM, 2008) Ağaçayak, Tevfik; Aydoğan, Salih; Zedef, Veysel
In this study, leaching of Ni and Fe in suphuric acid medium with K2Cr2O7 was investigated. The samples of the lateritic nickel ore were taken from Karacam (Eskisehir) region of Turkey. Mineralogical investigations showed that the ore sample contains, goethite, hematite, wustite, retgersite, gaspeite and clay type minerals together with quartz. The shrinking core model was applied to the results of experiments investigating the effects of leaching temperature range of 50-96 degrees C. Two equations were applied from obtained results from each temperature value. Their correlation coefficients for each temperature are calculated. These results indicate that the dissolution rate of Ni is controlled by diffusion. The activation energy for the leaching process was found to be 68.43 kJ/mol and the Arrhenius constant was calculated to be 8.231 s(-1).
The economic importance of the Kizilda? ultramafic rocks, Kizildag, Akseki, SW Turkey
(2006) Doyen, A.; Zedef, Veysel
The ultramafic rocks around Kizildag have very important economic reserves of chromite and olivine. The ultramafic rocks are mainly composed of dunites and in lesser amount diabases. The dunites are mainly made of forsteritic olivine which is about 90% of the rock mass. The chemical composition of the rock is as follows: MgO 52.25%, SiO2 37.5% and Fe2O3 8.3%. These mineralogical and chemical characteristics are met the need of iron-steel and refractory industry. The olivine deposits of Kizildag with 9 billion (9,000,000,000) tons of reserve is one of the largest olivine resource in the world (The largest deposit is found in Aheim, Norway). The ultramafic rocks are also the host rocks for chromite deposits which can be counted as important. Between the years of 1990 and 2000, approximately 100,000 tons of chromite was exploited. After the year of 2000, economical disadvantages of the chromite mining in the region, the extraction of chromite were ended since the olivine mining was found much more profitable in the mass. The chromitiferous ore is in lentile shape in general and sometimes banded and disseminated. The grade of chromite ore is about 50.54% as Cr2O3. The chromites can be classified as Al-rich, ferrous chromite ore according to their chemical composition. The geological and chemical features of the chromites can be compared to the well known Alpine type chromite deposits. © 2006. International Scientific Conference SGEM.
Effect of Coatings on Hardness of Commercial Marbles
(AMER INST PHYSICS, 2016) Zedef, Veysel
In this study, three type of marble and one granite were chosen to understand if the coating is effective on hardness of the commercial rocks. To understand the hardness of the rock, Schmidt hammer tests were undertaken. The used device allowed us uniaxial compressive strength (UCS) as well as Schmidt rebound (R). The coated samples have clearly high R and UCS values when compared to uncoated samples. The Elazig visne, the well-known marble of Turkey, have 35.6 R and 44.2 MPa UCS values of coated samples. On the other hand, uncoated surface of the same marble have 30.5 R and 35.4 MPa UCS.
Effect of salt crystallization on stones of historical buildings and monuments, Konya, Central Turkey
(PERGAMON-ELSEVIER SCIENCE LTD, 2007) Zedef, Veysel; Kocak, Kerim; Doyen, Adnan; Ozsen, Hakan; Kekec, BlIgehan
In this study, we investigated the chemical and physical properties of the volcanic rocks used as building stones in historical places and monuments. The chemical weathering effect of salt crystallization on these stones was measured on the laboratory conditions (in most cases, used samples were very small). For this purpose, the dry weight loss (DWL) test was conducted. The rocks of dacite, andesite and tuffs of volcanic origin have different durability against salt crystallization. The most stable rocks are dacites (DWL 2.06%) which were used in the construction of Hittite monuments at Eflatun. The durability of the stones is closely related to their chemical, mineralogical, petrographical and mechanical properties. The stones used in the historical buildings are generally much more stable than present-day building stones. (c) 2005 Elsevier Ltd. All rights reserved.
Genesis of Vein Stockwork and Sedimentary Magnesite and Hydromagnesite Deposits in the Ultramafic Terranes of Southwestern Turkey: A Stable Isotope Study
(2000) Zedef, Veysel; Russell, Michael J.; Fallick, Antony E.; Hall, Allan J.
Vein stockworks and lacustrine developments of cryptocrystalline magnesium carbonates of Neogene and Quaternary age occur within the partially serpentinized, discontinuous ultramafic belts of southwestern Turkey. They are comparable to the Neogene cryptocrystalline magnesite bodies elsewhere in the Alpine orogen to the northwest and southeast. Our previous work (Fallick et al., 1991) suggested that cool (?100°C) modified meteoric water was the mineralizer, that ultramafic rock was the source of the magnesium, but that there were three separate sources of the (bi)carbonate. These sources were distinguishable by their stable isotope composition as follows: (1) low-temperature carbonate with ? 18O((SMOW)) values of ~36 per mil and ? 13C((PDB)) values of ~4 per mil, derived from atmospheric CO 2; (2) moderate-temperature carbonate with ? 18O((SMOW)) values of +28 per mil and ? 13C((PDB)) values of -15 per mil, derived by decarboxylation of organic-rich sediments; and (3) higher temperature carbonate with ? 18O((SMOW)) values of ~19 per mil and ? 13C((PDB)) values of ~3 per mil, assumed to have been generated by thermal contact metamorphism of Paleozoic marine limestone at depth. In general these magnesite deposits were found to fall into two groups, comprising carbonate generated on two mixing lines. The first group spanned the putative mixing line from the 'atmospheric' source (1) to 'organically derived' source of CO 2 (2). The second group extended between atmospheric source (1) and the 'thermal' source (3), although there were concentrations either around the atmospheric end, or precisely at the contact metamorphic end of the line. In the present study we found that large stockwork deposits at Helvacibaba and Koyakci Tepe have ? 13C((PDB)) and ? 18O((SMOW)) values averaging ~-12 and ~+27 per mil, respectively, indicating a derivation mainly by oxidation of organic-rich metasediments perhaps underthrust at depth (end-member 2), with some involvement of atmospheric carbon dioxide as bicarbonate in the circulating, hot, and modified meteoric water (end-member 1). Calcite veinlets in a meta-argillite of the Cambro-Ordovician Seydisehir Formation, most likely to have been underthrust beneath the stockworks, yielded ? 13C((PDB)) values of -20 per mil, consistent with, though not proving, oxidized organic carbon being one of the sources of carbonate. The ? 18O((SMOW)) values of these same veinlet carbonates are also rather low (22‰), indicating precipitation from heated ground water, though their age is unknown. The major stratiform magnesite deposit at Hirsizdere in the center of the Menderes graben has ? 13C((PDB)) and ? 18O((SMOW)) values averaging ~3 and ~25 per mil, respectively, and thus appears to be an example of the hydrothermal-sedimentary (i.e., exhalative) type (Ilich, 1968). In contrast, the hydromagnesite stromatolites presently growing in Salda Golu (Lake Salda) are apparently developing at cool ground-water seepages. The gross morphology of the Salda Golu stromatolites and the hydromagnesite sediments derived therefrom is reminiscent of that revealed in the Bela Stena magnesite pit in Serbia. These lacustrine deposits have mean ? 13C((PDB)) value of ~4 and ~2 per mil and mean ? 18O((SMOW)) values of ~36 and ~33 per mil, respectively, i.e., they both plot broadly over the atmospheric CO 2-meteoric water field (end-member 1), consistent with microbially mediated precipitation at cool ground-water seepages in enclosed evaporating lakes.
Geological and geomechanical properties of some carbonate marbles and basalt stone from Morocco
(Selçuk Üniversitesi Mühendislik Fakültesi, 2017) Zedef, Veysel; Koçak, Kerim; Zaghloul, Najib Mohamed; Döyen, Adnan; Söğüt, Ali Rıza; Özşen, Hakan; Kekeç, Bilgehan; Aras, Ali; Doğan, Kemal; Ağaçayak, Tevfik
The natural rocks used today as well as in the history for a variety of purposes were a subject of different alteration, weathering and deterioration conditions. These conditions are strictly controlled by environment and nature of rock varieties (marble and stone). This study is a first approach to understand the relation between some geological features and behavior against salt (Na2SO4) decay of Moroccan marbles and stones. For this purpose, widely used four dolomitic limestones, two crystalline limestones, one limestone and one basalt sample (total 8) were chosen from Morocco. Extra attention paid to choose locations being a representative of all Moroccan country. The carbonate samples (limestone and dolomite) consist of mainly dolomite and calcite with micritic and sparitic cement. The sole, non-carbonaceous sample is basalt of Khenifra containing mainly plagioclase and pyroxene. In general, both bulk-dry and powder density values of the studied rock samples are homogeneous. The limestone of Bir Jdid has the highest (10.81 %) effective porosity and dry weight loss value (4.61 %). The loss on ignition value of the Khenifra basalt has the lowest value with 1.26 %. The loss on ignition values are also relatively uniform. The obtained data indicate that outdoor uses (especially in coastal areas) of limestones of Bir Jdid and dolomitic limestones of Taza are more risky than the others.
Güdürüf (Bozkır-Konya) Formasyonundaki Barit Zuhurlarının Jeolojik ve Jeokimyasal Özellikleri
(1998) Zedef, Veysel; Özkan, Ali Müjdat; Döyen, Adnan; Arslan, Mehmet
Damar ve mercek şekilli barit oluşumları Bozkır (Konya) yakınlarında riyolitik tüf ve tüffitler içeren Güdürüf formasyonu içinde çok sayıda ancak sınırlı bir alanda bulunurlar. Derlenen barit örnekleri % 48.9 ile 87.7 (ortalama % 77.4) arasında saf barit, 824 ile 4761 (ortalama 3446) ppm arasında Sr içerirler. Zuhurlarda baskın mineral barit olup buna az miktarda kalsit de eşlik eder. Baritlerde BaO-Sr, Sr-Ce, BaO-SCO3 arasında pozitif ilişki, SO3-CaO arasında da negatif bir ilişki mevcuttur. Güdürüf tüflerinin üst seviyelerdeki Orta Triyas yaşlı kireçtaşı seviyeleriyle ardalanmalı oluşu ve stratigrafik olarak bu tüffitlerin üzerinde bulunan Jura yaşlı Kuztepe -formasyonunda barit mineralizasyonunun yokluğu Orta Triyas yaşlı bir mineralizasyona işaret eder. Baritler muhtemelen Orta Triyas döneminde Tetis'in Anadolu'ya uzanan kollarından birinin içinde, sığ-denizel bir ortamda, kıta kenarında oluşmuşlardır. Barit damarlarının tüflerlerle birlikte tüffitler içindeki kireçtaşı seviyelerini de kesmesi hidrotermal bir kökene işaret eder. Zuhurlardaki baryumun kaynağı büyük bir olasılıkla tüfler ve/veya volkanik faaliyete bağlı olarak oluşan hidrotermal çıkışlardır.
Hydromagnesite Stromatolites and Sediments in an Alkaline Lake, Salda Golu, Turkey
(SEPM-SOC SEDIMENTARY GEOLOGY, 1996) Braithwaite, C. J. R.; Zedef, Veysel
Salda Lake in SW Turkey is a highly alkaline (pH > 9) water body with waters enriched in magnesium, Microbial stromatolites along shorelines contain a microflora of diatoms and cyanobacteria with extensive associated biofilms. Together these are responsible for precipitation of hydromagnesite, although distribution is not congruent with either cells or films. Deposition has continued over several thousand years and is independent of both lake volume and the general concentration of lake waters. The lake is rimmed on three sides by serpentinites and on the fourth by dolomite, The bulk of the water entering the lake is meteoric, fed via extensive gravelly alluvial fan deltas (with predominantly serpentinite pebbles) whose total areas and catchments exceed that of the lake. These waters are significantly cooler than surface waters of the lake, and there is no evidence for derivation from hot springs, The magnesium is thought to have been leached from the gravels. Extensive areas of recent sediments accumulating on shorelines have apparently formed by mechanical breakdown of microbialites. Similar deposits form conspicuous terraces in two areas and point to the longterm effectiveness of these processes, Terrace deposits are modified by a variety of subaerial processes, including growth of hydromagnesite cements. No microbial structures are preserved in these, and it is presumed that they are destroyed during reworking. Fine-grained hydromagnesite sediment derived from shorelines and from terraces is suspended in the water column during storms and is probably redeposited as turbidites in the deeper parts of the lake, Sediments of this kind may be a useful analogue for some ancient and economically important stratiform magnesite deposits.

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