The Serinhisar-Acıpayam basin of western Anatolia hosts a Neogene alkaline lake which formed in some graben and semi-graben depression zones as a result of N–S tension. The basin is filled with fluvial and lacustrine sediments dominated by clayey materials. The filling of the basin with fine sediments and associated water level changes caused the development of swampy and/or semi-swampy, alkaline-lake environments where sepiolite, palygorskite, saponite and dolomitic sepiolite or palygorskite precipitated periodically in the basin. Sepiolite is predominant in the Kuyucak section and is intercalated with saponite-dominated levels, whereas saponite accompanied palygorskite at Kocapınar where basaltic volcanism occurred. The contacts between sepiolite-palygorskite and saponite levels are more or less sharp, reflecting rapid changes in the physicochemical conditions of the depositional environment. Micromorphological images reveal that both sepiolite and palygorskite grew as interwoven fibers or fiber bundles and masses where dolomite was absent, indicating direct precipitation from solution, whereas fibrous networks grew authigenically on and out of dolomite in dolomitic sepiolite and dolomitic palygorskite. Saponite is either green or reddish brown due to its organic material-rich content and derivation from products of basaltic volcanism. Synsedimentary basaltic volcanism was the main source of Fe and Al, whereas Si and Mg were derived from surrounding ultrabasic and detrital units and partly from the volcanism. It can be concluded that sepiolite, palygorskite and saponite formed either by direct precipitation from alkaline lake water or authigenically from interstitial pore-water between dolomite rhombs as controlled by concentration of Si, Mg, Al and Fe, rather than by mutual transformation.

Editor: John Adams)AB ST R ACT : The Tas°oluk kaolinite deposits of Afyonkarahisar (western Anatolia) are hosted by both pre-Early Cambrian sericitic mica-chlorite schists and Neogene volcanites, the latter comprising tuffs and agglomerates. These units have been affected by hydrothermal alteration controlled by faults resulting in complex, irregular, lateral mineralogical zonation. The occurrence of a siliceous cap on altered schists and in claystone, of quartz veins in schists and tuffs, and the development of explosion cones and pit fillings indicate that alteration in both the schists and the volcanites is due to hydrothermal processes. Altered schists have generally large (locally small) Fe contents, and claystones are generally silicified and have small Fe contents. Kaolinite predominates south and west of Tas°oluk, whereas high (Fe+Ti)-bearing illite + kaolinite predominate in other altered sections. The kaolinite exhibits a stacked micromorphology within altered schists, and the altered volcanites record in situ precipitation, derived from a mechanism of paired dissolution and precipitation. Illite fibres coexist with kaolinite, smectite, chlorite, mica and sericitized feldspar in markedly altered schists, revealing that the illite formed either authigenically or by conversion of smectite to illite. A relative increase in Cr+Ni and decrease in Sr+Ba in the kaolinite deposits and their schistose host rock relative to the upper level of the kaolinite deposits and their volcanic parent rocks came about by the alteration of chlorite, mica and feldspar in the sericitic mica-chlorite schists, and feldspar, glass shards and schist fragments in the volcanites as a result of extensive faulting, fracturing and hydrothermal activity during Late Miocene-Pliocene volcanism, which contributed to the development of kaolinite deposits under acidic environmental conditions. With regard to industrial applications, the low-Fe kaolinized schists are suitable for use in refractories and paper coatings, while the claystone is suitable for use in ceramics and in the white-cement industry.

Extremelywhite huntite having friable,earthy characteroccurs in the Cameli basin which was downthrown along reverse faults duringneotectonicactivity. The basementcomprisesdolomiticlimestoneandperidotitewhichwere themainsourcesofMg forhuntiteformation, These unitsareoverlainunconformably by conglomerate,sandstone,andmudstoneofa fan-deltaenvironmentand, locally,by swampyfacies,and by dolomite-dolomitic marl-huntiteand karsticlimestonewhich representmud-flatand open-lakesediments,respectively. The huntiteoccursas 0.5-3-m-thickmassivedepositsas wellasfillingsoffenestraldissolutionvoidsandas sheetcracksindolomiticmarl,dolomiteandlimestonewhich areevidenceofaridtosemi-aridclimaticconditions. Massivehuntitewithdolomiteand/orhydromagnesite/magnesite probablyformedby diagenetic processesin lightofthe gradationalcontactofhuntite with dolomite inthe Sucati huntite deposit. Whilediscoidaland fenestralhuntiteformed by directprecipitationofMg-rich pore watersin shallowcoastalsedimentsof a mud-flatenvironment,thehuntiteflocculatedduringtheprecipitation ofkarstic limestone,probablyina pluvialclimaticregime.

The Hirsizderemagnesitedepositis foundin the upperMiocene-Pliocene lacustrinesedimentsofthe Cameli formation in the western Aegeandepression zone, whichwas upliftedto form a broad anticlineand in which consecutivefaults and fractures developeddue to the neotectonic activities. Thick alternation of carbonatecementedand weaklycementedconglomerate, sandstone,mudstoneintercalated with a fewthindolomiteand magnesitelayersis exposedat the lowerpartof the sequence. Theseunitsareoverlainby magnesiteanddolomite in associationwiththin claystoneand sandstone layersandlenses. Greenandclaretred-brownsmectiteis observedin detritalmaterialsas well as in sandycarbonateunits,and isaccompaniedbyserpentine,amphibole, illite,feldsparand quartz,whereassepioliteis developedinthe form of3-5 em thick,yellowandgreenishbrowncoloredveins,or asthin filmsliningparallelto theveinaxiswithinthe magnesiteunit. SEMstudies showthat sepiolitefibersare grown in theformof meshworks and bridgesbetweenrelictcarbonatemineralgrains. Thepresenceofplantstem imprints, and the abundance of gastropod and ostracode shells in carbonate units indicate shallow and alkaline lake conditions. Field observations and detailed mineralogical, chemicaland micromorphological determinations indicate that sepiolite is formed by diagenetical transformation of magnesiteduring the movementof silica-richmeteoricwater through the fractures of carbonate units under near-surface alkalineconditions.

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