Michael G. Stamatakis

Zeolitic tuffs of Kimolos Island, Aegean Sea, Greece and their industrial potential

Abstract Tuffaceous rocks and lavas of the Pliocene age exist on Kimolos Island, Aegean Sea, Greece. These tuffaceous rocks have been locally transformed to clinoptilolite and mordenite tuffs. The former are porous and relatively soft, whereas the latter are massive and hard. The diagenetic transformation of volcanic glass to clinoptilolite and mordenite took place in an open hydrological system by circulation of alkaline ground waters. The fluids responsible for mordenite formation had probably higher temperature than that of clinoptilolite due to high heat flow rates originating from the emplacement of lavas in their vicinity. Even though clinoptilolite and mordenite tuffs have similar chemical analyses, the composition of mordenite exhibits lower variability than that of clinoptilolite. Regarding cement properties, those cements containing mordenite tuff have a slightly higher strength than that of cements with either Milos pozzolana or clinoptilolite tuff. The higher strength of mordenite cement is probably due to the higher zeolite content of the mordenite tuff and also its higher reactive silica content. In addition, when compared to Milos pozzolana, the zeolite tuffs demand more water to produce paste of the same consistency. This means that when zeolitic cement is used for concrete production, it is likely that a superplasticizer needs to be added in the mixture. In conclusion, the use of zeolitic tuffs as an additive in cement is promising. However, the full evaluation of these materials demands a thorough examination in areas related to their specialised properties and also extended testing on concrete produced with these materials.

Trace metal-rich Quaternary hydrothermal manganese oxide and barite deposit, Milos Island, Greece

Abstract The Cape Vani Mn oxide and barite deposit on Milos Island offers an excellent opportunity to study the three-dimensional characteristics of a shallow-water hydrothermal system. Milos Island is part of the active Aegean volcanic arc. A 1 km long basin located between two dacitic domes in northwest Milos is filled with a 35-50 m thick section of Quaternary volcaniclastic and pyroclastic rocks capped by reef limestone that were hydrothermally mineralized by Mn oxides and barite. Manganese occurs as thin layers, as cement of sandstone and as metasomatic replacement of the limestone, including abundant fossil shells. Manganese minerals include chiefly δ-MnO2, pyrolusite and ramsdellite. The MnO contents for single beds range up to 60%. The Mn oxide deposits are rich in Pb (to 3.4%), BaO (to 3.1%), Zn (to 0.8%), As (to 0.3%), Sb (to 0.2%) and Ag (to 10 ppm). Strontium isotopic compositions of the Mn oxide deposits and sulphur isotopic compositions of the associated barite show that the mineralizing fluids were predominantly sea water. The Mn oxide deposit formed in close geographical proximity to sulphide-sulphate-Au-Ag deposits and the two deposit types probably formed from the same hydrothermal system. Precipitation of Mn oxide took place at shallow burial depths and was promoted by the mixing of modified sea water (hydrothermal fluid) from which the sulphides precipitated at depth and sea water that penetrated along faults and fractures in the Cape Vani volcaniclastic and tuff deposits. The hydrothermal fluid was formed from predominantly sea water that was enriched in metals leached from the basement and overlying volcanogenic rocks. The hydrothermal fluids were driven by convection sustained by heat from cooling magma chambers. Barite was deposited throughout the time of Mn oxide mineralization, which occurred in at least two episodes. Manganese mineralization occurred by both focused and diffuse flow, the fluids mineralizing the beds of greatest porosity and filling dilatational fractures along with barite.

The zeolite deposits of Greece

Zeolites are present in altered pyroclastic rocks at many localities in Greece, and large deposits of potential economic interest are present in three areas: (1) the Evros region of the province of Thrace in the north-eastern part of the Greek mainland; (2) the islands of Kimolos and Poliegos in the western Aegean; and (3) the island of Samos in the eastern Aegean Sea. The deposits in Thrace are of Eocene-Oligocene age and are rich in heulandite and/or clinoptilolite. Those of Kimolos and Poliegos are mainly Quaternary and are rich in mordenite. Those of Samos are Miocene, and are rich in clinoptilolite and/or analcime. The deposits in Thrace are believed to have formed in an open hydrological system by the action of meteoric water, and those of the western Aegean islands in a similar way but under conditions of high heat flow, whereas the deposits in Samos were formed in a saline-alkaline lake.

The influence of biogenic micro-silica-rich rocks on the properties of blended cements

Diatomaceous rock samples of a different origin and with amorphous, biogenic micro-silica (opal-A) as their major siliceous constituents were studied and their behaviour as a cement additive was determined. The raw materials were collected from Hungary, Romania and Greece. These diatomite rocks varied in geological age from Miocene to Pleistocene, and were deposited respectively in lacustrine, brackish and marine conditions. The depositional environment affected the size of the opal-A particles, those of lacustrine origin being the smaller (<10 μm). Most of the opal-A particles were represented by disk-shaped diatom frustules. Laboratory tests showed that these diatomite rocks exhibited good pozzolanic properties and could replace the most commonly used natural pozzolanas. The use of diatomaceous rocks as cement additives has drawbacks such as higher water demand, but the compressive strength of the laboratory produced cements exhibit higher values than OPC. The highest compressive strength values were obtained with the use of the Hungarian diatomite rock that had the greatest amount of reactive silica content reflecting its high opal-A content.

Geochemistry and diagenesis of Miocene lacustrine siliceous sedimentary and pyroclastic rocks, Mytilinii basin, Samos Island, Greece

Abstract A Late Miocene non-marine stratigraphic sequence composed of limestone, opal-CT-bearing limestone, porcelanite, marlstone, diatomaceous marlstone, dolomite, and tuffite crops out on eastern Samos Island. This lacustrine sequence is subdivided into the Hora Beds and the underlying Pythagorion Formation. The Hora Beds is overlain by the clastic Mytilinii series which contains Turolian (Late Miocene) mammalian fossils. The lacustrine sequence contains volcanic glass and the silica polymorphs opal-A, opal-CT, and quartz. Volcanic glass predominantly occurs in tuffaceous rocks from the lower and upper parts of the lacustrine sequence. Opal-A (diatom frustules) is confined to layers in the upper part of the Hora Beds. Beds rich in opal-CT underlie those containing opal-A. The occurrence of opal-CT is extensive, encompassing the lower Hora Beds and the sedimentary rocks and tuffs of the Pythagorion Formation. A transition zone between the opal-A and opal-CT zones is identified by X-ray diffraction patterns that are intermediate between those of opal-CT and opal-A, perhaps due to a mixture of the two polymorphs. Diagenesis was not advanced enough for opal-CT to transform to quartz or for volcanic glass to transform to opal-C. Based on geochemical and mineralogical data, we suggest that the rate of diagenetic transformation of opal-A to opal-CT was mainly controlled by the chemistry of pore fluids. Pore fluids were characterized by high salinity, moderately high alkalinity, and high magnesium ion activity. These pore fluid characteristics are indicated by the presence of evaporitic salts (halite, sylvite, niter), high boron content in biogenic silica, and by dolomite in both the opal-A and opal-CT-bearing beds. The absence of authigenic K-feldspar, borosilicates, and zeolites also support these pore fluid characteristics. Additional factors that influenced the rate of silica diagenesis were host rock lithology and the relatively high heat flow in the Aegean region from Miocene to Holocene.

Use of secondary mineralizing raw materials in cement production. The case study of a stibnite ore

It has been found that certain foreign elements, despite their low concentration in cement raw mix, may accelerate the sintering reactions and improve the reactivity of the cement raw mix. The subject of this paper is to investigate the possibility to introduce small amounts of minerals, containing these elements, in the cement raw mix. The mineral stibnite was selected in order to introduce Sb and S in the cement raw mix. One reference and four modified mixtures, prepared by mixing the reference sample with 0.5, 1.0, 1.5 and 2.0% w/w of the above mineral, were studied. The effect on the reactivity of the raw mix was evaluated on the basis of the unreacted lime content in samples sintered at 1000, 1100, 1200, 1300, 1350, 1400 and 1450 °C. The sintering reactions in all samples were recorded by means of differential thermal analysis (DTA). Scanning electron microscopy (SEM) was used in order to examine the texture of the clinker and study the distribution of the foreign elements in its main phases. Finally, the hydration rate in the cement pastes and some cement properties were measured. It was concluded that the added mineral improves the burnability of the cement raw mixture without affecting considerably the hydration rate and cement properties.

Mineralogy and technical properties of clayey diatomites from north and central Greece

Two bulk samples of clayey diatomite of Upper Miocene age originated from Western Macedonia, northern Greece and Thessaly central Greece were examined for their efficiency to be used as industrial absorbents. The samples were characterized using X-Ray Diffraction, Thermo-Gravimetric and Fourier Transform Spectroscopy, Scanning Electron Microscopy and ICP-MS analytical methods. The absorption capability of the clayey samples in oil and water were also examined. The mineralogy of both samples is predominated by the presence of clay minerals and amorphous silica. The clay minerals prevailed in the Klidi (KL) bulk sample, with muscovite being the dominant phase, and kaolinite and chlorite occurring in minor amounts. In the Drimos (DR) bulk sample, vermiculite was the predominant clay phase. Smectite was not found in either sample, whereas detrital quartz and feldspars were present in significant amounts. The amorphous silica phase (opal-A) occurs mainly with the form of disck-shaped diatom frustules. The chemistry of the samples is characterized by the predominance of silica, alumina, and iron, whereas all the other major and the trace elements are in low concentrations. Both clayey diatomite rocks exhibited sufficiently good oil and water absorption capacity, ranging between 70 to 79% in the clay-rich sample KL and 64 to 70% in the opal-A-rich sample DR. Comparing the properties of the rocks studied with other commercial absorbents, it is concluded that they may find applications as absorbents in industrial uses.

Clastic Huntite in Upper Neogene Formations of the Kozani Basin, Macedonia, Northern Greece

ABSTRACT An unusual carbonate mineral, huntite (Mg3Ca(CO3)4), is present in Upper Neogene lacustrine formations of the Kozani Basin, Northern Greece. This carbonate, either pure or mixed with variable proportions of hydromagnesite and magnesite, forms extensive deposits that accumulated in ponds on a lake-margin carbonate flat. Although labile and metastable, huntite also is the main detrital component of fluvial-dominated delta sequences in some parts of the basin. Clastic huntite is present mainly in foresets, trough cross-stratified units, and channel forms in terrigenous lithofacies towards the basal part of deltaic assemblages. Detachment of fragments from cohesive huntite pond deposits may have been favored by expansion through wetting rather than by desi cation and further contraction of the chemical sediment. This first documented occurrence of clastic huntite places some uncertainties on the presumed chemical and mechanical instability of huntite under natural conditions.

Hydrotalcite and an Amorphous Clay Mineral in High-Magnesium Mudstones from the Kozani Basin, Greece

ABSTRACT The paper describes two unusual lithologies that occur in a sequence of Mg-rich lacustrine sediments in northern Greece. The first is a laminated mudstone in which layers composed of magnesian smectite alternate with layers composed of an amorphous clay of similar chemical composition. The second lithology is a thin bed of mudstone in which the only crystalline constituent is hydrotalcite (a magnesium aluminum hydroxide), accompanied by amorphous high-magnesium clay. Hydrotalcite has not previously been recorded from sedimentary rocks except as a product of industrial pollution. The high-magnesium clay is considered to have formed by precipitation from Mg-rich lake water onto volcanic ash particles, whilst the hydrotalcite has filled the molds left by dissolution of volcanic glass within the clay-coated particles.

Petrology and Diagenetic Changes in Miocene Marine Diatomaceous Deposits from Zakynthos Island, Greece

Silica diagenesis in a diatomaceous section of marly limestone and chert from central Zakynthos Island, Ionian sea, was investigated. This section, underlain by Cretaceous-Eocene reefal limestone and overlain by a middle-upper Miocene terrigenous—evaporitic succession, is defined as the Romiri Formation. Diatom and planktonic foraminiferal assemblages occur, the latter determining the biostratigraphic interval N4-N7 of the Blow zonation (Aquitanian-Burdigalian).