Limestone Host Rock Research Articles

Geology and Fe-Skarn Mineralization in Lolo Prospect, Solok West Sumatra, Indonesia

The study area is situated in Lolo village, Pantai Cermin district, Solok regency, West Sumatra province, Indonesia. Several mining companies have been operated for skarn-related iron ore type in this area and its vicinity. Although the study area has been explored, the detailed geology and Fe skarn characteristics remain unclear. This paper therefore, is dealing with the geological framework and characteristics of skarn mineralogy employing some laboratory analyses such as petrography, ore microscopy, X-Ray Diffraction, micro-XRF and AMICS, ICP-AES and ICP-MS analyses. The geological framework of the prospect was defined by a surface geological mapping and observation. Skarn alteration of limestone host-rock is typified by the presence of prograde minerals such as garnet, clinopyroxene, and wollastonite. The retrograde mineral is peculiarly not found in the limestone wall-rock, but in altered causative intrusion i.e. granodiorite. The altered granodiorite is composed of some key propylitic minerals such as chlorite, epidote, and a few clay minerals. Fe skarn mineralization is represented in magnetite, hematite, goethite and limonite which are associated with several sulphide minerals such as covellite, pyrite, and chalcopyrite. Mass balance analysis on limestone indicates a mass gain of 0.16%, whereas mass balance analysis on granodiorite indicating mass loss of 3.36%. Ore mineralization and skarn alteration are strongly controlled by NW-SE and NE-SW trending faults and the distribution of limestone. Follow-up subsurface exploration is needed to define the Fe skarn orebody.

Reactive transport investigations of the long-term geochemical evolution of a multibarrier system including bentonite, low-alkali concrete and host rock

The Canadian concept for a deep geological repository for used nuclear fuel includes highly-compacted and homogenized bentonite (HB) and low-alkali concrete such as Low-Heat High-Performance Concrete (LHHPC) as engineered barrier materials. The initial mineralogy and pore water compositions are different for bentonite, LHHPC and potential host rocks, such as granite and limestone. Consequently, chemical alterations are expected at the interfaces between these materials. Two scenarios were simulated to investigate the alterations at the material interfaces: 1) HB/LHHPC/host rock; 2) HB/host rock. For both scenarios, excavation damage zones (EDZs) were taken into consideration. Because of the low reactivity of bentonite compared to LHHPC, for the second scenario, only relatively minor mineral volume fraction and porosity changes were predicted for the HB/granite and HB/limestone host rock cases, with limited impact on radionuclide migration. For the first scenario; however, due to the relatively high pH of pore water in LHHPC, substantial mineral dissolution and precipitation were predicted to occur at the HB/LHHPC and/or LHHPC/host rock interfaces, leading to porosity reduction or even pore clogging in close proximity (<1 cm) of the interfaces. The predicted geochemical evolution depends mainly on the mineralogy and pore water chemical composition of the host rock. In the case of granitic host rock, Calcium Silicate Hydrate (C–S–H) phases initially present in LHHPC are predicted to transform into tobermorite, phillipsite, saponite and gypsum within 1,000 years. The simulations indicate a complex evolution of porosity, with an initial reduction, followed by a slight increase, and subsequent pore clogging. In the case of limestone host rock, saponite and sepiolite are the dominant minerals formed in the LHHPC. A sensitivity analysis shows that higher initial effective diffusion coefficients in the LHHPC enhance the diffusive fluxes of ions and result in earlier pore clogging in the host rock. The simulations illustrate that reactive transport modelling accounting for barrier reactivity and pore clogging provides a useful tool for assessing the migration of radionuclides across material interfaces for various canister failure scenarios.

Geological, geochemical and fluid inclusion investigations on the Duna Pb-Ba-(Ag) deposit, Central Alborz, North Central Iran

The Duna Pb-Ba-(Ag) mine is located ca. 155 km north of Tehran in the central Alborz structural zone, northern Iran. The ore mineralization occurs as stratabound, epigenetic, E-W and WSWENE trending veins and veinlets in fracture-controlled as well as massive and open-space filling textures within a Permian dolomitic limestone host rock. Field observations as well as mineralogical and petrographic studies show dolomitization, silicification and possibly haematisation in the host rock. In the mineralization zone, galena and barite are the main minerals, followed by pyrite, quartz, chalcopyrite, tetrahedrite, sphalerite, calcite and supergene minerals such as covellite, malachite, azurite, cerussite, anglesite, and Fe-oxides. The chemical analyses of the highgrade ore samples show an average grade of 18.66 wt. % for Pb, 19.99 wt. % for Ba, and 120 ppm for Ag together with substantial quantities of Zn (0.15 wt. %), As (690 ppm), Cu (0.86 wt. %), Sb (0.25 wt. %), and Sr (0.56 wt. %). The amount of silver in some samples from the tunnel and discordant layers is up to 7030 ppm. The positive Eu/Eu⃰ ratio and the weak negative Ce/Ce⃰ anomaly in the ore samples were most likely inherited from magmatic water. The presence of minerals such as pyrite and chalcopyrite together with the co-precipitation of sphalerite and chalcopyrite suggest a high-temperature for mineralizing fluids. The homogenization temperatures of fluid inclusions from barite in concordant layers span between 135 and 165 ºC with salinities between 18.54 and 23.65 wt. % NaCl equivalent, while the homogenization temperatures of fluid inclusions from barite of discordant layers span between 113 and 285 ºC with salinities between 7.34 and 23.65 wt. % NaCl equivalent. The structural, geological, geochemical, and mineralogical studies together with the paragenesis of the ore minerals and fluid inclusion data allow consideration of the Duna Pb-Ba-(Ag) mine as a two stage mineralization scenario; 1st stage /older/MVT-type (Early Cimmerian tectonic phase), and the second stage/younger/Irish-type (Laramide orogenic movements). The structural data, high temperature of the fluid inclusions, positive Eu/Eu⃰ ratio and high silver content, especially in the discordant layers, indicate the involvement of a magmatic water mixed with meteoric and connate fluids comparable to the Irishtype mineralization in the second stage, which formed along brecciated zones of the thrust faults. The second stage of mineralization was most likely influenced by the Akapol granitoid intrusive mass, which overprinted the 1st stage/older/MVT-type.

Cassiterite U–Pb, mica 40Ar–39Ar dating and cassiterite trace-element composition of the Furong tin deposit in the Nanling Range, South China

The Furong tin deposit (530,000 t Sn @ 0.8% Sn) is located in the southern part of the Mid–Late Jurassic, multiphase, granitic Qitianling batholith in the Nanling Range, South China. The spectrum of tin mineralization comprises skarn, chloritized granite, greisen, and quartz vein types, of which the skarn type is the most important. Cassiterite U–Pb dating provided Tera-Wasserburg lower intercept ages of 157.1 ± 1.5 Ma and 156.3 ± 1.5 Ma for skarn-type mineralization, 158.1 ± 1.4 Ma and 158.7 ± 1.6 Ma for chloritized granite-type mineralization, 155.8 ± 3.4 Ma for greisen-type mineralization, and 160.1 ± 1.7 Ma for quartz vein-type mineralization. These ages overlap with each other and define a pooled weighted mean age of 157.9 ± 1.1 Ma (2σ) for the tin ore system. Hydrothermal phlogopite from tin skarn and muscovite from tin greisen yielded younger 40Ar–39Ar plateau ages of 154.3 ± 1.9 Ma and 150.0 ± 1.5 Ma, respectively, which may reflect resetting due to post-ore fluid circulation. Distinctive cathodoluminescence textures and trace-element patterns of various cassiterite types indicate that the four ore types resulted from pulsed ore-forming fluids and changes in temperature in a single magmatic-hydrothermal system. In combination with the geological characteristics, the geochronological and trace-elemental data of cassiterite indicate that the formation of different ore types at Furong was associated with the most fractionated and latest alkali-feldspar granite of the Qitianling batholith, and resulted from the specific interactions of the ore-forming fluids with their granite and limestone host rocks.

Thalliomelane, TIMn7.54+Cu0.52+O16, a new member of the coronadite group from the preglacial oxidation zone at Zalas, southern Poland

Abstract Thalliomelane, a new member of the coronadite group (hollandite supergroup), was discovered at Zalas near Kraków in southern Poland (the southern margin of the Kraków-Silesia Monocline) in relics of a preglacial supergene mineralization disseminated in a fault breccia in Middle Jurassic sandy limestone. The mineralization formed at the expense of a sulfide assemblage, which was most likely the source of thallium, related to rejuvenation of Early-Paleozoic fault zones in the Sava phase of the Alpine orogeny. Thalliomelane occurs rarely and exclusively in the form of fibrous and highly porous tiny aggregates &amp;lt;50 µm in size that fill small fractures and voids in the sandy limestone host rock. Microprobe analyses based on 16 O and 8 octahedral cations per formula unit resulted in the mean empirical formula [Tl0.77(10)Ba0.21(3)K0.03(1)Na0.01(0)Pb0.01(0)]Σ1.03(7)[Mn7.15(11)4+Cu0.63(4)2+Co0.08(3)2+Fe0.06(3)3+Ni0.03(1)2+Si0.03(2) Mg0.01(1)]Σ8[O15.67(24)(OH)0.33(24)], corresponding to the formula Tl(Mn7.54+Cu0.52+)O16 for the thalliomelane end-member. The mineral crystallizes in the tetragonal system, space group I4/m, and has unit-cell parameters a = 9.8664(12), c = 2.8721(4) Å, V = 279.59(8) Å3, Z = 1. The crystal structure of thalliomelane, measured with 3D electron-diffraction, was refined to an R1 index of 23.74%. Thalliomelane has the hollandite-type structure. The Mn4+ cations, substituted by Cu2+ at an amount of ~0.5 apfu, are octahedrally coordinated by oxygen atoms. Four double chains of edge-sharing (Mn,Cu)-O octahedra share corners with each other to form tunnels along the [001] direction. Tl+ cations are located in the tunnels, occupying partially the origin and center of the unit cell. The formation of thalliomelane was most probably connected to the weathering of a sulfide mineral assemblage under semi-arid to arid climate. It resulted in the release of Tl and other components of the mineralization into water under the influence of Cl-, Br-, and I-bearing brines and pore waters from the Carpathian flysch or from sediments of the Carpathian foredeep mobilized by compaction during the Sava phase. Via the interaction of these waters, the primary ores altered mainly into goethite, cuprite, malachite, Mn oxides of the coronadite type, with subordinate Cu sulfates, Pb arsenates, Bi oxy-chlorides, and traces of iodargyrite. This assemblage indicates oxidation at a progressively increasing pH of ~8–10 and Eh of the order of +0.4–0.5 V. In this setting, thalliomelane could have formed from a cryptomelane-type Mn oxide in contact with Tl-bearing aqueous solutions through Tl-for-K exchange over time.

The nature of Zn-phyllosilicates in the nonsulfide Mina Grande and Cristal zinc deposits (Bongará District, Northern Peru): The TEM-HRTEM and AEM perspective

Abstract Zn-phyllosilicates are common minerals in nonsulfide Zn deposits and can give crucial information about the genesis of these oxidized mineralizations. They seldom represent the prevailing economic species but might have a significant impact on mineral processing. This study has been carried out on the Mina Grande and Cristal Zn-sulfide/nonsulfide deposits, which occur in the Bongará district (Amazonas region, northern Peru). The Cristal and Mina Grande orebodies are hosted by the sedimentary (prevailingly carbonate) successions of the Pucará Group (Condorsinga formation, Lower Jurassic), in an area affected by Neogene tectonics and characterized by Late Miocene and Pliocene-Early Pleistocene uplift phases (Andean and Quechua tectonic pulses). The Cristal deposit consists of both sulfide (sphalerite with minor pyrite and galena) and nonsulfide concentrations. The nonsulfides consists of smithsonite, hemimorphite, hydrozincite, chalcophanite, goethite, and greenockite, locally associated with Zn-bearing phyllosilicates. The Mina Grande deposit consists almost exclusively of Zn-oxidized minerals in limestone host rocks. The nonsulfides association consists of hydrozincite, hemimorphite, smithsonite, fraipontite, and Fe-(hydr)oxides, also containing a clayey fraction. The study deals with TEM-HRTEM and AEM investigations on clayey materials, to determine their crystal-chemical features and the origin of the complex Zn-clays-bearing parageneses. In both deposits, Zn-bearing illites (1Md and 2M polytypes) and I/S clay minerals (I3) are the main detected phases, with few compositions close to (Zn-bearing) muscovite. In the clayey fraction at Mina Grande, fraipontite, a Zn-bearing mica called K-deficient hendricksite, and (Zn-bearing) kaolinite also occur. Zn-illites and smectites (always containing Zn in variable amounts) characterize the mineral association at Cristal. The investigated compositional gap between di- and tri-octahedral Zn-phyllosilicates gives indications on the genetic relationships between them and advances on the knowledge of these species. The present work gives an insight into the Zn-bearing phyllosilicates systems by determining the amount/mode of metal incorporation in their lattices and understanding the relationships of natural occurring clay-rich complex associations, which can act as models for possible synthetic counterparts.

The role of trapped fluids during the development and deformation of a carbonate/shale intra-wedge tectonic mélange (Mt. Massico, Southern Apennines, Italy)

Numerous studies exist on exhumed tectonic mélanges along subduction channels whereas, in accretionary wedge interiors, deformation mechanisms and related fluid circulation in tectonic mélanges are still underexplored. We combine structural and microstructural observations with geochemical (stable and clumped isotopes and isotope composition of noble gases in fluid inclusions of calcite veins) and U-Pb geochronological data to define deformation mechanisms and syn-tectonic fluid circulation within the Mt. Massico intra-wedge tectonic mélange, located in the inner part of the central-southern Apennines accretionary wedge, Italy. This mélange developed by shear deformation at the base of a clastic succession. Deformation was characterized by disruption of the primary bedding, mixing, and deformation of relicts of competent olistoliths and strata within a weak matrix of deformed clayey and marly interbeds. Recurrent cycles of mutually overprinting fracturing/veining and pressure-solution processes generated a block-in-matrix texture. The geochemical signatures of syntectonic calcite veins suggest calcite precipitation in a closed system from warm (108°-147 °C) paleofluids, with δ18O vlaues between +9‰ and 14‰, such as trapped pore waters after extensive 18O exchange with the local limestone host rock and/or derived by clay dehydration processes at T > 120 °C. The 3He/4He ratios in fluid inclusions are lower than 0.1 Ra, indicating that He was exclusively sourced from the crust. We conclude that: (1) intraformational rheological contrasts, inherited trapped fluids, and low-permeability barriers such as marly-shaly matrix, can promote the generation of intra-wedge tectonic mélanges and the development of transient fluid overpressure; (2) clay-rich tectonic mélanges, developed along intra-wedge décollement layers, may generate low-permeability barriers hindering the fluid redistribution within accretionary wedges.

Applying Rare Earth Elements, Uranium, and87Sr/86Sr to Disentangle Structurally Forced Confluence of Regional Groundwater Resources: The Case of the Lower Yarmouk Gorge

The conjoint discussion of tectonic features, correlations of element concentrations,δ18O,δD, and87Sr/86Sr of groundwater leads to new insight into sources of groundwater, their flow patterns, and salinization in the Yarmouk Basin. The sources of groundwater are precipitation infiltrating into basaltic rock or limestone aquifers. Leaching of relic brines and dissolution of gypsum and calcite from the limestone host rocks generate enhanced salinity in groundwater in different degrees. High U(VI) suggests leaching of U from phosphorite-rich Upper Cretaceous B2 formation. Both very low U(VI) and specific rare earth element including yttrium (REY) distribution patterns indicate interaction with ferric oxyhydroxides formed during weathering of widespread alkali olivine basalts in the catchment area. REY patterns of groundwater generated in basaltic aquifers are modified by interaction with underlying limestones. Repeated sampling over 18 years revealed that the flow paths towards certain wells of groundwater varied as documented by changes in concentrations of dissolved species and REY patterns and U(VI) contents. In the Yarmouk Gorge, groundwater with basaltic REY patterns but high U(VI) and low Sr2+and intermediate sulfate concentrations mainly ascends in artesian wells tapping a buried flower structure fault system crossing the trend of the gorge.

An experimental and numerical investigation on the hydromechanical behaviour of carbonate fault zones upon reactivation: the impact of carbonate mud sealing layers and overall research outcomes

Abstract To contribute to the understanding of the impacts of fault reactivation induced by reservoir exploitation, we describe the final series of laboratory experiments, numerical simulations and microstructural analysis conducted during the ‘Fault Reactivation in Carbonates’ research project. In the project, the structure and hydromechanical properties of carbonate-hosted fault zones were investigated. For the analyses here reported, faults were artificially generated by direct shearing composite blocks made of layers of reservoir analogue rocks (outcrop travertine or synthetic grainstone) intercalated with one layer of a sealing analogue rock (synthetic carbonate mudstone). Post-direct shearing, cylindrical plugs containing the fault zone and parts of intact rock were cored out from the blocks and tested in a triaxial test rig, simulating fault reactivation. Varied stress paths and pore-pressure conditions representative of fluid depletion and injection were considered. In parallel, two-dimensional mechanical models representative of the direct shear experiments were developed using smoothed particle hydrodynamics (SPH). We observed a continuous reduction in fault transmissibility during direct shearing, followed by a permeability reduction of 50–80% with increasing mean effective stress in the subsequent fault reactivation tests. Experimental fault zone geometries produced during direct shear were broadly reproduced by the two-dimensional modelling approach. We also detected that the inclusion of the carbonate mud sealing rock into the fault zone caused greater compaction of the fault materials when compared to experiments conducted without carbonate mud layers. We conclude that with fault displacement, increasing incorporation of carbonate mud sealing material into the fault zone and the concomitant development of gouge results in the continuous reduction of fault transmissibility/permeability. This occurs in the two very different limestone host-rock types and for all the stress configurations investigated. Discussions on these results and also on the outcomes of the research project as a whole are presented in the paper.

Application of Non-Extensive Statistical Physics on the particle size distribution in natural carbonate fault rocks

This contribution focuses on the results of combined generalized statistical mechanics and microstructural analyses of carbonate fault rock samples, which derive from active extensional fault zones cropping out in peninsular Italy. Specifically, this work is aimed at deciphering the role played by both pre-existing structural elements and structural diagenesis on the dimension and distribution of the largest survivor grains. The studied extensional fault zones were exhumed from shallow crustal depths during the Plio-Quaternary downfaulting of the Apennines. They crosscut Mesozoic platform limestones and dolostones. Despite the different host rocks, all carbonate fault rocks exhibit very similar cataclastic textures but dissimilar pore characteristics. In this work, we apply for the first time the principles of the Non-Extensive Statistical Physics to the study of fault rocks. By considering the Tsallis entropy, which is expressed by the Q-value representing the hierarchical organization of the system, we consider the crossover point value, V0, computed for both 1cm2 and 9cm2 representative fault rock images at the transition from Q-exponential to exponential behaviors. As a result, we document that the limestone grain-supported rocks, which mainly localize in the outer fault cores, are always characterized by smaller V0 values with respect to the dolostone ones. These data are interpreted as due to both burial and thrusting-related pressure solution seams, which pervasively formed in the limestone host rocks. Conversely, the amount of V0 variations computed from outer to inner fault cores are associated to the effects of widespread calcite cement precipitation, which mainly occurred in the limestone matrix-supported fault rocks. By considering the weighted, average areas of survivor grains with dimension larger than V0 a as a proxy for sorting, we document an increase from outer to inner fault cores in all the study fault zones. At a close view, all dolomite-rich fault rock samples show very similar median values, whereas the matrix-supported fault rock samples of the inner limestone fault cores are characterized by smaller median values relative to the grain-supported of the limestone outer fault cores. This discrepancy is interpreted as also due to widespread cementation processes, which formed aggregate grains in the fine-grained fault rocks encompassing the main slip surfaces of the limestone fault cores.

Fluid storage and migration properties of sheared Neptunian dykes

Abstract Neptunian dykes are widely reported along the Tethyan carbonate platforms and are commonly considered as subsurface baffles or barriers to fluid flow. However, the fluid storage and migration properties of sheared Neptunian dykes are poorly known. For this reason, we investigate the inner structure and fluid flow properties of two Neptunian dykes, which can be characterized by different architectures if involved or not in brittle shearing processes. The dykes strike ca. WNW-ESE and crosscutting the tight Jurassic limestones exposed at Maranfusa Mt., NW Sicily, Italy. The unsheared and sheared Neptunian dykes are almost sub-vertical and at high-angle with respect to the horizontal plane, respectively. The first one includes a homogeneous pelagic limestone infill whereas the second one includes a heterogeneous, marl-rich pelagic limestone infill and also thin veneers of tectonic breccias vertically persistent throughout the investigated outcrop. The sheared Neptunian dyke shows evidences of transtensional faulting, which likely occurred during the early Jurassic up to middle Cretaceous times, with throw up to 2 m. The amount of fracture porosity and equivalent permeability are computed by integrating geological and structural field data with petrographic data obtained from selected samples and Discrete Fracture Network modelling of geocellular volumes representative of the study outcrops. Results are consistent with the sheared Neptunian dyke forming a combined barrier-conduit permeability structure, in which the low-permeability and low–porosity cataclastic core is flanked by a fractured damage zone that enhance the dyke-parallel fluid flow in the subsurface. Accordingly, the amount of fluid storage in the fractured damage zone is sensitively higher than in the surrounding limestone host rock. Data we present highlight that the m-offset, sheared Neptunian dyke, due to its inherited sedimentary infill, is characterized by a permeability structure that it is often associated to large fault zones made up of cataclastic fault cores that impede the cross-fault fluid flow.

Drones in carbonate geology: Opportunities and challenges, and application in diagenetic dolomite geobody mapping

Unmanned aerial vehicles (UAVs) or drones have become widely available for use in a broad range of disciplines. Despite the decreased cost and technological developments of platforms, sensors and software, the use of drones in carbonate geology has yet to be exploited. Nevertheless, drones offer multiple advantages over traditional field work or high-altitude remote sensing techniques, in that they enable the reconstruction of three dimensional models of inaccessible or unsafe outcrops, and can bridge the spatial scale gap in mapping between manual field techniques and airborne, high-altitude remote sensing methods. In this contribution, we present our methodology of structure from motion photogrammetry on drone-captured images and highlight opportunities and challenges of using drones in carbonate geological studies. Moreover, we apply this method to document the spatial distribution and dimensions of diagenetic dolomite geobodies in Carboniferous limestone host rock of the Picos de Europa, northern Spain. The results of our study indicate that dolomite geobodies occur preferentially near to strike-slip faults, rather than thrust faults or specific types of limestone host rock lithology, in the study area. The geobody dimensions appear to be related to the strain magnitude of the strike-slip faults. We propose that these identified links and controls are applicable to structurally-controlled dolomitization on a more general basis. Our study has demonstrated the potential for using drones in carbonate geological studies.

A combined pumping test and heat extraction/recirculation trial in an abandoned haematite ore mine shaft, Egremont, Cumbria, UK

A pumping test at rates of up to 50 L s−1 was carried out in the 256 m-deep Florence Shaft of the Beckermet–Winscales–Florence haematite ore mine in Cumbria, UK, between 8th January and 25th March 2015. Drawdowns in mine water level did not exceed 4 m and the entire interconnected mine complex behaved as a single reservoir. Pumping did, however, induce drawdowns of around 1 m in the St. Bees Sandstone aquifer overlying the Carboniferous Limestone host rock. During a second phase of the pumping test, a proportion of the 11.3–12 °C mine water was directed through a heat pump, which extracted up to 103 kW heat from the water and recirculated it back to the top of the shaft. Provided that an issue with elevated arsenic concentrations (20–30 µg L−1) can be resolved, the Florence mine could provide not only a valuable resource of high-quality water for industrial or even potable uses, it could also provide several hundred to several thousand kW of ground sourced heating and/or cooling, if a suitable demand can be identified. The ultimate constraint would be potential hydraulic impacts on the overlying St Bees Sandstone aquifer. The practice of recirculating thermally spent water in the Florence Shaft produced only a rather modest additional thermal benefit.

Effect of Limestone and Buffer Solution in the Aqueous Speciation and pH of Brines for CO2 Sequestration

Oil-field brines, a by-product of oil and natural gas extraction whose fate is mainly disposal, is gaining attention for the storage of CO2 into geologically stable mineral carbonates. The suitable pH range for the formation of carbonates is 7.8 or higher, where CO32− dominates. Therefore, to boost the precipitation of mineral carbonates by reaction between brine and CO2, the pH of the brine must be modified before any brine-CO2 interaction takes place. In this work, pH stability studies were conducted to study how synthetic brines respond in the presence of a natural limestone host rock or a tris buffer solution in both closed and open atmospheres and to evaluate the efficiency of both buffers at increasing brine pH. An aqueous and solid speciation model was used to investigate the influence of the buffer used in the aqueous and solid speciation of two synthetic brines. pH stability studies identified that both buffers can enhance brine pH, being tris buffer the one with the strongest buffer efficiency. Both XRD and geochemical modelling results suggest the suitability of brines containing SO42-and the use of both host rock and tris buffer, respectively, to enhance oil-field brines pH for mineral carbonates precipitation.

BRYOPHYTES AND FERNS AS PART OF LAMP FLORA CAVES

Abstract. Aim. The study comparative analysis of flora of bryophytes and vascular spore plants four excursions caves. Objects. Two caves (Vorontsovskaya and Ahshtyrskaya) are located in the Krasnodar region, one cave (Novoafonskaya) in Abkhazia and one cave (Mramornaya) in Crimea. All the caves laid limestone host rocks, have similar climatic conditions and permanent artificial lighting. Methods. In the Novoafonskaya cave, the study was conducted in 2005-2007, Mramornaya in 2007-2008, Vorontsovskaya in 2003-2009, Ahshtyrskaya in 2008-2009. Mosses and ferns of lamp flora communities studied traditional botanical methods. We determined the abundance and occurrence of species in communities. Results. The study shows that species diversity is higher in caves that have not been cleaned from lamp flora. The similarity of the species composition of the flora found only in two caves of Novoafonskaya and Ahshtyrskaya. Identified a number of species and genera that can be considered characteristic of communities of lamp flora. Conclusions. Each cave is formed by a unique species composition of lamp flora, consisting mainly by species of ubikvist and cosmopolitan. Species richness varies depending on operating conditions of the cave the periodic removal of flora leads to a decrease in species diversity. Species composition is determined by the predominance of the areas of the cave of certain substrates, especially the morphology of the cavity and its connection with the surface.

Fracturation des carbonates dans la zone de faille normale active d’Aigion (Grèce) à partir des carottes du puits: conséquences sur les propriétés de transfert de fluides

Abstract La faille d’Aigion appartient à un système de failles normales à pendage nord affectant la bordure sud du golfe de Corinthe, témoin d’une extension active d’échelle régionale caractérisant la région égéenne. Les carottes du forage AIG-10, qui a traversé cette faille, montrent la présence d’une zone endommagée et d’une gouge. Ce travail présente une analyse des lames minces faites à partir de ces carottes. Il confirme la zonation en termes de fracturation à l’approche de la faille. Loin de cette dernière, la fracturation héritée de la phase compressive de l’orogenèse hellénique est dominante, bien qu’il existe aussi une famille E-W liée à l’extension actuelle. Toutes ces fractures sont scellées et le remplissage est similaire d’un point de vue luminescence au calcaire hôte. A l’approche du coeur, la quantité de fractures liées à la faille augmente; le remplissage de ces fractures indique, en cathodoluminescence, le passage de plusieurs fluides qui seraient d’origine externe, et la dernière génération de fractures est encore ouverte. Au mur de la faille, sous 5 m d’épaisseur verticale de cataclasite et d’ultracataclasite dans les calcaires et radiolarites (coeur de faille) et 13 m d’épaisseur verticale de gouge dans les radiolarites, les observations sont plus limitées, car la présence d’un karst a restreint les possibilités de carottage. Néanmoins, on peut observer que le remplissage des fractures liées à l’extension est différent de ce qui nous a été dévoilé au toit. Ceci suggère que la faille, transversalement imperméable aujourd’hui, l’a toujours été. L’analyse de la succession des ciments met en évidence une perméabilité parallèle à la faille à la faveur d’un système de fractures et fentes jeunes et ouvertes, pendant qu’est discuté le transfert de fluides par rapport aux stades de propagation de la faille.

Genetic constraints on world-class carbonate- and siliciclastic-hosted stratabound fluorite deposits in Burgundy (France) inferred from mineral paragenetic sequence and fluid inclusion studies

Stratabound fluorite deposits occur at the unconformity between the Variscan crystalline basement and the Mesozoic sandstone, conglomerate, limestone, and dolomite rocks of the Morvan Massif in central Burgundy. This study describes their petrographic characteristics in an attempt to determine the nature and temperature of mineralizing fluids in order to better understand the fluid migrations that led to massive stratabound fluorite deposition. The general paragenesis encompasses two major mineralizing events causing a succession of fluorite, barite, and quartz in all deposits. The two mineralizing events were preceded by two corrosion (dissolution or karstification) events affecting both the dolomite host rock at Pierre-Perthuis and Marigny-sur-Yonne and the limestone host rock at Courcelles-Frémoy with the creation of 1–10m cavities and microscopic vugs. At Antully, the blocky calcite initially cementing the sandstone was partially dissolved. Microthermometric data on aqueous two-phase inclusions attest to CaCl2-rich fluids giving rise to fluorite deposition in the Pierre-Perthuis, Courcelles-Frémoy, and Antully deposits. Homogenization temperatures range from 80 to 100°C at Pierre-Perthuis and Courcelles-Frémoy, with sporadically higher temperatures. The range of CaCl2 contents is 6.5–15wt.% at Pierre-Perthuis, 1.7–9.4wt.% at Courcelles-Frémoy, and 1.6–16.3wt.% at Antully. The thermal history of the northwestern Morvan, compiled from organic matter, clay minerals and apatite fission track data indicates that the temperatures in fluorite and barite are higher than the maximum temperature recorded in sediments. This implies deep ascendant hydrothermal brine circulation during the Early Cretaceous. The impermeable cap rock retained the ascendant hydrothermal brine and allowed the deposition of massive fluorite stratabound mineralizations.

Three-dimensional reconstruction of diagenetic geobodies for geological carbon dioxide storage

Geological storage of carbon dioxide (CO2) may help in mitigating greenhouse gas emissions, the main cause of global warming. Deep saline aquifers form ideal storage sites for CO2, but these are often complex due to differences in porosity and permeability, referring to heterogeneity, especially in carbonate reservoirs. Diagenetic heterogeneities, such as the presence of less reactive dolomite bodies in a more reactive limestone host rock, have huge impacts on CO2 storage. As upscaling still poses a challenge, we bridge the gap between micrometre–centimetre lab experimental scale and reservoir scale by documenting heterogeneity at the inter-well, subseismic scale. We developed a method using satellite images, field pictures, GPS data and distance measurements to reconstruct diagenetic dolomite geobodies in three dimensions from outcrops (in Picos de Europa, northern Spain). The dolomite bodies studied have higher porosity than the limestone host rock, which is also observed in CO2 reservoir targets. The geobodies are elongated in the direction of the main faults and their length/width ratio is about 2.5 in the Picos de Europa Formation. Geobodies hosted in different formations seem to vary in dimension. We suggest that large dolomite bodies are favoured in zones with large fluid input and flow rate slow enough to allow for extensive chemical reaction based on the disconnected dolomite body distribution and inferred fluid migration from the source. Understanding how these diagenetic bodies form helps with prediction of heterogeneity crucial in CO2 storage reservoir modelling.

Geochronology of the giant Beiya gold-polymetallic deposit in Yunnan Province, Southwest China and its relationship with the petrogenesis of alkaline porphyry

The Beiya gold-polymetallic deposit, located at the junction of the “Sanjiang” Tethys–Himalaya orogenic belt and the Yangtze craton in southwestern China, is the largest gold deposit in the region. Mineralization mainly occurs in skarn, which formed along the contacts between porphyry intrusions and limestone host rocks. The ore formation process is suggested to be closely related to the Himalayan age alkaline porphyries. U–Pb dating of magmatic zircons from the Beiya quartz syenite porphyry yields a weighted average 206Pb/238U ages of 36.07±0.43Ma (n=25, MSWD=1.17). Calculated isochron age of five molybdenite samples from Beiya is 34.7±1.6Ma (MSWD=0.99, initial 187Os of 0.21±0.16ppb), which indicates that mineralization is coeval with the intrusion of the Beiya alkaline porphyry. This age is also in agreement with the results of apatite fission track analysis in the porphyry. Magmatic zircon εHf(t) values range from −7.4 to +0.1, which correspond to the two-stage Hf model with ages between 1112Ma and 1588Ma. This finding suggests that the main source of porphyry was probably melting of thickened Mesoproterozoic lower crust triggered by partial melting of the lithospheric mantle. Zircon Ce (IV)/Ce (III) ratios of ore-related porphyry are high (given that all EuN/EuN* ratios are above 0.4), which demonstrates that the magma source of the porphyry was highly oxidized, which was favorable for Cu–Au mineralization. The medium Re concentrations in molybdenite (Re=2.08–20.54ppm) suggest that the ore-forming materials were characterized by mixed crustal–mantle sources. Mineralization in the Beiya deposit was one of the many metallogenic events related to the India–Eurasia collision that was responsible for the fertile deep-sourced magmatism.

A simulator for modeling of porosity and permeability changes in near field sedimentary host rocks for nuclear waste under climate change influences

A new simulation tool is developed to model coupled thermo-hydro-mechanical-geochemical (THM-GeoC) processes that would occur in the near field of deep geological repositories (DGRs) for nuclear wastes, and their impacts on the evolution of the rock porosity and permeability. First, a coupled thermo-hydro-mechanical-chemical (THMC) model, in which, the chemical (C) process is limited to solute transport, is developed and then implemented into COMSOL Multiphysics finite element code. Then, two types of numerical software are coupled; the first is COMSOL Multiphysics code and the second is the PHREEQC geochemical code. The coupling of the two types of software is performed by developing a special code that has been written by using MATLAB. COMSOL Multiphysics is used to solve the coupled THMC processes (the C process is limited to solute transport) and PHREEQC is used to solve the geochemical reactions resultant of the transport of chemical species. Simulation results obtained by using the THM-GeoC simulator are compared with experimental data and data from modeling reactive transport, with good agreement in the results. The developed simulator is applied to investigate the coupled effect of climate changes and water enriched with carbon dioxide gas, which would be generated from low and intermediate nuclear wastes, on the dissolution of the limestone host rock in Ontario (Canada) for nuclear wastes, and porosity and permeability changes within the near field rock. The results show that the maximum change in porosity is approximately 3.5%, with a gradual decrease to approximately zero. The zone affected by the dissolution process is mainly located on the first 10m within the host rock and does not cause a significant increase in permeability. From safety and environmental assessment perspectives, the impact of dissolution is not significant. However, parametric studies and experimental investigations need to be implemented to support the predicted results.