Study of the alkali-silica reaction rate of Spanish aggregates. Proposal of a classification based in accelerated mortar bars tests and petrographic parameters

The alkali-silica reaction has been studied in depth due to the evolution in the knowledge of the expansive phenomenon. One of its most important aspects is the reaction rate of the aggregates. In Spain, at the early 90s of the 20th century, aggregates were considered almost non-reactive. However, the use of accelerated curing and other environmental factors revealed that there were potentially reactive siliceous aggregates. Nevertheless, there are several siliceous and limestone aggregates with siliceous inclusions that show reactivity over long period. In the present work, open porosity, expansion and petrography with quartz reactivity index have been determined, in 68 siliceous, limestone and dolomitic aggregates, from quarries located in areas with diagnostic reactivity. Based on these parameters and their interrelation, a classification method is proposed to detect slow-reacting aggregates.

Petro-mineralogical and geochemical characteristics of Shahaba Limestone from Gogi-Kanchankayi sector, Bhima Basin, Karnataka with reference to Uranium mineralisation

The Shahabad Limestone Formation of Bhima Basin from Gogi-Kanchankayi area occurs in heterogeneous forms like massive/blocky limestone, argillaceous/ siliceous limestone and laminated/ flaggy limestone. These limestones are primarily composed of micrite, which often alters into sparry calcite on diagenesis with associated impurities of quartz, feldspar, barite, chlorite, glauconite, sulphides and carbonaceous matter. Geochemically, these limestones comprises of variable CaO with low MgO and P2O5 content. Trace elements concentration shows elevated Ba, Rb and depleted Sr. The current study classified these limestones as non-dolomitic and non-phosphatic types deposited in shallow marine carbonate platform setting with low energy conditions. Post-sedimentation, basin tectonics has resulted in reactivation of the basin margin fault causing intense fracturing of limestone. Subsequent hydrothermal movement along those fractures has resulted in re-mobilisation and re-precipitation of sulphides and carbonaceous matter, and along with alteration has facilitated the precipitation of the uranium bearing minerals.

HYDROTHERMAL MODELING OF SECONDARY RESERVOIR FORMATI ON IN SILICEOUS LIMESTONS (H2O–CO2 SYSTEM)

We have discussed the first results of hydrothermal modeling of the formation of secondary reservoirs (hydrothermal silicites) in siliceous limestones, which are widespread in the Pre-Jurassic complex of West Siberia, namely, in the H2O-CO2 system, in which the mole fraction of CO2 varied from 0.0 to 1.0, and the temperature from 215 to 410оС. It has been found that in this system there is a predominant dissolution of carbonates and, first of all, dolomite, as a result of which the surface of siliceous limestone is silicified and secondary porosity is formed in them. In some samples, quartz microcrystals with varying degrees of perfection of crystal faceting are shaped. It is found that pyrite is also unstable under these hydrothermal conditions and decomposes forming iron-containing carbonates at its sacrifice. Its transformation into pyrrhotite and copper and nickel sulfides is also observed. Biogenic quartz dissolved by a hydrothermal fluid is released from it either in the form of microcrystalline quartz, or in the form of quenching phases represented by cristobalite and/or amorphous silica. It is also found that at temperatures above 360°C, instead of iron-containing carbonates, chlorite is formed due to pyrite, while kaolinite also decomposes along with pyrite. It was experimentally established for the first time that at a high temperature (410°C), carbon dioxide acquires oxidizing properties and, as a result of its interaction with copper, oxide and red oxide of copper are formed. In addition, under these conditions, pyrite passes into iron-containing carbonates rather than chlorite. The main regularities of the formation of secondary reservoirs, i. e. hydrothermal silicites, in the Paleozoic siliceous limestone have been revealed.

Preliminary archaeometric investigation on Middle Neolithic siliceous tools from Limba-Oarda de Jos (Transylvania, Romania)

The present archaeometric study focuses on a set of archaeological siliceous lithic tools that are assigned to the early Vinča culture period (Vinča A and Vinča B1). They were found in several pit-houses at Limba-Oarda de Jos (SW Transylvania, Romania), an open settlement that has been dated to 5,405-5,310 cal. BCE, a period in the Middle Neolithic. A total of 322 retouched tools and débitage pieces were typologically and macroscopically investigated. From these, 20 pieces were analyzed by polarized light optical microscopy (OM) and 10 pieces were analyzed by Fourier-transform infrared spectroscopy (FTIR) in order to identify compositional characteristics, define the petrographic type, and establish the spectral fingerprint of each material. Four petrographic types were discriminated: radiolarite, chert, fossiliferous chert, and siliceous limestone. Mineralogically, the tools primarily consist of a mass of microquartz and fibrous microquartz (called also ‘chalcedony’) associated with radiolarians remnants (in radiolarites); fossil shell fragments (in the fossiliferous chert); and limestone components, such as ooliths and pellets (in the siliceous limestone). All samples show distinct FTIR bands, most of which are assigned to microquartz, quartz, and fibrous microquartz. The deconvolution of the FTIR spectra in the 950-1300 cm-1 domain reveals the contribution of several other phases, such as calcite and clay minerals. The results support the assumption that the tools made of chert, fossiliferous chert, and siliceous limestone were produced at the site from nodules that probably originated from the Upper Jurassic chert-bearing limestone that crops out nearby in the Trascău Mts. The tools made of radiolarite were most likely brought to the site as finished products from the Trascău Mts.

Column experiments to study the interaction between acid mine drainage and rock and Portland cement

Interaction between Portland cement, rock (siliceous limestone) and acid mine drainage (AMD) from the Iberian Pyrite Belt (IPB) was studied by means of column experiments at laboratory scale. Synthetic acidic solutions (pH = 2) containing sulfate, Fe(II), Al, Mg and minor elements such as divalent cations (Cd, Zn, Cu, Ni and Cd) and an anion As(V) were injected. The interaction was dominated by the dissolution of calcite (main rock phase) and portlandite (one of the main phases of cement). Dissolution of these phases increased the pH up to ≈ 12 as portlandite dissolved and up to ≈ 6 when calcite dissolved. This change in pH resulted in (1) the precipitation of gypsum, aragonite, schwertmannite, brucite and Feand Al-amorphous phases and (2) the precipitation of Cd, Ni and Zn hydroxides and the adsorption of Cu and As(V) on iron hydroxides.

Geological investigation of river terraces along the Modi Khola valley, Parbat district, western Nepal Lesser Himalaya

Fluvial terraces are remnants of the former floodplain of a stream or river. Wide river valley with spectacular terraces are the well-known places of the Himalaya because of their unique morphology and history of origin. The Modi Khola and Kali Gandaki valleys in west Nepal, Lesser Himalaya are characterized by a number of spectacular river terraces. In the present study, the river terraces along the Modi Khola valley were mapped at 1:25,000 scale and their lithological and sedimentological characteristics were investigated. The river terraces along the Modi Khola are distributed in at least three levels. They are named as Godam Formation (Higger Terrace), Badagaun Formation (Middle Terrace) and the Modibeni Formation (Lower Terrace). The Godam Formation is standing out at an elevation between 860 m and 1100 m. The upper surface of the terrace is extremely rugged with karstic features. The Godam Formation is characterized by matrix-supported, calcite cemented conglomerate with angular to sub-angular clasts of calcareous shale, laminated siliceous limestone and quartzite. The Badagaun Formation (Middle Terrace) is distributed at an altitude from 700 to 860 m on both sides of the Modi Khola valley. It is deeply weathered forming a very thick (almost 3-5 m) residual soil (mostly lateritic soil). Karst features such as caves and sink holes are common in this terrace. This formation is mainly composed of matrix-supported conglomerate with granule-, cobble- and boulder-sized clasts of calcareous shale, siliceous limestone and rarely quartzite. The Lower Terrace (Modibeni Formation) is fluvial deposit consisting of rounded and subrounded clast-supported conglomerate. Both the Upper and Middle Terraces have been interpreted as cohesive debris flow facies derived from the Annapurna Range. Presence of three levels of terraces indicates at least three phase of uplift in the area in the Holocene time. The debris flow deposit in the upper and Middle Terraces indicates catastrophic outbursts from natural dams or large rock-ice avalanches in the Annapurna Range triggered probably by megaearthquakes as in Pokhara valley as suggested by Schwanghart et al. (2015).

Middle Palaeolithic technical behaviour: Material import-export and Levallois production at the SU 13 of Oscurusciuto rock shelter, Southern Italy

The Oscurusciuto rock shelter, located in southern Italy (Puglia), has yielded a long Middle Palaeolithic stratigraphy rich in lithic assemblages, fireplaces and faunal remains, attesting Neanderthal occupation during the MIS 3. This paper is focused on the stratigraphic unit 13, consisting of a sandy compact deposit mixed with pyroclastic sediment above a thick level of tephra-US 14, identified as Mt. Epomeo green tuff (dated Ar/Ar ~ 55 ka).Level 13 represents the first stable human occupation after the deposition of tephra. Our goal was to examine the lithic assemblage of this stratigraphic unit by means of an interdisciplinary approach (technology, RMU, refitting program) in order to identify the economic behaviour and technical strategies of Neanderthals occupying the stratigraphic unit 13 of Oscurusciuto.The technical strategies applied indicate fragmentation of the reduction processes, as well as probable events of importation and exportation of objects. The lithic material were introduced at different stages of manufacturing. Pieces were introduced in the form of rough objects (pebbles), as well as semi-finished items, and as finished tools. This fragmentation of the chaîne opératoire also demonstrate the palimpsest nature of the level which is made up of different events happening one after another.The main concept of debitage was Levallois, generally realized on local jasper and siliceous limestone pebbles or cortical flakes. Jasper and siliceous limestone flakes, backed flakes and convergent flakes were the technological objectives of the debitage. A marginal volumetric debitage aimed at producing bladelets was also attested.

Contribution of magnetic resonance soundings for characterizing water storage in the unsaturated zone of karst aquifers

Understanding the role of the unsaturated zone in aquifer recharge and contaminant attenuation processes is a major challenge for the protection and management of karstic water resources. We present the potential of the magnetic resonance soundings (MRS) geophysical method for characterizing the vadose zone of karst aquifers composed of epikarst and infiltration layers. To investigate the hydraulic functioning of the Durzon karst system located on the Larzac plateau (southern France), we used the MRS method at 16 sites. The MRS results have been compared with available geologic information and to core water content measurements. The remarkable spatial variability of the MRS response observed in the study area makes it possible to determine ranges of water storage properties in relation to the lithology of the investigated carbonate formations (dolomite, marly, and siliceous limestone). All soundings found either constant or increasing MRS water content with depth, which demonstrates that the infiltration zone might be the major water storage entity for permanent water storage, with important consequences for recharge quality and quantity. These results show the feasibility and potential of the MRS method for the characterization of the karst unsaturated zone and for understanding the vertical distribution of water content, which impacts the overall functioning of karst systems.