Local Dolomite Research Articles

Biochemically induced diagenesis of Jurassic micrite: evidence from phase analysis, carbon, oxygen, and strontium isotopes (Franconian Alb, Germany)

The marine Upper Jurassic rocks of the Franconian Alb consist largely of micritic carbonate of partly dolomitized reef mounds and bedded basinal limestone. All carbonates were lithified in the shallow (centimeters, meters) subsurface and have a wide range of ∂13C (≤ + 3‰ to − 10‰VPDB) but always negative ∂18O (− 1 to − 6‰VPDB). Dolomite and reef limestone show the highest ∂18O and ∂13C values. The most negative ∂13C (≥ − 10‰) occurs mainly as cement in dolomite of a basinal, partly dolomitic, biostrome interval. Basinal limestone shows intermediate ∂13C values. Because freshwater diagenesis and elevated temperatures cannot explain the observed isotope values, pH is here considered a major factor influencing the isotope signal of micritic limestone. The bulk sediment isotope signal was reset to lower values, from an original lime mud with ∂13C ≥ 3‰ and a ∂18O of ≥ + 1‰, as a result of biochemically induced diagenesis. Carbonate, probably mostly aragonite but occasionally including dolomite, was dissolved in a zone where low pH developed as a result of organic matter degradation. Dissolved carbonate was translocated by diffusion and re-precipitated as cement (ca. 50vol%) in a zone with elevated pH where all in situ lime mud ∂18O was reset. Imported cement carbonate precipitated in equilibrium with the pore fluid with negative isotope values, whereas ∂13C of the in situ lime mud remained unmodified. The negative shift of the bulk ∂13C and ∂18O is variable and depends on pH and the contribution of 12C from anaerobic sulfate reduction in the zone of cement precipitation. This produced an ubiquitous covariance of ∂18O and ∂13C. Incorporation of seawater-derived Mg2+ during recrystallization of carbonate can account for the local dolomitization. Elevated 87Sr/86Sr ratios are explained as a result of interaction of clay minerals with the stationary pore fluids. This study shows that the isotopic signal produced by biochemically induced shallow submarine subsurface carbonate diagenesis can be indistinguishable from freshwater diagenesis, that ∂18O and ∂13C of the bulk rock are always reset, and that carbonates can show, in the presence of clay minerals, elevated 87Sr/86Sr ratios even when the pore fluids were never exchanged.Graphical

Three-stage hydrocarbon accumulations in the Middle Permian in the Central Sichuan Basin

The Middle Permain Maokou Formation (P2m) is a new region of natural gas exploration in the Sichuan Basin, is characterized by bioclastic limestone with localized dolomitization, and karst fractured-vuggy reservoirs. Currently, on the gas source, hydrocarbon accumulation process and control factors in the Sichuan Basin during the Permian are lacking. To bridge this gap, herein, we identified the filling sequence minerals inside the pores/vugs, along with the oil charge of the Maokou Formation using drill cores, thin sections, oil inclusion analysis, and U-Pb dating of calcite cements. The results showed that the reservoir space of the Maokou Formation was predominated by the residual dissolved pores/vugs, fractures, and dissolved fractures. The pores/vugs underwent four stages of mineral filling by very fine-fine (-crystalline, CC1) calcite → fine-medium calcite (CC2: from 256.4 ± 1.7 to 244.1 ± 6.3 Ma) → fibrous calcite (FC; ∼183.9 ± 8.2 Ma) → coarse-macro calcite (CC3; ∼171.5 ± 5.3 Ma). Combined with the homogenization temperature and salty of fluid inclusion, we considered that three stages of oil charge were present in the Maokou Formation reservoirs. The first stage involved the formation of paleo-oil reservoirs during the Late Permian to Early Triassic, corresponding to the high-maturity aqueous inclusions in CC2, with a homogenization temperature of 106.7°C–137.8°C. At that time, the oil generation from the Lower Cambrian Qiongzhusi Formation rocks peaked, and the generated hydrocarbons migrated upward into the Maokou Formation through the strike-slip faults in the basin center. The second stage involved the formation of paleo-oil reservoirs during the Early Jurassic. The Permian source rocks reached the oil generation window with hydrocarbon expulsion, which was consistent with the oil inclusions in FC. The third stage involved the formation of paleo-gas reservoirs during the Middle Jurassic to Early Cretaceous, corresponding to the high-density methane inclusions and bitumen inclusions occurring in CC3, with the homogenization temperature peaking at 151.9°C–178°C. The natural gas in the Middle Permian of the Central Sichuan Basin is predominantly sourced from the Lower Cambrian Qiongzhusi Formation mudstone and partially from the source rocks of the Middle Permian, indicating a significant source-reservoir conduit of the strike-slip faults in the basin center. The findings provide considerable baseline data to advance further research in the Sichuan Basin.

Stromatolite‐rimmed thrombolite columns and domes constructed by microstromatolites, calcimicrobes and sponges in late Cambrian biostromes, Texas, USA

ABSTRACTMicrobial carbonates formed stromatolitic, thrombolitic, dendrolitic and maceriate (mazelike) fabrics in shallow marine Cambrian–Early Ordovician carbonates encircling Laurentia. However, poor preservation often hinders recognition of their specific components. Well‐preserved examples of normal shallow marine limestones in the ca 490 Ma upper Cambrian Point Peak Member, Wilberns Formation, central Texas, include stromatolitic cones, steep‐sided laminated rimmed columns with grainy interiors, and laminated and maceriate domes. Together these form decimetre to metre‐thick biostromes. In these examples, a single component, microstromatolite, on its own or with minor calcimicrobes, creates macroscopic stromatolitic, dendrolitic, thrombolitic and maceriate fabrics. Microstromatolites constructed upward widening stromatolitic cones that developed into columns with laminated rims surrounding slightly depressed interiors. These columns accumulated allochthonous sediment by a ‘bucket effect’. Their interiors contain either clusters of dendrolitic microstromatolite or ragged columns of laminated stromatolite–sponge biolithite, and are often characterized by a ‘mottled’ fabric that superficially resembles thrombolite. This mottling was formed by localized dolomitization around millimetric burrows that otherwise do not appear to have significantly influenced the biolithite fabric. Calcimicrobes, including cyanobacteria (Razumovskia) and microproblematica (Renalcis and Tarthinia), impart a mesoscopic clotted appearance to maceriate fabric, and locally to column rims, both of which are dominated by microstromatolite. Similar component‐fabric relationships should be recognizable in rimmed columns and domes that were locally abundant elsewhere in Cambrian–Early Ordovician shallow carbonate seas.

Aceh Local Dolomite Modified by Alkali Metals as a Low-Cost Solid Inorganic Catalyst for Biodiesel Synthesis

Solid inorganic-based catalyst which mainly contains calcium oxide and magnesium oxide has been successfully prepared from local Aceh dolomite minerals. The calcination process of dolomite particles (150 μm) in the air environment for 4 hours changed those calcium and magnesium carbonates compounds into their oxide form, which are subsequently referred to as inorganic oxides. Furthermore, the calcined local dolomite has been chemically modified using alkaline metal precursors (lithium, sodium and cesium precursors). Physicochemical investigation on the modified dolomite indicated that introduction of lithium metal on modified dolomite surface has a positive impact on increasing the number and strength of basic sites on the catalyst. The modified catalyst had proved its catalytic activity for biodiesel synthesis with the yield values of 82;78;51 respectively.

Akermanite-based ceramics from Moroccan dolomite and perlite: Characterization and in vitro bioactivity assessment

The present paper focuses on the elaboration and characterization of akermanite-rich bioceramics from abundantly available local dolomite and perlite. Different mixtures have been prepared for low-cost ceramic manufacturing by uniaxial pressing method and firing at 1250 °C for 2 h. The obtained results showed that akermanite is the predominant crystalline phase through the addition of natural perlite for a maximum of 30% in weight, accompanied by some small traces of diopside and periclase. The experimental results indicated that the sample M2-B (25 wt% of perlite) is the optimized body from all the tested specimens. The optimized ceramic was subjected to an SBF test to evaluate the bioactivity of the sample, and experimentally the combination between the microstructural and the mineralogical composition of the obtained material after soaking in SBF solution has confirmed the quality of the developed bioceramic by the formation of apatite layer.

Sedimentary characteristics of microbialites influenced by volcanic eruption: a case study from the Lower Cretaceous Shipu Group in Zhejiang Province, East China

This study describes a sequence of microbialites and volcanics of the Lower Cretaceous Shipu Group, an example of microbialites influenced by volcanic activity. It is located at Shipu town in eastern Zhejiang Province on the coast of southeastern China. Based on macroscopic outcrop observations, microscopic examination of thin sections, electron probe microanalysis (EPMA), field emission scanning electron microscopy (FESEM) imaging analysis, and energy dispersive X-ray spectrometry (EDS) analysis, nine microbialite–tuffite assemblages have been recognized in the section. Their thickness increased gradually upwards as volcanism decreased. There are ooids, bioclastic grains, intraclasts and tuffaceous grains in the grain shoal with local dolomitization. Above the grain shoal, microbial reefs develop either individually or conjoining with adjacent ones, and consist of stromatolites and serpulid tubes with common recrystallization. Tubes of serpulids are calcified and the tube wall is micrite. The tube and intertube parts are filled by sparry calcite. Colonial serpulids are surrounded by microbes to form stromatolites. Black layers of stromatolites contain many calcite crystals with fan-shaped growth pattern and preserved organic matter. Microbes are so well preserved in crystal lattices that the original microstructure of the microbes can be clearly observed by FESEM imaging analysis. Microbial reefs develop at a local high point near or above fair-weather wave-base where waves removed fine volcanic ashes. Interreef deposits are coarse tuffite due to physical differentiation. Volcanic activity could provide rich nutrition for microbes, but too much fine volcanic ash inhibits microbial growth. As a result, a moderate supply of volcanic ash favors the development of microbialites.

How a mud-dominated ramp changed to a carbonate–clastic oil reservoir: Sea-level fluctuations in cretaceous of the central Persian Gulf

Abstract Mud-dominated facies distribution of Barremian–Turonian succession in the northeastern Arabian Plate in the central Persian Gulf represents a shallow ramp platform. On the basis of petrographical studies, core analysis data and gamma ray logs, this succession has been studied for facies analysis, defining depositional environment, sequence stratigraphy and reservoir properties. A total of 6 microfacies and 3 petrofacies types are recognized in this succession. Lagoonal environment was dominated during the deposition of Dariyan, Kazhdumi and Sarvak formations. The lagoon rapidly changed to a sand shoal by falling sea-level and increasing energy level of the depositional environment. Sequence stratigraphy of Barremian–Turonian succession shows that mud-dominated facies have been deposited in TSTs and grain dominated facies in HSTs of the sequences. Although grain-dominated facies like packstone to grainstone and algal floatstone were spread during the HSTs of sequences, the changes in the texture and size of the grains had a negligible effect on reservoir quality. During this period (Barremian–Turonian), two major sea-level falls caused considerable environmental changes such as platform emergence, incised valley fills and clastic sediments influx into the carbonate platform. Meteoric diagenesis during the falling sea-level had a major effect on the reservoir properties of the reservoirs, under the sequence boundaries. Grains, matrix and micrite dissolution and subsequent selective blocky and equant calcite cementation, strongly modified the primary reservoir properties. Local dolomitization also enhance the porosity and permeability of the samples. While large pores have been filled by cements, microporosities remained unfilled until the late stages of diagenesis and burial.

Characterization and evaluation of dolomite and kaolin as filler on the properties of poly art marble

This research work is to characterize and evaluate local dolomite and kaolin as filler on the physical and mechanical properties in producing poly art marble. In the marble preparation, the origin size of dolomite particle used is 1.60–3.00 mm, while kaolin was sieved with a sieve opening size of 150 µm. Poly art marble was prepared by two different base ratio of filler to the resin which are 70:30 (Series 1) and 75:25 (Series 2) by wt.%. The mixture of filler, resin and hardener were well mixed using a planetary mixer and cast into a mold for setting. In this study, an effect of dolomite and kaolin filler loading is being studied. Test specimens were evaluated for water absorption test, flexural, compression and Barcol hardness properties. It is found that there are no distinctive changes of value of the properties between Series 1 and Series 2. An addition of kaolin by 10% (wt.) in the composition of poly art marble has reduced the water absorption rate and increase the flexural and compression strength.

New weighting agent for water-based mud, um-bogma area, central Sinai, Egypt

A successful oil well drilling depends largely on a good mud Program. During drilling, mud provides sufficient hydrostatic pressure, removes drill cuttings and cools drill bits. Mud additives are always required to provide sufficient hydrostatic pressure to ensure borehole stability. Barium Sulphate (BaSO4) also known as barite is the prevalent weighting material but there is needed to develop local materials to augment the use of Barite. The present search is concerned on the early Carboniferous succession exposed in Um Bogma Formation, west central Sinai, Egypt as a new weighting agent in drilling fluids. The increases in the cost of drilling fluids and a shortage of using barite have introduced the locale dolomite as alternative weighting materials. The rheological properties of mud drilling samples weighted by local dolomite samples are being examined and investigated to know its potential to be used as a weighting material in drilling mud. Two mud samples were prepared which comprised of fresh water, caustic soda, bentonite and the weighting material. The weighting materials are added to achieve the required density. The first sample: Water-based mud with commercial barite of density between 10.00 lb/gm and 18.00 lb/gm. The second sample: Water-based mud with dolomite of density between 10.00 lb/gm and 18.00 lb/gm. These samples were analyzed and the density, rheological properties, aging of barite and dolomite and solid contents were investigated. At 10.00 lb/gm, the yield point of dolomite was 20.00 lb/100ft2 and barite 22.00 lb/100ft2 while the 10 second gel strength of dolomite was 30.00 lb/100ft2 and 22.00 lb/100ft2 for barite. Similarly, little difference was observed in plastic and apparent viscosities. At 10.00 lb/gm, the plastic and apparent viscosities of dolomite were 8.00 cp and 20.00 cp while barite was 8.00 cp and 24.00 cp. The result show that dolomite mud sample gave a little higher yield point and gel strength than barite mud sample. Therefore, dolomite has the potential to be used as weighting material in drilling mud in place of barite thereby enhancing the local content initiative of the government. When dolomite is sourced locally and used it will reduce overall mud and drilling costs.

Trace-element geochemistry of transform-fault serpentinite in high-pressure subduction mélanges (eastern Cuba): implications for subduction initiation

ABSTRACTThe Sierra del Convento and La Corea mélanges (eastern Cuba) are vestiges of a Cretaceous subduction channel in the Caribbean realm. Both mélanges contain blocks of oceanic crust and serpentinite subducted to high pressure within a serpentinite matrix. The bulk composition of serpentinite indicates spinel-harzburgite and -herzolite protoliths. The samples preserve fertile protolith signatures that suggest low melting degrees. High concentration of immobile elements Zr, Th, Nb, and REE contents (from ~0.1 to ~2 CI-chondrite) point to early melt–rock interaction processes before serpentinization took place. Major- and trace-element compositions suggest an oceanic fracture-zone–transform-fault setting. A mild negative Eu anomaly in most samples indicates low-temperature fluid–rock interaction as a likely consequence of seawater infiltration during oceanic serpentinization. A second, more important, serpentinization stage is related to enrichment in U, Pb, Cs, Ba, and Sr due to the infiltration of slab-derived fluids. The mineral assemblages are mainly formed by antigorite, lizardite, and chlorite, with local minor talc, tremolite, anthophyllite, dolomite, brucite, and relict orthopyroxene. The local presence of anthophyllite and the replacements of lizardite by antigorite indicate a metamorphic evolution from the cooling of peridotite/serpentinite at the oceanic context to mild heating and compression in a subduction setting. We propose that serpentinites formed at an oceanic transform-fault setting that was the locus of subduction initiation of the Proto-Caribbean basin below the Caribbean plate during early Cretaceous times. Onset of subduction at the fracture zone allowed the preservation of abyssal transform-fault serpentinites at the upper plate, whereas limited downward drag during mature subduction placed the rocks in the subduction channel where they tectonically mixed with the upward-migrating accreted block of the subducted Proto-Caribbean oceanic crust. Hence, we suggest that relatively fertile serpentinites of high-pressure mélanges were witness to the onset of subduction at an oceanic transform-fault setting.

Termination of BIF deposition in the Paleoproterozoic: the Tongwane Formation, South Africa

The Tongwane Formation (~2.4 Ga) conformably overlies banded iron formations (BIF; Penge Iron Formation) on the Kaapvaal Craton, South Africa. As such, it provides a unique window into depositional processes and environmental conditions in the aftermath of major Archean-Paleoproterozoic BIF deposition, and on the eve of irreversible environmental oxygenation in the Great Oxidation Event (GOE, ~2.35 Ga). This study presents the first sedimentological and bulk-rock geochemical characterization of the Tongwane Formation to provide a sedimentological and stratigraphic framework for further studies of early Paleoproterozoic environments. The Tongwane Formation is 220m thick and consists from the base up of shales, siliceous mudstones with local BIF facies, interbedded mudstones and dolomites, and a massive dolomite unit at the top. Strata record the progressive shallowing of depositional environments from deep shelf (BIF) to a wave-swept carbonate ramp. Intervening slope environments record increased detrital sedimentary input in the form of shales and distal turbidites. The carbonate ramp had a distally steepened margin as documented by an important margin collapse breccia. Extension due to seismic forces and/or slope steepening caused progressive deformation of slope deposits, from slumping and fracturing through sedimentary boudinage, to brecciation, and mass wasting. Termination of BIF deposition could have been related to (a) shutdown of Fe-precipitating processes, (b) shutdown of the hydrothermal Fe source, (c) shallowing of environments to restrict BIF deposition to deeper parts of the basin, (d) masking of Fe deposition by increased detritus, or a combination of these. Although a partial or complete shutdown of the Fe source or of Fe precipitating processes cannot be excluded, the weight of evidence from the Tongwane Formation favors external factors such as relative sea level fall and Fe dilution by increased detrital input as the main drivers for the BIF-carbonate transition. All samples fall on a mixing curve between hydrothermal and detrital end members, and despite metamorphic overprint, a weak hydrothermal signature is observed up to below platform deposits. These results stress the importance of understanding sedimentary factors in studies of Archean-Paleoproterozoic environments.

Performance evaluation of high modulus asphalt concrete mixes

Dolomite is one of the most available sedimentary rocks in the territory of Latvia. Dolomite quarries contain about 1000 million tons of this material. However, according to Latvian Road Specifications, this dolomite cannot be used for average and high intensity roads because of its low quality (mainly, LA index). Therefore, mostly imported magmatic rocks (granite, diabase, gabbro, basalt) or imported dolomite are used which makes asphalt expensive. However, practical experience shows that even with these high quality materials roads exhibit rutting, fatigue and thermal cracks. The aim of the research is to develop a high performance asphalt concrete for base and binder courses using only locally available aggregates. In order to achieve resistance against deformations at a high ambient temperature, a hard grade binder was used. Workability, fatigue and thermal cracking resistance, as well as sufficient water resistance is achieved by low porosity (3-5%) and higher binder content compared to traditional asphalt mixtures. The design of the asphalt includes a combination of empirical and performance based tests, which in laboratory circumstances allow simulating traffic and environmental loads. High performance AC 16 base asphalt concrete was created using local dolomite aggregate with polymer modified (PMB 10/40-65) and hard grade (B20/30) bitumen. The mixtures were specified based on fundamental properties in accordance to EN 13108-1 standard.

Continental carbonate facies of a Neoproterozoic panglaciation, north‐east Svalbard

AbstractThe Marinoan panglaciation (ca 650 to 635 Ma) is represented in north‐east Svalbard by the 130 to 175 m thick Wilsonbreen Formation which contains syn‐glacial carbonates in its upper 100 m. These sediments are now known to have been deposited under a CO2‐rich atmosphere, late in the glaciation, and global climate models facilitate testing of proposed analogues. Precipitated carbonates occur in four of the seven facies associations identified: Fluvial Channel (including stromatolitic and intraclastic limestones in ephemeral stream deposits); Dolomitic Floodplain (dolomite‐cemented sand and siltstones, and microbial dolomites); Calcareous Lake Margin (intraclastic dolomite and wave‐rippled or aeolian siliciclastic facies); and Calcareous Lake (slump‐folded and locally re‐sedimented rhythmic/stromatolitic limestones and dolomites associated with ice‐rafted sediment). There is no strong cyclicity, and modern analogues suggest that sudden changes in lake level may exert a strong control on facies geometry. Both calcite and dolomite in stromatolites and rhythmites display either primary or early diagenetic replacive growth. Oxygen isotope values (−12 to +15‰VPDB) broadly covary with δ13C. High δ13C values of +3·5 to +4·5‰ correspond to equilibration with an atmosphere dominated by volcanically degassed CO2 with δ13C of −6 to −7‰. Limestones have consistently negative δ18O values, while rhythmic and playa dolomites preserve intermediate compositions, and dolocretes possess slightly negative to strongly positive δ18O signatures, reflecting significant evaporation under hyperarid conditions. Inferred meltwater compositions (−8 to −15·5‰) could reflect smaller Rayleigh fractionation related to more limited cooling than in modern polar regions. A common pseudomorph morphology is interpreted as a replacement of ikaite (CaCO3·H2O), which may also have been the precursor for widespread replacive calcite mosaics. Local dolomitization of lacustrine facies is interpreted to reflect microenvironments with fluctuating redox conditions. Although differing in (palaeo)latitude and carbonate abundance, the Wilsonbreen carbonates provide strong parallels with the McMurdo Dry Valleys of Antarctica.

High Modulus Asphalt Concrete with Dolomite Aggregates

Dolomite is one of the most widely available sedimentary rocks in the territory of Latvia. Dolomite quarries contain about 1,000 million tons of this material. However, according to Latvian Road Specifications, this dolomite cannot be used for average and high intensity roads because of its low quality, mainly, its LA index (The Los Angeles abrasion test). Therefore, mostly the imported magmatic rocks (granite, diabase, gabbro, basalt) or imported dolomite are used, which makes asphalt expensive. However, practical experience shows that even with these high quality materials roads exhibit rutting, fatigue, and thermal cracks. The aim of the research is to develop a high performance asphalt concrete for base and binder courses using only locally available aggregates. In order to achieve resistance against deformations at a high ambient temperature, a hard grade binder was used. Workability, fatigue and thermal cracking resistance, as well as sufficient water resistance is achieved by low porosity (3-5%) and higher binder content compared to traditional asphalt mixtures. The design of the asphalt includes a combination of empirical and performance based tests, which in laboratory circumstances allow simulating traffic and environmental loads. High performance AC 16 base asphalt concrete was created using local dolomite aggregate with polymer modified (PMB 10/40-65) and hard grade (B20/30) bitumen. The mixtures were specified based on fundamental properties in accordance with EN 13108-1 standard.

High Modulus Asphalt Concrete with Dolomite Aggregates

Dolomite is one of the most widely available sedimentary rocks in the territory of Latvia. Dolomite quarries contain about 1,000 million tons of this material. However, according to Latvian Road Specifications, this dolomite cannot be used for average and high intensity roads because of its low quality, mainly, its LA index (The Los Angeles abrasion test). Therefore, mostly the imported magmatic rocks (granite, diabase, gabbro, basalt) or imported dolomite are used, which makes asphalt expensive. However, practical experience shows that even with these high quality materials roads exhibit rutting, fatigue, and thermal cracks. The aim of the research is to develop a high performance asphalt concrete for base and binder courses using only locally available aggregates. In order to achieve resistance against deformations at a high ambient temperature, a hard grade binder was used. Workability, fatigue and thermal cracking resistance, as well as sufficient water resistance is achieved by low porosity (3-5%) and higher binder content compared to traditional asphalt mixtures. The design of the asphalt includes a combination of empirical and performance based tests, which in laboratory circumstances allow simulating traffic and environmental loads. High performance AC 16 base asphalt concrete was created using local dolomite aggregate with polymer modified (PMB 10/40-65) and hard grade (B20/30) bitumen. The mixtures were specified based on fundamental properties in accordance with EN 13108-1 standard.

Investigation of Physical and Chemical Properties of Low-temperature Hydraulic Binder from Latvia’s Raw Materials

A necessity of compatible material to historical romancement for restoration needs has led to research of artificially made binders from mixtures of clay and dolomite. Low temperature hydraulic binder or so called dolomitic romancement synthesis of mixture composed from local Quaternary period clay and dolomite (both in powder state) in mass ratio 24:76 is discussed in this paper. The chemical composition of the raw materials was analyzed. Specimens were prepared by homogenizing the mixture of requisite amounts of clay and dolomite in dry state and shaping samples measuring 56x26x6 mm by semidry pressing. After firing at temperatures between 650 and 1050°C crystalline phases formed in samples were determined by XRD. Afterwards, water was added to the samples and formation of new crystalline phases was detected in the period of 28 days. Natural dolomitic marl was treated at the same conditions in order to compare the crystalline phases formed in naturally and artificially made binders. DOI: http://dx.doi.org/10.5755/j01.sace.1.2.2838

The Angouran Zn (Pb) deposit, NW Iran: Evidence for a two stage, hypogene zinc sulfide–zinc carbonate mineralization

The unusually high grade hypogene zinc ore at Angouran in northwestern Iran (40.4% Zn, 1.9% Pb in the sulfide ore, 28.1% Zn, 4.4% Pb in the carbonate ore, and 110g/t Ag) formed from an initially highly saline, reduced, relatively acid hydrothermal brine at two successive sulfide and carbonate ore stages. The early ore stage consists of multiple phases of sphalerite dominated sulfide ore breccia with subordinate amounts of galena (±Pb sulfosalts), minor pyrite, and abundant barite. Sphalerite precipitated at moderate temperatures (≥155°C) because of pH increase in the presence of hangingwall marble. Smithsonite precipitated at a higher pH value (≥7) and at lower temperatures (≤120°C) from dilute solutions (salinities close to zero) by mixing of the Zn bearing brines with cool, HCO3− bearing waters. The first melting points of the primary (LV) fluid inclusions in sphalerite and in hydrothermal quartz are unusually low (≤−60°C), close to the eutectic point of the ZnCl2–H2O system (−62°C). Total salinities taken from the ZnCl2–H2O system as a best approximation correspond to 26–41eqmass % ZnCl2. The initial brine evolved to a CaCl2–NaCl rich solution with 27eqmass % salinity. Gas densities (≤0.1gcm−3 for water vapor and ≤0.18gcm−3 for CO2) in the fluid inclusions indicate low pressure (≤5bar for water vapor, and ≤100bar for CO2) at the entrapment temperatures.At the first carbonate ore stage sulfides continued to precipitate characteristically as arsenopyrite with minor amounts of galena and pyrite. The abrupt change of the fluid composition at the sulfide–carbonate boundary was accompanied by a change of the fluid temperature and pressure that produced brecciation of the sulfide ore matrix and an almost total dissolution of barite and replacement by the hypogene smithsonite. Alteration is restricted to ore deposition and consists of weak sericitization and silicification with local dolomitization at the sulfide ore stage, and pervasive dissolution of the hangingwall marble, in particular at the carbonate ore stage.The breccia orebody at Angouran is sited at the crestal portion of a domed antiform at the lithological and thrust boundary of Neoproterozoic–Lower Cambrian footwall schists and the hangingwall marble in rapidly uplifted and exhumated Angouran Block east of the Geynardjeh Thrust Fault. The footwall schists occupy a detachment fault zone above imbricated nappe sheets of the basement metamorphic complex of the Sanandaj–Sirjan zone. During the Pliocene, the nappe sheets were thrust toward the southwest onto the Miocene felsic volcanic rocks of the Urumieh Dokhtar Volcanic Belt that are intruded by 10Ma late Miocene basalts. The 11.9Ma and 18.4Ma zircon ages of the felsic volcanic rocks indicate the lower age limit of the ore body emplacement.The associations with large scale, mid-late Miocene, felsic volcanism along the active Tethyan belt, as well as the ubiquitous presence of the volcanic rock clasts in the sphalerite ore matrix, provide strong evidence of the involvement of hydrothermal processes at Angouran. Ore fluids were successively and pulsatorily generated within the seismically active region. A following geothermal activity appears to have had a significant input in the formation of the carbonate ore of the hypogene, as well as the supergene stage. Stable isotope data suggest complex interaction of element sources and processes. Allowing a broad interpretation, the sulfur isotopic composition of the sulfides δ34S (3.9 to 7.4‰) suggests that the sulfur could be sourced from evolving, mixed magmatic–basinal brine. The isotopic composition of the hypogene smithsonites (δ13C: 2.72 to 5.51‰, δ18O: 18.4 to 22.8‰) broadly supports the local geology and field relationships, which comply with a marble wallrock source for the carbonate ores. They lend support to the assumption that smithsonite was deposited from solutions with isotopic composition similar to those involved in the hydrothermal dolomitization of the marbles. The excess of dissolved marble precipitated as large volumes of travertine and as late calcite veins (δ13C: 18.8 to 20.3‰, δ18O: 3.1 to 6.4‰) at the mineralization site. Isotope values of the travertine (δ13C: 4.5 to 6.6‰, δ18O: 20.1 to 21.1‰ V-SMOW) are consistent with the involvement of CO2 derived from thermogenic decarbonization of the host marble by waters of dominantly meteoric origin, most likely concomitantly with ore forming processes.The Angouran deposit is the only reported case of a two stage, hypogene zinc sulfide–zinc carbonate mineralization, and represents a new style of nonsulfide zinc mineralization.

Lithuanian Mineral Resources, Their Reserves and Possibilities for Their Usage in Road Building

This article has an aim to review the range and value of the underground resources of the Republic of Lithuania, to analyse the quality of local aggregates used for road building purposes and to recommend how local aggregates have to be used in order to give the max benefit for the state and public welfare. All the investigated in detail mineral resources of the Republic of Lithuania make almost one third of the value of the property the country. All the deposits of dolomite, gravel and sand explored in detail and used for road building, construction and other purposes occur under the less than 0.1% of the territory of the country. It was found that extraction and processing of local dolomite and gravel resources up to the max use of their potential properties for road building and other purposes saves over 700 mln LTL (over 200 mln EUR) per year in the cash flow of the Republic of Lithuania. It was determined that the physical and mechanical indices of asphalt concrete, containing crushed pebble and crushed dolomite, differ insignificantly. Based on the comparison to the normative requirements, local aggregate products consumption in asphalt concrete could be increased by extra 8–10% compared to the use of imported materials. It was recommended, that various subbase material mixtures from local, imported or mixed compositions were extra tested and analysed after at least of 350–700 freezing and thawing cycles corresponding to the average of 10–20 years subbase service under Lithuanian mild winter climate conditions with a high number of freezing and thawing cycles. The article gives a complex analysis of the research results versus the condition of the underground mineral resources and presents conclusions valuable for both geologists, road building scientists and engineers as well as decision makers finalising The Strategy for the Optimum Use of Lithuanian Underground Mineral Resources potential and implementing the Communications of the European Commission the Raw Materials Initiative ‒ Meeting our Critical Needs for Growth and Jobs in Europe and Improving Framework Conditions for Extracting Minerals for the EU.

Depositional setting and diagenetic processes and their impact on the reservoir quality in the late Visean–Bashkirian Kashagan carbonate platform (Pre-Caspian Basin, Kazakhstan)

The Kashagan isolated carbonate platform developed from the Visean to the Bashkirian in the Pre-Caspian Basin. Sedimentation is organized in shallowing-upward cycles marked at the top by subaerial exposure surfaces. This study is based on analyses of 12 cored wells, integrated sedimentology, petrography, fluid inclusion, stable isotopes, and trace element data. We reconstructed the pore-system evolution in the platform interior and margin. Near-surface diagenesis includes marine cement fringes followed by meteoric dissolution and cementation. Meteoric diagenesis was stronger in the Bashkirian sequence and progressively decreased down section in the Visean. The main karst surfaces are evidenced by root traces, sharp 13C depletion, and meteoric water-fluid inclusions in calcites. Porosity in the platform interior follows a cyclic pattern due to the interaction of the freshwater dissolution and cementation and compaction that destroyed the porosity at the tops and bases of the cycles. Burial diagenesis, represented by some calcite cementation, did not significantly alter the cyclic porosity distribution in the platform interior. In the platform margin, porosity distribution is more heterogeneous due to more poorly defined sedimentary cyclicity and stronger burial diagenetic overprint linked to exotic fluid circulation. Basin-sourced fluids caused dissolution, cementation, and local dolomitization. These cements show bright luminescence, a high manganese content, depleted 18O, a high homogenization temperature, and low-salinity fluid inclusions. The complex diagenetic evolution diagenesis produced better matrix porosity in the platform interior and heterogeneous porosity with larger pores and fractures but with poor matrix porosity in the platform margin.

Using Strontium Isotopes to Study Site Accumulation Processes

Strontium isotopes (87Sr/86) in tooth enamel reflect the geological subtrate on which an animal lived during tooth development. Therefore, strontium isotopes of tecth in fosil cave accumulations are potentially useful in determining whether an animal was native to the vicinity of the site or was brought in by other agents such as predators from farther afield. In this study, we tested the ability of strontium isotopes to help determine the origins of fossil rodents in Gladysvale Cave, South Africa. First, biologically available 87 Sr/86) ratios were established using modern plants recovered from three geologically distintct areas, the Malmani dolomite, the Hekpoort andesite/basalt, and the Timeball Hill shale, all of which were found to be significantly different. Strontium isotope values were then measured on tooth enamel of rodents from a moder barn ow (Tyto alba) roost in Gladysvale (67%) versus those from other geological zones. We then measured strontium isotope values of enamel from 14 fossil rodent teecth from Gladysvale Cave. The average and range of values for the fossil rodents is similar to that of the modern owl roost rodents. Fifty-seven percent of the fossil rodent probably derived from the local dolomite, while others were brought in from at least 0.8 km away. A pilot study of 87Sr/86Sr ratios of fossil rodent teeth from Swartkrans Member 1 and Sterkfontein Member 4 indicates that 81% and 55% of those rodents, respectively, are from the local dolomite subtrate. Overall, this study shows that strontium isotopes can be a useful tool in taphonomy analyses by identifying non. Local individuals, and has great potential for elucidating more of the taphonomic history of fossil accumulations in the dolomitic cave sites of South Africa.