Showing papers on "Ankerite published in 2015"

Depositional Environment of the Paleoproterozoic Yuanjiacun Banded Iron Formation in Shanxi Province, China

Abstract: The Paleoproterozoic (~2.38–2.21 Ga) Yuanjiacun banded iron formation (BIF), located in Shanxi Province, is a Superior-type BIF in the North China craton. This BIF is within a metasedimentary rock succession of the Yuanjiacun Formation, in the lower Luliang Group, which has undergone lower greenschist-facies metamor phism. Iron oxide (magnetite and hematite), carbonate, and silicate facies are all present within the iron-rich layers. The eastward transition from carbonate- into oxide-facies iron formations is accompanied by a change in mineralogical composition from siderite in the west through magnetite-ankerite and magnetite-stilpnomelane assemblages in the transition zone to magnetite and then hematite in the east. These distinct lateral facies are also observed vertically within the BIF, i.e., the iron mineral assemblage changes upsection from sider ite through magnetite into hematite-rich iron formation. The oxide-facies BIF formed near shore, whereas carbonate (siderite)- and silicate-facies assemblages formed in deeper waters. Based on detailed analyses of these variations on a basinal scale, the BIF precipitated during a transgressive event within an environment that ranged from deep waters below storm wave base to relatively shallow waters. The BIF samples display distinctively seawater-like REEs + Y profiles that are characterized by positive La and Y anomalies and HREEs enrichment relative to LREEs in Post-Archean Australian shale-normalized diagrams. Consistently positive Eu anomalies are also observed, which are typical of reduced, high-temperature hydrothermal fluids. In addition, slightly negative to positive Ce anomalies, and a large range in ratios of light to heavy REEs, are present in the oxide-facies BIF. These characteristics, in combination with consistently positive δ 56Fe values, suggest that deposition of the BIF took place along the chemocline where upwelling of deep, anoxic, iron- and silicarich hydrothermal fluids mixed with shallower and slightly oxygenated seawater. The ankerite displays highly depleted δ13C values and the carbonate-rich BIF has a high content of organic carbon, suggesting dissimilatory Fe(III) reduction of a ferric oxyhydroxide precursor during burial of biomass deposited from the water column; that same biomass was likely tied to the original oxidation of dissolved Fe(II). The fact that the more ferric BIF facies formed in shallower waters suggests that river-sourced nutrients would have been minimal, thus limiting primary productivity in the shallow waters and minimizing the organic carbon source necessary for reducing the hematite via dissimilatory Fe(III) reduction. By contrast, in deeper waters more proximal to the hydrothermal vents, nutrients were abundant, and high biomass productivity was coupled to increased carbon burial, leading to the deposition of iron-rich carbonates. The deposition of the Yuanjiacun BIF during the onset of the Great Oxidation Event (GOE; ca. 2.4–2.2 Ga) confirms that deep marine waters during this time period were still episodically ferruginous, but that shallow waters were sufficiently oxygenated that Fe(II) oxidation no longer needed to be tied directly to proximal cyanobacterial activity.

In situ Sr isotope analysis of apatite by LA-MC-ICPMS: constraints on the evolution of ore fluids of the Yinachang Fe-Cu-REE deposit, Southwest China

Abstract: Apatite is a ubiquitous accessory mineral in a variety of rocks and hydrothermal ores. Strontium isotopes of apatite are well known to retain petrogenetic information and have been widely used to investigate the origin of igneous rocks, but such attempts have rarely been made to constrain ore-forming processes of hydrothermal systems. We here report in situ LA-MC-ICPMS Sr isotope data of apatite from the ~1660-Ma Yinachang Fe-Cu-REE deposit, Southwest China. The formation of this deposit was coeval to the emplacement of regionally distributed doleritic intrusions within a continental-rift setting. The deposit has a paragenetic sequence consisting of sodic alteration (stage I), magnetite mineralization (stage II), Cu sulfide and REE mineralization (stage III), and final barren calcite veining (stage IV). The stage II and III assemblages contain abundant apatite, allowing to investigate the temporal evolution of the Sr isotopic composition of the ore fluids. Apatite of stage II (Apt II) is associated with fluorite, magnetite, and siderite, whereas apatite from stage III (Apt III) occurs intimately intergrown with ankerite and Cu sulfides. Apt II has 87Sr/86Sr ratios varying from 0.70377 to 0.71074, broadly compatible with the coeval doleritic intrusions (0.70592 to 0.70692), indicating that ore-forming fluids responsible for stage II magnetite mineralization were largely equilibrated with mantle-derived mafic rocks. In contrast, Apt III has distinctly higher 87Sr/86Sr ratios from 0.71021 to 0.72114, which are interpreted to reflect external radiogenic Sr, likely derived from the Paleoproterozoic strata. Some Apt III crystals have undergone extensive metasomatism indicated by abundant monazite inclusions. The metasomatized apatite has much higher 87Sr/86Sr ratios up to 0.73721, which is consistent with bulk-rock Rb-Sr isotope analyses of Cu ores with 87Sr/86Sri from 0.71906 to 0.74632. The elevated 87Sr/86Sr values of metasomatized apatite and bulk Cu ores indicate that later fluids were dominated by highly radiogenic Sr equilibrated with the Paleoproterozoic country rocks. Results of this study highlight the utilization of in situ Sr isotope analysis of apatite in unraveling the evolution of hydrothermal systems.

GEOLOGY, Re-Os AGES, SULFUR AND LEAD ISOTOPES OF THE DIYANQINAMU PORPHYRY Mo DEPOSIT, INNER MONGOLIA, NE CHINA

Abstract: The Diyanqinamu porphyry Mo deposit in the southern Greater Khingan Range of the Central Asian orogenic belt contains 800 million metric tons (Mt) of ore with an average grade of 0.097% molybdenum. The deposit is hosted in Late Jurassic volcanic rocks of tuff, andesite, and volcanic breccia. Multiple-stage hydrothermal activities have resulted in propylitic, phyllic, and argillic alteration in this deposit. Five stages (I–V) of hydrothermal activity are identified. Stage I is represented by a mineral assemblage of epidote, chlorite, and magnetite, with some discontinuous barren veinlets of quartz + K-feldspar ± fluorite ± magnetite ± epidote ± chlorite. Stage II is marked by occurrence of quartz + fluorite + molybdenite + magnetite ± pyrite ± sericite ± siderite veinlets/veins with phyllic halos. Stage III consists of fluorite + siderite + quartz + molybdenite + pyrite ± ankerite ± calcite ± chalcopyrite veins that are commonly related to phyllic alteration and dissemination of fluorite in the altered rocks. Stage IV has an assemblage of fluorite + quartz + pyrite ± ankerite ± calcite ± molybdenite ± chalcopyrite ± sphalerite ± galena in coarse veins (10–20 mm wide). Stage V consists of narrow (≤5-mm wide) veinlets of calcite + fluorite + pyrite ± quartz. Molybdenite mainly occurs in Stages II and III. Re-Os dating results for molybdenite samples from these two stages yielded an isochron age of 156.2 ± 4.2 Ma (2 σ , MSWD = 0.96, n = 10). Most molybdenite samples have high δ 34S values (≥8.4‰) relative to other sulfide minerals (i.e., galena, sphalerite, pyrite, and chalcopyrite) of Stages II to V ( δ 34S = 2.5–8.3‰, n = 22). Molybdenite also has low 207Pb/204Pb and 208Pb/204Pb ratios relative to other sulfide minerals although there are minor overlaps. In a diagram of 206Pb/204Pb versus 207Pb/204Pb, these Pb isotope data display a positive trend transecting the growth curves of crustal lead, which could be invoked by mixing of crustal and mantle sources with distinct Pb isotopes. In combination with the S isotope data and mineral paragenesis, we suggest that magmas were the main source of molybdenum, whereas other metals (i.e., Pb, Zn, and Cu) were possibly sourced from the country rocks.

Fluid Inclusion and Isotopic Constraints on the Origin of the Paleoproterozoic Yinachang Fe-Cu-(REE) Deposit, Southwest China

Abstract: The Yinachang deposit in the Kangdian Fe-Cu metallogenic province, Southwest China, contains approximately 20 Mt ore @ 41.9 to 44.5 wt % Fe and 15 Mt ore @ 0.85 to 0.97 wt % Cu, with potentially significant REEs. Orebodies are hosted in the late Paleoproterozoic Dongchuan Group, and consist mainly of massive and banded replacement ores. The paragenetic sequence of this deposit includes pre-ore Na-(Fe) alteration (stage I), Fe-(REE) mineralization dominated by magnetite and siderite with subsidiary apatite and fluorite (stage II), and Cu-(REE) mineralization with chalcopyrite, ankerite, biotite, and subordinate apatite, fluorite, allanite, and synchysite (stage III). This sequence is similar to those of many iron oxide copper-gold (IOCG) deposits elsewhere. There are two distinct types of fluid inclusions within apatite of both stages II and III. Type 1 fluid inclusions with liquid and vapor phases have relatively low homogenization temperatures (98°–345°C) and salinities (4.7–16.2 wt % NaCl equiv), whereas type 2 fluid inclusions with one or more solid phases, a liquid phase, and a vapor phase have higher homogenization temperatures (273°–>500°C) and salinities (36.2–>59.8 wt % NaCl equiv). Fluids in sulfur isotope equilibrium with chalcopyrite of stages III have δ 34 S CDT values ranging from −2.8 to +2.7‰, consistent with a magmatic origin for the sulfur. Thus, sulfur isotopie compositions imply that magmatic-hydrothermal fluids, probably represented by the hot and saline type 2 fluid inclusions, were involved in the ore-forming process, although δ 34 S close to 0 might also mean that sulfur was leached from igneous rocks by nonmagmatic fluids. Siderite of stage II and ankerite of stage III have δ 13 C PDB values ranging from −12.4 to −7.5‰ and from −8.5 to −4.4‰, respectively. The large variation of δ 13 C PDB values reveals a strong interaction between the magmatic-hydrothermal fluids and the dolostone in the ore-hosting sequence. Calculated δ 18 O SMOW values of the fluids in stages II and III are broadly similar, and vary from 11.1 to 17.1‰ (avg = 13.5‰). Such values are higher than that of magmatic-hydrothermal fluids and thus, may indicate extensive fluid–wall-rock interaction and/or mixing of magmatic-hydrothermal fluids with shallow-level nonmagmatic fluids. This interpretation is consistent with the radiogenic Sr isotope compositions of bulk ores (( 87 Sr/ 86 Sr) i = 0.710404–0.734034) and fluorite separated from ores (( 87 Sr/ 86 Sr) i = 0.709851–0.723658). These nonmagmatic fluids are probably representative of the type 1 fluid inclusions. Bulk ores and mineral separates have ɛ Nd(t) values ranging from −8.1 to +0.4 (mostly −0.9 to +0.4), similar to the coeval mafic intrusions in the region (+2.0 to +2.8). This similarity suggests that REEs in the Yinachang deposit might have been derived dominantly from mantle-derived magmas. On the other hand, relatively low ɛ Nd(t) values (−5.5 and −8.1) of some samples indicate insignificant REE contributions from wall rocks. The Yinachang deposit is temporally associated with regional mantle-derived mafic magmatism, and may have a genetic relationship with it. Fluids derived from deep-seated magmas may have supplied abundant sulfur and carbon as well as some of the ore metals in this deposit. The mafic magmatism could also have provided heat to induce the shallow level nonmagmatic fluids to interact with the sedimentary-volcanic sequence, thus leaching additional ore metals into the ore-forming system. Fluid mixing can effectively trigger saturation and deposition of ore minerals. Our work highlights that nonmagmatic fluids are not a prerequisite for Cu-(Au-REE) mineralization, but may facilitate metal deposition in magmatic-hydrothermal IOCG systems.

Utilization of the Permian Coal Deposits of West Bokaro, India: A Petrochemical Evaluation

Abstract: In the present investigation an attempt has been made to study the petrographic and geochemical characteristics of coal deposits of West Bokaro coalfield of India. Coal samples were subjected to detailed petrographic and geochemical analyses. The results reveal that these coals are rich in vitrinite with significant concentration of inertinite and a meager amount of liptinite. The mineral matter is dominated by argillaceous matter (clay minerals, quartz, etc.) followed by carbonate (ankerite, siderite, calcite, etc.) and suplphides (mainly pyrite), which occurs in different forms, such as dispersed, cavity filling, fissure filling, as well as massive impregnation. The volatile matter (d.a.f. basis) and reflectance values (Rom) suggest these coals to be between high volatile bituminous type B to medium volatile bituminous in rank. These coals can be best used for blending to produce metallurgical coke. The petrochemical characteristics of these coals favor their use in gasification and hydrogenation.

Characteristics of uranium uptake of Boda Claystone Formation as the candidate host rock of high level radioactive waste repository in Hungary

Abstract: In Hungary two geological sites of the Boda Claystone Formation (BCF) located in the W-Mecsek mountains (South Hungary) have been selected for the study of potential host rocks for high level radioactive waste, Gorica (G) Block and W-Mecsek Anticline (WMA) Block. The aim of the study was to obtain information on the uranium uptake characteristics of both sites. Our results revealed that in the sample, taken from WMA Block, where dolomites have ankerite rims and U-bearing rings, newly formed FeOOH precipitations were observed, which partly replaced the ankerite at near neutral pH (6.8). UO2 2+ ions were adsorbed easily due to the enhanced specific surface area and high adsorption capacity of FeOOH formed from the dissolution of ankerite. The oxidation of Fe2+ leads to the formation of FeOOH parallel to partial reduction of U6+ to U4+. 75 % of uranium was taken up by clay minerals and 25 % by FeOOH although the ankerite concentration is as low as 6 % in WMA Block of BCF. In G Block, the argillaceous matrix was found to be mainly responsible for the UO2 2+ uptake. The study demonstrated that the U retention capacity of different BCF locations was significantly influenced by the mineralogy of these sites.

Experimental modeling of CO2-fluid-rock interaction: The evolution of the composition and properties of host rocks in the Baltic Region

Abstract: The objective of this study was to determine the influence of the possible CO2 geological storage in the Baltic Region on the composition and properties of host rocks to support more reliable petrophysical and geophysical models of CO2 plume. The geochemical, mineralogical, and petrophysical evolution of reservoir sandstones of Cambrian Series 3 Deimena Formation and transitional clayey carbonate caprocks of Lower Ordovician Zebre Formation from two offshore structures in Latvia and Lithuania and two onshore structures in Latvia, induced by laboratory-simulated CO2 geological storage, was studied for the first time in the Baltic Region. The geochemical, mineralogical, and petrophysical parameters were measured in 15 rock samples, before and after the alteration experiment. The diagenetic alterations of reservoir rocks were represented by carbonate cementation in the top of the onshore South Kandava structure, and quartz cementation and compaction, reducing the reservoir quality, in the deepest offshore E7 structure in Lithuania. The shallowest E6 structure offshore Latvia was least affected by diagenetic processes and had the best reservoir quality that was mainly preserved during the experiment. Carbonate cement was represented by calcite and ankerite in the transitional reservoir sandstones of very low initial permeability in the upper part of the South Kandava structure. Its dissolution caused a significant increase in the effective porosity and permeability of sandstones, a decrease in the weight of samples, bulk and matrix density, and P and S wave velocities, demonstrating short-term dissolution processes. Only slight geochemical changes occurred during the experiment in offshore reservoir sandstones. Minor dissolution of carbonate and clay cements, feldspar and some accessory minerals, and possible minor precipitation of pore-filling secondary minerals associated with slight variations in rock properties, demonstrating both short-term and long-term processes, were suggested. As a novelty, this research shows the relationship between diagenetic alterations of the Cambrian Series 3 Deimena Formation reservoir sandstones and their changes caused by the CO2 injection-like experiment.

Geology of the Fishtie deposit, Central Province, Zambia: iron oxide and copper mineralization in Nguba Group metasedimentary rocks

Abstract: The Fishtie copper deposit, located in the Central Province of Zambia, contains approximately 55 Mt of 1.04 % Cu at a 0.5 % Cu cut-off in oxide, sulfide, and mixed oxide–sulfide ores. The deposit is hosted in Neoproterozoic diamictites and siltstones of the Grand Conglomerat Formation and overlying Kakontwe Limestone Formation of the lower Nguba Group. The Grand Conglomerat Formation at Fishtie directly overlies basement schists and quartzites. Mineralized zones are located adjacent to high-angle normal faults that appear to control thickness variations in the Grand Conglomerat Formation suggesting synsedimentary fault movement. Iron-rich rocks consisting of nearly monomineralic bands of magnetite and ankerite occur within the Grand Conglomerat Formation. The absence of magnetite-rich clasts in overlying diamictites and the presence of disseminated magnetite, ankerite, and apatite in adjacent diamictites suggest this iron-rich rock formed by replacement of siltstone beds. These magnetite-rich rocks thicken towards normal faults suggesting the faults formed conduits for oxidized hydrothermal solutions. The magnetite–ankerite–quartz rock was overprinted by later hydrothermal alteration and sulfide mineralization. Copper sulfide precipitation was associated with growth of both muscovite and chlorite, together with weak silicification. Sulfides are zoned relative to normal faults with bornite more common in proximity to faults and ore stage pyrite most common in an outer zone with chalcopyrite. Copper sulfides display generally heavy sulfur isotopic values, suggesting sulfide derivation from thermochemical reduction of Neoproterozoic seawater sulfate. Copper mineralized zones in the Grand Conglomerat at Fishtie are megascopically similar to those observed in the newly discovered Kamoa deposit in the southern Democratic Republic of Congo. Alteration and mineralization at Fishtie display lateral zoning relative to normal faults unlike the broad vertical zonation observed at the giant Kamoa deposit. The small size of the known mineralized zones at the Fishtie deposit relative to Kamoa is probably due to the absence of a thick siliciclastic palaeoaquifer beneath the Grand Conglomerat Formation as is present at Kamoa.

Ankerite grains with dolomite cores: A diffusion chronometer for low- to medium-grade regionally metamorphosed clastic sediments

Abstract: Ankerite grains with dolomite cores occur in marls, pelites, and psammites from a Buchan terrain in Maine and a Barrovian terrain in Vermont (U.S.A.). Dolomite cores are typically ≤20 μm in diameter, have sharp but irregular contacts with ankerite, and have the same crystallographic orientation as ankerite rims. Ankerite grains with dolomite cores are common in the chlorite zone, less abundant in the biotite and garnet zones, and rare (Vermont) or absent (Maine) at higher grades. The texture and crystallographic orientation of dolomite and ankerite and the sharpness of the dolomite-ankerite contact are consistent with partial replacement of detrital dolomite by ankerite by solution-reprecipitation. Metamorphic biotite is in Fe-Mg exchange equilibrium with ankerite rims but not with dolomite cores, implying that ankerite did not form long after biotite (biotite has no phlogopite cores). Possible sources of iron for the formation of ankerite are reduction of ferric iron hydroxide or the smectite-to-illite reaction during diagenesis. The sharpness of the dolomite-ankerite contact is a diffusion chronometer that constrains timescales of metamorphic process. Relatively low spatial resolution analyses of Fe/Mg across the contact with a NanoSIMS instrument and a FEG TEM give upper bounds on the thickness of the transition from ankerite to dolomite of ~2 and ~0.5 μm, respectively. Higher resolution analysis of BSE grayscale contrast with a FEG SEM gives a thickness ~100 nm. Fit of the grayscale profile to a model of one-dimensional diffusion across an infinite plane gives Dt = 10^(−15) m^2 (± a factor of 5), where D is the effective Fe-Mg interdiffusion coefficient and t is the duration of diffusion. Using the published experimental determination of D, upper bounds on the residence time of ankerite grains with dolomite cores at peak T = 400–500 °C, on the duration of linear cooling from peak T to 100 °C, and on the duration of linear heating from 100 °C to peak T followed by linear cooling to 100 °C are all 100 °C. The question is what explains the occurrence of ultrasteep composition gradients between dolomite and ankerite. Regional metamorphism on a timescale of a year or less is unrealistic. No barrier to diffusion at the dolomite-ankerite contact was observed in TEM images. Post-metamorphic formation of ankerite at very low temperature is ruled out by Fe-Mg exchange equilibrium between biotite and ankerite but not dolomite. It is unlikely that the steep composition gradients were preserved by intracrystalline pressure gradients. Alternatively, the steep composition gradients would be consistent with timescales of metamorphic process ~10^6 years or longer if D values during metamorphism were approximately six orders of magnitude or more smaller than those measured in the laboratory. The error of measurement is much less, approximately ± a factor of 2. A correction to D for the difference in P between measurements (0.1 MPa) and metamorphism (350–800 MPa) is likely an order of magnitude or less. Oxygen activity (a_(O2)), however, was 17–20 orders of magnitude larger during the laboratory measurements than during metamorphism. A correction to measured D for the difference in a_(O2_ between experiment and metamorphism appears to be the likeliest way to reconcile the steep composition gradients with realistic timescales of metamorphism. Before ankerite grains with dolomite cores are fully realized as a useful diffusion chronometer for low- and medium-grade metamorphic rocks, the rates of Fe-Mg interdiffusion in ankerite and dolomite need to be calibrated as a function of a_(O2).

Will mercury impurities impact CO2 injectivity in deep sedimentary formations? II. Mineral dissolution and precipitation

Abstract: Numerical simulations of carbon dioxide (CO2) injection into a sandstone reservoir (∼2 km depth) were used to investigate the geochemical effects of trace amounts of mercury (Hg, 7 and 190 ppbV), with and without hydrogen sulfide (H2S, 200 ppm). Geochemical reaction-path modeling shows that cinnabar precipitates as soon as the Hg-bearing CO2 reacts with the formation. Mercury does not condense to liquid, and the net volume change from mineral dissolution and precipitation is found to be negligible. Two-dimensional radial reactive transport simulations of CO2 injection at a rate of 14.5 kg/s (∼0.5 Mt/y) into a 400-m-thick formation at 106°C and 215 bar, with varying amounts of Hg and H2S, show that porosity changes only by about ±0.05% absolute (i.e., new porosity% = initial porosity% ±0.05), and that Hg readily precipitates as cinnabar in a zone mostly coinciding with the single-phase CO2 plume. This essentially negligible porosity change is not expected to affect permeability and CO2 injectivity. The precipitation of minerals other than cinnabar dominates the evolution of porosity. Although the predicted porosity change is small, the dissolution and precipitation predicted for individual minerals is not negligible. The main reactions include the replacement of primarily Fe-chlorite by siderite, of calcite by dolomite, and of K-feldspar by muscovite. Chalcedony is also predicted to precipitate from the dissolution of feldspars. Except for some replacement of pyrite by ankerite when H2S is deficient, the cases with and without H2S show similar results. Experimental measurements are needed to decrease uncertainty in simulation results.

Carbonates reactivity in temperature and interactions with Fe- minerals

Abstract: The carbonate system is the one of most reactive in the mineralogical assemblages of clay-rocks. Consequently, pristine clay-rocks pore water compositions are expected to be at equilibrium with carbonate minerals. However, it is difficult to fully reconcile the concentration data obtained from seepage water sampled in equipped in situ boreholeswith the equilibrium concentrations obtained from pore water modeling (Pearson et al., 2011). It is especially true for dolomite whose solubility spans a large range of values in thermodynamic database as a function of crystallinity considerations, and for siderite/ankerite or other Fe-bearing carbonates whose compositions influence their solubility. The understanding of the carbonate system in clay-rock is necessary for a number of predictions including the effect of an increase of temperature on the pore water chemistry. In this respect, experiments were conducted to study the kinetics of equilibration of carbonate mineral assemblages as a function of temperature (25-80°C) in chemical conditions otherwise similar to those encountered in the Callovian-Oxfordian clay-rock.

Ipari CO2 tárolásra alkalmas hazai üledékes kőzetek petrográfiai vizsgálata és a rendszerben várható geokémiai változások modellezése

Abstract: Sub-surface storage of CO2 in saline aquifers is considered as a potential solution to reduce the atmospheric concentration of CO2. Moreover, CO2 is used as a working fluid in EOR and EGR (enhanced oil and gas recovery) activities. To ensure the long-term stability of the geologically trapped CO2, behavior of the CO2‒reservoir rock‒pore water system should be predictable on geological timescales. To obtain a realistic picture about the geochemical behavior of a potential CO2 storage system in Hungary, I developed batch kinetic geochemical models with PHREEQC using measured pore water composition and mineral composition of the possible CO2 reservoir rocks, which are fine-grained sandy turbidites interlayered by thin argillaceous beds and formed during the Late Miocene in the deepest part of the subsiding Pannonian Basin. In the present work particular attention was given to the reservoir mineralogy because the mineralogical composition of the reservoir rocks may significantly affect the geochemical changes that are taking place as the effect of injected CO2. Eight sandstone and six argillaceous core samples were studied in detail with polarization and scanning electron microscopy (SEM), X-ray diffraction (XRD), attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) and laser scattering particle size distribution analysis. The main detrital components of the samples are quartz, mica, K-feldspar and plagioclase, sedimentary and metamorphic rock fragments (dolomite, limestone and quartzite). Furthermore, authigenic mineral phases are mostly carbonates (Fe-calcite, Fe-dolomite, ankerite and siderite), clay minerals (kaolinite, illite), quartz cement, and minor amount of albite, pyrite and barite cements. Ankerite commonly occurs as overgrowth on detrital dolomite grains. Accessory minerals are apatite, rutile/anatase, zircon, glauconite and tourmaline. The results of the geochemical models show that pH of the pore water drops rapidly after the CO2 injection and causes fast dissolution of primary carbonates and slow dissolution of silicate minerals such as albite, K-feldspar and illite after 100 years. As a result of these reactions, the slow increase of pH and precipitation of secondary phases (quartz, kaolinite and carbonates) can be observed. As the effect of CO2, the results of the models suggest the precipitation of a new mineral phase, namely dawsonite (NaAlCO3(OH)2), furthermore, indicate that the formation of this mineral is related to the dissolution of albite (NaAlSi3O8). This newly formed mineral phase consumes significant amount of CO2 in solid phase, therefore supports the safe storage. The estimated maximum amount of dawsonite, that can be formed from the given primary rock composition is 3-4 v/v% based on the models, which is in agreement with previous observations from a natural CO2 occurrence in Hungary (Mihalyi-Repcelak area in the Little Hungarian Plain) deposited in the same geological facies. As a consequence of the dissolution and precipitation of different mineral phases during the modelled time period, the models indicate an early (<100 years) increase of porosity, followed by its reduction after 100 years. Sensitivity analyses of the models were carried out by changing the CO2 partial pressure, the temperature, the specific surface area of the minerals, and the water-rock ratio. The results show that the lower are the temperature and the specific surface area of the minerals, the slower are the dissolution and precipitation reactions. The models are less sensitive to pressure compared to temperature sensitivity simulation results. An additional sensitivity analysis was made based on petrographic observations that dolomite grains are generally covered by ankerite overgrowth. Therefore, it was assumed that dolomite cannot react with the CO2 saturated pore water, because of the absence of direct contact with the pores. In this case, there was no significant change in the reactivity of silicate minerals and dawsonite, but differences were observed in the carbonate minerals’ reactions. Contrary to the basic models where dolomite was precipitated during the simulation, the result of the sensitivity analysis indicates ankerite precipitation. This outcome may be more realistic compared with the observations of several natural CO2 occurrences, where besides the formation of dawsonite, generally quartz, kaolinite and ankerite precipitation were described. The result of this sensitivity analysis draws attention to the fact that taking into account the textural position of different mineral phases may affect the forecasted mineral reactions caused by CO2 in the reservoirs. Therefore, besides the analytical measurements (e.g. XRD), detailed microscopic analyses are indispensable to build more realistic models.

Some New Opinions concerning the Genesis of the Lacustrine Hydrothermal Deposits in Wudaoliang Group, Eastern Hoh Xil Basin

Abstract: Located in Hoh Xil basin in the north of the Tibetan Plateau, Wudaoliang area possesses a lot of carbonate deposits. The authors studied the mineralogy and element geochemistry of the sediments from the south and north sections of Wudaoliang. The main mineral is calcite with a small amount of quartz in the north sections, while there are ankerite, calcite, quartz and albite in south section. According to the discovery of ankerite and secondary enlarged pore-fringes in albite, the authors hold that Wudaoliang area was affected by hydrothermal activity. The characteristic elements such as As, Sb, Ba, Fe, and the ratios like Ni/Co, Mn, Sr/Cr, V, V/Sc are relatively high. The REE patterns and the carbon and oxygen isotope characteristics also indicate the hydrothermal activities. The emergence of the laminated algae also reflects the water temperature of at least 20 to 30℃. The results obtained by the authors suggest that the Wudaoliang Group is lacustrine hydrothermal sediments. In addition, a large number of volcanic rocks were developed in Miocene, which can be used as the important clues to finding the volcano-sedimentary boron deposits.

Characteristics of diagenesis, isotopic relations and reservoir properties of the Middle Miocene sandstones in the Carpathian Foredeep (Poland and Ukraine)

Abstract: The Upper Badenian and Sarmatian sandstones recognized from boreholes in southeastern Poland and western Ukraine are very fine to medium-grained subarkosic and sublithic arenites and wackes. The deposits underwent diagenesis well below 100°C, and their evolutionary pathways of diagenetic and related reservoir properties represent eo- and mesodiagenesis. Eodiagenesis here comprised mechanical compaction, development of chlorite, microcrystalline calcite, pyrite, siderite, kaolinite and quartz, and dissolution of feldspar and mica grains. Mesodiagenesis included quartz and K-feldspar overgrowths, albitisation, crystallisation of dolomite and ankerite and coarsely crystalline calcite, dissolution of feldspar grains and carbonate cement, and illite growth. The isotopic data of δ 18 O VPDB of carbonate cements suggest their crystallisation from porewater which is a mixture of marine and meteoric waters. The δ 13 C VPDB values suggest derivation of carbon from microbial methanogenesis of organic matter. The 87 Sr/ 86 Sr values in coarsely crystalline calcite are higher than those of Badenian seawater. The radiogenic strontium may have been supplied during diagenesis by meteoric waters draining the continental area. The Middle Miocene sandstones show better filtration abilities (good and very good) in the western part of the study area (Poland) than in the east. Primary intergranular porosity is more frequent than secondary intragranular and intercrystalline porosities.The primary porosity was diminished due to compaction and cementation from west to east. Some increase in porosity was caused by dissolution of detrital grains and by decay of soft parts of organisms.

Study of opaque phases in carbonatites of the Grønnedal-Íka alkaline complex, Southwest Greenland

Abstract: Opaque phases from carbonatites of the Gronnedal-Ika alkaline complex (1299±17 Ma) of Southwest Greenland were analyzed in terms of their mineralogy and microstructure. The analysis demonstrates that a later intrusion by a 55 m wide dolerite dyke of unknown age has prompted the mineralization of magnetite by activating hydrothermal fluid convection. The fluid has interacted with the carbonatite, replacing siderite and ankerite by magnetite, which at places constitutes over half of the rock volume. Magnetite is shown to have become partly replaced by hematite at a later stage. A paragenetic sequence is suggested for the opaque phases that com- prise major magnetite and hematite, accessory pyrite and trace amounts of sphalerite, chalcopyrite and galena.

Thermodynamic Modelling of Geo-Biometallurgical Oxidation of Sulfide Ores

Abstract: Heap bioleaching of sulfide ores (geotechnology) simulates naturally occurring processes when sulfides convert to oxides. This process is environmentally-friendly. Gold-bearing sulfide ore from a Russian deposit was studied. The samples were composed of quartz (38-48%), feldspars (22-24%) and micaceous minerals (18-21%). Carbonates occurred as ankerite, calcite, dolomite and siderite. The host minerals were pyrite (2.2-2.3%) and arsenopyrite (1.2-1/7%). The grade of gold was 1.6-2.0 g/t. Russian software package Selector was used to develop the model. Thermodynamics of the reaction pathway for the conversion of the gold-bearing sulfide ore in H2SO4 environment with and without using bacteria was calculated. Phases and their components which are able to form in these given conditions were selected during modeling. Modeling of irreversible evolution of the rocks caused by bacteria was carried out in the three reservoir system. They are interconnected by the flows of three movable phases: gases, solid phase and liquid phase. In this case, the composition of the solutions which were obtained under steady state conditions without bacteria and metastable equilibrium using bacteria can be compared. Bacterial oxidation occurs under acidic conditions. Oxidation without using bacteria occurs under more alkaline conditions. Bacteria increase the rate of sulfides oxidation and retard the formation of mixed-layer aluminum silicates (illites, montmorillomonites) and carbonates (magnesian calcite). It was found that bacteria have the potential to achieve the required destruction of sulfides in favorable environment. Bacteria make the rate of sulfide oxidation higher. In the presence of bacteria, the rate of aluminosilicates oxidation is slower compared to the conditions without using bacteria. Mineralogical analyses of the leach products confirmed this. Results show that thermodynamic approach can be successfully used for the modeling of bacterial-oxidation circuits and geology of the rocks and ores.

Rietveld Structure Refinement of the Stibnite Crystals from Herja (Romania) using X-ray Powder Diffraction Data

Abstract: The Herja area is located between Chiuzbaia Valley and Firiza Valley, about 5km NW of Baia Sprie town. From geological point of view the Herja perimeter belongs to the Neogene vulcanite zone of Eastern Carpathians, locally being situated in the Gutâi Mountains. The Herja ore deposit belongs to the Baia Mare Neogene metallogenetic district and is associated to a complex stock of Pannonian age [1]. In the Herja area are known sedimentary tertiary and Neogene magmatic formations. The sedimentary formations belong to the Eocene, Sarmatian and Pannonian. The Neogene magmatites are represented by volcanic products and by intrusive bodies. The volcanic products are represented by lava flows and subordinately, pyroclastic rocks. The vulcanites are represented by pyroxene and quartz andesites [1]. This ore deposit represented by hydrothermal veins oriented NE-SW, is located in andesitic eruptions from the Neogene period. The polymetallic mineralized veins contains a wide variety of metallic minerals: sphalerite, galena, pyrite, pyrrhotite, stibnite, chalcopyrite, arsenopyrite, jamesonite, tetrahedrite, semseyite, and nonmetallic minerals: quartz, siderite, ankerite, calcite, gypsum, baryte and vivianite. The hydrothermal veins show different types of structures: massive, rubanate, brecciated and concentric [2].

Diageneza a porowatość piaskowców jury dolnej na niżu polskim

Abstract: DIAGENESIS AND POROSITY OF THE LOWER JURASSIC SANDSTONES IN THE POLISH LOWLANDS Abstract. Sandstones from the boreholes located in Szczecin–Radom area have been subjected to petrographic and petrophysical analysis. Sandstones are represented mostly by quartz arenites and wacks, from very fine- to middle-grained. The main type of cements are matrix and cements, among which quartz, carbonates, clay minerals and locally pyrite were distinguished. Quartz cement occurring as syntaxial overgrowths developed on the quartz grains displays the greatest significance in the Lower Jurassic sandstones. Authigenic clay minerals are represented mainly by vermiform kaolinite. Authigenic illite and Fe/Mg chlorites are locally observed. Carbonate cements are represented mainly by early and late generation of siderite (mineral of series of siderite–magnesite). The early diagenetic siderite represented by siderite and sideroplesite is predominant. The siderite δ 18 C values are in the range from –24.50 to –4.56‰ PDB and δ 13 O values range from –14.37 to –0.33‰ PDB . The late siderite of pistomesite and sideroplesite chemical composition also occurs, but occasionally. Furthermore, there are Fe-dolomite/ankerite and occasionally calcite. The Jurassic sandstones are characterized by very good and good filtration properties. The primary porosity is dominant, it often exceeds 20%, and permeability is in the range of 0.001 to 1930.756 mD. The most important diagenetic processes operating in the sandstones are: compaction, cementation and dissolution. Compaction reduced primary porosity on average by about 30%, and cementation by about 21%.

Mineral Reconstruction Model for Spectroscopy Logging Data

Abstract: With the deepening of the unconventional reservoir exploration, formation lithology evaluation is becoming more and more difficult, because in addition to the common minerals such as quartz, calcite, illite, some special minerals like pyrite, gypsum, dolomite, ankerite can also been seen. However, conventional well logging curves are difficult to identify these complex minerals. Spectroscopy tool, such as Element Capture Spectroscopy tool (ECS) can measure the capture spectrums of the main elements in formation such as silicon, calcium, iron, sulfur, and then the absolute contents of different minerals can be derived. This provides a new train of thought for unconventional reservoir lithology evaluation. But if feldspar, chlorite, dolomite, pyrite minerals are rich in the formation, default outputs from ECS will differ from core analysis results greatly. Based on a certain amount of core samples, this study analyzed the absolute contents of elements and minerals, and established the suitable complex mineral reconstruction model for the target formation in K block, and laid a solid foundation for tight sand mineral evaluation and reservoir evaluation. KeywordsElement Capture Spectroscopy; Mineral reconstruction model; Core analysis; Dual Range Fourier Transform Infrared Spectroscopy; Complex Lithology