Hasil untuk "Petrology"

Elahe Kamel Targhi, Mohammad Emami Niri, Mohammad Reza Rasaei et al.

Abstract This study addresses the critical challenge of excessive water production in mature oil and gas reservoirs. It focuses on the effectiveness of polymer gel injection into porous media as a solution, with an emphasis on understanding its impact at the pore scale. A step-wise Lattice Boltzmann Method (LBM) is employed to simulate polymer gel injection into a 2D Berea sample, representing a realistic porous media. The non-Newtonian, time-dependent characteristics of polymer gel fluid necessitate this detailed pore-scale analysis. Validation of the simulation results is conducted at each procedural step. The study reveals that the methodology is successful in predicting the effect of polymer gel on reducing permeability as the gel was mainly formed in relatively larger pores, as it is desirable for controlling water cut. Mathematical model presented in this study accurately predicts permeability reductions up to 100% (complete blockage). In addition, simulations conducted over a wide range of gelation parameters, TD_factor from 1 to 1.14 and Threshold between 0.55 and 0.95, revealed a quadratic relationship between permeability reduction and these parameters. The result of this research indicates LBM can be considered as promising tool for investigating time-dependant fluids on porous media.

Pedro Esteves Aranha, Nara Angelica Policarpo, Marcio Augusto Sampaio

Abstract Predicting oil well behavior regarding the integrity of its equipment during production and anticipating behavioral changes and anomalies are among the main challenges in oil production. In this context, this study focuses on the development of predictive models for real-time monitoring of well behavior using sensor data from production wells. An unsupervised Novelty and Outlier Detection model has been introduced with a specific focus on predicting instances of unexpected subsurface safety valve closures in subsea wells. This model effectively classifies anomalies observed in these systems by leveraging real-world pressure and temperature data sourced from published literature. The methodology involves the implementation of a floating window for assembling training and test sets. Additionally, a comprehensive investigation is conducted into the impact of hyperparameters and the model’s threshold value (cp threshold). The results highlight the effectiveness of the developed model, observed through the accuracy achieved around 99.9% in predicting spurious closure events of the Downhole Safety Valve. On the same dataset, previous works reported 99.9% accuracy by using long short-term memory (LSTM) autoencoder, 87.1% by using random forest, and 60% with the Decision Tree method. Looking at F1-SCORE values, the developed model performs the best, followed by the LSTM model, both of which are significantly superior to the Decision Tree and random forest models. Furthermore, the model’s applicability is validated through testing in ultradeep water subsea wells within the pre-salt area of the Santos Basin. The significance lies in the potential for this research to enhance anomaly prediction in offshore wells, consequently reducing the costly interventions due to equipment malfunctions. Timely detection and corrective actions, facilitated by the model, can mitigate production loss and safeguard well integrity, addressing critical concerns in the oil and gas industry.

Tatiana A. Mingaleva, Sergey V. Shakuro, Natalia P. Senchina et al.

The information on geological structure as well as on the degree of contamination and geometrical parameters of a pollutant in oil-contaminated areas is necessary for risk assessment, planning of oil products recovery and territory remediation. Geophysical methods are actively used for solving such problems. The work considers the site on the Volga River bank, where soils are contaminated with petroleum products. The aim of the work is to delineate the distribution area of petroleum products. In order to achieve the goal, the set of near-surface geophysical methods (vertical electric sounding, seismic survey) and gas geochemistry were implemented. The results of a new approach to characterization of contaminated sites by RGB-data synthesis have been demonstrated as one of the ways of data interpretation. The method is based on the generalization of the available materials by optically mixing of the data of three spatially distributed characteristics presented in the form of three channels – red, green, and blue – for the purpose of localizing the lenses of gravity-mobile and immobilized oil products. According to the results of the qualitative interpretation of geophysical information, the authors have built a scheme with the proposed contour of oil products distribution in the studied territory. The proposed method can be used for the delineation of oil spills along with the sufficient information obtained by geophysical or other methods (at least three) at the stage of determining the spread of contamination for the sites. This approach can speed up the interpretation process, as such maps overlaying sets the color distribution of different petrophysical characteristics of the soils for the selected depth level, and also eases the task of determination of coordinates when correlating various anomalies, identified by different methods.

Astrid Švara, Andrej Mihevc, Nadja Zupan Hajna

So far, the longest known unroofed cave in Slovenia has been found on the Slavinski ravnik, southwest of Postojna. From its position on the surface, its shape, and its containing sediments, we can infer its spatial and temporal development, as well as the processes and evolution of the contact karst in its hinterland. The corrosional plain Slavinski ravnik is a small area of the Dinaric Karst in Slovenia, located at the contact between impermeable flysch and karstified carbonate rocks, where many contact karst features formed. Due to erosion, multi-phase regional tectonic uplift, and sedimentation, a paragenetic cave system, active and relict blind valleys have formed. During the geomorphological mapping, elements were examined and drawn using ESRI ArcMap and Golden Software Surfer, and the stages of their formation were observed. During the survey, the active cave system Markov spodmol and Vodna jama v Lozi, the relict unroofed cave Brezstropa jama v Lozi, Biščevci blind valley, Sajevško polje blind valley, Ivačevci blind valley, and Sajevško polje sediment accumulation were studied. The changing hydrological regime, the allogenic sediments, the distribution of active and relict ponors, and the placement of active and relict elements of these contact karst forms, show different stages of formation and subsequent development of the northern border of Slavinski ravnik. The geomorphological map of these contact karst features and their following studies give us an insight into the morphogenesis of the southern karst periphery of the Postojna Basin as an exceptional - relatively small but highly variable Slovenian contact karst site.

Piyaphong Chenrai, Piyaphong Chenrai, Piyaphong Chenrai et al.

The main carbon dioxide (CO2) emissions in Thailand come from the energy sector. Gas-based power plants, including natural gas and biogas, are CO2 point sources, and are mostly located in the Khorat Plateau. Geological CO2 storage is an important element in the effort to reduce CO2 emissions from CO2 point sources. This study is a preliminary assessment of the geological CO2 storage potential of the onshore Khorat Plateau. A potential geological formation is screened and ranked in terms of its suitability as a CO2 storage site (storage optimization, risk minimization and feasibility). The results of this screening and ranking indicate that, among the tested sites in this study, the Khorat Permian carbonate is the most suitable for geological CO2 storage, followed by the Khorat Group sandstone, and Khorat evaporite. However, the Khorat Cenozoic basalts are not suitable for geological CO2 storage in the Khorat Plateau. The results from this study should advance the understanding of petroleum exploration and carbon capture and storage technology in Thailand, especially in the Khorat area. However, it should be noted that more subsurface studies are needed, and more criteria should be included in the future to improve the reliability of the assessment of geological CO2 storage potential in the Khorat Plateau.

Amir Shokry, Ahmed Elgibaly, Adel Salem

Abstract A high-quality wellbore is generally considered to have a gauge hole, a smooth wellbore and a wellbore with minimum tortuosity. Therefore, dog leg reamers (DLRs) have been recently proposed and implemented to specifically provide a high-quality wellbore which in turn improves the overall drilling performance. These improvements include smoothening the wellbore from high in place dogleg, lowering drag values, improving the tripping performance, increasing the success ratio of wireline logging tools to reach total depths and enhancing the casing and cement jobs. DLRs are an eccentric string reamers which have been recently designed and optimized using modelling software, and a mathematical model has been deduced to specify the weight and torque distribution between the bit and DLR based on mechanical specific energies at bit and DLR with a model accuracy closely matches the field data. A total of twenty five runs all over the world have been performed to date in hole sizes ranging from 12¼″ to 6″. Directional work has also been performed showing good directional control with this system, and no vibration issues have been reported. The development of this down hole tool has added new capability to the industry in the optimization of hole enlargement applications. The benefit is realized in a reduced number of days required to drill the well and in reduced total well cost. In addition, getting casing into the hole sooner reduces the accompanying risks and can contribute to reducing operational nonproductive time. Several case studies from three fields X, Y and Z from Egypt, Oman and Saudi Arabia, respectively, will be discussed to demonstrate the positive economic impact of deploying DLR in not only the deviated holes but also in vertical wells.

Dalmo S. Amorim, Otto L.A. Santos, Ricardo C. Azevedo et al.

Abstract This article proposes a novel methodology to solve an existing gap in benchmark definition by the adoption of statistically defined benchmarks as references to test products or technical procedures. In a win–win partnership, remuneration is made upon realistic bases of comparison being proportional to existing risks. However, establishing values for benchmarks is rarely unanimous if asked to different persons involved in drilling analysis. Conventional benchmarking, which enhances few results and leaves aside poor operational performances, produces references that do not properly represent the geological environment. Nonetheless, when testing new products, it serves as reference to remunerate suppliers. The review of an optimization program, which resulted in a world record of drilling rate of penetration, reveals the financial magnitude of the savings produced, proposing the method discussed as a reliable solution to the development of technology.

Mohsen Mobasheri, Habibollah Ghasemi, Behnam Rahimi et al.

Introduction The Mashhad- Virani complex has been sandwiched between the collided Lut block and Turan plate. This complex is composed of the following four units: 1) ultramafic-mafic rocks, 2) metamorphosed sedimentary rocks, 3) pyroclastic rocks and 4) Mashhad’s granitoids including quartz-diorite, tonalite, granodiorite and monzogranite (interpreted as granitoids formed in an arc regime during the subduction of the Paleo-Tethys Ocean under the Turan Plate by Karimpour et. al., 2011). The association rocks in the Mashhad-Virani complex have experienced varying degrees of hydrothermal alteration and regional metamorphism. These rocks are typically metamorphosed in lower to upper green-schist facies, but rarely to pyroxene hornfels facies along the contacts with the Mashhad granitoids. Researchers have challenging ideas on the nature of these rocks. Firstly, Majidi (1981) reported the komatiitic nature of these rocks. However, most of the geologists believed that these rocks are a part of an ideal ophiolitic sequence (Alavi, 1979; Fazel-Valipour, 2002). However, some geological studies have provided strong evidence that contradicts the ophiolite nature of these ultramafic- mafic rocks. Detailed studies of this research show that according to the petrological issues, field relationships, textures and internal stratigraphy, these rocks are not only an ophiolitic sequence but are also an ultramafic- mafic volcanics precisely named komatiite. In this complex, although the contact of the ultramafic rocks with the adjacent sediments is not visible in the majority of cases due to the coverage of Quaternary sediments and tectonic processes. However, this contact is partly preserved in the Khurshid Park and Zuh peak where there is some evidence of ultramafic lava eruption on the sediments. In these places, sediments in the border with komatiitic rocks has been clearly baked. They also have very interesting skeletal, microspinifex, and harrisite textures. These observations suggest that the ultramafic rocks in the Mashhad-Virani complex are ultramafic volcanic flows. Materials and Methods Field studies have been carried out in more than twenty cross sections in the southwest-northwest of Mashhad. More than 400 thin and polished sections were made from rock samples and studied in the petrography laboratory of the Faculty of Earth Sciences at the Shahrood University of Technology. Moreover, after detailed petrography studies, five samples with the least alteration were selected for preparing polished thin sections. Major element analyses on selected minerals (amphibole, plagioclase, pyroxene and olivine) were performed on a JEOL EPMA JXA-8900R electron microprobe at the Institute of Earth Sciences, Academia Sinica, Taiwan. Analytical conditions included an accelerating voltage of 15 kV, a beam current with 2μm diameter of 12nA and counting times of 10s on peaks and 5s on the background. For calibration of all elements, a set of mineral and synthetic standards has been used. Discussion The Mashhad-Virani complex includes an assemblage of ultramafic-mafic rocks with approximate length of 32km along the western side of the city of Mashhad. This complex consists of dunite, ortho- meso and crescumulate (harrisite) wherlite, clinopyroxenite, cumulative and noncumulative amphibole gabbro and differentiated- undifferentiated komatiitic flows. These komatiites have been shown with a wide range of textures such as random acicular pyroxene, hopper and chevron olivine, hopper pyroxene, skeletal olivine, skeletal pyroxene, micrographic intergrowth of plagioclase and clinopyroxene, dendritic pyroxene, olivine harrisitic, olivine orthocumulate, olivine mesocumulate, and olivine adcumulate textures. The rate of cooling and thermal gradient in the volcanic rocks along with super-saturation, exsolution of volatiles and magma mixing in the sub-volcanic rocks are the most important controlling factors in creation of these disequilibrium textures. Amphibole gabbro sills are one of the main magmatic units of the upper parts of the lower horizons in the Mashhad-Virani complex. After detailed petrographical studies, five samples were analyzed for mineral chemistry measurements. In this study, only the composition of clinopyroxenes has been used for thermobarometry studies. Based on the obtained results, the clinopyroxenes are in the range of Ca-Mg-Fe sub-types in the Q-J diagram and in the diopside to augite fields on the Wo-En-Fs ternary diagram (Morimoto et. al., 1988). The results of the thermo-barometeric calculations by single clinopyroxene method indicate mean temperature of 1222°C and pressure of 2.4 kb that are in concord with the dyke and sill forms of gabbroic outcrops and also are very close to the crystallization temperatures of these magma types. Results Skeletal, spinifex and harrisite textures are the first unequivocal evidences reported from komatiitic sills and lava flows in the Mashhad-Virani Complex. These rocks are a part of the upper Paleozoic volcano-sedimentary sequence with approximately 32km length with NW-SE trend in the South and Southwest of Mashhad. This complex consists of dunite, ortho- meso and crescumulate (harrisite) wherlite, clinopyroxenite, cumulative and noncumulative amphibole gabbro and differentiated- undifferentiated komatiite flows. Application of the thermobarometry calculations on the single clinopyroxene from the amphibole gabbros (average pressure of 2.4 kb and average temperature of 1222 °C) are highly acceptable and consistent with the field and petrographic evidences. Acknowledgments The authors are most grateful to the vice chancellor of research at the Shahrood University of Technology for their financial and spiritual supports of this research. References Alavi, M., 1979. The Virani ophiolite complex and surrounding rocks. Geologisch Rundschau, 68(1): 334–341. Fazel-valipour, M.E., 2002. Petrography, petrology of mafic-ultramafic rocks of Mashhad. Ph.D. Thesis, Islamic Azad University, Science and Research Branch, Tehran, Iran, 174 pp. (in Persian) Karimpour, M.H., Farmer, G.L. and Stern, C.R., 2011. Rb–Sr and Sm–Nd Isotopic Compositions, U-Pb Age and Petrogenesis of Khajeh Mourad Paleo-Tethys Leucogranite, Mashhad, Iran. Scientific Quarterly Journal Geosciences, 20(80): 171–182. (in Persian) Majidi, B., 1981. The ultrabasic lava flows of Mashhad, NE Iran. Geological Magazine, 118(1): 49–58. Morimoto, N., Fabrise, J., Ferguson, A., Ginzburg, I.V., Ross, M., Seifert, F.A., Zussman, J., Akoi, K. and Gottardi G., 1988. Nomenclature of pyroxenes. American Mineralogist, 173(9–10): 1123–1133.

Shan e Zehra Lashari, Ali Takbiri-Borujeni, Ebrahim Fathi et al.

Abstract Drilling performance monitoring and optimization are crucial in increasing the overall NPV of an oil and gas project. Even after rigorous planning, drilling phase of any project can be hindered by unanticipated problems, such as bit balling. The objective of this paper is to implement artificial intelligence technique to develop a smart model for more accurate and robust real-time drilling performance monitoring and optimization. For this purpose, the back propagation, feed forward neural network model was developed to predict rate of penetration (ROP) using different input parameters such as weight on bit, rotations per minute, mud flow (GPM) and differential pressures. The heavy hitter features identification and dimensionality reduction are performed to understand the impacts of each of the drilling parameters on ROP. This will be used to optimize the input parameters for model development and validation and performing the operation optimization when bit is underperforming. The model is first developed based on the drilling experiments performed in the laboratory and then extended to field applications. From both laboratory and field test data provided, we have proved that the data-driven model built using multilayer perceptron technique can be successfully used for drilling performance monitoring and optimization, especially identifying the bit malfunction or failure, i.e., bit balling. We have shown that the ROP has complex relationship with other drilling variables which cannot be captured using conventional statistical approaches or from different empirical models. The data-driven approach combined with statistical regression analysis provides better understanding of relationship between variables and prediction of ROP.

Saeed Parvizi Ghaleh, Ali Kordavani

Abstract Thinly bedded and laminated shale-sand sequences are very common in most of the producing formations in Iran. Historically, traditionally well logging methods such as conventional resistivity measurement is employed to evaluate pay intervals in order to extract information about hydrocarbon saturation. However, there is the practical matter of resolution of these methods to detect thin laminated shaly sand layers. In order to cope with this limitation, other technique such as: high-resolution method should be utilized. For doing this method, we receive low-resolution logs and a high-resolution log from a well logging tool that is disposed in a wellbore which has laminated shaly sand layers. Firstly, square log is produced then these logs are convolved with vertical response function of well logging tools to generate constructed log. The constructed logs are compared with low-resolution logs, if these two logs are matched we choose that square logs as optimum square logs and analyze them. But if these two logs do not match, the square logs undergo interactive refinement then these refined logs are subsequently convolved with a vertical response function of the well logging tool thereby producing a constructed log. Then these constructed logs compare with low-resolution logs. This work repeated until these logs are matched and the optimum square logs are chosen. High-resolution square log method is an iterative method, time consuming and also has very mathematical calculations because we developed a computer program with MATLAB software which can do all these works with high accuracy and low time.

Chidozie Izuchukwu Princeton Dim, Ayonma Wilfred Mode, Ikenna Christopher Okwara

Abstract Although several works have proved the existence of oil and gas in the Campanian to Maastrichtian strata of the Anambra Basin, it is still considered a frontier basin due to the challenges associated with interpretation of stratigraphy and structure arising from non-availability of subsurface data. This has led to poor understanding of the petroleum system and hindered exploration activity within the basin. This research paper aims to discuss the signatures of essential petroleum system elements, based on the study of high-quality outcrop examples. Detailed field studies reveal the presence of source, reservoir and seal rocks, and traps exposed within the four lithostratigraphic units outcropping in the basin, across the southeastern part of Nigeria. The shales of Enugu Formation, offer good source rocks. The shales, coals, coaly shales and sandstones with repeated occurrence of shale–silt–sand heteroliths of the Mamu Formation provide possible source and reservoir rocks. Thick extensive sandstones with clay laminae of the Ajali Formation offer potential reservoir that are partly compartmentalized. The shales with interstratified sandstone of the Nsukka Formation provide potential cap and overburden rocks. The presence of anastomosing fracture bands, extensional joints and faults, small-scale growth faults, and rollover anticlinal structures are good evidence of structural and stratigraphic configuration that could allow for possible migration, accumulation and entrapment of hydrocarbon. These recognized signatures of the key elements of a petroleum system and oil seeps encountered in the basin are an indication of the presence of an active petroleum system.

Arefeh Saiedi, Mir Ali Asghar Mokhtari, Hossein Kouhestani

Khanchay-Aliabad area as a part of Tarom magmatic belt contains some shallow depth intrusions which are intruded the Eocene volcanic- sedimentary rocks and have very close association with Cu mineralization. The Eocene volcanic- sedimentary rocks include alternation of basalt, basaltic andesite and andesite, various kinds of tuff, tuffaceous sandstone, sandstone, siltstone and occasionally shale. Petrographical studies demonstrate that intrusions are pyroxene quartz monzonite and olivine gabbro in composition. The Khanchay pyroxene quartz monzonite have porphyritic to porphyroidic, hetero-granular to sereitic, ophitic and sub- ophitic textures and composed of plagioclase, clinopyroxene, hornblende, quartz, K-feldspar and biotite. The Aliabad pyroxene quartz monzonite shows porphyritic to porphyroidic textures composing of plagioclase, clinopyroxene and hornblende in the quartz- feldspatic matrix. The Khanchay olivine gabbro is characterized by the presence of coarse grained granular, ophitic and sub- ophitic textures as well as the occurrence of plagioclase, clinopyroxene and olivine. Geochemical studies indicate that the Khanchay- Aliabad pyroxene quartz monzonitic intrusions have SiO2 content varying from 59.58 to 61.34 %. These intrusions have high- K calc- alkaline nature and are classified as I-type metaluminous granitoids. Their similar patterns on spider diagrams are indication of genetic relation of these intrusions. On these diagrams LILEs (Ba, K, Th and Pb) enrichment along with negative anomalies of HFSEs (Nb and Ti) are observed. Moreover, the Chondrite normalized REE patterns demonstrate LREE enrichment with high ratio of LREE/HREE and Lan/Ybn ratio ranging from 3.08 to 3.72. The overall  field investigation, petrological and geochemical studies as well as  tectonic setting discrimination diagrams confirm that the Khanchay- Aliabad high-K intrusions were formed from a subduction related metasomatized lithospheric mantle in a post- collisional setting.

Assef Mohamad-Hussein, Juliane Heiland

Abstract Wellbore failure can occur at different stages of operations. For example, wellbore collapse might happen during drilling and/or during production. The drilling process results in the removal of an already stressed rock material. If the induced stresses near the wellbore exceed the strength of rock, wellbore failure occurs. The production process also changes the effective stresses around the wellbore. Such changes in stresses can be significant for high drawdown pressures and can trigger wellbore failure. In this paper, the Mohr–Coulomb failure criterion with a hyperbolic hardening is used. The model parameters are identified from triaxial compression tests. The numerical simulations of laboratory tests showed that the model can reproduce the mechanical behaviour of sandstone. In addition, the simulations of multilateral junction stability experiments showed that the model was able to reproduce yielding and failure at the multilateral junction for different levels of applied stresses. Finally, a numerical example examining multilateral junction stability in an open borehole during drilling and production is presented. The results illustrate the development of a localized failure zone proximate to the area where two wellbore tracks join, particularly on the side with a sharp approaching angle, which would significantly increase the risk of wellbore collapse at the junction.

Farouk I. Metwalli, El-Arabi H. Shendi, Mohamed S. Fagelnour

Abstract The detection of thin sandstone reservoirs on seismic sections is a matter of seismic resolution and bed thickness. Usually, layers thinner than 50 ft. thick are difficult to visualize on vertical seismic sections. The problem is observed in the northwestern desert of Egypt, where several thin oil-bearing sandstone reservoirs are located, among them Qasr Field which produces oil from the Lower Cretaceous Alam El Bueib Formation, specially unit AEB-3D (D2). The aim is to follow unit (D2) sandstone channels using available horizontal and vertical seismic sections coupled with other well logs and well data. The analytical method includes interpreting lithostratigraphic units from wells logs, mapping sandstone channels, generating synthetic seismograms and correlation with stratigraphy from wells, and finally to detect channels on seismic sections using positive and negative amplitudes with proper time slice. Finally, results show that, although unit AEB-3D (D2) sandstone is ± 50 ft. thick, it can be detected using seismic modeling and well data with some efficiency.

Shailesh Kumar, Vikas Mahto

Abstract The most economical way to overcome flow assurance problems associated with transportation of heavy crude oil through offshore pipelines is by emulsifying it with water in the presence of a suitable surfactant. In this research, a novel surfactant, tri-triethanolamine monosunflower ester, was synthesized in the laboratory by extracting fatty acids present in sunflower (Helianthus annuus) oil. Synthesized surfactant was used to prepare oil-in-water emulsions of a heavy crude oil from the western oil field of India. After emulsification, a dramatic decrease in pour point as well as viscosity was observed. All the prepared emulsions were found to be flowing even at 1 °C. The emulsion developed with 60% oil content and 2wt% surfactant showed a decrease in viscosity of 96%. The stability of the emulsion was investigated at different temperatures, and it was found to be highly stable. The effectiveness of surfactant in emulsifying the heavy oil in water was investigated by measuring the equilibrium interfacial tension (IFT) between the crude oil (diluted) and the aqueous phase along with zeta potential of emulsions. 2wt% surfactant decreased IFT by almost nine times that of no surfactant. These results suggested that the synthesized surfactant may be used to prepare a stable oil-in-water emulsion for its transportation through offshore pipelines efficiently.

Mir Ali Asghar Mokhtari, Mohammad Ebrahimi, Mohammad Reza Ghorbani

Introduction The Avan Cu-Fe skarn is located at the southern margin of Qaradagh batholith, about 60 km north of Tabriz. The Skarn-type metasomatic alteration is the result of Qaradagh batholith intrusion into the Upper Cretaceous impure carbonates. The studied area belongs to the Central Iranian structural zone. In regional scale, the studied area is a part of the Zangezour mineralization zone in the Lesser Caucasus. Several studies (Karimzadeh Somarin and Moayed, 2002; Calagari and Hosseinzadeh, 2005; Mokhtari, 2008; Baghban Asgharinezhad, 2012; Mokhtari, 2012) including master’s theses and research programs have been done on some skarns in the Azarbaijan area considering their petrologic and mineralization aspects. However, before this study, the Avan skarn aureole has not been studied in detail. In this paper, various geological aspects of the Avan skarn including mineralogy, bi-metasomatic alteration, metasomatism and mineralization during the progressive and retrograde stages of the skarnification processes have been studied in detail. Research Method This research consists of field and laboratory studies. Field studies include preparation of the geological map, identifying the relationship between the intrusion and the skarn aureole, identifying the relationship between different parts of the skarn zone and also collecting samples for laboratory studies. Laboratory studies include petrography, mineralography and microprobe studies. Cameca SX100 Microprobe belonging to Geological Survey of the Czech Republic was used in order to determine the chemical composition of the calc-silicate minerals such as pyroxene and garnet in garnet skarn and pyroxene- garnet skarn sub-zones. Discussion and conclusion Qaradagh batholith is composed of discrete acid to mafic phases including gabbro, diorite, quartz diorite, quartz monzonite, quartz monzodiorite, tonalite, granodiorite, monzogranite and granite porphyry which is dominated by granodiorite-quartz monzonite. Granitoids of this batholith are metaluminus, high K calc-alkaline I-type granite (Mokhtari, 2008). The Avan Cu-Fe skarn is related to the intrusion of granodioritic-quartz monzonitic part of the Qaradagh batholith into the Upper Cretaceous flysch- type rocks consisting of biomicrite, clay limestone, marl, siltstone and mudstone. The Avan skarn consists of three zones of endoskarn, exoskarn and marble. The main Cu-Fe mineralized zone is related to the exoskarn zone, which has 600 meters of length and 50 meters of thickness, respectively. The Exoskarn zone consists of garnet skarn, pyroxene-garnet skarn and ore skarn sub-zones. Garnet, belonging to ugrandite series (Ad53-89) with more than 50 percentage in volume, is the most important anhydrous calc-silicate mineral in the garnet skarn and the pyroxene-garnet skarn sub-zones. Some of the garnet crystals are zoned and their chemical composition changes toward the rim to almost pure andradite (Ad99). Clinopyroxene which has diopsidic composition (Di75-96), is another anhydrous calc-silicate mineral in the exoskarn zone with an abundance that reaches up to 50 percent in volume in pyroxene-garnet skarn sub-zone. The ore skarn sub-zone is located toward the outer part of the exoskarn zone and close to the border of the marble zone. The abundance of ore minerals in this sub-zone reaches up to 50 percentage in volume and includes magnetite, hematite, pyrite, chalcopyrite, bornite, malachite and goethite among which pyrite is the most abundant. In this sub-zone, anhydrous calc-silicate minerals of garnet and clinopyroxene have undergone intensive alteration and are replaced with hydrous calc-silicate (epidote and tremolite- actinolite), oxide (magnetite and hematite) and sulfide (pyrite, chalcopyrite and bornite) minerals. Based on the textural and mineralogical studies, the skarnification processes in the studied area can be categorized into two main stages: 1) prograde and 2) retrograde. During the prograde stage, the heat flow of the granitoid has caused isochemical metamorphism and changing more pure limestones to marble and marlly limestones to skarnoid (metamorphism and bi-metasomatism). The high temperature magmatic fluids have caused prograde metamorphism during which anhydrous calc-silicate minerals including garnet and pyroxene have appeared. During the early retrograde stage, i.e. the mineralization sub-stage, lower temperature hydrothermal fluids have caused hydrolysis and carbonization because of which anhydrous calc-silicate minerals along with their fractures and microfractures are changed to hydrous calc-silicate (epidote and tremolite-actinolite), oxide (magnetite and hematite), sulfide (pyrite, chalcopyrite and bornite) and carbonate (calcite) minerals. During the late retrograde stage, relatively low temperature fluids have altered anhydrous and hydrous calc-silicate mineral assemblage formed during the previous stages into a very fine grained mineral assemblage including clay minerals, chlorite and iron hydroxides. Presence of replacement textures in ore minerals and anhydrous calc-silicate minerals accompanied with open filling textures in the anhydrous calc-silicate minerals, for example oxide and sulphide veinlets within the garnet crystals, indicate that the mentioned ore minerals have been simultaneously generated with hydrous calc-silicate minerals (epidote and tremolite-actinolite) during the early prograde stage. The presence of minor amounts of wollastonite among the mineral assemblage of the Avan skarn, intergrowth of garnet and pyroxene, absence of reaction rim between garnet and clinopyroxene and absence of replacement textures indicate that these minerals have been simultaneously generated within the temperature ranges of 430–600 ºC and ƒO2 > 10-26, respectively. Acknowledgements The authors are grateful to the Journal of Economic Geology reviewers and editors for their constructive suggestions to the manuscript. Reference Baghban Asgharinezhad, S., 2012. Investigation of genesis, mineralogy and geochemistry of Fe-Cu skarn in Astamal area, NE Kharvana, Eastern Azarbaijan. MSc. Thesis, University of Tabriz, Tabriz, Iran, 185 pp. (in Persian with English abstract) Calagari, A.A. and Hosseinzadeh, G., 2005. The mineralogy of copper-bearing skarn to the east of the Sungun-Chay River, East-Azarbaijan, Iran. Journal of Asian Earth Sciences, 28(4-6): 423-438. Karimzadeh Somarin, A. and Moayed, M., 2002. Granite and gabbro-diorite associated skarn deposits of NW Iran. Ore geology reviews, 20(3-4): 127-138. Mokhtari, M.A.A., 2008. Petrology, geochemistry and petrogenesis of Qaradagh batholith (east of Syahrood, Eastern Azarbaijan) and related skarn with considering mineralization. Ph.D. Thesis, Tarbiat Modares University, Tehran, Iran, 347 pp. (in Persian with English abstract) Mokhtari, M.A.A., 2012. The mineralogy and petrology of the Pahnavar Fe skarn, in the Eastern Azarbaijan, NW Iran. Central European Journal of Geosciences, 4(4): 578-591.

Maša Surić, Mladen Juračić, Nada Horvatinčić

Z metodama 14C oziroma U-Th smo datirali 16 sig iz sedmih podmorskih jam v Jadranu. Dve sigi smo datirali z obema metodama. Primernost metod za datacijo sig je različna zaradi različnih okoljskih pogojev, ki so vladali med izločanjem sige oziroma po zalitju jame. Obe metodi sta zanesljivi na dobro ohranjenih sigah. U-Th metoda je slabša, ko so karbonati onesnaženi z detritičnim materialom oz. preraščeni s plastjo morskega izvora . Vendar metoda U-Th z uporabo MC ICPMS analize, kjer potrebujemo le 100-300mg vzorca (namesto 30 g pri metodi 14C), omogoča boljšo časovno ločljivost datacij, kar je pri datiranju sig zelo pomembno. Among the 16 speleothems that were collected from 7 submarine caves and pits for the purpose of 14C and U-Th dating and reconstructing sea-level changes, two speleothems were dated by both methods. Different environmental conditions during the speleothem deposition and after the submergence resulted with different appropriateness for speleothem dating by these techniques. Well preserved speleothems gave reliable results by both methods, while U-Th method showed disadvantage in the case of carbonates contaminated with detrital material, as well as in the case of carbonate from marine overgrowth that covers the speleothems. However, U-Th method using MC ICPMS technique which requires only 100-300 mg of sample per analysis (instead of ca. 30 g for 14C conventional method), offers better age resolution that is essential for speleothem dating.

Fabiana P. Fabri, Augusto S. Auler, Allan S. Calux et al.

An area of 417 km2 in southeastern Brazil was mapped in detail regarding karst features in quartzite. Landforms typically assigned to carbonate karst terrains are largely absent, except for discrete occurrences of towers and collapse dolines. Caves are the most conspicuous landform, although occurring at a lower density than in most Brazilian carbonate areas. A total of 11 caves were mapped and studied in detail. Caves tend to develop at shallow depths parallel to the slope surface, controlled by lithological facies and the hydraulic gradient. Petrographical analyses suggest that mica (sericite) lenses within the quartzite and both sericite and iron around quartz grains may favour grain disaggregation and later erosional removal in a shallow phreatic environment. Quartzite caves represent a common feature in southeastern Brazil but tend to be isolated features rather than an integrated and areally extensive hydrological system typical of many carbonate settings.

Marconi Souza Silva, Leopoldo Ferreira de Oliveira Bernardi, Rogério Parentoni Martins et al.

Caves are permanently aphotic environments, a fact that precludes the occurrence of photosynthetic organisms. In these systems the resource is allochthonous, coming mainly from the surrounding epigean environment, being imported by physical and biological agents. Even knowing about the importance of the organic allochthonous resources in caves, little is known of their importation and processing. The present work had as an objective, the measuring the coarse particulate organic matter processing and import rates in the subterranean environment. The cave studied was Lapa da Fazenda Extrema I, limestone cave, located in Brazilian savanna biome. Through bimonthly collections, it was observed that the organic detritus penetrated into the cave in low amounts in dry season and high amounts in rainy season. The processing of the organic plant matter in the aquatic hypogean environment was moderate (K-day=0.025), in the epigean environment the processing was predominantly slow (K-day =0.0104). The detritus commonly brought to the interior of the cave were large woods (58.18 g/day), followed by leaves and fragmented material (12.76 g/day), fruits and seeds (0.0069 g/day), animal carcasses (0.002 g/day) and roots (0.001 g/day). The highest richness and abundances of invertebrates were found in the same periods in which there were the highest rates of organic matter import to the cave. Keywords: cave, detritus processing, energy flow.

Franci Gabrovšek