Mineralogy Of Rocks Research Articles

ВУЛКАН БОЛЬШОЙ ПАЯЛПАН (СРЕДИННЫЙ ХРЕБЕТ, КАМЧАТКА). К ПРОБЛЕМЕ КОНВЕРГЕНТНОСТИ «ОСТРОВОДУЖНЫХ» И «ВНУТРИПЛИТНЫХ» ПЕТРОЛОГО-ГЕОХИМИЧЕСКИХ ПРИЗНАКОВ В МАГМАТИЧЕСКОЙ СИСТЕМЕ

The paper presents the data on age, mineralogy, geochemistry, and isotope composition of rocks from the Bolshoi Payalpan Volcano (Sredinny Range, Kamchatka). We compared these data with those on the Nosichan and Belogolovsky volcanoes, located within the Belogolovsky volcanic center. The basalts of the neck and the upper lava complex of Bolshoi Payalpan are compositionally similar to the intraplate-type trachybasalts of the Belogolovsky Volcano, and the basaltic andesites of the lower lava and the cone complex are similar to the island arc rocks of the Nosichan Volcano. Analysis of the data obtained evidences that spatial and temporal manifestations of intraplate and island-arc volcanism at the Bolshoi Payalpan Volcano are not accidental, but may be a consequence of a change in the degree and depth of melting of the same deep source with the involvement of a mantle diapir. The Belogolovsky volcanic center formed in a setting of the Late Miocene-Early Pliocene rifting. Its evolution, right up to its extinction, proceeded in the same geodynamic setting with an increase in depth of the mantle source and a decrease in the degree of its melting. Rock compositions of the Lower-Middle Pliocene Nosichan Volcano remain of the island-arc type under conditions of rifting, since they are associated with the mantle reservoir located at a shallower depth, which has experienced a higher degree of melting. There is good reason for considering large volcanic centers as spontaneously-developing geological entities. As the endogenous activity dies down, the degree of melting decreases and the depth of melting increases with the replacement of island-arc volcanism by intraplate volcanism. The volcanic center becomes extinct.

Spectroscopy of Gossans and associated lithology and its implication in geo exploration- A Case Study in the Parts of Rajpura-Dariba Group, Rajasthan, India

The gossan exposures are sparsely distributed in the Dariba area and for detection and mapping of gossan and its associated lithology, spectral signatures have been used. Spectral reflectance and absorption features in VNIR-SWIR (visible and near-infrared - shortwave infrared) domain provide the scope for delineating the mineralogy of rocks. In the study, a few spectral mapping methods like Spectral angle mapper, Spectral information divergence and Band ratio indices were applied to ASTER (Advanced Space borne Thermal Emission Reflection Radiometer) calibrated data for delineating the lithology. These mapping methods could delineate boundaries for gossan and its associated rocks of Dariba; but above out of all mapping methods, spectral angle mapper spatial map has been validated with base detailed geological map in quantitatively and accuracy much better than spectral information divergence indices. The band ratio can demarcate the boundaries for gossans in the 4/2 ratio map, in the same way for associated rocks of Carbonates were well delineated in the (7+9)/8 ratio map and Quartzite 4/6 ratio map. Finally, the overextended boundaries of Dariba gossans and associated units found in the above validated spatial map, can be confirmed with field evidence can be helpful to update the base map of Dariba

The Role of Reservoir Fluids and Reservoir Rock Mineralogy on In-Situ Combustion Kinetics

The Role of Reservoir Fluids and Reservoir Rock Mineralogy on In-Situ Combustion Kinetics

The Influence of Oil Composition, Rock Mineralogy, Aging Time, and Brine Pre-soak on Shale Wettability.

Experimental and field studies have indicated that surfactants enhance oil recovery (EOR) in unconventional reservoirs. Rock surface wettability plays an important role in determining the efficacy of this EOR method. In these reservoirs, the initial wettability of the rock surface is especially important due to the extremely low porosity, permeability, and resulting proximity of fluids to the solid surface. This study is designed to investigate the effect of oil components, rock mineralogy, and brine salinity on rock surface wettability in unconventional shale oil/brine/rock systems. Six crude oils, seven reservoir rocks, and seven reservoir brine samples were studied. These oil samples were obtained from various shale reservoirs (light Eagle Ford, heavy Eagle Ford, Wolfcamp, Middle Bakken, and Three Forks) in the US. SARA (saturates, aromatics, resins and asphaltenes) analysis was conducted for each of the crude oil samples. Additionally, this study also aims to provide a guideline to standardize the rock sample aging protocol for surfactant-related laboratory experiments on shale reservoir samples. The included shale reservoir systems were all found to be oil-wet. Oil composition and brine salinity showed a greater effect on wettability as compared to rock mineralogy. Oil with a greater amount of aromatic and resin components and higher salinity rendered the surface more oil-wet. Rock samples with a higher quartz content were also observed to increase the oil-wetness. The combination of aromatic/resin and the quartz interaction resulted in an even more oil-wet system. These observations are explained by a mutual solubility/polarity concept. The minimum aging time required to achieve a statistically stable wettability state was 35 days according to Tukey’s analysis performed on more than 1100 contact angle measurements. Pre-wetting the surface with its corresponding brine was observed to render the rock surface more oil-wet.

Diagenesis of Palaeozoic-Mesozoic Tethys Ocean Carbonate succession- Oman Mountains

This paper studies the uppermost unit of Kharus Formation (Cambrian) and the Autochthonous Akhdar Group (Permian-Triassic), which unconformably covers the pre-Permian strata. The petrographic and geochemical as well as field observations indicate that the succession underwent different stages of dolomitization that produced rocks inheriting the original host rock textures and structures (fabric-preserving dolomitization) and rocks with complete obliteration of the pre-existing textures (fabric-destroying dolomitization). Dolomites that retain the original fabric of the limestone are indicators of the host rock mineralogy, i.e., whether it was made up of high Mg-calcite or aragonitic allochems and indicate early dolomitization. The top part of the Kharus Formation consists of pervasively dolomitized units, whereas dolomites belonging to the Autochthonous Akhdar Group display variable degrees of structural and textural preservation. The evidence suggests very early dolomitization in a relatively short time interval for the Permian-Triassic carbonates. The preserved depositional features in the Permian-Triassic carbonates indicate deposition in shallow marine environments with variable energy levels. Seven facies are inferred: stromatolites, mudstones, wackestones, intraformational breccias, grainstones, packstones and grain/packstones. Petrographic as well as field observations exclude evidence of evaporites within Palaeozoic-Mesozoic rocks. Five paragenetic phases are determined to explain the type of dolomitization and to indicate the type and severity of diagenesis that affected the Palaeozoic-Mesozoic Tethys Ocean carbonates from the Oman Mountains.

Evaluation of radiological hazards due to natural radionuclide in rocks and the dependence of radioactivity on the mineralogy of rocks in Udupi district on the south west coast of India

Evaluation of radiological hazards due to natural radionuclide in rocks and the dependence of radioactivity on the mineralogy of rocks in Udupi district on the south west coast of India

Impact of reservoir geochemistry on low salinity waterflooding: Global sensitivity analysis

Low salinity waterflooding (LSW) has been receiving an increasing attention in the industry as it has several advantages over alternative strategies to enhanced oil recovery (EOR), i.e. i) outperforms conventional EOR methods in terms of additional oil recovery, ii) involves lower chemical costs, iii) it is environmentally friendly, and iv) requires a relatively simple field process implementation. We quantify low salinity effect (LSE) on oil recovery upon employing a mechanistic geochemical model under parametric uncertainty. Our ultimate goal is to characterize the impact of the reservoir rock and fluid properties on the performance of LSW. To this end, we propose a geochemical model of LSW built within a commercial compositional reservoir simulator. The model is designed to account for geochemical processes recently identified through experimental and pore-scale analyses, i.e. double layer expansion, multiple ion exchange and mineral dissolution/precipitation. The geochemical model outputs were first compared with two low salinity coreflood experiments reported in the literature and then applied to predict oil recovery under parametric uncertainty. Our study encompasses the effect of formation water ionic concentrations, rock mineralogy and reservoir temperature on LSW performance. Global sensitivity indices were calculated considering reasonable intervals of variability of the studied parameters. Our analysis focuses on the total oil recovery at three different time scales: 6 months (before water breakthrough), 2 years (after water breakthrough), and 10 years (the end of the injection). The results are discussed in the frame of quantitative screening criteria development, which is necessary to assess whether a given reservoir may be a promising candidate for LSW. Our results indicate that reservoir temperature is the parameter which demonstrated the most significant impact on the LSW performance. Ion concentration also displays a significant influence on oil recovery, and we identify different chemical species in carbonate and sandstone environments. On the contrary, mineral composition shows a limited influence on oil recovery. In particular, our results show that clay presence might be not essential for LSW to be effective in sandstone reservoirs. We discuss the impact of our results in the context of experimental design aimed at an improved constraining of LSW parameterization. Our study suggests that reservoir fluid composition (e.g., concentration of Ca2+, SO42− and Na+), in addition to reservoir temperature, should be prioritized in future experimental campaigns to better understand its influence on LSW under different reservoir and operation conditions.

Alteration of high alkaline and alkaline basaltic rocks: parent rocks in the Lava Durian orchard, Sisaket Province, NE Thailand

Lava Durian Sisaket is the first geographically identified (GI) fruit related to the volcano in Thailand and distributed in three districts of Sisaket Province, the southernmost edge of the Khorat Plateau. The parent rocks of orchards are important for the description of soil and rock relation with respect to mineralogical and geochemical characteristics. This work aims to study lithology, mineralogy, and geochemistry of basaltic rocks, parent rocks of in situ soil in these orchards, and delineate the existing basaltic soil models. The several orchards are covered by reddish-brown to brown in situ soils, weathered from mafic volcanic rocks: porphyritic olivine basalt, vesicular olivine basalt, and nephelinite. The microscopic image analysis, XRD, and MiniSEM-EDS are used to classify mineralogy, while XRF and analysis of large and rare elements in ICP-MS/ICP-OES were used to determine parental rocks geochemistry and alteration. The olivine basalts comprise forsterite microphenocrysts associated with bytownite, diopside, augite, pigeonite, and ilmenite groundmass, while nephelinite is composed of nepheline groundmass and bytownite-labradorite, diopside, augite, pigeonite, and ilmenite crystals. In addition, these basalts display high alteration rates, especially olivine highly altered to iddingsite. According to the geochemical data, Sisaket's basalts were identified as alkali basalt and nepheline basanite with high LILEs and LREEs (La, Nd, Pr, Gd, Eu). The kaolinite, smectite, and illite are altered from felsic minerals, while the chlorite and iddingsite are from mafic minerals. The mineralogical analyses classified secondary phyllosilicates related to low-moderate temperature hydrothermal fluid, very high cation exchange capacity (H+, K+, Ca2+, Mg2+), and tropical weathering. The alkaline and high alkaline basalts, presenting as parent rocks, are one of the parameters that produced good nitisal soil of Sisaket's agricultural areas.

Convergence of micro-geochemistry and micro-geomechanics towards understanding proppant shale rock interaction: A Caney shale case study in southern Oklahoma, USA

As a direct outcome of economic development coupled with an increase in population, global energy demand will continue to rise in the coming decades. Although renewable energy sources are increasingly investigated for optimal production, the immediate needs require focus on energy sources that are currently available and reliable, with a minimal environmental impact; the efficient exploration and production of unconventional hydrocarbon resources is bridging the energy needs and energy aspirations, during the current energy transition period. The main challenges are related to the accurate quantification of the critical rock properties that influence production, their heterogeneity and the multiscale driven physico-chemical nature of rock–fluid interactions. A key feature of shale reservoirs is their low permeability due to dominating nanoporosity of the clay-rich matrix. As a means of producing these reservoirs in a cost-effective manner, a prerequisite is creation of hydraulic fracture networks capable of the highest level of continued conductivity. Fracturing fluid chemical design, formation brine geochemical composition, and rock mineralogy all contribute to swelling-induced conductivity damage. The Caney Shale is an organic-rich, often calcareous mudrock. Many studies have examined the impact that clay has on different kinds of shale productivity but there is currently no data reported on the Caney Shale in relation to horizontal drilling; all reported data on the Caney Shale is on vertical wells which are shallow, compared to an emerging play that is at double the depth. In this work we develop geochemical–geomechanical integration of rock properties at micro-and nanoscales that can provide insights into the potential proppant embedment and its mitigation. The novel methodology amalgamates the following: computed X-ray tomography, scanning electron microscopy, energy dispersive spectroscopy, micro-indentation, and Raman spectroscopy techniques. Our results show that due to the multiscale heterogeneity in the Caney Shale, these geochemical and structural properties translate into a variation in mechanical properties that will impact interaction between the proppant and the host shale rock.

Hydrothermal alteration and mineralization of the prospects at the northern flank of the Baimka ore zone, Western Chukotka

Background. Some papers describing the deposits and prospects in the Baimka ore zone (Baimka Trend), the Chukotka Autonomous Region have been recently published. It should be noted that those publications concern with the large Peschanka porphyry copper-molybdenum-gold deposit and Nakhodka ore field. At the same time, some copper prospects were found at the zone flanks and their nature is not clear. There are no data available in the literature that would clarify the mineralogy of hydrothermal alteration and ores at those prospects, including Top and Luchik located at the northern flank. To understand the nature of these prospects, we studied in depth mineralogy of hydrothermal alteration and ores.Aim. This study aims to describe mineralogy of metasomatic rocks and ores from the Top and Luchik prospects in the northern part of the Baimka zone, Western Chukotka.Materials and methods. Several dozen polished thin sections were microscopic studied at the Department of Mineralogy of Moscow State University using an optical microscope. The chemical composition of minerals was determined using electron microprobe at the Laboratory of Analytical Techniques of High Spatial Resolution, Department of Petrology and Volcanology, Moscow State University.Results. It was found that propylitic is the major hydrothermal alteration at the prospects studied here. Metasomatic rocks are cut by mineralized quartz and carbonate-quartz veins. Chalcopyrite and pyrite are the major ore minerals; galena, sphalerite, pyrite enriched in As and Sb, and marcasite are minor; Hg-bearing tetrahedrite-(Zn), native gold with the fineness of ~830, petzite, hessite, and acanthite are rare.Conclusions. The data obtained suggest that mineralization at the Top and Luchik prospect is attributed to the epithermal intermediate sulfidation type. Considering the occurrence of the epithermal mineralization in the upper part of the hydrothermal column and the porphyry mineralization in the Baimka zone, the porphyry mineralization is possible at depth at the Top and Luchik prospects.

A Novel Method To Assess Stimulation of Sandstone Cores Damaged by Fines Migration

SummarySandstone stimulation remains challenging because of formation heterogeneity and the sensitivity of clay minerals to acids such as hydrochloric acid (HCl) and mud acid [HCL/hydrofluoric acid (HF)]. Fines migration complicates the well-stimulation process and reduces formation productivity. Multiple field studies show that some stimulation methods can result in permanent damage to the rock matrix near the wellbore because of fines migration. This study aims to locate, quantify, and describe the damage resulting from fines migration after the stimulation of sandstone formations, and examine the composition of clay content in the formation and its effects on the stimulation process and subsequent fines migration.This work evaluates the fines-migration damage during well stimulation in Bandera, Gray Berea, and Kentucky Sandstones. Fines migration was induced by injecting deionized water between brine stages to trigger the mobilization of the clay minerals in sample cores. HCl, formic acid (HCOOH), and HF stimulation stages were then injected after the fines-migration induction. The new formation-damage-evaluation method proposed in this work uses computed-tomography (CT) scanning and nuclear-magnetic-resonance (NMR) measurements before and after the fines-migration induction and experimental stimulation. The CT and NMR data were then combined and processed to generate a 3D representation of the pore structure throughout the core samples, which yields insight on how the clay composition affects the stimulation process and changes the pore system.The developed technique exhibited an excellent ability to visualize the pore-size distribution and the changes in the pore structure after the fines-migration damage and the acid treatment. The mapping of the pore-size distribution using CT and its comparison with the rock mineralogy of Bandera, Gray Berea, and Kentucky Sandstones successfully predicted the changes in the pore structure of these formations upon induction of fines-migration damage using deionized water. These changes in pore structure prevailed as a controlling variable of the acidizing process. The stimulation of the damaged cores at 150 and 250°F resulted in aluminosilicate deposition toward the core outlet. These deposits are attributed to the acid leaching of aluminum (Al) and iron (Fe) ions from the aluminosilicate structures. The higher temperature resulted in the deposition of aluminosilicates closer to the injection point. However, an enhancement in permeability was noticed in all of the sampled formations, which was because of the propagation of narrow channels between heavily deformed pore structures.This work adds to the understanding of sandstone-stimulation technology and contributes a new process to assess the effects of acid stimulation on fines-migration damage. The high level of resolution in visualizing the changes in the pore structure facilitates the optimization of treatments to reduce costs while improving production from clay-rich sandstone formations. This technique offers further potential as a formation-evaluation tool for real-time assessment of a variety of formation-damage mechanisms, such as fracturing fluids and water blockage.

The carbonic acid-rock reaction in feldspar/dolomite-rich tightsand and its impact on CO2-water relative permeability during geological carbon storage

CO2 injection contributes to formation energy supplement to remedy the fast production decline in tight oil reservoir and CO2 storage at the same time.CO2 Here, we report CO2-water relative permeability with consideration of acid-rock reaction. The minerals of a tight rock sample were analyzed at first. CO2Then we established an experimental method to measure the relative permeability of CO2-water at reservoir conditions based on steady state method. After carbonic acid-rock reaction, the variation in rock mineralogy was compared. The pore size distribution in the rock sample was obtained by LF-NMR after dynamic corrosion at different pressure. Both small and large pore and throat were enlarged after corrosion. And the Klinkenberg permeability of tight sandstone was increased 7.4–18.8%. From the CO2-water relative permeability with corrosion, the irreducible water saturation was decreased for more than 15.1% in average, which indicates more flowing spaces for other fluids. In the two-phase flow regime, a good linear relationship was found between Krw/Krg and gas saturation in tight sand samples. It can be used for the estimation of relative permeability at different gas conditions.CO2CO2 Injection of CO2 in tight oil reservoir indicates improvement in EOR and GCS potential. Acid-rock reaction results in better fluid flow capacity for liquid and additional trapping of CO2.

Deducing Mineralogy of Serpentinized and Carbonated Ultramafic Rocks Using Physical Properties With Implications for Carbon Sequestration and Subduction Zone Dynamics

AbstractSerpentinization of ultramafic rocks is fundamental to modern plate tectonics and for volatile (re‐)cycling into the mantle and magmatic arcs. Serpentinites are also highly reactive with CO2such that they are prime targets for carbon sequestration. Serpentinization and carbonation of ultramafic rocks results in changes in their physical properties such that they should be detectable using geophysical surveys; this could provide constraint on the reactivity of rocks without extensive sample characterization. We constrain the physio‐chemical relationships in altered ophiolitic ultramafic rocks using petrographic observations, major‐element chemistry, quantitative X‐ray diffraction, and physical properties on a suite of >400 samples from the Canadian Cordillera. Serpentinization results in a systematic decrease in density that reflects the increase in serpentine abundance and carbonation results in an increase in density, mostly reflecting the formation of magnesite; based on these data, we present two formulations for determining extent of serpentinization: one based on major‐element chemistry and the other on density. Magnetic susceptibility is variable during serpentinization; most harzburgitic samples show a 100‐fold increase in magnetic susceptibility, whereas most dunitic samples and a minor proportion of harzburgitic samples show very little change in magnetic susceptibility. We use quantitative mineralogy and physical properties of the samples to constrain a model for using density and magnetic susceptibility to approximate the mineralogy of ultramafic rock. Although further work is required to understand the role of remanence in applying these models to geophysical data, this presents an advancement and opportunity to prospect for the most reactive ultramafic rocks for carbon sequestration.

Reservoir Formation Damage; Reasons and Mitigation: A Case Study of the Cambrian–Ordovician Nubian ‘C’ Sandstone Gas and Oil Reservoir from the Gulf of Suez Rift Basin

Reservoir formation damage is a major problem that the oil and gas industry has to mitigate in order to maintain the oil and gas supply. A case study is presented that identifies the impacts of formation damage and their causes in the Nubian ‘C’ hydrocarbon reservoir within Sidki field located in the Southern Gulf of Suez, Egypt. In addition, a formation damage mitigation program was designed and implemented involving an effective stimulation treatment for each well experiencing reservoir damage. The data available for this study include core analysis to provide rock mineralogy and lithology; analysis of production fluid data; water chemistry; drilling fluid composition; perforations and well completion details; workover operations; and stimulation history. The diagnosis of formation damage based on the integrated assessment of the available data is associated with several benefits, (1) The integration of the data available helps provide a robust analysis of formation damage causes and in establishing suitable remediation actions, (2) Workover fluid is confirmed as the primary cause of reservoir damage in the studied well, (3) Several reservoir damage mechanisms were identified including water blockage, solids and filtrate invasion, fluid/rock interaction (deflocculation of kaolinite clay), salinity shock and/or high-sulfate content of the invaded fluid, (4) Irrespective of the potential causes of formation damage, the primary objective of a gas production company is to mitigate its effects and the integrated dataset helps to design appropriate and effective stimulation treatments to overcome formation damage, and (5) In gas reservoirs, especially low permeability ones, extra precautions are necessary to avoid potential reservoir damage due to workover fluid invasion.

Application of Rock Weathering and Colonization by Biota for the Relative Dating of Moraines from the Arid Part of the Russian Altai Mountains

For the Altai Mountains’ region, especially the arid southeastern part of the Russian Altai, the data on glacier fluctuations in the Pleistocene and Holocene are still inconsistent. The study area was the Kargy River’s valley (2288–2387 m a.s.l.), a location that is not currently affected by glaciation and the glacial history of which is poorly studied. Field observations and geomorphological mapping were used to reveal the configuration of Pleistocene moraines. The relative dating method was applied to define the degree of weathering as an indicator of age. Three moraine groups of different ages (presumably MIS 6, MIS 4, and MIS 2) were identified based on a detailed investigation of their morphological features and the use of relative dating approaches. The latter were primarily based on weathering patterns. Data on the rock mineralogy, porosity, and specificity of biological colonization as an agent of weathering were obtained for the moraine debris. The studied moraines were composed of fine-grained schist, in which the specific surface area and fractality (self-similarity) were more developed in the older moraine. The growth of biota (crustose lichen and micromycetes) colonizing the rock surface led to rock disintegration and the accumulation of autochthonous fragments on the rock surface. Despite the fact that the initial stage(s) of moraine weathering affected by biota was fixed, the correlation trends of biota activity and moraine ages were not determined.

Integrated reservoir, geology, and production data for reservoir damage analysis: A case study of the Miocene sandstone reservoir, Gulf of Suez, Egypt

Reservoir damage is considered one of the major challenges in the oil and gas industry. Many studies have been conducted to understand formation damage mechanisms in borehole wells, but few studies have been conducted to analyze the data to detect the source, causes, and mitigations for each well where damage has occurred. I have investigated and quantified the reasons and mitigation of reservoir damage problems in the middle Miocene reservoir within the El Morgan oil field at the southern central Gulf of Suez, Egypt. I used integrated production, reservoir, and geologic data sets and their history during different operations to assess the reservoir damage in El Morgan-XX well. The collected data include the reservoir rock type, fluid, production, core analysis, rock mineralogy, geology, water chemistry, drilling fluids, perforations depth intervals, workover operations, and stimulation history. The integration of different sets of data gave a robust analysis of reservoir damage causes and helps to suggest suitable remediation. Based on these results, I conclude the following: (1) Workover fluid has been confirmed as the primary damage source, (2) the reservoir damage mechanisms could be generated by multisources including solids and filtrate invasions, fluid/rock interaction (deflocculating of kaolinite clay), water blockage, salinity chock, and the high sulfate content of the invaded fluid, and (3) multidata integration leads to appropriate reservoir damage analysis and effective design of the stimulation treatment. Furthermore, minimizing fluid invasion into the reservoir section by managing the overbalance during drilling and workover operations could be very helpful. Fluid types and solids should be considered when designing the stimulation treatment and compatibility tests should be performed. Long periods of completion fluid in boreholes are not recommended, particularly if the completion fluid pressure and reservoir pressure are out of balance, as well as the presence of sensitive formation minerals.

Geological and geochemical characterization of the Nanlia and Makorongo gold prospects, Mozambique Belt, northeastern Mozambique

Northern Mozambique hosts numerous occurrences of gold mineralization in metamorphic terranes, which are little known because of the insufficient studies. In this work, we describe the main geological and geochemical characteristics of the Nanlia and Makorongo gold prospects located in the Namuno district, northeastern Mozambique. We report the mode of occurrence of gold, petrography and mineralogy of the host rocks and ores, fluid inclusion characteristics and stable isotope data, to understand the genesis of gold mineralization in the study area. The gold mineralization in the Nanlia and Makorongo prospects is hosted by the Neoproterozoic Xixano Metamorphic Complex in the Mozambique Belt, which is composed of mafic granulite, amphibolite, paragneiss and marble. The host rock amphibolite consists mainly of amphibole, plagioclase, biotite and minor quartz, titanite and sulfides. The gold mineralization is associated with E-W to ENE-WSW trending quartz veins, oriented parallel to low angle to the foliation of the host rock amphibolite. The ore mineralogy consists of pyrite, pyrrhotite, chalcopyrite, magnetite, galena and sphalerite, with minor tellurides, xilingolite, electrum and native gold. Mineralized quartz veins in the Nanlia and Makorongo prospects host two types of fluid inclusions which locally coexist in the same assemblage: type 1, one-phase CO2 inclusions with final melting temperature between −58 and −52 °C; and type 2, two-phase H2O + NaCl (±CO2 ± N2 ± CH4) inclusions with homogenization temperature ranging from 246 to 370 °C and 239 to 382 °C in the Nanlia and Makorongo prospects, respectively, and salinity of 12–21 wt% NaCl eq. Pressure and temperature (P-T) conditions of ore-formation were estimated from fluid inclusions and sphalerite geobarometry at 420–620 °C and 160–280 MPa, and 330–440 °C and 150–200 MPa in the Nanlia and Makorongo prospects, respectively. The Nanlia and Makorongo gold prospects are classified as orogenic-type gold deposits. We suggest that gold mineralization was caused by an aqueous-carbonic fluid with low-moderate salinity originated by devolatilization during prograde metamorphism of underlying rocks. The gold mineralization post-dates the peak of metamorphism of the host rocks, thus formed during the retrograde metamorphism of the host rocks. The precipitation of gold in the Nanlia and Makorongo prospects was caused by fluid phase separation induced by pressure drop as the mineralizing fluid migrated to shallower depths.

Mineralogy and petrology of alkaline rocks and carbonatites: Celebrating the life and work of Gregory Yu. Ivanyuk (1966–2019)

Mineralogy and petrology of alkaline rocks and carbonatites: Celebrating the life and work of Gregory Yu. Ivanyuk (1966–2019)

Hydrothermal alteration and Cu–Co mineralization at the peripheral zone (Target H) of the Kitumba iron–oxide copper–gold system, Mumbwa District, Zambia

AbstractTarget H is a new Cu prospect discovered in the Mumbwa district of central Zambia. Copper mineralization in the Mumbwa district is linked to the hydrothermal system associated with the granite‐quartz syenite intrusions of the Hook batholith. The extent of the hydrothermal system has not been documented, but various Cu prospects, including Target H, have been discovered at the margins of the granite‐quartz syenite bodies. The objective of this study is to investigate the geological characteristics of the Target H prospect using petrographic, geochemical, and sulfur isotope data in order to understand the features of mineralization at the margin of the hydrothermal system. The Cu‐ and Co‐rich orebodies are hosted in siltstone and breccia correlated to the Kundelungu Group of the Neoproterozoic Katanga Supergroup rocks. The siltstone consists of alternating beds of sandstone and mudstone that are composed of diagenetic quartz, albite, dolomite, calcite, and muscovite. Breccia occurs parallel to the bedding planes and in the folded and fractured siltstone units. Lithostratigraphy is characterized by three domains: breccia, transition, and host rock, which are defined depending on the proportion of siltstone and breccia. The diagenetic minerals have been modified by hydrothermal alteration, resulting in alteration products controlled by the primary mineralogy of the host rocks: K‐feldspar and muscovite replace albite and muscovite in siltstone, while siderite and hematite replace dolomite and calcite in breccia. Hydrothermal calcite is observed in the veinlets with or without siderite and hematite. Copper mineralization is associated with hydrothermal alteration and occurs as chalcopyrite, bornite, and chalcocite in breccia and stockwork veins. Diagrams correlating geochemistry to lithology show that the bulk of Cu mineralization is hosted in the breccia. An anomalous concentration of Co occurs with Cu in breccia, but the two metals do not show similar enrichment and depletion behaviors. The Cu‐rich orebody forms in hematite‐dominated breccia domain, whereas Co‐rich orebody forms in siderite‐dominated breccia units in the transition domain. In addition to Cu and Co, geochemical data show significant enrichment of Fe, P, Ba, Mo, Pb, W, U, V, and light rare earth elements in the breccia. Sulfur isotopic values of sulfide minerals show lighter δ34S values between 5 and 9‰ in the breccia and heavy δ34S signatures of approximately 17–28‰ in the siltstone. The δ34S values measured from sulfides in the breccia were comparable to the values obtained from the Kitumba deposit, which is located at the center of the hydrothermal system. We propose a magmatic‐hydrothermal origin for the Cu‐ and Co‐rich orebodies in the breccia at Target H. Breccia was the conduit for iron‐oxide‐rich metal‐bearing fluids that originated from the Kitumba deposit. Cooling and reaction of the fluids with dolomite‐rich siltstone triggered a redox reaction that deposited Cu sulfide minerals and an anomalous concentration of Co.

An evaluation of organic acids implementation in stimulating tight Saudi reservoirs: A case study on Sarah sandstone formation

Sandstone formations are stimulated with mud acid when matrix acidizing is most competent. In terms of high-pressure, high-temperature (HP-HT) conditions, the corrosive impact of hydrochloric (HCl) acid prompted the need to explore other alternatives to mud acid. This study examines the efficiency of organic acids in stimulating Sarah sandstone, a tight gas formation of potential.The optimum injection of acid volume was tested on Berea cores. Besides, the mineralogy of outcrop rocks of Sarah formation was identified using X-ray diffraction (XRD) aided by Scanning Electron Microscopy (SEM). Formation mineralogy led to the selection of acetic-hydrofluoric (C₂H₄O₂-HF) and oxalic-HF (C₂H₂O₄-HF) as proper acids for stimulation experiments. Bentonite water-base mud was used to alter the permeability of three fresh Sarah sandstone core samples. The organic-HF acids were used to stimulate two core samples, while mud acid (HCl-HF) was tested in the third core for comparison. Energy-dispersive X-ray spectrometer (EDX) and SEM were utilized to study the impact of acids on porous media.Experiments conducted in Berea core samples led to the execution of five pore volumes (PV) of preflush and one PV of main treatment as the optimum volume during the acidizing trials. XRD and SEM identified pore-filling clay minerals causing the low permeability of Sarah formation. Furthermore, the water-base mud injected decreased the permeability further by 80%. Oxalic-HF and acetic-HF mixtures recovered the initial permeability of core samples by 46% and 35%, respectively. SEM-EDX results showed how organic acids have partially unblocked the pathways of the structural pores leading to permeability enhancement.This research not only recommends the use of oxalic-HF Acid for acidizing Sarah sandstone formation but also spotlights the ability of organic acids to employment as preflush in hydraulic fracturing operations.