Alteration Mineralogy Research Articles

Fresh and Aged Chromite Ore Processing Residues (COPR): Weathering-Induced Alteration of Chemical Properties, Cr(VI) Mobility and Mineralogy At Open Dumpsites in Kanpur, India

Chromite ore processing residue (COPR) is a hazardous waste retaining relic Cr(VI). Large amounts are generated during the high-lime production of leather tanning salts in the region of Kanpur, India. Here, COPR is often deposited on open and uncontrolled landfills, leading to severe groundwater contamination. This study aimed at elucidating how ageing under these ambient conditions alters COPR properties and Cr(VI) mobility. For this, aged COPR obtained from surface and subsurface horizons of a visibly weathered open dumpsite was systematically compared to fresh high-lime COPR collected at two tanning salt factories. Elemental composition of the samples was characterized using X-ray fluorescence analysis while Cr(VI) mobility was assessed photometrically in alkaline and aqueous batch extracts. Mineralogical composition of the COPR was studied using X-ray powder diffractometry, scanning electron microscopy and thermogravimetry–mass spectrometry. The fresh COPR were highly alkaline and contained characteristic Cr(VI) host phases like calcium aluminum chromate hydroxide (CAC) and katoite. These were absent in the aged samples due to their lower pH of ~ 9. The pH drop was likely caused by uptake of atmospheric CO2, which was corroborated by elevated carbon and calcite levels. This carbonation coincided with vertical translocation of Cr(VI) to the subsurface of the landfill, where leachate concentrations in excess of 1.6 g · L−1 and chromatite (CaCrO4) precipitations were found. The results highlight the importance of carbonation as a key ageing process which will likely exacerbate Cr(VI) groundwater contamination at open COPR dumpsites.Graphical

Mitigating acid attack-induced deterioration of cement mortar through the application of montmorillonite nanosheets

This work aimed to examine the efficacy of montmorillonite nanosheets (MNs) in mitigating ‎nitric acid's impact on cement mortar. External/internal acid-induced damages and residual ‎mechanical strengths, were evaluated in 28-day mortars with varying MN contents, exposed to the ‎nitric acid solution over a 90-day period. ‎Mineralogical alterations due to acid attack ‎were explored using X-ray ‎diffraction, ‎thermogravimetric analysis, and field emission-scanning ‎‎electron microscopy.‎ Results demonstrated that exposure to the acid solution induced various ‎external damages, such as softening, cracking, and a porous texture, accompanied by reduced ‎adhesion among cementitious composite constituents. Internally, damages were manifested through ‎indicators like ultrasonic pulse velocity (UPV) loss, cross-sectional area loss, and corrosion depth. ‎. ‎Notably, after 90-day exposure‎, the plain mixture exhibited UPV loss, ‎‎c ross-sectional area loss, and corrosion depth values of 75.0 %, 81.7 %, and 12.5 mm, respectively; ‎‎meanwhile the mortar containing 2 wt% MNs (MN2) recorded measurements of 57.0 %, 50.3 %, and 6.2 mm, ‎‎respectively.‎ Furthermore, MN2 specimen demonstrated the highest residual mechanical strengths. Importantly, although MN inclusion had no impact on the mineralogy of the altered ‎cementitious ‎matrix ‎exposed to ‎‎acid solution, it hindered acid species penetration‎ into ‎cementitious ‎‎composites, enhancing ‎resistance to ‎calcium ion leaching from the binder ‎phases in acidic solution.‎

Alteration and mineralization features of the Akcal Epithermal Gold Deposit, Biga Peninsula, Western Anatolia, Turkey: Evidence for low-sulfidation Au-Ag-Sb mineralization

The Akcal epithermal Au-Ag deposit, located on the Biga Peninsula, southwestern Turkey is estimated to contain 32.5 million tonnes of mineralization at an average grade of 1.03 g/t Au, equivalent to 1.2 million ounces of gold. Epigenetic mineralization is hosted by the lower Miocene Sapci volcanic suite, a calc-alkaline subduction-related volcanic arc consisting mainly of andesitic and basaltic andesitic rocks, while the coeval Soma Formation is composed of sandstone, claystone, conglomerate, marl-limestone, siltstone, and tuffite. Near the base of the volcanic pile, the Karakaya Complex is represented by limestone blocks of various sizes (from a few millimetres to several kilometres) within the Sapci volcanic suite. Short wave infrared (SWIR) and X-ray diffraction (XRD) analyses have shown that kaolinite, illite-smectite, montmorillonite, illite, beidellite, gypsum, vermiculite, quartz, and chlorite are the most common alteration minerals at Akcal. The alteration mineralogy indicates that the temperature of hydrothermal fluids broadly varied from 150° to 230°C, with a mildly acidic pH range of 5.0 to 6.5; these conditions accompanied by a lack of alunite suggest low-sulfidation epithermal conditions for the formation of the Akcal epithermal Au-Ag deposit. Petrographic examination and microanalysis by scanning electron microscopy indicate that mineralization at Akcal consists of pyrite and arsenopyrite with lesser hematite, ilmenite, rutile, and apatite. The occurrence of pyrite and hematite on cleavage planes of hydrothermal biotite is evidence of replacement of an earlier potassic alteration phase. Further petrographic examination of the basal limestone reveals replacement by sulfides displaying complex colloform intergrowths of pyrite and marcasite. The lack of skarn alteration and marble supports a carbonate-replacement origin for sulfides occurring in the basal limestone and is likely related to epithermal mineralization at Akcal. Geochemical results show that an Au-Ag-As-Sb±Pb±Zn signature is dominant across the volcanic-hosted epithermal mineralization and carbonate-replacement occurrences in the basal limestone; the lack of Cu mineralization (< 92 ppm) is typical of low-sulfidation epithermal systems. Strong positive correlations between Au and Ag (r′=0.77), As (0.80), and Sb (0.86) indicate that gold is likely hosted as a sub-microscopic phase within pyrite, arsenian pyrite, and arsenopyrite; visible gold (or free gold) and (or) electrum were not identified at Akcal. A model of fluid mixing involving shallow circulating meteoric waters with deeper magmatic-hydrothermal fluids is proposed for the genesis of gold mineralization at Akcal; a positive Au correlation with Mo (r′=0.74) and Mo concentrations of up to 582 ppm, support the involvement of magmatic-hydrothermal fluids in the epithermal system. Boiling as a mechanism for gold precipitation is unlikely given paleodepths of greater than 250 meters (3.0-5.0 MPa) and model temperatures of 150° to 230 °C. Mineralogical and textural evidence of boiling, such as adularia, bladed calcite, and lattice-texture quartz, have not been observed at Akcal. However, the presence of a silica-rich blanket with chalcedony (at Akcal surface) and having formed near the paleo water table may indicate some involvement of CO 2 – rich steam-heated waters, which could suggest some influence from boiling at depth, although evidence of boiling has not been confirmed in samples from Akcal. Precipitation of gold during the fluid mixing process would have occurred through a shift to higher f O 2 conditions and destabilization Au-thiosulphide complexes. This shift towards higher f O 2 is supported by the occurrence of gypsum and hematite with gold mineralization at depth.

Basalt Alteration in a CO2–SO2 Atmosphere: Implications for Surface Processes on Venus

AbstractVenus' surface and interior dynamics remain largely unconstrained, due in great part to the major obstacles to exploration imposed by its 470°C, 90 bar surface conditions and its thick, opaque atmosphere. Flyby and orbiter‐based thermal emission data provide opportunities to characterize the surface composition of Venus. However, robust interpretations of such data depend on understanding interactions between the planet's surface basaltic rocks and its caustic carbon dioxide (CO2)‐dominant atmosphere, containing trace amounts of sulfur dioxide (SO2). Several studies, using remote sensing, thermodynamic modeling, and laboratory experiments, have placed constraints on basaltic alteration mineralogy and rates. However, constraints on the effects of SO2‐bearing reactions on basalts with diverse compositions remain incomplete. Here, we present new data from a series of gas‐solid reaction experiments, in which samples of two basalt compositions were reacted in an SO2‐bearing CO2 atmosphere, at relevant Venus temperatures, pressure, and oxygen fugacity. Reacted specimens were analyzed by scanning electron microscopy and scanning transmission electron microscopy using sample cross‐sections produced with focused ion beam milling. Surface alteration products were characterized, and their abundances estimated; subsurface cation concentrations were mapped to show the depth of alteration. We demonstrate that the initial development of reaction products progresses rapidly over the course of 30‐day runs. Alkaline basalt samples are coated by Na‐sulfate (likely thenardite, Na2SO4) and amorphous calcium carbonate (CaCO3) alteration products, and tholeiitic basalt samples are primarily covered by anhydrite (CaSO4), Fe‐oxide (FexOy: likely magnetite, Fe3O4), and other minor phases. These mineralogies differ from previous experiments in CO2‐only atmospheres.

Changes in the structure of alkali activated slag mortars subjected to accelerated leaching

The chemically induced degradation of alkali-activated materials exposed to the surrounding environment is a critical concern for durability. In this study, the leaching of alkali activated slag mortars (AASs) subjected to a 6M NH4NO3 solution was investigated by integrating techniques including ICP-OES, XRD/QXRD, TGA/DSC, ATR-FTIR, and 29Si MAS-NMR. The results revealed that the main leachable elements from the AASs and their leaching rates decreased in the following order: Na, K, Ca, and Mg. In contrast, Si and Al, the key elements in the C-A-S-H gel, displayed a remarkable resistance to leaching. Upon NH4NO3 attack, the primary phase (C-A-S-H) becomes more siliceous and has a greater mean chain length through decalcification and dealumination. The second phase, Mg, Al-layered double hydroxide (Mg, Al-LDH, or hydrotalcite), incorporated nitrate from the surrounding solution, sulfate from precursor dissolution, and Ca from gel decalcification to form nitrate/sulfate-bearing Ca, Al-LDH phases. Remarkably, the water-to-binder ratio exerted a nuanced influence, dictating the pace of element leaching, while exhibiting a relatively modest impact on the stability of the solid phases after 28 days of exposure. This work proposes a leaching mechanism for understanding the leaching process occurring in AASs based on an in-depth experimental exploration of mineralogical alterations.

Three-dimensional interpretation of magnetotelluric data at Fogo Volcano, Azores Islands

The resistivity structure of Fogo volcano and the seismically active Congro region of São Miguel Island has been determined by 3-D inversion from 44 magnetotelluric soundings to yield new insights into the internal architecture of this volcanic island. Following comprehensive testing of processing codes to yield optimum magnetotelluric responses from the collected time-series, a robust electrical resistivity model was obtained. Sensitivity analysis of various features from the inversion process was used to determine their reliability, and aid geological interpretation. The magnetotelluric data imaged, and provided new structural insights into the Ribeira Grande geothermal system on the northern flank of Fogo volcano, where a shallow low resistivity (1 - 5Ωm) region has strong correlation with borehole data, and is shown to be an excellent proxy for mapping temperature and clay alteration mineralogy. Beneath the central edifice of Fogo volcano and also throughout the Congro region, the geology is very resistive, however the new magnetotelluric observations do not yield any further constraints on the origin of the seismicity that poses threats to the local populations residing on this hazardous island.

Depositional control on composition, texture and diagenesis of modern carbonate sediments: A comparative study of tidal channels and marshes, Abu Dhabi, United Arab Emirates

Petrography, geochemistry, radiocarbon dating, and porewater chemistry of modern carbonate sediments in the mangrove marshes and tidal channels along the Abu Dhabi coast, United Arab Emirates, were conducted to compare sediment composition, texture and diagenesis between these two adjacent but distinct depositional environments. Tidal currents and extensive micritization of the allochems in the tidal channels have led to the enrichment of skeletal fragments (average 25 %) and peloids (average 70 %). Ooids, however, are relatively scarce (average 1 %), which is attributed to strong tidal currents flushing them out of channels and depositing them on shoals and deltas. The severe environmental conditions in the tidal channels forced the microorganisms to bore into allochems, promoting micritization via carbonate dissolution and reprecipitation of spheroidal microbial micrite. Spheroidal micrite with the same mineral composition as the host skeletal fragments fills the microbial borings, indicating that micritization does not involve mineralogical alteration. Radiocarbon dating suggests that microbial boring is an important source of micrite, which is transferred into the marshes from channels by tidal currents. The oxidizing environment in marshes, due to the presence of mangrove pneumatophores and crab burrows, reduces the likelihood of anaerobic respiration. In contrast, microbial sulfate reduction and carbonate dissolution induced by microbial boring in tidal channels caused an increase in porewater alkalinity and dissolved inorganic carbon (DIC) concentration, resulting in more abundant aragonite and high-Mg calcite cements. Stable carbon (+2.3 ‰ to +4.6 ‰) and oxygen (+0.8 ‰ to +1.5 ‰) isotopes of the allochems and micrite corroborate derivation of DIC from seawater. The formation of rare scattered rhombic dolomite as cement only in tidal channels is attributed to microbial metabolic processes. This study provides important insights into the characteristics and controlling factors of diagenesis in modern carbonate sediments, which can have wide implications for understanding the early diagenesis of ancient limestones.

Assessment of the spaceborne EnMAP hyperspectral data for alteration mineral mapping: A case study of the Reko Diq porphyry Cu[sbnd]Au deposit, Pakistan

For over four decades, spaceborne multispectral data have played a crucial role in supporting mineral exploration and geologic mapping. The spaceborne multispectral datasets, however, have a restricted number of bands with coarse spectral resolution and, thus are very limited in mineral mapping. The advent of high-quality spaceborne imaging spectroscopic data like the Environmental Mapping and Analysis Program (EnMAP), has bridged this gap initiating a new era in global hyperspectral mineral mapping. The EnMAP satellite, operational since November 2022, covers the spectral range of 420 and 2450 nm in 224 bands, offering a spatial resolution of 30 m and a mean spectral sampling distance of 8.1 and 12.5 nm in the visible-near infrared and shortwave infrared regions, respectively. In this paper, we demonstrate the enhanced mapping capabilities of EnMAP using datasets acquired over the Reko Diq mining district, a cluster of Miocene porphyries located in Pakistan's Chagai Belt hosting an undeveloped world-class porphyry Cu-Au ± Mo deposit. The EnMAP's Level 2A data product was processed using the polynomial fitting technique to characterize the diagnostic absorption features of the alteration minerals in the Reko Diq porphyry system. This involved retrieving the minimum wavelength, depth, width, and asymmetry parameters for key absorption features and employing them interactively for mineral characterization. A diverse array of minerals were successfully mapped over the study area and validated by ground spectroscopy. This includes abundance/composition maps for white micas, chlorite, epidote, calcite, kaolinite, gypsum, jarosite, and ferric and ferrous iron minerals. The minimum wavelength of white mica was found to vary between 2195 and 2210 nm, with the shorter wavelengths (Al-rich) white mica occurring proximal to the known mineralized zones. The potassic alteration cores and the outer propylitic zones were identified by the ferrous iron and chlorite-epidote-calcite mineral maps, respectively. This study demonstrated the superiority of EnMAP hyperspectral data in delineating the alteration mineralogy and zonation pattern of porphyry copper systems. This capability can potentially contribute to the exploration of new deposits in exposed terrains worldwide.

Soil hydraulic properties, mineralogical alteration and pore formation in Regosols from southern Brazil

ABSTRACT Regosols (Neossolos) are soils with use limitations mainly related to effective depth, abundant presence of rock and saprolite fragments, and frequently high slope gradients; besides that, they represent a new agricultural frontier for grain production in southern Brazil. This study evaluated soil saturated hydraulic conductivity (K sat ) and water retention and availability in Regosols and saprolites derived from volcanic rocks in southern Brazil and the relationship of these variables with porosity in saprolithic horizons characterized by mineralogical weathering. The study was carried out on eight profiles derived from basic and acidic volcanic rocks of the Serra Geral Formation. We evaluated soil morphology, granulometry, porosity, bulk density (BD), K sat , water retention, electronic/ optical microscopy and chemical composition of parent materials, and soil mineralogy. Soil K sat ranged from 0.0 to 6.40 cm h -1 in the evaluated horizons, without significant difference between the A and Cr horizons. Seven soil profiles showed BD equal to or less than 1.28 Mg m -3 for the Cr samples. Total porosity in the Cr horizons was above 0.5 m 3 m -3 and not significantly different from A horizons. In five of the eight soil profiles, one or more Cr horizons presented greater available water than A horizons. Electronic and optical microscopy evidenced abundant cracks and mineralogical weathering in the rock samples. X-rays diffraction data also indicated advanced degree of weathering of Cr horizons, evidencing abundant formation of pores in the saprolite. and justifying the high-water retention in Regosols profiles in southern Brazil.

Alteration Mineralogy and Fluid Inclusion Microthermometry of the Hes-Daba Area in Gagade, Republic of Djibouti

This study focuses on fluid inclusions from the Hes-Daba area. Microthermometric measurements were conducted on quartz collected from surface veins that hosted inclusions in two phases: liquid and vapor. The mean homogenization temperature ranged from 150 °C to 367 °C and the melting point of ice ranged from −0.05 °C to −1.14 °C, indicating that the inclusion solutions consisted of 0.1 to 1.9 eq. wt% NaCl. The thermal history and thermal structure were evaluated to estimate the formation temperature. Selected samples were analyzed via x-ray diffraction to provide direct data on geothermal reservoirs; this was necessary because geothermal fluids, through their interactions, can alter the composition and properties of rocks. The main alteration minerals were quartz; calcite; alunite; epidote; hematite; and the clay minerals illite, smectite, and chlo- rite. Therefore, the clay constituted a transition to a high-temperature environment, as evidenced by high-temperature hydro- thermal alteration minerals such as quartz (>180 °C) and epidote (~250 °C).

Mineralogical and geochemical composition of a cementitious grout and its evolution during interaction with water

In the present study, the chemical composition, mineralogy, and mechanisms of alteration of a cementitious grout based on a CEM III/C with addition of smectite, hydrotalcite, and silica fume, are studied using a combination of chemical and physical methods. This material was designed in the context of geological repository of radioactive wastes, with a twofold aim: first, to fill the technical voids left by drilling operations at the interface between the geological formation and the disposal galleries. Second, to neutralize a potential acidic transient due to pyrite oxidation, and to create an environment that favors low corrosion rates of carbon steels. The grout is mainly composed of calcium silicate hydrates having a Ca/Si ratio of ~0.8, incorporating Al in the bridging site of the Si chains (C-A-S-H), and accounting for 29–36 wt.% of the sample. It also contains silica fume (38–48 wt.%), smectite with interlayer Na (11–17 wt.%), hydrotalcite with interlayer CO32− (3–4 wt.%), and lower amounts of portlandite, calcite, and possibly gibbsite and gypsum. Upon alteration by water in a flow-through reactor, the main modifications affecting the sample are calcite and gypsum dissolution, hence releasing aqueous Ca2+ that is adsorbed in smectite interlayer by replacing Na+, and stoichiometric C-A-S-H dissolution. The evolution of solution chemistry and of the solid phase composition are reproduced successfully using a thermokinetic model.

Integrated approach for geothermal exploration: Case study from Salar area (Afyonkarahisar, Turkey)

The intense investment demand in the geothermal sector in Afyonkarahisar province in recent years has enabled the utilization of geothermal waters such as district heating and greenhouse heating, electricity generation, and spa facilities and accelerated the exploration of new geothermal areas in the region. In this study, the Salar (Afyonkarahisar) region's geothermal potential was investigated using the mineralogy and geochemistry of hydrothermal alteration, hydrogeochemistry, and resistivity models obtained from magnetotelluric data. The Salar region is located within the Afyon-Akşehir Graben (AAG) and 10 km south of Afyonkarahisar province. The most important manifestations of the geothermal system are the geothermal water at temperatures of 25 °C and 31 °C obtained from the boreholes and hydrothermal alteration in Salar. Afyon volcanoclastics are reservoir rocks. Smectite and illite are the most important clay minerals in the hydrothermal alteration zones. The transformation from volcanic glass and alkali feldspar to smectite and illite reflects neutral-alkaline alteration conditions in felsic rocks. The clay minerals' stable isotopes (δD and δ18O) indicate hypogene conditions. Discharge temperature, electrical conductivity and pH of Salar region geothermal waters vary from 25 to 31 °C, 320–357 µs/cm, and 6.8, respectively. The Salar geothermal waters are Ca-(Na)-HCO3 type chemically. The electric resistivity models reveal shallow low resistivity (10 < ρ < 80 Ωm) layer related to the alluvium, Gebeceler formation, and Afyon volcanoclastics and deeper high resistivity (80 <ρ < 200 Ωm and ρ > 200 Ωm) layer based on Deresinek and Değirmendere formation respectively. The difference in electrical resistivity arises from the geothermal waters and hydrothermal alteration zones, influenced by the AAG tectonics.The stable isotopes (δD and δ18O) and alpha cristobalite geothermometer calculations indicate that the condition of the temperature in the active and fossil geothermal systems in the Salar does not change, and the condition of the temperature is between 44 °C and 112 °C.

Improvements in recovery of rare earth elements (REEs) from coal via fluidized-bed combustion: Thermal alteration of REE mineralogy and its impact on element extractability

The extraction of rare earth elements (REE) from coal ash has attracted significant attention, but satisfactory solutions have not yet been achieved. Indeed, the REE extractability is largely determined by the transformation behavior of REE during coal combustion. This study found that the controlled combustion conditions of circulated fluidized-bed boiler (CFB) can both utilize the heating value and enhance the recovery of REE from coal. Tests were conducted using a bituminous coal with REE concentration of approximately 149 ppm in an industrial 35 t/h CFB boiler with controlled boiler loads and coal sources. Advanced automated image analysis by scanning electron microscopy (AIA-SEM) and sequential leaching procedure were employed to clarify the speciation transformation behavior of REE in boilers and investigate the effects of these transformations on the leachability of REE. Approximately 75 % of REE partitioned into fly ash and enriched in particles < 45 μm (∼710 ppm) after combustion. Acid leaching tests under mild conditions (1 M HCl at 60 ℃ and S/L = 1:25) performed on coal, bulk ashes, and sieved ashes revealed an improvement in REE leaching ratio from coal (21.34 %) to fly ash (71.07 %). Particle size played a crucial role in acid extractability, particularly for middle and heavy REE in cyclone ash but had no influence on those in fly ash. The dominant forms of REE in coal including Ca-REE fluorocarbonates (36.7 %), aluminophosphates (12.0 %), and organic-bound REE (approximately 20 %) significantly decreased, contributing to the formation of leachable rare earth oxides (∼65 %) in ash. Furthermore, the small size of REE mineral grains in coal (over 50 % below 5 μm) and extensive mineral fragmentation occurring in boiler resulted in the enrichment and enhanced REY leachability in fine ash.

Epithermal Ag–Au mineralization at Galim-Legalgorou, Cameroon Volcanic Line: insights from alteration mineralogy and mineral chemistry of electrum and sphalerite

The Galim-Legalgorou area, located along the north-western branch of the Cameroon Volcanic Line (CVL), is known for artisanal gold mining and primary gold exploration, but the style and origin of the mineralization has not been fully described in the scientific literature. The close spatial association of the mineralization with Tertiary volcanic rocks raises the question of whether or not this is an epithermal system in a region where all previously studied gold occurrences have been classified as orogenic. In this contribution, we use ore mineral and alteration assemblage and mineral microchemistry to constrain the origin and evolution of the mineralization. Gold is alloyed mainly with Ag (max. 53.1 wt%) and show fineness values that vary 379 and 721 with an average of 455. A cumulative percentile plot of Ag concentrations in the cores of all electrum particles, and the observed step-change from Au-rich cores to more Ag-rich mantles in zoned electrum particles, suggest that the mineralization was deposited by two distinct hydrothermal fluid influxes. The observed ore mineral association-electrum, Se/Tl-acanthite, pyrite, Fe-rich sphalerite, ± galena; the measured FeS contents of sphalerite (average 23.1 mol%), and the presence of colloform banded chalcedony and hydrothermal breccia are all consistent with features of low sulfidation epithermal deposits. This study, therefore, demonstrates for the first time, the presence of significant low sulfidation epithermal Ag–Au mineralization on the CVL, an intracontinental rift region only previously known for orogenic gold mineralization.Graphical

Exploring in-situ combustion effects on reservoir properties of heavy oil carbonate reservoir

Laboratory modeling of in-situ combustion is crucial for understanding the potential success of field trials in thermal enhanced oil recovery (EOR) and is a vital precursor to scaling the technology for field applications. The high combustion temperatures, reaching up to 480 °C, induce significant petrophysical alterations of the rock, an often overlooked aspect in thermal EOR projects. Quantifying these changes is essential for potentially repurposing thermally treated, depleted reservoirs for CO2 storage.In this study, we depart from conventional combustion experiments that use crushed core, opting instead to analyze the thermal effects on reservoir properties of carbonate rocks using consolidated samples. This technique maintains the intrinsic porosity and permeability, revealing combustion's impact on porosity and mineralogical alterations, with a comparative analysis of these properties pre- and post-combustion. We characterize porosity and pore geometry evolution using low-field nuclear magnetic resonance, X-ray micro-computed tomography, and low-temperature nitrogen adsorption. Mineral composition of the rock and grain-pore scale alterations are analyzed by scanning electron microscopy and X-ray diffraction.The analysis shows a significant increase in carbonate rocks’ porosity, pore size and mineral alterations, and a transition from mixed-wet to a strongly water-wet state. Total porosity of rock samples increased in average for 15%–20%, and formation of new pores is registered at the scale of 1–30 μm size. High-temperature exposure results in the calcite and dolomite decomposition, calcite dissolution and formation of new minerals—anhydrite and fluorite. Increased microporosity and the shift to strongly water-wet rock state improve the prospects for capillary and residual CO2 trapping with greater capacity. Consequently, these findings highlight the importance of laboratory in-situ combustion modeling on consolidated rock over tests that use crushed core, and indicate that depleted combustion stimulated reservoirs may prove to be viable candidates for CO2 storage.

Alteration mineralogy, characteristics and shortwave infrared spectroscopy of white mica in the Zijinshan ore field, Fujian Province: Implications for porphyry Cu prospecting

The Zijinshan ore field is situated in the southeastern part of China. in which contains the large Zijinshan high-sulfidation Cu-Au deposit, the Luoboling porphyry Cu-Mo deposit, the Yueyang low-sulfidation Au-Ag deposit, the Longjiangting and the Wuziqilong tansitional Cu deposit, and the Xi’nan porphyry Cu-Mo prospect. Debates on genetic relationship among these deposits, especially the relationship between the Zijinshan Cu-Au deposit and the adjacent Luoboling deposit is a question of importance for further exploration in this ore field. In this contribution, the alteration mineralogy, alteration texture, zonation and mineral chemistry, in combination with shortwave infrared spectroscopy (SWIR) analysis of white mica were used to help focus exploration and assessment of hydrothermal deposits in the Zijinshan ore field.In this study, diaspore-pyrophyllite alteration zone, chlorite-sericite alteration zone and propylitic alteration zone were first identified in the deep drill core of the Zijinshan Cu-Au deposit, which gives way upward to quartz-alunite-kaolinite zone, quartz-alunite zone and the silicic alteration zone. In the Xi’nan Cu-Mo prospect, diaspore-pyrophyllite alteration zone was first recognized in the shallow level with the chlorite-sericite alteration zone and propylitic alteration zone in the deeper level. Andalusite- sericite ± diaspore alteration zone was first recognized in the upper part of the Luoboling Cu-Mo deposit and the deeper part of the Wuziqilong Cu deposit. It indicates that a pervasive occurrence of diaspore -pyrophyllite ± andalusite alteration zones in the Zijinshan ore field, which may potentially represent a transitional environment between the top of porphyry alteration zones and the base of advanced argillic alteration zones. Minerals of the white mica group are extensively distributed in various alteration zones of the Zijinshan ore field. The SWIR analysis of white mica indicated that the wavelength position of the Al-OH (∼2,200 nm; wAlOH) absorption feature increases gradually from the shallow kaolinite-dickite alteration zone to the deep potassic alteration zone. In the advanced argillic alteration zones, the range of wAlOH values of white mica is less than 2205 nm. Conversely, in the porphyry alteration zones, it always exceeds 2205 nm. It is evident that the andalusite-sericite alteration zone with higher wAlOH values (average of 2203 nm) is always proximal to the porphyry mineralization, which may act as indicators for deep porphyry prospecting. The results of electron probe microanalysis (EPMA) reveal that the early enrichment of Mg and depletion of Fe in white mica can be attributed to the preferential incorporation of Fe into iron oxides and iron sulfides in the potassic and propylitic alteration zones. Overall, there is a negative correlation between wAlOH and Al, while wAlOH exhibits a positive correlation with the sum of Fe + Mg + Mn. The distribution characteristics of alteration zones and the variation patterns of the wAlOH of white mica indicate that there are probably several paleo-thermal centers in the deep parts of the Zijinshan ore field, located respectively in the deep parts of the Xi’nan Cu-Mo prospect and the deep part of the Zijinshan Cu-Au deposit and the deep parts of the Wuziqilong Cu deposit, and the latest seems to be more fertile and deserves further exploration.

Physico-chemical constraints associated with hypogene hydrothermal alteration and supergene oxidation at the Farallón Negro intermediate-sulfidation epithermal Au-Ag deposit, NW Argentina

The Farallón Negro deposit is located in the Farallón Negro Volcanic Complex (FNVC; ∼9.40 to 4.88 Ma) in NW Argentina and includes intermediate-sulfidation, epithermal Au-Ag mineralization in the Alto de la Blenda deposit. Detailed mineralogical and geochemical investigations of the Esperanza-Esperanza Sureste, Cecilia veins, both hosted in the Alto de la Blenda monzonite, and the Laboreo vein, hosted in the volcaniclastic Morada Central andesitic breccia, reveal four hypogene vein stages. Each of these four stages are comprised of a texturally early quartz, followed by a sulfide-sulfosalt and a late Mn-carbonate sub-stage. Stage 1 is characterized by a quartz, base metal and Mn-carbonate sub-stage showing high δ18OVSMOW (δ18OQuartz = 13.7 ± 0.4‰ and δ18OMn-Calcite = 11.6 ± 0.2‰) and low δ13CVPDB values (δ13CMn-Calcite = –4.7 ± 0.2‰). Stage 2 includes most gold and silver minerals in a tennantite-tetrahedrite-sphalerite-pyrite-galena±electrum sub-stage. Fluid inclusions trapped in vein-anhydrite, only associated with stage 2, record the highest temperatures (TEntrapment = 327–335°C) and highest salinity (3.8NaCleq.wt.%) when compared to all other stages. Stage 2 quartz (δ18OQuartz = 9.9 to 11.9‰) and carbonate display lower δ18OVSMOW (δ18OMn-Calcite = 7.9 to 10.3‰), as well as lower δ13CVPDB values (δ13CMn-Calcite = -5.2 to 4.7‰) than all other stages. Stages 3 and 4 consist of barren quartz and carbonate sub-stages that show lower temperatures (TEntrapment = 187–262°C) and higher δ18OVSMOW (δ18OQuartz = 13.4 to 13.9‰ and δ18OMn-Calcite = 10.7 to 11.8‰) and δ13CVPDB values (δ13CMn-Calcite = –3.5 to −3.9‰) when compared to earlier stages.Petrographic, sulfide mineral chemistry, microthermometric, and stable isotope data combined with distinct alteration mineral assemblages allow the reconstruction of a model for the Alto de la Blenda deposit. During the hypogene hydrothermal fluid flow stage, around 7.16 Ma, at ∼2.2 km depth (PHYDROSTATIC = 220 bars), the high temperature alteration mineralogy, low fluid salinities and 18O and 13C isotope compositions indicate cooling of ascending magmatic-hydrothermal fluids. These fluids were derived from a contracted magmatic vapor phase that exchanged with unexposed sedimentary rocks of the Sierras Pampeanas. Hypogene quartz-R3 illite/smectite-chlorite-calcite-pyrite alteration in the andesitic-breccia and quartz-illite-R3 illite/smectite-chlorite-calcite-pyrite alteration in the monzonite are temporally and spatially to the hydrothermal vein minerals deposited between 187 and 335°C. During the post-hydrothermal supergene weathering event, around 2.70 Ma, sulfuric acids generated by meteoric fluids and supergene oxidation of hypogene sulfides, particularly pyrite, descended along normal fault zones and related vein and fracture networks to at least 450 m depth below the surface level, forming the supergene alteration assemblage of dioctahedral smectite-kaolinite-Mn-/Fe-oxides/-hydroxides-gypsum±interstratified chlorite/smectite±interstratified R1 illite/smectite in both wall rock types at temperatures <50°C.The dominant hypogene alteration assemblage, present in the monzonite and volcaniclastic andesitic breccia, may be indicative of deeper-seated, transitional magmatic-hydrothermal systems (>1 km depth), generally controlled by fluid cooling, as is the case at Farallón Negro. Pervasive supergene alteration can conceal these systems but the identified supergene alteration assemblage of dioctahedral smectite-kaolinite-interstratified chlorite/smectite-interstratified R1 illite/smectite that replaces the hypogene alteration assemblage along the permeable fault, vein and fracture zone network may present a useful vectoring tool towards concealed, deeper-seated, epithermal Au-Ag mineralization in arid climates.

Biotite chemistry as an indicator of hydrothermal deposit types and fluid sources: Insights from big data compilation, multivariate statistical analysis, and machine learning

Identification of a deposit type in an early stage of exploration can save money and time. However, despite several studies, there is a lack of simple deposit classifiers based exclusively on the major and trace element chemistry of minerals, which is relatively easier to measure. Furthermore, the identification of fluid source is crucial for any ore-genetic study, as it exerts a first order control on physicochemical characteristics of fluid, which ultimately control the alteration mineralogy, metal solubility and mobilization, and metal association in a deposit. The stable isotope composition (e.g., δ34S, δ13C, δ18O, δ11B, etc.) of rocks and minerals is conventionally used to constrain the source of ore-forming fluids, however, the potential of mineral chemistry for constraining fluid source is not well-explored. In this study, we compile the major element composition (wt% of oxides) of a large number (n = 1932) of hydrothermal biotite from various ore settings and execute multivariate statistical analysis and machine learning-based predictive modeling to explore the potential of using biotite chemistry as an indicator of deposit type and fluid sources. The atoms per formula units (i.e., apfu values), and calculated parameters (e.g., Xphl, chlorine intercept value, log(fH2O/fHCl)fluid) is used to perform principle component analysis (PCA) and partial least square discriminant analysis (PLS-DA). The results show that among the different ore settings, iron-oxide copper‑gold, Archean gold, porphyry, and magmatic-hydrothermal rare earth metals deposits and among the fluid sources, (meta-)evaporitic, magmatic-hydrothermal, and metamorphic fluid sources can be reliably discriminated using biotite chemistry. We also show that skarn, hydrothermal platinum group elements, and carbonatite-related rare earth elements deposits may not be discriminated using biotite chemistry. Similarly, mafic rock-derived, carbonatite-derived, and meteoric fluid sources may not be discriminated by biotite chemistry. We propose multiple binary and ternary classifier diagrams, which can be used as discriminator of deposit types and fluid sources. Furthermore, we have developed four different PLS-DA predictive modeling, two for deposit types and two for fluid sources, which can predict deposit types and fluid sources with good accuracy. We provide a Windows© based program that can be used to discriminate deposit types using our PLS-DA predictive modeling. The binary and ternary classifiers and the Windows© programs are tested with recently published biotite data, and it has been shown that these classifiers and programs can efficiently separate deposit types and fluid sources. We also discuss about the limitations of the classifiers.

Mineralogy and Ore Characteristics of the Kujang Pb-Zn Skarn Deposit, Sukabumi Regency, West Java

The Kujang Pb-Zn skarn deposit is known to be the newest skarn deposit found in the Sunda-Banda magmatic arc. The skarn orebodies are mostly hosted by limestone which might be the part of the Jampang Formation where dacite porphyry is interpreted to be the ore causative intrusion. Orebodies are mostly found at the contact between marbleized limestone and volcanic rocks and are controlled by NW-SE-trending strike-slip faults. Previous research on the mineralogy and ore characteristics of the Kujang Prospect remains limited on the preliminary studies. Using fieldwork data, petrography, ore microscopy, and assay data from core samples, this study is aimed to characterize the mineralogy of both alteration and ore of the deposit. The alteration of the Kujang Prospect skarn can be divided into 2 phases of alteration i.e. prograde and retrograde. The prograde alteration is characterized by the occurrence of clinopyroxene, wollastonite, and vesuvianite. Garnet is present in very rare amounts. the retrograde alteration is typified by epidote, chlorite, calcite and actinolite. Metalliferous minerals are represented by sphalerite, galena, pyrrhotite, chalcopyrite and pyrite. All ore minerals are formed at the early retrograde stage. the deposit’s average grade is 2.06% Pb, 6.45% Zn and 1.81% Cu.

Extensive two-tier structure and breccia stockwork formation by hydrothermal processes in the first Paraná lava flow covering the Botucatu paleoerg-turned-Guarani Paleoaquifer

The Catalán Flow in the southernmost Paraná Volcanic Province exhibits two extensive red and gray to white tiers and an areally vast breccia stockwork, both of which are unique within intraplate large igneous provinces. To comprehend the processes responsible for the formation of these structures, we integrated the study of satellite images with field surveys and the interpretation of published geochemical analyses. During the Early Cretaceous, a 30-m-thick layer of quartz andesite known as the Catalán Flow covered the 160-m-thick Botucatu + Guará formations, which had transformed into the Guarani Paleoaquifer. This flow consists of a lower Tier 1, which appears gray in satellite images and medium gray to white in the field, and an upper Tier 2, which is red in both images and in the field. Amethyst and agate geodes are present in Tier 1 but are absent in Tier 2. Within an area exceeding 100 by 100 km, a breccia stockwork composed of quartz andesite fragments can be found. These fragments either include silicified sandstone or hydrothermal zeolites. The chemical composition of rocks from Tier 2 features a loss on ignition (LOI) of less than 1.5 wt% and a composition similar to the original lava. In contrast, Tier 1 underwent significant alteration, particularly a reduction in SiO2 and K2O, along with an increase in Fe2O3T, with LOI exceeding 1.5 wt% and reaching up to 8 wt%. The formation of hematite and the reddening of the rock in Tier 1 were a result of heated, oxidizing aquifer water percolating through the lava. Subsequently, reducing, aquifer hot water percolated, causing intense chemical and mineralogical alteration in the previously oxidized flow, resulting in a gray to white color and the formation of amethyst and agate deposits. Tier 1 represents the reduced lower layer of the flow, while Tier 2 is the remaining red upper portion. Comparative fluid activity is observed in red and white dunes in the Etendeka, as well as in basalts from various environments. The breccia stockwork was formed through explosive hydrothermal processes beneath the upper crust, where overpressured fluids came into direct contact with the atmosphere, leading to flash vaporization. The structures observed are the outcome of the distant influence of paleodune patterns on the Catalán Flow, which corresponds to the presence of higher dunes in the two tiers and sand sheets in the breccia stockwork. The processes responsible for the two-tier (oxidation and reduction) and breccia formation (explosive pressure release and sand injection near the surface) are recognized in various hydrothermal systems worldwide. However, the extensive areal coverage and homogeneity of these features, coupled with the presence of world-class amethyst deposits, make the Paraná Volcanic Province unique among large igneous provinces worldwide.