Hasil untuk "Mineralogy"

Alyssa Ang De Guzman, Anish Mathai Varghese, Saif Alshalloudi et al.

Permanent lunar settlements will rely on in situ oxygen production from regolith for life support and propulsion. While oxygen is abundant in lunar materials, it is chemically bound within metal oxides whose extractability depends strongly on regolith composition and processing strategy. In this study, we validate and characterize high-fidelity lunar regolith simulants representative of the lunar highlands and south pole using scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller surface area and pore structure analysis, and hydrogen temperature-programmed reduction. The simulants exhibit strong mineralogical and compositional fidelity to returned Apollo and Chang'e samples, with ilmenite confirmed as the most readily reducible oxygen-bearing phase. However, despite low ilmenite abundance, bulk highland simulants display favorable reduction behavior arising from distributed Fe-bearing silicate and glassy phases, as well as surface and microstructural properties that influence gas-solid interactions. Adsorption experiments with gases (H2, CH4, and CO2) and water indicate that mineralogical heterogeneity and pore accessibility influence their uptake in simulants. These results indicate that oxygen extraction behavior in realistic lunar regolith is governed by whole-regolith response rather than ilmenite content alone, supporting the option of whole-regolith processing strategies for oxygen production in lunar in situ resource utilization architectures.

R. Jaimes-Gutierrez, M. Prieur, D. J. Wilson et al.

<p>The Palaeocene-Eocene Thermal Maximum (PETM), a hyperthermal event <span class="inline-formula">∼</span> 56 Ma ago, allows the Earth system response to abrupt climate change to be explored. Recent investigations link the PETM with a negative lithium isotope (<span class="inline-formula"><i>δ</i>⁷</span>Li) excursion, interpreted as an increase in continental silicate weathering fluxes, which can regulate Earth's surface temperature over geological timescales. However, the silicate weathering response under different climatic regimes has yet to be constrained. Here we aim to address the chemical weathering response to the PETM in the semi-arid Southern Pyrenees, and to explore how different archives (i.e. clays and carbonate nodules) record the weathering changes.</p> <p>We investigated two continental sections in the Southern Pyrenees. In the Esplugafreda section, we measured <span class="inline-formula"><i>δ</i>⁷</span>Li values as a silicate weathering proxy and <span class="inline-formula"><i>ε</i>_Nd</span> values as a provenance proxy in the clay minerals. In the Rin section, we characterised the PETM locally by analysing <span class="inline-formula"><i>δ</i>¹³</span>C values in organic matter and examined the clay mineralogy in the paleosols, as well as measuring <span class="inline-formula"><i>δ</i>⁷</span>Li values in clays and carbonate nodules to trace silicate weathering. In the Esplugafreda section, we observe temporally stable <span class="inline-formula"><i>ε</i>_Nd</span> values, while the <span class="inline-formula"><i>δ</i>⁷</span>Li<span class="inline-formula">_clays</span> record shows two small positive excursions, one during the Pre-Onset Excursion (<span class="inline-formula">∼</span> 0.7 ‰) and a second during the body of the PETM (<span class="inline-formula">∼</span> 0.8 ‰). In the Rin section, the PETM is characterised by a negative carbon isotope excursion of 2.8 ‰. The clays consist mostly of illite/smectite, illite, kaolinite, and chlorite, consistent with a seasonal climate in the region, and we find a positive <span class="inline-formula"><i>δ</i>⁷</span>Li<span class="inline-formula">_clays</span> excursion of <span class="inline-formula">∼</span> 0.8 ‰.</p> <p>The combined <span class="inline-formula"><i>δ</i>⁷</span>Li<span class="inline-formula">_clays</span> and <span class="inline-formula"><i>ε</i>_Nd</span> records indicate increased clay formation and increased silicate weathering fluxes in the semi-arid Pyrenees, while the sediment provenance was stable. The <span class="inline-formula"><i>δ</i>⁷</span>Li values in the carbonate nodules indicate more variability, potentially due to clay contamination. Constrained by the bedrock type of dominantly reworked sediments and the seasonal precipitation regime, the initially low weathering fluxes, despite a comparatively high weathering intensity, evolved towards higher weathering fluxes with enhanced erosion during the PETM.</p>

Jorge A. Sanchez, Peter C. B. Smith, Krishna Kanumalla et al.

The elemental compositions of exoplanets encode information about their formation environments and internal structures. While volatile ratios such as carbon-to-oxygen (C/O) are used to trace formation location, the rock-forming elements - magnesium (Mg), silicon (Si), and iron (Fe) - govern interior mineralogy and are commonly assumed to reflect the host star's abundances. Yet this assumption remains largely untested. Ultra-hot Jupiters, gas-giant exoplanets with dayside temperatures above 3000 K, provide rare access to refractory elements that remain gaseous. Here we present high-resolution thermal emission spectroscopy of the exoplanet WASP-189b (Teq = 3354^{+27}_{-34} K) obtained with the Immersion Grating Infrared Spectrometer (IGRINS) on Gemini South. We detect neutral iron (Fe I), magnesium (Mg I), silicon (Si I), water (H_2O), carbon monoxide (CO), and hydroxyl (OH) at signal-to-noise ratios exceeding 4, and retrieve their elemental abundances. We show that the Mg/Si, Fe/Mg, and Si/Fe ratios are consistent with stellar values, while the refractory-to-volatile ratio is enhanced by roughly a factor of ~2. These findings demonstrate that giant-planet atmospheres can preserve stellar-like rock-forming ratios, providing an empirical validation of the stellar-proxy assumption that underpins planetary composition and formation models across exoplanet systems.

Yao Liu, Dafa Li, Hongchi Wang et al.

Dust grains in protoplanetary disks are the building blocks of planets. Investigating the dust composition and size, and their variation over time, is crucial for understanding the planet formation process. The PDS 70 disk is so far the only protoplanetary disk with concrete evidence for the presence of young planets. Mid-infrared spectra were obtained for PDS 70 by the Infrared Spectrograph (IRS) on the Spitzer Space Telescope (SST) and the Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST) in 2007 and 2022, respectively. In this work, we investigate the dust mineralogy through a detailed decomposition of the observed mid-infrared spectra. The results show that both the dust size and crystallinity increased by a factor of about two during the two epochs of observation, indicating evident dust processing in the terrestrial planet-forming region of the PDS 70 disk. The dust size (~0.8 micron) and crystallinity (~6%) in the PDS 70 disk are similar to those of other disks, which implies that the two nascent planets, PDS 70b and PDS 70c located at radial distances of ~22AU and ~34AU, do not have a significant impact on the dust processing in the inner disk. The flux densities at wavelengths longer than ~16 micron measured by JWST/MIRI are only ~60% of those obtained by Spitzer/IRS. Based on self-consistent radiative transfer modeling, we found that such a strong variability in mid-infrared fluxes can be produced by adjustments to the dust density distribution and structure of the inner disk probably induced by planet-disk interaction.

Eric Bescher, Sabina Dolenec, Daniel Jansen et al.

Calcium sulfoaluminate (CSA)-based cements represent a promising alternative to traditional Portland cement, offering benefits such as rapid strength development, low shrinkage, and reduced carbon footprint. Despite their commercial availability and proven performance, the adoption of CSA cements remains hindered by gaps in standardization and understanding. This RILEM Technical Committee (TC) CSA aims to review current knowledge, identify research needs, and address challenges related to clinkering, hydration mechanisms, durability, applications, nomenclature, standardization, and testing of CSA-based cements. The outcomes will further the understanding of manufacturing, technical performance, use, and specification of CSA-based cements, ultimately leading to broader acceptance in concrete construction.

Muhammad Fahad Ullah, Hesheng Tang, Arshad Ullah et al.

Abstract In recent decades, the partial substitution of cement with sugarcane bagasse ash (SCBA) has received attention for construction applications because of its pozzolanic characteristics. However, regional-scale studies are encouraged to increase the use of SCBA at the industrial level. Limited literature is available on the effect of SCBA on concrete Alkali-silica reactivity (ASR), CO2 emissions and economic feasibility. In the current study, the influence of adding 0%, 5%, 10%, and 15% locally available SCBA from Khyber Pakhtunkhwa on the consistency, mechanical strength, ASR, N2 adsorption, mineralogy, microstructure, and elemental compositions of concrete was investigated. In addition, CO2 emissions and cost analysis were conducted for all the concrete mixes. Experimental findings revealed that consistency increased with the addition of SCBA percentages, whereas a delay in the setting time was recorded. The Compressive strength (CS) and split tensile strength for all SCBA-based mixtures increased with ageing, due to the finer particles and higher surface area of SCBA. Additionally, SCBA effectively reduces the expansion resulting from the alkali-silica reaction. The incorporation of SCBA significantly improved the microstructure with no sign of cracks, resulting in higher reactivity and the formation of additional CSH gel than the control mix. The findings confirmed that incorporating 10% of SCBA resulted in eco-friendly construction material with enhanced strength and cost savings. Furthermore, this study is beneficial to promote the use of locally available SCBA in concrete instead of disposal in landfills.

M. Shadchin, G. Shvedov, V. Makarov et al.

New data on ore mineralogy of the Ak-Sug porphyry Au-Mo-Cu deposit (Northeastern Tuva) are presented as a result of study of ore composition using optical and scanning electron microscopy. Previously unknown minerals of Se (bohdanowiczite and berzelianite), Co (carrollite and Co-bearing pyrite), Bi (native bismuth, wittichenite, volynskite, and miharaite), Cu and Ag (mckinstryite and stromeyerite), W (scheelite), and U (brannerite) are found in ores of the deposit. The analysis of new mineral assemblages allowed us to significantly expand the list of minerals found at this deposit. The characterized minerals formed in a wide range of temperatures during several successive stages of ore formation: porphyry (carrolite and Co-bearing pyrite), epithermal and subepithermal (miharaite, volynskite, wittichenite, native bismuth, Se-bearing galena). Brannerite, berzelianite, bohdanowiczite, stromeyerite, mckinstryite, and scheelite formed at the late low-temperature stage.

Michaël Gillon, Peter P. Pedersen, Benjamin V. Rackham et al.

Located at the bottom of the main sequence, ultracool dwarf stars are widespread in the solar neighbourhood. Nevertheless, their extremely low luminosity has left their planetary population largely unexplored, and only one of them, TRAPPIST-1, has so far been found to host a transiting planetary system. In this context, we present the SPECULOOS project's detection of an Earth-sized planet in a 17 h orbit around an ultracool dwarf of M6.5 spectral type located 16.8 pc away. The planet's high irradiation (16 times that of Earth) combined with the infrared luminosity and Jupiter-like size of its host star make it one of the most promising rocky exoplanet targets for detailed emission spectroscopy characterization with JWST. Indeed, our sensitivity study shows that just ten secondary eclipse observations with the Mid-InfraRed Instrument/Low-Resolution Spectrometer on board JWST should provide strong constraints on its atmospheric composition and/or surface mineralogy.

Taehyun Kim, Xuehui Wei, Stella Chariton et al.

Many sub-Neptune exoplanets have been believed to be composed of a thick hydrogen-dominated atmosphere and a high-temperature heavier-element-dominant core. From an assumption that there is no chemical reaction between hydrogen and silicates/metals at the atmosphere-interior boundary, the cores of sub-Neptunes have been modeled with molten silicates and metals (magma) in previous studies. In large sub-Neptunes, pressure at the atmosphere-magma boundary can reach tens of gigapascals where hydrogen is a dense liquid. A recent experiment showed that hydrogen can induce the reduction of Fe$^{2+}$ in (Mg,Fe)O to Fe$^0$ metal at the pressure-temperature conditions relevant to the atmosphere-interior boundary. However, it is unclear if Mg, one of the abundant heavy elements in the planetary interiors, remains oxidized or can be reduced by H. Our experiments in the laser-heated diamond-anvil cell found that heating of MgO + Fe to 3500-4900 K (close to or above their melting temperatures) in a H medium leads to the formation of Mg$_2$FeH$_6$ and H$_2$O at 8-13 GPa. At 26-29 GPa, the behavior of the system changes, and Mg-H in an H fluid and H$_2$O were detected with separate FeH$_x$. The observations indicate the dissociation of the Mg-O bond by H and subsequent production of hydride and water. Therefore, the atmosphere-magma interaction can lead to a fundamentally different mineralogy for sub-Neptune exoplanets compared with rocky planets. The change in the chemical reaction at the higher pressures can also affect the size demographics (i.e., "radius cliff") and the atmosphere chemistry of sub-Neptune exoplanets.

Miguel Faé Linhares, Jamilla Emi Sudo Lutif Teixeira, Verônica Teixeira Franco Castelo Branco et al.

Fatigue cracking is one of the most common types of distress in asphalt pavements. Each asphalt concrete (AC) constituent and its interactions are relevant to characterize the resistance to fatigue cracking of the ACs. Also, for the selection of materials, it is essential to consider not only the capacity of the material resist to fatigue cracking but also its ability to heal. Materials owning self-heal properties can enlarge the ACs fatigue life. Many former studies investigated the self-healing of bituminous materials at the binder level. However, this material property can be dependent on the binder-aggregate interactions. Thus, the current work aims to evaluate the influence of using different fine aggregates on the fatigue cracking resistance and self-healing capacity behavior of fine aggregate matrices (FAMs). First, granite, basalt, and mica schist aggregates were subjected to physical, morphological, and mineralogical characterization. Then, three FAMs were fabricated with the same asphalt binder and these different fine aggregates. To evaluate the fatigue cracking resistance and self-healing capacity of the FAMs, frequency sweep and time sweep tests were conducted. The simplified viscoelastic continuum damage (S-VECD) theory was used to interpret the results of those tests. The mineral composition of the aggregates impacted the stiffness and the fatigue life of the FAMs. However, there was no significant influence of the aggregates on the self-healing capacity of the FAMs, since there was no significant increase in the fatigue life of the materials after the resting periods in the time sweep tests.

S.G. Skublov, A. Yosufzai, A.N. Evdokimov et al.

The study of trace element composition of beryl from the Chambalak and Digal deposits of the Darai Pech pegmatite field of the Kunar province (Afghanistan) using secondary ion mass spectrometry (SIMS) revealed the sectoriality of the beryl crystal from the Chambalak deposit. The inner and outer parts of the profile are identified as the pinacoid (0001) and prism (10 1 0) growth zones, respectively. At the boundary of these two simple forms, the Cs, Na, Ca, Fe, Mg, and V content strongly increases. The prism growth zone exhibits the growth pyramids: a decrease in the Na, Fe, V, Ni, and Cr content during growth towards the edge of the beryl crystal. The H2O and Mg content increases in the prism growth zone. No boundary between the pinacoid and prism growth zones is observed in beryl from the Digal deposit. There is a reason to consider its profile as the prism growth zone. A comparison of beryl based on the content of indicative elements, the increase of which corresponds to the fractionation trend of pegmatite melt (Cs, Li, and Rb), from pegmatite deposits of the Kunar province with beryl from other objects showed that pegmatite melt in the studied deposits was moderately fractionated corresponding to the initial evolution stages. It is shown that the content of some elements of beryl from the prism and pinacoid growth zones can fundamentally differ.

B-G Andersson, Janik Karoly, Pierre Bastien et al.

We present SCUBA-2/POL-2 850 $μ$m polarimetric observations of the circumstellar envelope (CSE) of the carbon-rich asymptotic giant branch (AGB) star IRC+10216. Both FIR and optical polarization data indicate grains aligned with their long axis in the radial direction relative to the central star. The 850 $μ$m polarization does not show this simple structure. The 850 $μ$m data are indicative, albeit not conclusive, of a magnetic dipole geometry. Assuming such a simple dipole geometry, the resulting 850 $μ$m polarization geometry is consistent with both Zeeman observations and small-scale structure in the CSE. While there is significant spectral line polarization contained within the SCUBA-2 850 $μ$m pass-band for the source, it is unlikely that our broadband polarization results are dominated by line polarization. To explain the required grain alignment, grain mineralogy effects, due to either fossil silicate grains from the earlier oxygen-rich AGB phase of the star, or due to the incorporation of ferromagnetic inclusions in the largest grains, may play a role. We argue that the most likely explanation is due to a new alignment mechanism \citep{arXiv:2009.11304} wherein a charged grain, moving relative to the magnetic field, precesses around the induced electric field and therefore aligns with the magnetic field. This mechanism is particularly attractive as the optical, FIR, and sub-mm wave polarization of the carbon dust can then be explained in a consistent way, differing simply due to the charge state of the grains.

İbrahim Çemen, Adrian Wıggıns,

The Büyük Menderes Graben (BMG) is an E-W oriented active extensional geothermal basin within the Menderes Massif, a metamorphic core complex, in Western Anatolia, Turkey. 1500 (megawatts-energy) MWe of installed geothermal capacity for power production exist as of December 2019 in Western Anatolia, mostly generated in the BMG. While the BMG is a vastly producing geothermal resource, it is predicted that it has higher production potential. However, other studies do not include field scale 3D geologic models or geothermal gradient maps. This study aims to first quantitatively test the geothermal gradients in the Aydın-İncirliova-Osmanbükü Geothermal Field (IGF), then map the information. This study also aims to compare the IGF with a neighboring geothermal field. To complete this study, information from stratigraphic columns, bottom hole temperatures, and continuous temperature logs from 13 geothermal wells is utilized with Leapfrog Geothermal to create 3D models of the geology and subsurface temperature distribution. Then, isothermal contour maps of the field are created. The geologic modeling suggests that synextensional deposition has occurred within the graben. The temperature modeling suggests both that thermal breakthrough may have occurred in the field, and that the IGF has a higher geothermal gradient than the nearby Germencik Geothermal Field

Shogo Tachibana

Kiran Mantripragada, Faisal Z. Qureshi

We present a method for hyperspectral pixel {\it unmixing}. The proposed method assumes that (1) {\it abundances} can be encoded as Dirichlet distributions and (2) spectra of {\it endmembers} can be represented as multivariate Normal distributions. The method solves the problem of abundance estimation and endmember extraction within a variational autoencoder setting where a Dirichlet bottleneck layer models the abundances, and the decoder performs endmember extraction. The proposed method can also leverage transfer learning paradigm, where the model is only trained on synthetic data containing pixels that are linear combinations of one or more endmembers of interest. In this case, we retrieve endmembers (spectra) from the United States Geological Survey Spectral Library. The model thus trained can be subsequently used to perform pixel unmixing on "real data" that contains a subset of the endmembers used to generated the synthetic data. The model achieves state-of-the-art results on several benchmarks: Cuprite, Urban Hydice and Samson. We also present new synthetic dataset, OnTech-HSI-Syn-21, that can be used to study hyperspectral pixel unmixing methods. We showcase the transfer learning capabilities of the proposed model on Cuprite and OnTech-HSI-Syn-21 datasets. In summary, the proposed method can be applied for pixel unmixing a variety of domains, including agriculture, forestry, mineralogy, analysis of materials, healthcare, etc. Additionally, the proposed method eschews the need for labelled data for training by leveraging the transfer learning paradigm, where the model is trained on synthetic data generated using the endmembers present in the "real" data.

Giulia Ceriotti, Giovanni M Porta, Claudio Geloni et al.

We develop a methodological framework and mathematical formulation which yields estimates of the uncertainty associated with the amounts of CO2 generated by carbonate-clays reactions (CCR) in large-scale subsurface systems to assist characterization of the main features of this geochemical process. Our approach couples a one-dimensional compaction model, providing the dynamics of the evolution of porosity, temperature and pressure along the vertical direction, with a chemical model able to quantify the partial pressure of CO2 resulting from minerals and pore water interaction. The modeling framework we propose allows (i) estimating the depth at which the source of gases is located and (ii) quantifying the amount of CO2 generated, based on the mineralogy of the sediments involved in the basin formation process. A distinctive objective of the study is the quantification of the way the uncertainty affecting chemical equilibrium constants propagates to model outputs, i.e., the flux of CO2. These parameters are considered as key sources of uncertainty in our modeling approach because temperature and pressure distributions associated with deep burial depths typically fall outside the range of validity of commonly employed geochemical databases and typically used geochemical software. We also analyze the impact of the relative abundancy of primary phases in the sediments on the activation of CCR processes. As a test bed, we consider a computational study where pressure and temperature conditions are representative of those observed in real sedimentary formation. Our results are conducive to the probabilistic assessment of (i) the characteristic pressure and temperature at which CCR leads to generation of CO2 in sedimentary systems, (ii) the order of magnitude of the CO2 generation rate that can be associated with CCR processes.

A. I. M. Ismail, M. S. Elmaghraby, B. N. A. Shalaby

Abstract Background The present title is aiming to study the effects of trachyte additions on the sinterability of the ceramic tiles. Four batches were designed with different trachyte/clay ratios from 10 to 40% and 3% of bentonite. Results Chemical and phase composition of the raw materials were investigated using XRF and XRD techniques as well as petrographic examination. The prepared batches were fired from 1140 to 1280 °C, their densification parameters and phase compositions as well as microstructure were investigated. Petrographically, the studied trachytic rocks are fine to medium grained, grayish to dark gray, massive rocks, built up, essentially, of alkali feldspars phenocrysts, mainly sanidine and albite, with less frequent pyroxenes and amphiboles, held together in fine to very fine-grained groundmass. The XRD patterns of the fired batches exhibited mullite and quartz as the main mineral phases. Conclusions The densification parameters declared that by rising temperature, the bulk density increased in batches of lower trachyte contents and apparent porosity decreased, while in batches of higher trachyte contents exhibited slight increase. It is evident that the main factors controlling the formation present mullite crystallization are: (A) trachyte/clay content which, consequently, affects the Al2O3/SiO2, (B) alkali contents and (C) firing temperature.

Meng Zhao, Meng Zhao, Hong-Gang Wu et al.

Loess, distributed all over the world, exhibits the behavior that is related to their formation history, mineralogy, and microstructure, which can cause serious geotechnical engineering problems. This paper presents the Baozhong railway is a key transportation channel for Guyuan city in Ningxia province of northwestern China. Based on field investigations treasure middle section of the railway in the study area, it is found that the more serious diseases subgrade settlement, local roads embankment platform dislocation occurs and lots of cracks were founded. For several years, with the train speed increasing, and due to the influence of widespread flood irrigation on the farmland, the subgrade experienced a degree of settlement. This settlement was not alleviated after three treatments, which seriously affected train safety. In order to analyze the reason for the railway line settlement, soil samples were collected from the collapsible loess subgrade. Consolidation test, particle size analysis test, X-ray diffraction test (XRD), and scanning electron microscopy test (SEM) were performed to investigate the mechanism of the subgrade disease. The results reveal that loess collected from severe differential settlements at locations has a highly compressible, and its clay content and agglomeration level was generally low. These results illustrated that the particle size of 20–50 microns has a direct effect on its mechanical properties of loess. This part of the particles has a cementation effect. It can effectively connect the large particles of the skeleton to form particle agglomerates and is an effective composition of loess clay minerals. Therefore, the loess structure was not stable due to its relatively low internal molecular attraction. When such saturated collapsible loess subgrade subjected to train vibration load, the soil might be liquefied, and its structure might be instable. If the drainage of the subgrade was not well designed, severe differential settlements would occur. The research is of great significance to clarify the relationship between loess particle composition, microstructure and its macromechanics, providing a vital reference for the engineering construction in the loess-dominated areas.

Jessica L. Luna, Caroline V. Morley

Most brown dwarfs have atmospheres with temperatures cold enough to form clouds. A variety of materials likely condense, including refractory metal oxides and silicates; the precise compositions and crystal structures of predicted cloud particles depend on the modeling framework used and have not yet been empirically constrained. Spitzer has shown tentative evidence of the silicate feature in L dwarf spectra and JWST can measure these features in many L dwarfs. Here, we present new models to predict the signatures of the strongest cloud absorption features. We investigate different cloud mineral species and determine how particle size, mineralogy, and crystalline structure change spectral features. We find that silicate and refractory clouds have a strong cloud absorption feature for small particle sizes ($\leq$ 1 $μ$m). Model spectra are compared to five brown dwarfs that show evidence of the silicate feature; models that include small particles in the upper layers of the atmosphere produce a broad cloud mineral feature, and that better match the observed spectra than the Ackerman & Marley (2001) cloud model. We simulate observations with the MIRI instrument on JWST for a range of nearby, cloudy brown dwarfs, demonstrating that these features could be readily detectable if small particles are present. Furthermore, for photometrically variable brown dwarfs, our predictions suggest that with JWST, by measuring spectroscopic variability inside and outside a mineral feature, we can establish silicate (or other) clouds as the cause of variability. Mid-infrared spectroscopy is a promising tool to empirically constrain the complex cloud condensation sequence in brown dwarf atmospheres.

Joseph Madondo, Carles Canet, Fernando Núñez-Useche et al.

Large outcrops of jasperoids occur in the ‘Montaña de Manganeso’ mining district in north-central Mexico. They range from massive manganiferous jasperoids to highly brecciated, hematitic jasperoid. The jasperoids of ‘Montaña de Manganeso’ occur mainly as replacements of limestone, sandstone and shale, commonly nearby high-angle fault systems. The mineralogy of the jasperoids consist of quartz and its polymorphs (chalcedony, tridymite and cristobalite), Fe-Mn oxyhydroxides, calcite and minor barite. Many outcrops show evidence of several periods of brecciation and silicification. The geochemical signature of the jasperoids suggests that silicification was product of hydrothermal activity. The jasperoids display enrichment in elements of hydrothermal provenance such as Ba, Sr, As, Cr, Mo, Sb, Ni, Zn and Cu, whereas are strongly depleted in the elements indicative of clastic sources such as Ti, K, Th and Zr. Element ratios such as (Fe+Mn)/Ti, Al/(Al+Fe+Mn), Fe/Mn and U /Th, along with the Al-Fe-Mn and Fe-Mn-(Ni+Co+Cu)×10 ternary diagrams confirm a hydrothermal origin. Low ∑REE, an enrichment of LREE over HREE, negative Ce anomalies and positive Y anomalies (YPASS/HoPAAS) also support the hydrothermal processes. The geological evidence, in the form of a feeder zone and extensive hydrothermal alteration, show that the silica forming the rocks originated from ascending hot fluids.