Search

Mineral reactions were studied in metamorphic rocks from the Meyeri tectonic zone, and the P–T path of the development of this structure was calculated. According to the P–T path, the Proterozoic granulite complex of the Svecofennian Belt was thrust onto low-temperature rocks of the Archean Karelian Craton. Relict staurolite and other minerals preserved as inclusions in the garnet porphyroblasts made it possible to identify the pre-peak stage of metamorphism with P–T parameters no higher than the low-temperature amphibolite facies of moderate and low pressure. The peak metamorphic conditions of the tectonic zone are estimated at T > 700°C and P ~ 7 kbar using the composition of relict minerals, while the temperature on the prograde trend of metamorphism was 500–600°C at a pressure of about 5 kbar. The post-peak stage began with a distinct decompressional P–T path at the aforementioned high temperatures, with a change from granulite hypersthene-containing assemblages to lower-temperature hydrous ones. The subsequent metamorphic retrogression was characterized by the development of numerous hydrous minerals as a result of the activation of fluids in the shear zone. The P–T path of the tectonic zone is clockwise and reflects the exhumation of the Svecofennian granulite complex during the orogenic events. [ABSTRACT FROM AUTHOR]

The demand for economical means of evaluating soil nutrients' unpredictability triggered the use of physical factors against the costlier, laborious, and time-consuming chemical approach. This drive led to resolving its capability in evaluating intricate soil properties as a productivity checker. This study aimed at assessing the efficiency of apparent electrical conductivity as a useful alternative to the conventional chemical examination of available nutrients. A petrographic examination was conducted on four rock samples for their classification as the source of soil formation. Apparent Electrical Conductivity (ECa) measurements were seasonally executed in the wet (912-station) and dry (906-station); the ArcGIS 10.2 programme was used in generating the ECa maps for classifying the ECa into low, moderate, and high sections. Ten cored (in-situ) soil samples were subjected to permeability test to ascertain water infiltration rate and retention. Twenty soil samples were examined for pH, Electrical Conductivity (EC), available phosphorus, acidity, Na, Mg, K, and Ca using standard soil science procedures. The mineralogical composition of six samples (two samples per ECa region) was determined with X-ray diffraction. The soils ECa were 10--344 µS/cm, categorized as low (1--49 µS/cm), moderate (50--99 µS/cm), and high (>100 µS/cm). The ECa distribution varied from moderate (61%) to high (64%), suggesting a heterogeneous pattern of soil attributes. The infiltration rate was slow in high ECa (5.56x10-5-1.67x10-4 cm/s), signifying good retention capability, whereas the low and moderate ECa (moderate-moderately rapid) sections promote nutrient leaching. 'Positive correlation was observed between CEC and ECa in the low ECa (2.99 cmol/kg), the same was observed in the moderate and high ECa (3.30-4.85 cmol/kg) segments'. The base cation saturation varied from high (81.38%), moderate (73.34%) and low (71.89%), characterizing the high ECa as the higher fertility status. Soils with moderate and high ECa have a greater ability to adsorb cations onto their surfaces than soils with low ECa; similarly, the deduction from base saturation showed that more cations are available in soils with high ECa. The high ECa region had low quartz (41.3%) and microcline (15.7%), but high kaolinite (31.1%) had an affinity to adsorb more cations compared to other ECa regions in terms of quantity. The rock is biotite granite gneiss, containing plagioclase (22%), microcline (24%), orthoclase (4%), quartz (25%), biotite (7%), and others (18%). ECa variability is practicable in predicting the spatial distribution of soil properties and delineating the management zones. Thereby reducing the cost that would have been expended on geochemical sampling of the entire farm. [ABSTRACT FROM AUTHOR]

Petrographic and thermobarometric data obtained on a blastolite lens hosted in sheared rocks of the Gonzhinskii block indicate that the lens contains four mineral assemblages: relict, main, an assemblage corresponding to biotitization, and that of retrograde alterations. The relict assemblage was likely eclogitic. The main mineral assemblage corresponds to zoisite amphibolite developing after eclogite. The P−T metamorphic parameters of this assemblage are P = 13.0−15.0 kbar and T = 580−670°C. However, if the calculations are done using the iron richest outer rim of amphibole 1, the P−T parameters are P = 13.0−17.0 kbar and T = 660−780°C. The mineral assemblage corresponding to the overprinted biotitization is clearly distinct texturally. The lines of the monomineral equilibria of the biotite assemblage plotted using various combinations of the composition of the garnet, biotite, and plagioclase well converge within a compact field of P = 12.5−13.2 kbar and T = 810−830°C. The latest assemblage of retrograde minerals includes low-Al amphibole 2. Our original Sm−Nd isotope date were used to calculate an isochron for a whole-rock sample, garnet, and two amphiboles. The isochron age of the rock is 171 ± 3 Ma and is interpreted as the age of the main mineral assemblage, i.e., its crystallization at the metamorphic peak. [ABSTRACT FROM AUTHOR]

Central Europe and the area of the UNESCO Global Geopark Bohemian Paradise have been affected by global tectonic events, especially during the last 500 million years. Volcanic phenomena are the most striking traces today of such past tectonic events. At the end of the Paleozoic, there were a number of volcanic eruptions connected to the waxing and waning of the Variscan Orogeny. Further volcanic activity came in the Neogene as a distal reaction to Alpine Orogenic processes. All volcanic phases show the variability of volcanic processes and have been studied intensively. In addition, these volcanic events and the production of various volcanic products enabled the emergence of local world-famous mineral deposits. The extraordinarily varied geology and the large number of volcanic features is a great tourist attraction and an excellent opportunity for a vivid interpretation of the geoheritage of Central Europe.

The reasons for the formation of rare minerals and mineral assemblages during metamorphism and metasomatosis are found to be the atypical composition of the protolith, the structural–textural heterogeneity, restricted mass transfer, and high temperatures. This is often observed under shallow conditions (pressure up to 3 kbar) during additional heating of rocks by igneous intrusions. In this paper, these questions are discussed with a series of domestic examples, the processes of mineral formation in which are studied in detail. [ABSTRACT FROM AUTHOR]

The paragenesis and composition of bavenite–bohseite were investigated in fifteen granitic pegmatites from the Bohemian Massif, Czech Republic. Three types distinct in their relation to primary Be precursors, mineral assemblages, morphology and origin were recognised: (1) primary hydrothermal bavenite–bohseite crystallised in miarolitic pockets from residual pegmatite fluids; and secondary bavenite– bohseite in two distinct types: (2) a proximal type restricted spatially to pseudomorphs after a primary Be mineral (beryl > phenakite, helvine–danalite); and (3) a distal type on brittle fractures and fissures of host pegmatite. The mineral assemblages are highly variable: (1) axinite-(Mn), smectite, calcite and pyrite; (2) bertrandite, milarite, secondary beryl, bazzite, K-feldspar, muscovite–illite, scolecite, gismondine-Ca, analcime, chlorite; and (3) muscovite, albite, quartz, epidote, pumpellyite-(Mg), pumpellyite-(Fe3+), titanite and chlorite. Electron microprobe analyses showed, in addition to major constituents (Si, Ca and Al), minor concentrations (in apfu) of Na (≤0.24), Fe (≤0.10), Mn (≤0.10) and F (≤0.36). The type 1 hydrothermal miarolitic bavenite–bohseite is mostly Al-rich (2.00–0.67 apfu) relative to type 2 proximal bavenite–bohseite and bohseite after beryl, phenakite and helvine–danalite (1.56–0.46, 0.70–0.05, 1.02–0.35 apfu, respectively); and type 3 distal bavenite–bohseite typically after beryl (1.63–0.09 apfu). Raman spectroscopy revealed that the distance between the OH– vibrational modes decreases with increasing bohseite component. The Al content of secondary type 2 proximal bavenite–bohseite is controlled by the composition of the Be precursor whereas type 3 distal bavenite–bohseite with beryl as the Be precursor is more variable and the composition is governed mainly by the composition of fluids. Calcium, a crucial component for bavenite– bohseite origins, was derived from residual pegmatite fluids (Vlastějovice, Vepice IV or Třebíč Plutons) or external sources (e.g. Drahonín IV, Věžná I or Maršíkov). Primary type 1 hydrothermal bavenite–bohseite from miarolitic pockets might have crystallised at T ≈ 300– 400°C and P ≈ 200 MPa, whereas the secondary type 2 and 3 bavenite–bohseite formed at T ≈ 300–100°C and P ≈ 200–20 MPa. [ABSTRACT FROM AUTHOR]

Central Europe and the area of the UNESCO Global Geopark Bohemian Paradise have been affected by global tectonic events, especially during the last 500 million years. Volcanic phenomena are the most striking traces today of such past tectonic events. At the end of the Paleozoic, there were a number of volcanic eruptions connected to the waxing and waning of the Variscan Orogeny. Further volcanic activity came in the Neogene as a distal reaction to Alpine Orogenic processes. All volcanic phases show the variability of volcanic processes and have been studied intensively. In addition, these volcanic events and the production of various volcanic products enabled the emergence of local world-famous mineral deposits. The extraordinarily varied geology and the large number of volcanic features is a great tourist attraction and an excellent opportunity for a vivid interpretation of the geoheritage of Central Europe. [ABSTRACT FROM AUTHOR]

Geological position, mineral assemblages, and compositional evolution of several types of mostly hydrothermal zeolite mineralizations were examined in the easternmost part of the Moldanubian Zone (Strážek Unit), Czech Republic, using EPMA and Raman spectroscopy. The zeolite mineralizations are related to the following geological processes: (A1) late magmatic to (A2, A3) hydrothermal crystallization (pseudomorphs, brittle tectonic fractures) in granitic pegmatites; (B) retrograde stages of the Variscan metamorphism - (B1) Alpine-type hydrothermal veins on ductile to brittle fractures with epidote, prehnite and zeolites, (B2) laumontite and (B3) natrolite veinlets; the latter two on thin brittle fissures; (C) hydrothermal zeolite veins with dominant stilbite-(Ca) + heulandite-(Ca) and sulfides on ductile to brittle fractures, and (D) thin brittle fissure-filling veinlets lined with harmotome ± calcite. The zeolite mineralizations include pollucite (A), analcime (A, B), phillipsite-(Ca) (A), harmotome (A, D), chabazite-(Ca) and chabazite-(K) (A, B), thomsonite-(Ca) (A), natrolite (A, B), laumontite (A, B, C), stilbite-(Ca) (B, C), scolecite (B), and heulandite-(Ca) (B, C). The individual zeolite mineralizations differ significantly in their regional distribution: (B) Alpine-type hydrothermal veins and laumontite and natrolite veinlets are widespread within almost the whole region, whereas zeolites in (A) granitic pegmatites and in (C, D) hydrothermal veins are concentrated along the eastern border of the Strážek Unit, the latter two assemblages restricted to the Rožná-Olší ore field. Fluids with variable composition and origin facilitated the formation of individual zeolite mineralizations. They evolved from moderate-T (~400 °C) to low-T (~50 °C) conditions characterized by the following extra-framework cations ± volatiles with dominant H2O: (A1) - Cs, Ba, Ca, Na ˃ K, (A2) - Ca, K, Ba ˃ Na, (A3) - Ca, Na, Ba (A: T ~400-50 °C); (B1) - Ca ± B, (B2) - Ca, (B3) - Na, Ca (B: T ~350-50 °C); (C) - Ca ˃ Na ± S, F (C: T ~240-50 °C); (D) - Ba, Ca ± CO2 (D: T ~100-50 °C). Sources of fluids include - residual fluids exsolved from pegmatite melt (A1) and external fluids derived from host rock (A2, A3); fluids related to retrograde stages of the Variscan metamorphism (A3?, B1, B2, B3, C?); likely post-Variscan fluids of various origin (C, D). The zeolite assemblages demonstrate that the PTX conditions suitable for their origin were attained in the late stages of distinctive geological processes. Zeolites may be used as a valuable indicator of alkaline to neutral and low-T to very low-T hydrothermal fluids with high activity of Ca, K, Na and/or Ba, and variable aSiO2 on tectonic fractures and fissures. [ABSTRACT FROM AUTHOR]

Fe–Mg staurolite is a typical and widespread mineral of medium-temperature high-alumina metapelites, whereas magnesian staurolite is only relatively rarely found in metamorphosed mafic rocks (metabasites). The most significant factors controlling staurolite stability in metabasites were identified by thermodynamic modeling and analysis of the common features of the mineral-forming processes. In contrast to staurolite in low- and medium-pressure metapelites, staurolite in metabasites is stable at medium- and high-pressure metamorphism. An increase in the proportion of carbon dioxide in the water–carbon dioxide fluid shifts the staurolite-forming mineral reactions to lower temperatures and higher pressures. Al, Fe, Mg, and Ca are the major components of rocks that are critically important for the formation of magnesian staurolite in these rocks, and the contents and ratios of these components are of crucial importance for the stability of staurolite in metabasites. To understand the processes forming the mineral in metabasites, it is instrumental to subdivide metabasites into subgroups of predominantly magnesian, ferruginous–magnesian, and ferruginous protoliths. With regard to this subdivision, three petrochemical modules are proposed in the form of ratios of major components: MgO/CaO, CaO/FM, and Al2O3/FM, based on which it is possible to predict the stability of staurolite in mafic rocks at appropriate P–T parameters of metamorphism. [ABSTRACT FROM AUTHOR]

Gold-silver mineralization in the Rodnikovoe LS epithermal deposit is characterized by selenium speciation. Two main alternating ore assemblages have been identified: silver-aguilarite-acanthite and gold-uytenbogaardtite-acanthite. The former mineral association is intergrown with secondary silver (Ag0.77–0.91), whereas the latter assemblage is closely associated with high-grade gold (Au0.63–0.67). However, both are dominated by Ag0.49–0.56Au0.44–0.51 alloys. The geochemical evolution of the ore-forming system developed in the direction: Fe → Cu; Ag → Au; S → Se; As → Sb. Organic compounds (1 relative %) of both biogenic and thermogenic origin were found in fluid inclusions. These molecules participated in the formation of Ag,Au-complexes and transported noble metals along with selenium. Hydrothermal fluids are characterized by fSe2/fS2 ratios < 1, conditions such that the deposition of selenide minerals is inhibited, except for the naumannite and acanthite series. These conditions allow active entry of selenium into sulfosalts (the selenium substitutes for sulfur). [ABSTRACT FROM AUTHOR]

The significance of mineralogical maturity as a provenance indicator has long been debated and we use this study to demonstrate that it can indeed be a powerful tool to track the distribution of sandstone reservoirs. We investigate the cause of the pronounced geographic and stratigraphic differences in mineralogical composition that are found in the Upper Triassic–Lower Jurassic Gassum Formation across the Norwegian–Danish Basin and surrounding areas. Zircon U-Pb dating of 46 sandstone samples including analysis of 4816 detrital grains are combined with quantifications of the detrital mineralogical composition and placed in a sequence stratigraphic framework. The results show that the Gassum Formation can be divided into a southeastern region with high mineralogical maturity and a less mature region to the northwest with more feldspars, rock fragments, micas, and heavy minerals. Both the mineralogical assemblage and the provenance signature have been thoroughly homogenized in the SE region where sediment supplies from the Fennoscandian Shield and the Variscan Orogen are evident. In the NW region, sediment was initially supplied from Fennoscandia only, but the provenance abruptly changed from the Telemarkia Terrane to comprising also the more distant Caledonian Orogen resulting in a different mineralogical assemblage. The change occurred during a basinwide regression and may be caused by tectonic movements in the hinterland that permanently changed the composition of the sediment supplied to the basin. [ABSTRACT FROM AUTHOR]

Gabbro–norites and gabbros from the Lukkulaisvaara layered ultramafic massif (Northern Karelia) was studied. The T–P parameters of its formation were determined from data on the compositions of the minerals making up these rocks. It is suggested that the Lukkulaisvaara massif was formed in three stages: the first, magmatic stage was associated with intrusion of a mafic melt and the onset of rock crystallization at temperatures above 1000–1200°C and pressure of ~10–13.5 kbar; autometasomatic reworking by fluids took place at the second, late magmatic stage; the third (hydrothermal) stage was associated with later processes. Temperatures below 800°C may reflect either the last stages of a magmatic process or a postmagmatic high-temperature hydrothermal stage. [ABSTRACT FROM AUTHOR]

The heavy minerals present in lithologic sand and sandstone units of Nanka Formation are mainly zircon, rutile, tourmaline, apatite, staurolite, and opaque minerals (Goethite, hematite, ilmenite), which are present dominant in weathered sandstones when analysed using petrographic varietal studies to infer provenance, diagenesis and source area weathering history. The low-diversity and relative abundance of heavy mineral assemblages are controlled by provenance and diagenetic processes, and these present limitations in accurate reconstruction of the paleo-history of these lithologic units using heavy minerals analysis alone. These lithologic Eocene units are derived from intensely weathered granitic and metamorphic source rocks and they are composed dominantly of matured polycyclic sediments.

[Display omitted] • Non-numerical geological data helps significantly improve model prediction accuracy. • The SHAP method assesses the importance of each input feature. • Provided an executable program for the identification of deposit types. Sphalerite is a commonly occurring mineral in natural systems and a prominent indicator mineral used in resource exploration. Its chemistry and associated mineral assemblages are both controlled by the physicochemical conditions of the local environment, such as temperature and sulfur fugacity. Accordingly, the chemistry of sphalerite and the nature of the associated minerals provide valuable clues about the classification of mineral deposits and their environment of formation. Nevertheless, exclusive reliance on the trace-element chemistry of sphalerite for deposit classification has its limitations given the multitude of factors (For example, deposit type, temperature, pressure, and background concentrations of elements) that affect its chemistry. To address this challenge, we develop machine learning models using the SHapley Additive exPlanations (SHAP) method to assess the importance of sphalerite trace-element chemistry and mineral assemblage information to distinguishing between five petrogenetically distinct mineral deposit types. This contribution demonstrates that a composite model that incorporates both data types markedly improve the accuracy of deposit type discrimination. The composite model is composed of two sub-models, Random Forest (RF) and Extra Random Trees (ERT), which are specifically employed for processing trace-element data and mineral assemblage data, respectively, due to their superior performance in handling these two distinct types of datasets. To simplify the end-user experience, we provide an executable file of the machine learning-based classifier, allowing it to be readily applied as an exploration tool using simple inputs. In summary, this work substantially enhances the confidence of Pb-Zn deposit type classification using sphalerite and introduces an innovative perspective on the application of machine learning to resolving complex geological problems. [ABSTRACT FROM AUTHOR]

Common rock-forming and accessory minerals in marbles from various localities in Slovenia were studied using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS). Minerals and their chemical composition were identified in order to verify the variability of mineral assemblages in marbles from different localities in Slovenia. The analysis showed that marbles from Košenjak are the most mineralogically diverse, followed by Pohorje and finally Strojna marbles. Common rock-forming minerals calcite and dolomite are more abundant in Pohorje marbles where calcite contains higher levels of magnesium but no strontium and iron as compared with Strojna and Košenjak marbles. Accessory minerals like quartz, mica, titanite, apatite, rutile, zircon, chlorite group minerals, kaolinite and iron oxides/hydroxides were found in marbles from all localities. Clinopyroxene, amphibole, epidote and smectite group minerals, talc, tungsten-bearing ilmenorutile, psilomelane and bismuth oxides/carbonates, were observed only in marbles from Pohorje, while tourmaline and allanite group minerals, thorite or huttonite, chalcopyrite and synchysite group minerals were detected in marbles from Košenjak and Strojna. Variations in mineral assemblages in marbles from different locations are likely a consequence of different sedimentary environment and conditions and metamorphic grade of marble. These differences indicate that marbles from Košenjak and Strojna are genetically different from those from Pohorje and probably reflect mineral composition of the protolith. Thus, they enable rough distinction between more distant locations, but not between individual sub-localities.

The late Triassic Baolun gold deposit hosted by Silurian phyllites is a large‐scale high‐grade gold deposit in Hainan Island, South China. The ores can be classified into quartz‐vein dominated type and less altered rock type. Three mineralization stages were recognized by mineral assemblages. The early stage, as the most important mineralization stage, is characterized by a quartz–native gold assemblage. The muscovite−quartz−pyrite−native gold assemblage is related to the intermedium mineralization stage. In late mineralization stage, native gold and Bi‐bearing minerals are paragenetic minerals. Microthermometry analyses show that the early mineralization stage is characterized by two types of fluid inclusions, including CO2‐rich inclusions (C‐type) and aqueous inclusions (W‐type). C‐type inclusions homogenize at 276–335°C with an averaged value of 306°C and have salinities of 1.0–10.0 wt% NaCl equivalent (mean value of 4.9 wt% NaCl equivalent). W‐type inclusions homogenize at 252–301°C (mean value of 278°C) with salinity of 4.0–9.7 wt% NaCl equivalent (mean value of 7.4 wt% NaCl equivalent). In intermedium mineralization stage, C‐type and W‐type inclusions homogenize at 228–320°C (mean value of 283°C) and 178–296°C (mean value of 241°C), with salinities of 2.4–9.9 wt% NaCl equivalent (mean value of 6.5 wt% NaCl equivalent) and 3.7–11.7 wt% NaCl equivalent (mean value of 7.7 wt% NaCl equivalent), respectively. No suitable mineral, such as quartz or calcite, was found for fluid inclusion study from late mineralization stage. In contrast, only aqueous inclusions were found from post‐ore barren veins, which yielded lower homogenization temperatures ranging from 168–241°C (mean value of 195°C) and similar salinities (2.6–12.6 wt% NaCl equivalent with averaged value of 7.2 wt% NaCl equivalent). The different homogenization temperatures and similar salinities of C‐type and W‐type from each mineralization stage indicate that fluid immiscibility and boiling occurred. The Baolun gold deposit was precipitated from a CO2‐bearing mesothermal fluid, and formed at a syn‐collision environment following the closure of the Paleo‐Tethys. [ABSTRACT FROM AUTHOR]

The article discusses the features of the composition, age, and genesis of gold–antimony mineralization of the East Sayan based on the example of the largest Tumannoe ore occurrence. It is shown that objects of this type are rare in the considered region. In the course of studies, it was found that stibnite, pyrite, and arsenopyrite predominate in ores; Bi minerals (tetradymite, cobaltite, native Bi), antimonides and sulfosalts (zinkenite, chalcostibite, aurostibite, tetrahedrite, and andorite), and three generations of native gold are also present. The mineralization contains gold–bismuth and gold–antimony ore assemblages, which are the evolutionary products of a single ore-forming system, during which a sequential decrease in the PTX parameters of ore deposition occurred, where temperatures decreased from more than 380 to 180°С. Sulfur activity decreased during ore deposition, which led to the deposition of alternating ore assemblages from simple sulfides to sulfosalts, in the direction of increasing deposited components, and to the formation of different generations of native gold with a gradual increase in fineness from early to late assemblages. The results of mineralogical–genetic and isotope–geochemical studies evidence the magmatogenic nature of gold–antimony mineralization. The isotopic age of parent granitoids, obtained by LA-ICP-MS zircon dating, is Early Ordovician; age values are 491–486 Ma. 40Ar/39Ar dating of muscovite from ore veins shows a relatively young age value (439 Ma), which is due to the influence of late tectonic and thermal events associated with the Early Paleozoic orogeny occurred at that time throughout the territory of the present-day East Sayan. [ABSTRACT FROM AUTHOR]

Certain martian hydrated silica deposits have been hypothesized to represent ancient hot spring environments, but many environments can produce hydrated silica on Earth. This study compares the mineral assemblages produced in terrestrial hot springs to those observed in silica-producing volcanic fumarolic environments to determine which diagnostic features of hot springs could be remotely sensed on Mars. We find that hot spring environments are more likely to produce geochemically mature silica (i.e., opal-CT and microcrystalline quartz) in addition to opal-A, whereas volcanic fumarolic environments tend to produce only opal-A, potentially reflecting differences in water-to-rock ratios. Neutral/alkaline hot springs contain few accessory minerals (typically calcite and Fe/Mg clays), while acidic hot springs commonly contain accessory kaolinite. By comparison, mineral assemblages at volcanic fumaroles contain protolith igneous minerals and a diversity of alteration minerals indicative of acidic conditions. Based on these terrestrial observations, the presence of opal-CT and/or microcrystalline quartz could be more diagnostic of a hot spring origin rather than a fumarolic origin, and accessory mineralogy could provide information on formation pH. On Mars, we observe that most orbital opal detections in outcrop are opal-A, sometimes accompanied by Fe/Mg clays, suggestive of neutral/alkaline conditions. However, these observations do not uniquely distinguish between hot springs and fumarolic environments, as opal-A can occur in both environments. Many martian silica detections occur in regionally extensive units, and sometimes in association with fluvial landforms suggesting a detrital or lower temperature authigenic origin. Thus, only a few martian opal detections may be mineralogically, spatially, and morphologically consistent with a hot spring origin. However, although it is difficult to unambiguously identify martian hot spring environments from orbital data sets, the orbital data are still valuable for identifying siliceous sites that are consistent with higher biosignature preservation potential, that is, sites with opal-A (not opal-CT), for future in situ investigations. [ABSTRACT FROM AUTHOR]

Copyright of Geologija (0016-7789) is the property of Geological Survey of Slovenia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Minerals in stratigraphic sections are valuable tools for reconstructing past environmental conditions. Given the state of preservation of clay minerals, it is possible to determine under what conditions they formed, which provides clues about continental weathering (inherited minerals) and geochemical conditions in the water column or pore waters (neoformed or transformed) of the sedimentary environment. This study presents new mineralogical and chemical data from the Baskil section, a well-preserved middle Eocene Neo-Tethys sequence from eastern Turkey. Greater terrigenous input is marked by the increase of silicate minerals (e.g. phyllosilicates, quartz, and albite) in the section from 40.5 to 40 Ma, which diluted the marine carbonate content. This period is correlative with the global Middle Eocene Climatic Optimum (MECO) event. Authigenic palygorskite increased from the middle to the uppermost portion (~40 to 37.3 Ma) of the section, indicating dryer conditions in the continent and availability of Si and Mg in the water column and pore waters favorable for its formation. Additionally, we suggest a stratified water column with warmer and more saline conditions at greater depths (e.g. >200 m) after ~40 Ma favoring palygorskite and possibly authigenic dolomite precipitation. The mineralogical variations and element chemistry of rocks in the Baskil section reflect how detrital sources and weathering regimes changed in this area during the middle Eocene, and how these changes can be related to global, regional, and local processes. [ABSTRACT FROM AUTHOR]

The Nanling and adjacent regions of South China host a series of tin deposits related to Mesozoic granites with diverse petrological characteristics. The rocks are amphibole-bearing biotite granites, or (topaz-) albite-lepidolite (zinnwaldite) granites, and geochemically correspond to mealuminous and peraluminous types, respectively. Mineralogical studies demonstrate highly distinctive and critical patterns for each type of granites. In mealuminous tin granites amphibole, biotite and perthite are the typical rock-forming mineral association; titanite and magnetite are typical accessory minerals, indicating high fO magmatic conditions; cassiterite, biotite and titanite are the principal Sn-bearing minerals; and pure cassiterite has low trace-element contents. However, in peraluminous tin granites zinnwaldite-lepidolite, K-feldspar and albite are typical rock-forming minerals; topaz is a common accessory phase, indicative of high peraluminity of this type of granites; cassiterite is present as a uniquely important tin mineral, typically rich in Nb and Ta. Mineralogical distinction between the two types of tin granites is largely controlled by redox state, volatile content and differentiation of magmatic melts. In oxidized metaluminous granitic melts, Sn is readily concentrated in Ti-bearing rock-forming and accessory minerals. Such Sn-bearing minerals are typical of oxidized tin granites, and are enriched in granites at the late fractionation stage. In relatively reduced peraluminous granitic melts, Sn is not readily incorporated into rock-forming and accessory minerals, except for cassiterite at fractionation stage of granite magma, which serves as an indicator of tin mineralization associated with this type of granites. The nature of magma and the geochemical behavior of tin in the two types of granites thus result in the formation of different types of tin deposits. Metaluminous granites host disseminated tin mineralization, and are locally related to deposits of the chlorite quartz-vein, greisen, and skarn types. Greisen, skarn, and quartz-vein tin deposits can occur related to peraluminous granites, but disseminated mineralization of cassiterite is more typical. [ABSTRACT FROM AUTHOR]

The Lower Paleozoic Silgará Formation in the northern Santander Massif was affected by Caledonian prograde regional metamorphism, which varies from low to medium grade and is represented by greenschist, epidote-amphibolite and amphibolite facies. The Silgará Formation shows evidence of a regional metamorphism of Buchan type (andalusite-cordierite) attributed to a crust that was affected by a considerable addition of heat due to magmas which was overimposed on the Barrovian metamorphism that characterize this massif. An anticlockwise PT path reveals that the initial conditions are represented by the mineral assemblage of chloritoid+pryrophyllite+chlorite (all assemblages with quartz+muscovite) in greenschist facies and the final conditions correspond to the mineral assemblage of sillimanite+biotite+cordierite (+muscovite+quartz+garnet if sufficient MnO and CaO are present) in amphibolite facies due to the reaction andalusite = sillimanite occurred at 600 °C and 2.4 kbar. Additionally, in these rocks several deformation events and evidences of shearing and intracrystalline deformation were found. [ABSTRACT FROM AUTHOR]

Based on the type locality mineral associations of the Arquía Group metamorphic rocks in Colombia, the pressure-temperature conditions of metamorphism were obtained and the associated P-T path was built. The analysis of the mineral assemblages indicates a prograde regional metamorphism, which varies from low to medium grade and is represented by greenschist, epidote-amphibolite and amphibolite facies. The results that are based on the prograde mineralogy [actinolite + chlorite + albite + quartz + muscovite + epidote minerals for greenschist facies and hornblende + epidote minerals + garnet + albite ± quartz for epidote-amphibolite and amphibolite facies] indicate a constant increase of metamorphic conditions from 433°C/11.8 kbar to 696°C/14.4 kbar in the metamorphic peak. Retrograde mineral assemblages [muscovite + chlorite + epidote minerals + albite + actinolite] indicate new metamorphic conditions between 417-357°C and 8.1-6.5 kbar. In addition, four deformation events and evidence of shear zone and intracrystalline deformation were found in these rocks. Resumen Con base en las asociaciones minerales existentes en las rocas metamórficas del Grupo Arquía en su sección tipo en Colombia, se determinaron las condiciones de presión-temperatura del metamorfismo y se construyó la trayectoria P-T que siguieron estas rocas. El análisis de las asociaciones minerales es consistente con un metamorfismo regional progrado de bajo a medio grado, representado por facies de esquistos verdes, facies epidota-anfibolita y facies anfibolita. Las asociaciones minerales progradas [actinolita + clorita + albita + cuarzo + moscovita + epidota en facies de esquistos verdes y hornblenda + epidota + granate + albita ± cuarzo en facies epidota-anfibolita and anfibolita] indican un aumento cons- tante en las condiciones del metamorfismo, desde 433°C/11.8 kbar hasta 696°C/14.4 kbar en el pico metamórfico. Las asociaciones minerales retrogradas [moscovita + clorita + epidota + albita + actinolita] señalan nuevas condiciones metamórficas entre 417-357°C y 8.1-6.5 kbar. Adicionalmente, estas rocas evidencian cuatro eventos de deformación, presencia de zonas de cizalla y deformación cristalina.

Based on the type locality mineral associations of the Arquía Group metamorphic rocks in Colombia, the pressure-temperature conditions of metamorphism were obtained and the associated P-T path was built. The analysis of the mineral assemblages indicates a prograde regional metamorphism, which varies from low to medium grade and is represented by greenschist, epidote-amphibolite and amphibolite facies. The results that are based on the prograde mineralogy [actinolite + chlorite + albite + quartz + muscovite + epidote minerals for greenschist facies and hornblende + epidote minerals + garnet + albite ± quartz for epidote-amphibolite and amphibolite facies] indicate a constant increase of metamorphic conditions from 433°C/11.8 kbar to 696°C/14.4 kbar in the metamorphic peak. Retrograde mineral assemblages [muscovite + chlorite + epidote minerals + albite + actinolite] indicate new metamorphic conditions between 417-357°C and 8.1-6.5 kbar. In addition, four deformation events and evidence of shear zone and intracrystalline deformation were found in these rocks. [ABSTRACT FROM AUTHOR]

Al-F sphene (grothite) was found in mineralized rocks at the Berezitovoe Deposit in the Russian Far East. The paper is devoted to the mineral assemblages and composition of the mineral and its thermodynamic crystallization conditions. The average Al and F concentrations (p.f.u., microprobe data) in the grothite are 0.45 and 0.42 in sample 1374, 0.32 and 0.32 in sample 1306, and 0.35 and 0.33 in sample 96. Grothite was found in the rocks in association with chlorite, ilmenite (pyrophanite), and magnetite, and this mineral assemblage was obviously overprinted on the primary garnet-biotite assemblages. We estimated the temperature of grothite crystallization at 400-500°C. With regard for available experimental data on the mineral equilibrium between Al-F sphene, fluid, and anorthite, a tool is proposed for evaluating F concentrations in fluids by the equilibrium of Al-F sphene with plagioclase, rutile, and F-bearing aqueous fluid. Our model simulations indicate that the maximum F concentration in fluid during the crystallization of Al-F sphene richest in F at the temperatures and pressures of metasomatic rocks at the Berezitovoe deposit could reach 300-500 mg per kg of the aqueous solution. The level of F concentration in the fluid during the crystallization of Al-F sphene at the deposit is comparable with the F concentration in fluid during the development of greisens and rare-metal pegmatites, but these high F concentrations were reached only during the final evolutionary stages of the deposit. [ABSTRACT FROM AUTHOR]

The two-pyroxene mafic granulite of Patharkhang area belongs to the Shillong-Meghalaya Gneissic Complex and includes orthopyroxene-clinopyroxene- hornblende-plagioclase ± quartz as common mineral assemblages, which are stable at thermal peak of regional metamorphism. In this study electron probe microanalysis data have been used to discuss mineral chemistry and pressure-temperature (P-T) condition of metamorphism of the mafic granulite. The average P-T condition suggests a thermal peak of metamorphism at 1029 ± 62°C/7.6 ± 1.7 kbar. [ABSTRACT FROM AUTHOR]

The Bundelkhand gneissic complex includes the highgrade metapelites, amphibolites, calc-silicates and granite-gneisses, which are invaded by 3.2-3.3 Ga old tonalite-trondjemite-grainodiorite. Detailed petrographic studies and EPMA analyses of metapelites reveal the presence of garnet-sillimanite-cordierite-biotite-K-feldspar-plagioclase-quartz, biotite-sillimanite-cordierite-K-feldspar-plagioclase-quartz and garnet-sillimanite-biotite-K-feldspar-plagioclase-quartz mineral assemblages which belong to upper amphibolite to granulite facies rocks and have been reported for the first time from the Bundelkhand craton. The average P-T conditions estimated by different models of geothermobarometry yield the core composition at 730°C/5.4 kbar and rim composition at 640°C/5.1 kbar. [ABSTRACT FROM AUTHOR]

The chemical study shows that fahlores from the Prasolovka deposit are complex compounds with significant variations in their composition and the proportions of their constituent elements. Based on their major-element composition, they are subdivided into 3 species and 11 inter-and intra-species varieties. The chemical composition of the fahlores in different mineral assemblages from different ore types indicates that As fahlores subsequently replaced by Sb, Te-Sb, and Te fahlores during ore precipitation. The revealed evolution of the ore solutions from the early to late stages testifies that different ores at the Prasolovka deposit were formed under different physicochemical conditions. [ABSTRACT FROM AUTHOR]

Edge operators are widely used on gray-level images and are recently improved to work with multispectral and even hyperspectral imagery. The high spectral information content in hyperspectral images allows a detailed description of boundaries and thus a supervised boundary detection. In this letter, we describe a template matching algorithm for the detection of fuzzy and crisp boundaries. For this purpose, the template has a one-dimensional design consisting of two different spectra. This template is matched to a remote sensing image by moving and rotating the template over the image. A statistical spatial and spectral fit of the template is calculated for every position and orientation. Important steps in this approach are the design of a template according to our knowledge of a boundary, and, mainly depending on the template design, the interpretation of the algorithm output. The algorithm has been used for the detection of boundaries between selected mineral assemblages in a hyperspectral image that covers a hydrothermal alteration system. Results show that the algorithm successfully detects the boundaries that had been defined in the templates. In addition, it is shown that rotation of the template in the algorithm reveals information on the type of boundary (crisp or fuzzy) and identifies pixels where only one of the template endmembers is present [ABSTRACT FROM PUBLISHER]

Abstract: One hundred and thirty-seven samples of ooidal ironstones from 38 localities in 8 countries (U.K., Czech Republic, Germany, France, Luxembourg, Egypt, Nigeria, U.S.A.) were investigated. The ages of these ironstones vary from Ordovician up to Late Cretaceous. The investigation is based on ore-microscopic studies, electron microprobe analysis and XRF analysis which were augmented by the determination of the H2O−, LOI, Fe2+ and Fe3+ contents. The ironstones were classified on the basis of the (FeO+MnO)–Fe2O3–SiO2 diagram. Combining these data with mineralogical aspects derived from petrographic descriptions and electron microprobe analyses, two types of ironstones, namely, the chamosite and the kaolinite types, were identified. These types may be divided into the following subtypes: unaltered, ferruginized and redeposited. Transitional subtypes which are of minor significance are the slightly oxidized, the magnetite-bearing and the moderately ferruginized chamosite subtypes. The classification of the types and subtypes is based on varying (FeO+MnO):Fe2O3-ratios. Within the (FeO+MnO)–Fe2O3–SiO2- diagram, the analytical points are distributed within three fields (I to III). Field I contains three chamosite subtypes. These subtypes consists of chamosite which occurs as groundmass and in the form of ooids (pisoids, peloids). Chamosite consists of the end-members Fetot (ranging from 73.9 to 42.2 atom%), Mg (16.2 to 5.2 atom%) and AlVI (19.9 to 41.6 atom%) and may be replaced by carbonate. Carbonate consists of the end members siderite (69.5–90.6 mol%), magnesite (6.7–17.4 mol%), calcite (1.6–12.2 mol%) and rhodochrosite (0.2 to 2.3 mol%). Other rock constituents are pyrite (mainly framboidal) and magnetite (formed at the expence of siderite under conditions of the prehnite-pumpellyite-facies). The three subtypes are (Ia) unaltered chamosite subtype (chamosite has green and siderite white internal reflections; the FeO+MnO:Fe2O3-ratio is higher than 80:20); (Ib) slightly oxidized chamosite subtype (chamosite and siderite have yellowish to brownish or reddish internal reflections; the FeO+MnO:Fe2O3-ratio is marked higher than 60:40); (Ic) magnetite-bearing chamosite subtype (the FeO+MnO:Fe2O3-ratio, which mainly depends on the quantity of magnetite Fe2+Fe3+ 2O4 is higher than 75:25 and lower than 20:80). Field II contains the analytical points of the moderately ferruginized chamosite subtype and the redeposited chamosite type. Their FeO+MnO:Fe2O3-ratios vary from about 20:80 to 5:95. The redeposited chamosite subtype consists of ferruginized ooids which are embedded in green chamosite in which authigenic siderite may occur. The moderately ferruginized chamosite subtype contains chamosite and siderite which are slightly altered and incompletely replaced by goethite and/or hematite. Field III having a FeO+MnO:Fe2O3-ratio smaller than 5:95 contains the analytical point of four ironstone subtypes: the strongly ferruginized chamosite subtype and the ferruginized kaolinite, the redeposited kaolinite and unaltered kaolinite subtypes. The latter subtype in which the ooids and the groundmass consist of kaolinite, senso stricto does not belong to ironstones, but is the proto-ore of the ferruginized kaolinite subtype. Within the (FeO+MnO)–Fe2O3–SiO2 diagram, the unaltered kaolinite type is located close to the SiO2-corner. The redeposited kaolinite subtype consists of ferruginized ooids that are embedded in kaolinite. With increasing quantity of the iron-rich ooids, the analytical points shift along the SiO2–Fe2O3 join the direction of the Fe2O3-corner. Both, the strongly ferruginized chamosite subtype and the ferruginized kaolinite subtype, which cannot be differentiated within the diagram, consist of limonite and/or hematite which replaced either chamosite or kaolinite. Remnants of altered chamosite or kaolinite may be preserved in low quantities. In the ferruginized ironstones, diagenetic pyrite and siderite occur almost only in the form of pseudomorphic replacements that are composed of goethite. Additional constituents of all the ironstones types are detrital quartz grains, apatite, organic material, pyrite (mainly framboidal) and calcite. Quartz grains may be absent, but may also occur in high quantities leading to ironstones with and without detrital quartz grains. Ironstones with high quantities of quartz grains resemble ooid-bearing sandstones. Apatite does not occur in the form of visible grains, but whole-rock analyses generally show that there is a distinct correlation between the CaO and P2O5, indicating the occurrence of apatite. Some ironstones may also be enriched in CaCO3 either in the form of detrital shelly material or as the youngest mineral in the form of calcite replacing many of the pre-existing minerals. [Copyright &y& Elsevier]

Lake Annecy in Haute Savoie, France, receives about two-thirds of its fluvial input from three rivers that flow to its southern end-point. The channels of the Eau Morte. Ire, and Bornette rivers are almost completely channelized in their lower reaches as a result of human activity, with flow contained along parallel, but separate, paths from headlands in the proximal drainage basin directly to the lake, Petrographic data from river samples collected in this study serve to differentiate sand-size material carried by each fluvial system. Proportions of the dominant (limestone) and five additional (dolomite, quartz, gypsum, rock fragments, and 'other') components in the 3 rivers are more closely related to source supply than to fluvial transport effects or sampling strategy. Of the 7 components, mica hest records the influence of depositional mechanisms. Much of the carbonate sand and coarser material at the lake shore is derived from widespread Mesozoic outcrops. Non-carbonate sand input, partially resulting from erosion of glacial till deposits and pedogenic horizons in the southern drainage basin, provides key compositional markers to differentiate between sediment carried to the lake by each river. Until several centuries ago, deposits of the Eau Morte, Ire, and Bornette flowed to the Bou du Lac, and formed a merged, multifluvial lacustrine delta. As drainage and channel containment projects related to agricultural development intensified in lake margin lowlands, the 3 channels were separated on the delta surface, allowing bypass of river material directly onto subaqueous deltas in the lake. Specific mineral assemblages, especially quartz, mica and rock fragments, may prove useful as key tracers of human-altered sediment between the margin and deeper lake sectors. [ABSTRACT FROM AUTHOR]

The Parnaíba River Delta (PRD) is the second major delta in NE Brazil and occupies approximately 100 km of the Brazilian equatorial coast. This delta is highly asymmetric due to a large tidal channel complex in the western portion that has at present time no natural connection to the Parnaíba River (PR) and the actual PR mouth in the eastern part of the PRD. A sedimentological, stratigraphic, and mineralogical study was performed on vibracores acquired in late Holocene sediments from the PRD to investigate how this environment developed during the Holocene. The core acquired in the western portion of the delta (VC-10/16) contains a medium sand layer with fluvial facies between depths of 1.50 and 0.52 m, dated by the radiocarbon method at 4.057 ± 22 BP. However, above a depth of 0.52 m, a transition to silt with tidal channel facies and higher organic matter contents (OM) and calcium carbonate (CaCO 3) is observed. Moreover, a fining-upward trend was also observed in the other four cores located farther west, and the mineral assemblage at the bases of these cores has strong similarities with cores collected in the eastern portion of the PRD (VC-07/16) in the main channel of the PR. However, the core-tops show significant variations in the assemblage of the key minerals (cordierite, cummingtonite, and garnet), indicating that in the past, the PR was connected to the western portion of the delta. The sedimentary provenance and the variations in the depositional environment indicate that a lobe switching process changed the main channel's course and caused the isolation of the delta's western portion during the late Holocene. During this period, the main channel ran through the western portion, and the large tidal channels of the delta are the ancient main channels that were abandoned during the lobe switching process probably caused by tectonics influence. • Mineral assemblages to identify delta lobe switching. • Parnaíba River Delta sedimentology and evolution during Holocene. • Vibrocores in shallow sediments. • Age dating, compositional and textural features of sediments. [ABSTRACT FROM AUTHOR]

Deterioration of mineralogical and physical characteristics of mineral raw materials results in the formation of the primary task for the comminution processes—reduction in the size of ore to obtain a material with a certain granulometric composition, which in turn is achieved by overgrinding of raw materials and, consequently, an increase in energy costs. The work aimed to justify the possibility of selective disintegration of mineral assemblages of polymetallic ores of various genesis at the stage of crushing based on in-depth investigation and revealing of interrelation and mutual influence of mineralogical-geochemical features, textural-structural and technological properties. Structural and textural features have been studied by the methods of computed X-ray microtomography. Experimental and theoretical investigations of mineralogical and technological parameters of raw materials, as well as research on crushing using different types of crushers, made it possible to substantiate the possibility of selective disintegration for polymetallic ores. [ABSTRACT FROM AUTHOR]