Textural Relationships Research Articles

Promotion effect of different lanthanide doping on Co/Al2O3 catalyst for dry reforming of methane

In this paper, a series of cobalt catalysts modified by different lanthanide metals were synthesized via co-impregnation method using inexpensive industrial-grade alumina as a support for dry reforming of methane. The effect of lanthanide metals as accelerators of cobalt-based catalysts on catalytic performance and anti-coking properties was mainly investigated. The textural relationships between the catalytic performance and physicochemical properties of cobalt-based catalysts doped with different lanthanide metals were further investigated. Different characterization techniques demonstrate the positive effect of lanthanide metals on the physicochemical properties of catalysts. The results show that the electron transfer between cobalt species and lanthanide metal oxides is significantly enhanced due to the introduction of lanthanide elements. The process generates more active sites, which is favorable for the adsorption and activation of methane. In addition, the abundant medium basic sites and oxygen vacancies on the surface of cobalt-based catalysts with the effect of lanthanides promoted the adsorption and activation of carbon dioxide and the gasification of carbon accumulation, which greatly improved the anti-carbon accumulation performance of the catalysts. Therefore, the prepared cobalt-lanthanum-based catalysts showed the best catalytic effect and have great potential for application.

Mantle transition zone-derived eclogite xenolith entrained in a diamondiferous Mesoproterozoic (∼1.1 Ga) kimberlite from the Eastern Dharwar Craton, India: evidence from a coesite, K-omphacite, and majoritic garnet assemblage

AbstractSubduction-related kimberlite-borne eclogite xenoliths of the Precambrian age may provide significant information about the evolution and recycling of a subducting crust as exhumed/orogenic eclogites of the pre-Mesoproterozoic time-frame are globally rare. In this paper, we report a kimberlite-borne eclogite xenolith from the diamondiferous Kalyandurg kimberlite cluster of the Eastern Dharwar Craton, India, which contains a plethora of ultra-high-pressure minerals such as coesite, majoritic garnet, and supersilicic K-rich omphacite. The presence of these ultra-high-pressure minerals is confirmed byin situX-ray diffractometry, laser Raman spectra and electron probe microanalysis. The presence of coesite undisputedly pinpoints a subduction origin for the eclogite at ∼2.8 GPa pressure, which corresponds to ∼100 km depth. The geothermobarometric estimations involving garnet–omphacite–kyanite–coesite reveal that such an eclogitic assemblage equilibrated at ∼5–8 GPa (∼175–280 km) pressure during ultra-deep subduction. The textural relationship between omphacite, coarse-grained garnet and majoritic garnet coupled with the laser Raman spectra and geobarometric estimations obtained from the majoritic garnet demonstrate that the majoritic garnet formed at ∼8–19 GPa (∼280–660 km) owing to disassociation of omphacite and coarse-grained garnet to majoritic garnet during increment of pressure up to the mantle transition zone. Thus, the mineralogical and geothermobarometric data suggest that the studied eclogite possibly travelled down to the mantle transition zone before it was rapidly carried up by a pre-Mesoproterozoic mantle plume, and subsequently entrained as a xenolith by the Mesoproterozoic (∼1.1 Ga) kimberlite.

Mineralogy and geochemistry of pattern formation in zebra rock from the East Kimberley, Australia

Rhythmic patterns are widespread in geological materials. A particularly striking, macroscale example is zebra rock from the East Kimberley region of northwestern Australia. The rock is famous for its distinctive, rhythmically ordered, iron-oxide pattern, which transforms an Ediacaran-aged siltstone into an attractive semi-precious gemstone. Several different formation mechanisms of this pattern have been proposed in previous studies, with the two most prominent being redoximorphic banding in acid-sulfate soils and Liesegang banding in an acidic hydrothermal system. Using a combination of mineralogy, geochemistry and geological context, this study attempts to confirm both the occurrence and relative timing of acid-sulfate fluid rock interactions in zebra rock and seeks to determine whether pedogenic processes or hydrothermal alteration can better explain the origin of these patterns. We present the first evidence that the iron-oxide banding developed simultaneously with a period of aluminosilicate dissolution, clay precipitation, and fluid flow, consistent with the infiltration of an acidic fluid. This conclusion was evidenced through the hexagonal-platelet morphology of the hematite pigment, kaolinite-hematite textural relationships, and a paleoflow direction preserved in the asymmetric intensity of the hematite concentration. However, while the mineralogy of zebra rock strongly suggests interactions with acid-sulfates, the origin and temperature of the fluid could not be conclusively determined. Supporting a hydrothermal origin, a thorough analysis of zebra rock mineralogy revealed a mineral assemblage consistent with advanced argillic hydrothermal alteration, wherein pyrophyillite, kaolinite, and dickite indicate minimum palaeotemperatures upwards of 120 °C and the presence of alunite and a svanbergite-woodhouseite solid solution suggests oxidising, acidic (pH <5) conditions. The low Rb/Sr ratio and relative immobility of rare earth elements in most zebra rock deposits are also consistent with an acidic hydrothermal origin. Further support was also observed in the mineralogical trends between examined outcrops, grading from alunite-type to kaolinite/dickite-type facies in a south-west direction. But despite this evidence, the acid-sulfate soil hypothesis could not be refuted and was itself supported by the large number of pyrite dissolution voids both underlying and within the patterned layer. Furthermore, the consistent compaction of reduction spheroids, dissolution voids, and pseudomorphic inclusions within the light banding of zebra rock are in agreement with near-surface supergene weathering, ruling out hypogene hydrothermal alteration. A mechanism of pattern formation is proposed whereby zebra rock banding is formed by the Liesegang phenomenon, driven by the oxidation of Fe2+ ions during the infiltration of an Fe2+-rich, acid-sulfate fluid into oxidising host sediments.

Two discrete gold mineralization events recorded by hydrothermal xenotime and monazite, Xiaoqinling gold district, central China

Abstract We present in situ LA-ICP-MS U-Pb dating of xenotime and monazite in assemblages with native gold and Au (Ag) tellurides from the Xiaoqinling lode gold district in central China. Composite xenotime and monazite grains formed through coupled dissolution-reprecipitation reactions reveal two discrete gold mineralization events. The first gold mineralization event, recorded by monazite (158.6 ± 3.3 Ma, Tera-Wasserburg lower intercept age) and xenotime cores (157.11 ± 0.83 Ma, weighted mean 206Pb/238U age), is characterized by the mineral assemblage of lingbaoite (AgTe3)-sylvanite ([Au,Ag]2Te4)-stützite (Ag5–xTe3)/native tellurium-sylvanite-stützite. The second gold mineralization event, recorded in the rims of xenotime (135.46 ± 0.93 Ma, weighted mean 206Pb/238U age), is characterized by the mineral assemblage of native gold-calaverite (AuTe2)-petzite (AuAg3Te2)-tellurobismuthite (Bi2Te3). Our study implies that the large-scale Jurassic mineralization event in eastern China, related to flat subduction of the paleo-Pacific plate beneath the eastern China continent, also caused widespread gold mineralization in the Qinling-Dabie Orogen, in addition to production of its world-class porphyry Mo deposits. The fact that only a few Jurassic gold mineralization ages have been reported before, may be due to the lack of suitable geochronometers to record the earlier Jurassic hydrothermal processes, which have been overprinted by the better-recognized Early Cretaceous gold mineralization event. This study also presents a rare example of xenotime compositional alterations and resetting of U-Pb ages induced by low to moderate salinity carbono-aqueous fluids at low temperatures. The textural relationships between gold minerals in contact with such composite xenotime crystals demonstrate that they could have precipitated before, coeval with, or after the dated domains. Since low to moderate salinity carbono-aqueous fluids are commonly involved in the formation of lode gold deposits, it is crucial to examine xenotime textures and recognize potential alteration textures before carrying out isotopic dating of xenotime collected from these deposits. Without prior compositional and textural characterization, attempts to date such composite crystals could yield mixed dates and meaningless ages.

Rutile to Titanite Transformation in Eclogites and its Geochemical Consequences: An Example from the Sumdo Eclogite, Tibet

AbstractThe formation of titanite coronae after rutile is common in retrograde high‐ to ultrahigh‐pressure meta‐mafic rocks, which provides a good opportunity to address the geochemical behavior of HFSE in crustal environments. In the Sumdo eclogite, titanite occurs either as a corona around rutile grains or as semi‐continuous veins cross‐cutting the major foliation, whereas rutile grains occur either as inclusions in garnet or omphacite or as a relict core surrounded by titanite. Textural relationships and trace elements characteristics of rutile and titanite with different occurrences indicate that both minerals preferentially incorporate Nb and Hf over Ta and Zr in aqueous fluid. Moreover, the breakdown of omphacite and epidote could release substantial amounts of aqueous fluids enriched in Ca, Si, Fe and REE, which would react with rutile to form titanite coronae and veins. During this process, water‐insoluble elements, like HFSE and HREE, behave like mobile elements, but they do not migrate substantially out of the system, instead, tending to react in situ. This suggests that the aqueous fluids released during the retrograde metamorphic reactions in mafic rocks could not substantially transfer fluid‐immobile elements into the overlying mantle wedge in subduction environments.

Genesis of greenockite (CdS) and associated sulphide‐gold mineralization from Mahakoshal belt, Central Indian Tectonic Zone

The Zn‐Cd‐S critical minerals system is a significant mineralogical indicator of hydrothermal ore‐forming processes. The understanding of greenockite (CdS) formation in natural mineral systems is very restricted due to low crustal abundances (Cd &lt;0.2 ppm). We report the first occurrence of greenockite from the Bagada orogenic gold prospect, Paleoproterozoic Mahakoshal belt, Central Indian Tectonic Zone (CITZ). This provides an ideal opportunity to access the occurrence and its genesis. Greenockite occurs in discrete sheared quartz veins hosted in phyllites. Sulphide mineralization is closely associated with hydrothermal chlorite alterations. Pyrrhotite, arsenopyrite, pyrite, and chalcopyrite assemblages are formed at high temperatures, while sphalerite and galena precipitated when the temperature decreased. Greenockite, native silver and bismuth with gold precipitated during the breakdown of arsenopyrite to scorodite in progressively oxidizing conditions. Greenockite precipitation occurred in a transforming hydrothermal environment from a reducing to an oxidizing one during late‐stage hydrothermal alteration. Sphalerite and chlorite thermometry yielded temperatures in the range from 266 to 366°C for this late‐stage hydrothermal alteration. Textural relations show two modes of occurrence of greenockite, one (Gck‐1) as exsolution within sphalerite (Sp‐2) and the other (Gck‐2) occurring as a discontinuous rim replacing the Cd‐rich sphalerite (Sp‐3). The Gck‐1 contains high Zn and low Cd, while as compared to Gck‐2. Zinc and Cd in greenockite show diadochy relation (Zn2+ ↔ Cd2+). Laser ablation ICPMS analyses of sphalerite (Sp‐2) reveal remarkably high Cd contents (1.9–12 wt%). Cd &gt;0.02 ppm suggests possible Cd derivation from sphalerite (Sp‐2) under variable fS2, T, pH, fO2 conditions, fluid–rock interaction, and change in the Zn/Cd ratio. Sphalerite compositions display a low Zn/Cd (av.22) ratio and high temperature of formation, with characteristics intermediate between volcanogenic massive sulphides (VMS) and magmatic‐hydrothermal Cu‐Pb‐Zn system.

Mineralogical and sulfur isotopic characteristics of Archean greenstone belt‐hosted gold mineralization at the Tau deposit of the Mupane gold mine, Botswana

AbstractThe Mupane gold deposit, which is one of the numerous gold occurrences in the Tati Greenstone Belt in the northeastern part of Botswana, consists of four orebodies, namely Tau, Tawana, Kwena, and Tholo deposits. The present research, which focuses on the genesis of the Tau deposit, was based on ore petrography, mineral chemistry of sulfides, and sulfur isotope data. Mineralogical characteristics of the host rocks indicate that banded iron formation at the Tau deposit includes iron oxides (magnetite), carbonates (siderite and ankerite), silicates (chlorite and amphibole), and sulfides (arsenopyrite and pyrrhotite). The deposit features arsenopyrite‐rich zones associated with biotite‐chlorite veins, which are indicative of the precipitation of arsenopyrite concomitant with potassic alteration. The replacement of magnetite by pyrrhotite in some samples suggests that sulfidation was likely the dominant gold precipitation mechanism because it is considered to have destabilized gold‐thiocomplexes in the ore‐forming fluids. Based on textural relationships and chemical composition, arsenopyrite is interpreted to reflect two generations. Arsenopyrite 1 is possibly early in origin, sieve textured with abundant inclusions of pyrrhotite. Arsenopyrite 1 was then overgrown by late arsenopyrite 2 with no porous textures and rare inclusions of pyrrhotite. Gold mineralization was initiated by focused fluid flow and sulfidation of the oxide facies banded iron formation, leading to an epigenetic gold mineralization. The mineralogical assemblages, textures, and mineral chemistry data at the Tau gold deposit revealed two‐stage gold mineralizations commencing with the deposition of invisible gold in arsenopyrite 1 followed by the later formation of native gold during hydrothermal alteration and post‐depositional recrystallization of arsenopyrite 1. Laser ablation inductively coupled plasma mass spectrometric analysis of arsenopyrite from the Tau deposit revealed that the hydrothermal event responsible for the formation of late native gold also affected the distribution of other trace elements within the grains as evidenced by varying trace elements contents in arsenopyrite 1 and arsenopyrite 2. The range of δ34S of gold‐bearing assemblages from the Tau deposit is restricted from +1.6 to +3.9‰, which is typical of Archean orogenic gold deposits and indicates that overall reduced hydrothermal conditions prevailed during the gold mineralization process at the Tau deposit. The results from this study suggest that gold mineralization involved multi‐processes such as sulfidation, metamorphism, deformation, hydrothermal alteration, and gold remobilization.

The Hydrothermal Evolution of the Alvo Açaí Cu (Au, Mo) Skarn Deposit, Carajás Province, Brazil

Abstract The Alvo Açaí Cu (Au, Mo) skarn deposit forms part of several poorly explored copper deposits in the western sector of the Carajás province in Brazil. Here, a 2.86 Ga metasyenogranitic basement and a 2.71 Ga quartzite of the Liberdade Group are crosscut by diabase and granitic pegmatite dikes in the deposit area. The sequence of hydrothermal alteration at Alvo Açaí is marked by (1) early pervasive calcic-sodic alteration (hastingsitealbite) and (2) potassic iron alteration (biotite-almandine-grunerite) overprinted by (3) silicification (quartz), (4) prograde (grossular-hedenbergite), and (5) retrograde (actinolite-biotite-epidote) skarn stages. Late pervasive chloritization along with epidote-calcite veinlets crosscut the previous alteration zones. The main stage of copper mineralization (I) is spatially and temporally related to the retrograde skarn alteration for which three chalcopyrite-bearing mineral assemblages are distinguished on the basis of textural relationships and mineral associations: (1) actinolite-chalcopyrite-pyrrhotite-pyrite-magnetite-molybdenite, (2) biotite-chalcopyrite-pyrite-magnetite, and (3) epidote-pyrite-chalcopyrite-sphalerite. Minor chalcopyrite occurs along rare latestage epidote-calcite veinlets (mineralization II). The evolution of a single hot H2O-NaCl-CaCl2–dominated magmatic fluid of moderate salinity (22.8–28.6 wt % NaCl + CaCl2 equiv) toward a cooler H2O-NaCl fluid, with likely variable amounts of FeCl2, MgCl2, and KCl of low to moderate salinity (0.1–33.2 wt % NaCl equiv). Fluid evolution as a result of progressive crystallization of the granitic pegmatite was likely the trigger for mineralization I as supported by calculated δ18OH2O values from retrograde quartz. The chalcopyrite and pyrite δ34S values (–1.5, –1.1, and –0.7‰) point to a magmatic origin for the sulfur, which was most probably leached from surrounding igneous host rocks. The evolution of the Alvo Açaí deposit encompasses the development of the first copper skarn mineralization recognized in the Carajás province.

Upcycling of composite materials waste into geopolymer-based mortars for applications in the building sector

The possibility to use quartz-composite industrial swarfs as aggregate component in geopolymer-based mortars, to produce materials for upcycling applications, was evaluated. Two different composites (A-type: 90 wt.% quartz, 10 wt.% unsaturated polyester resin; B-type: 60 wt.% quartz, 40 wt.% acrylic resin) were ground to the grainsize < 2 mm, then mixed with metakaolin and potassium silicate (K2SiO3), with the aim to obtain samples with high waste content. The samples produced, with 60–70–80 wt.% waste, show low water absorption, isolated porosity, and good textural relations among components. Mechanical tests indicated very good results at 7 and 28 days, with best data obtained for A-type 70 wt.% waste-bearing sample showing values of 7.5 MPa for flexural strength and 62.5 MPa for compressive strength. The study revealed that quartz-composite waste, usually destined to landfill, could be effectively recycled using geopolymeric binders, postponing therefore their end-of-life. The new materials are very promising for applications in the building sector, e.g., as tiles, slabs or even structural panels and bricks.

Triassic amphibolite-facies metamorphism in northeastern Hainan Island, South China

The Permian-Triassic tectonic evolution of Southeast Asia has long been a subject of considerable debate. Hainan Island in China is located at the junction of the South China and Indochina blocks adjacent to the Pacific (Philippine) Plate. Studies of metamorphic complexes in Hainan Island may shed lights on the Permian-Triassic tectono-thermal events of the eastern Paleo-Tethys. Among these complexes, the newly recognized Mulantou Metamorphic Complex is sporadically exposed in northeastern Hainan Island provides evidence for above-mentioned issues. In this paper, we present the result of a combined petrological and geochronological study of paragneisses in this complex. The paragneisses consist mainly of biotite, plagioclase, quartz, and rutile/ilmenite, with or without garnet, sillimanite, and muscovite. Textural relationships, mineral compositions, and thermobarometric calculations show that these paragneisses record peak metamorphic P − T conditions of 720–770 ℃ and 4.4–5.8 kbar. Zircon and monazite U − Pb dating by laser ablation–inductively coupled plasma–mass spectrometry indicates that metamorphism occurred at 250–235 Ma. Integrating published geochronological, geochemical, and structural data of Hainan Island and along the Jinshajiang − Ailaoshan − Song Ma suture zone, we infer that the Triassic amphibolite-facies metamorphism of the Mulantou Metamorphic Complex resulted from collision between the South China and Indochina blocks after closure of the Paleo-Tethys.

Alteration history of Séítah formation rocks inferred by PIXL x-ray fluorescence, x-ray diffraction, and multispectral imaging on Mars.

Collocated crystal sizes and mineral identities are critical for interpreting textural relationships in rocks and testing geological hypotheses, but it has been previously impossible to unambiguously constrain these properties using in situ instruments on Mars rovers. Here, we demonstrate that diffracted and fluoresced x-rays detected by the PIXL instrument (an x-ray fluorescence microscope on the Perseverance rover) provide information about the presence or absence of coherent crystalline domains in various minerals. X-ray analysis and multispectral imaging of rocks from the Séítah formation on the floor of Jezero crater shows that they were emplaced as coarsely crystalline igneous phases. Olivine grains were then partially dissolved and filled by finely crystalline or amorphous secondary silicate, carbonate, sulfate, and chloride/oxychlorine minerals. These results support the hypothesis that Séítah formation rocks represent olivine cumulates altered by fluids far from chemical equilibrium at low water-rock ratios.

Mineralogy and paragenesis of the Meso-Proterozoic Rohil uranium deposit, North Delhi Fold Belt, Rajasthan, India

The Rohil uranium deposit, located about 70 km south of the Khetri copper deposit in the North Delhi Fold Belt, Rajasthan, India, is albitite-hosted. This deposit is associated with Na-metasomatism, mainly affecting the metasedimentary wall rocks. Quartzite, quartz biotite schist, quartz amphibole schist, and graphite schist underwent variable degrees of albitization, as documented by a wide range of altered wall rocks, including weakly altered metasediments to almost pure albitites. These host rocks consist of metamorphic mineral assemblages such as Ca plagioclase – quartz – biotite – Ca amphibole – graphite – garnet – sillimanite – corundum – ilmenite. The hydrothermal alteration assemblages contain variable amounts of albite, chlorite, biotite, sericite, orthoclase, sphene, rutile, allanite, actinolite, and calcite. The textural relationships between primary host rock minerals and hydrothermal alteration products suggest four main stages of metasomatism: (1) an early pre-albitization stage, (2) a Na-metasomatic stage, that are followed by (3) a Na‐Ca-Mg- and (4) K- metasomatic stage. Albites are of two types: albite-1 is subhedral to euhedral and equidimensional, formed by the alteration of metamorphic plagioclase during the Na-metasomatic stage. Albite-2 is feathery and formed in fractures/cavities by precipitation of alkali-rich fluid during Na-Mg-Ca metasomatic stages. Albitization is pervasive on a regional scale. The hydrothermal metasomatic fluids utilized structures such as shears and breccias in the metasediments as conduits and as the loci of uranium mineralization. Major uranium minerals are uraninite, U-silicate, and brannerite. Uranium-bearing minerals occur as disseminations, in veins and as minute inclusions in biotite and titanite within albitized metasediments. The petrographic studies suggest that the metasomatic alteration of host rocks is characterized by albitization, actinolitization, carbonatization, chloritization, sericitization, biotitization, sulfidation, and silicification. The close association of U, REE-bearing minerals, and albite-2 indicates that the main U-REE mineralization stage was coeval with the Na-Ca-Mg and K-metasomatic stages.

Integrated fluid inclusion studies and source rock parameters in constraining hydrocarbon potential in offshore Lamu Basin, Kenya

Fluid inclusion signal strength and visual inclusion abundance are generally lower along migration pathways than in charged reservoirs from the same area. A zone that displays strong fluid inclusion stratigraphy (FIS) hydrocarbon indications and high visualized petroleum inclusion abundance, indicates paleo-charge or in some cases a migration pathway, e.g, where inclusion abundance is enhanced by extensive microfracturing. In this study, fluid inclusion data are interpreted in seven offshore wells of the Lamu Basin to enhance the understanding of hydrocarbon generation, migration and migration pathways. The study also examines the interrelationship among rock texture, rock composition and trapped fluid distribution in the study area. The studies were based on FIS analyzed data courtesy of Fluid Inclusion Technologies (FIT) Inc. in USA laboratories. FIT conducted analysis on 391 samples from the Paleocene to Upper Jurassic (Kiboko-1 well), 249 from the Paleoecene to Campanian (Kubwa-1 well), 106 from the Maastrichtian to Turonian (Mbawa-1 well), 59 from the Eocene to Campanian (Pomboo-1 well), 26 form the Lower Eocene to Maastrichtian (Simba-1 well), 16 from the Eocene to Maastrichtian (Kipini-1 well) and 11 from the Maastrichtian to Campanian (Kofia-1 well). It also made analysis on sidewall core sample plates, with 44 from the Maastrichtian to Campanian (Kubwa-1 well), 108 from the Campanian to Upper Jurassic (Kiboko-1 well) and 8 from the Campanian (Pomboo-1 well) for petrographic evaluation. For photomicroscopy, thin sections were examined under a petrographic microscope using Ultra Violet (UV) fluorescence and microthermometry, in order to verify the presence of petroleum bearing inclusions in the rock samples and to explore textural relationships that may yield additional information on the timing of hydrocarbon migration or generation. Gas shows in Mbawa-1 well is a result of generated hydrocarbons from the carbonate interbeds in the Upper Cretaceous. Gas shows are pockets trapped in the thin carbonate rich beds. There is low abundance of upper-low, moderate and upper-moderate gravity liquid petroleum inclusions in Kubwa-1 well (central deep offshore). The low abundance suggests migration events rather than paleo-accumulations, possibly involving several discrete charges. Despite sufficient vitrinite reflectance and total organic carbon (TOC) content, the temperatures are still insufficient for hydrocarbon generation in the southern deep offshore in the region where Kiboko-1 well is located. There is no sufficient evidence for access to mature source rocks in the deep offshore basin.

Discriminating Between Primary and Secondary Au Events in a Paragenetically Complex Archean Lode-Gold Deposit, Wawa Gold Corridor, Ontario, Canada

AbstractThe Wawa gold corridor, located in the Michipicoten greenstone belt of the Superior province, Canada, comprises Au-bearing shear zones that crosscut the 2745 Ma Jubilee stock and that evolved during protracted deformation (D1-D3). Numerous generations of sulfide minerals crystallized before, during, and after these deformation events, and gold is associated with D1 arsenopyrite, D2 pyrite, and Bi-Te phases and chalcopyrite in assemblages that crosscut D3 veins. Observations of porosity and inclusions in D1 arsenopyrite and D2 pyrite suggest these sulfides underwent coupled dissolution-reprecipitation reactions. By coupling these textural observations with trace element analysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), it is evident that such replacement reactions generated gold from Au previously in solid solution. Conversely, textural relationships among paragenetically late gold and Bi-Te minerals are consistent with the precipitation of these phases from Bi-rich polymetallic melts. Mass balance calculations involving comparisons of the mass of Au in sulfides and the total mass of Au in their associated host rocks indicate that only D1 arsenopyrite contained enough Au to account for whole-rock Au content and overall deposit grade. Although D1 arsenopyrite is less volumetrically abundant than the various pyrite generations present in the deposit, it is often replaced by the later pyrite types, which is compatible with higher initial volumes of arsenopyrite than what is presently observed. It is concluded that the D1 Au + arsenopyrite event was the principal Au-mineralizing event in the Wawa gold corridor and that the other gold-bearing assemblages (i.e., gold + D2 pyrite, gold + Bi-Te phases + chalcopyrite) largely represent secondary mobilization of this primary enrichment. Given that LA-ICP-MS sulfide chemistry is regularly used in orogenic Au research, the approach outlined herein to assess the relative impact of distinct Au- and sulfide-mineralizing events could easily be applied to the study of other Au deposits in which complex hydrothermal parageneses are recognized.

Phase equilibria modelling and textural relationship of metapelitic granulites and Grt-Bt-bearing gneisses from Mauranipur area, Bundelkhand Craton, central India

Phase equilibria modelling and textural relationship of metapelitic granulites and Grt-Bt-bearing gneisses from Mauranipur area, Bundelkhand Craton, central India

The Magmatic Evolution and the Regional Context of the 1835 AD Osorno Volcano Products (41°06’S, Southern Chile)

Abstract Osorno volcano (41°06’S, 72°20’W) is a composite stratovolcano of the Central Southern Volcanic Zone of the Chilean Andes. It is the southernmost member of a NE–SW trending alignment of volcanic edifices including La Picada and Puntiagudo volcanoes and the Cordón Cenizos chain. According to contemporary descriptions recorded by Charles Darwin in 1835, two eruptive events occurred: the first during January–February, and the second during November–December 1835 and January 1836. The volcano erupted basaltic andesite lavas and tephra fall deposits (52.4 to 52.9 SiO2 wt. %), which contain phenocrysts of olivine, plagioclase, clinopyroxene, and spinel. The compositions of these phenocryst phases, together with those of olivine-hosted melt inclusions, allowed us to constrain intensive parameters for the pre-eruptive magmas. These varied from 1060°C to 1140°C, with an oxygen fugacity buffer of ~ΔQFM +1.1, dissolved water concentrations of up to 5.6 wt. % (average of ~4.2 wt. %) and maximum pressures equivalent to ~7-km depth. Textural relations, such as crystal accumulations and clots, zoning in crystals and other indications of disequilibrium, lead us to infer the involvement of a crystal mush, rich in individual crystals and clots of crystals, which underwent a degree of disaggregation and entrainment into the transiting magma prior to eruption. Comparison of trace element abundances, including rare earth elements, fluid-mobile elements, and relatively fluid-immobile elements, combined with 87Sr/86Sr and 143Nd/144Nd isotope ratios, allows us to consider variations in slab-derived fluid input and the minor role of crustal contamination on the Osorno eruptive products and those from neighboring volcanic systems. Our results suggest both a greater contribution from slab-derived fluid and a higher degree of partial melting in the systems supplying stratovolcanoes (Osorno, Calbuco, and La Picada) relative to those supplying small eruptive centers built over the major regional Liquiñe-Ofqui Fault Zone.

Composition and Petrology of a Mush-Bearing Magma Reservoir beneath Tenerife

AbstractDeciphering the dynamics of sub-volcanic magmatic processes requires a detailed understanding of the compositional and textural relationships between melt and crystals. To examine these relationships, we investigated material from one of the largest caldera-forming explosive eruptions on the ocean island of Tenerife, the 312-ka Fasnia event. This eruption ejected juvenile pyroclasts of melt-bearing, partially crystalline cumulate nodules alongside phonolitic pumice and accidental lithic clasts. Nodules contain an average of 26% melt that is preserved as vesiculated and microcrystalline basanite in segregations, pathways and interstitial domains. Both the microcrystalline groundmass and crystal framework are generally unaltered as this crystal ‘mush’ remained supra-solidus until the eruption. We find no surficial or intrinsic evidence that the nodules were transported from their reservoir in a ‘carrier’ magma, and it is most likely that the mush was in situ when it was explosively fragmented and ejected during eruption. As such, the nodules preserve a record of the proportions and relationships between the crystal framework and pre-eruptive melt in an active magma mush reservoir, importantly, capturing a snapshot of the sub-volcanic system at a single point in time. We have analysed &amp;gt;100 of the mush nodules from the massive lithic breccia facies within the Fasnia Member of the Diego Hernández Formation. These cumulates span a diverse range of alkaline plutonic lithologies, from wehrlite and pyroxenite, through hornblende gabbros, to monzodiorite and syenite. Their textures record a range of crystallization environments, including both crystal- and melt-rich groundmass domains, and invasion of near-solidus domains by ascending reactive melts. In addition, the cumulus phases record complex interactions between felsic and mafic magmas throughout their development, providing evidence for mush remobilization and disequilibrium. Relative homogeneity of melt compositions through the mafic and felsic lithologies testifies to melt mobility through the cumulates. Nevertheless, all melts are of different basanite-intermediate composition to the juvenile phonolitic pumice ejected during the same eruption. This observation implies that the mafic–felsic cumulate mush and the phonolite did not experience significant two-way mixing and existed as separate crustal reservoirs. However, the Fasnia eruption simultaneously fragmented and removed material from both reservoirs, implying the mafic system was subjacent to the felsic, but they did not form a contiguous body.

Formation of polymetallic ores in the metasedimentary rocks of Rangpo area, Sikkim Lesser Himalaya, India: Mineralogical and geochemical attributes

Present work investigates the ore mineralogy, geochemistry of host metasedimentary rocks, and the mineral chemistry of the main sulphide minerals, namely, sphalerite, chalcopyrite, galena, and pyrite from the Rangpo sulphide mineralization, Sikkim. Based on the textural relationships of the oxide and sulphide minerals such as mutual boundary, exsolution blebs, and replacement features, three stages including two stages of primary ore mineral formation, and an alteration stage of secondary mineral development is established. Oxide and sulphide minerals predominantly magnetite, chalcopyrite, sphalerite, galena, pyrrhotite, and cobaltite occur as stage‐I ore minerals, and the sulphide minerals namely galena, pyrrhotite chalcopyrite, arsenopyrite, sphalerite, and pyrite are identified as stage‐II minerals. The alteration minerals malachite and azurite represent stage‐III. The geochemistry of host metasedimentary rocks is characterized by SiO2 in the range of 53.28 to 85.62 wt%, Mg# values between 25.48 and 49.60, MgO and K2O having a strong negative correlation with SiO2, high values of Zr/Sc (32.5) versus Th/Sc (3.44), and enrichment of trace elements like Cr (30–87 ppm), V (27–81 ppm), Ni (13–49 ppm), and Sc (3–12 ppm). The Th/Sc versus Zr/Sc, K2O/Na2O versus SiO2, and Th/Co versus La/Sc plots attribute that the host metasedimentary rocks are recycled sediments largely of passive continental margin with a felsic source. However, the Mg# versus SiO2 and K2O/Na2O versus SiO2 point to the incorporation of mantle material from the orogenic margin, possibly arc‐related and mafic in nature. The features such as the mineral assemblage, the simultaneous crystallization shown by mutual boundaries and exsolution blebs, and the mineral chemical data of ore minerals favour a high‐temperature hydrothermal environment of ore deposition. This inference is substantiated by general high Fe concentration in sphalerite and other ore minerals, 800 to 2,400 ppm Cd in sphalerite, Ag and Sb in galena from 1,000 to 2,500 ppm and 400 to 800 ppm respectively, and noticeable Ag in chalcopyrite. The inferred depositional and tectonic environment of host metasedimentary rocks, the petrographic features of ores, and their mineral chemical data altogether invoke that the Rangpo ore mineralization in metasedimentary rocks was formed at high temperature in an environment where mafic mantle material from the active arc was amalgamated with the passive margin sediments derived from the felsic source rocks.

Relationship of Textures from Tomato Fruit Images Acquired Using a Digital Camera and Lycopene Content Determined by High-Performance Liquid Chromatography

This study aimed at correlating image features with the lycopene content of tomato fruit. Tomato cultivars with different fruit colors, such as ‘Ożarowski’ (yellow), ‘Marvel Striped’ (yellow-orange-pink), ‘Green Zebra’ (green), Sandoline F1 (red), Cupidissimo F1 (red), and Sacher F1 (brown) were selected for the study. The tomato fruits were imaged using a digital camera. The texture parameters were computed from the images converted to color channels R, G, B, L, a, b, X, Y, and Z based on the histogram, autoregressive model, gradient map, co-occurrence matrix, and run-length matrix. Lycopene content was determined using high-performance liquid chromatography (HPLC). Pearson’s correlation coefficients (R), regression equations, and coefficients of determination (R2) were determined. The lycopene content in fruit ranged from 0.31 mg 100 g−1 for ‘Green Zebra’ to 11.83 mg 100 g−1 for Sacher F1. The correlation coefficient (R) between lycopene content and selected image textures reached −0.99 for selected textures from color channels G, b, and Y. The highest positive correlation (R parameter equal to 0.98) was obtained for texture from color channel Y. Based on the individual color channel providing the highest results, one texture was selected for the determination of regression equations. Coefficients of determination (R2) of 0.99 were obtained for texture from color channel G. The regression equations may be used in practice for nondestructive, objective, and precise estimation of the lycopene content in tomato fruit.

Low temperature eclogite facies rocks discovered in the Eastern Himalayan Syntaxis: Poly‐cyclic metamorphic evolution and implications

AbstractWe report the first occurrence of poly‐cyclic high‐pressure low‐temperature (HP‐LT) rocks from the easternmost Indus‐Yarlung suture zone, formed during subduction of Neo‐Tethyan oceanic lithosphere. Petrology, mineral composition and P–T pseudosection modelling reveal two low‐temperature eclogite facies metamorphic events with an initial high‐pressure P–T condition of 16.4–18.7 kbar and 510–520°C, exhumation to 10.5–12.0 kbar and 580–590°C and a subsequent second high‐pressure P–T condition of ~16 kbar and ~560°C and exhumation to ≤9 kbar and ≤600°C. This history implies a complex ‘yo‐yo type’ P–T path. In situ monazite dating and textural relationships show that late‐stage exhumation, cooling and garnet breakdown occurred at c. ~25–22 Ma. We interpret the first burial event to represent subduction of the Neo‐Tethys Ocean at the eastern Indus‐Yarlung suture zone. Initial exhumation, reburial and final exhumation represent material transport in a large‐scale convective circulation system in the subduction channel. Convective overturn in the subduction channel evidently serves both as a mechanism to produce poly‐cyclic metamorphism and to exhume LT eclogite facies rocks.