Mineral Assemblages Research Articles

Fluid exsolution during disequilibrium crystallization in the border and wall zones of internally zoned pegmatites

Understanding processes that occur during pegmatite crystallization are important for understanding magma evolution and enrichment processes of e.g. strategic and rare metals in pegmatites. Several processes are involved in the formation of pegmatites, and among these the timing of fluid saturation and exsolution is a critical area of investigation. The primary question focuses on if the timing of these processes influences pegmatite crystallization and the concentration of elements. The understanding of the relationship between fluid dynamics and mineralization is essential to develop comprehensive models of pegmatite formation. The unidirectional tourmaline prisms and quartz-tourmaline intergrowths (QTIs), composed of a central tourmaline surrounded by skeletal tourmaline intergrown with quartz are anisotropic textures, linked to disequilibrium crystallization at high degrees of undercooling. This study aims to trace fluid saturation and evolution in the outer zones of internally zoned pegmatites and to provide more accurate temperature constraints for their crystallization, using the Emmons pegmatite (Maine, USA) as a case study. The methodology comprises detailed inclusion petrography, microthermometric analyses, Raman spectroscopy, and LA-ICP-MS analyses. The results indicate that localized fluid saturation occurs early during the magmatic stage of pegmatite crystallization. At this point, the crystallizing mineral assemblages are composed of feldspar, muscovite, quartz, tourmaline, and minor garnet. The exsolved fluid is similar throughout the host tourmalines and is characterized by an H2O-NaCl-CO2-(N2-CH4) composition. Temperatures, which are obtained from primary fluid inclusion isochores vary between 315 °C and 440 °C and confirm that the pegmatite crystallized at undercooled conditions. A decrease in temperature occurs on a centimeter scale between the central tourmaline and the skeletal tourmaline of the QTIs, which could be caused by a nucleation delay within individual boundary layers that are formed around the central tourmaline of the QTI. The higher concentration of water and other incompatible components, including fluxes, in the boundary layer led to fluid exsolution localized at the crystal-melt interface. The increased concentration of fluxes causes a nucleation delay, increasing the degree of undercooling and consequently leading to the skeletal morphologies seen in the QTIs. Furthermore, studied melt inclusions indicate that a compositionally modified melt was present during tourmaline crystallization, confirming the existence of a boundary layer at centimeter to decimeter scale.

Magmatic (Cr-Ni-PGE) and secondary/hydrothermal (emerald-peridot-rodingite-nephrite jade) mineralization associated with mafic-ultramafic rock complexes of Pakistan

Mafic magmatism has repeatedly taken place in Pakistan throughout its geologic history from the earliest Proterozoic to Recent. Much of it, however, does not have associated metallic mineralization. This paper concerns mineralization associated with mafic-ultramafic plutonic rock occurrences in the western- and northern suture zones of Pakistan, which demarcate the collision boundary between the northwestern Indian plate and Eurasian blocks. We discuss the petrology of the ophiolites and basaltic magma-related chromite deposits, showings of PGE and Ni minerals, and secondary mineral deposits (emerald and peridot gems, rodingite, and nephrite jade) associated with mafic-ultramafic complexes of the two suture zones. Chromite with high Cr#s (68 to 85) occurs in fair quantity and is mostly considered to be genetically related to basaltic magma of subduction-related environments. PGE and nickeliferous minerals are insignificant in quantity; PGE's are formed by a higher degree of partial melting and melt-rock reaction, whereas Ni-sulphides are the product of serpentinization of the ultramafic rocks. Emerald occurs in several localities in the ISZ, whereas the peridot has so far been reported from only one locality. Emerald is associated with Mg-carbonate ± quartz ± fuchsite ± talc ± serpentine, and peridot (Fo 89-92 ) is associated with chrysotile ± magnesite ± talc ± magnetite ± ludwigite. Both are formed via hydrothermal alteration of ultramafic rocks through the introduction of hydrous fluids incorporating CO 2 , Be, B, K, Al, and possibly Na. In view of the undeformed nature of the emerald and peridot and the 23 Ma age of emerald formation, the mineralization appears to post-date deformation and may be of Late Oligocene-Early Miocene age. The metasomatising fluids were either derived from the subducting Indian plate crust underneath the Kohistan arc or were related to 23-26 Ma silicic magmatism in this area of the NW Indian plate. The nephrite jade in the ophiolite mélange is hosted in serpentinites and has disseminated grains of chrome spinel with elevated Fe/(Mg + Fe) ratios (0.10–0.18), implying low-grade metamorphism of ultramafic rocks (protolith of serpentinite) with loss of Al and introduction of SiO 2 during accompanying metasomatism. The rodingite in Dargai ophiolite could have formed by the action of seawater channeled through fractures and cracks in rocks. However, their mineral assemblages indicate that they formed as a result of the influx of Ca, Al, and Na-bearing hydrothermal fluids related to the intrusion of gabbros/sheeted dykes in the serpentinized ultramafic rocks, resulting in Ca-metasomatism.

Origin of Felsic Microgranitoid Enclaves in Granite in Zhangjiakou District, China: Implication for Process and Lifespan of Granitic Magma Chambers

AbstractSparse felsic microgranitoid enclaves (FMEs) in the Shangshuiquan granite of the Zhangjiakou district, the north margin of the North China Craton, are fine‐grained, dark‐colored and exhibit subangular to subspherical shapes. They share similar mineral assemblages, chemical compositions, and zircon Hf isotope compositions to the host granite. New zircon U‐Pb geochronology reveals that the FMEs crystallized at 156–153 Ma, while the Shangshuiquan granite formed at ca. 146 Ma. The FEMs are, therefore, 10 to 7 Ma older than the host granite. Combined with petrological evidence, we suggest that the FMEs are fragments of rapidly crystalized magmas, which were captured by the younger Shangshuiquan magma. Magmas of the FMEs and Shangshuiquan granite originated from the same reservoir. The Shangshuiquan granite is the result of small batches of magma being built up incrementally, and the FMEs belong to the earlier batches of magma. The lifespan of the Shangshuiquan magma reservoir exceeds 10 Ma. FMEs derived from cogenetic fragments have the potential to offer critical information about the formation process and timescale of granitic plutons.

GOLD ENRICHMENT MECHANISM IN MID-OCEAN RIDGE HYDROTHERMAL SYSTEMS: AN EXAMPLE FROM THE LONGQI HYDROTHERMAL FIELD ON THE ULTRASLOW-SPREADING SOUTHWEST INDIAN RIDGE

Abstract In mid-ocean ridge (MOR) hydrothermal systems, the gold grade of sea-floor massive sulfides (SMSs) is negatively correlated with the spreading rate of the ridge. Previous investigations have addressed the distribution of gold in sulfides from hydrothermal fields hosted by ultramafic rocks. In contrast, the gold enrichment mechanisms in sulfides from hydrothermal fields hosted by mafic rocks in ultraslow-spreading ridge environments are less well constrained. The basalt-hosted Longqi hydrothermal field, located on the classic ultraslow-spreading Southwest Indian Ridge, provides an opportunity to examine gold enrichment mechanisms in such an environment. Two ore-forming stages are identified in chimney fragments: anhydrite + barite + colloidal/porous pyrite (Py1) + marcasite + fine-grained sphalerite (stage 1); euhedral-subhedral pyrite (Py2) + coarse-grained sphalerite + chalcopyrite + isocubanite (stage 2). Py1 is usually overgrown by marcasite, which is in turn enclosed by Py2. Py2 coexists with coarse-grained sphalerite and chalcopyrite. Abundant native gold nanoparticles occur in Py1 or at the transition zone between Py1 and Py2. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis suggests that Py1 contains higher Mo, V, Sn, and Pb and lower As, Co/Ni, and Se/Tl values compared to Py2. In situ LA-multicollector (MC)-ICP-MS analyses show that Py1 has a higher mean δ34S (+7.1‰) value than Py2 (+6.6‰). Sulfur primarily derives from MORB and seawater sulfate, of which the proportion of sulfur from seawater sulfate is between 20.5 and 47.6%. Textures, mineral assemblages, and trace element contents of sulfides indicate that the degree of mixing between hydrothermal fluids and seawater decreases as the chimney grows and is accompanied by a gradual increase in temperature. Based on data compiled from 41 hydrothermal fields hosted by basalt, the large range of sulfide δ34S from slow- and ultraslow-spreading MORs may be attributed to the wide range of sulfur sources (e.g., leaching from MOR basalt, thermochemical reduction of seawater sulfate, magma degassing, and bacterial activity), fluid-basalt interaction, and redox state (CH4/CO2 ratios). Prolonged fluid-basalt interaction and the type of chimneys, such as beehive chimneys, may lead to higher gold grades in hydrothermal fields. Moreover, low H2S content may be an important contributor to gold enrichment in basalt-hosted SMS deposits in ultraslow-spreading MOR environments.

Preliminary Geological Mapping, Petrographic, and Structural Studies of Precambrian Basement Complex Rocks in Part of Chulwe-Matale, South Kivu, DR Congo

A geological map is a veritable planning tool for the economic development of any nation. This map contains the distribution of various types of bedrock in the area. A geological map of Congo’s geographic landmass has been produced since 1974 with the recently updated map of Kivu (Eastern part of Congo) in February 2018. This map largely omits some local geology of interest, possibly owing to its large area coverage. Thus, local geologic mapping must be encouraged to bridge this lacuna; the focus of this study. Field traversing and rock sample collections were carried out and thin sections of the different rock types were prepared and mounted on glass slides for microscopic observation. Geological mapping revealed that the study area is made of ferruginous, graphitic sandstone schists and quartzite with interbedded metadoleritic sills. The petrographic studies revealed the mineral assemblages of quartz-feldspars-muscovite and olivine-pyroxene and plagioclase feldspars respectively for the first and the second group geological units. The structural investigations come out of two deformation phases: the strike-slip type would be at the origin of the cleavages and folds. It’s related to the D1 of the Kibarian orogeny. The second is an extensive phase responsible for the NW-SE fracturation mapped in the study area. The Matale discordance crosses all these lithologies, a later phase is possible. This discontinuity would have acted in the region studied by switching the lithology units from NE-SW to ENE-WSW orientation. This research recommends that the Chulwe-Matale formations would be typical of the Lower Kibarian (Bugarama group) but the geochronology and geochemical data are lacking to confirm this hypothesis.

Microimpurities in pyrite of gold ore occurrences of the Manitanyrd ridge (the Polar Urals)

The microelement composition was studied of pyrite, the main concentrator of gold in sulfidization zones in ore occurrences of the Manitanyrd Ridge. The ore mineralization is assigned to the gold-sulfide-quartz vein and gold-sulfide types. We determined a wide range of ore-forming elements, associated with gold in pyrite. These elements correspond to geochemical features of the late galena-chalcopyrite-sphalerite mineral assemblage of the ore process, as well as to its final stage expressed in the appearance of elements reflecting the mineralogy of gray ores and bismuth sulfosalts. Pyrites from the vein and mineralized zones, from the ores of the deposit and from the secondary lithochemical anomalies, were found to contain the same set of the gold satellite elements: Ag, Cu, Zn, Pb, As. In pyrite of the gold-sulfide-quartz veins, Au has close correlations with the main elements of the ore association. In pyrite of the mineralized zones, all the correlations between Au and the ore-forming elements are absent. The pair-wise correlation between the ore-forming elements in these zones also changes completely. It is demonstrated that the identified differences in correlations between Au and the ore-forming elements in pyrite are a criterion for assessment of the lithochemical anomalies and allow one to propose a strategy of prospecting for new ore objects in the Manitanyrd region.

An inorganic silicate simulant to represent the interior of enceladus

Enceladus, an icy moon of Saturn, consists of an ice shell, global subsurface ocean and a silicate interior. By sampling plume material, the Cassini spacecraft found evidence of ongoing water-rock reactions between the silicate interior and the subsurface ocean. These data showed that these reactions provide a source of bioessential elements to the ocean, making Enceladus one of the leading astrobiological targets in our Solar System. Understanding these water-rock reactions is critical in understanding the potential habitability of Enceladus. To study these reactions experimentally, a chemical simulant to represent the contemporary silicate interior of Enceladus has been designed. Based on the available interpretations of Cassini data about the density, chemical composition, and aqueous alteration of the interior, the chosen starting point for the simulant is a CI chondrite. However, Enceladus is still undergoing active aqueous alteration, thus its silicate mineral assemblage cannot have reached the fully altered assemblage seen in a CI chondrite. To account for this, adaptations have been made to a CI chondrite mineral assemblage, extrapolating back to an assemblage of less aqueously altered minerals whilst maintaining the same chemical composition in terms of major oxide phases. Thus, the chemical and mineralogical composition of this simulant represents a best estimate of the silicate components in the ongoing water rock interactions on Enceladus today.

Post-orogenic magmatic-hydrothermal system in the southern Songpan-Ganze Orogen, eastern Tibetan Plateau

ABSTRACT Post-orogenic magmatism is uncommon in the Songpan-Ganze Orogen (SGO), and could provide deep insights into geodynamic evolution and related metallogenesis. Here we present zircon U-Pb-Hf isotopes and whole-rock geochemical data, for post-orogenic granitoids newly identified in the southern SGO. The Longxigou and Yangfanggou granites yield crystallization age of ca. 165 Ma and εHf(t) values of +3.8 to −9.1. This age post-dates regional ca. 220–200 Ma orogenic magmatism and ca. 205–190 Ma peak metamorphism, and corresponds to ca. 200–150 Ma post-orogenic magmatism which is exemplified by neighbouring and coeval Wenjiaping and Wulaxi felsic plutons. They are crosscut by ca. 133 Ma granitic pegmatites, with εHf(t) values of −4.3 to −14.2. These post-orogenic granites show high SiO2 contents, as well as low Mg# values, (Zr + Nb + Ce + Y) concentrations and zircon saturation temperatures. They have continental crust-like REE patterns and trace element profiles, and exhibit negative Eu anomalies, enrichment in large ion lithophile elements and depletion in high field strength elements. Their mineral assemblages lack typical high-temperature (e.g. pyroxene and fayalite) and peraluminous (e.g. garnet and cordierite) varieties. All these features indicate an I-type granite affinity, and a dominant derivation from thickened lower crust. In comparison, these post-orogenic granites are compositionally distinct from regional late-orogenic (>200 Ma) categories, which have more positive εHf(t) values and higher Mg# values, with subduction-related signatures involving significant mantle components. Further, several high-grade stratiform Cu deposits and a tungsten deposit occur to the south of these granitic plutons, and have mineralization ages of 164–151 Ma together with biotite alteration age of ca. 134 Ma. Hence, ca. 165–133 Ma magmatic-hydrothermal system was most likely responsible for Cu-W mineralization and effective upgrading of metal deposits in the southern SGO.

High-pressure mafic granulite and supracrustal rocks in the southern Hengshan area, North China Craton: Metamorphic P-T-t evolution and geotectonic significance

Amphibolite- to granulite-facies rocks are widely distributed in the Hengshan Complex, middle Trans-North China Orogen, and the high-pressure (HP) mafic granulite has been recently identified in the southern Hengshan area. The HP mafic granulite and amphibolite occur as rootless tectonic boudins/lenses within the TTG (tonalite–trondhjemite–granodiorite) gneiss/metapelite, indicative of typical “block-in-matrix” texture of metamorphic-tectonic mélange. Three to four generations of metamorphic mineral assemblages that correspond to the prograde (M1), peak (M2), and retrograde (M3-M4) stages, are recognized in these rocks. Conventional geothermobarometry and phase equilibrium modeling yield peak P–T conditions of 10.8–13.8 kbar/754–799 °C for the HP mafic granulite and 7.3–9.0 kbar/690–725 °C for the supracrustal rocks, respectively. A clockwise P–T path with near-isothermal decompression (ITD) and subsequent near-isobaric cooling (IBC) segments is reconstructed for the HP mafic granulite, indicating a dynamic subduction–collision–exhumation process that unfolded during an orogenic event. Secondary ion mass spectrometry (SIMS) U-Pb dating of zircon yields metamorphic ages of ca. 1.91–1.83 Ga, representing the long-lived tectono-metamorphic event caused by collision between the Eastern and Western Blocks along the Trans-North China Orogen. It is hypothesized that the tectono-metamorphic mélange in the area originated from the tectonically juxtaposition of metamorphic rocks that had diverse protoliths, different peak P–T conditions and discrepant metamorphic ages. This complexity may be a hallmark of Paleoproterozoic orogens, drawing intriguing parallels with the intricate characteristics observed in Phanerozoic orogenic belts.

Jurassic tectonic regime transition of the southwestern Yangtze Block, SW China: evidence from sedimentary provenance analysis

The Lufeng Basin (LFB) in central Yunnan is located on the southwestern margin of the Yangtze Block in the eastern segment of the Tethys tectonic domain, where the Paleo-Tethys and the Paleo-Pacific tectonic domains converge. Jurassic red beds in this basin record the closure of the Paleo-Tethys Ocean and key information of the tectonic transition driven by the spreading of the Paleo-Pacific plate. We present sedimentary provenance analysis on these Jurassic red beds based on heavy mineral assemblages and detrital zircon geochronology. The results indicate that the strata in this basin were deposited after 214 Ma, and the Early Jurassic Lufeng Formation (Lufeng Fm.) mainly sourced from the west of the LFB with minor contributions from the western Yunnan. In contrast, the sedimentary provenance of the Middle Jurassic Chuanjie Formation (Chuanjie Fm.) and Laoluocun Formation (Laoluocun Fm.) shifted to the proximal ancient basement surrounding the basin and the east of the LFB. The regional unconformity between the Early and the Middle Jurassic may have resulted from the subduction of the Paleo-Pacific plate, jointly influenced by two tectonic domains. The sedimentary provenance shift in the Middle Jurassic may be related to the local uplift of the southwestern Yangtze Block caused by the subduction of the Paleo-Pacific plate. The tectonic regime transition associated with this highest peak of local uplift occurred at ∼170 Ma.

Visible-Near Infrared–Short-Wave Infrared Spectroscopy and Mineral Mapping of Hydrothermal Alteration Zones at the Brejuí W-Mo Skarn Deposit, Seridó Mobile Belt, Borborema Province, Brazil

Abstract The Brejuí W-Mo skarn deposit is the main scheelite deposit of the Seridó tungsten province (Borborema province, NE Brazil). It constitutes the largest Brazilian W ore reserve. The orebodies are hosted in the metasedimentary Jucurutu Formation of the Seridó Group (650–610 Ma), close to the margin of the Neoproterozoic Acari pluton (Brasiliano orogeny). Skarns include prograde and retrograde mineral assemblages. Infrared spectral analysis shows that the skarns mainly reflect retrograde mineral assemblages, formed in three different hydrothermal alteration stages with overprinting. Mineral phases spectrally detected include (1) vesuvianite, actinolite, and phlogopite (alteration stage 1), (2) epidote, prehnite, and illite (alteration stage 2), and (3) laumontite, montmorillonite, chlorite, and gypsum (alteration stage 3; main ore zone). Phlogopite chloritization and actinolite recrystallization were observed in the main W-Mo skarn orebodies. Chloritization is marked by a displacement in the Fe-OH–related absorption wavelength (2,246.5–2,250.5 nm). A spectral index using spectral mixtures of laumontite + montmorillonite + actinolite is proposed here to map mineralized skarn layers (WO3 + Mo ≥ 0.1%) in drill cores. It was used to vector to richer mineralized bodies of the Brejuí deposit successfully and may be applied to similar skarn deposits with the same aim.

Automated pipeline processing X-ray diffraction data from dynamic compression experiments on the Extreme Conditions Beamline of PETRAIII.

Presented and discussed here is the implementation of a software solution that provides prompt X-ray diffraction data analysis during fast dynamic compression experiments conducted within the dynamic diamond anvil cell technique. It includes efficient data collection, streaming of data and metadata to a high-performance cluster (HPC), fast azimuthal data integration on the cluster, and tools for controlling the data processing steps and visualizing the data using the DIOPTAS software package. This data processing pipeline is invaluable for a great number of studies. The potential of the pipeline is illustrated with two examples of data collected on ammonia-water mixtures and multiphase mineral assemblies under high pressure. The pipeline is designed to be generic in nature and could be readily adapted to provide rapid feedback for many other X-ray diffraction techniques, e.g. large-volume press studies, in situ stress/strain studies, phase transformation studies, chemical reactions studied with high-resolution diffraction etc.

Insights into the indium enrichment of the Ashele VMS Cu-Zn deposit, Altay, NW China

Indium (In) is a critical metal used in the photovoltaic and semiconductor industries, which have exhibited extraordinary growth in demand. Indium is produced as a by-product of mining from different ore deposits (e.g., epithermal, sediment-hosted, and skarn). Volcanogenic massive sulfide (VMS) deposits are an important source of In; however, the mechanism of In enrichment is not fully understood. Here, we combine mineralogy with in situ trace element and S-Pb isotope geochemistry to reveal the enrichment of indium in the Ashele VMS Cu-Zn deposit (1.08 Mt. Cu, 0.43 Mt. Zn) located in Altay, NW China. The Ashele deposit is hosted in the metamorphosed Devonian felsic-bimodal volcanic rocks. This deposit consists of seafloor hydrothermal, metamorphic hydrothermal, and supergene stages. The seafloor hydrothermal stage comprises macro-scale Cu-rich bands (chalcopyrite, pyrite, and minor sphalerite) and Zn-rich bands (sphalerite, pyrite, and minor chalcopyrite). Indium is mainly hosted by chalcopyrite (mean 178 ppm) and sphalerite (mean 214 ppm) and occurs in the lattice. Mineral assemblages and trace element geochemistry suggest that the Cu-rich bands were deposited under high temperatures (> 300–350 °C) and sulfur fugacity (−7.2 to −4.9), whereas the Zn-rich bands were formed under lower temperatures (180–220 °C) and sulfur fugacity (−15.7 to −11.5). The interlayered Cu-rich and Zn-rich bands may reflect the oscillating temperature and sulfur fugacity variations. In situ S isotopic compositions of sulfides cluster within two ranges: 1–3 ‰ and 3–6 ‰, suggesting two endmembers: volcanic origin and reduced seawater sulfate. Pb isotopic ratios are similar to those of the host volcanic rocks, indicating that the metals may be derived from the felsic volcanic system. During metamorphism, the indium may be retained, but Cu contents of sphalerite become more homogeneous. Most In-rich VMS deposits worldwide are hosted by the felsic-dominant system in island arc and back-arc settings. These tectonic settings are conducive to the production of felsic volcanic systems, which are more likely to contain In mineralization. This study highlights the enrichment mechanism of indium in VMS deposits and suggests that the South Altay could become an important source of In.

Soil development and ancient Maya land use in the tropical karst landscape: Case of Busiljá, Chiapas, México

AbstractThe soil mantle of the tropical karstic landscapes of Southern Mexico was shaped by specific processes of pedogenesis and long‐term human impacts of ancient Maya agriculture. To understand the interaction between natural and human‐induced soil‐forming processes in the calcareous mountains of Chiapas state, we studied soil toposequences around the Classic Maya site of Budsilhá and related them to the archaeological evidence of settlement and land‐use distribution. Soil chemical analysis, micromorphological observations, and clay mineral identification were carried out in key soil profiles at the main geoforms. Limestone hills are occupied by shallow Rendolls which are usually perceived as incipient soils. However, high content of silicate clay composed of kaolinite and vermiculite and ferruginous clayey soil material observed at macro‐ and microscale backed the hypothesis that these soils were formed from the residues of thick Terra Rossa after their erosion. Swampy lowlands are occupied by thick clayey gleyic soils with clay mineral assemblages similar to those in the upland Rendolls. We suppose that the mineral matrix of the lowland soils is largely derived from the pedosediments of eroded upland Terra Rossa, which lost original ferruginous pigmentation and aggregation due to redoximorphic processes. Some wetland soils contain neoformed gypsum that is atypical for humid tropics; sulfide‐sulfate transformation under fluctuating redox conditions could promote gypsum synthesis. Ancient Maya land use was closely related to soil‐geomorphic conditions: settlements with homegardens occupied calcareous hills, whereas the primary agricultural domain was developed on lowland soils after their drainage by artificial canals.

Hydrothermal Alteration, Ore Mineralization, and Fluid Inclusions Study of the Mount Muro Low Sulphidation Epithermal Deposit, Murung Raya Regency, Central Kalimantan Province, Indonesia

Abstract Mount Muro is a part of the ‘Central Kalimantan Gold Belt’, which is found in Murung Raya Regency, Central Kalimantan Province, Indonesia. The study area is part of the Mount Muro mineralized district which includes Serujan Project, Bantian Project, and Kerikil Project. In order to optimize the production yield of the Mount Muro mine, it is important to understand the update data and analyses about the ores characteristics along with their mineral associations and the paleo-fluids involved in it. This research aims to elucidate the mineralization model based on their alteration mineral assemblages, ore minerals formation, and their hydrothermal fluids characteristics. This research is dealing with characteristics of wallrock hydrothermal alteration using X-Ray Diffraction (XRD) and thin section to identify the associations of hydrothermal alteration minerals, ore microscopy to identify the type, associations, and paragenesis of the ore minerals, and fluid inclusions studies which include fluid inclusions petrography and microthermometry measurements to identify paleo-fluid characteristics in the research location. Four alteration types based on their mineral assemblages are identified, namely argillic, silicification, propylitic, and sericitization alterations. Silicification is marked by abundant quartz ± illite ± smectite. Propylitic alteration is typified by chlorite + smectite + calcite + quartz ± epidote ± illite ± adularia. Argillic alteration is presence by clay minerals such as illite + smectite + kaolinite + palygorskite. Sericite + chlorite + illite + smectite assemblage is key minerals of sericitization alteration. Metalliferous and ore minerals are found as native gold, acanthite-argentite, native silver, electrum, pyrite, sphalerite, galena, chalcopyrite, tetrahedrite, tennantite, chalcosite, covellite, goethite, and hematite. Based on fluid inclusion studies on the quartz veins, four fluid inclusion types are identified, namely type I (monophase, liquid rich) where L = 100%, type II (liquid rich, L+V) where L>50%, type III (vapor rich, V+L) where V>50%, type IV (vapor rich, V) where V = 100%. Homogenization temperature (Th) mean of banded vein ranged from 279°C - 284°C, with salinity mean 4.2 - 2.6 wt% eq. NaCl and formed around 806 - 711 meters depth under paleosurface. Homogenization temperature (Th) mean of cockade vein 278°C, with salinity mean 2.3 - 2.4 wt% eq. NaCl and formed around 728 - 726 meters depth under paleosurface. Homogenization temperature (Th) mean of massive barren vein is 267°C, with salinity 2.2 wt% eq. NaCl and formed around 607 meters depth under paleosurface. Binary plot between Th and salinity result and coexisting liquid-rich and vapor-rich fluid inclusions confirm that boiling processes took major place during the ore mineralization. Based on ore mineralogy, hydrothermal alteration mineral assemblage, and fluid inclusions characteristics, deposit is categorized into a deep low sulphidation epithermal deposits type, specifically in transition of precious metal to basemetal zone.

Cobalt remobilization during tectonic–hydrothermal overprinting: A case from the Tuolugou Co(–Au) deposit in East Kunlun Orogenic Belt, China

Stratiform Cu-Co deposits hosted in (meta-) sedimentary and volcaniclastic rocks contribute two-thirds of the global Co supply. However, the mechanisms driving Co remobilization during tectonic-hydrothermal overprinting events remain poorly understood. As a dominant Co repository, pyrite can provide valuable insights into mineralization history due to its refractory nature. Here, we present the first micro-analytical investigation of pyrite from the Tuolugou Co(–Au) deposit in East Kunlun Orogenic Belt. Ore textures indicate that Co mineralization is attributed to two distinct stages: primary enrichment and subsequent overprinting processes. The former is characterized by pyrite (PyI with up to 3.92 wt% Co) remnants exhibiting oscillatory zones, while the latter is marked by deformation of pyrite (PyII) ores. Three overprinting episodes, namely Da, Db, and Dc, are further distinguished according to varying extents of deformation and mineral assemblages. The Da is characterized by synkinematic PyIIa (up to 4.18 wt% Co) augens, which were most likely formed via pressure–solution mechanism. The Db is represented by polygonal PyIIb (up to 4.75 wt% Co) and siegenite with 120° triple–point junctions. The random orientation and rare intragrain misorientation of cobaltiferous sulfides at Db suggest their formation by recrystallization without plastic strains. The Dc resulted in the formation of Co ± As–rich PyIIc (up to 5.36 wt% Co) along with minor occurrence of cobaltite–gersdorffite, pyrrhotite (up to 1.25 wt% Co), and marcasite (up to 1.28 wt% Co). The PyIIc replacing PyI underscores the role of fluid-coupled dissolution and precipitation during fluid–rock interactions in the formation of these cobaltiferous sulfide assemblages at Dc. The presence of PyIIc infilling within the PyI fissures, in conjunction with the transition from siegenite to cobaltite–gersdorffite, suggests a shift towards low fO2 and low temperature conditions under relatively brittle setting. There is a discernible disparity in sulfur isotope compositions between the two mineralization stages. The PyI exhibits a narrow range of δ34SV–CDT values from –2.14 to 1.35 ‰, indicating a magmatic sulfur origin. In contrast, PyII displays a wide δ34SV–CDT range of –5.22 to 6.16 ‰, suggesting an involvement of strata sulfur during the overprinting stage. Monazite U-Pb dating has effectively constrained two mineralization events. The ca. 453 Ma age implies a potential correlation of the primary Co mineralization with the Late Ordovician to Early Silurian exhalative-syngenetic processes in a Proto–Tethyan-related post–collisional extension setting. Conversely, the ca. 190 Ma age indicates that Co remobilization was instigated by the early Mesozoic ductile–brittle deformation associated with the Paleo-Tethyan orogenesis. Finally, geochemical modeling was performed by simulating the interaction of a Co-rich acidic, reducing fluid with typical quartz-albitite rocks. The simulations demonstrate the appearance of independent Co minerals such as Co-pentlandite during the reaction progression, greatly supporting ore upgrading via tectonic-hydrothermal overprinting.

Magmatic degassing and fluid metasomatism promote compositional variation from I-type to peralkaline A-type granite in the late Cretaceous Fuzhou felsic complex, SE China

Abstract A-type granites generally have much lower water, higher temperature, and incompatible element concentrations than I-type granitoids. Yet it remains unclear why I-A-type granitic complexes occur in convergent plate margins. Here we conduct geochemical analyses on apatite and mafic minerals from the late Cretaceous I-A-type granitic complex in Fuzhou area, SE China, aiming to decipher differentiation, fluid metasomatism, and degassing that primarily control the compositional diversity of felsic magmas. Apatites in both rock types are F-rich and show large H2O and δD variations, i.e., 341–3892 ppm H2O and –325 to +336‰ δD in I-type granitoids; 67–1366 ppm H2O and –251 to +1439‰ δD in A-type granites. H2O in apatite is negatively correlated with La/Sm and Sr/Y in the I-type granitoids, whereas it is positively correlated with Ce and total rare earth element (REE) concentrations in the A-type granites. Once H2O increases up to hundreds of ppm, both rock types show a rapid decrease of H2O/Ce, an increase of F/Cl, and extensive H isotope fractionation. Arfvedsonite occurs as a late crystallizing mineral in the A-type granite and has much higher contents of Na2O, K2O, F, and high field strength elements (HFSE) than hornblende in the I-type granitoids, indicating the addition of F-HFSE-rich alkaline fluids during its magmatic evolution. The consumption of arfvedsonite and formation of aegirine further indicate the role of fluid metasomatism and H2 degassing via a reaction of 3Na3Fe5Si8O22(OH)2 + 2H2O = 9NaFeSi2O6 + 2Fe3O4 + 6SiO2+5H2. The combined geochemical data demonstrate that the systematic differences in mineral assemblage, whole-rock composition, magma temperature, H2O content, and δD of apatite between the I- and A-type granites are likely attributed to varying degrees of differentiation, fluid metasomatism and magmatic degassing. The I-type granitoids experienced hornblende, biotite, plagioclase, K-feldspar, and apatite fractionation and close-system degassing. The A-type granite was likely formed from the I-type monzogranitic magma that was metasomatized by the mantle-derived F-HFSE-rich alkaline fluids to produce the peralkaline magma, which further experienced K-feldspar + plagioclase + biotite + apatite fractionation and open-system degassing. Further numerical estimation indicates that the primary magma of Fuzhou granitic complex contained ~3.0 wt% H2O, and the lower water content of A-type granite was likely attributed to strong degassing during its emplacement. Our results indicate that some peralkaline A-type granites can be generated from relatively water-poor I-type granitic magmas by fluid metasomatism and degassing.

Variable Iron Mineralogy and Redox Conditions Recorded in Ancient Rocks Measured by In Situ Visible/Near‐Infrared Spectroscopy at Jezero Crater, Mars

AbstractUsing relative reflectance measurements from the Mastcam‐Z and SuperCam instruments on the Mars 2020 Perseverance rover, we assess the variability of Fe mineralogy in Noachian/Hesperian‐aged rocks at Jezero crater. The results reveal diverse Fe3+ and Fe2+ minerals. The igneous crater floor, where small amounts of Fe3+‐phyllosilicates and poorly crystalline Fe3+‐oxyhydroxides have been reported, is spectrally similar to most oxidized basalts observed at Gusev crater. At the base of the western Jezero sedimentary fan, new spectral type points to an Fe‐bearing mineral assemblage likely dominated by Fe2+. By contrast, most strata exposed at the fan front show signatures of Fe3+‐oxides (mostly fine‐grained crystalline hematite), Fe3+‐sulfates (potentially copiapites), strong signatures of hydration, and among the strongest signatures of red hematite observed in situ, consistent with materials having experienced vigorous water‐rock interactions and/or higher degrees of diagenesis under oxidizing conditions. The fan top strata show hydration but little to no signs of Fe oxidation likely implying that some periods of fan construction occurred either during a reduced atmosphere era or during short‐lived aqueous activity of liquid water in contact with an oxidized atmosphere. We also report the discovery of alternating cm‐scale bands of red and gray layers correlated with hydration and oxide variability, which has not yet been observed elsewhere on Mars. This could result from syn‐depositional fluid chemistry variations, possibly as seasonal processes, or diagenetic overprint of oxidized fluids percolating through strata having variable permeability.

Alterations of High-Carbon (Shungite) Rocks by the Lake Onega Waters: Mineralogy and Geochemistry of the Process

Abstract ––Carbonaceous (shungite) rocks have high contents of trace elements, which can get to the environment through natural weathering. Shungite rocks are a group of Precambrian carbonaceous rocks of volcanic and sedimentary genesis in Karelia. In this work we present results of studying the mineral and geochemical compositions of shungite rocks at their outcrops on the shoreline of Lake Onega. The interaction of the Onega waters with shungite rocks led to: (1) the removal of most elements, except for K, Mn, Ba, and Mg, whose contents in the rocks increased; (2) the formation of an assemblage of secondary minerals, such as hematite, jarosite, goethite, chalcocite, anglesite, brookite, and Mn hydroxides. Based on the results obtained, we propose a model of the transformation of high-carbon (shungite) rocks by the Onega waters.

OS MINERAIS PESADOS E IDADES DE ZIRCÕES DOS SEDIMENTOS DE PRAIAS (BARRAS EM PONTAL) DOS RIOS PURUS E ACRE NO ESTADO DO ACRE (BRASIL)

The Purus River and its largest tributary, the Acre River, originate in Peru and constitute the main drainage system for the northeast and southeast portions of the State of Acre. These rivers and their smaller tributaries develop their beds over the Solimões Formation (Miocene to Pliocene-Late) and form a broad dendritic drainage pattern. During the rainy season, due to the high rainfall in the region and the low resistance of the drained rocks, these rivers mobilize a large volume of sediment, which is deposited mainly during the dry season, forming beaches (pointed bars), predominantly composed of fine sand, silt and clay. To investigate the probable primary sources of these sediments and their possible geographic locations, a mineralogical and morphological study of their heavy minerals and a geochronological analysis of their detrital zircons were used. Heavy minerals were extracted from fractions between 0.062-0.125 and 0.125-0.250. The transparent ones were investigated using a petrographic microscope and the opaque non-magnetic ones, together with the lithic fragments using a Scanning Electron Microscope (SEM/SED). In descending order, the main transparent heavy minerals of the Purus River are epidote (19%), kyanite (17%), zircon (14.5%), andalusite (8%), tourmaline (7.4%) and sillimanite (5 .5%), in addition to these, in amounts less than 5%, staurolite, garnet, apatite, amphibole, chlorite, muscovite, biotite, anatase, pyroxene and cassiterite occur. With similar content and different proportions, the assemblage of heavy minerals from the Acre River consists of andalusite (22.5%), kyanite (22.5%), zircon (12%), epidote (8%), sillimanite (5%) and tourmaline (5%), its accessories are: garnet muscovite, chlorite, apatite, amphibole, biotite, staurolite, titanite, anatase, serpentine and rutile. The non-magnetic opaque minerals of both rivers were shown to be predominantly formed by ilmenite, and the ages obtained in the zircons varied from 180 Ma to 3000 Ma, with great frequency in the intervals between 200-400 Ma and 900-1200 Ma.