Search

The Archean Cheechoo stockwork gold deposit is hosted by a felsic intrusion of tonalitic-granodioritic composition and crosscutting pegmatite dikes in the Eeyou Istchee James Bay area of Quebec, Canada (Archean Superior craton). The evolution of the stockwork is characterized herein using field relationships, vein density, and connectivity measurements on drill core and outcrop zones. The statistical distribution of gold is used to highlight mechanisms of stockwork emplacement and gold mineralization and remobilization. Two statistical populations of gold concentration are present. Population A is represented by gold grades below 1 g/t with a lognormal cumulative frequency. It is widespread in the hydrothermally altered (albite and quartz) and mineralized facies of the pluton. It is controlled by the development of quartz-feldspar-diopside veins as shown by the similar lognormal distribution of grades and vein density and by the correspondence of grades with network connectivity. Diopside and actinolite porphyroblasts in deformed veins within sodic and calcsilicate alteration zones are evidence for auriferous vein emplacement prior to the amphibolite facies peak of metamorphism. Population B (>1 g/t) is erratic and exhibits a strong nugget effect. It is present throughout the mineralized portion of the pluton and in pegmatites. This population is interpreted as the result of gold remobilization during prograde metamorphism and pegmatite emplacement following the metamorphic peak. The pegmatites are interpreted to have scavenged gold emplaced prior to peak metamorphism. These results show the isotropic behavior of the investigated stockwork during regional deformation and its development during the early stages of regional prograde metamorphism.

The Hera Au–Pb–Zn–Ag deposit in the southeastern Cobar Basin of central New South Wales preserves calc-silicate veins and remnant sandstone/carbonate-hosted skarn within a reduced anchizonal Siluro-Devonian turbidite sequence. The skarn orebody distribution is controlled by a long-lived, basin margin fault system, that has intersected a sedimentary horizon dominated by siliciclastic turbidite, with lesser gritstone and thick sandstone intervals, and rare carbonate-bearing stratigraphy. Foliation (S1) envelopes the orebody and is crosscut by a series of late-stage east–west and north–south trending faults. Skarn at Hera displays mineralogical zonation along strike, from southern spessartine–grossular–biotite–actinolite-rich associations, to central diopside-rich–zoisite–actinolite/tremolite–grossular-bearing associations, through to the northern most tremolite–anorthite-rich (garnet-absent) association in remnant carbonate-bearing lithologies and sandstone horizons; the northern lodes also display zonation down dip to garnet present associations. High-T, prograde skarn assemblages rich in pyroxene and garnet are pervasively replaced by actinolite/tremolite–biotite-rich retrograde skarn which coincides with the main pulse of sulfide mineralization. The dominant sulfides are high-Fe–Mn sphalerite–galena–non-magnetic high-Fe pyrrhotite–chalcopyrite; pyrite, arsenopyrite; scheelite (low Mo) is locally abundant. The distribution of metals in part mimics the changing gangue mineralogy, with Au concentrated in the southern and lower northern lode systems and broadly inverse concentrations for Ag–Pb–Zn. Stable isotope data (O–H–S) from skarn amphiboles and associated sulfides are consistent with magmatic (or metamorphic) water and sulfur input during the retrograde skarn phase, while hydrosilicates and sulfides from the wall rocks display comparatively elevated δD and mixed δ34S consistent with progressive mixing or dilution of original magmatic (or metamorphic) waters within the Hera deposit by unexchanged waters typical of low latitude (tropical) meteoritic waters. High precision titanite (U–Pb) and biotite (Ar–Ar) geochronology reveals a manifold orebody commencing with high-T skarn and retrograde Pb–Zn-rich skarn formation at ≥403 Ma, Au–low-Fe sphalerite mineralization at 403.4 ± 1.1 Ma, foliation development remobilization or new mineralization at 390 ± 0.2 Ma followed by thrusting, orebody dismemberment at 384.8 ± 1.1 Ma and remobilization or new mineralization at 381.0 ± 2.2 Ma. The polymetallic nature of the Hera orebody is a result of multiple mineralization events during extension and compression and involving both magmatic and likely formational metal sources.

Asbestos is a naturally occurring fibrous silicate that has been widely used as electrical insulator and heat-resistant material in buildings, yet inhalation of asbestos fibers can lead to serious lung diseases such as asbestosis and cancer. Practically no research has been conducted on the size distribution and morphological characteristics of airborne asbestos, and airborne asbestos concentrations in South Korea are unknown. Here we studied type, concentration, size, morphology and composition of asbestos fibers in the ambient air of several regions in South Korea. Asbestos concentrations were analyzed in 7 urban areas, 7 rural areas including agricultural and fishing areas, 17 mines and their surrounding areas, 7 residential areas constructed with asbestos-containing stones near rivers, 2 baseball fields and 2 background sites. Results show that the highest air asbestos concentrations were 0.00161 for residential areas and 0.00122 for baseball fields according to phase-contrast microscopy, and 0.00057 for asbestos mines and 0.00055 for baseball fields, according to transmission electron microscopy. Asbestos types included chrysotile, tremolite, and actinolite. Chrysotile fibers measured 5.24–35.5 µm in length with aspect ratios of 12.6–202.6; tremolite fibers measured 6.07–40.2 µm in length with aspect ratios of 5.7–81.2; and actinolite fibers measured 5.01–28.5 µm in length with aspect ratios of 3.2–108.9. Chrysotile was distributed in bundles or single fibers, whereas tremolite and actinolite exhibited fibrous, acicular, and cleavage forms.

Calc-silicate rocks occurring in and around Lunavada town belong to the Kadana Formation of the Lunavada Group of the Aravalli Supergroup. These rocks are embedded within pelitic schists in the form of sporadically distributed lensoidal bodies and are surrounded by quartzitic ridges. Rocks of the Kadana Formation and its surrounding area have experienced intrusive event named as ‘Godhra granite’ which occupy the SW part of this area. Some prominent field characteristics shown by these calc-silicates include fine to medium grained size, dark grey colour, unoriented/star shaped amphibole needles and maculose structure. These rocks have contact metamorphic textural features and the typical mineral assemblage viz., Act +Di + Qtz + Ttn+ Cal ± Mc ± Bt ± Pl ± Ep ± Scp ± Chl with minor proportion of apatite, zircon and opaques. EPMA studies revealed that the Ca-amphibole composition of these rocks ranges from magnesio-hornblende to actinolite whereas the clinopyroxene is salitic to diopsidic and the mica is found to be phlogopitic biotite. Certain prograde and retrograde reactions textures present within these rocks have been interpreted, for e.g. the development of diopside (salite) from ankeritic composition which is then retrogressed and actinolite appeared, prograde reaction leading to the formation of titanite from ilmenite and calcite and breakdown of scapolite into calcite and quartz with plagioclase lacking co-existence with these scapolites, indicating retrogression. Mineral assemblage and mineral chemistry data interpretation points towards the calcareous sandstone or marl as a probable protolith having impure calcareous composition, moreover, field characteristics and reaction textures observed give indication that the protolith might had passed through the contact metamorphic event to give rise to the present day calc-silicates.

Rocks of gabbronoritic composition occur in three principal tectono-stratigraphic units forming the lower and middle parts of the Kohistan Island arc (KIA). These include the Jijal complex (JC), the Kamila Amphibolite belt (KAB) and the Chilas complex (CHC). The Jijal complex constitutes the lowermost part and hence is regarded as the root zone of KIA. Its north-eastern part adjacentto KAB contains gabbronorite as a minor component in the form of small irregular patches and layers within garnet granulite. The JC gabbronorite is sub-equigranular, medium to coarse grained, largely massive and consists of variable amounts of plagioclase(53-71 %), orthopyroxene (14-27 %) and clinopyroxene (11-19 %) as essential constituents and accessory to minor amounts of amphibole (1-9 %), opaque ore (1-6 %) and orthoclase (1-4 %). The occurrence and distribution of biotite, epidote, chlorite, clay, sericite, muscovite, quartz and actinolite in the studied samples suggest their formation through alteration and/ or reaction between pre-existing minerals. In many cases, these minerals are disposed such that a variety of simple and complex corona structures are produced. The principal petrographic features (modal composition, optical properties of the major mineral phases, exsolution in pyroxenes, products of alteration and reactions and the resulting corona textures) of the JC gabbronorite are broadly similar to gabbronorites from both the KAB and CHC. Although the observed similarities could reflect identical physico-chemical conditions during subsolidus or metamorphic re-equilibration, the possibility of a genetic relationship among gabbronorites from all the three tectono-magmatic units of the KIA (i.e. the JC, KAB and CHC) cannot be ruled out.

Background/Objectives: Talcose rocks within Precambrian Basement Complex serve as relics of Archean greenstones. alterations associated with polycyclic-orogenies that affected this complex is studied to understand mineralogical and geochemical alterations. Methods: Five fresh samples of talcose rocks were collected during field mapping. These samples were cut into thin sections to reveal modal mineralogy, altered minerals and degree of alteration of such minerals. Mineral phase identification of the talcose rocks was conducted using X-ray Broker D8 ADVANCE diffractometer while whole rock analysis was carried out using Inductively Coupled Plasma Mass Spectrometry. Findings: Lithological relationship revealed from field evidence showed that the talc bodies occurred in close association with micaceous schist. The mineral assemblage of talc, tremolite, actinolite, chlorite and calcite suggest low grade greenschist metamorphic facies from possible hydrothermal alteration. Geochemical results revealed the following range of concentrations; SiO2 42.19-59.03%; Al2O3 1.1 - 11.8%; Fe2O3 7.64-9.56%; MgO 24.47-26.639%; Ni 594-1207ppm; Co 43.2-113.9ppm; Sn 6-41ppm; V 32-75ppm and Zr 1.3-58.7ppm, and these are typical of talcose rocks. Petrogenetic studies suggest a komatiitic origin with a peridotitic komatiite precursor for the talc-chlorite-tremolite schist. Enrichment in LREE, depletion in HREE and a negative Eu anomaly suggest alteration of the parent magma for the talcose rock and plagioclase fractionation. The trends observed for the LILE, HFSE and REE suggest possible contamination or mixing of crustal and mantle materials during the formation of the protolith. Ni and Co concentrations are higher than average crustal values with implication for ultrabasic to basic magma composition for the komatiitic progenitor and also suggestive of possible mineralisation. Conclusion: Mineralogical examination has revealed a talc-chlorite-tremolite composition for the talcose rocks with peridotitic komatiite precursory while geochemical composition supported ultrabasic magmatism similar to those with the Ilesha schist belt.Keywords: Ila Orangun-Oyan; Talcose rocks; Hydrothermal alteration; Peridotitic Komatiite; Ilesha schist belt

In 2006, LKAB tackled a challenging expansion strategy that included studying known iron ore deposits in Northern Sweden to investigate the possibilities of increasing the ore resources and, in an extension, to have the opportunity to mine iron ore at several sites in the future. One of the iron ore deposits under investigation is the Mertainen iron ore deposit, in which magnetite is the main and practically the only ore mineral of economic value. The most important gangue mineral in the ore deposit is dark green actinolite. Magnetite is also locally accompanied by some apatite and calcite. At LKAB, the iron ore deposits and their amenability with respect to mineral processing have earlier been characterized and evaluated mainly based on the grade of important elements such as iron (Fe), phosphorus (P), vanadium (V) and silicon (Si). However, there are drawbacks when the crude ore shows more complex mineralogy and where a specific element is distributed in several different minerals. There are several challenges with the mineralogy of the Mertainen iron ore deposit. A high amount of SiO2 including alkali (Na and K) might end up in the final concentrate without successful beneficiation process. Another challenge is the loss of fine magnetite material that can occur in the separation via flotation. A process design for the test work in pilot scale, corresponding to the flotation process at the LKAB’s beneficiation plant in Svappavaara suite was established at the Geological Survey (GTK) in Finland. The results from the pilot flotation test work showed that the required silica grade (0.50% SiO2) was achieved at an iron (Fe) recovery of over 95% with both tested flotation collectors.

Unlike classic skarn-type scheelite deposits directly acquiring sufficient Ca2+ from surrounding limestones, all of the scheelite orebodies of the Shangfang tungsten (W) deposit occur mainly in amphibolite, and this provides a new perspective on the mineralization mechanism of W deposits. The ability of hydrothermal scheelite (CaWO4) to bind REE3+ in their Ca2+ crystal lattices makes it a useful mineral for tracing fluid-rock interactions in hydrothermal mineralization systems. In this study, the REE compositions of scheelite and some silicate minerals were measured systematically in-situ by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to assess the extent of fluid-rock interactions for the Late Mesozoic quartz-vein-type Shangfang W deposits. According to the variations in CaO and REE among scheelite and silicate minerals, the amphibole and actinolite in amphibolite may be able to release large amounts of Ca2+ and REE3+ into the ore-forming fluids during chlorite alteration, which is critical for scheelite precipitation. Furthermore, an improved batch crystallization model was adopted for simulating the process of scheelite precipitation and fluid evolution. The results of both the in-situ measurements and model calculations demonstrate that the precipitation of early-stage scheelite with medium rare-earth elements (MREE)-rich and [Eu/Eu*]N 1. Even though the partition coefficient of REE is constant, the later-stage scheelite will also inherit a certain degree of MREE-depletion and [Eu/Eu*]N future from the residual fluids. As a common mineral, sheelite forms in various types of hydrothermal ore deposits (e.g., tungsten and gold deposits). Hence, the improved batch crystallization model is also possible for obtaining detailed information regarding fluid evolution for other types of hydrothermal deposits. The results from model calculations also illustrate that the Eu anomalies of scheelite are not an effective index correlated to oxygen fugacity of fluids but rather are dominantly controlled by the continuous precipitation of scheelite.

As rochas ortoderivadas de composição básicas e ultrabásicas são constituídas por anfibolitos, metabasitos e metaultrabásitos de idade meso- a neoproterozoica, que se localizam no sudoeste do estado de São Paulo, na porção sul do Cinturão Ribeira e norte do Terreno Apiaí. Encontram-se inseridas em rochas da sequência metavulcanossedimentares do Supergrupo Açungui, especificamente na Formação Água Clara e no Grupo Itaiacoca. A paragênese mineral principal é constituída de ferrotschermakita- ferrohornblenda- magnesiohornblenda ± oligoclásio/andesina, representando o ápice do metamorfismo regional progressivo M1, de 611°C a 621°C de temperatura e 6,5 kbar a 7,3 kbar (±0,6) (Fácies anfibolito médio); e uma paragênese mineral de actinolita/tremolita ± albita, do retrometamorfismo regional M3 (fácies xisto verde baixo a médio). Dados geoquímicos composicionais classificam as rochas como gabro, basanito e picrito, sub alcalinos de baixo potássio a alcalinos, Fe-toleíticos a Mg-toleíticos, com leve tendência à basaltos komatiíticos. Já os dados geotectônicos, corroborados pelo comportamento dos elementos traços e dos ETRs, indicam três assinaturas principais para os grupos anfibolíticos: rochas básicas toleíticas a komatiíticas associadas a cadeia mesoceânicas (MORB), com possível interação da crosta na fase de subducção; rochas ultrabásicas alcalinas de ilha oceânica (OIA); e basaltos toleíticos de arco de ilha. Portanto, os magmatismos estão correlacionados ao estágio inicial de abertura de bacia ou ao início de fechamento à fase inicial de natureza toleítica de fundo oceânico, associado a basaltos alcalinos de ilha oceânica.

The limited literature data on gold-bearing albite–pyroxene rodingites are summarized for the Agardag ultramafic massif in southern Tuva. These data are supplemented by new mineralogical, geochemical, thermobarogeochemical, and isotopic–geochemical results in order to reveal the physicochemical mineral formation conditions and sources of ore matter and fluids on gold deposition in rodingites. Rodingites and associated schistose nephritoids are near-fault metasomatites and are confined to a latitudinal tectonic zone in antigorite serpentinites. They formed in two stages. Stage I minerals (pyroxene, albite, etc.) are rodingites and stage II minerals (Na-bearing actinolite, albite, etc.) are nephritoids and veinlets that intersect rodingites. Disseminated sulfides of the Cu–S series (chalcocite, digenite, etc.) and Au minerals (tetra-auricupride and electrum) were deposited during both stages. The temperature regime (500–250°C) and low amount of CO2 in fluid ( $${{{\text{X}}}_{{{\text{C}}{{{\text{O}}}_{{\text{2}}}}}}}$$ = 0.017–0.025) correspond to the formation conditions of typical bimetasomatic rodingites. The degree of oxidation of gas components in fluids CO2/(CO2 + Σreduced gases) increases from rodingites (0.189) to nephritoids (0.299) and antigorite serpentinites (0.738). The O isotopic composition of silicates and calculated O isotopic composition of the fluid during antigorite serpentinization (5.8 to 7.6‰ δ18Оfl and –66 to –69‰ δDfl) correspond to juvenile and magmatic water in contrast to metamorphic water during nephritization and rodingitization (6 to 9.9‰ δ18Оfl and –39 to –46‰ δDfl) with involvement of heavy oxygen that was subjected to the sedimentary cycle. It is suggested that the magmatic ore-bearing fluid (7.3–7.6 wt % NaCl-equiv) separated from gabbroic melts. The oxidized fluid was modified to a reduced fluid during interaction with ultramafic rocks. The mafic and ultramafic rocks were the source of Na, REE, Au, Ag, Cu, and Ni. Deformations with the formation of veins and filling of veinlets are favorable for a high local gold concentration.

The onset of malignant mesothelioma (MM) is linked to exposure to asbestos fibers. Asbestos fibers are classified as serpentine (chrysotile) or amphibole, which includes the crocidolite, amosite, anthophyllite, tremolite, and actinolite types. Although few studies have been undertaken, anthophyllite has been shown to be associated with mesothelioma, and tremolite, a contaminant in talc and chrysotile, is a risk factor for carcinogenicity. Here, after characterizing the length and width of these fibers by scanning electron microscopy, we explored the cytotoxicity induced by tremolite and anthophyllite in cells from an immortalized human mesothelial cell line (MeT5A), murine macrophages (RAW264.7), and in a rat model. Tremolite and short anthophyllite fibers were phagocytosed and localized to vacuoles, whereas the long anthophyllite fibers were caught on the pseudopod of the MeT5A and Raw 264.7 cells, according to transmission electron microscopy. The results from a 2‐day time‐lapse study revealed that tremolite was engulfed and damaged the MeT5A and RAW264.7 cells, but anthophyllite was not cytotoxic to these cells. Intraperitoneal injection of tremolite in rats induced diffuse serosal thickening, whereas anthophyllite formed focal fibrosis and granulomas on peritoneal serosal surfaces. Furthermore, the loss of Cdkn2a/2b, which are the most frequently lost foci in human MM, were observed in 8 cases of rat MM (homozygous deletion [5/8] and loss of heterozygosity [3/8]) by array‐based comparative genomic hybridization techniques. These results indicate that tremolite initiates mesothelial injury and persistently frustrates phagocytes, causing subsequent peritoneal fibrosis and MM. The possible mechanisms of carcinogenicity based on fiber diameter/length are discussed., MeT5A (immortalized mesothelial cells) and RAW264.7 (macrophage lineage cells) were damaged by tremolite but not anthophyllite. Tremolite induced diffuse peritoneal thickening, whereas anthophyllite induced focal fibrosis. Furthermore, tremolite‐induced malignant mesothelioma frequently lost Cdkn2a/2b.

Tremolite–actinolite (TA) fibers from the lungs of deceased former Quebec mine workers were found to be coated with sub-nanometer particles. Qualitative chemical analyses were performed on the particles indicating that they were composed of silicon and oxygen. The crystal lattice structure of all amphibole minerals, including the TA series, is arranged as pairs of linear chains of SiO4 tetrahedra that are linked together to form double chains. Our observations of the TA fibers from miner’s lungs, made using a high-resolution transmission electron microscope, indicated that the tetrahedral silica chains were progressively split, forming dispersed sub-nanometer particles. The non-tetrahedral sites were removed at the surface of the TA fibers, presumably by the oxidation process involved in attempted phagocytosis, which also resulted in fragmentation of the tetrahedral chains. It was found that the silicon-rich particles (SRPs) were variable in diameter, consistent with fragments formed from the splitting of the tetrahedral chains. The TA fibers from lungs displayed coatings and linear interior zones of SRP parallel to the planes of longitudinal fiber splitting. The literature on very small nanoparticles is consistent with deep penetration of SRP into cell DNA interiors, oxidative stress, and carcinogenesis.

Heavy mineral assemblages have been widely used to effectively trace sediment sources. Heavy mineral assemblages are rarely used in research to trace sediment sources in the southern Okinawa Trough compared with geochemical proxies. In this study, the TESCAN Integrated Mineral Analyzer (TIMA) revealed the full-size heavy mineral assemblages in the five layers of the core sediment H4-S2 in the southern Okinawa Trough. During the past 700 years, the heavy mineral assemblages in the sediments of the southern Okinawa Trough were very similar to the East China Sea shelf/Yangtze River, mainly composed of mica and chlorite, dolomite, actinolite, and hematite/magnetite. The grain size distribution of heavy minerals is in the clay–sand range and mainly in silt. Actinolite and hornblende can indicate the supply of sediments from the East China Sea shelf/Yangtze River to the southern Okinawa Trough. Due to their complex sources, pyrite, epidote, and hematite/magnetite are not adequate indicators for distinguishing between the different provenance areas. Because previous studies have used a variety of analytical methods, especially using heavy liquids with different densities, dolomite cannot be used as a marker for sediments on the Yangtze River/East China Sea shelf. Therefore, the East China Sea shelf/Yangtze River is a vital provenance of sediments from the southern Okinawa Trough since the late Holocene period.

This study determines the properties of hot spring waters and associated rocks, calculates reservoir temperatures and depths in the Mongolian Altai region, and constructs a conceptual model for geothermal water based on these results. The hot springs consist of HCO3-Na, SO4-Na, and HCO3-SO4-Na mixed type waters. The waters exhibit alkaline pH levels and temperatures in the range of 21.3–35°C. X-ray diffraction analyses of outcrop rocks reveal silicate and carbonate-type minerals such as quartz, albite, orthoclase, dolomite, mica, and actinolite, while correlation analysis indicates that the chemical composition of the hot spring water is directly related to rock mineral composition. Dissolution of albite, orthoclase, and dolomite minerals has played an important role in the chemical composition of the waters. Reservoir water circulation depths were 2615–3410 m according to quartz and chalcedony geothermometry. The results indicate that the spring water in the Mongolian Altai region comprises a low mineral content with alkaline pH levels and the reservoir temperature can reach up to 106°C. We also propose a conceptual model for geothermal water in the Chikhertei hot spring. The geothermal water in the Mongolian Altai region exhibits a potential for use in heating systems. Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues

Iron oxide-copper-gold deposits are a globally important source of copper, gold and critical commodities. However, they possess a range of characteristics related to a variety of tectono-magmatic settings that make development of a general genetic model challenging. Here we investigate micro-textural and compositional variations in actinolite, to constrain the thermal evolution of the Candelaria iron oxide-copper-gold deposit in Chile. We identify at least two mineralization stages comprising an early 675–800 °C iron oxide-apatite type mineralization overprinted by a later copper-rich fluid at around 550–700 °C. We propose that these distinct stages were caused by episodic pulses of injection of magmatic-hydrothermal fluids from crystallizing magmas at depth. We suggest that the mineralisation stages we identify were the result of temperature gradients attributable to changes in the magmatic source, rather than variations in formation depth, and that actinolite chemistry can be used as a proxy for formation temperature in iron oxide-copper-gold systems. The Candelaria iron oxide-copper-gold deposit in Chile was formed by superimposed, episodic hydrothermal pulses with contrasting composition and temperature, according to micro-textural and compositional variations in actinolite, a common alteration mineral.

This study presents petrology and evidence for possible gold occurrences in Seruwila copper–iron oxide–apatite (IOA) deposit, hosted in an ultramafic intrusion which is located at the boundary between the Highland and Vijayan complexes, within the intermediate-granitic basement in north-eastern Sri Lanka. The study is complemented with petrological observations and XRD and SEM analysis, respectively, to investigate the petrology/subsurface geology of the deposit and identify possible gold occurrences in the deposit. The ore-bearing rocks are mainly composed of magnetite and apatite in various proportions, hosted in an ultramafic intrusion with cumulate features within the granitic-intermediate basement. The secondary veins contain magnetite, chalcopyrite, pyrrhotite, and pyrite together with apatite and scapolite, tremolite, diopside, and minor actinolite and calcite, serpentinite, anhydrite, or gypsum. The clinopyroxene euhedral crystals show cumulus textures including grain triple junctions and large dihedral angles (∼120°), showing magmatic origin. Texturally two types of amphiboles are identified as coarse-grained (0.5–1 mm), pale green euhedral amphibole that is free of inclusions, and fine-grained (

Nielsenite, a rare intermetallide of palladium and copper, was described previously as a late-magmatic formation. A different genetic type of nielsenite was studied in the layered ultrabasite–basite Yoko-Dovyren intrusive. The maximum concentrations of Pd, Pt, Au, and Ag minerals are confined to crosscutting bodies of pegmatoid sulfide-bearing anorthosites within the contact zone between the troctolites and overlapping gabbro-norites strata in this intrusive. Postmagmatic pneumatolytic (fluid-metasomatic) Pd, Pt, Au, and Ag minerals, such as kotulskite, moncheite, michenerite, zvyagintsevite, telargpalite, paolovite, electrum, and sperrillite, compose metasomes in Fe–Ni–Cu sulfides and in the silicate matrix nearby. The Yoko-Dovyren intrusive is tectonized and tilted, crossed by inclined faults with streamlined serpentinized rocks, which contain lizardite, antigorite, clinozoisite, chlorite, actinolite, prehnite, pectolite, and hydrogarnet and are often transformed into rodingites of a prehnite–pumpellyite facies. The serpentinization process is younger than the intrusive rocks by 55 million years. In metamorphosed anorthosites, chalcopyrite is replaced by bornite, chalcocite, digenite, and magnetite; pentlandite is replaced with violarite, heazlewoodite, …; pyrrhotine is replaced by magnetite, …; moncheite is replaced with cuproplatinum–tulameenite; the veins of clinozoisite and pectolite with chlorite inclusions of chalcosine and native copper are well developed. Curved veins of nielsenite in brecciated chalcopyrite occasionally extend such veins. The size of the veins of metamorphogenic-hydrothermal nielsenite reaches up to 200 × 10 microns. Nielsenite metasomes up to 12 microns in diameter are developed nearby. The composition of the Yoko-Dovyren nielsenite is stable and close to stoichiometric with the formula Pd1.01Cu2,81Fe0,17Ni0,01. The Yoko-Dovyren nielsenite differs from the holotype of nielsenite of the Skergaard intrusive by the absence of Pt and Au impurities and a significant impurity of Fe. Yoko-Dovyren nielsenite was likely to appear under conditions of the prehnite–pumpellyite metamorphism facies at a high fugacity of О2 and at an extremely low fugacity of sulfide sulfur (log f S2 < –24 at ≈300°C).

With the sharp decrease of sulfide nickel resources, the nickel laterite is becoming more attractive as nickel oxide, nickel matte, and nickel-iron. This study investigated the mineral phase structure, chemical analysis, thermal properties, and element distribution characteristics of the rotten rock layer deposited in the Southeast Sulawesi Ophiolite Belt. The results show that the nickel laterite deposited in Southeast Sulawesi Island, Indonesia, belongs to the typical high-nickel and low-iron garnierite-type laterite. The concentrations of nickel and iron of the nickel laterite are 1.99 wt% and 17.55 wt%, respectively. The serpentine, olivine, clay, chlorite, hematite, and magnetite are the major minerals, and the pyroxene, actinolite, limonite, and chromite are the minor minerals in the nickel laterite in Southeast Sulawesi, Indonesia. Serpentine and olivine are the main nickel minerals with an average nickel concentration of 3.65 wt% and 1.73 wt%, respectively. The Fe and Ni have homogeneity and symbiosis in the serpentine and olivine, and their concentrations are often positively correlated.

Nipalarsite, Ni8Pd3As4, is a new platinum-group mineral discovered in the sulfide-bearing orthopyroxenite of the Monchetundra layered intrusion, Kola Peninsula, Russia (67°52′22″N, 32°47′60″E). Nipalarsite forms anhedral grains (5–80 µm in size) in intergrowths with sperrylite, kotulskite, hollingworthite, isomertieite, menshikovite, palarstanide, nielsenite and monchetundtraite enclosed in pentlandite, anthophyllite, actinolite and chlorite. Nipalarsite is brittle, has a metallic lustre and a grey streak. In plane-polarised light, nipalarsite is light grey with a blue tinge. Reflectance values in air (in %) are: 46.06 at 470 nm, 48.74 at 546 nm, 50.64 at 589 nm and 54.12 at 650 nm. Values of VHN20 fall between 400.5 and 449.2 kg.mm–2, with a mean value of 429.9 kg.mm–2, corresponding to a Mohs hardness of ~4. The average result of 27 electron microprobe wavelength dispersive spectroscopy analyses of nipalarsite is (wt.%): Ni 44.011, Pd 28.74, Fe0.32, Cu 0.85, Pt 0.01, Au 0.05, As 25.42, Sb 0.05, Te 0.39, total 99.85. The empirical formula (normalised to 15 atoms per formula unit) is: (Ni8.10Fe0.06)Σ8.16(Pd2.94Cu0.18)Σ3.12(As3.68Te0.03)Σ3.71 or, ideally, Ni8Pd3As4. Nipalarsite is cubic, space group Fm$\bar{3}$m, with a = 11.4428(9) Å, V = 1498.3(4) Å3 and Z = 8. The strongest lines in the powder X-ray diffraction pattern of synthetic Ni8Pd3As4 [d, Å (I) (hkl)] are: 2.859(10)(004), 2.623(6)(313), 2.557(6)(024), 2.334(11)(224), 2.201(35)(115,333), 2.021(100)(044), 1.906(8)(006,244) and 1.429(7)(008). The crystal structure was solved and refined from the single-crystal X-ray diffraction data of synthetic Ni8Pd3As4. The relation between natural and synthetic nipalarsite is illustrated by an electron back-scattered diffraction study of natural nipalarsite. The density calculated on the basis of the empirical formula of nipalarsite is 9.60 g.cm–3. The mineral name corresponds to the three main elements: Ni, Pd and As.

The Dalma metavolcanic belt is composed of ultramafics at the base, tuffs on top and basalts in-between. It extends for about 200kms east-west in the middle of the Proterozoic Singhbhum Mobile Belt. Ultramafics are chiefly composed of actinolite, hornblende, relic pyroxene and olivine. The main mineral constituents of basalts are actinolite, hornblende, chlorite, epidote, clinozoisite and plagioclase whereas; tuffs are composed of xenocrysts of biotite, quartz, k-feldspar, plagioclase and iron oxides. Ultramafic samples have high MgO (> 21 wt.%) and low SiO2 (< 42 wt.%), Al2O3 (< 10 wt.%) and Na2O+K2O (< 1 wt.%). CaO shows large variation in these samples from 3.91 to 7.77 wt. %. In studied basalt samples SiO2, TiO2, Al2O3, MgO and alkalis (Na2O+K2O) show variation like (45.7–48.3 wt.%), (0.64–0.97 wt.%), (9.3–13.9 wt.%), (8.5–13.6 wt.%) and (0.95–4.64 wt.%) respectively. In studied tuffs the SiO2, TiO2, Al2O3, MgO and alkalis show variation from (48.9–49.8 wt.%), (0.7–0.8 wt.%), (13.6–13.9 wt.%), (8.4–9.1 wt.%) and (2.39–2.85 wt.%) respectively. In general, studied samples show light rare earth element depleted patterns and flat patterns for heavy rare earth elements similar to MORBs on chondrite normalized REE diagrams. The overall enrichment of LILEs (e.g., Rb, K and Th) and depletion of HFSEs (e.g., Nb-Ta trough) on primitive mantle normalized multi-element diagrams are similar to subduction zone or islamd arc basalts. Ratios like Ti/Y, Ti/Zr, Zr/Nb and Ti/V are also similar to those found in arc related volcanic suites. Sm/Yb vs La/Sm diagram indicates generation of melts from the spinel lherzolite mantle source. On tectonic setting discrimination diagrams like Zr vs Zr/Y, Zr vs Ti and Ti vs V majority of studied samples clearly show island arc tectonic affinity.

International audience; Asbestos consists in natural minerals crystallized in a specific habit and possessing in particular properties. In the case of Naturally Occurring Asbestos, usual methods applied to the identification of mineral fibers and the determination of their possible asbestiform nature seems not efficient, especially in the case of mineral fibers included in mineral matrix. We present a new in-situ method based on the use of confocal Raman-in-SEM imaging implemented in a Scanning Electron Microscope as an efficient method for in-situ mineralogy. The limitation of conventional methods is discussed. We applied 2D-Raman imaging to the identification of sub-micrometric fibers included in different mineral matrix. We were able to identify actinolite fibers down to 400 nm in diameter, included in feldspar, quartz and/or calcite matrix. Moreover, Confocal Raman allows the collection of 3D data that would provide access to critical information on the morphology of the amphibole fibers in the volume, such as aspect ratio, fibers distribution and amphibole volume fraction. We performed this method on various examples of rocks containing actinolite fibers of mean structural formula is: Na0,04-0,12Mg2,79-3,73Al0,29-0,58K0,01Ca1,79-1,98Mn0,01-0,09Fe 2+ 0,99-1,91Fe 3+ 0,12-0,25Si7,64-7,73O22(OH)2. We demonstrated that coupling confocal Raman imaging and SEM is a new and efficient in-situ method for identification and morphological characterization of amphibole fibers. Highlights New methods are requested for characterizing asbestos fibers in a mineral matrix SEM-Raman imaging is efficient for characterizing mineral fibers in-situ Confocal Raman imaging makes 3D analysis possible 3D analysis provides information on the aspect ratio and volume fraction of asbestos Fibers thinner than 400nm can be identified by confocal Raman in SEM ( = 532 nm)

Actinolite is one of the six minerals belonging to the group of asbestos minerals. There is increasing concern regarding the potential health risks from exposure to naturally occurring asbestos and asbestos-containing materials. The correct distinction of the fibrous asbestos minerals is very important not only from a scientific point of view, but also from a legislative perspective. Asbestos actinolite is currently the only asbestos mineral that has not been fully characterized from the thermal point of view. In order to compensate for this gap in scientific literature, this paper discusses the thermal behaviour of actinolite asbestos using thermogravimetric and differential scanning calorimetry. X-ray powder diffraction, Scanning and Transmission Electron Microscopy combined with energy-dispersive spectrometry were used for the characterization of actinolite fibres before and after heating at 1000 and 1200 °C in order to determine their resistance to high-temperature changes and the products of thermal recrystallization. Actinolite asbestos breaks down at approximately 1030 °C. The thermal decomposition process of actinolite asbestos consists of two distinct events followed by recrystallization into new stable crystalline phases which preserved the original fibrous morphology (known as pseudomorphosis). The thermal analysis may prove to be useful for actinolite identification and discrimination, particularly in the case of natural massive samples where asbestos tremolite–actinolite amphiboles are mutually intermixed. Furthermore, profound knowledge of the thermal behaviour of this asbestos mineral may provide us with the relevant data for understanding the crystal–chemical transformations of asbestos through thermal inertization treatment.

The Cristalino deposit, located in the Serra do Rabo region (Para State, Brazil), is related to a hydrothermal system in which two major alteration stages could be distinguished most likely with the involvement of a hyper-saline fluid. The first stage (410-650 °C) is characterized by a distal sodic metasomatism that produced almost pure chessboard albite, minor schorlitic tourmaline and REE-rich minerals (allanite-Ce, monazite). It was followed by a pervasive calcic-ferric alteration that generated abundant actinolite (XMg = 0.87–0.69, Cl up to 0.59 wt %) in addition to Ce-allanite and magnetite associated with sulfide disseminations and breccia-like bodies composed of chalcopyrite-pyrite-magnetite-Au (early ore association). Locally, Fe-edenite (XMg = 0.67–0.42, Cl up to 2.94 wt %) replaced calcic-ferric assemblages within restrict sodic-calcic alteration halos. From 410° down to 220 °C, the previous alteration assemblages were overprinted by the hydrothermal products of the second stage. Potassic (K-feldspar, minor biotite) and propylitic (epidote, chlorite, calcite) alterations came into play successively. K-feldspar is practically stoichiometric, but it contains some impurities, notably BaO (up to 1.21 wt %). Chlorite shows the greatest compositional variation among all minerals and its composition seems to have been particularly controlled by the type of host rock, chemistry of the hydrothermal fluid and temperature. Both chamosite and clinoclore (XFe = 0.37–0.80) are present, the former being more common. Chlorine contents are in general

Research subject . High-magnesium rocks associated with the granitoid massifs of the Urals are represented by gabbro-diorites and their melanocratic varieties (hornblendites), as well as by diorites and quartz diorites. These rocks are composed of amphibole porphyrocrists frequently combined with clinopyroxene and phlogopite immersed in a basis of acid plagioclase with interstitial quartz and potassium feldspar. In addition to a high magnesium content of 0.5–0.8 units, these rocks are characterized by extremely high chromium contents of up to 1200 ppm. Methods . The study of the composition of high-magnesium rocks was performed using an ELAN 9000 inductively coupled plasma mass spectrometer, an SX-100 Cameca electron probe microanalyzer and an energy dispersive device INCAEnergy 450 X-Max 80. The detection limit for Cr 2 O 3 was equal to 0.05 wt. % and 0.2 wt. % for the microanalyzer and the energy dispersive device, respectively. Results . The two main mineral associations related to magmatic and post-magmatic processes are found to be different in terms of chromium behaviour. The average concentrations of chromium oxide in the minerals from the magmatic association varied within the range (wt. %) of 0.10–0.50, 0.29–0.68, 0.08-0.36 and 0.0–1.6 for different samples of clinopyroxene, amphibole, phlogopite and their variations, respectively. The post-magnetic association included minerals representing the products of postmagmatic (hydrothermal) transformation of pyroxenes and alumina amphibole into low-alumina magnesia hornblende, actinolite, titanite, epidote and muscovite. The transformation of chromospinelide at this stage had been accompanied by exchange processes with silicates, as a result of which the silicates were enriched with chromium. The average concentrations of chromium oxide in the minerals of this association were (wt. %) 0.24–0.80, 1.38–3.08, 1.03 and 3.5 in the samples of amphibole, epidote, titanite and muscovite, respectively. Conclusion . It is assumed that the crystallization of the early association of iron-magnesium silicates proceeded from aqueous high-magnesium melts. The subsequent post-magmatic change of such silicates led to the development of phases with a similar and occasionally higher chromium content. This fact can be explained by the interaction of silicates with chromite under the conditions of low fluid oxidation, which was insufficient for the formation of magnetite.

An investigation of the economically important Mashava Igneous Complex (MIC) in Zimbabwe was conducted using petrographic and silicate mineral compositions to gain some insights into its origin. The MIC, an ultramafic-mafic complex located in the western extremity of the Masvingo greenstone belt (MGSB), is composed of amphibole, serpentine, epidote, chlorite, clinopyroxene, orthopyroxene, plagioclase, and olivine. Spinel, sulfide minerals, and minor quartz as well as other opaque minerals are also present. The dominant mineral is serpentine, which displays a wide range in both FeO and SiO2 compositions, and the majority of this mineral belongs to the lizardite, chrysotile, and antigorite varieties. Amphiboles display a wide range in composition from tremolite and actinolite which are both consistent with greenschist facies metamorphism, through magnesiohornblende to tschermakite which are both consistent with amphibolite facies metamorphism. Clinozoisite is the only epidote type occurring in the MIC, whereas chlorite varies widely in composition which reflects the varying concentrations in iron and silica in this mineral. Chlorite types range from talc chlorite through penninite, diabantite, pycnochlorite, brunsvigite, ripidolite, and pseudothuringite. Plagioclase shows a wide compositional range from high albite to bytownite, with only two samples plotting in the alkali feldspar anorthoclase field. Pyroxene ranges in composition from enstatite through pigeonite and augite to diopside whereas olivine is rich in MgO with forsterite contents ranging from 80 to 89. Application of the chlorite geothermometry equation of Kranidiotis and MacLean (1987) yields temperatures ranging from ∼200–320 °C whereas temperatures ranging from 130 to 445 °C are obtained using equations of Lanari et al. (2014) for the formation of this mineral, generally consistent with low- to medium-grade metamorphic conditions. Chlorites in the North West Arm were formed at relatively lower temperatures (97–234 °C) than those at which chlorites in the Central Sector were formed (204–445 °C). Pressure estimates for the metamorphism of the MIC range from 3.8 to 7.3 kbars, which corresponds to depths of ∼13–25 km, respectively. Based on the different silicate mineral compositions of the North West Arm and the Central Sector, it is inferred that these two blocks underwent different petrogenetic and evolutionary histories but they were later juxtaposed, possibly during thrusting of the former onto its present position.

Early Cambrian volcanic rocks characterized by pyroclastic and lava flows of basaltic composition form the Cerro Rajon Formation are exposed in the Caborca region, northwest Sonora, Mexico. These rocks underwent greenschist facies metamorphism characterized by a metamorphic paragenesis of actinolite, sphene, chlorite, epidote and calcite with minor interstitial albite. This mineralogical association was characterized by electron microprobe analysis. Metamorphic temperatures were calculated by amphibole-plagioclase geothermometry, which indicates temperatures as high as 548 ± 40 °C. U Pb geochronology of the pluton that may cause the metamorphism yielded an age of 71.1 ± 0.4 Ma, and an average estimated temperature of 664 ± 40 °C. Preliminary pressures in this intrusive show an average of 3.08 ± 1.5 kbar. Two metamorphic events where identified by 40Ar/39Ar geochronology. Metabasalt samples from the western part of the study area yielded ages from 55.89 ± 0.6 Ma to 60.26 ± 0.33 Ma, while an age of 81.37 ± 0.81 Ma was obtained from a sample collected in the eastern part. Combined results suggest that Laramide intrusives metamorphosed the Neoproterozoic and Cambrian rocks in the Caborca region.

The Arqiale deposit, located in the southern Yili Block of Western Tianshan, Xinjiang, China, is a newly discovered large Zn-Pb deposit with a resource of approximately 10 million tons ore grading 9.65% Zn+Pb, and a certain amount of Cu and Ag. The Zn-Pb orebodies are tabular and lentoid in shape, developed along SW-striking and NW-dipping interlayer structures between the Lower Carboniferous Akeshake (mainly carbonate rocks) and Dahalajunshan (mainly volcanic rocks) formations. Garnet and pyroxene-rich skarn, formed in the early (prograde) stage of skarnization, occurs only locally as lenses within skarn bodies enriched in actinolite, tremolite, ilvaite, biotite, epidote, chlorite, calcite, quartz and fluorite, which were formed in the retrograde stage. Metallic minerals comprise sphalerite, galena, chalcopyrite, pyrite, and hematite. They mainly occur as disseminations, patches and massive ores, replacing retrograde skarn minerals and crosscut by later stage quartz and calcite veinlets. There is a general trend of increasing Cu contents and decreasing Zn/Pb ratios from the upper and south portion to the lower and north portion of the orebody. Rb-Sr dating of seven sphalerite samples yielded an isochron age of 339.5 ± 2.7 Ma, which is almost identical to the 341.8 ± 2.5 Ma age obtained from Sm-Nd dating of eight actinolite samples. Furthermore, zircon U-Pb dating yielded an age of 343 ± 6 Ma for a gabbro-diorite stock that is located about 600 m south of the Zn-Pb orebody. The age data indicate that the mineralization and retrograde skarnization were contemporaneous, and they are likely related to a magmatic intrusion of similar age which may be linked to the gabbro-diorite stock. Thus, although the direct causative intrusion has not been identified, the Arqiale deposit can be classified as a distal skarn deposit. The δ34SV-CDT values of 26 ore sulfide samples range from −7.1‰ to +1.3‰ with an average of −1.5‰. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 25 ore sulfide samples range from 18.266 to 18.880, 15.577 to 15.668 and 38.068 to 38.720, respectively, which are similar to the Early Carboniferous intrusions of the Wusun Range and partly overlap with the volcanic rocks of the Dahalajunshan Formation, and are different from the carbonate rocks of the Akeshake Formation. Based on these data, we propose that the Arqiale deposit formed from magmatic-hydrothermal fluids emanated from a concealed magmatic intrusion which may be located beneath the northern and deep part of the deposit. Much of the metals and sulfur may have been derived from the magmatic intrusions, although some of them may have also been extracted from the volcanic rocks underlying the deposit. The results of this study indicate that there is a great potential of finding more skarn Zn-Pb mineralization in Western Tianshan, where numerous Early Carboniferous arc-related intrusions with similar ages as the Arqiale deposit, in relation to the subduction of the Southern Tianshan Oceanic plate underneath the Yili-Central Tianshan Block, were emplaced into or beneath carbonate rocks.