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Gold mineralisations in the Canan area (Honduras) occur within altered metamorphic rocks crossed by quartz veins which filled the fractures where the hydrothermal fluids carrying gold flowed. Quartz crystals of the veins contain abundant fluid inclusions which have been divided into four main types on the basis of the petrographic features and microthermometric data. The association of L-rich and V-rich inclusions with the same major components supports boiling at the time of entrapment. The trapped hydrothermal fluid consists of an aqueous solution (0.9–4.8 wt.% NaCl equivalent) plus a CO 2 –CH 4 -bearing bubble. Some fluid inclusions contain graphite of hydrothermal origin. Microthermometric and spectroscopic data on fluid inclusions indicate that hydrothermal fluids carrying gold were at T = 300 °C, P = 500–1400 bar, log f O 2 ~ − 37.6 ± 2.5 and with a pH value of 2.9 ± 0.4. Large amounts of sulphides (mainly pyrite) are associated with gold. We infer that Au was transported as Au–S complex, in particular as Au(HS)°. The activity of sulphur in the hydrothermal fluids was at least 10 − 2 . The precipitation of gold can be related to several processes that reduced the stability of AuHS°: 1) boiling and vapour loss following the pressure drop caused both by fracture opening and fluid uprise, 2) sulphidation as a result of the presence of Fe 2 + (and other metal cations) from the mineralogical alteration (mainly of biotite and chlorite) in the wall-rocks and 3) hydrothermal alteration of feldspars and micas into kaolinite and diaspore with increase in pH of the hydrothermal fluids. The mineralogical, petrological, geochemical features and the geological setting are broadly consistent with those of orogenic-type gold deposits. [ABSTRACT FROM AUTHOR]

The boron stable isotope ratio δ11 B of 12 water samples representative of three chemical facies (fresh Na-bicarbonate, brackish Na-chloride, saline, and brine Ca-chloride) has been analyzed. Interpretation of the δ11 B data, along with the chemical compositions, reveals that Na-carbonate waters from the Northern Apennine are of meteoric origin, with boron contributions from clay desorption and mixing with seawater-derived fluids of Na-chloride or Ca-chloride compositions. The comparison of our new results with the literature data on other sedimentary basins of Mediterranean, and worldwide, confirms the contribution of Na-bicarbonate waters to the genesis of mud volcano fluids. The Na-chloride sample of Salvarola ( SAL), which may represent the end-member of the mud volcanoes, and the Ca-chloride brine water from Salsomaggiore ( SM) indicate boron release from clays compatible with the diagenetic process. The empirical equation: [ABSTRACT FROM AUTHOR]

Serpentinites are rocks, often used in buildings, formed in large extent by minerals of the serpentine group: chrysotile, antigorite, lizardite, and polygonal serpentine. The fibrous type (e.g. chrysotile) of serpentine group minerals, along with several amphibole varieties (e.g. actinolite and tremolite), are the major components of asbestos family. The exposure to fine fibrous asbestos powder is linked to diseases such as pleural mesothelioma and asbestosis. The identification of the main varieties of the serpentine group, laminated or fibrous, becomes an issue of great interest for public health. This work introduces an analytical strategy able to distinguish the different serpentine polymorphs directly on the sample, allowing the analysis within their textural environment, evidencing at the micrometer scale the mineral reactions of the phases. Samples coming from the Koniambo massif (Grande Terre Island, New Caledonia) were studied by means of optical microscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy, and Raman spectroscopy. Raman peaks observed in the high wavenumber spectral range of 3550-3850 cm−1, associated with OH stretching vibrations, allow the discrimination of the all four serpentine varieties. The relationship between the different varieties of serpentine, at a micrometric scale, in complex samples, has been investigated by two-dimensional Raman mapping. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The occurrence of crystallized and glassy melt inclusions (MI) in high-grade, partially melted metapelites and metagraywackes has opened up new possibilities to investigate anatectic processes. The present study focuses on three case studies: khondalites from the Kerala Khondalite Belt (India), the Ronda migmatites (Spain), and the Barun Gneiss (Nepal Himalaya). The results of a detailed microstructural investigation are reported, along with some new microchemical data on the bulk composition of MI. These inclusions were trapped within peritectic garnet and ilmenite during crystal growth and are therefore primary inclusions. They are generally isometric and very small in size, mostly ≤15 μm, and only rarely reaching 30 μm; they occur in clusters. In most cases inclusions are crystallized ('nanogranites') and contain a granitic phase assemblage with quartz, feldspar and one or two mica depending on the particular case study, commonly with accessory phases (mainly zircon, apatite, rutile). In many cases the polycrystalline aggregates that make up the nanogranites show igneous microstructures, e.g. granophyric intergrowths, micrographic quartz in K-feldspar and cuneiform rods of quartz in plagioclase. Further evidence for the former presence of melt within the investigated inclusions consists of melt pseudomorphs, similar to those recognized at larger scale in the host migmatites. Moreover, partially crystallized inclusions are locally abundant and together with very small (≤8 μm) glassy inclusions may occur in the same clusters. Both crystallized and partially crystallized inclusions often display a diffuse nanoporosity, which may contain fluids, depending on the case study. After entrapment, inclusions underwent limited microstructural modifications, such as shape maturation, local necking down processes, and decrepitation (mainly in the Barun Gneiss), which did not influence their bulk composition. Re-homogenized nanogranites and glassy inclusions show a leucogranitic and peraluminous composition, consistent with the results of partial melting experiments on metapelites and metagraywackes. Anatectic MI should therefore be considered as a new and important opportunity to understand the partial melting processes. [ABSTRACT FROM AUTHOR]