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The W–Sn Panasqueira ore deposit is a magmatic-hydrothermal system, which includes a high-grade quartz-vein type mineralization and a disseminated greisen-type mineralization occurring in the upper part of the Panasqueira two-mica granite. We investigated the genetic and chronological relationships between the greisenization of the Panasqueira granite and the formation of ore-bearing quartz veins by monitoring major and trace elements variations in quartz-white mica assemblages composing the two-mica granite, greisen and W–Sn-bearing quartz veins. The greisen is characterized by an overall depletion in Mg, Ti, Ca, Na, Ba, Sr, REE and enrichment in Fe, Li, Rb, Cs, Sn, W which reflect the breakdown of feldspars and fluid-rock interactions with W–Sn-bearing fluids. White-mica from greisen and mineralized quartz veins are enriched in granophile elements (F, Rb, Cs, Li, Sn, W and Zn) compared to magmatic muscovite from the two-mica granite. Trace elements contents in quartz depict trends which show the progressive enrichment in Ge and B and depletion in Al, Ti and Li from magmatic to hydrothermal quartz that emphasize the progressive evolution and cooling of the magmatic-hydrothermal system of Panasqueira. Geochemical similarities between quartz-white mica assemblages from greisen and wolframite-bearing veins suggest that greisenization and the formation of mineralized veins result from the same hydrothermal event and derived from the same source of hydrothermal fluids. Apatite from greisen and quartz vein yielded U–Pb ages of 292 ± 10 Ma and 295 ± 5 Ma respectively confirming that greisenization and the formation of mineralized veins occurred roughly at the same time. These ages also overlap with the emplacement age of the Panasqueira granite (296 ± 4 Ma), indicating a temporal link between greisenization, W–Sn mineralization and granite crystallization. Temperatures of the magmatic-hydrothermal system constrained by Ti-in quartz thermometry depicts a cooling trend from magmatic quartz of granite (700–600 °C) to hydrothermal quartz of greisen (500–400 °C) and veins (450–350 °C). These results suggest that greisenization and the formation of W–Sn bearing quartz veins occurred at the magmatic-hydrothermal transition, during which orthomagmatic fluids rich in volatils, incompatible elements and W–Sn were exsolved during the final solidification stage of the Panasqueira two-mica granite.

Massive greisens are commonly associated with Sn-W mineralization and constitute low-grade high-tonnage deposits. The formation of this type of deposit results from an intense pervasive metasomatic alteration involving a major fluid and mass transfer through a nominally impermeable parental granite. A decrease in the volume of the solid phases associated with the mineral replacement reactions may be a potential process for creating pathways to enhance fluid flow. Here, we explore the effects of the replacement reactions related to greisenization on the granite's mineralogy and petrophysical properties (density, porosity, and permeability), as well as their potential implications for fluid flow in the case of the world-class Panasqueira W-Sn-(Cu) deposit, Portugal. Mineralogical and microtextural analyses of greisenized facies show that the total replacement of feldspars by muscovite is associated with a volume decrease of the solid phases that induces a significant porosity generation in greisen (~8.5%). Greisenization experiments coupled with permeability measurements show that the replacement of feldspars by muscovite permits new pathways at the crystal scale that significantly enhance the transient permeability. Moreover, permeability measurements performed on representative samples with different degrees of greisenization show that permeability increases progressively with the level of alteration from 10-20 m2 in least granite to 10-17 m2 in greisen. The correlation between the permeability and porosity evolutions demonstrates that the porous texture developed during replacement reactions creates new pathways that enhance significantly the permeability in greisen systems. The occurrences of mineral-bearing metals such as cassiterite in the newly formed porosity of greisen provide evidence that greisenization can be a decisive process for enhancing fluid flow and promoting transport of metals in Sn-W deposits. Finally, we present a model involving a positive feedback between greisenization and permeability, in which mineralizing fluids are able to generate their own pathways in initially impermeable granite via replacement reactions, which in turn promote further hydrothermal alteration and mass transport. [ABSTRACT FROM AUTHOR]

Deciphering the behavior of fluid flow at the magmatic-hydrothermal transition is crucial to understanding the physical processes leading to the formation of intrusion-related ore deposits and hence to predicting the locations of mineralized bodies. However, the hydrodynamics (direction and velocity) of the hydrothermal fluid flows related to this transitional stage remains poorly constrained. Here we present a coupled textural and chemical study performed on tourmaline growth bands to constrain fluid flow during the initiation of the hydrothermal system of the Panasqueira W–Sn–(Cu) deposit. This exceptional deposit consists of a dense network of flat wolframite and cassiterite-bearing quartz veins intensely developed above a well-known but hidden greisen cupola. The W–Sn mineralization is preceded by a tourmalinization stage occurring as metasomatic halos around veins and as selvages developed along the vein–wall-rocks contacts. Results emphasize the key role of the greisen cupola in fluid focusing and the role of fluid overpressure during vein opening. Velocity values highlight an efficient transport of metals in veins largely dominated by advective processes (10 −4 to 10 −3 m s −1 ), whereas fluid flow in the altered wall-rocks is slow and pervasive (10 −6 to 10 −5 m s −1 ), suggesting that element transport through the metasedimentary host rock was low and limited to the alteration haloes. LA-ICP-MS analyses of tourmaline growth bands reveal that fluids coming from the cupola are enriched in Na, K, Li, Sr and Sn, emphasizing the contribution of magmatic fluids during vein formation and the metasomatic alteration of the wall-rocks. More generally, this study demonstrates that the apical portions of granite bodies act as emanative centers of mineralizing fluids, and highlights the usefulness of mineral growth band analysis in the search for intrusion-related mineralization. [ABSTRACT FROM AUTHOR]

This study aims to uses paleomagnetic and anisotropy of magnetic susceptibility (AMS) methods to recognize the initial deposit position and to track the paleoflow at the origin of an iron skarn-related deposit. The Yamansu deposit is located in eastern Tianshan. This province has a substantial mining potential for Fe–(Cu) skarn, Cu–Ni and V–Ti orthomagmatic deposits, and orogenic Au lodes. Recent publication dates the Yamansu deposit at 323 Ma, and uses this deposit to define a model of Submarine Volcanogenic Iron Oxide (SVIO) deposits (Hou et al., 2014a,b). In the proposed model the Yamansu stratoïd ore bodies formed horizontally within the central venting part of a large submarine composite volcano in a back-arc environment. However, at Yamansu the ore bodies are tilted vertically by the large scale dextral strike-slip faulting during the Permian. The Carboniferous positions are thus overprinted and unknown. Understanding the initial geometry and structures of the Yamansu deposit is then necessary to test and/or improve the proposed SVIO model. Field observations evidence an emplacement of the basalt as sill and their alteration into skarn. Magnetic mineralogy results show that the magnetic remanence and susceptibility are carried by magnetite. Paleomagnetic measurements on massive garnet skarn and basaltic sill distinguish two groups of samples. The higher coercivity samples give a mean remanence direction that is compatible with regional Late Carboniferous directions after bedding correction. This result indicates that both the basaltic sill and the massive garnet skarn were horizontal when formed. The AMS results agree with the paleomagnetic data because the magnetic foliations after bedding correction are horizontal and the well-defined magnetic lineation suggests the existence of a horizontal fluid flow during metasomatism. These results indicate that the basaltic sill horizontally intruded the Carboniferous limestones intercalated within the volcanic pile. Metasomatic iron-rich fluid probably ascended along a pre-existing fault and was injected horizontally into the limestone and sill, and then caused extensive skarnization and deposited the magnetite before tilting due to the Permian right-lateral strike-slip. [ABSTRACT FROM AUTHOR]

The aim of this study was to provide information about the biological properties of iron oxide nanoparticles (IO-NPs) obtained in an aqueous suspension. The IO-NPs were characterized by transmission electron microscopy (TEM). Analysis of hysteresis loops data at room temperature for magnetic IO-NPs sample indicated that the IO-NPswere superparamagnetic at room temperature. The calculated saturation magnetization for magnetic iron oxide was Ms = 18.1 emu/g. The antimicrobial activity of the obtained PMC-NPs was tested against Gram-negative (Pseudomonas aeruginosa 1397, Escherichia coli ATCC 25922), Gram-positive (Enterococcus faecalis ATCC 29212, Bacillus subtilis IC 12488) bacterial as well as fungal (Candida krusei 963) strains. The obtained results suggested that the antimicrobial activity of IO-NPs is dependent on the metallic ions concentrations and on the microbial growth state, either planktonic or adherent. The obtained IO-NPs exhibited no cytotoxic effect on HeLa cells at the active antimicrobial concentrations. [ABSTRACT FROM AUTHOR]

In order to better define the dependence of the mineral texture on flow, anisotropy of magnetic susceptibility (AMS) and microscopic observations have been performed on calcite-rich precipitations occurring in a horizontal pipe where the flow direction is clearly defined. A total of 65 cubes were cut from five slices, magnetic studies identified-pseudo-single domain magnetite as the major AMS carrier. Horizontal foliation characterizes the magnetic fabrics and the lineation is parallel to the pipe axis, that is, the flow direction. The origin of this lineation is discussed and is interpreted to be mainly the consequence of elongated pseudo-single domain magnetite. To complete the magnetic fabric studies, shape preferred orientation statistics were performed on 563 calcite sections in the (0001) calcite plane. It shows elongated shapes with a general orientation parallel to the pipe axis. The mean shape orientation is the average of two distinct subpopulations that deviated slightly from the pipe axis. Observation on calcite shapes and the direction of the magnetic lineation are coherent, suggesting that it is possible to track hydrothermal palaeocirculation using magnetic lineation and petrographic fabrics. [ABSTRACT FROM AUTHOR]

As in several other anisotropy of magnetic susceptibility studies, the main direction of the magnetic lineation analysed in part I of this work, as well as crystal elongation, have been found to be roughly aligned with the direction of the surrounding flow. In order to explain the mechanisms responsible for such crystal shape anisotropy in a hydrodynamic context, we derive a mathematical model based on Falkner–Skan self-similar boundary layers at high Reynolds numbers. The model allows calculating local growth rates out of diffusion processes in the concentration boundary layer for crystal faces orientated arbitrarily in the range 90° to −18° with respect to the flow direction, and for any flow velocity. Hence, our work generalizes rationally previous attempts already done in the case of a flow parallel to the crystal face. This crystal growth model is applied to a natural case of calcite growth rate in 2-D section perpendicular to the 〈 c〉 axis. The reconstructed calcite growth reproduces the texture of a natural case observed in Part I, although the local Reynolds numbers are quite low. This approach may be applied for various geological settings, from deep metasomatism to flowing on the Earth surface. [ABSTRACT FROM AUTHOR]

The Chaillac deposit of Indre, France, occurs at the contact between Hercynian metamorphic basement in the Massif Central and Mesozoic sedimentary cover. The deposit consists of a stratiform Ba-F-Fe-rich deposit (Les Redoutières) and a F-Ba-(Pb)-rich vein (Le Rossignol). Most fluorite mineralization in the northern French Massif Central occurs in north-south extensional veins that were filled during two main mineralizing stages. These stages are characterized by green and purple fluorite, and yellow fluorite and barite. The early stage of the Rossignol vein is characterized by green and purple fluorite, quartz, minor adularia, and minor pyrite. Analysis of intravein sediments indicates that they were deposited in a low hydrodynamic regime (fluid velocities of <0.02 ms-1) during the mineralizing event. Primary fluid inclusions in the early-stage fluorite contain a very low salinity (<0.5 wt % NaCl equiv) aqueous fluid and have a median homogenization temperature of 135°C. Yellow fluorite-barite mineralization stage began with deposition of yellow fluorite, barite, and galena, and culminated in a late brecciation stage. Analysis of sedimentary textures indicates that the yellow fluorite-barite assemblage was deposited in a high hydrodynamic regime (fluid velocities of <0.4 ms-1). Primary fluid inclusions in fluorite from this stage contain brines (21.8 wt % NaCl equiv) and have a median homogenization temperature of 110°C. There is no evidence for fluids of intermediate salinity in the fluorite samples from either stage. The two stages of fluorite can be distinguished using Y and REE ratios; Y/Ho ratios average 100 for the yellow fluorite-barite and 50 for the green and purple fluorite stage. Both positive Eu anomalies and La/Ho ratios decrease with time and depth, suggesting that deposition of the yellow fluorite-barite assemblage began at the top of the vein and progressed downward. A genetic model is proposed,... [ABSTRACT FROM AUTHOR]

The Jbel Saghro is interpreted as part of a long-lived silicic large igneous province. The area comprises two lithostructural complexes. The Lower Complex consists of folded metagreywackes and N070–090°E dextral shear zones, which roughly results from a NW–SE to NNW–SSE shortening direction related to a D1 transpressive tectonic stage. D1 is also combined with syntectonic plutons emplaced between ca. 615 and 575 Ma. The Upper Complex is defined by ash-flow caldera emplacements, thick and widespread ignimbrites, lavas and volcaniclastic sedimentary rocks with related intrusives that were emplaced in three main magmatic flare ups at ca. 575, 565 and 555 Ma. It lies unconformably on the Lower Complex units and was affected by a D2 trantensive tectonic stage. Between 550 and 540 Ma, the magmatic activity became slightly alkaline and of lower extent. Ore deposits show specific features, but remain controlled by the same structural setting: a NNW–SSE shortening direction related to both D1 and D2 stages. Porphyry Au(–Cu–Mo) and intrusion-related gold deposits were emplaced in an earlier stage between 580 and 565 Ma. Intermediate sulfidation epithermal deposits may have been emplaced during lull periods after the second and (or) the third flare-ups (560–550 Ma). Low sulfidation epithermal deposits were emplaced late during the felsic alkaline magmatic stage (550–520 Ma). The D2 stage, therefore, provided extensional structures that enabled fluid circulations and magmatic-hydrothermal ore forming processes. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Amphibole-rich clots are vestiges of residual pyroxene-rich precursors from the source after partial melting. • The microgranular enclaves of the Tongshanling granodiorite are reworked restite enclaves. • A model illustrating the formation process of reworked restite enclave has been proposed. • The fertile amphibolitic source is beneficial to the formation of Cu-Pb-Zn-bearing granodiorites in the Nanling Range. Abstract Microgranular enclaves, which can provide important petrogenetic indications for the host granitoids, are commonly observed in the Middle-Late Jurassic Cu-Pb-Zn-bearing granodiorites in the Nanling Range of South China. The origin of these Cu-Pb-Zn-bearing granodiorites is still controversial, with two different hypotheses: crust-mantle mixing and partial melting of the mafic lower crust, primarily based on geochemistry and geochronology. Detailed petrographic and mineralogical studies have been carried out on the Tongshanling granodiorite and its microgranular enclaves to provide new textural and compositional constraints on the petrogenesis. The microgranular enclaves have dioritic compositions with a mineralogy dominated by plagioclase, amphibole, and biotite. Abundant residual materials, such as mafic mineral clots, inherited and metamorphic zircon, and Ca-rich core plagioclase, occur in the enclaves and are in favor of a restite origin. The amphibole-rich clots are considered as vestiges of residual pyroxene-rich precursors from the source. Three different types of amphibole, i.e., magmatic, metamorphic, and magma reworked metamorphic amphibole, have been recognized in the granodiorite and its enclaves. The magmatic amphibole occurs as enclosed and idiomorphic isolated crystals in the granodiorite with Al and Si contents of 1.34–2.12 apfu (atoms per formula unit) and 6.25–6.88 apfu, respectively, and a ΣREE content of 307–764 ppm. The metamorphic amphibole, with a granoblastic triple-junction texture, occurs as aggregated crystals dominantly in the enclaves and a few in the granodiorite. It has actinolitic compositions (Al: 0.31–0.81 apfu, Si: 7.33–7.72 apfu) and distinctly lower contents of incompatible elements (ΣREE: 99–146 ppm). The magma reworked amphibole has intermediate compositions (Al: 0.81–1.59 apfu, Si: 6.71–7.35 apfu, ΣREE: 317–549 ppm) between the magmatic and metamorphic amphibole. The zonal amphibole-rich clots exhibit increasing Al and decreasing Si contents from interior amphibole to exterior amphibole and also from core to rim in amphibole grains, and the outer parts of enclave magmatic zircon have higher ThO 2 + UO 2 contents and lower Zr/Hf ratios than the inner parts, showing the process of magma reworking of the restite enclaves. Based on the textural and compositional evidence, these microgranular enclaves are thought to be reworked restite enclaves. This is also supported by thermobarometric calculation. A model illustrating the formation process of reworked restite enclave has been proposed. Combined with previous experimental studies of partial melting, the Tongshanling granodiorite is deduced to be derived from dehydration melting of amphibolite in the mafic lower crust. The fertile amphibolitic source is beneficial to the formation of Cu-Pb-Zn-bearing granodiorites in the Nanling Range. [ABSTRACT FROM AUTHOR]

Permeability laboratory measurements under in situ pressures, temperature and strain have been performed on three different diabase alteration facies (metadiabase, chloritized diabase, epidosite) from the Troodos Ophiolite, Cyprus. This aims to study the relations between hydrodynamics, deformation and hydrothermal reaction in the sheeted dyke complex beneath oceanic ridges. The use of water as pore fluid in these experiments favors hydrothermal fluid–rock interactions. All experiments, performed with a Paterson gas-medium apparatus, were achieved at 400 °C, 100 MPa of confining pressure and 50 MPa of pore fluid pressure, conditions at the base of sheeted dykes. Permeability was measured by injection of water and argon before, during and after coaxial deformation. Resulting textures and mineralogy were studied by microscopy and X-ray microtomography in order to identify mineral reactions and to calculate the permeability by numerical simulation after decompression. During stress loading, a compaction/dilatant evolution is observed only in experiments on epidosite. Failure tends to increase permeability by one order of magnitude. For example, using water as pore fluid, permeability measurements after macroscopic failure give the following variations from 4 × 10 − 20 m 2 to 2.9 × 10 − 19 m 2 for metadiabase, 1 × 10 − 20 m 2 to 2.6 × 10 − 19 m 2 for chloritized diabase and 6.5 × 10 − 19 m 2 to 3 × 10 − 18 m 2 for epidosite. Textures suggestive of self-healing and sealing explain permeability reduction by hydrothermal reaction after macroscopic failure. Paradoxically, even using argon as pore fluid, hydrothermal reaction is possible in metadiabases due to dehydration of chlorite. Moreover, fractures appear much finer in rocks enriched in chlorite because of formation of gouge structures. After the experiments, 3D images of fracture networks enable calculation of permeability by numerical simulations which values are 4–6 orders of magnitude higher than the experimental measured values. Such results demonstrate that the geometry and the textures observed in unloaded samples are not suitable to estimate permeability and have to be very carefully interpreted. [ABSTRACT FROM AUTHOR]

Permian large-scale transcurrent tectonics and massive magmatism are prominent features of the Tianshan belt and neighboring regions of the Central Asian Orogenic Belt. Structural, geochronological and geochemical analyses of Carboniferous and Permian intrusive rocks associated with the Kangguer-Huangshan Shear Zone (eastern Chinese North Tianshan) provide constraints on their tectonic setting and the tectonic evolution of the Tianshan belt as well. Carboniferous granitic rocks were emplaced at 338 ± 4 Ma and 347 ± 2 Ma, respectively, and show geochemical features typical of the calc-alkaline series. These arc-type granites do not display ductile deformation, probably because they were completely cooled at the time of shearing tectonics, and are only offset by brittle strike-slip faults. In contrast, Permian granitoids display pervasive ductile tectonic features diagnostic of synkinematic emplacement. Four gabbro and diorite samples from the East Huangshan intrusive complex yielded zircon U-Pb ages of 267 to 275 Ma, and a granitic dike is dated at 290 ± 1 Ma. The granitic dike is cut by en-echelon right-lateral strike-slip faults, and the mafic intrusive complex displays a sigmoidal shape with mylonitic foliation localized at its margins. Other specific pluton shapes (such as tongue and tadpole-like) and syn-magmatic deformation can be observed in intrusions of the same age, showing similar fabrics and kinematics consistent with that of the Kangguer-Huangshan Shear Zone. Numerous mafic to felsic dikes occur within and off the shear zone with a dominant SE-NW orientation and minor varieties in N-S or NNE-SSW directions. One gabbro dike that intrudes the early Carboniferous granite of the East Kanggurtag area yielded a magmatic age of 274 ± 4 Ma, and contains older zircons (~340 Ma, ~390 Ma, ~450 Ma, and 1.3-2.2 Ga) probably inherited from intruded rocks. The Permian intrusive rocks have variable chemical compositions suggesting derivation of these rocks from depleted and undepleted (or enriched) mantle sources with involvement of subduction-related components. We conclude from our integrated analysis of the geological, structural, geochemical and geochronological data that the Permian magmatic rocks were formed in a post-collisional/post-orogenic setting from multiple sources, and were emplaced under the control of large-scale dextral transcurrent tectonics. [ABSTRACT FROM AUTHOR]

Abstract: To understand the processes and timing of their formation, six non-sulfide Zn–Pb ore deposits were investigated in the Moroccan High Atlas. Sulfide and non-sulfide ores are hosted in Lower Jurassic reefal to para-reefal limestone. Zn (Pb) carbonates, Zn silicates and associated hydrated phases directly replace the stratabound primary ore bodies or fill cavities along fractures related to the Atlasic compression. Field observation has been complemented by a multidisciplinary approach (e.g. XRD, Raman, SEM, EPMA) for the mineralogical characterization. All six ore deposits present similar paragenesis revealing three successive stages for ore deposition: 1) formation of the protore sulfides, 2) early supergene weathering with formation of Zn–Pb-bearing carbonates and iron oxi-hydroxides and 3) late supergene weathering with deposition of Zn-carbonates, Zn-silicates and hydrated phases. Direct replacement of primary sulfides is accompanied by precipitation of zinc non-sulfide minerals in cavities or internal sediments filling. The proposed three-step scenario can be placed within the tectonic evolution of the Moroccan High Atlas belt. Deposition of primary sulfides is contemporaneous with opening of the Tethyan and Atlantic oceans. During the Tertiary, intracontinental deformation has given rise to the High Atlas fold-and-thrust belt and to regional uplift. As a result, Zn–Pb sulfides, hosted in carbonates experienced oxidation under an arid climate to form karst-related Zn–Pb non-sulfide ore bodies. [Copyright &y& Elsevier]