Spatial and metallogenic relationships between different hydrothermal vein systems in the Southern Arburèse district (SW Sardinia)

The SW Sardinian basement hosts various ore deposits linked to geological processes active from Cambrian to post-Variscan times. In particular, the Southern Arburèse district hosts several granite-related W-Sn-Mo deposits and a 10 km-long system of Ni-Co-As-Bi-Ag±Au-bearing five-element veins. New investigations in the eastern and central parts of the district (Pira Inferida mine sector) were performed to understand the poorly documented spatial and metallogenic relationships between these systems. The granite-related deposits consist of massive wolframite quartz (W-Bi-Te-Au) and molybdenite-quartz veins, linked to the early Permian (289±1 Ma) Mt. Linas granite, that are cross-cut by the five-element veins. The wolframite-quartz veins, observed by optical and electron (SEM-EDS) microscopy, show abundant native Bi, Bi-Te phases and native Au suggesting a W-Bi-Te-Au hydrothermal system. The five-elements veins exhibit breccia and cockade textures enveloping clasts of the Ordovician host-rocks and locally small fragments of the earlier W-Mo-quartz veins. The five-element vein paragenesis includes three main stages, from older to younger: 1) native elements (Bi±Au); 2) Ni-Co arsenides-sulfarsenides in quartz gangue; and 3) Pb-Zn-Cu±Ag sulfides in siderite gangue. The mineralogical, geochemical and isotopic features of the five-element vein swarm are closely comparable to five-element deposits elsewhere in Europe (Germany, Switzerland, Italian Alps). While the source of Ni and Co is still unknown, the high Bi contents as well as Au enrichment in the five-element veins suggest selective remobilization of these elements, and perhaps others, from the granite-related W-Bi-Te-Au veins. The five-element vein system was likely formed during a post-289±1 Ma and post-Variscan metallogenic event

ARMENITE: A REALLY RARE MINERAL?

Armenite is a quite uncommon double-ring Ba-Al-Ca silicate hydrate belonging to the milarite-osumilite group and with the general formula BaCa2Al6Si9O30·2H2O. It generally forms pseudo-hexagonal whitish-pinkish crystals. However, in its structure, Si, Al ordering and H2O positions produce the deviation from hexagonal symmetry, explaining the belonging to the Pnna or Pnc2 space groups. In thin section, armenite is quite elusive. In fact, it appears colorless, with low relief and low first-order interference color. More complication arises from the tartan-like twinning patterns (resembling that of microcline), patchy-like and/or undulose extinction as well as the monoaxial to strongly biaxial (2V up to 65°) behavior. Its affinity to hexagonal or orthorhombic space groups as well as the reasons for its anomalous optical features have formerly been an object of debate. Up to now, armenite has only been found in a dozen of places worldwide, among which Armen mine (Norway), Quebec (Canada), New South Wales (Australia), Scotland, Switzerland, and Sardinia (Italy). It typically forms veins within the host rocks in different geological environments. These include metasomatic basic to intermediate igneous rocks, mineralized skarn and hornfels, and gneisses indicating that the interaction between fluid phases and a primary Ba source is required for its formation. Here we report the third occurrence of armenite in Sardinia, from the Rosas mine area (Mitza Sermentus mineworks, south-west Sardinia). Armenite-bearing samples were collected along the contact between a sulfide-mineralized skarn vein and a black phyllite host-rock. The black phyllite matrix consists of muscovite, chamosite and quartz with feldspars, clinozoisite, titanite, and calcite as accessory phases. The skarn is made up of clinopyroxene, amphibole, epidote, chlorite and wollastonite, and calcite; accessory minerals are titanite, apatite, prehnite, and baryte. The ore minerals mainly consist of galena, sphalerite, chalcopyrite, and pyrite. Armenite is usually concentrated in mm-wide white veinlets along the contact between the sulfide mineralization and the host rock or more rarely dispersed in the phyllite matrix. At first, interpreted as an altered feldspar, it was identified by SEM-EDS analyses. Despite being semi-quantitative, the analyses provided compositions very close to stoichiometric armenite, with SiO2 ~ 48 wt.%, Al2O3 ~ 28 wt.%, BaO ~ 13 wt.% and CaO ~ 10 wt.%. This finding was further confirmed by XRPD analyses on armenite-rich polymineralic samples in which more than 20 peaks were assigned to this phase leading to a good match with an armenite in the PDF database (Ref. code 00-037-0432). Beyond its supposed rarity and its peculiar crystal structure, three reasons make armenite deserving of attention: (i) understanding its genesis could better constrain the P-T-fluid conditions of rocks in which armenite is found and that are often mineralized; (ii) given its difficult recognition by base techniques, it is likely that armenite is more common than previously thought and is usually overlooked; (iii) since its formation requires a primary Ba source, armenite could be used as an indicator of the proximity of Ba-rich deposits

Shear zone development and structurally-controlled skarn ore mineralization in the Rosas district, SW Sardinia.

The Rosas Shear Zone (RSZ) is a 1 km thick brittle-ductile shear zone that outcrops in the Variscan fold and thrust belt foreland of SW Sardinia, where several important ore deposits were mined in the last century. The RSZ lies in the footwall and strikes parallel to the NE-dipping regional thrust that separates the Variscan foreland from the nappe zone. Two thrusts that developed along the limbs of two km-scale overturned antiforms, with NE-dipping axial plane, bound the RSZ. The folds show a SW-facing direction and a well-developed axial plane cleavage, and affect a lower Cambrianupper Ordovician stratigraphic succession mainly made, from bottom to top, by a sequence about 200 m thick of dolostones and massive limestone followed by 50 m of marly limestones overlain by about 150 m of sandstones, pelites and siltstones, finally unconformable capped by conglomerates and siltstones, ranging in thickness from a few to 200 m. Differently, within the RSZ the bedding is completely transposed along the cleavage and its internal structure is characterized by anastomosing thrusts that affect the stratigraphic succession defining map-scale slices mainly consisting of dolostones and limestones embedded into the siliciclastic formations. It is noteworthy the occurrence of a NE-dipping, up to 100 m thick gabbro-dyke that postdates the deformation phases and that can be related to the exhumation of the chain during late Carboniferous-Permian times. In the whole area, contact metamorphic and metasomatic processes selectively affected the Cambrian carbonate tectonic slices, originating several skarn-type orebodies. Mineralized rocks display the mineralogical assemblages and textures of Fe-Cu-Zn skarns, with relicts of anhydrous calcic phases related to the prograde metamorphic stage (garnet, clinopyroxene, wollastonite), frequently enclosed in a mass of hydrous silicates (actinolitic amphibole, epidote) and magnetite related to the retrograde metasomatic stage, in turn followed by chlorite, sulfides, quartz and calcite associated to the hydrothermal stage. Metasomatic reactions also involved mafic rocks, producing a mineral association marked by clinopyroxene, amphibole, epidote, prehnite and Barich K-feldspar. Sulfide ores are made of prevailing sphalerite, chalcopyrite and galena, with abundant pyrite and pyrrhotite and minor tetrahedrite and Ag-sulfosalts. Garnets are andraditic/grossularitic, distinctly zoned and optically anisotropic. Field surveys pointed out the tight structural controls on skarn and ore formation. On a local scale, the gabbro emplacement along high- to low-angle NNW-SSE structures bordering the carbonate tectonic slices accentuate the effects of contact metamorphism, and metric to decametric mineralogical zonation (garnet->pyroxene->wollastonite) are recognized. On a larger scale, extensive hydrothermal fluid circulations involved the structures of the RSZ. Infilling of metasomatic fluids in carbonate tectonic slices is fault-controlled and aided by the increase in permeability due to the alteration of prograde silicates. The causative intrusion related to skarn ores belongs to the early Permian (289±1 Ma) ilmenite-series, ferroan granite suite which intrudes the RSZ about 3 km east from the studied area. The Fe-Cu-Zn skarn ores of Rosas are best interpreted as distal, structurallycontrolled orebodies, connected to large-scale circulation of granite-related fluids in the km-sized plumbing system represented by the RSZ

MINERALOGICAL STUDIES OF THE W-Sn VEIN SKARNS OF MONTE TAMARA (NUXIS, SULCIS DISTRICT): INSIGHTS FOR STRATEGIC MINERALS EXPLORATION IN SW SARDINIA (ITALY).

Skarn deposits are a relevant source of critical raw materials such as W, Sn, and In. Recent studies conducted in South Sardinia pointed out the relationships between various Sn-W-Mo deposits and the early Permian (289-286 Ma) F-bearing, ilmenite-series ferroan granites (e.g., Sulcis pluton). This new evidence triggered a broad re-examination of granite-related deposits including skarn deposits hosted by Cambrian limestones of the low-grade Variscan basement of the Sulcis district (SW Sardinia). With this purpose, field investigations and OM, SEM-EDS, EMPA, and LA-ICP-MS observations, and analyses have been conducted on the skarn ores of Monte Tamara (Nuxis, northern Sulcis) where scheelite has been reported in the old San Pietro and Sinibidraxiu mines. The San Pietro mine exploited a 1-5 m thick and 70 m deep, steeply dipping skarn orebody located at the tectonized contact between early Cambrian sandstones and limestones. The orebody includes layers of Grt-Cpx-Wo, magnetite, and Zn-Pb-Cu-Fe sulfide bands. Prograde and retrograde stages with oxides and sulfides can be recognized. Clinopyroxene is the foremost mineral of the prograde stage; garnets (andradite-grossular) are usually dark green with typical anomalous birefringence and distinctly zoned (Fe-rich cores and Al-rich rims). Hematite turned to mushketovite, and Mo-rich scheelite, followed by In-bearing cassiterite, occasionally occur in the prograde assemblages. Amphiboles and epidotes mark the retrograde stage, together with abundant Zn-Cu-Fe-Pb sulfides and accessory molybdenite, stannite, bismuthinite, and Bi-Ag-Pb sulfosalts. At San Pietro, dominant sphalerite displays highly variable Fe, Mn, and Cd contents. Relictlooking blebs of Fe-Mn-poor Sp are scattered in high-Fe-Mn Sp where Sn EMPA peaks may correlate with cassiterite-stannite micro-inclusions. Galena composition suggests localized intergrowths with micro-inclusions of bismuthinite, Bi-Se, and Bi-Te sulfosalts. The stannite-sphalerite geothermometer provided a temperature range of 325-200°C for the sulfide stage. The Sinibidraxiu old mine exploited a 1,5 m thick and 60 m deep columnar body, hosted in early Cambrian marbles. It consists of a sphalerite-wollastonite assemblage with late sulfides, quartz, and calcite, hosting cm-sized arsenopyrite and scheelite. Scheelite is Mo-poor; Sn-, other Mo-phases and Bi-phases are absent. High-Fe Sp, rimmed by low-Fe Sp and blebby galena, is finely intergrown with wollastonite cockades. The results from this study suggest that a wide range of skarn-related mineralizing phenomena occurred in the Monte Tamara area. Both orebodies resulted from a structurally controlled migration of metasomatic fluids inside the hosting carbonate formation. Mineral zonation and composition of the San Pietro skarn point towards skarn development under varying fO2 conditions, oxidizing then rapidly turning to moderately reducing within the prograde W-Sn skarn stage and into the sulfide stage. The features of the Sinibidraxiu orebody (e.g., Mo-poor, As-devoid scheelite) suggest a formation from reducing metasomatic fluids but S-poor compared to San Pietro, probably at more distal environments (e.g. low Sn-Bi contents). From this point of view, the Monte Tamara area still maintains an economic potential, linked to the possible presence of proximal skarn ores at depth; thereby representing a key area for further exploration for granite-related strategic and critical metals in SW Sardinia

Increasing the maturity of measurements of essential climate variables (ECVs) at Italian atmospheric WMO/GAW observatories by implementing automated data elaboration chains

In the framework of the National Project of Interest NextData, we developed automatic procedures for the flagging and formatting of trace gases, atmospheric aerosols and meteorological data to be submitted to the World Data Centers (WDCs) of the Global Atmosphere Watch program of the World Meteorological Organization (WMO/GAW). In particular, the atmospheric Essential Climate Variables (ECVs) covered in this work are observations of near-surface trace gas concentrations, aerosol properties and meteorological variables, which are under the umbrella of the World Data Center for Greenhouse Gases (WDCGG), the World Data Center for Reactive Gases, and the World Data Center for Aerosol (WDCRG and WDCA). We developed an overarching processing chain to create a number of data products (data files and reports) starting from the raw data, finally contributing to increase the maturity of these measurements. To this aim, we implemented specific routines for data filtering, flagging, format harmonization, and creation of data products, useful for detecting instrumental problems, particular atmospheric events and quick data dissemination towards stakeholders or citizens. Currently, the automatic data processing is active for a subset of ECVs at 5 measurement sites in Italy. The system represents a valuable tool to facilitate data originators towards a more efficient data production. Our effort is expected to accelerate the process of data submission to WMO/GAW or to other reference data centers or repositories. Moreover, the adoption of automatic procedures for data flagging and data correction allows to keep track of the process that led to the final validated data, and makes data evaluation and revisions more efficient by improving the traceability of the data production process

A Meta-Analysis of Thyroid-Related Traits Reveals Novel Loci and Gender-Specific Differences in the Regulation of Thyroid Function

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