Geochemistry and origin of the Asimotrypes carbonate hosted mesothermal gold deposit, Pangeon mountain, N. Greece

The Asimotrypes mesothermal gold deposit located in the Pangeon Mt (E. Macedonia, N. Greece), is part of the Western Rhodope Massif (WRM), which represents the metamorphic core complex of an alpine collision orogen. Alpine metamorphism, of U. Cretaceous - M. Eocene age, reached upper greenschist to lower amphibolite conditions. A low-pressure greenshist fades retrograde overprint during uplift marked the end of Alpine metamorphism in the Miocene. Post-metamorphic Miocene uplift has been recognised in the Pangeon Mt and it was ascribed to Late Cainozoic extensional tectonics.The Asimotrypes ore, of replacement and shear-zone style consists mainly of arsenopyrite, pyrite and gold, with subordinate sphalerite, galena, chalcopyrite, pyrrhotite, tetrahedrite-tennantite, marcasite, covellite and malachite. Gold is either refractory occurring mainly in arsenopyrite and to a lesser extent in Aspyrite, or free in the oxide minerals.Three types of fluid inclusions (with subtypes) were recognised based on constituent phases at room temperature and microthermometric behaviour: (i) H2O-CO2 3-phase inclusions: L1 (H2O)+L2 (CO2)+V (CO2); (ii) Aqueous 2-phase inclusions: L+V; and (iii) Naturally decrepitated and/or leaked inclusions: V or L+V. The fluids have low salinity (<5 wt % NaCl equiv.), but variable CO2/H2O ratios. Microthermometric studies in gangue quartz indicate early ore deposition at P-T conditions of 275º-310ºC and 2.7-3.1 kb during unmixing of the mineralising fluids, followed by deposition at temperatures down to 130ºC and low near surface pressures. δ34S values of primary sulphide minerals suggest a magmatic source for the sulphur. δ13C values in marble calcite are indicative of a marine environment of deposition, also supported by a plot of δ13C versus δ18O for the same samples. Calculated isotopic composition of ore fluids in quartz, sericite and whole rock at 275ºC and 340ºC are consistent with values of metamorphic fluids. Whole rock hydrogen isotopic composition of -117±7.5 (lσ) indicates that the mineralising fluid was of meteoric origin. Sr isotope data implies seawater origin for strontium. Lead isotope data in ores from the Rhodope showed that Pb is derived from crustal rock types.  Sulphide species such as Au (HS)-2, were probably the most effective complexing agents for gold in the Asimotrypes fluids, which were typically low in salinity. A decrease of sulphur species activity and cooling are suggested to be the favoured depositional mechanism in a reducing environment. Combined with geological evidence, the fluid inclusion and stable data of the Asimotrypes gold ore, are consistent with genesis from deeply convecting meteoric waters driven by regional uplift through rocks undergoing retrogressive greenschist facies metamorphism

Trace Element Distribution in Magnetite Separates of Varying Origin: Genetic and Exploration Significance

Magnetite is a widespread mineral, as disseminated or massive ore. Representative magnetite samples separated from various geotectonic settings and rock-types, such as calc-alkaline and ophiolitic rocks, porphyry-Cu deposit, skarn-type, ultramafic lavas, black coastal sands, and metamorphosed Fe–Ni-laterites deposits, were investigated using SEM/EDS and ICP-MS analysis. The aim of this study was to establish potential relationships between composition, physico/chemical conditions, magnetite origin, and exploration for ore deposits. Trace elements, hosted either in the magnetite structure or as inclusions and co-existing mineral, revealed differences between magnetite separates of magmatic and hydrothermal origin, and hydrothermal magnetite separates associated with calc-alkaline rocks and ophiolites. First data on magnetite separates from coastal sands of Kos Island indicate elevated rare earth elements (REEs), Ti, and V contents, linked probably back to an andesitic volcanic source, while magnetite separated from metamorphosed small Fe–Ni-laterites occurrences is REE-depleted compared to large laterite deposits. Although porphyry-Cu deposits have a common origin in a supra-subduction environment, platinum-group elements (PGEs) have not been found in many porphyry-Cu deposits. The trace element content and the presence of abundant magnetite separates provide valuable evidence for discrimination between porphyry-Cu–Au–Pd–Pt and those lacking precious metals. Thus, despite the potential re-distribution of trace elements, including REE and PGE in magnetite-bearing deposits, they may provide valuable evidence for their origin and exploration

Mineralogical and geochemical characteristics of the Skouries porphyry-Cu-Au-Pd-Pt deposit (Greece): Evidence for the precious metal

SEM/EDS studies on drill core samples from the deeper parts of the Skouries deposit showed frequent association of magnetite and Cu-minerals (bornite and chalcopyrite) with inclusions of thorite, U-bearing thorite, hydroxyl-apatite and rare earth element (REE)-enriched silicates of the epidote-group (allanite), zircon and rutile, linked to pervasive potassic and propylitic alteration type, in the central parts of the deposit. Isotopic and fluid inclusion trends in the Skouries porphyry Cu deposit seem to be systematic, beginning with high delta 180 and low delta D values for fluids in equilibrium with vein quartz representative of the main stage of Cu, Au, Pd, Pt mineralization, to low delta 180 and high delta D values for fluids linked with the pyrite-chalcopyrite mineralization. Mineralised porphyry from the peripheral parts of the deposit, characterized by the presence of xenoliths of mafic rock contain up to 690 ppm Cr, which is mainly hosted in disseminated fine grained-magnetite. Its Cr content ranges from 0.30 to 2.26 wt% Cr2O3, in contrast to the Cr-free magnetite accompanying the quartz veins of the main porphyry. Such a relatively high Cr content, despite the evolved geochemical signature, indicates that the high Pd and Pt mineralization in the porphyry deposit of the Skouries may be linked to the incorporation of PGE-enriched material either in the mantle source and/or within the crust at depth, prior to final emplacement

Mineralogical and Geochemical Constraints on the Origin of Mafic–Ultramafic-Hosted Sulphides: The Pindos Ophiolite Complex

Sulphide ores hosted in deeper parts of ophiolite complexes may be related to either primary magmatic processes or links to hydrothermal alteration and metal remobilization into hydrothermal systems. The Pindos ophiolite complex was selected for the present study because it hosts both Cyprus-type sulphides (Kondro Hill) and Fe–Cu–Co–Zn sulphides associated with magnetite (Perivoli-Tsoumes) within gabbro, close to its tectonic contact with serpentinized harzburgite, and thus offers the opportunity to delineate constraints controlling their origin. Massive Cyprus-type sulphides characterized by relatively high Zn, Se, Au, Mo, Hg, and Sb content are composed of pyrite, chalcopyrite, bornite, and in lesser amounts covellite, siegenite, sphalerite, selenide-clausthalite, telluride-melonite, and occasionally tennantite–tetrahedrite. Massive Fe–Cu–Co–Zn-type sulphides associated with magnetite occur in a matrix of calcite and an unknown (Fe,Mg) silicate, resembling Mg–hisingerite within a deformed/metamorphosed ophiolite zone. The texture and mineralogical characteristics of this sulphide-magnetite ore suggest formation during a multistage evolution of the ophiolite complex. Sulphides (pyrrhotite, chalcopyrite, bornite, and sphalerite) associated with magnetite, at deeper parts of the Pindos (Tsoumes), exhibit relatively high Cu/(Cu + Ni) and Pt/(Pt + Pd), and low Ni/Co ratios, suggesting either no magmatic origin or a complete transformation of a preexisting magmatic assemblages. Differences recorded in the geochemical characteristics, such as higher Zn, Se, Mo, Au, Ag, Hg, and Sb and lower Ni contents in the Pindos compared to the Othrys sulphides, may reflect inheritance of a primary magmatic signature

Origin of Critical Metals in Fe-Ni Laterites from the Balkan Peninsula: Opportunities and Environmental Risk

As the global energy sector is expected to experience a gradual shift towards renewable energy sources, access to special metals in known resources is of growing concern within the EU and at a worldwide scale. This is a review on the Fe-Ni +/- Co-laterite deposits in the Balkan Peninsula, which are characterized by multistage weathering/redeposition and intense tectonic activities. The ICP-MS analyses of those laterites indicated that they are major natural sources of Ni and Co, with ore grading from 0.21 to 3.5 wt% Ni and 0.03 to 0.31 wt% Co, as well as a significant Sc content (average 55 mg/kg). The SEM-EDS analyses revealed that fine Fe-, Ni-, Co-, and Mn-(hydr)oxides are dominant host minerals and that the enrichment in these elements is probably controlled by the post-formation evolution of initial ore redeposition. The paucity of rare earth element (REE) within the typical Fe-Ni laterite ore and the preferential occurrence of Co (up to 0.31 wt%), REE content (up to 6000 mg/kg sigma REE), and REE-minerals along with Ni, Co, and Mn (asbolane and silicates) towards the lowermost part of the Lokris (C. Greece) laterite ore suggest that their deposition is controlled by epigenetic processes. The platinum-group element (PGE) content in those Fe-Ni laterites, reaching up to 88 mu g/kg Pt and 26 mu g/kg Pd (up to 186 mu g/kg Pd in one sample), which is higher than those in the majority of chromite deposits associated with ophiolites, may indicate important weathering and PGE supergene accumulation. Therefore, the mineralogical and geochemical features of Fe-Ni laterites from the Balkan Peninsula provide evidence for potential sources of certain critical metals and insights to suitable processing and metallurgical methods. In addition, the contamination of soil by heavy metals and irrigation groundwater by toxic Cr(VI), coupled with relatively high Cr(VI) concentrations in water leachates for laterite samples, altered ultramafic rocks and soils neighboring the mining areas and point to a potential human health risk and call for integrated water-soil-plant investigations in the basins surrounding laterite mines

The Cardioprotective PKA-Mediated Hsp20 Phosphorylation Modulates Protein Associations Regulating Cytoskeletal Dynamics

The cytoskeleton has a primary role in cardiomyocyte function, including the response to mechanical stimuli and injury. The small heat shock protein 20 (Hsp20) conveys protective effects in cardiac muscle that are linked to serine-16 (Ser16) Hsp20 phosphorylation by stress-induced PKA, but the link between Hsp20 and the cytoskeleton remains poorly understood. Herein, we demonstrate a physical and functional interaction of Hsp20 with the cytoskeletal protein 14-3-3. We show that, upon phosphorylation at Ser16, Hsp20 translocates from the cytosol to the cytoskeleton where it binds to 14-3-3. This leads to dissociation of 14-3-3 from the F-actin depolymerization regulator cofilin-2 (CFL2) and enhanced F-actin depolymerization. Importantly, we demonstrate that the P20L Hsp20 mutation associated with dilated cardiomyopathy exhibits reduced physical interaction with 14-3-3 due to diminished Ser16 phosphorylation, with subsequent failure to translocate to the cytoskeleton and inability to disassemble the 14-3-3/CFL2 complex. The topological sequestration of Hsp20 P20L ultimately results in impaired regulation of F-actin dynamics, an effect implicated in loss of cytoskeletal integrity and amelioration of the cardioprotective functions of Hsp20. These findings underscore the significance of Hsp20 phosphorylation in the regulation of actin cytoskeleton dynamics, with important implications in cardiac muscle physiology and pathophysiology

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field