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The studied Silurian nodules have hard light cores and dark shells. The cores consist of quartz with disseminated zonal carbonate mineral and pyrite. Zones in the carbonate have a variable composition from Mn-containing siderite, ankerite and dolomite to mixed Fe-Mn carbonate and Fe-containing rhodochrosite. The nodule shells are composed of quartz, chlorite, sericite, goethite, Mn-Fe oxyhydroxides and siderite. Fe-Mn oxyhydroxides in the nodule shells are formed due to an alteration of the carbonate minerals and inherited their composition. The formation of the nodules with Fe- and Mn-carbonates is related to diagenetic processes under reducing conditions of low Eh and high pH values. Later, carbonate minerals were altered into Fe-Mn oxyhydroxides. These alteration changes can be related to the influence of later magmatic activity in the area. An example of this activity is the presence of an igneous bodies established on both sides of the section.

Ninety-eight underground diamond holes (~102 km) drilled by Far Southeast Gold Resources Inc. at the Far Southeast porphyry Cu-Au deposit, Philippines, from 2011 to mid-2013, provide a three-dimensional exposure of the deposit between 700- and –750-m elevation, with surface at ~1,400-m elevation. Far Southeast contains an inferred resource of 891.7 million tonnes (Mt) averaging 0.7 g/t Au and 0.5 wt % Cu, equivalent to 19.8 Moz Au and 4.5 Mt Cu. This contribution reports the spatial and temporal distribution of alteration and mineralization at Far Southeast, notably a white-mica–chlorite-albite assemblage that formed after early secondary biotite and before late quartz–white-mica–pyrite alteration and that is associated with the highest copper and gold grades. Alteration assemblages were determined by drill core logging, short-wavelength infrared (SWIR) spectral analysis, petrographic examination, and a quantitative evaluation of materials by scanning electron microscopy (QEMSCAN) study. Alteration is limited around sparse veins or pervasive where vein density is high and the alteration halos coalesce. The alteration and mineralization zones with increasing depth are as follows: (1) the lithocap of quartz-alunite–dominated advanced argillic-silicic alteration that hosts part of the Lepanto high-sulfidation Cu-Au epithermal deposit (mostly above ~700-m elevation), (2) an aluminosilicate-dominated zone with coexisting pyrophyllite-diaspore ± kandite ± alunite and white mica (~700- to ~100-m elevation), (3) porphyry-style assemblages characterized by stockwork veins (below ~500-m elevation), (4) the 1 wt % Cu equivalent ore shell (~400- to –300-m elevation), and (5) an underlying subeconomic zone (about –300- to –750-m elevation, the base of drilling). The ore shells have a typical bell shape centered on a dioritic intrusive complex. The paragenetic sequence of the porphyry deposit includes stage 1 granular gray to white quartz-rich (± anhydrite ± magnetite ± biotite) veins with biotite-magnetite alteration. These were cut by stage 2 lavender-colored euhedral quartz-rich (± anhydrite ± sulfides) veins, with halos of greenish white-mica–chlorite-albite alteration. The white mica is largely illite, with an average 2,203-nm Al-OH wavelength position. The albite may reflect the mafic nature of the diorite magmatism. The quartz veins of this stage are associated with the bulk of copper deposited as chalcopyrite and bornite, as well as gold. Thin Cu sulfide (chalcopyrite, minor bornite) veins with minor quartz and/or anhydrite (paint veins), with or without a white-mica halo, also occur. These veins were followed by stage 3 anhydrite-rich pyrite-quartz veins with white-mica (avg 2,197 nm, illite)–pyrite alteration halos. Combined with previous studies, we conclude that this porphyry system, including the Far Southeast porphyry and Lepanto high-sulfidation Cu-Au deposits, evolved over a period of 0.1–0.2 m.y. Three diorite porphyry stocks were emplaced, and by ~1.4 Ma biotite-magnetite–style alteration formed with quartz-anhydrite veins and deposition of ≤0.5% Cu and ≤0.5 g/t Au (stage 1); coupled with this alteration style, a barren lithocap of residual quartz with quartz-alunite halo plus kandite ± pyrophyllite and/or diaspore formed at shallower depth (>700-m elevation). Subsequently, lavender quartz and anhydrite veins with bornite and chalcopyrite (high-grade stage, avg ~1 wt % Cu and ~1 g/t Au) and white-mica–chlorite-albite halos formed below ~400-m elevation (stage 2). They were accompanied by local pyrite replacement, the formation of hydrothermal breccias and Cu sulfide (paint) veins. Stage 2 was followed at ~1.3 Ma by the formation of igneous breccias largely along the margins of the high-grade zones and stage 3 pyrite-quartz-anhydrite ± chalcopyrite veins with white-mica (mostly illitic) halos. At shallower depths in the transition to the base of the lithocap, cooling led to the formation of aluminosilicate minerals (mainly pyrophyllite ± diaspore ± dickite) with anhydrite plus high-sulfidation-state sulfides and pyrite veinlets. Consistent with previous studies, it is likely that the lithocap-hosted enargite-Au mineralization formed during this later period.

The final stage of the Proterozoic, the Ediacaran, shields fascinating insights on the development and dispersal of complex metazoans related to dramatic compositional changes in the atmosphere and hydrosphere. Alternating sequences of siliciclastic and carbonate rocks of the Namibian Nama basin record the final stage of the Ediacaran and contain a vast amount of soft-bodied fauna, as well as some of the first biocalcifying organisms. However, the sparsity of ash beds at the base of the Nama group, preclude accurate and precise constraints on the onset of the Ediacaran biota in Nama group and correlation with chemo stratigraphic records worldwide. Due to the scarcity of ash layers, we apply U-Pb dating to carbonate rocks especially from the lower stratigraphic sections of the Nama Group combining the spatial resolution of LA-ICP-MS and the high-precision ID-TIMS U-Pb dating. The combination with mineralogical and geochemical techniques (d13C, d18O, XRD, SEM, EPMA, CL imaging, LA trace element transects, Raman spectroscopy, clumped isotope thermometry, QEMSCAN, SIMS) enables us to better understand the nature of the analyzed carbonates to distinguish between more pristine and diagenetic phases.This study elaborates on the potential and limitations of carbonate U-Pb dating for improved stratigraphic correlation on these ancient pre-Cambrian marine carbonates from the Nama Group.

To face the growing demand for raw materials, the discovery of new mineral deposits is essential for the future. Geophysical methods, and in particular electrical and electromagnetic tools, have an important role in mineral exploration. Recently, new technological developments made possible targetting deeper ore bodies and large areas with logistical challenges. We use the Deep Electrical Resistivity Tomography (DERT) method to investigate its application in mineral exploration. In particular, we use the Fullwaver technology developed by IRIS Instruments to study the full 3D resistive structure of the Calamita distal Fe-skarn deposit, Elba Island, Italy. This innovative hardware allows a full 3D deployment of autonomous and cable-less receivers and contrasts with traditional resistivity methods by its easy set-up and applicability in difficult contexts.In November 2022, a 3D DERT survey has been carried out to investigate the Calamita deposit, consisting of massive magnetite-hematite ore bodies hosted in marbles overlaying micaschists of Tuscan Units. Skarn mineralogy/geochemistry and fluid inclusion characteristics suggest a magmatic source for the mineralizing fluids. 148 current injections have been performed on 48 receivers over an area of 2km² with the aim to reach exploration depths ranging from 600 m to 700 m. Geophysical data were combined with a high-resolution 3D Digital Elevation Model acquired by standard and thermal drone imagery.The 3D inverted resistivity and induced polarization models match with the surface geology and shallow exploration drill hole data and highlight the architecture of Calamita deposit. Strong resistivity contrasts reveal the presence of sub-vertical conductive and chargeable pipes connecting the different skarn bodies at depth, interpreted to represent the paleo-hydrothermal upflow zones. The pipes point towards the inferred cupola of a magmatic intrusion that potentially triggered the formation of the ore deposit. High chargeability anomalies suggest the presence of hidden massive ore bodies and disseminated mineralisation on the flanks of the system.DERT has the potential to investigate and explore mineral deposits in full 3D, with high sensitivity, and in logistically complex settings.

The Elatsite–Chelopech ore field in the northern part of the Panagyurishte district in Central Bulgaria comprises numerous spatially associated porphyry copper and epithermal gold deposits and prospects. In addition to the mineralization and alteration features, trace elements, lead and sulfur isotope signatures of sulfide minerals from porphyry copper, base metal and gold-base metal deposits/prospects have been studied. LA-ICP-MS analyses of pyrite, arsenopyrite and sulfosalt minerals validate them as major carriers for Au, Ag, Sb, Se and Co. Pyrite from the three types of mineralization has specific geochemical characteristics. Pyrite from the porphyry copper deposits/prospects has generally lower total trace element content compared to pyrite from the epithermal prospects, except for Se, Co and Ni. Pyrite from the base metal and gold-base metal veins is enriched in As, Au, Ag, Sb and Pb. In pyrite from the base metal deposits, Co and Ni have contents comparable to the pyrite from the porphyry copper deposits, while pyrite from the gold-base metal veins shows lower Co and Ni. Arsenopyrite from these deposits shows similar features. Similarly, sphalerite from the gold-base metal veins also has lower Co content compared to sphalerite from the base metal veins but higher In and Cu contents. In addition to the close spatial relationships between the Elatsite and Gorna Kamenitsa porphyry Cu deposits and Negarstitsa-West and Dolna Kamenitsa base metal prospects, as well as similarities in the mineralization and alteration styles, the lead isotopic (206Pb/204Pb = 18.61–18.68, 207Pb/204Pb = 15.64–15.65 for porphyry and 206Pb/204Pb = 18.55–18.67, 207Pb/204Pb = 15.64–15.68 for base metal) and sulfur isotopic (δ34S values of −3 to +1‰ for porphyry and δ34S values of −1.7 to +3.5‰ for base metal) signatures of sulfides support the idea of a genetic link between these two types of deposits. The porphyry and base-metal mineralization result from a common major ore-forming event during the Late Cretaceous, corresponding to deep/higher-temperature and shallower/distal/lower-temperature environments, respectively. In particular, more radiogenic lead (206Pb/204Pb = 18.41–18.47, 207Pb/204Pb = 15.67–15.76) and slightly different sulfur isotopic compositions (δ34S values of +3.5 to +10.6‰) of sulfides from the distal gold-base metal veins of Kordunsko Dere, Svishti Plaz and Shipkite might be a consequence of the interaction of the ore-forming fluids with an external older crustal and isotopically positive S source. Alternatively, a different fluid source/event for the formation of these gold-base metal veins may be suggested., Minerals, 13 (5)

International audience; Pyrite (FeS 2), arsenopyrite (FeAsS) and löllingite (FeAs 2) are exceptional gold concentrators on Earth; yet the exact redox and structural state of this "invisible" gold and the forces driving its intake and release by these minerals remain highly controversial. Here we applied high resolution X-ray absorption spectroscopy to Au-bearing pyrite and iron sulfarsenides from hydrothermal deposits and their synthetic analogues. We show that Au preferentially enters octahedral Fe structural sites [Au(As,S) 6 ] enriched in As, by forming respectively [AuAs 1-3 S 5-3 ], [AuAs 3 S 3 ⋯AuAs 6 ] and [AuAs 6 ] atomic units in arsenian pyrite (>0.1-1.0 wt. % As), arsenopyrite and löllingite, implying a formal oxidation state of Au II in the minerals. In contrast, in As-poor pyrite, Au is dominantly chemisorbed as [Au I S 2 ] moieties in much lower concentrations. Combined with experimental data on Au mineral-fluid partitioning, our findings imply a universal control exerted by arsenic on gold incorporation in iron sulfides and sulfarsenides via coupled Au-As redox reactions. These reactions account for the observed variations in invisible gold contents in the minerals from different hydrothermal deposit types and enable quantitative prediction of iron sulfarsenide ability in controlling gold concentration and distribution in hydrothermal systems.

The world-class San Rafael tin (-copper) deposit (central Andean tin belt, southeast Peru) is an exceptionally large and rich (>1 million metric tons Sn; grades typically >2% Sn) cassiterite-bearing hydrothermal vein system hosted by a late Oligocene (ca. 24 Ma) peraluminous K-feldspar-megacrystic granitic complex and surrounding Ordovician shales affected by deformation and low-grade metamorphism. The mineralization consists of NW-trending, quartz-cassiterite-sulfide veins and fault-controlled breccia bodies (>1.4 km in vertical and horizontal extension). They show volumetrically important tourmaline alteration that principally formed prior to the main ore stage, similar to other granite-related Sn deposits worldwide. We present here a detailed textural and geochemical study of tourmaline, aiming to trace fluid evolution of the San Rafael magmatic-hydrothermal system that led to the deposition of tin mineralization. Based on previous works and new petrographic observations, three main generations of tourmaline of both magmatic and hydrothermal origin were distinguished and were analyzed in situ for their major, minor, and trace element composition by electron microprobe analyzer and laser ablation-inductively coupled plasma-mass spectrometry, as well as for their bulk Sr, Nd, and Pb isotope compositions by multicollector-inductively coupled plasma-mass spectrometry. A first late-magmatic tourmaline generation (Tur 1) occurs in peraluminous granitic rocks as nodules and disseminations, which do not show evidence of alteration. This early Tur 1 is texturally and compositionally homogeneous; it has a dravitic composition, with Fe/(Fe + Mg) = 0.36 to 0.52, close to the schorl-dravite limit, and relatively high contents (10s to 100s ppm) of Li, K, Mn, light rare earth elements, and Zn. The second generation (Tur 2)—the most important volumetrically—is pre-ore, high-temperature (>500°C), hydrothermal tourmaline occurring as phenocryst replacement (Tur 2a) and open-space fillings in veins and breccias (Tur 2b) and microbreccias (Tur 2c) emplaced in the host granites and shales. Pre-ore Tur 2 typically shows oscillatory zoning, possibly reflecting rapid changes in the hydrothermal system, and has a large compositional range that spans the schorl to dravite fields, with Fe/(Fe + Mg) = 0.02 to 0.83. Trace element contents of Tur 2 are similar to those of Tur 1. Compositional variations within Tur 2 may be explained by the different degree of interaction of the magmatic-hydrothermal fluid with the host rocks (granites and shales), in part because of the effect of replacement versus open-space filling. The third generation is syn-ore hydrothermal tourmaline (Tur 3). It forms microscopic veinlets and overgrowths, partly cutting previous tourmaline generations, and is locally intergrown with cassiterite, chlorite, quartz, and minor pyrrhotite and arsenopyrite from the main ore assemblage. Syn-ore Tur 3 has schorl-foititic compositions, with Fe/(Fe + Mg) = 0.48 to 0.94, that partly differ from those of late-magmatic Tur 1 and pre-ore hydrothermal Tur 2. Relative to Tur 1 and Tur 2, syn-ore Tur 3 has higher contents of Sr and heavy rare earth elements (10s to 100s ppm) and unusually high contents of Sn (up to >1,000 ppm). Existence of these three main tourmaline generations, each having specific textural and compositional characteristics, reflects a boron-rich protracted magmatic-hydrothermal system with repeated episodes of hydrofracturing and fluid-assisted reopening, generating veins and breccias. Most trace elements in the San Rafael tourmaline do not correlate with Fe/(Fe + Mg) ratios, suggesting that their incorporation was likely controlled by the melt/fluid composition and local fluid-rock interactions. The initial radiogenic Sr and Nd isotope compositions of the three aforementioned tourmaline generations (0.7160–0.7276 for 87Sr/86Sr(i) and 0.5119–0.5124 for 143Nd/144Nd(i)) mostly overlap those of the San Rafael granites (87Sr/86Sr(i) = 0.7131–0.7202 and 143Nd/144Nd(i) = 0.5121–0.5122) and support a dominantly magmatic origin of the hydrothermal fluids. These compositions also overlap the initial Nd isotope values of Bolivian tin porphyries. The initial Pb isotope compositions of tourmaline show larger variations, with 206Pb/204Pb(i), 207Pb/204Pb(i), and 208Pb/204Pb(i) ratios mostly falling in the range of 18.6 to 19.3, 15.6 to 16.0, and 38.6 to 39.7, respectively. These compositions partly overlap the initial Pb isotope values of the San Rafael granites (206Pb/204Pb(i) = 18.6–18.8, 207Pb/204Pb(i) = 15.6–15.7, and 208Pb/204Pb(i) = 38.9–39.0) and are also similar to those of other Oligocene to Miocene Sn-W ± Cu-Zn-Pb-Ag deposits in southeast Peru. Rare earth element patterns of tourmaline are characterized, from Tur 1 to Tur 3, by decreasing (Eu/Eu*)N ratios (from 20 to 2) that correlate with increasing Sn contents (from 10s to >1,000 ppm). These variations are interpreted to reflect evolution of the hydrothermal system from reducing toward relatively more oxidizing conditions, still in a low-sulfidation environment, as indicated by the pyrrhotite-arsenopyrite assemblage. The changing textural and compositional features of Tur 1 to Tur 3 reflect the evolution of the San Rafael magmatic-hydrothermal system and support the model of fluid mixing between reduced, Sn-rich magmatic fluids and cooler, oxidizing meteoric waters as the main process that caused cassiterite precipitation.

Distal skarns form by the metasomatic reactions of a host rock induced by far-traveled hydrothermal fluids. Physical and structural characteristics and geochemical patterns of distal Pb Zn skarn bodies were studied at the Petrovitsa deposit in southern Bulgaria. Skarn bodies formed from the interaction of hydrothermal fluids with reactive host lithologies (marble and gneiss). These fluids were transported along sub-vertical feeder structures and lithological contacts. Epidote skarn developed in gneiss protolith, and pyroxene (johannsenite) skarn developed in marble. Detailed geological mapping, complimented by measurements of the internal structure of the skarn body using pyroxene growth versors, quantifies the propagation direction of the skarn body: 1) away from the major local fluid conduit (feeder structure), and 2) away from lithological contacts between aluminosilicate rock and marble. Such growth suggests that fluid flow was generally orthogonal to the skarn front propagation direction in the pyroxene skarn. Textural, mineralogical and geochemical data from skarn samples reveal multiple growth generations of major skarn calc-silicates epidote and pyroxene. The epidote skarn is characterized by limited spatial distribution and fine-grained epidote/clinozoisite growth associated with massive replacement and sulfide mineralization. The pyroxene skarn consists of acicular clinopyroxene crystals which form spheroidal aggregates with discrete growth banding. These bands are the physical representation of the cyclic fluid pulses which resulted in rhythmic skarn growth marked by geochemical banding. In situ geochemical analyses in the epidote skarn reveal early Al-rich epidote overprinted by Fe-rich epidote associated with higher Mn and Sr contents and irregular compositional banding. Clinopyroxene (Jo60–95) shows general increase in Na, Al, Mn, and REE + Y with distance from the feeder structure and lithologic contacts. These elements correlate with the distance traveled by the hydrothermal fluid from the feeder to the site of skarnification, which we define using a proxy based on the Al content of pyroxene crystals. This reflects an increasing degree of fluid “contamination” by interaction with the aluminosilicate host rocks and functions as a proxy for fluid transport distance. The spatial distribution of trace-elements in pyroxene on an outcrop scale is indicative of discrete pulses of hydrothermal fluid resulting in precipitation of skarn calc-silicates along the increasingly tortuous fluid pathway between the feeder structure and the skarn front, resulting in both the macro- and micro-scale chemical and textural variability of the skarn body.

The Ayawilca deposit in Pasco, Peru, represents the most significant recent base-metal discovery in the central Andes and one of the largest undeveloped In resources globally. As of 2018, it hosts an 11.7 Mt indicated resource grading 6.9% Zn, 0.16% Pb, 15 g/t Ag, and 84 g/t In, an additional 45.0 Mt inferred resource grading 5.6% Zn, 0.23% Pb, 17 g/t Ag, and 67 g/t In, and a separate Sn-Cu-Ag inferred resource of 14.5 Mt grading 0.63% Sn, 0.21% Cu, and 18 g/t Ag. Newly obtained U–Pb dates for cassiterite by LA-ICP-MS (22.77 ± 0.41 and 23.05 ± 2.06 Ma) assign the Ayawilca deposit to the Miocene polymetallic belt of central Peru. The polymetallic mineralization occurs as up to 70-m-thick mantos hosted by carbonate rocks of the Late Triassic to Early Jurassic Pucara Group, and subordinately, as steeply dipping veins hosted by rocks of the Pucara Group and overlying Cretaceous sandstones-siltstones of the Goyllarisquizga Group. Relicts of a distal retrograde magnesian skarn and cassiterite (stage pre-A) were identified in the deepest mantos. The volumetrically most important mineralization at Ayawilca comprises a low-sulfidation assemblage (stage A) with quartz, pyrrhotite, arsenopyrite, chalcopyrite, Fe-rich sphalerite, and traces of stannite and herzenbergite. Stage A sphalerite records progressive Fe depletion, from 33 to 10 mol% FeS, which is compatible with the observed transition from low- to a subsequent intermediate-sulfidation stage (B) marked by the crystallization of abundant pyrite and marcasite. Finally, during a later intermediate-sulfidation stage (C) sphalerite (up to 11 mol% FeS), galena, native bismuth, Cu-Pb-Ag sulfosalts, siderite, Mn-Fe carbonates, kaolinite, dickite, and sericite were deposited. This paragenetic evolution shows striking similarities with that at the Cerro de Pasco Cordilleran-type polymetallic deposit, even if at Ayawilca stage C did not reach high-sulfidation conditions. The occurrence of an early retrograde skarn assemblage suggests that the manto bodies at Ayawilca formed at the transition between distal skarn and skarn-free (Cordilleran-type) carbonate-replacement mineralization. Mineral assemblages define a T-fS2 evolutionary path close to the pyrrhotite-pyrite boundary. Buffering of hydrothermal fluids by underlying Devonian carbonaceous phyllites of the Excelsior Group imposed highly reduced conditions during stage A mineralization (logfO2

We report indium, germanium, gallium, and other minor and trace elements contents in sphalerite, chalcopyrite, galena, and tetrahedrite-tennantite occurring in skarn and skarn-free (“Cordilleran”) polymetallic mantos and vein ore bodies in the Miocene porphyry-related Morococha District, Central Peru. Among the investigated minerals, LA-ICP-MS measurements indicate that In and Ga concentrate mostly in sphalerite (Inter-Quartile Range [IQR] 217–2.7 ppm and up to 4608 ppm In; IQR 61–2.0 ppm and up to 2137 ppm Ga) and chalcopyrite (IQR 109–32 ppm and up to 1070 ppm In; IQR 62–1.5 ppm and up to 630 ppm Ga). In coeval generations of sphalerite and chalcopyrite, the contents of In and Ga in sphalerite are at least two times higher than in chalcopyrite. Germanium content is generally low in the four analyzed minerals (IQR 1.2–0.19 ppm), although late Fe-poor sphalerite may yield much higher values (IQR 129–74 ppm). Certain trace element contents appear to correlate with (i) the evolving characteristics of the hydrothermal fluids during individual mineralization events, and (ii) the location of the studied ore bodies relative to the hydrothermal feeders. The highest In values in sphalerite are found in high-sulfidation assemblages in Cordilleran polymetallic veins and, with lower amounts, in low-sulfidation assemblages in skarn bodies. In intermediate-sulfidation assemblages in Cordilleran mineralization, In content decreases from early to late generations of sphalerite, while that of Ge increases. Spatial trace-element trends in Cordilleran veins and replacement bodies formed during the so-called “Morococha district-scale polymetallic event” include, from porphyry-distal to porphyry-proximal locations: i) In and Cu, and to a lesser extent Ga, enrichment in sphalerite; ii) Se and Hg enrichment and Sn and Ag depletion in chalcopyrite; iii) In enrichment in galena; and iv) Ag depletion in tetrahedrite-tennantite. Our dataset suggests that In is incorporated in the sphalerite crystal lattice via coupled substitutions involving Cu and subordinately also Sn and Ag. Availability of Cu in the mineralizing fluids is therefore key to In enrichment in sphalerite. Progressive dilution of metal-rich magmatic-hydrothermal fluids and Cu precipitation probably account for the progressive In depletion in distal-to-porphyry Zn-Pb-Ag and Ag-Pb Cordilleran polymetallic mineralization and in late sphalerite generations in intermediate-sulfidation assemblages.

Greece hosts a variety of magmatic-hydrothermal ore deposits/prospects with porphyry- and epithermal styles playing a major role in its total gold endowment. These deposit types are mainly clustered in two areas, the Rhodope- and Attico-Cycladic massifs, and formed from about 33 Ma to the Pleistocene, as a result of back-arc extension in the Aegean Sea, metamorphic core complex formation, and contemporaneous post-subduction and arc magmatism. In the Serbo-Macedonian massif, porphyry Cu-Au deposits include Skouries, Fisoka, Tsikara, Vathi and Gerakario. Causative intrusives are Oligocene to Miocene granodiorites to monzonites. Gold and PGE mineralization is associated with potassic alteration of the intrusives. In the eastern Rhodope massif and the NE Aegean islands, porphyry prospects occur at Pagoni Rachi, Konos Hill, Myli, Melitena (west Thrace), Fakos, Sardes, and Kaspakas (Limnos island) and Stypsi (Lesvos island). Mineralization is associated with Oligocene to Miocene subvolcanics of calc-alkaline to shoshonitic affinity. Feature of these prospects, which they share in common with several porphyry Au-only systems, is their shallow depth of emplacement, the presence of potassic/sodic-calcic and/or phyllic alteration, a strong epithermal overprint, their low Cu content, an extreme Re-enrichment, the multistage introduction of Au, the presence of banded quartz veinlets, and the local presence of tourmaline. New discoveries of porphyry-style mineralization at King Arthur, St. Philippos and Aisymi, increases the gold potential in west Thrace. High-intermediate sulfidation epithermal Au-Ag polymetallic deposits/prospects overprint and/or occur laterally from porphyry-style mineralization, where they are spatially associated with lithocaps of advanced argillic alteration. High-intermediate sulfidation Au-Ag epithermal mineralization at Perama Hill, Mavrokoryfi and Pefka in west Thrace, and at Pterounda, Mesotopos and Megala Therma on Lesvos island is controlled by steeply-dipping extensional faults within volcanic rocks, without any obvious genetic relationship to spatially-related porphyry-style mineralization. Polymetallic epithermal deposits and prospects contain critical and energy critical metals (e.g., Te, Se, Bi, Sb, In, Ge and Ga), which may be considered as by-products. In the Attico-Cycladic area, porphyry Mo-W mineralization occurs as sheeted quartz veins and stockworks cutting a potassic- to sericitic-altered Miocene granodiorite stock in the Lavrion district. Bonanza grade Au- and/or Ag-rich veins with epithermal affinities crosscut metamorphic rocks at Lavrion, and on Syros, Tinos, Antiparos and Anafi islands. Milos island is characterized by shallow submarine volcanic-hosted IS-HS epithermal Au-Ag-Te and base metal deposits. Antimony-As-Ag-Au deposits/prospects on Chios, Samos and Kos islands in the eastern Aegean Sea, indicate the potential for Carlin-style mineralization in Greece. Several factors played a role to the metal endowment of the Aegean porphyry-epithermal systems: magma fertility in the source regions, depth of emplacement of causative intrusives, relative contribution of mantle versus crustal material, redox state of subduction-related magmas, and physico-chemical fluid conditions at the site of ore deposition.

The Puy-les-Vignes W deposit, located in the northwestern French Massif Central (FMC), is a rare occurrence of a wolframite-mineralized hydrothermal breccia pipe hosted in high-grade metamorphic gneisses. We present an integrated study of this deposit aiming to characterize the ore-forming hydrothermal system in link with the Variscan late-orogenic evolution of the FMC. Based on a set of representative samples from the host rocks and mineralization, we describe a detailed paragenetic sequence and we provide the major and trace element geochemistry of the granitic rocks and W–Nb–Ta–Sn–Ti oxide minerals, in situ U/Pb and 40Ar/39Ar geochronology, and a fluid inclusion study of quartz and wolframite. We demonstrate that the formation of this W-mineralized breccia pipe results from a multistage development related to four major episodes during the late Carboniferous. The first episode corresponds to the emplacement of an unexposed peraluminous granite at ca. 324 Ma, which generated microgranite dykes exposed at the present-day surface. The second episode is the formation of the quartz-supported breccia pipe and wolframite mineralization at ca. 318 Ma at a paleodepth of 7 km. The mineralizing fluids have a H2O–NaCl–CO2–CH4–N2 composition, a moderate-salinity ( 400 °C) during lithostatic to hydrostatic pressure variations caused by hydrofracturing of the host rocks. Wolframite deposition is interpreted to result from a W-rich intermediate-density magmatic fluid that exsolved from an evolved leucogranite and interacted with volatile-rich metasedimentary country rocks and/or possibly mixed with low-salinity metamorphic fluids of deep origin. The third episode corresponds to magmatic-hydrothermal Nb–Ta mineralization overprinting the W-mineralized system interpreted to be related to the intrusion at ca. 311 Ma of a rare-metal granite, which is part of a regional peraluminous rare-metal magmatism during the 315–310 Ma period. Finally, the last episode corresponds to disseminated Bi ± Au–Ag mineralization emplaced at ca. 300 Ma, which shares similar mineralogical features with late Carboniferous orogenic gold deposits in the FMC. The Puy-les-Vignes W deposit records, therefore, a multistage and long-lived development that extends over a timespan of 25 million years in a regional setting dominated by protracted peraluminous magmatism and high-temperature and low-pressure metamorphism. Although the local environment of ore deposition is atypical, our results show that the mineral assemblages, alteration styles, and fluid characteristics of the Puy-les-Vignes breccia pipe are similar to those of other peri-granitic W deposits in the FMC.

Ore precipitation in mineral deposits formed in the upper parts of a porphyry system, at shallow crustal level (< 1.5 km), such as epithermal Au-Ag-(Cu)-(As) and polymetallic deposits is often triggered by fluid cooling and/or mixing between fluids from different sources. Commonly, in such deposits, two main fluid sources are identified a deeply sourced magmatic fluid and a shallow meteoric water stored in a surficial aquifer. Oxygen and hydrogen isotope compositions of gangue and alteration minerals using conventional bulk isotopic methods support the existence of mixing between these two fluid types. However, bulk isotope analysis provides only limited information on the exact mixing mechanisms and on the changing proportions of the involved fluids. Due to their high spatial resolution, SIMS in-situ oxygen isotope and LA-ICP-MS trace element analyses, in transects across growth zones of single crystals are adequate tools to trace the dynamics of this fluid mixing. In this study, in-situ SIMS oxygen isotope and LA-ICP-MS trace element analyses were performed on 10 selected quartz crystals from the giant Cerro de Pasco porphyry-related epithermal polymetallic deposit in central Peru. The results, combined with previous microthermometric and LA-ICP-MS fluid inclusion studies on the same or equivalent crystals, allow quantifying and documenting the mixing between different types of fluids that formed the large Cerro de Pasco epithermal polymetallic deposit. The δ 18 O quartz values range between 4‰ and 20‰ and display variations up to 11.5‰ inside single crystals that cannot be only, nor mainly ascribed to fluid temperature changes. Rather, these variations record variable mixing proportions of a rising moderate-salinity magmatic fluid with a δ 18 O H2O around 10‰ and a low-salinity fluid with a δ 18 O H2O between 0 and 4‰, the latter stored below the paleo-water table. Each analyzed quartz crystals also display important variation of their trace element content, with Al (43 to 2098 ppm), Li (0.7 to 18 ppm), Ge (1.1 to 24ppm) and Ti (0.8 to 10 ppm). These variations do not systematically correlate with oxygen isotope compositions. This suggests that quartz trace element content is controlled by a complex interplay of fluid composition, temperature, pressure, and growth rate. Application of published Ti-in-quartz geothermometers on quartz grains from which the precipitation temperature is well constrained by fluid inclusion microthermometry, shows that it can lead to overestimation or underestimation of precipitation temperatures by more than 50 • C. The obtained δ 18 O quartz patterns measured along profiles in the studied quartz crystals, and less clearly the in-situ trace element compositions, reveal abrupt changes and suggest that mixing between magmatic and surface-derived low-salinity fluids was not a continuous process. It rather took place through the influx of multiple short-lived pulses of magmatic fluid into the surface-derived low-salinity fluid surface aquifer.

We present a high-resolution in situ study of oxygen and boron isotopes measured in tourmaline from the world-class San Rafael Sn (–Cu) deposit (Central Andean tin belt, Peru) aiming to trace major fluid processes at the magmatic-hydrothermal transition leading to the precipitation of cassiterite. Our results show that late-magmatic and pre-ore hydrothermal tourmaline has similar values of δ 18 O (from 10.6‰ to 14.1‰) and δ 11 B (from −11.5‰ to −6.9‰). The observed δ 18 O and δ 11 B variations are dominantly driven by Rayleigh fractionation, reflecting tourmaline crystallization in a continuously evolving magmatic-hydrothermal system. In contrast, syn-ore hydrothermal tourmaline intergrown with cassiterite has lower δ 18 O values (from 4.9‰ to 10.2‰) and in part higher δ 11 B values (from −9.9‰ to −5.4‰) than late-magmatic and pre-ore hydrothermal tourmaline, indicating important contribution of meteoric groundwater to the hydrothermal system during ore deposition. Quantitative geochemical modeling demonstrates that the δ 18 O- δ 11 B composition of syn-ore tourmaline records variable degrees of mixing of a hot Sn-rich magmatic brine with meteoric waters that partially exchanged with the host rocks. These results provide thus direct in situ isotopic evidence of fluid mixing as a major mechanism triggering cassiterite deposition. Further, this work shows that combined in situ δ 18 O and δ 11 B analyses of tourmaline is a powerful approach for understanding fluid processes in dynamic magmatic-hydrothermal environments.

The late Palaeocene to the middle Eocene (57.5 to 46.5 Ma) recorded a total of 39 hyperthermals – periods of rapid global warming documented by prominent negative carbon isotope excursions (CIEs) as well as peaks in iron content – have been recognized in marine cores. Documenting how the Earth system responded to rapid climatic shifts during hyperthermals provides fundamental information to constrain climatic models. However, while hyperthermals have been well documented in the marine sedimentary record, only a few have been recognized and described in continental deposits, thereby limiting our ability to understand the effect and record of global warming on terrestrial systems. Hyperthermals in the continental record could be a powerful correlation tool to help connect marine and continental deposits, addressing issues of environmental signal propagation from land to sea. In this study, we generate new stable carbon isotope data (δ13C values) across the well-exposed and time-constrained fluvial sedimentary succession of the early Eocene Castissent Formation in the south central Pyrenees (Spain). The δ13C values of pedogenic carbonate reveal – similarly to the global records – stepped CIEs, culminating in a minimum δ13C value that we correlate with the hyperthermal event “U” at ca. 50 Ma. This general trend towards more negative values is most probably linked to higher primary productivity leading to an overall higher respiration of soil organic matter during these climatic events. The relative enrichment in immobile elements (Zr, Ti, Al) and higher estimates of mean annual precipitation together with the occurrence of small iron oxide and iron hydroxide nodules during the CIEs suggest intensification of chemical weathering and/or longer exposure of soils in a highly seasonal climate. The results show that even relatively small-scale hyperthermals compared with their prominent counterparts, such as PETM, ETM2, and ETM3, can leave a recognizable signature in the terrestrial stratigraphic record, providing insights into the dynamics of the carbon cycle in continental environments during these events.

International audience; Rare metals (Ge, Ga, In, Cd) are key resources for the development of green technologies and are commonly found as trace elements in base-metal mineral deposits. Many of these deposits are in orogenic belts and the impact of recrystallization on rare metal content and distribution in sphalerite needs to be evaluated. Based on laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses, and micro-imaging techniques such as laser-induced breakdown spectroscopy (LIBS) and electron backscattered diffraction (EBSD), we investigate the minor and trace element composition related to sphalerite texture for three types of mineralization from the Pyrenean Axial Zone (PAZ). Vein mineralization (type 2b) appears significantly enriched in Ge and Ga compared to disseminated and stratabound mineralizations (type 1 and type 2a, respectively). In vein mineralization, the partial recrystallization induced by deformation led to the remobilization of Ge, Ga, and Cu from the sphalerite crystal lattice into accessory minerals. We propose that the association of intragranular diffusion and fluid-rock reaction were likely responsible for the formation of patchy-oscillatory zoning in sphalerite, and the crystallization of Ge-rich accessory minerals. Chemical and textural heterogeneity is common in sphalerite from various world-class deposits and a full understanding of these heterogeneities is now crucial to assess the rare metal potential, and associated extraction processes of deformed base-metal ores.

This study aims to identify the dominant fast pathways for 39Ar loss during step-heating 40Ar/39Ar analysis of alkali feldspar from the Shap granite (UK). In our analysis we combined step-heating 40Ar/39Ar data acquired from variably sized feldspar fragments (0.4 to 2.2 mm in the shortest dimension) and optical and electron microscopy observations of microtextural modifications caused by heating in a muffle furnace in air. Our optical and electron microscopy results suggest that laboratory heating of the Shap feldspar causes it to fracture. The resulting cracks form an interconnected network, which may link with some of previously documented nanoscale defects such as nanotunnels, slots, pull aparts and bubbles. Our step-heating 40Ar/39Ar analyses yielded non-linear Arrhenius trajectories of 39Ar release. The non-linearity is best explained by heating-induced reduction of the effective diffusion length due to fracturing, likely with some contribution from nanotunnels, pull-aparts, slots and bubbles. Incoherent grain boundaries apparently played a minor role in providing fast pathways for 39Ar loss, if any. Importantly, unambiguous evidence for a reduction of the diffusion length during step-heating was only observed in experiments with large fragments (≥1 mm in the shortest dimension). The Arrhenius trajectory obtained from the smaller fragments (≤0.5 mm in the shortest dimension) appears to be consistent with the presence of variably-sized non-interacting intra-grain diffusion domains that existed prior to mineral separation. Heating-induced fracturing must be taken into account when interpreting 40Ar/39Ar dates of alkali feldspar, with particular focus on the following two points. First, this process is clearly inconsistent with the underlying assumptions of commonly utilised multi-diffusion domain (MDD) theory, although it can result in 39Ar release patterns that appear consistent with them. Therefore, it is important to identify on a case by case basis the dominant fast pathways for 39Ar loss from alkali feldspar during step-heating before applying MDD theory. Second, if heating-induced fracturing is ubiquitous in alkali feldspar and affects even gem-quality samples, then presently available diffusion parameters of Ar in alkali feldspar structure may be inaccurate to some degree, since all of them were obtained without considering the presence of cracks.

The Passa Três granite is a 5 km2 intrusion in southern Brazil with an NNE–SSW-elongated shape, hosting gold-bearing quartz veins with fluorite, carbonates, sulphides (pyrite, chalcopyrite, aikinite, molybdenite) and native gold. Orebodies are hosted by the pluton roof zone, which is marked by various textures indicating magmatic–hydrothermal transition processes. Mineralisation formed between 613 and 608 Ma in extensional pull-apart structures controlled by two conjugated N–S and E–W fault systems. We report results from petrography, quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN), scanning electron microscopy (SEM), electron probe microanalyses (EPMA), X-ray fluorescence (XRF), trace element analyses of pyrite by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), sulphur isotope (δ34S) analyses, and fluid inclusion microthermometry. Hydrothermal alteration is dominantly developed as phengite–quartz–carbonate and sericite–carbonate–chlorite assemblages along mineralised structures. Fluid inclusion study indicates mineralising fluids with H2O-CO2-NaCl composition, low to moderate salinity (0.2–12.84 wt % NaCl eq.), and temperatures from 400 to 150 °C. The sulphur isotopic composition of pyrite (−0.1 to 1.1‰) suggests magmatic origin. These data, in conjunction with structurally controlled mineralisation enriched in Au-Bi minerals shortly post-dating the granite emplacement, appoint towards similarities between the Passa Três deposit and intrusion-related gold systems. The specific location of the mineralisation in the core (and in the roof zone, regarding its vertical position) of the Passa Três granitic intrusion defines it as “granite-hosted” thus, it is representative of a specific model that can be used for exploration of other intrusion-related/hosted gold deposits near the studied area or in other locations.

Physical properties and compositions of ore-forming fluids in magmatic-hydrothermal systems have been mostly investigated by conventional fluid inclusion studies in transparent gangue minerals that are assumed to be “co-genetic” with the mineralization. However, ore precipitating fluids can be directly studied by analyzing fluid inclusions in opaque ore minerals, such as wolframite, stibnite, pyrite and enargite, by using near-infrared (NIR) petrography and microthermometry in combination with laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis of individual inclusions. Although results of NIR fluid inclusion studies of ore minerals were first published in 1984, the technique is still not commonly used in fluid inclusion research due to a number of limitations related to the analytical equipment used, sample preparation and NIR mineral transmittance. In this contribution we present new data on the applicability of NIR fluid inclusion studies in ore minerals (pyrite, stibnite, enargite, and wolframite) from a series of magmatic-hydrothermal systems, according to their chemical composition and physical behavior during microthermometry. Our results reveal strong correlation between NIR transmittance and high trace element (Co, Ni, Cu, As) content in pyrite, enargite (Fe, Bi), and wolframite (Sc, V, Fe). Despite this, the restricted distribution of these elements in oscillatory and sector zoning has allowed observation of NIR mineral features and fluid inclusions. Energy absorption of opaque minerals, either as light energy during microscopy or as thermal conductive energy during fluid inclusion microthermometry, presents a second limitation for NIR fluid inclusion studies. Our results confirm the relevance of fluid inclusion studies in ore minerals by combining NIR microscopy and microthermometry. Despite some limitations due to trace element composition of the host mineral and its physical behavior at high temperature, a successful NIR fluid inclusion study can be performed on some ore minerals that are opaque in the visible light range, allowing the direct study of hydrothermal ore-forming fluids.

The giant mid-Miocene Cerro de Pasco Cordilleran polymetallic (Zn-Pb-Ag-Cu-Bi) deposit in central Peru formed during three successive mineralization stages resulting in low- to high-sulfidation mineral associations emplaced at a paleodepth from 1 wt % Mn, Fe, Zn, and Pb), and its high Li, B, As, and Sb contents (up to several thousands of ppm). The obtained results suggest that the moderate-salinity metal-rich magmatic fluid results from mixing at depth between metal-rich hypersaline fluids and low-salinity magmatic fluids exsolved late in the lifetime of the magmatic-hydrothermal system. The moderate-salinity metal-rich magmatic fluid resulting from this deep mixing rose to the epithermal environment, where it in turn mixed with low-salinity fluids that were stored below the paleowater table and had similar temperatures to the moderate-salinity fluid. In contrast, enargite-pyrite veins of stage C2 were formed by the ascent of CO2-bearing, contracted vapor-like fluids that subsequently mixed with cold meteoric water. No interaction with the moderate-salinity, metal-rich magmatic fluids has been registered in stage C2. The similarity between fluid compositions and evolution during stages A, B1, B2, and C1 contrasts with their significantly different mineral assemblages that are rather controlled by changing fO2, pH, fS2, and temperature. Trace element LA-ICP-MS analyses of sphalerite, pyrite, and enargite also reveal important compositional differences. The trace elements in the measured minerals reside to a significant extent in micro- to nanoscale solid sulfide and/or sulfosalt inclusions. A direct correlation between fluid composition recorded in the studied fluid inclusion assemblages and the measured trace element composition of sphalerite, pyrite, and enargite has not been found in most cases. The cyclic rise of metal-rich, moderately saline fluids that issued from dilution of hypersaline fluids stored at depth by low-salinity magmatic fluids is a major process in the formation of stages A, B1, B2, and C1 of the giant epithermal polymetallic deposit of Cerro de Pasco. Such a mechanism may also explain moderate-salinity fluids (≈20 wt % NaCl equiv) recorded in other magmatic-related polymetallic epithermal deposits worldwide.

The composite Meghri-Ordubad pluton (MOP) is located in the southernmost Lesser Caucasus and outcrops over ~1000 km2 in southern Armenia and Nakhitchevan. It is characterized by nested intrusions incrementally emplaced over ~30 Myr from the Middle Eocene to Early Miocene, coeval with the closure of the Neotethyan Ocean and the regional Arabia-Eurasia continental collision. We recognize three compositionally distinct intrusive series in the MOP: a medium- to high-K calc-alkaline series 1 dominated by gabbro, quartz diorite and tonalite, a shoshonitic to high-K calc-alkaline series 2 including gabbro, monzogabbro, monzodiorite, monzonite and syenite, and a high-K calc-alkaline adakitic series 3 characterized by the emplacement of lamprophyre dikes followed by porphyritic granodioritic intrusions and dikes. Thermobarometry calculations together with detailed petrography, mineral chemistry and experimental mineral stability P-T diagrams indicate a polybaric crystallization history and magma emplacement at mid- to upper crustal levels (0.1-0.3 GPa). Mineral textures and compositions reveal open-system magmatic processes such as mafic magma replenishment and reactivation of crystal mushes prior to transport towards shallower crustal levels in the MOP. The evolution of magma chemistry (calc-alkaline vs shoshonitic) and mineral assemblages (amphibole-bearing vs amphibole-free) indicate fluctuation in primary melt alkali and water contents over time. Such chemical evolution is ascribed to a decrease in the degree of partial melting of a chemically heterogeneous, but isotopically homogeneous, mantle source. Overall, the MOP is characterized by the successive emplacement of hydrous magma batches in the mid- to upper crust and petrological processes that were dominated by fractional crystallization (± crustal assimilation) upon cooling and, or, decompression (± degassing). We propose a new temporal and spatial petrogenetic model for the MOP, encompassing three long-lived, chemically distinct magmatic series incrementally assembled over 30 Myr within a pre-, syn- and post-collisional geodynamic setting.

Physicochemical conditions under which early sulfide saturation occurs and the role of this process in the mineralising potential of magmas in different geodynamic settings have been the subject of interest in many recent studies. Here we present new temperature-pressure-fO2 data on sulfide-saturated magmatic enclaves and host lavas from volcanic systems in subduction, post-subduction and intraplate geodynamic settings, some of which are associated with porphyry and epithermal deposits. Petrographic investigations coupled with mineral chemistry of sulfide inclusions and their host minerals and with bulk chemistry of amphibole, plagioclase and pyroxene-rich enclaves and their host lavas indicate that sulfide occurrence, abundance, and composition depend on magma evolution. Sulfides are more abundant and have higher Ni/Cu bulk ratios when found in mafic enclaves compared to sulfide inclusions occurring in more evolved lavas. Thermo-oxibarometry estimates indicate that mafic hornblende-rich cumulates (SiO2 < 45 wt%) occurring at the studied intraplate setting evolve and reach sulfide saturation already in the mantle (61 ± 7 km) at high temperature and pressure conditions (17 kbar and 1135 ± 28 ◦C) and low ΔNNO (< 􀀀 1). These cumulates are associated with a greater sulfide abundance (up to 0.23 area %) compared to other types of enclaves and have Cu-poor sulfides (mostly pyrrhotite, with Cu median = 0.16 wt%) with high Ni/Cu values (up to 65). In contrast, more evolved (SiO2 > 50 wt%) gabbroic plutonic enclaves found in arc settings saturate sulfides at shallower crustal levels (~26 ± 10 km, i.e. ≤ 7 kbar) and at lower temperature (1014 ± 28 ◦C) and higher ΔNNO (> +1), and are characterised by a lower sulfide abundance (down to 0.01 area %), dominated by Cu-rich sulfides (mostly chalcopyrite and bornite with Cu median = 50 wt%). By accounting for the sulfide volume, our results suggest that sulfides can retain significantly higher amounts of metals in the enclaves (Cu = 32–113 ppm) compared to sulfides in the host lavas (Cu < 8 ppm). Considered altogether, our results indicate that alkaline mafic, less oxidised, and barren magmas corresponding to intraplate and back-arc settings saturated in sulfides in the upper mantle. In contrast, calc-alkaline felsic, oxidised and ore-related magmas corresponding to convergent margins started to be saturated in sulfides at the expected depth of the MASH zone and at shallower crustal levels. This seems to be a consequence of the investigated alkaline systems not forming shallow crustal magma chambers allowing magma differentiation, rather than the fact that late and shallow sulfide saturation is necessary for porphyry formation.

Hydrothermal fluids related to the development of the Aracuai Orogen during the Brasiliano Cycle have affected Paleoproterozoic banded iron formation-bearing sequences along the eastern border of the Sao Francisco Craton. Controversy surround the origin of specularite in high-grade schistose iron ore-bodies in the Serpentina Range (“Serpentina-type” ore) versus specularite-rich, S-free Au-PGE quartz veins (“Jacutinga-type”) that occur at the eastern border of the Quadrilatero Ferrifero mining district. Chemical and thermobarometric characteristics of fluid inclusions from Serpentina-type quartz-specularite veins show that metamorphic aqueous-saline fluids of low to moderate temperature (i.e. salinity between 6.3 and 13.7 wt% NaCl eqv and homogenization temperatures from 91° to 228 °C) were responsible for silica leaching and Fe enrichment along shear zones in the Statherian Serra da Serpentina Group. These Serpentina-type fluids present a distinct pattern with Na > Ca ≫ K. The fluids are depleted in Li, Na, Ba, Ca, K, Cu and Mg; and enriched in As and Sr in comparison to the Jacutinga-type fluids. In contrast, other two distinct fluids and chemical processes were involved to precipitate Fe oxides with Au-PGE in Jacutinga-type veins. The first type is an aqueous-carbonic fluid from the Catas Altas and Itabira deposits. These Jacutinga-type fluids present a pattern with Na > K > Ca ≫ Mg and K > Li > Ba > Sr. The fluids are interpreted to be of Brasiliano age and are typically associated with anatectic pegmatites from Santa Maria de Itabira. The high salinity of these brines (23.2–25.3 wt% NaCl eqv ) from the Itabira ore likely originated from their percolation through evaporitic layers, from salt concentration during deformation, or from fluid/rock interactions. Mixing between high-temperature aqueous-carbonic pegmatite-forming fluids and low-temperature aqueous metamorphic brines could have induced an abrupt change in the physical-chemical conditions of the system, which led to Au and PGE precipitation in the Itabira Jacutinga-type deposit. A second Jacutinga-type fluid is observed at the Gongo Soco and Barao de Cocais deposits. This fluid is interpreted as an aqueous-saline metamorphic fluid with the pattern Na > Ca > K ≫ Mg, low-to-moderate-salinity (4.3–16.4 wt% NaCl eqv ) and temperatures of 77° to 305 °C. It is relatively enriched in B; depleted in Li, Ba, Na, Cu, Zn and K; and follows the trend K > Li > Ba. In both types of fluids responsible for Jacutinga-type mineralization, gold was transported as chlorine complexes under acidic and oxidizing conditions. The metal precipitation may have occurred due to a rapid depressurization during failure of shear zones operating in the upper levels of the crust, or variations in the pH and redox conditions during the interaction with the host dolomitic itabirite.

The Takidani pluton represents one of a few locations where melt extraction from a crystal mush is preserved in the natural rock record, making it an extremely good case study for investigating the generation of evolved melt reservoirs in the upper crust. Located in the Japan Alps, the Takidani pluton shows a clear vertical zonation consisting of granite and granodiorite in the lower and mid- dle section, a fine-grained porphyritic granitic unit in the upper section and a marginal granodiorite at the roof contact with the host-rock. We present a detailed petrographic and geochemical study using samples collected along a section that traverses the entire vertical section of the pluton. No sharp contacts are found between units. Instead, gradual changes in rock fabric and mineralogy are observed between the lower granodiorite and overlying porphyritic unit. Major and trace elem- ent bulk-rock compositions show sigmoidal variations from the bottom to top of the pluton. Incompatible elements and silica contents increase roofwards within the porphyritic unit. Plagioclase chemistry reveals three main crystal populations (P1, P2 and P3) with Fe contents increasing towards the base of the pluton. Comparison with existing crystallization experiments, thermobarometry and hygrometry indicate that the magmas were emplaced at around 200 MPa, 850–900 C and bulk water contents of 3–4wt %. Whole-rock major and trace element analyses to- gether with mineral chemistry and textural observations suggest that the fine-grained porphyritic unit was extracted from the underlying granodiorite at temperatures between 800 and 740 C and crystallinities of 45–65 wt %. Radiogenic isotopes indicate only minor assimilation (2–6 wt %) and support melt evolution through crystal fractionation. The fine-grained matrix of the porphyritic unit may have been the result of pressure quenching associated with a volcanic eruption.

International audience; Germanium (Ge) is often found as trace element in undeformed sphalerite (ZnS). However, the presence of Ge-minerals (oxides, chloritoids and/or sulphides with up to 70 wt% Ge) is remarkable in Pb-Zn deposits from the Variscan Pyrenean Axial Zone. Their abundance is controlled by the chemical and/or the mechanical processes that affect rare element concentration from sulphides which have undergone deformation and metamorphism. In this study, we document the microstructures and chemical heterogeneities in sphalerite, based on EBSD (electron backscatter diffraction) coupled to LA-ICPMS in situ analyses. Deformation induces the dynamic recrystallization of sphalerite. Recrystallized domains have low Ge contents (1-50 ppm Ge) whereas porphyroclastic sphalerite grains commonly show higher Ge concentrations (up to 650 ppm Ge). Ge-minerals (up to 70 wt% Ge) are exclusively hosted by the Ge-poor recrystallized domains. We propose that Ge was removed from the sphalerite crystal lattice during sulphide recrystallization, and was subsequently concentrated in Ge-minerals, leaving behind a Ge-depleted fine-grained recrystallized sphalerite matrix. Numerous sulphide ore types enriched in rare elements like Pyrenean deposits may present recrystallization features and we suggest evaluating the potential of such deposits by integrating chemical and structural informations at the micrometer scale using state-of-the-art analytical techniques in exploration methods.

During the late Palaeocene to the middle Eocene (57.5 to 46.5 Ma) a total of 39 hyperthermals – periods of rapid global warming recorded by prominent negative carbon isotope excursions (NCIEs) as well as peaks in iron content – have been recognized in marine cores. Understanding how the Earth system responded to rapid warming during these hyperthermals is fundamental because they represent potential analogues, in the geological record, to the ongoing anthropogenic modification of global climate. However, while hyperthermals have been well documented in the marine sedimentary record, only few have been recognized and described in continental deposits, thereby limiting our ability to understand the effect and record of global warming on terrestrial surficial systems. Hyperthermals in the continental record could be a powerful correlation tool to help connect marine and continental records, addressing issues of environmental signal propagation from land to sea. In this study, we generate new stable carbon isotope data (δ13C values) across the well-exposed and time-constrained fluvial sedimentary succession of the early Eocene Castissent Formation in the South-Central Pyrenees (Spain). The δ13C values of pedogenic carbonate reveal – similarly to the global records – stepped NCIEs, culminating in a minimum δ13C value that we correlate with the hyperthermal event U at ca. 50 Ma. This general trend towards more negative values is most probably linked to higher primary productivity leading to an overall higher respiration of soil organic matter during these climatic events. The relative enrichment in immobile elements (Zr, Ti, Al) and higher estimates of mean annual precipitation together with the occurrence of small iron-oxides/hydroxides nodules during the NCIEs suggest intensification of chemical weathering and/or longer exposure of soils in a highly seasonal climate. The results show that even relatively small-scale hyperthermals compared with their prominent counterparts, such as PETM, ETM2 and 3, have left a recognizable trace in the stratigraphic record, providing insights into the dynamics of the carbon cycle in continental environments during these events.

International audience; This paper aims at providing new insights into W-Sn ore-forming processes within one of the largest granitic provinces in the world (Nanling Range, South China), which was emplaced during the Jurassic-Cretaceous period. The origin, composition and pressure-temperature conditions of fluids involved in the W-Sn ore-forming processes have been investigated by microthermometry, Raman spectroscopy, LA-ICPMS, hydrogen isotope analyses of fluid inclusions and oxygen isotope analyses of minerals from the Maoping and Piaotang W-Sn deposits. For each deposit, pre- (quartz), syn- (wolframite and cassiterite) and post-ore (quartz, topaz and fluorite) minerals were studied. In both deposits, the vast majority of fluid inclusions are aqueous with salinities between 0.0 and 12.6 wt. % equiv. NaCl and homogenization temperatures between 136 and 349 °C. A minor proportion (~5%) of inclusions observed in the ore-stage quartz from Maoping have aquo-carbonic compositions. For both deposits, four compositional groups are defined. Early quartz fluid inclusions are characterized by salinities between 0.4 and 9.0 wt. % equiv. NaCl, trapping temperatures between 150 and 350 °C, and pressures between 20 and 150 MPa. LA- ICPMS analyses of these fluid inclusions reveal a wide range of Na, K and Li concentrations, as well as relatively low metal contents (W < 40 ppm). Values of δ18O in quartz range from -3.6 to 5.3 ‰ VSMOW while δD values of the fluid inclusions range from -59 to -51 ‰ VSMOW. The salinity of fluid inclusions in wolframite, cassiterite, topaz and fluorite is between 2.4 and 11.2 wt. % equiv. NaCl, trapping temperatures are between 200 and 600 °C, and pressures range from 20 to 250 MPa. LA-ICPMS analyses of these fluid inclusions reveal higher concentrations of Na, K and Li as well as Cs and metals (e.g. between 10 and 220 ppm W). Values of δ18O in wolframite, cassiterite, topaz and fluorite crystals range from -3.0 to 3.3 3 ‰ VSMOW while δD values of fluid inclusions in these mineral phases range from -78 to -72 ‰ VSMOW. At Piaotang, fluid inclusions in wolframite as well as in post-ore quartz and fluorite have salinities of 5.6 to 12.6 wt.% eq. NaCl, trapping temperatures between 150 and 400 °C and pressures of 20 to 150 MPa. LA-ICPMS analyses of these fluid inclusions reveal similar compositions to early quartz fluid inclusions. Values of δ18O in wolframite and quartz crystals range from -0.8 to 5.2 ‰ VSMOW, while the δD values of fluid inclusions range from -66 to -62 ‰ VSMOW. Collectively, the data suggest the involvement of four aqueous fluid end-members, mixed episodically in the mineralization process: (A) a low-salinity, low-temperature, metal-poor, low-δ18O, low-δD fluid derived from meteoric water; (B) a high-salinity, high-temperature, metal-poor, high-δ18O, low-δD fluid derived from a differentiated peraluminous granitic magma; (C) a high-salinity, high-temperature, metal-rich, lower δD magmatic fluid derived from a more differentiated peraluminous granitic magma; and (D) a high-salinity, high-temperature, metal-rich, high-δ18O, low-δD magmatic fluid. This study shows that multiple fluids with distinct magmatic and meteoric origins were involved in the formation of these W-Sn deposits and that the dilution of metal-bearing magmatic fluids by meteoric fluids was probably the main driver for ore deposition. The common fluid history of the two deposits studied, as well as similarities with other deposits in the Jiangxi province, points towards common ore-forming processes at the regional scale.

In the magmatic-hydrothermal environment, fluids with similar metal concentrations and sources may yield contrasting mineral assemblages in successive stages of sulphide mineralization. These differences are linked to the physico-chemical conditions of the mineralizing fluids (e.g., T, pH, fS2, fO2) acquired during their interaction with country rocks and/or by mixing with groundwater. Here, we integrate petrography and osmium (Os) isotope (187Os/188Os) sulphide geochemistry, and discuss novel constraints on magmatic fluid-rock interaction and magmatic fluid-groundwater mixing that are deemed to govern sulphide deposition in magmatic-hydrothermal systems. We studied pyrite (FeS2) and enargite (Cu3AsS4) from the porphyry-related polymetallic Cerro de Pasco (14.54–14.41 Ma) and Colquijirca (10.83–10.56 Ma) epithermal deposits in the Central Andes, Peru. Sulphide mineralization is genetically associated with Miocene magmatism and includes breccia and replacement bodies of carbonate country rocks, and veins cutting the magmatic and sedimentary country rocks. At both deposits, pyrite is followed by enargite in the paragenesis. Pyrite has a radiogenic initial 187Os/188Os isotopic composition (187Os/188Osi-pyrite or Osi-pyrite = 0.80 to 1.45). Enargite (I) enclosing pyrite or filling in cracks in pyrite also has a radiogenic initial 187Os/188Os isotopic composition (Osi-enargite I = 0.56 to 1.24). Conversely, enargite (II) that formed on irregular surfaces on earlier pyrite has an unradiogenic 187Os/188Os isotopic composition (Osi-enargite II = 0.13 to 0.17). Our data show that the paragenetic evolution from pyrite to enargite records a sharp change in the osmium isotope composition within these sulphides. Pyrite and enargite (I) record radiogenic initial 187Os/188Os isotopic compositions, indicating interaction of magmatic hydrothermal fluids with the sedimentary country rocks. However, the unradiogenic initial 187Os/188Os isotopic composition of enargite (II) suggests that magmatic fluids with a mantle-like 187Os/188Os signature ascended from parental magmatic chambers to the epithermal environment without incorporation of crustal Os via fluid-rock interaction or mixing with groundwater. This difference may be due to the country rocks being altered during previous stages, with the radiogenic crustal Os signature being flushed by earlier magmatic pulses. Our findings imply that ore metals (i.e., Cu, Au) are magma-derived, whereas the Os isotopic composition of pyrite and some enargite in epithermal deposits may capture the signature of the interaction of magmatic fluids with country rock lithologies (e.g., the Eifelian black shale in the study area) and/or groundwater. Thus, the isotopic composition of the siderophile and chalcophile trace element Os in sulphides may act as a tracer of metal source, and degree of wall-rock interaction. © 2020 The Author(s), Chemical Geology, 564, ISSN:0009-2541, ISSN:1872-6836

Recently identified occurrences of porphyry-style mineralization evidence the link of the world's second largest known epithermal base metal Cerro de Pasco deposit (Peru) to a porphyry system emplaced at depth. They consist of (i) quartz-monzonite dykes and (ii) the south-western part of the large diatreme-dome complex adjacent to the main ore bodies of Cerro de Pasco, and (iii) stockwork of banded quartz-magnetite-chalcopyrite-(pyrite) porphyry-type veinlets crosscutting trachyte porphyritic intrusion cropping out at surface in the central part of the diatreme-dome complex. The latter porphyry-type mineralization observed at the same erosion level as the main epithermal base metal carbonate-replacement ore bodies is the subject of this work. Geological constraints indicate a shallow emplacement level (depth < 1 km, P < 270 bar), implying rather unusual low-pressure and high-temperature environment for the formation of porphyry-style mineralization. The banded porphyry-type veinlets record a multiphase history of formation with two successive high-temperature (N600 °C) stages, followed by a lower-temperature (b350 °C) stage.More than 90% of the quartz in veinlets precipitates during the first two high-temperature stages. Stage 1 is characterized by the entrapment in hydrothermal quartz of inclusions containing variable proportions of both silicate melt and metal-rich hypersaline (N90 wt% NaCl eq.) liquid, hereafter referred to as heterogeneous silicate melt inclusions (HSMIs). The latter are rarely described in porphyry-type mineralization. We suggest that during stage 1, the inclusions result from heterogeneous entrapment of an evolved hydrous rhyolitic melt mixed with a hypersaline fluid phase at low pressure (270 bar) and high temperature (N600 °C). The stage 2 is marked by the entrapment of metaland sulfur-rich hypersaline liquid inclusions, with salinity around 70 wt% NaCl eq., originated from the adiabatic ascent of magmatic hypersaline fluids transferred fromdeeper parts of the system. The lower-temperature stage 3 is characterized by an important temperature drop from N600 °C to b350 °C as revealed bymicrothermometry of aqueous two-phase liquid-vapor (L-V) inclusions. Quartz textures revealed by SEM-CL imaging allowascribing the sulfide precipitation to the low-temperaturemineralization stage 3. In-situ SIMS 18O/16O isotope analyses of quartz across the veinlets are indicative of a magmatic signature of the fluids during the first two stages; while quartz from stage 3 has oxygen isotopic compositions suggestive of minor contribution of meteoric waters to a predominantly magmatic aqueous fluid (~10 vol.% of meteoric input), which probably triggered Cu-Fe sulfide precipitation in the stockwork. High metal and sulfur contents of HSMIs and hypersaline liquid inclusions determined by LA-ICP-MS are interpreted to represent the fluid composition prior to the main sulfide precipitation event. The similar Pb-Zn ratio of the bulk ore extracted from the epithermal ore bodies at Cerro de Pasco and the HSMIs and hypersaline liquid inclusions suggest a common source of the fluids associated with the different mineralization styles at Cerro de Pasco.

Active and inactive hydrothermal chimneys composed almost entirely of enargite and luzonite, rare minerals in seafloor hydrothermal deposits, were found at the summits of two submarine volcanoes, North Su and Kaia Natai, in the Manus Back-Arc Basin. Detailed mineralogical and geochemical studies revealed that most probably these deposits precipitated at T = 200°–330 °C and high fS2. The negative δ34S values (− 8.58 to − 3.70‰) of the enargite-luzonite are best explained by disproportionation reactions of magmatic SO2 and suggest that the high fS2 is likely provided by direct magmatic input of SO2 into the hydrothermal system. Fractionation of Cu stable isotopes during the precipitation of enargite-luzonite (δ65Cu ranges from − 0.20 to + 0.35‰) is inferred to be associated with either Rayleigh-type fractionation, or redox processes (Cu+ oxidation to Cu2 +) and the mass balance of dissolved Cu+ and Cu2 + species in the hydrothermal fluid. The trace element composition of enargite and luzonite indicates a temporal fluctuation of the chemistry of the ore-forming fluid with an increase of Fe, Ga, Tl, Au, Hg, Pb and Ag, and decrease of Sb, Sn, Te, Ge and V concentrations with time and points out that this type of deposits is the richest in Au (average 11.9 ppm) and Te (average 169 ppm) among all other types of seafloor metal deposits. In addition to the widespread inorganic precipitation of enargite and luzonite in this setting, there is evidence that this mineralization may be biogenically mediated on the external surfaces of the active vents. Fungi-like filaments mineralized by luzonite imply that the fungi (Dikarya subkingdom) may be implicated in a mechanism of bio-sequestration of As, S and Cu, and provide the initial substrate for luzonite precipitation. The studied enargite-luzonite deposits have characteristics similar to those of subaerial high-sulfidation epithermal mineralization: back-arc basin setting; acid-sulfate and boiling ore-forming fluids; altered (advanced argillic stage) dacitic host rocks; major enargite-luzonite and minor pyrite, barite and S0; δ34S < 0‰. Therefore, they may be considered as submarine analogues of subaerial high-sulfidation epithermal deposits with the potential for concealed porphyry Cu(single bondAu) mineralization at depth.

The Cerro de Pasco district in central Peru hosts one of the world largest porphyry-related epithermal polymetallic deposits. The district is centered onto a large diatreme-dome complex crosscut by numerous dacite to rhyodacite bodies showing domal structures and quartz-monzonite dykes. Three temporally distinct high-temperature porphyry-type mineralization events have been recognized (PM1, PM2, and PM3). Dating of the latter by molybdenite Re-Os and by zircon U-Pb (LA-ICP-MS and CA-ID-TIMS) geochronology complements the already available dataset of zircon U-Pb ages of the subvolcanic and volcanic rocks mostly dacitic in composition occurring in the district and shows the existence of successive short-lived episodes (50%) at pressures between 0.9 and 3.4 kbar and at temperatures between ~680 °C and ~725 °C. At such conditions, magma is beyond the point of rheological lock-up and is not eruptible. The emplacement of the mostly dacitic subvolcanic and volcanic rocks has required a series of rejuvenation events of the upper crustal high-crystallinity silicic magma reservoir. Field relationships and geochronology indicate that emplacement of the subvolcanic and volcanic rocks is preceded each time by high-temperature (>600 °C) quartz-pyrite-magnetite ± chalcopyrite and quartz-molybdenite veining forming the three recognized porphyry-type mineralization events. Hydrothermal quartz of these veins host silicate melt inclusions, a rare feature in hydrothermal veins. Their composition determined by LA-ICP-MS analysis indicates that the mineralizing fluids, potentially sourced from intermediate magma recharges, have circulated in a magma reservoir in which the residual interstitial melt was more evolved than the melt trapped as inclusions in the magmatic quartz. The combined geochemical and geochronological data obtained show that several episodes of rejuvenation of a highly crystallized upper-crustal silicic magma reservoir, probably triggered by intermediate magma recharges and by circulation of CO2- and S-rich fluids exsolved from them, are at the origin of the large diatreme-dome complex and porphyry-type mineralization events at Cerro de Pasco.

Cerro de Pasco (Peru) is known for its large epithermal polymetallic (Zn-Pb-Ag-Cu-Bi) mineralization emplaced at shallow level, a few hundred meters below the paleo-surface, at the border of a large diatreme–dome complex. Porphyry-style veins crosscutting hornfels and magmatic rock clasts are found in the diatreme breccia and in quartz–monzonite porphyry dikes. Such mineralized veins in clasts allow investigation of high-temperature porphyry-style mineralization developed in the deep portions of magmatic–hydrothermal systems. Quartz in porphyry-style veins contains silicate melt inclusions as well as fluid and solid mineral inclusions. Two types of high-temperature (> 600 °C) quartz–molybdenite–(chalcopyrite)–(pyrite) veins are found in the clasts. Early, thin (1–2 mm), and sinuous HT1 veins are crosscut by slightly thicker (up to 2 cm) and more regular HT2 veins. The HT1 vein quartz hosts CO2- and sulfur-rich high-density vapor inclusions. Two subtypes of the HT1 veins have been defined, based on the nature of mineral inclusions hosted in quartz: (i) HT1bt veins with inclusions of K-feldspar, biotite, rutile, and minor titanite and (ii) HT1px veins with inclusions of actinolite, augite, titanite, apatite, and minor rutile. Using an emplacement depth of the veins of between 2 and 3 km (500 to 800 bar), derived from the diatreme breccia architecture and the supposed erosion preceding the diatreme formation, multiple mineral thermobarometers are applied. The data indicate that HT1 veins were formed at temperatures > 700 °C. HT2 veins host assemblages of polyphase brine inclusions, generally coexisting with low-density vapor-rich inclusions, trapped at temperatures around 600 °C. Rhyolitic silicate melt inclusions found in both HT1 and HT2 veins represent melt droplets transported by the ascending hydrothermal fluids. LA-ICP-MS analyses reveal a chemical evolution coherent with the crystallization of an evolved rhyolitic melt. Quartz from both HT1 and HT2 veins also contains secondary, low-temperature (~ 300 °C) brine and aqueous fluid inclusions that record the cooling of the system. Both vein types are locally crosscut and/or reopened by a pre-diatreme polymetallic event consisting of pyrite, sphalerite with “chalcopyrite disease,” galena, chalcopyrite, tetrahedrite–tennantite, and minor quartz. LA-ICP-MS analyses of mineral and high-temperature fluid inclusions hosted in HT1 and HT2 veins and in situ secondary-ion mass spectrometry oxygen isotope analyses of vein quartz indicate a magmatic signature for the mineralizing fluids with no major meteoric water input and allow reconstruction of the source and chemical evolution of fluids that formed these porphyry-style veins as snapshots of the early and deep mineralizations at Cerro de Pasco. This detailed study of the porphyry-type mineralization hosted in clasts offers a unique opportunity to reconstruct the late magmatic and early hydrothermal evolutions of porphyry mineralization underlying the world-class Cerro de Pasco epithermal polymetallic (Zn-Pb-Ag-Cu-Bi) deposit.

Fluid inclusion studies give unique insights into physical conditions and composition of fluids involved in geological processes. Most studies to date are performed on transparent minerals. Near-infrared (NIR) microscopy allows also microthermometry to be performed on minerals that are opaque to the visible light such as pyrite, hematite, wolframite, enargite and stibnite. The main drawback of this technique is the underestimation of the recorded phase-change temperatures with increasing light intensity, up to several hundred percent in the case of ice-melting temperatures. Although this issue has been known for a decade, it is poorly understood. We address this problem based on a systematic study of synthetic fluid inclusions in a variety of opaque minerals. For the first time, fluid inclusions have been co-synthetized with success in quartz and opaque minerals. Fracturing the host minerals by in-situ quenching allowed for fluid–mineral equilibration prior to fluid inclusion formation. In this study, we assess the impact of mineral intrinsic parameters, mainly absorption and thermal-conductivity, and experimental settings (light source operative power, diaphragms aperture, and the use of filters) on recorded phase-change temperatures. We show that these are underestimated due to local overheating of the sample caused by radiative heating from the light source. It affects all minerals and the extent of the temperature shift of the observed phase-changes depends on sample thickness, mineral characteristics, and the amount of light reaching the sample. Thus, any calibration of the temperature shift as a function of the amount of light is complicated and in most cases impracticable. However, we demonstrate, based on co-generated inclusions in opaque minerals and quartz that yield similar values during NIR-microthermometry that for any mineral, there is a range of light power and microscope settings for which no shift is noticeable within the thermal stage accuracy. These are defined as "ideal measuring conditions" ensuring reliability of acquired microthermometry data.

The current study has aimed to refine the previously proposed two-fluid mixing model for the Laisvall (sphalerite Rb-Sr age of 467 ± 5 Ma) and Vassbo Mississippi Valley-type deposits hosted in Ediacaran to Cambrian sandstone, Sweden. Premineralization cements include authigenic monazite, fluorapatite, and anatase in the Upper Sandstone at Laisvall, reflecting anoxic conditions during sandstone burial influenced by the euxinic character of the overlying carbonaceous middle Cambrian to Lower Ordovician Alum Shale Formation (δ13Corg = −33.0 to −29.5‰, δ15Norg = 1.5 to 3.3‰, 0.33 to 3.03 wt% C, 0.02 to 0.08 wt% N). The available porosity for epigenetic mineralization, including that produced by subsequent partial dissolution of pre-Pb-Zn sulfide calcite and barite cements, was much higher in calcite- and barite-cemented sandstone paleoaquifers (29 % by QEMSCAN mapping) than in those mainly cemented by quartz (8 %). A major change in the Laisvall plumbing system is recognized by the transition from barite cementation to Pb-Zn sulfide precipitation in sandstone. Ba-bearing, reduced, and neutral fluids had a long premineralization residence time (highly radiogenic 87S/86Sr ratios of 0.718 to 0.723) in basement structures. As a result of an early Caledonian arc-continent collision and the development of a foreland basin, fluids migrated toward the craton and expelled Ba-bearing fluids from their host structures into overlying sandstone where they deposited barite upon mixing with a sulfate pool (δ34Sbarite=14 to 33‰). Subsequently, slightly acidic brines initially residing in pre-Ediacaran rift sediments in the foredeep of the early Caledonian foreland basin migrated through the same plumbing system and acquired metals on the way. The bulk of Pb-Zn mineralization formed at temperatures between 120 and 180 °C by mixing of these brines with a pool of H2S (δ34S = 24 to 9‰) produced via thermochemical sulfate reduction (TSR) with oxidation of hydrocarbons in sandstone. Other minor H2S sources are identified. Upward migration and fluctuation of the hydrocarbon-water interface in sandstone below shale aquicludes and the formation of H2S along this interface explain the shape of the orebodies that splay out like smoke from a chimney and the conspicuous alternating layers of galena and sphalerite. Intimate intergrowth of bitumen with sphalerite suggests that subordinate amounts of H2S might have been produced by TSR during Pb-Zn mineralization. Gas chromatograms of the saturated hydrocarbon fraction from organic-rich shale and from both mineralized and barren sandstone samples indicate that hydrocarbons migrated from source rocks in the overlying Alum Shale Formation buried in the foredeep into sandstone, where they accumulated in favorable traps in the forebulge setting.

Heating of quartz crystals in order to study melt and high-temperature fluid inclusions is a common practice to constrain major physical and chemical parameters of magmatic and hydrothermal processes. Diffusion and modification of trace element content in quartz and its hosted melt inclusions have been investigated through step-heating experiments of both matrix-free quartz crystals and quartz crystals associated with sulfides and other minerals using a Linkam TS1500 stage. Magmatic and hydrothermal quartz were successively analyzed after each heating step for Cu, Al, and Ti using electron probe micro-analyzer. After the last heating step, quartz crystals and their hosted melt inclusions were analyzed by laser ablation inductively coupled plasma mass spectrometry and compared to unheated samples. Heated samples reveal modification of Cu, Li, Na, and B contents in quartz and modification of Cu, Li, Ag, and K concentrations in melt inclusions. Our results show that different mechanisms of Cu, Li, and Na incorporation occur in magmatic and hydrothermal quartz. Heated magmatic quartz records only small, up to a few ppm, enrichment in Cu and Na, mostly substituting for Li. By contrast, heated hydrothermal quartz shows enrichment up to several hundreds of ppm in Cu, Li, and Na, which substitute for originally present H. This study reveals that the composition of both quartz and its hosted melt inclusions may be significantly modified upon heating experiments, leading to erroneous quantification of elemental concentrations. In addition, each quartz crystal also becomes significantly enriched in Cu in the sub-surface layer during heating. We propose that sub-surface Cu enrichment is a direct indication of Cu diffusion in quartz externally sourced from both the surrounding sulfides as well as the copper pins belonging to the heating device. Our study shows that the chemical compositions of both heated quartz and its hosted inclusions must be interpreted with great caution to avoid misleading geological interpretations.

Hydrothermal ore deposits are large geochemical anomalies of sulfur and metals in the Earth’s crust that have formed at

Minerals from the tennantite-tetrahedrite series (fahlores) are found as single euhedral crystals and crustiform aggregates in hydrothermal veins of the Gradishte and Petrovitsa Pb-Zn deposits of the Madan ore field, southern Bulgaria. Unusually large compositional variations and fine oscillatory crystal zoning were investigated with electron microprobe analysis. The Gradishte samples correspond dominantly to tennantite, while Petrovitsa crystals have exclusively tetrahedrite composition. Fahlore compositions at Madan correspond to zincian varieties (1.6–1.95 apfu), with low Fe-content (

The large Cerro de Pasco Cordilleran base metal deposit in central Peru is the result of three successive mineralizing stages comprising both low- and high-sulfidation mineral associations: (A) several pyrrhotite pipes grading outward to sphalerite and galena replacement bodies, (B) a massive, funnel-shaped pyrite-quartz replacement orebody, and (C) E-W–trending Cu-Ag-(Au-Zn-Pb) enargite-pyrite veins and well-zoned Zn-Pb-(Bi-Ag-Cu) carbonate-replacement orebodies. This superposition of hydrothermal events leads to complex replacement textures and crosscutting relationships. A detailed study of the textures and mineral composition of the up to 15-m-wide replacement front existing between the pyrrhotite pipes and the pyrite-quartz body allows for clarification of the relative chronology of the hydrothermal events. The results show that, in contrast to previous interpretations, the emplacement of the pyrrhotite pipes and their Zn-Pb mineralized rims precedes that of the pyrite-quartz body. The replacement textures affecting pyrrhotite and arsenopyrite and the nature of the newly formed minerals have been used as a qualitative way to track the evolution of fS2, fO2, and pH of the mineralizing fluids. Two steps of pyrrhotite replacement have been recorded. The first one takes place under moderate acidity and relatively reduced to moderately oxidized conditions and is marked by replacement of pyrrhotite by euhedral nonporous pyrite. The second step occurs under more acidic and oxidized conditions and is characterized by replacement of pyrrhotite by porous marcasite and replacement of arsenopyrite by pyrite. Subsequently, marcasite is partly replaced by fine-grained euhedral nonporous pyrite. LA-ICP-MS trace element analyses of the replaced pyrrhotite and arsenopyrite and of the newly formed marcasite and pyrite support dissolution-reprecipitation as the main mechanism for replacement. Positive correlations between some of the elements (e.g., Pb-Sb, Pb-Ag) are indicative of the possible presence of nanoscale solid inclusions as main carriers for those elements; however, coupled substitutions and incorporation of some of the elements at a ppm level into the pyrite and marcasite structures cannot be excluded. The obtained As, Sb, Pb, and Bi values in pyrite are systematically higher than published data of pyrite in epithermal and porphyry systems. Nature and trace element content of the newly formed minerals yield information on the physicochemical conditions during their precipitation, the initial trace element content of replaced minerals, and the subsequently dissolved neighboring phases. The results show that the metal concentration of the fluid is locally influenced by the composition of the dissolved minerals. This study leads to a simpler interpretation of the fluid evolution than previously proposed, with a progressive increase of fS2, fO2, and pH as a result of decreasing wall-rock buffering during the three successive mineralizing stages at Cerro de Pasco.

International audience; Chemical and isotopic compositions of magmatic crystals provide important information to distinguish between deep juvenile and crustal contributions. In this work, high-resolution multicollector secondary ion mass spectrometry data reveal strong variations of δ18O values in three plagioclase crystals (800 – 1700 μm) from two representative basaltic andesite samples of the 2010 Merapi eruption (Central Java, Indonesia). The δ18O values (from 4.6 to 7.9 ‰) are interpreted to reflect oxygen isotope heterogeneity in the melt composition during plagioclase growth. The lowest δ18O values (4.6 – 6.6 ‰) are found in anorthite-rich cores (An82–97), whereas higher δ18O values (5.7 to 7.9 ‰) are found in anorthite-poorer zones (An33–86), typically in crystal rims. Combining these new plagioclase δ18O data with δ18O of calc-silicate crustal xenoliths erupted between 1994 – 1998, the composition of glass inclusions hosted by the anorthite-rich plagioclase (An82-92), available experimental data, and the results of thermodynamic modelling using the Magma Chamber Simulator code, we conclude that the abundant anorthite-rich cores crystallized from a mantle-derived hydrous basaltic to basaltic trachyandesite melt that recharged a deeper (200-600 MPa) magma storage zone, whereas lower anorthite zones crystallized at shallower levels (100-200 MPa). The oxygen isotope variations in the plagioclase are explained by a two-stage model of interaction of the hydrous, mafic mantle-derived magma (1) with old crustal rocks depleted in 18O due to high temperature alteration that yielded the low δ18O values in the anorthite-rich cores at deep levels (13 – 20 km), and later (2) with 18O-enriched carbonate material that yielded the high δ18O values in anorthite-poorer zones at shallow levels (∼4.5 – 9 km). Thermodynamic modelling is consistent with ∼18 wt.% assimilation of crustal calc-silicate material at 925 – 950°C and 100 – 200 MPa by the 2010 Merapi basaltic andesite magma prior to eruption. Timescales for plagioclase phenocryst growth and residence in the magmatic plumbing system are ⩽34 years. The combined data thus reveal efficient magma recharge and crustal assimilation processes that characterize the open-system magma storage and transport systems associated with the 2010 Merapi eruption.

SwitzerlandAbstractPorphyry related Cordilleran polymetallic mineralization in the Morococha district central Peru displays a deposit scale base metal zonation a common feature observed in many ore deposits of this type. The distinct pattern of zonation consists of Cu rich ores in the core area and increasingly Zn Pb and Ag rich ores in more distal veins and replacement orebodies. We investigated the changing composition of key ore minerals throughout these zones. They are important indicators for the conditions of mineral precipitation and evolving hydrothermal fluid. The mineral species stannoidite Cu8(FeZn)3Sn2S12 vinciennite Cu10Fe4Sn(AsSb)S16 and tennantite tetrahedrite have variable Cu content and Fe2+/Fe3+ values between the different base metal zones. Controlled by coupled substitution mechanisms they show Cu excess and predominantly ferric Fe compositions in the central areas (Cu and Zn Cu zones) whereas stoichiometric Cu values and mixed Fe3+ and Fe2+ compositions are typical in the more distal zones (Zn Pb Ag and Ag Pb). These compositional changes are interpreted to reflect decreasing oxidation state of the cooling and evolving fluid and increasing reaction with the host rock toward outer parts of the deposits. Initially high Cu Fe and S values in the fluid decrease with precipitation of Cu and Fe sulfides. As result of decreasing oxidation state and Fe and Cu values in the fluid Fe in tennantite tetrahedrite is increasingly substituted by competing Zn and Cu by Ag. These data show that compositions of major and even minor ore forming minerals reflect metal content oxidation and sulfidation state and degree of buffering of an evolving hydrothermal fluid by the host rock on a district scale.

Ten sphalerite separates isolated from mineralized samples in proximal and distal positions relative to the proposed main feeder fault systems at the Laisvall deposit were used to obtain an absolute age determina- tion of this world-class Pb-Zn deposit hosted by autochthonous Ediacaran to Lower Cambrian sandstone and located currently along the erosional front of the Scandinavian Caledonides in northern Sweden. Residue and leachate fractions of each separate were obtained using the crush-leaching technique. All samples correspond to sphalerite formed using reduced sulfur derived from thermochemical sulfate reduction, three of them from disseminated ore in the Lower Sandstone, two from the disseminated ore in the Upper Sandstone, and five from steeply dipping galena-sphalerite-calcite veinlets interpreted in previous works as remobilization of dis- seminated ores. The isotope dilution-thermal ionization mass spectrometry (ID-TIMS) data yield an overall complex Rb-Sr isotope pattern with two distinct trends in the 87Sr/86Sr vs. 87Rb/86Sr isochron diagram. The three sphalerite residues of disseminated mineralization from the Lower Sandstone orebody show Rb-Sr isotope sys- tematics indicative of undisturbed primary precipitates, and yield an isochron model age of 467 ± 5 Ma (mean square weighted deviation, MSWD, 1.4). Since the isochron is based on three points, the obtained age is to be considered as preliminary. Yet, the obtained age is fully consistent with geologic evidence reported by previous authors and pointing to Middle Ordovician timing of ore formation. The ID-TIMS data were complemented by laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) analyses on the same sphalerite samples. The data support the hypothesis that the measured ID-TIMS Rb and Sr contents in these sphalerite residues are held in the sphalerite structure itself and are not related to micro-inclusions. The most viable hypothesis, in agreement with published work, is that during rapid growth, sphalerite may incorporate Rb and Sr ions from the hydrothermal fluids in its structure, most probably in octahedral voids. By contrast, the second trend in the 87Sr/86Sr vs. 87Rb/86Sr space defined by most other sphalerite residues and corresponding inclusion fluid leachates from the Upper Sandstone orebody and the veinlet samples is too steep to account for a realistic isochron age determination. This steep linear trend is interpreted to represent a post- mineralization disturbance involving fluids rich in Sr. This disturbance of the Rb-Sr isotope system is consistent with the presence of the steeply dipping galena-sphalerite-calcite veinlets and the fact that the Upper Sandstone is, in places, tectonically disrupted because of its proximity to the basal Caledonian décollement. The attempt to date the Granberget deposit, located in tectonically disrupted allochthonous units inside the Caledonian orogen, failed because the Rb-Sr isotope systematics of the three analyzed sphalerite samples are also disturbed. The obtained Middle Ordovician (467 ± 5 Ma) mineralization age at Laisvall can be interpreted as a far-field foreland response to an early Caledonian arc-continent collision and the subsequent development of a foreland basin. Basinal brines formed in the foredeep of the orogen could be conveyed cratonward, interact with per- meable Baltica crystalline basement rocks, and resurge as metal-bearing fluids in sandstone at Laisvall along reactivated Paleoproterozoic crystalline basement faults. Mixing of metal-bearing brines with hydrocarbon and H2S-rich fluids in Ediacaran to Lower Cambrian sandstone may explain the initial Sr isotope signature (87Sr/86Sr = 0.715900 ± 60) of the isochron intersect.

Porphyry-related base metal vein and replacement mineralization (i.e., Cordilleran polymetallic mineralization) in the Morococha district, central Peru, is part of a large magmatic-hydrothermal system associated with the emplacement of several late Miocene porphyry intrusions and formation of important Cu-Mo mineralization. Zn-Pb-Ag-Cu veins overprint the giant Toromocho porphyry Cu-Mo deposit in the center of the district and display a typical concentric base metal zonation (Cu → Zn, Pb → Ag) covering an area of approximately 50km2. A detailed fluid inclusion study supports the hypothesis that base metal mineralization precipitated from cooled and evolved metal-rich, intermediate-density porphyry-type fluids. In early stages of Cordilleran base metal vein formation, fluid inclusions have low salinities of ~2 to 5 wt % NaCl equiv, CO2 contents of 3 to 10mol %, and homogenization temperatures (Th) of 380° to 340°C. They are similar to intermediate-density fluid inclusions trapped in a milky quartz vein predating Cordilleran polymetallic mineralization, with similar low salinities (3.0–3.8 wt % NaCl equiv) and low CO2 contents (6.5–8 mol %), but higher Th of ~420° to 410°C. During cooling of the intermediate-density fluids from 400° to 300°C, the lithostatic pressure regime changed to a hydrostatic one. The fluids underwent pressure drop as well as phase separation (i.e., unmixing) and lost most of their CO2. They acquired moderate salinities, in some cases intermediate (~up to 16 wt % NaCl) to brine compositions. However, the bulk of the magmatic fluid retained low salinity while it continued to cool under open-system conditions and precipitated tennantite-tetrahedrite, chalcopyrite, enargite, sphalerite, and galena. Upon cooling below 270°C, the fluids deposited abundant rhodochrosite and quartz, while following the boiling curve toward lower P-T conditions. These data record an evolution of mineral precipitation from deep (minimum depth of 2–1.5 km) to shallow environments (300–800 m). Oxygen, hydrogen, and carbon stable isotope data indicate that the hydrothermal fluids have a dominantly magmatic signature and were diluted by meteoric waters during the carbonate stage. Copper (5,000–18,000 μ g/g), sulfur (up to 12,000 μ g/g), and iron (2,100–6,000 μ g/g) concentrations in the intermediate-density fluid inclusions in the milky quartz veins are approximately 5 to 10 times higher than in intermediate-density inclusions of the early Cordilleran base metal veins. The base metals Zn, Pb, and Mn have comparable concentrations between 100 and 1,000 μ g/g for both types of fluid. These findings suggest that the fluids identified in Cordilleran polymetallic veins are compositionally similar to the porphyry-type fluids and could have derived from the latter after precipitation of Cu- and Fe-bearing sulfides in a deeper porphyry environment. The new data explain the commonly observed base and precious metal zonation patterns encountered in porphyry-centered districts (e.g., Bingham, Butte) and show that both porphyry and polymetallic mineralization can precipitate from similar magmatic-hydrothermal fluid pulses.

The breccia-hosted epithermal Au-Ag deposit of Rosia Montana is located 7 km northeast of Abrud, in the northern part of the South Apuseni Mountains, Romania. Estimated total reserves of 214.91 million metric tons (Mt) of ore at 1.46 g/t Au and 6.9 g/t Ag (10.1 Moz of Au and 47.6 Moz of Ag) make Rosia Montana one of the largest gold deposits in Europe. At this location, Miocene calc-alkaline magmatic and hydrothermal activity was associated with local extensional tectonics within a strike-slip regime related to the indentation of the Adriatic microplate into the European plate during the Carpathian orogenesis. The host rocks of the magmatic complex consist of pre-Mesozoic metamorphosed continental crust covered by Cretaceous turbiditic sediment (flysch). Magmatic activity at Rosia Montana and its surroundings occurred in several pulses and lasted about 7 m.y. Rosia Montana is a breccia-hosted epithermal system related to strong phreatomagmatic activity due to the shallow emplacement of the Montana dacite. The Montana dacite intruded Miocene volcaniclastic material (volcaniclastic breccias) and crops out at Cetate and Cârnic Hills. Current mining is focused primarily on the Cetate open pit, which was mapped in detail, leading to the recognition of three distinct breccia bodies: the dacite breccia with a dominantly hydrothermal matrix, the gray polymict breccia with a greater proportion of sand-sized matrix support, and the black polymict breccia, which reached to the surface, contains carbonized tree trunks and has a dominantly barren clastic matrix. The hydrothermal alteration is pervasive. Adularia alteration with a phyllic overprint is ubiquitous; silicification and argillic alteration occur locally. Mineralization consists of quartz, adularia, carbonates (commonly Mn-rich), pyrite, Fe-poor sphalerite, galena, chalcopyrite, tetrahedrite, and native gold and occurs as disseminations, as well as in veins and filling vugs within the Montana dacite and the different breccias. The age of mineralization (12.85 ± 0.07 Ma) was determined by 40 Ar- 39 Ar dating on hydrothermal adularia crystals from vugs in the dacite breccia in the Cetate open pit. Microthermometric measurements of fluid inclusions in quartz phenocrysts from the Montana dacite revealed two fluid types that are absent from the hydrothermal breccia and must have been trapped at depth prior to dacite dome emplacement: brine inclusions (32–55 wt % NaCl equiv, homogenizing at T h > 460°C) and intermediate density fluids (4.9–15.6 wt % NaCl equiv, T h between 345°–430°C). Secondary aqueous fluid inclusion assemblages in the phenocrysts have salinities of 0.2 to 2.2 wt percent NaCl equiv and T h of 200° to 280°C. Fluid inclusion assemblages in hydrothermal quartz from breccias and veins have salinities of 0.2 to 3.4 wt percent NaCl equiv and T h from 200° to 270°C. The oxygen isotope composition of several zones of an ore-related epithermal quartz crystal indicate a very constant δ 18 O of 4.5 to 5.0 per mil for the mineralizing fluid, despite significant salinity and temperature variation over time. Following microthermometry, selected fluid inclusion assemblages were analyzed by laser ablation-inductively coupled-plasma mass spectrometry (LA-ICPMS). Despite systematic differences in salinity between phenocryst-hosted fluids trapped at depth and fluids from quartz in the epithermal breccias, all fluids have overlapping major and trace cation ratios, including identical Na/K/Rb/Sr/Cs/Ba. Consistent with the constant near-magmatic oxygen isotope composition of the hydrothermal fluids, these data strongly indicate a common magmatic component of these chemically conservative solutes in all fluids. Cu, Pb, Zn, and Mn show variations in concentration relative to the relatively non-reactive alkalis, reflecting the precipitation of sulfide minerals together with Au in the epithermal breccia, and possibly of Cu in an inferred subjacent porphyry environment. The magmatic-hydrothermal processes responsible for epithermal Au-Ag mineralization at Rosia Montana are, however, not directly related to the formation of the spatially associated porphyry Cu-Au deposit of Rosia Poieni, which occurred about 3 m.y. later.

The Inner Carpathians comprise several distinct Neogene late-stage orogenic Pb–Zn–Cu–Ag–Au ore districts. The mineral deposits in these districts are closely related to volcanic and subvolcanic rocks, and represent mainly porphyry and epithermal vein deposits, which formed within short periods of time in each district. Here, we discuss possible geodynamic and structural controls that suggest why some of the Neogene volcanic districts within the Carpathians comprise abundant mineralization, while others are barren. The Neogene period has been characterized by an overall geodynamic regime of subduction, where primary roll-back of the subducted slab and secondary phenomena, like slab break-off and the development of slab windows, could have contributed to the evolution, location and type of volcanic activity. Structural features developing in the overlying lithosphere and visible in the Carpathian crust, such as transtensional wrench corridors, block rotation and relay structures due to extrusion tectonics, have probably acted in focusing hydrothermal activity. As a result of particular events in the geodynamic evolution and the development of specific structural features, mineralization formed during fluid channelling within transtensional wrench settings and during periods of extension related to block rotation. In the Slovakian ore district of the Western Carpathians, Neogene volcanism and associated mineralization were localized by sinistral, NE-trending wrench corridors, which formed part of the extruding Alcapa block. The Baia Mare ore district, in the Eastern Carpathians, reflects a transtensional wrench setting on distributed oversteps close to the termination of the Dragos Voda fault. There, mineralization was spatially controlled by the transtensional Dragos Voda master fault and associated cross-fault systems. The Golden Quadrangle Cu–Au ore district of the Southern Apuseni Mountains reflects an unusual rotated transtensional/extensional setting close to the termination of a graben system. There, fluid flow was probably localized by fault propagation at the inner tip of the graben system. The spatial and temporal evolution of the magmatism and its changing geochemical signature from (N)W to (S)E strongly suggests a link with the contemporaneous northeastward roll-back of the subducted slab and a progressive southeastward detachment during accelerating roll-back. This geodynamic evolution is further supported by the present-day overall and detailed mantle lithospheric density images, the present-day heat flow patterns, the crustal architecture and its interpreted evolution, and the spatial and temporal evolution of depocentres around the Carpathian arc. In contrast to all these features, the mineral deposits in the West Carpathians, East Carpathians and Apuseni Mountains are too synchronous with respect to their individual volcanic history and contrast too much with younger volcanics of similar style, but barren, in southeastern parts of the Carpathians to simply link them directly to the slab evolution. In all three districts, the presence of magmatic fluids released from shallow plutons and their mixing with meteoric water were critical for mineralization, requiring transtensional or extensional local regimes at the time of mineralization, possibly following initial compressional regimes. These three systems show that mineralization was probably controlled by the superposition of favourable mantle lithospheric conditions and partly independent, evolving upper crustal deformation conditions. In the 13 to 11 Ma period the dominant mineralization formed all across the Carpathians, and was superimposed on structurally favourable crustal areas with, at that time, volcanic–hydrothermal activity. The period may reflect the moment when the (upper part of the) crust failed under lithospheric extension imposed by the slab evolution. This crustal failure would have fragmented the overriding plate, possibly breaking up the thermal lid, to provoke intensive fluid flow in specific areas, and allowed subsequent accelerated tectonic development, block rotation and extrusion of a “family of sub-blocks” that are arbitrarily regarded as the Tisia–Dacia or Alcapa blocks, even though they have lost their internal entity.