The Cogne magnetite deposit (Western Alps, Italy): a Jurassic seafloor ultramafic-hosted hydrothermal system?

The Cogne magnetite deposit (Western Alps, Italy) is the largest in a series of apatite and sulphide-free magnetite orebodies that are hosted in serpentinites belonging to western Alpine ophiolitic units. The nearly endmember composition of magnetite, which is unusual for an ultramafic setting, and the relatively high tonnage of the deposit (18 19 10^6 tons at 45-50 wt% Fe) make Cogne an intriguing case study to explore magnetite-forming processes in ophiolites. The Cogne magnetite shows variable textures, including nodular ores, veins and fine-grained disseminations in serpentinites after mantle peridotites and totally serpentinized melt-impregnated peridotites (troctolites). An increase in Co/Ni ratio from magnetite-poor serpentinized peridotites (0.05) to nodular ores (>1) is observed. Trace element analyses of magnetite from different sites and lithologies by laser-ablation inductively-coupled mass spectrometry indicate that magnetites have typically hydrothermal compositions, characterized by high Mg and Mn (median values up to ~24100 and ~5000 ppm, respectively), and low Cr, Ti and V (median values up to ~30, ~570 and ~60 ppm, respectively). Moreover, the variations in trace element compositions distinguish magnetite that has hydrothermal fluid-controlled composition [highest (Mg, Mn, Co, Zn)/Ni ratios] from magnetite whose composition is affected by host-rock chemistry (highest Ni \ub1 Ti \ub1 V). U-Th-Pb dating of magnetite-associated uraninite constrains the formation of the deposit to the Late Jurassic (ca. 150 Ma), during an advanced stage of the opening of the Alpine Tethys. Thermodynamic modelling of fluid-rock interactions indicates that fluids produced by seawater\u2013peridotite or seawater\u2013Fe-gabbro are not sufficiently Fe-rich to account for the formation of the Cogne deposit. This suggests that fractionation processes such as phase separation were critical to generate hydrothermal fluids capable to precipitate large amounts of magnetite in various types of ultramafic host-rocks. The oceanic setting and geochemical and mineralogical similarities with some modern ultramafic-hosted volcanogenic massive sulphide deposits on mid-ocean ridges suggest that the exposed mineralized section at Cogne may represent the deep segment of a seafloor, high-temperature (~300\u2013400\ub0C) hydrothermal system. The occurrence of similar magnetite enrichments in present-day oceanic settings could contribute to explain the presence of significant magnetic anomalies centred on active and inactive ultramafic-hosted hydrothermal fields

Eclogitic metatrondhjemites from metaophiolites of the Western Alps

In the Urtier valley (southern Aosta Valley, Italy), the Piemonte metaophiolites mainly consist of serpentinized peridotites including pods and boudinaged layers of Fe-metagabbro and trondhjemite transposed in the main eclogitic foliation. The contact between serpentinized peridotites and Fe-metagabbro/trondhjemite is locally lined by chloriteschist and rodingite. The high pressure parageneses in the Fe-metagabbro are omphacite-garnet-rutile-glaucophane-phengite, and in the metatrondhjemite plagioclase-quartz-phengite-clinozoisite-epidote-garnet, respectively. Bulk-rock major and trace elements in addition to O isotope analyses were performed in both rock types. Fe-metagabbros are characterized by MgO wt% ranging between 6.11 and 9.63%, EREE= 20-101 ppm, (La/Yb)N = 0.22-0.91; trondhjemites have SiO2 43%, Al2O3 ranging between 21 and 24%, CaO ranging between 17 and 20%, EREE = 172 - 272 ppm, (La/Yb)N ranging between 7.78 and 13.70. The 18O is 5.9 per-mil in a Fe-metagabbro sample and 7.4 per-mil in a trondhjemite sample, suggesting that these rocks have been affected by a weak oceanic low temperature alteration. The high CaO content may indicate a metasomatic process which could have occurred during the oceanic stage or at high pressure conditions

Sulfide breccias from the Semenov-3 hydrothermal field, Mid-Atlantic Ridge: authigenic mineral formation and trace element pattern

The aim of this paper is the investigation of the role of diagenesis in the transformation of clastic sulfide sediments such as sulfide breccias from the Semenov-3 hydrothermal field (Mid-Atlantic Ridge). The breccias are composed of marcasite\u2013pyrite clasts enclosed in a barite\u2013sulfide\u2013quartz matrix. Primary hydrothermal sulfides occur as colloform, fine-crystalline, porous and radial marcasite\u2013pyrite clasts with inclusions or individual clasts of chalcopyrite, sphalerite, pyrrhotite, bornite, barite and rock-forming minerals. Diagenetic processes are responsible for the formation of more diverse authigenic mineralization including framboidal, ovoidal and nodular pyrite, coarse-crystalline pyrite and marcasite, anhedral and reniform chalcopyrite, inclusions of HgS phase and pyrrhotite\u2013sphalerite\u2013chalcopyrite aggregates in coarse-crystalline pyrite, zoned bornite\u2013chalcopyrite grains, specular and globular hematite, tabular barite and quartz. The early diagenetic ovoid pyrite is enriched in most trace elements in contrast to late diagenetic varieties. Authigenic lower-temperature chalcopyrite is depleted in trace elements relative to high-temperature hydrothermal ones. Trace elements have different modes of occurrence: Se is hosted in pyrite and chalcopyrite; Tl is related to sphalerite and galena nanoinclusions; Au is associated with galena; As in pyrite is lattice-bound, whereas in chalcopyrite it is related to tetrahedrite\u2013tennantite nanoinclusions; Cd in pyrite is hosted in sphalerite inclusions; Cd in chalcopyrite forms its own mineral; Co and Ni are hosted in chalcopyrite

Corrigendum: Experimental dissolution of carbonaceous materials in water at 1 GPa and 550°C: assessing the role of carbon forms and redox state on COH fluid production and composition during forearc subduction of organic matter

Biogenic carbonaceous material (CM) is the main carrier of organic carbon in the subduction zone and contributes to COH fluid production and volcanic arc gaseous emissions. Here we investigated the effect of the structural, textural and chemical heterogeneity of CM on its reactivity and redox dissolution by conducting short-lived (1 h) experiments, where synthetic analogues of CM (ordered graphite, graphite oxide (GO), mesoporous carbon (MC), Vulcan® carbon (VC) and glass-like carbon (GC)), are reacted with water at P = 1 GPa and T = 550°C—conditions typical of a warm forearc subduction—and fO2 buffered from ΔFMQ ≈ +4 to −7. We show that the amount of dissolved CM (CMdissolved) and the proportion of volatile carbon species (Cvolatile) in the fluid is related both to the structure and the peculiar surficial properties of the carbon forms, such as carbon sp2-and sp3-hybridization, amount of oxygen heteroatoms, presence of oxygenated functional groups (OFGs) and of active sites. MC and graphite (C(sp2) > 93 at%, O dissolved 2 + CO and CO2 + CH4 Cvolatile mixtures at ΔFMQ ≈ +4 and −7, respectively), while the latter has a maximum of Cvolatile production (CO2 + CH4) at ΔFMQ ≈0, which is not observed in a 10-day long run; partly-ordered GO (C(sp3) > 98 at%, O ∼31 at%, OFGs ∼41 at%) is the most reactive material at all redox conditions (CMdissolved > 2.6 mol%) and produces CO2 as the dominant Cvolatile species; disordered GC and VC (C(sp3) dissolved ∼1 mol%) and ΔFMQ ≈ –7 (CMdissolved > 1 mol%), where Cvolatile is dominantly CO2 and CH4, respectively. Besides the significant deviations from thermodynamically predicted graphite-saturated COH fluid composition and speciation, our results suggests that: 1) immature CM (disordered, rich in C(sp3), O, OFGs) is preferentially dissolved under high fluid fluxes and may buffer fluids to rather oxidizing conditions; 2) a descending flux of oxygen (and hydrogen) bond to CM may exist.</p

Association of kidney disease measures with risk of renal function worsening in patients with type 1 diabetes

Background: Albuminuria has been classically considered a marker of kidney damage progression in diabetic patients and it is routinely assessed to monitor kidney function. However, the role of a mild GFR reduction on the development of stage 653 CKD has been less explored in type 1 diabetes mellitus (T1DM) patients. Aim of the present study was to evaluate the prognostic role of kidney disease measures, namely albuminuria and reduced GFR, on the development of stage 653 CKD in a large cohort of patients affected by T1DM. Methods: A total of 4284 patients affected by T1DM followed-up at 76 diabetes centers participating to the Italian Association of Clinical Diabetologists (Associazione Medici Diabetologi, AMD) initiative constitutes the study population. Urinary albumin excretion (ACR) and estimated GFR (eGFR) were retrieved and analyzed. The incidence of stage 653 CKD (eGFR &lt; 60 mL/min/1.73 m2) or eGFR reduction &gt; 30% from baseline was evaluated. Results: The mean estimated GFR was 98 \ub1 17 mL/min/1.73m2 and the proportion of patients with albuminuria was 15.3% (n = 654) at baseline. About 8% (n = 337) of patients developed one of the two renal endpoints during the 4-year follow-up period. Age, albuminuria (micro or macro) and baseline eGFR &lt; 90 ml/min/m2 were independent risk factors for stage 653 CKD and renal function worsening. When compared to patients with eGFR &gt; 90 ml/min/1.73m2 and normoalbuminuria, those with albuminuria at baseline had a 1.69 greater risk of reaching stage 3 CKD, while patients with mild eGFR reduction (i.e. eGFR between 90 and 60 mL/min/1.73 m2) show a 3.81 greater risk that rose to 8.24 for those patients with albuminuria and mild eGFR reduction at baseline. Conclusions: Albuminuria and eGFR reduction represent independent risk factors for incident stage 653 CKD in T1DM patients. The simultaneous occurrence of reduced eGFR and albuminuria have a synergistic effect on renal function worsening

The Cogne magnetite deposit (Western Alps, Italy): a Late Jurassic seafloor ultramafic-hosted hydrothermal system?

The Cogne magnetite deposit (Western Alps, Italy) is the largest in a series of apatite and sulphide-free magnetite orebodies that are hosted in serpentinites belonging to western Alpine ophiolitic units. The nearly endmember composition of magnetite, which is unusual for an ultramafic setting, and the relatively high tonnage of the deposit (18 ∙ 10^6 tons at 45-50 wt% Fe) make Cogne an intriguing case study to explore magnetite-forming processes in ophiolites. The Cogne magnetite shows variable textures, including nodular ores, veins and fine-grained disseminations in serpentinites after mantle peridotites and totally serpentinized melt-impregnated peridotites (troctolites). An increase in Co/Ni ratio from magnetite-poor serpentinized peridotites (0.05) to nodular ores (>1) is observed. Trace element analyses of magnetite from different sites and lithologies by laser ablation inductively coupled plasma mass spectrometry indicate that magnetites have typically hydrothermal compositions, characterized by high Mg and Mn (median values up to ~24100 and ~5000 ppm, respectively), and low Cr, Ti and V (median values up to ~30, ~570 and ~60 ppm, respectively). Moreover, the variations in trace element compositions distinguish magnetite that has hydrothermal fluid-controlled composition [highest (Mg, Mn, Co, Zn)/Ni ratios] from magnetite whose composition is affected by host-rock chemistry (highest Ni ± Ti ± V). U-Th-Pb dating of magnetite-associated uraninite constrains the formation of the deposit to the Late Jurassic (ca. 150 Ma), during an advanced stage of the opening of the Alpine Tethys. Thermodynamic modelling of fluid-rock interactions indicates that fluids produced by seawater–peridotite or seawater–Fe-gabbro are not sufficiently Fe-rich to account for the formation of the Cogne deposit. This suggests that fractionation processes such as phase separation were critical to generate hydrothermal fluids capable to precipitate large amounts of magnetite in various types of ultramafic host-rocks. The oceanic setting and geochemical and mineralogical similarities with some modern ultramafic-hosted volcanogenic massive sulphide deposits on mid-ocean ridges suggest that the exposed mineralized section at Cogne may represent the deep segment of a seafloor, high-temperature (~300–400°C) hydrothermal system. The occurrence of similar magnetite enrichments in present-day oceanic settings could contribute to explain the presence of significant magnetic anomalies centred on active and inactive ultramafic-hosted hydrothermal fields.Il giacimento di magnetite di Cogne (Alpi Occidentali, Italia) è il più grande tra le mineralizzazioni a magnetite prive di apatite e solfuri che sono ospitate nelle serpentiniti appartenenti alle unità ofiolitiche delle Alpi Occidentali. La magnetite di composizione prossima al termine puro, insolita in rocce ultramafiche, e il tonnellaggio significativo del giacimento (18 ∙ 10^6 tonnellate con concentrazioni di Fe del 45-50% in peso), rendono Cogne un interessante caso studio per indagare i processi responsabili della formazione di magnetite nelle ofioliti. La magnetite di Cogne si presenta come minerale nodulare, vene e disseminazioni in serpentiniti derivanti da peridotiti di mantello e in peridotiti impregnate da fuso (troctoliti) totalmente serpentinizzate. Il rapporto Co/Ni aumenta a partire dalle serpentiniti povere in magnetite (0.05) fino al minerale nodulare (>1). L'analisi degli elementi in traccia nella magnetite proveniente da differenti siti e litologie, ottenuta tramite laser ablation inductively coupled plasma mass spectrometry, indica che la magnetite ha una composizione tipicamente idrotermale, caratterizzata da alte concentrazioni di Mg e Mn (valori mediani fino a ~24100 e ~5000 ppm, rispettivamente) e bassi Cr, Ti e V (valori mediani fino a ~30, ~570 e ~60 ppm, rispettivamente). Inoltre, le variazioni nel contenuto di elementi in traccia distinguono la magnetite che ha una composizione controllata dal fluido idrotermale [alti rapporti (Mg, Mn, Co, Zn)/Ni] dalla magnetite la cui composizione risente della geochimica della roccia incassante (alti Ni ± Ti ± V). La datazione radiometrica con il metodo U-Th-Pb dell'uraninite associata alla magnetite vincola l'età della formazione del giacimento al Giurassico superiore (circa 150 Ma), durante uno stadio avanzato dell'apertura della Tetide alpina. La modellazione termodinamica delle interazioni fluido-roccia indica che i fluidi risultanti dalle reazioni acqua marina-peridotite e acqua marina-Fe-gabbro non sono sufficientemente ricchi in Fe per generare il giacimento di Cogne. Ciò suggerisce che processi di frazionamento, come la separazione di fase, furono di cruciale importanza per produrre fluidi idrotermali in grado di precipitare grandi quantità di magnetite in varie tipologie di rocce incassanti ultramafiche. Il contesto oceanico e le somiglianze geochimiche e mineralogiche con alcuni moderni depositi vucanogenici a solfuri massivi di dorsale oceanica ospitati in ultramafiti suggeriscono che la sezione mineralizzata di Cogne possa rappresentare il segmento profondo di un sistema idrotermale di fondale oceanico di alta temperatura (~300-400°C). La presenza di analoghe concentrazioni di magnetite nella litosfera oceanica attuale potrebbe contribuire a spiegare l'esistenza di significative anomalie magnetiche situate in corrispondenza di sistemi idrotermali idrotermali sia attivi che inattivi impostati su rocce ultramafiche

Studio dell’antico sito metallurgico di Misérègne (Fénis, AO): la miniera, le scorie.

Mining operations in the Aosta Valley ended in 1979, when the Cogne Mine was abandoned. However this territory preserves the traces of an ancient mining activity. In 1776 Nicolis de Robilant recognized the Roman mining-style in the Servette Mine, in Saint-Marcel Valley (AO). The first attempt to demonstrate archaeometrically the Roman origin of the Servette Mine was carried by Tumiati et al. (2005) However they only obtained High Medieval ages by radiocarbon dating of charcoal fragments included in metallurgical slags. Further 14C dating of metallurgical slags from the site of Misérègne (Fénis, AO) was documented in my bachelor thesis. Calibrated ages for the metallurgical activity responsible of the slag production are between the 4th and the 1st century BC (see appendix A. 1.; Toffolo et al., in print), which predate the Roman conquer of the Aosta Valley, dated to 25 B.C. These are the oldest ages ever obtained on metallurgical slags in the Aosta Valley. The aim of this thesis is to characterize for the first time the metallurgical slags from Misérègne by the mineralogical and petrological point of view, following the same approach as in previous studies on ancient slags by Saez et al. (2003), Tumiati et al., (2005) and Addis (2013). This thesis starts with a general outline of the mining district of the Piedmont Zone in the Aosta Valley, which metallurgical activity in Misérègne is directly linked to; in the next chapter, an overview of the extractive metallurgy of copper, necessary to introduce slags, is then provided; the thesis ends with a geothermometrical study applied to the slags, which combined with the mineralogical and microtextural observations, allowed me to gain information on the adopted metallurgical technologies

Ancient extractive metallurgy of copper in the Aosta Valley (Western Alps, Italy): new evidence from pre-Roman slags from the Mis\ue9r\ue8gne site...........................................................................................

Many metallurgical sites are scattered across the Aosta Valley territory (e.g. Tumiati et al., 2005). The age of some of them is unknown and often the slag heaps are the sole vestiges of metallurgical activities. Such is the case of Miséregne (Fénis), where the village is built on an enormous slag deposit. We performed radiocarbon dating on charcoal fragments included in the slags and obtained ages comprised between the 4th and 1st century BC. So far, these are the most ancient ages for early mining activity in the Aosta Valley, probably carried out by the local population of the Salassi. We studied the slags following a petrologic approach. The occurrence of matte inclusions in the slags indicates that the processed raw minerals were Cu-Fe sulfides. Relying on morphologic and micro-textural features, we classified the slags into three categories, i.e., coarse, massive and flat, as suggested by Addis (2013). In all the slag classes the most abundant phase is olivine. Other common phases are spinel group minerals and sulfides, mainly pyrrhotite and bornite solid solutions. The olivine crystal shapes allowed us to qualitatively estimate the degree of undercooling (ΔT) and the rate of cooling of the slags: the coarse slags show a high ΔT; the massive slags seem to record an initial, long-lasting low-ΔT stage, followed by an increase in the cooling rate; the flat slags underwent a brief low-ΔT stage, followed by a sudden marked increase in ΔT. Combining this information with the slag bulk chemistry, the sulfide compositions, the slag morphology and the presence of inclusions of charcoal, quartz and other slag fragments, we hypothesize that the massive and coarse slags come from the lower and, respectively, the upper portion of the same slag contained in the furnace, while the flat ones were tapped slags. Minimum furnace working temperatures estimated by means of olivinespinel geothermometry are in the ranges 932-964°C, 968-1037°C, 1202-1239°C for the coarse, massive and flat slags, respectively. According to the above observations, the flat slags should record conditions that are the closest to the actual furnace working temperature

Ancient extractive metallurgy of copper in the Aosta Valley (Western Alps, Italy): new evidence from pre-Roman slags from the Misérègne site

Many metallurgical sites are scattered across the Aosta Valley territory (e.g. Tumiati et al., 2005). The age of some of them is unknown and often the slag heaps are the sole vestiges of metallurgical activities. Such is the case of Miséregne (Fénis), where the village is built on an enormous slag deposit. We performed radiocarbon dating on charcoal fragments included in the slags and obtained ages comprised between the 4th and 1st century BC. So far, these are the most ancient ages for early mining activity in the Aosta Valley, probably carried out by the local population of the Salassi. We studied the slags following a petrologic approach. The occurrence of matte inclusions in the slags indicates that the processed raw minerals were Cu-Fe sulfides. Relying on morphologic and micro-textural features, we classified the slags into three categories, i.e., coarse, massive and flat, as suggested by Addis (2013). In all the slag classes the most abundant phase is olivine. Other common phases are spinel group minerals and sulfides, mainly pyrrhotite and bornite solid solutions. The olivine crystal shapes allowed us to qualitatively estimate the degree of undercooling (ΔT) and the rate of cooling of the slags: the coarse slags show a high ΔT; the massive slags seem to record an initial, long-lasting low-ΔT stage, followed by an increase in the cooling rate; the flat slags underwent a brief low-ΔT stage, followed by a sudden marked increase in ΔT. Combining this information with the slag bulk chemistry, the sulfide compositions, the slag morphology and the presence of inclusions of charcoal, quartz and other slag fragments, we hypothesize that the massive and coarse slags come from the lower and, respectively, the upper portion of the same slag contained in the furnace, while the flat ones were tapped slags. Minimum furnace working temperatures estimated by means of olivinespinel geothermometry are in the ranges 932-964°C, 968-1037°C, 1202-1239°C for the coarse, massive and flat slags, respectively. According to the above observations, the flat slags should record conditions that are the closest to the actual furnace working temperature

The Lovignanaz Cu-Fe sulphide mine: safeguard of a pre-Roman mining site

The antique Lovignanaz mine (also known as Molina mine) is located in the western side of the Clavalit\ue9 valley (1350-1425 m a.s.l.), to the South of the F\ue9nis village, in the southern side of the Aosta Valley (Italy). The mine galleries are developed within chloriteschists, talcschists and metagabbros transposed with calcschists belonging to the Piedmont nappe (Zermatt-Saas zone). The rocks hosting the Fe-Cu sulphide mineralization show blueschist to eclogite facies mineral associations like those studied in Saint-Marcel rocks (Martin et al., 2008, and ref. therein). The mineralization is characterized by disseminated chalcopyrite and pyrite associated with minor ilmenite, rutile, pyrrhotite and magnetite (F\ue9nis. Une communaut\ue9 au fil de l'histoire, 2000 and ref. therein). The oldest galleries were dug with techniques described by Agricola in De Re Metallica (1556) and have been attributed to the Romans. These techniques consist in excavation along mineralized layers after \u201cfire-setting\u201d, that is after weakening the rocks with a fire (De Re Metallica, book V). Other galleries have been excavated with more recent techniques, revealing the use of explosives, and have been attributed to XVIII-XIX centuries mining activity (Gerbore E. E., in: F\ue9nis\u2026, op. cit.). The remnants of a furnace for rock-roasting have been found along the right side of the Clavalit\ue9 river (lat. N 45\ub0 41\u2019 46\u2019\u2019; long. E 7\ub0 29\u2019 51\u2019\u2019). In the same site, slags with charcoal and red burnt soil, probably related to an old activity, were observed during the field work. Several glassy slags, maybe produced during XVIII-XIX centuries mining activity, were found below a large landslide that partly covers the mine adits. Near the oldest mine entrances traces of old working instrument have been found. These mines were also used to extract millstones: few metres from the mine entrances in the Mouil\ue9 locality (F\ue9nis\u2026, op. cit.), some of these stones are still unexcavated on the rock walls. In the lower part of the valley, in correspondence of Miser\ue8gne village (F\ue9nis), there is a dump where many large slags with charcoal fragments are piled up. Some of these fragments were analyzed with 14C method and one of them has been dated to IV century b.C.. This age is the oldest found for charcoal associated to slags of the Cu mines in the Aosta Valley. Other slags from the Saint Marcel valley yielded early medieval ages (Tumiati et al., 2005). The Lovignanaz mining site has been destroyed by landslide events, the last one having occurred in 2000, which partly covered mine entrances and other structures linked to mining activity. The presence of structural lineaments and the practice of \u201cfire-setting\u201d during mining activity may have contributed to trigger the landslide. References: AAVV, 2000, F\ue9nis. Une communaut\ue9 au fil de l'histoire., Musumeci Editore; Agricola [Bauer G.], 1556, De Re Metallica, ed. 1950 by Hoover H. C. and Hoover L. H., Dover Publications, New York, book V, 118-121; Casartelli P., 2003, Archeometallurgia nella valle di Saint-Marcel (AO): studio preliminare delle scorie di fusione della miniera di Servette, tesi di laurea, Univ. degli studi dell\u2019Insubria; Lorenzini C., 1995, Le antiche miniere della Valle d\u2019Aosta, Musumeci Editore, 62-64; Martin S., Rebay G., Kienast J.-R., M\ue9vel C., 2008, An eclogitised oceanic palaeo-hydrothermal field from the St. Marcel valley (Italian Western Alps), Ofioliti, 33 (1), 49-63; Tumiati S., Casertelli P., Mambretti A., Martin S., 2005, The ancient mine of Servette (Saint-Marcel, Val d\u2019Aosta, Western Italian Alps): a mineralogical, metallurgical and charcoal analysis of furnace slags, Archaeometry 47, 2, 317-34