1,720,984 research outputs found
Reverse telescoping in a distal skarn system (Campiglia Marittima, Italy)
Full text linkThe Campiglia Marittima Fe-Cu-Zn-Pb(-Ag) skarn deposit has long been regarded as a reference example of an exoskarn showing a symmetric outward mineralogical zoning of both skarn and ore minerals with respect to an axial mafic porphyry dike. Detailed field and underground mapping, along with three-dimensional reconstruction of the geometries of skarn and magmatic bodies, integrated with new petrographic, mineralogical and geochemical data, argue against this model. The shapes of the skarn bodies and the growth versors of skarn minerals in particular, are ascribed to the focusing of metasomatic fluids in sigmoid-shaped volumes of fractured host marble. After skarn formation, a mafic magma was emplaced, forming dikelets and filling residual pockets in the skarn. Field evidence and geochemical data show that the "hot" mafic magma interacted with the previously formed Zn-Pb(-Ag) skarn, triggering textural reworking and chemical redistribution of Zn-Pb sulfides as well as contributing to a late Fe-Cu mineralization. Campiglia Marittima skarn-ore system behaved at odd: a telescoping process is recorded, yet in a reverse way
Sulfosalt melts from low-grade metamorphic terrains: The case of the Monte Arsiccio mine (Tuscany, Italy)
No full textTimescale of a magmatic-hydrothermal system revealed by (40)Ar–(39)Ar geochronology: the Mio-Pliocene Campiglia Marittima system (Tuscany, Italy)
Full text linkPetrology and timing of magmatic-hydrothermal systems and the linkage between plutonic and volcanic domains are central topics in geosciences, because of broad implications for natural hazards and exploitation of natural resources. We investigated by the (40)Ar–(39)Ar method the timescale of a well-characterized natural example, the Mio-Pliocene Campiglia Marittima magmatic-hydrothermal system (Tuscany, Italy). (40)Ar–(39)Ar data from pristine and homogeneous trioctahedral micas and sanidine from the plutonic-hydrothermal-subvolcanic-volcanic sequence (from the Botro ai Marmi Granite to the San Vincenzo Rhyolite) record crystallization ages and define a temporal sequence lasting 973 ± 43 ka, starting from 5.409 ± 0.043 Ma. K-feldspar from mafic and felsic porphyries, unlike micas, are affected by submillimetre, micropore laden, alteration domains consisting of secondary K-feldspar and albite, and yielded staircase-shaped age spectra, compatible with a ternary mixing. Results document that the San Vincenzo Rhyolite consists of two diachronous batches, the first emplaced at 5.0024 ± 0.0062 Ma, closely following emplacement of mafic porphyries, the second at 4.4359 ± 0.0045 Ma. Bulk of hydrothermal deposits, consisting of skarns and associated Zn–Pb(-Ag) mineralization predating Fe–Cu ore, formed within the first ~ 400-ka lifetime of the whole sequence and was closely followed by the first eruption which should have run out most of the ore-forming potential of the system
Porphyry dikes and skarn pockets filled by mafic magma at Temperino mine (Campiglia Marittima, Italy)
No full textMobilization of Tl-Hg-As-Sb-(Ag,Cu)-Pb sulfosalt melts during low-grade metamorphism in the Alpi Apuane (Tuscany, Italy)
No full textInside the mine: interactions between hydrosphere, atmosphere, biosphere and the thallium-rich pyrite ores from southern Apuan Alps
No full textPyrite is the most common sulfide mineral of the Earth’s crust and the main responsible for the production of acid rock drainage (ARD) and acid mine drainage (AMD). Where the geologic, climatic and biologic conditions are those most favourable to the oxidation of pyrite (i.e. circulation of oxygenated water through fine-grained pyrite ores in presence of iron-oxidizers bacteria), the production of acidic waters can pose severe environmental issues. This is the case of the southern Apuan Alps (one of the rainiest area of Italy), where several types of polymetallic sulfide/oxide ore deposits, hosted within highly to moderately permeable metamorphic rocks, have been mined since ancient times and up to the end of the last century. One of the most important of these ore deposits is represented by a series of baryte-pyrite-iron oxide orebodies aligned along a ~10 km SW-NE discontinuous mineralized belt located between Valdicastello Carducci (Pietrasanta, LU) and Fornovolasco (Fabbriche di Vergemoli, LU). Pyrite ores mainly occur as microcrystalline lensoidal masses, often in association with baryte, within the quartz-muscovite-chlorite phyllites of the Paleozoic basement or at the contact between the phyllites and the overlying Triassic dolostones. Only recently it was recognized that the pyrite ores still occurring in large amounts in this mining area, and widely exposed in the abandoned tunnels, is strongly enriched in thallium (typically 200-300 mg/kg and up to 1100 mg/kg). In some specific localities (i.e. Monte Arsiccio mine, Sant’Anna di Stazzema, LU) Tl also occurs as macroscopic Tl-Pb-Sb-As-Hg sulphosalts, emphasizing the exceptional nature of these mineralizations. Thallium is a relatively rare but highly toxic element that is readily transferred, along with other toxic or potentially toxic elements (particularly As, Sb, Pb, Hg, Cd, Zn, etc.), from pyrite ores to the aqueous phase. Indeed the internal waters of these mines may reach extreme concentrations of Tl (typically 500-1000 μg/l and up to 9000 μg/l). The stability of the main Tl species – the Tl+ ion – dissolved in the AMD-contaminated waters over extended intervals of pH and Eh conditions, enhances the dispersion of this element into the environment; indeed it is neither easily precipitated as an insoluble solid phase nor easily adsorbed onto jarosite/ferrihydrite/schwertmannite/goethite precipitating from Fe- and sulphate-rich waters
Thallium-rich pyrite ores from the Apuan Alps, Tuscany, Italy:constraints for their origin and environmental concerns
Full text linkThe southern sector of the Apuan Alps (AA) massif, Tuscany, Italy, is characterized by the occurrence of a series of baryte–pyrite–iron oxide orebodies whose Tl-rich nature was recognized only recently. The geochemistry of the pyrite ore was investigated through inductively coupled plasma mass spectrometry. In addition, lead isotope data for selected pyrite ores from AA were collected. Pyrite ores are characterized by a complex geochemistry, with high concentrations of Tl (up to 1100 μg/g) coupled with high As and Sb contents; the Co/Ni ratio is always <1. Geochemical data of pyrite and marcasite ore samples from other mining districts of Tuscany have been collected in order to compare them with those from the AA. These samples usually have very low Tl content (less than 2 μg/g) and high to very high Co/Ni and As/Sb ratios. Only some samples from the Sb–Hg ore deposits showed very high Tl concentrations (up to ~3900 μg/g). Another difference is related to the lead isotope composition, with pyrite ores from AA markedly less radiogenic than those from the other deposits from Tuscany. Geochemical data of pyrite ores from AA give new insights on the genesis of the baryte–pyrite–iron oxide orebodies, relating their formation to low-temperature hydrothermal systems active during early Paleozoic; in addition, these data play a fundamental role in assessing the environmental impact of these deposits
The barite-pyrite-iron oxide deposits from Alpi Apuane (Tuscany, Italy): a new reference locality for thallium-bearing mineralizations hosted in low-grade metamorphic rocks
No full textLateral extrusion of a thermally weakened pluton overburden (Campiglia Marittima, Tuscany)
No full textThe ascent and emplacement of magmas in the upper crust modify the local pre-existing thermal and rheological settings. Such changes have important effects in producing anomalous structures, mass extrusion, rock fracturing, and in some conditions, hydrothermal mineralizations. In the Campiglia Marittima area, detailed field mapping led to the reconstruction of a local deformation history that overlaps, chronologically and spatially, with regional extension. This local deformation was triggered at the MioceneâPliocene boundary by the intrusion of a monzogranitic pluton beneath a carbonate sedimentary sequence. The emplacement of the pluton produced a perturbation in the rheological behaviour of the carbonate host rocks, producing transient ductile conditions in the very shallow crust. The carbonate rocks were thermally weakened and flowed laterally, accumulating downslope of the pluton roof, mainly toward the east. As the thermal anomaly was decaying, the brittleâductile boundary moved progressively back towards the pluton, and large tension gash-shaped volumes of fractured marble were generated. These fractured volumes were exploited by rising hydrothermal fluids generating sigmoidal skarn bodies and ore shoots. This work presents the Campiglia Marittima case study as a prime example of structural interference between regional extensional structures and local, lateral mass extrusion in a transient ductile rheological regime triggered by pluton emplacement
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