13 research outputs found
The Čanište Epidote-bearing pegmatite, Fyro Macedonia : an example of the magmatic-hydrothermal transition
Get PDFDivergent drift of Adriatic-Dinaridic and Moesian carbonate platforms during the rifting phase witnessed by triassic MVT Pb-Zn and SEDEX deposits; a metallogenic approach
Get PDFEarly-intracontinental rifting of Pangea is result of thermal doming in Uppermost Permian time giving rise to the formation of horst-graben structures, followed by slow subsidence, marine transgression and evaporate deposition. Consequence of incipient magmatism are numerous geothermal fields and subterrestrial hydrothermal siderite-barite-polysulfide deposits (PALINKAŠ et al, this issue). Advanced rifting magmatism as a successive stage in Middle Triassic brought intensive submarine volcanism, accompanied by coeval sedimentation of chert and siliciclastics, building up volcanogenic-sedimentary formations. Volcanic activity with explosive phases and generation of large volumes of pyroclastic rocks in the rifts produced concomitant mineralization with numerous SEDEX deposits of Fe-Mn-Ba-polysulfides. Passive continental margins flanked by the Adria-Dinaridic carbonate platform as passive continental margin of the northern Gondwanaland and Moesian carbonate platform, as a counterpart on the European passive continental margin, were divergently drifted in the coarse of the advanced rifting. A fast growing carbonate platforms, developing gradually, covered evidences of the earlier intracontinental rifting and their ore formations. On the other hand, the carbonate platforms themselves host specific Pb-Zn deposit, well known as Mississippi valley type, (MVT) or Bleiberg-Mežica type according the traditional european terminology. Triassic MVT and SEDEX deposits are symmetrically situated on the both sides of the divergent passive margins in this early history of the Tethyan ocean.</p
Safe, accurate, and precise sulfur isotope analyses of arsenides, sulfarsenides, and arsenic and mercury sulfides by conversion to barium sulfate before EA/IRMS
Get PDFThe stable isotope ratios of sulfur (δ(34)S relative to Vienna Cañon Diablo Troilite) in sulfates and sulfides determined by elemental analysis and isotope ratio mass spectrometry (EA/IRMS) have been proven to be a remarkable tool for studies of the (bio)geochemical sulfur cycles in modern and ancient environments. However, the use of EA/IRMS to measure δ(34)S in arsenides and sulfarsenides may not be straightforward. This difficulty can lead to potential health and environmental hazards in the workplace and analytical problems such as instrument contamination, memory effects, and a non-matrix-matched standardization of δ(34)S measurements with suitable reference materials. To overcome these practical and analytical challenges, we developed a procedure for sulfur isotope analysis of arsenides, which can also be safely used for EA/IRMS analysis of arsenic sulfides (i.e., realgar, orpiment, arsenopyrite, and arsenian pyrite), and mercury sulfides (cinnabar). The sulfur dioxide produced from off-line EA combustion was trapped in an aqueous barium chloride solution in a leak-free system and precipitated as barium sulfate after quantitative oxidation of hydrogen sulfite by hydrogen peroxide. The derived barium sulfate was analyzed by conventional EA/IRMS, which bracketed the δ(34)S values of the samples with three international sulfate reference materials. The protocol (BaSO(4)-EA/IRMS) was validated by analyses of reference materials and laboratory standards of sulfate and sulfides and achieved accuracy and precision comparable with those of direct EA/IRMS. The δ(34)S values determined by BaSO(4)-EA/IRMS in sulfides (arsenopyrite, arsenic, and mercury sulfides) samples from different origins were comparable to those obtained by EA/IRMS, and no sulfur isotope fractionations were introduced during sample preparation. We report the first sulfur isotope data of arsenides obtained by BaSO(4)-EA/IRMS. GRAPHICAL ABSTRACT: [Image: see text] SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00216-021-03854-y
Environmental geochemistry of the polymetallic ore deposits: Case studies from the Rude and the Sv. Jakob historical mining sites, NW Croatia
Get PDF This paper presents the results of the sampling surveys carried out in order to evaluate the environmental impact of the Rude and the Sv. Jakob historical mining sites, NW Croatia. The studied polymetallic ore deposits are differing in the mineralogical and geochemical features as well as in the host rock lithology. The Rude Fe-Cu-Pb-Zn-Ba deposit is hosted by Permian siliciclastic sediments. Siderite, hematite, galena, sphalerite, chalcopyrite, pyrite, barite and gypsum are the major ore minerals, whereas quartz is the principal gangue mineral. The Sv. Jakob Pb-Zn-Ag deposit occurs in the Middle Triassic dolostone. The most abundant ore minerals are galena, sphalerite and pyrite. Calcite and quartz represent the principal gangue minerals. Although the deposits represent the potential sources of numerous toxic metals, the pollution of the drainage streams and associated stream sediments was not recorded. The studied mining sites are characterized by the high carbonate/sulfide ratios responsible for the alkaline character of the drainage streams. Consequently, the mining sites have very low potential for generation of acid mine drainage as well as very low potential for leaching of heavy metals into the drainage systems. Furthermore, the presented study revealed that the populated areas (stream waters with decreased redox potential, increased organic matter content, high NO3-, NH4+ and PO43- concentrations; stream sediments enriched in exchangeable Pb and Zn) and the Sava river alluvium (overflowing streams enriched in Hg) represent bigger environmental threat than the investigated polymetallic ore deposits. </span
Origin and K-Ar age of the phreatomagmatic breccia at the Trepča Pb-Zn-Ag skarn deposit, Kosovo: Implications for ore-forming processes
Get PDFThe Trepča Pb-Zn-Ag skarn deposit in Kosovo is spatially and temporarily related to the phreatomagmatic breccia of Oligocene age (~23 Ma). The deposit shows features typical for skarn deposits worldwide, including a stage of isochemical metamorphism, a prograde stage of an anhydrous, low oxygen and low sulfur fugacity character and a retrograde stage characterized by an increase in the water activity as well as by an increase in oxygen and sulfur fugacities. The mineralization is hosted by the recrystallized Upper Triassic limestone. The prograde mineralization consists mainly of Ca-Fe-Mn±Mg pyroxenes. The host recrystallized limestone at the contact with the prograde (skarn) mineralization have the increased content of Fe, Mn, Mo, As, Au, Cs, Ga, REE and Y suggesting their transport by infiltrating magmatic fluids. The decreased d13C and d18O values reflect a contribution of magmatic CO2. The retrograde mineral assemblage comprises ilvaite, magnetite, arsenopyrite, pyrrhotite, marcasite, pyrite, Ca-Fe-Mn±Mg carbonates and quartz. Hydrothermal ore minerals, mostly galena, sphalerite and pyrite, were deposited contemporaneously with the retrograde stage of the skarn development. Syn-ore and post-ore carbonates reflect a diminishing influence of magmatic CO2. Syn-ore carbonates are enriched in Fe, Mg, Mn, many chalcophile elements, including Ag, As, Bi, Cd, Cu, Pb, Sb and Zn, as well as in Au, Y and REE. The post-ore stage accompanied the precipitation of significant amount of Ca-rich carbonates including the travertine deposits at the deposit surface. The phreatomagmatic breccia was developed along a NW dipping contact between the ore bearing recrystallized limestone and the overlying schist. It has an inverted cone shape with the vertical extension up to 800 m and diameter up to 150-m. The upper part of the diatreme (an underground segment of the phreatomagmatic breccia) is characterized by the presence of a hydrothermally altered rootless quartz-latite dike surrounded by an unsorted polymict breccia mantle. Despite the alteration processes, the dike has a preserved porphyritic texture. Partly preserved sanidine, accompanied with the mixture of muscovite and quartz, reflects a near-neutral to weakly acidic environment. The clasts of country rocks and skarn mineralization underwent intense milling and mixing due to repeated magmatic penetrations. Sericitization of the breccia matrix, locally accompanied with minor kaolinitization, point to an increased water activity under near-neutral to weakly acidic conditions. Large fragments originally composed of anhydrous skarn minerals (pyroxenes) are usually completely altered to a mixture of fibroradial magnetite, quartz and various amount of carbonates suggesting an increase in oxygen fugacity. Their pyrite rims reflect that the increase in oxygen fugacity was followed by an increase in sulfur fugacity. The clast predominantly composed of Fe-sulfides and minor Bi-sulfides point that the increase in sulfur fugacity was locally sufficient to complete sulfidation of hedenbergite to pyrrhotite and/or pyrite. Although the phreatomagmatic breccia at the Trepča Pb-Zn-Ag skarn deposit does not carry significant amounts of the ore mineralization, its formation was crucial for the ore deposition. Phreatomagmatic explosions and formation of the breccia turned the system from the lithostatic to hydrostatic regime and triggered the retrograde stage increasing the water activity and oxygen fugacity in the system. In addition, cooling and decompression of the system contributed to more effective degassing of magmatic sulfur increased the sulfur fugacity. </p
Permian–polysulphide-siderite–barite–haematite deposit Rude in Samoborska Gora Mts., Zagorje–Transdanubian zone of the Inner Dinarides
Get PDFSamoborska Gora Mts. is situated within westernmost part of the Zagorje–Mid–Transdanubian zone of the Inner Dinarides. The Samoborska Gora Mts. consists dominantly of Permian unmetamorphosed siliciclastic sediments and evaporites, overlain by Lower Triassic sediments. Rude mineralization is hosted by Permian siliciclastic sediments, beneath gypsum and anhydrite strata. Central part of the deposit consists of 1.5 km long stratabound mineralization, grading laterally into ferruginous sandstone and protruding vertically into a gypsum–anhydrite layer. Siderite–polysulfide–barite–quartz veins are located underneath the stratabound mineralization. Late stage galena–barite veins overprints the formerly formed mineralization types. The Rude ore deposit was generated by NaCl±CaCl2–H2O solutions. Stratabound mineralization was precipitated from solutions with salinities between 7 and 11 wt. % NaCl equ., homogenizing between 150°C to 230°C. Vein type mineralization derived from solutions with salinities between 4 and 20 wt. % NaCl equ., homogenizing between 80°C and 160°C, while late stage galena–barite veins were precipitated from solutions with salinities between 11 and 16 wt. % NaCl equ., homogenizing between 100°C to 140°C. Fluid inclusions bulk leachate chemistry recorded Na+>Mg2+>K+>Ca2+>Li+ and Cl–>SO42– ions. Sulfur isotope composition of barites and overlying gypsum steams from the Permian seawater sulfate, supported by increased Br– content, which follows successively the seawater evaporation line. The sulfur isotopic composition of sulfides varies between –0.2 and +12.5 ‰, as a result of thermal reduction of Permian marine sulfate. Ore–forming fluids were produced by hydrothermal convective cells (reflux brine model) and derived primarily from Permian seawater,- modified by evaporation and interaction with the Permian sedimentary rocks. Rude deposits in Samoborska Gora Mts. may be declared as a prototype of the Permian siderite–polysulfide–barite deposits, products of the rifting along the passive Gondwana margin, in the Inner Dinarides, and their equivalents in extension northeastward into Zagorje–Transdanubian Zone and Gemerides, and southeastward to Hellenide–Albanides.Samoborska Gora Mts. is situated within the westernmost part of the Zagorje–Mid–Transdanubian zone of the Inner Dinarides. The Samoborska Gora Mts. predominantly consists of Permian unmetamorphosed siliciclastic sediments and evaporites, overlain by Lower Triassic sediments. Rude mineralization is hosted by Permian siliciclastic sediments, below gypsum and anhydrite strata. The central part of the deposit consists of a 1.5 km long stratabound mineralization, grading laterally into ferruginous sandstone and protruding vertically into a gypsum–anhydrite layer. Siderite–polysulphide–barite–quartz veins are located below the stratabound mineralization. The stratiform part of the deposit is situated above the stratabound and consists of haematite lajer with barite concretions and veinlets. Late stage galena–barite veins overprint earlier types of mineralization. The Rude ore deposit was generated by predominantly NaCl ±} CaCl2–H2O solutions. Detrital quartz from stratiform mineralization was precipitated from solutions with salinities between 7 and 11 wt. % NaCl equ., homogenizing between 150 °C to 230 °C. Stratabound/siderite–polysulphide–barite–quartz vein type mineralization was derived from solutions with salinities between 5 and 19 wt. % NaCl equ., homogenizing between 80 °C and 160 °C, while late stage galena–barite veins were precipitated from solutions with salinities between 11 and 16 wt. % NaCl equ., homogenizing between 100 °C to 140 °C. Fluid inclusion bulk leachate chemistry recorded Na+>Mg2+>K+>Ca2+>Li+ and Cl–>SO4 2–ions. Sulphur isotope composition of barites and overlying gypsum stems from Permian seawater sulphate, supported by increased Br– content, which follows successively the seawater evaporation line. The sulphur isotopic composition of sulphides varies between –0.2 and +12.5 ‰, as a result of thermal reduction of Permian marine sulphate. Ore–forming fluids were produced by hydrothermal convective cells (reflux brine model), and were derived primarily from Permian seawater, modified by evaporation and interaction with Permian sedimentary rocks. Rude deposits in SamoborskaGora Mts. may be declared as a precursor? of the Permian siderite–polysulphide–barite deposits (products of rifting along the passive Gondwana margin), in the Inner Dinarides, and their equivalents extending northeastward into the Zagorje–Transdanubian Zone and the Gemerides, and southeastward to the Hellenide–Albanides
The evolution of the Čanište epidote-bearing pegmatite, Republic of Macedonia: evidence from mineralogical and geochemical features
Get PDFThe epidote-bearing Čanište pegmatite and adjacent Upper Carboniferous granodiorites cut Precambrian gneises, at the western slopes of the Selečka Mts., the Eastern Pelagonian zone, FYRO Macedonia. The pegmatite exhibits zonal internal structure with the following sub-units: the wall zone (amazonite microcline ± biotite, quartz), the first intermediate zone (epidote + hematite + grossular + muscovite + quartz + almandine ± zircon, beryl, microcline, quartz), the second intermediate zone (albite + quartz ± microcline) and the core (massive quartz). According to the microprobe data epidote belongs to clinozoisite subgroup with formula (Ca1.96-1.99Mn0.02-0.03Fe2+0.00-0.02)(Al2.17-2.46Fe3+0.51-0.82Ti0.00-0.01)(Si2O7)(Si0.99-1.00Al0.00-0.01O4)O(OH). The occurrences of almandine and zircon with low U, Th and REE content, are indicative to weakly evolved granitic/granodioritic rocks. The absence of aplites suggests steady pressure condition during the course of pegmatite crystallization. Microthermometric data combined by the two-feldspar geothermometer gained pressure from 4.8 to 5.6 kbar for the second intermediate zone. The wall zone, composed of amazonite microcline, crystallized at temperature between 650 and 760. Dropping of melt temperature below 550°C, under the oxygen fugacity between 10-22 and 10-19.5 bar, was the principal trigger for deposition of minerals in the first intermediate zone. The residual fluid, depleted in Ca, Fe and K, and enriched in water, Na and Si, caused deposition of the second intermediate zone (albite + quartz) at temperature between 445 and 465°C. The massive quartz core crystallized in the very last stage of the pegmatite evolution (T ≈ 400-480°C) from melt residue enriched in silica, water and CO2 content.</p
Volcanoes in the Adriatic Sea: Permo-Triassic magmatism on the Adriatic-Dinaridic carbonate platform
Get PDFAn experimental study of the effect of water and chlorine on plagioclase nucleation and growth in mafic magmas: application to mafic pegmatites
Get PDFInternational audienceIn this study, the effects of H2O and Cl on the grain size and nucleation delay of plagioclase in basaltic magma were investigated using dynamic and equilibrium experiments at 1150 ∘C, 300 MPa, and oxygen fugacity between FMQ − 1.65 and FMQ + 0.05 (fayalite-magnetite-quartz). Each experiment consisted of five samples of basaltic composition (from the Hamn intrusion in Northern Norway) containing varying amounts of H2O (up to 2 wt %) and Cl (up to 1 wt %). The equilibrium experiments were used as a reference frame for the phase assemblage, geochemical composition, and liquidus temperatures and were compared to thermodynamic models using MELTS software. Experimental phase abundances and plagioclase compositions are in good agreement with the predictions of MELTS. The dynamic experiments were initially heated above the liquidus temperature to destroy crystal nuclei and then kept at 1150 ∘C for 100, 250, or 1800 min. These experiments show that as the concentration of H2O in the melt increases, plagioclase nucleation is delayed, plagioclase abundance decreases, but its size increases. Therefore, the addition of H2O seems to favor plagioclase growth at the expense of nucleation. Thermodynamic and kinetic calculations corroborate an increase in the nucleation delay of plagioclase with increasing H2O content dissolved in the melt, suggesting that H2O decreases the undercooling of the silicate melt. The addition of Cl also seems to delay plagioclase nucleation, although this is not supported by kinetic calculations. Increasing the Cl content decreases plagioclase abundance but does not significantly affect its size. The homogeneous pegmatitic pockets of the mafic-ultramafic Hamn intrusion exhibit several petrological and geochemical features, suggesting that H2O and Cl enrichment in the silicate melt was the origin of the pegmatitic texture. The experimental results presented here indicate that H2O, rather than Cl, may have played an important role in the formation of the pegmatitic texture
Formation Conditions and <sup>40</sup>Ar/<sup>39</sup>Ar Age of the Gem-Bearing Boqueirão Granitic Pegmatite, Parelhas, Rio Grande do Norte, Brazil
Get PDFThe Boqueirão granitic pegmatite, alias Alto da Cabeça pegmatite, is situated in Borborema Pegmatitic Province (BPP) in Northeast Brazil. This pegmatitic province hosts globally important reserves of tantalum and beryllium, as well as significant quantities of gemstones, including aquamarine, morganite, and the high-quality turquoise-blue “Paraíba Elbaite„. The studied lithium-cesium-tantalum Boqueirão granitic pegmatite intruded meta-conglomerates of the Equador Formation during the late Cambrian (502.1 ± 5.8 Ma; 40Ar/39Ar plateau age of muscovite). The pegmatite exhibits a typical zonal mineral pattern with four defined zones (Zone I: muscovite, tourmaline, albite, and quartz; Zone II: K-feldspar (microcline), quartz, and albite; Zone III: perthite crystals (blocky feldspar zone); Zone IV: massive quartz). Huge individual beryl, spodumene, tantalite, and cassiterite crystals are common as well. Microscopic examinations revealed that melt inclusions were entrapped simultaneously with fluid inclusions, suggesting the magmatic–hydrothermal transition. The magmatic–hydrothermal transition affected the evolution of the pegmatite, segregating volatile compounds (H2O, CO2, N2) and elements that preferentially partition into a fluid phase from the viscous silicate melt. Fluid inclusion studies on microcline and associated quartz combined with microthermometry and Raman spectroscopy gave an insight into the P-T-X characteristics of entrapped fluids. The presence of spodumene without other LiAl(SiO3)2 polymorphs and constructed fluid inclusion isochores limited the magmatic–hydrothermal transition at the gem-bearing Boqueirão granitic pegmatite to the temperature range between 300 and 415 °C at a pressure from 1.8 to 3 kbar
