Composition Of Pyrite Research Articles

Diagenetic formation of gypsum and dolomite in a cold-water coral mound in the Porcupine Seabight, off Ireland

Authigenic gypsum was found in a gravity core, retrieved from the top of Mound Perseverance, a giant cold-water coral mound in the Porcupine Basin, off Ireland. The occurrence of gypsum in such an environment is intriguing, because gypsum, a classic evaporitic mineral, is undersaturated with respect to sea water. Sedimentological, petrographic and isotopic evidence point to diagenetic formation of the gypsum, tied to oxidation of sedimentary sulphide minerals (i.e. pyrite). This oxidation is attributed to a phase of increased bottom currents which caused erosion and enhanced inflow of oxidizing fluids into the mound sediments. The oxidation of pyrite produced acidity, causing carbonate dissolution and subsequently leading to pore-water oversaturation with respect to gypsum and dolomite. Calculations based on the isotopic compositions of gypsum and pyrite reveal that between 21·6% and 28·6% of the sulphate incorporated into the gypsum derived from pyrite oxidation. The dissolution of carbonate increased the porosity in the affected sediment layer but promoted lithification of the sediments at the sediment-water interface. Thus, authigenic gypsum can serve as a signature for diagenetic oxidation events in carbonate-rich sediments. These observations demonstrate that fluid flow, steered by environmental factors, has an important effect on the diagenesis of coral mounds.

Nucleation, growth and oxidation of framboidal pyrite associated with hydrocarbon-derived submarine chimneys: lessons learned from the Gulf of Cadiz

In order to establish the history and conditions of nucleation and growth of pyrite formed inside methane-derived carbonate chimneys collected in the seafloor of the Gulf of Cadiz, we compared the size distributions, morphologies, textures and geochemical compositions of framboidal and euhedral pyrite as well as iron oxyhydroxides pseudomorphs. More than 2400 framboids and crystals were measured and four types of statistical populations were identified. Framboid size (diameter) ranges from 6 to 12.5 μm with a mean size of 10.4 μm and a maximum value of 27.9 μm, whereas euhedral crystal size (maximum dimension) ranges from 6.3 to 9 μm with a mean size of 7.2 μm and a maximum value of 21.6 μm. Crystal size distributions (CSD) of different populations of framboidal iron oxyhydroxides show strongly negatively skewed shapes, close to the universal steady-state CSD curve for Ostwald ripening, an unequivocal signal of closed-system growth. Euhedral crystal populations of pyrite and iron oxyhydroxides present CSDs with lognormal or slightly negatively skewed lognormal shapes and low size variances, indications of open-system growth. This was confirmed by simulating framboidal and euhedral crystal populations with different growth mechanisms using the GALOPER (Growth According to the Law of Proportionate Effect) program. From CSDs shapes and the values of α and β 2 , the populations of framboids are inferred to have grown initially in an open system (surface and then transport-controlled) and then in a closed system (Ostwald ripening) and the populations of euhedral crystals only in an open system. In this case, the initial stage of surface-controlled growth is shorter than that deduced for the framboidal populations. We suggest that: (1) the concentration and availability of reactive iron and hydrogen sulphide are the main factors controlling the morphology and growth of pyrite, and (2) the higher reactive surface of framboidal textures would govern their preferential oxidation, dissolution and recrystallization during the closed-system growth and consequently the development of higher sizes in comparison with euhedral forms.

THE LEAD ISOTOPE COMPOSITION OF ORE MINERALS FROM PRECIOUS METAL-BEARING, POLYMETALLIC VEIN SYSTEMS IN THE COBALT EMBAYMENT, NORTHERN ONTARIO: METALLOGENETIC IMPLICATIONS

The Cobalt Embayment is a large (~60,000 km 2 ), irregular domain of Paleoproterozoic (2.5–2.2 Ga) siliciclastic sedimentary rocks (i.e., the Huronian Supergroup) that unconformably overlies Archean basement rocks of the Abitibi greenstone belt. The Nipissing Diabase, regionally distributed complex of mafic sills and dikes intruded the Huronian sedimentary rocks ca. 2.2 Ga. The sedimentary rocks were subsequently affected by subgreenschist facies metamorphism and by a regionally distributed K and Na metasomatic events, at ca. 1.7 Ga, related to the Penokean orogeny. Although best known for the economically important Ag-Co veins of the Cobalt mining camp, the Cobalt Embayment also hosts numerous other hydrothermal, base and precious metal-mineralized calcite-quartz vein systems. The lead isotope compositions of pyrite and chalcopyrite from nine widely separated polymetallic vein systems yield a Pb-Pb errorchron age of 2236 ± 180 Ma ( n = 24). In contrast, the Pb isotope compositions of late-stage galena ( n = 11) from six regionally distributed vein systems yield a Pb-Pb secondary isochron age of ca. 1675 Ma. These Pb isotope data for the mineralized vein systems demonstrate the occurrence of at least two major episodes of hydrothermal fluid activity throughout the Cobalt Embayment, ca. 2220 Ma and ca. 1700 Ma, indicate that the emplacement of the Nipissing Diabase was the most likely driver of regional hydrothermal fluid circulation at ca. 2200 Ma, and provide supporting evidence for the basin-wide extent of the regional K and Na metasomatic event at ca. 1700 Ma, most likely related to the waning stages of the Penokean orogeny.

Multiple sulphur and iron isotope composition of detrital pyrite in Archaean sedimentary rocks: A new tool for provenance analysis

Multiple S ( δ 34S and δ 33S) and Fe ( δ 56Fe) isotope analyses of rounded pyrite grains from 3.1 to 2.6 Ga conglomerates of southern Africa indicate their detrital origin, which supports anoxic surface conditions in the Archaean. Rounded pyrites from Meso- to Neoarchaean gold and uranium-bearing strata of South Africa are derived from both crustal and sedimentary sources, the latter being characterised by non-mass dependent fractionation of S isotopes ( Δ 33S as negative as − 1.35‰) and large range of Fe isotope values ( δ 56Fe between − 1.1 and 1.2‰). Most sediment-sourced pyrite grains are likely derived from sulphide nodules in marine organic matter-rich shales, sedimentary exhalites and volcanogenic massive sulphide deposits. Some sedimentary pyrite grains may have been derived from in situ sulphidised Fe-oxides, prior to their incorporation into the conglomerates, as indicated by unusually high positive δ 56Fe values. Sedimentary sulphides without significant non-mass dependent fractionation of S isotopes were also present in the source of some conglomerates. The abundance in these rocks of detrital pyrite unstable in the oxygenated atmosphere may suggest factors other than high pO 2 as the cause for the absence of significant non-mass dependent fractionation processes in the 3.2–2.7 Ga atmosphere. Rounded pyrites from the c. 2.6 Ga conglomerates of the Belingwe greenstone belt in Zimbabwe have strongly fractionated δ 34S, Δ 33S and δ 56Fe values, the source of which can be traced back to black shale-hosted massive sulphides in the underlying strata. The study demonstrates the utility of combined multiple S and Fe isotope analyses for provenance reconstruction of Archaean sedimentary successions.

Origin of siderite mineralisation in Petrova and Trgovska Gora Mts., NW Dinarides

The Petrova and Trgovska Gora Mts. (Gora=Mountain) are Variscan basement units incorporated into the northwestern Dinarides during the Alpine orogeny. They host numerous siderite-quartz-polysulphide, siderite-chalcopyrite, siderite-galena and barite veins, as well as stratabound hydrothermal-replacement ankerite bodies within carbonates in non-metamorphosed, flysch-like Permo-Carboniferous sequences. The deposits have been mined for Cu, Pb, Ag and Fe ores since Medieval times. Fluid inclusion studies of quartz from siderite-polysulphide-quartz and barite veins of both regions have shown the presence of primary aqueous NaCl−CaCl2±MgCl2−H2O±CO2 inclusions. The quartz-sulphide stage of both regions show variable salinities; 2.7–26.2 wt% NaCl eq. for the Trgovska Gora region and 3.4–23.4 wt% NaCl eq. for the Petrova gora region, and similar homogenisation temperatures (100–230°C). Finally, barite is precipitated from low salinity-low temperature solutions (3.7–15.8 wt % NaCl equ. and 115–145°C). P-t conditions estimated via isochore construction yield formation temperatures between 180–250°C for the quartz-sulphide stage and 160–180°C for the barite stage, using a maximum lithostatic pressure of 1 kbar (cc. 3 km of overburden). The sulphur isotope composition of barite from both deposits indicates the involvement of Permian seawater in ore fluids. This is supported by the elevated bromium content of the fluid inclusion leachates (120–660 ppm in quartz, 420–960 ppm in barite) with respect to the seawater, indicating evaporated seawater as the major portion of the ore-forming fluids. Variable sulphur isotope compositions of galena, pyrite and chalcopyrite, between −3.2 and +2.7‰, are interpreted as a product of incomplete thermal reduction of the Permian marine sulphate mixed with organically- and pyrite-bound sulphur from the host sedimentary rocks. Ore-forming fluids are interpreted as deep-circulating fluids derived primarily from evaporated Permian seawater and later modified by interaction with the Variscan basement rocks. 40Ar/39Ar data of the detrital mica from the host rocks yielded the Variscan age overprinted by an Early Permian tectonothermal event dated at 266–274 Ma. These ages are interpreted as those reflecting hydrothermal activity correlated with an incipient intracontinental rifting in the Tethyan domain. Nevertheless, 75 Ma recorded at a fine-grained sericite sample from the alteration zone is interpreted as a result of later resetting of white mica during Campanian opening/closure of the Sava back arc in the neighbouring Sava suture zone (Ustaszewski et al. 2008).

Stable isotope analysis of the Cretaceous sulfur cycle

We report the sulfur and oxygen isotope composition of sulfate (δ 34S SO4 and δ 18O SO4, respectively) in coexisting barite and carbonate-associated sulfate (CAS), which we use to explore temporal variability in the marine sulfur cycle through the middle Cretaceous. The δ 34S SO4 of marine barite tracks previously reported sulfur isotope data from the tropical Pacific. The δ 18O SO4 of marine barite exhibits more rapid and larger isotopic excursions than the δ 34S SO4 of marine barite; these excursions temporally coincide with Ocean Anoxic Events (OAEs). Neither the δ 34S SO4 nor the δ 18O SO4 measured in marine barite resembles the δ 34S SO4 or the δ 18O SO4 measured in coexisting CAS. Culling our data set for elemental parameters suggestive of carbonate recrystallization (low [Sr] and high Mn/Sr) improves our record of δ 18O SO4 in CAS in the Cretaceous. This suggests that the CAS proxy can be impacted by carbonate recrystallization in some marine sediments. A box model is used to explore the response of the δ 34S SO4 and δ 18O SO4 to different perturbations in the marine biogeochemical sulfur cycle. We conclude that the δ 34S SO4 in the middle Cretaceous is likely responding to a change in the isotopic composition of pyrite being buried, coupled possibly with a change in riverine input. On the other hand, the δ 18O SO4 is likely responding to rapid changes in the reoxidation pathway of sulfide, which we suggest may be due to anoxic versus euxinic conditions during different OAEs.

Origin of two distinct multiple-sulfur isotope compositions of pyrite in the 2.5 Ga Klein Naute Formation, Griqualand West Basin, South Africa

Quadruple sulfur isotope ratios ( 32S / 33S/ 34S/ 36S) were measured by a high precision SF 6 method for early diagenetic pyrite in the 2.5 Ga upper Prieska facies of the Griqualand West Basin from the Agouron drill core GKP01. Measured Δ 33S (≈ δ 33S–0.515δ 34S) values range between −2.3 and +8.5‰ with no apparent meter-scale stratigraphic trend for 70 m section. It was found that early diagenetic pyrites occur in two texturally and isotopically distinct populations such that bulk rock isotope data would reflect mixing of these two sulfur pools. Nodular and layered pyrite yield mostly negative (down to −2.3‰) and relatively constant Δ 33S values over a few tens of cm scale. Disseminated pyrites, in contrast, yield positive (0.0–8.5‰) Δ 33S values that are heterogeneous in sub-cm scales. The former pyrite sulfur was likely derived from seawater sulfate through microbial sulfate reduction, and the latter preferentially sampled aqueous H 2S-S 0 reservoirs in late Archean oceans. Relatively constant Δ 33S values for layered pyrite suggest Archean sulfate reservoirs had residence times of a few million years. Most data yield a well-defined Δ 36S/Δ 33S ratios of −0.9, suggesting predominance of a single S-MIF source reaction. Four analyses of a two cm length sample (306.5 m) yield Δ 36S/Δ 33S slope of −1.6. This slope is consistent with the relationship expected for a symmetry-breaking isotope effect during the S + S 2 reaction, but deviations from the main Archean array (i.e., Δ 36S/Δ 33S = −0.9) may also result from various combinations of SO photolysis and SO 2 oxidation. High spatial resolution-high precision SF 6 measurements of Archean pyrite provide significant new insights into the origin of Archean sulfur mass-independent fractionation (S-MIF) and the late Archean sulfur cycle.

A geochemical study of the Sweet Home Mine, Colorado Mineral Belt, USA: hydrothermal fluid evolution above a hypothesized granite cupola

Deposition of quartz–molybdenite–pyrite–topaz–muscovite–fluorite and subsequent hübnerite and sulfide–fluorite–rhodochrosite mineralization at the Sweet Home Mine occurred coeval with the final stage of magmatic activity and ore formation at the nearby world-class Climax molybdenum deposit about 26 to 25 m.y. ago. The mineralization occurred at depths of about 3,000 m and is related to at least two major fluid systems: (1) one dominated by magmatic fluids, and (2) another dominated by meteoric water. The sulfur isotopic composition of pyrite, strontium isotopes and REY distribution in fluorite suggest that the early-stage quartz–molybdenite–pyrite–topaz–muscovite–fluorite mineral assemblage was deposited from magmatic fluids under a fluctuating pressure regime at temperatures of about 400°C as indicated by CO2-bearing, moderately saline (7.5–12.5 wt.% NaCl equiv.) fluid inclusions. LA-ICPMS analyses of fluid inclusions in quartz demonstrate that fluids from the Sweet Home Mine are enriched in incompatible elements but have considerably lower metal contents than those reported from porphyry–Cu–Au–Mo or Climax-type deposits. The ore-forming fluid exsolved from a highly differentiated magma possibly related to the deep-seated Alma Batholith or distal porphyry stock(s). Sulfide mineralization, marking the periphery of Climax-type porphyry systems, with fluorite and rhodochrosite as gangue minerals was deposited under a hydrostatic pressure regime from low-salinity ± CO2-bearing fluids with low metal content at temperatures below 400°C. The sulfide mineralization is characterized by mostly negative δ34S values for sphalerite, galena, chalcopyrite, and tetrahedrite, highly variable δ18O values for rhodochrosite, and low REE contents in fluorite. The Pb isotopic composition of galena as well as the highly variable 87Sr/86Sr ratios of fluorite, rhodochrosite, and apatite indicates that at least part of the Pb and Sr originated from a much more radiogenic source than Climax-type granites. It is suggested that the sulfide mineralization at the Sweet Home Mine formed from magmatic fluids that mixed with variable amounts of externally derived fluids. The migration of the latter fluids, that were major components during late-stage mineralization at the Sweet Home Mine, was probably driven by a buried magmatic intrusion.

Study of the effect of ultrasonic treatment on the surface composition and the flotation performance of high-sulfur coal

This paper highlighted the use of X-ray diffraction, scanning electron microscopy and X-ray fluorescence spectroscopy to investigate the changes on the surface composition of high-sulfur coal and pyrite before and after ultrasonic conditioning. The results showed that ultrasonic conditioning resulted in a decrease in the contents of iron and sulfur in coal, an increase in the content of element carbon, and an increase in the purity of the coal. Conversely, ultrasonic conditioning led to an increase in the content of iron and sulfur in pyrite, a decrease in the impure content of calcium, and a relative increase in the purity of the pyrite after ultrasonic conditioning. This study verified that on the one hand, ultrasonic conditioning can promote the pyrite separation from the high-sulfur coal, with the separated pyrite taking the form of FeS; on the other hand, it can produce a cleaning effect on the surface of coal and pyrite with the consequent increase both in hydrophobicity of coal and hydrophilicity of pyrite. The paper introduced ultrasonic pre-treatment of the slurry and stepped froth removal tests of high-sulfur coal and the study on the yield, ash and sulfur content of clean coal in different phases. The results gave further evidence of the increases both in the rate and the selectivity of flotation. This study shows that ultrasonic conditioning can enhance the performance of de-sulphurization of high-sulfur coal flotation.

Fluid inclusion and Re–Os isotopic evidence for hot, Cenozoic mineralization in the central Pennsylvanian Valley and Ridge Province

Hypotheses concerning processes and timing of hydrothermal sulfide mineralization in the central Pennsylvanian Appalachians utilize Mississippi Valley-type (MVT) models with Paleozoic ages. To examine this model, we studied sulfide-bearing veins in the Skytop sulfide occurrence that contain pyrite<galena<sphalerite and occurs in central Pennsylvania, USA. In this study, we obtained Re–Os isotope compositions of hydrothermal pyrite and fluid inclusion data from hydrothermal quartz intergrown with these pyrites.

Carbon and sulfur isotopic compositions of basal Datangpo Formation, northeastern Guizhou, South China: Implications for depositional environment

Isotopic compositions of Mn-carbonate and organic carbon from the same individual samples and sulfur isotopic compositions of pyrites in the basal Datangpo Formation were analyzed. Highly 34S-enriched pyrites ( δ 34S pyrite = 31.7–59.4‰) were precipitated in relatively occlusive pore water under anoxic condition in sediments, which is consistent with the observation of large and scattered pyrite framboids. The sulfidic deep ocean was not “oxidized” in the early Datangpo interglacial interval, thus the level of seawater sulfate remained low and marine δ 34S sulphate remained high. Low δ 13C car (average −7.4‰) and abnormal relationship between δ 13C car and fractionation ( Δ car–org) imply that the negative δ 13C car excursion may have resulted from oxidation of part of a large organic carbon reservoir. High Δ car–org (average 25.1‰) implicates high CO 2 level in the atmosphere. Small standard deviation (1.0‰) of δ 13C car values indicates the Mn-carbonate was precipitated near the water–sediment interface under dysoxic conditions rather than in occlusive pore water in sediments.

GOLD-BEARING As-RICH PYRITE AND ARSENOPYRITE FROM THE EL VALLE GOLD DEPOSIT, ASTURIAS, NORTHWESTERN SPAIN

The El Valle deposit is included within the El Valle – Boinas Au–Cu deposit in Asturias, northwestern Spain, an important gold-producer in Europe. Gold mineralization occurs within a Cu–Au skarn overprinted by a younger hydrothermal process accompanying the intrusion of subvolcanic rocks, which produced oxidation, silicification, argillization and sulfidation. The gold produced by this process is “invisible gold”, and the main ore minerals in unoxidized zones are pyrite and arsenopyrite. Their textures and major- and trace-element composition, determined by EPMA and SEM, allowed us to distinguish three generations of arsenopyrite and four of pyrite. Among these, pyrite II is the only one that is rich in trace elements, As being the most abundant (up to 9.5 wt%), together with Au (up to 800 ppm), Sb (5000–18000 ppm), Ni (1000–2000 ppm), Tl (500–9000 ppm), Cu (100–6000 ppm), Hg (600–1200 ppm) and Se (up to 2000 ppm). This As-rich pyrite II displays various textures, sizes and morphologies. Where it occurs as a late colloform overgrowth, it has the highest amount in As and other trace elements except Au, which mainly occurs where this pyrite has a pyritohedral habit and small size. The pyritohedra commonly result from sulfidation of pre-existing Fe-bearing minerals. All types of arsenopyrite contain gold (1250–3000 ppm) and other trace elements such as Cu (200–1300 ppm), Sb (up to 9000 ppm) and Tl (3000–4500 ppm). This study shows that the highest contents of Au are in the As-rich zones of Py II pyritohedra and in arsenopyrite. Moreover, a slightly negative correlation between the Au and Fe is observed in the compositions of Au-bearing pyrite and arsenopyrite crystals, and the Au/As values are below the solubility limit proposed in the literature. We favor a mechanism in which gold is removed from ore fluids by chemisorption at As-rich, Fe-deficient surface sites and incorporated into the sulfides as solid solution. This process took place during sulfidation of the host rocks.

Fluid Evolution and Origins of Iron Oxide Cu-Au Prospects in the Olympic Dam District, Gawler Craton, South Australia

Geologic observations suggest two stages of hydrothermal activity at a number of presently subeconomic iron oxide copper-gold systems in the Olympic Dam district, eastern Gawler craton. They contain high-, and moderate- to low-temperature Fe oxide-rich hydrothermal alteration. The mineral assemblages include magnetite-calc-silicate-alkali feldspar ± Fe-Cu sulfides and hematite-sericite-chlorite-carbonate ± Fe-Cu sulfides ± U, REE minerals. In all documented prospects, the minerals of the hematitic assemblages replace the minerals of the magnetite-rich assemblages. The bulk of the subeconomic Cu-Au mineralization is associated with the hematitic alteration assemblages. Microanalysis by proton ion probe (PIXE) of hypersaline fluid inclusions in magnetite-rich assemblages, however, demonstrates that significant amounts of copper (>500 ppm) were transported by the early-stage high-temperature (>400°C) fluids responsible for the magnetite-rich alteration. These brine inclusions contain multiple solid phases (liquid + vapor + multiple solids) including chalcopyrite in some cases. In comparison, inclusions of the hematitic stage are relatively simple liquid + vapor types, with homogenization temperatures of 200° to 300°C and containing 1 to 8 wt percent NaCl equiv. The Br/Cl ratios of the magnetite-forming fluids measured by PIXE lie beyond the range of typical magmatic and/or mantle values, allowing for the possibility that the fluids originated as brines from a sedimentary basin or the crystalline basement. Sulfur isotope compositions of chalcopyrite and pyrite demonstrate that sulfur in both alteration assemblages was derived either from cooling magmas and/or crystalline igneous rocks carried by relatively oxidized fluids (∑SO42− ≈ ∑ H2S, δ34Ssulfides from −5 to +2‰) or from crustal sedimentary rocks (δ34Ssulfides from +5 to +10‰). Oxygen and hydrogen isotope compositions of waters calculated for minerals of the magnetite-rich assemblage have δ18O values of +7.7 to +12.8 per mil and δD values of −15 to −21 per mil. The only available δ18O and δDfluid values for the hematitic assemblage are +4.7 and −9 per mil, respectively. The isotopic compositions of both fluids, coupled with the available literature data, can be explained in terms of fluid reequilibration with felsic Gawler Range Volcanics or other felsic igneous rocks in the region and with metasedimentary rocks of the Wallaroo Group at low water-to-rock ratios prior to their arrival at the mineralization sites. The lack of significant copper mineralization associated with magnetite-forming fluids that carried copper suggests that there was no effective mechanism of saturation of copper minerals or the quantity of these fluids was not sufficient to produce appreciable copper mineralization. Association of the copper-gold mineralization with the hematitic alteration in the subeconomic prospects can be explained by a two-stage model in which preexisting hydrothermal magnetite with minor associated copper-gold mineralization was flushed by late-stage oxidized brines that had extensively reacted with sedimentary or metamorphic rocks. The reduction of these brines, driven by conversion of magnetite to hematite, resulted in precipitation of copper and gold. The oxidized brines may have contributed additional copper and gold to the system in addition to upgrading preexisting subeconomic Cu-Au mineralization. When compared to published models for the Olympic Dam deposit, the new data for fluids in subeconomic Fe-oxide Cu-Au prospects of the Olympic Dam district indicate the diversity of origins of iron oxide-copper-gold systems, even within the same geologic region.

Geochronology and stable isotope signature of alteration related to hydrothermal magnetite ores in Central Anatolia, Turkey

Hydrothermal iron ores at Divrigi, east Central Anatolia, are contained in two orebodies, the magnetite-rich A-kafa and the limonitic B-kafa (resources of 133.8 Mt with 56% Fe and 0.5% Cu). The magnetite ores are hosted in serpentinites of the Divrigi ophiolite at the contact with plutons of the Murmano complex. Hydrothermal biotite from the Divrigi A-kafa yield identical weighted mean plateau ages of 73.75 ± 0.62 and 74.34 ± 0.83 Ma (2σ). This biotite represents a late alteration phase, and its age is a minimum age for the magnetite ore. Similar magnetite ores occur at Hasancelebi and Karakuz, south of Divrigi. There, the iron ores are hosted in volcanic or subvolcanic rocks, respectively, and are associated with a voluminous scapolite ± amphibole ± biotite alteration. At Hasancelebi, biotite is intergrown with parts of the magnetite, and both minerals formed coevally. The weighted mean plateau ages of hydrothermal biotite of 73.43 ± 0.41 and 74.92 ± 0.39 Ma (2σ), therefore, represent mineralization ages. Hydrothermal biotite from a vein cutting the scapolitized host rocks south of the Hasancelebi prospect has a weighted mean plateau age of 73.12 ± 0.75 Ma (2σ). This age, together with the two biotite ages from the Hasancelebi ores, constrains the minimum age of the volcanic host rocks, syenitic porphyry dikes therein, and the scapolite alteration affecting both rock types. Pyrite and calcite also represent late hydrothermal stages in all of these magnetite deposits. The sulfur isotope composition of pyrite between 11.5 and 17.4‰ δ34S(VCDT) points towards a non-magmatic sulfur source of probably evaporitic origin. Calcite from the Divrigi deposit has δ18O(VSMOV) values between +15.1 and +26.5‰ and δ13C(VPDB) values between −2.5 and +2.0‰, which are compatible with an involvement of modified marine evaporitic fluids during the late hydrothermal stages, assuming calcite formation temperatures of about 300°C. The presence of evaporite-derived brines also during the early stages is corroborated by the pre-magnetite scapolite alteration at Divrigi, and Hasancelebi-Karakuz, and with paleogeographic and paleoclimatic reconstructions. The data are compatible with a previously proposed genetic model for the Divrigi deposit in which hydrothermal fluids leach and redistribute iron from ophiolitic rocks concomitant with the cooling of the nearby plutons.

Changes in biomarker abundances and sulfur isotopes of pyrite across the Permian–Triassic (P/Tr) Schuchert Dal section (East Greenland)

In this study, we report on biomarker abundances through parts of the Permian/Triassic boundary (PTB) of Schuchert Dal (East Greenland) that contains rich marine faunal records and excellent terrestrial palynological records. Biomarker abundances and sulfur isotopes are used to correlate the series of events (including changes in element cycling and associated redox conditions of the ocean) surrounding the collapse of the marine and terrestrial ecosystems through this record of a major crisis of life on Earth during a mass extinction episode. The Upper Schuchert Dal Formation contains a low diversity palynological assemblage, ascribed to arborescent cordiaite–conifer–pteridosperm vegetation. Samples from this pre-collapse interval are characterised by high abundances of dibenzofuran (DBF), dibenzothiophene (DBT) and biphenyl. Since these compounds have similar base structures, and show comparable abundance curves, it is plausible that they probably derive from a common source. We propose that phenolic compounds of lignin of the woody plants present during this period could be the source for DBF, DBT and biphenyl. The redox conditions during this period of time also support the formation of DBF and DBT. Just above the extinction interval, there is a dramatic decrease in the abundances of DBF and DBT which occurs at the same time as a sudden change in the stable sulfur isotopic composition ( δ 34S) of pyrite, indicating a change in redox conditions from oxic to anoxic/euxinic conditions. δ 34S values leading up to the extinction are highly depleted in the heavy sulfur isotope (about − 40‰ vs. VCDT), whilst shortly after the extinction interval much more positive isotope values are observed (about − 25‰). An inferred change in the biogeochemical sulfur cycle is supported by facies evidence from similar neighbouring sections. It is suggested that two processes are operating closely here; 1) Changes in redox conditions and 2) extinction and/or transgression accounting for the absence of woody material.

Pb ISOTOPE COMPOSITIONS OF PYRITE FROM THE C QUARTZ-TOURMALINE VEIN OF THE SISCOE GOLD DEPOSIT, VAL D'OR, QUEBEC: CONSTRAINTS ON THE ORIGIN AND AGE OF THE GOLD MINERALIZATION

The Siscoe mine was one of the richest in the Val d’Or mining camp, producing 27.5 tonnes (t) of gold and 9.5 t of silver from 1929 to 1949. The C quartz-tourmaline vein at the Siscoe mine, which is the youngest auriferous vein on the property, is an excellent example of a high-grade Archean lode gold deposit; it contains an average of 45 g/t Au and locally up to 221 g/t Au. This vein cuts all dikes, the main regional foliation (S2), and several auriferous quartz-carbonate veins, and is interpreted to be a shear structure that formed during the development of a late- to post-D2 reverse fault. The vein comprises mainly alternating tourmaline- and quartz-rich layers, and gold occurs commonly in late fractures cutting the vein. The visible wall-rock alteration is characterized by the occurrence of tourmaline, pyrite, and calcite. In this study, we report the Pb isotope compositions of hydrothermal pyrite separates taken from the C quartz-tourmaline vein and its wall rock. Pyrite is abundant in the wall rock, where it occurs as grains with inclusions of chalcopyrite, gold, tetradymite, pyrrhotite, rutile, silicates, and carbonates. In the vein, it forms euhedra generally devoid of inclusions. Locally, the euhedra are fractured, and the fractures are filled with native gold, calcite, and tetradymite. Textural relationships suggest that pyrite precipitated synchronously with and/or after gold in the wall rock, but predated gold in the vein. Pyrite separates from the vein and its wall rock yielded similar 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios (13.63–13.83, 14.58–14.62, and 33.42–33.76, respectively), which are more radiogenic than those reported for volcanic supracrustal and syntectonic plutonic rocks of the southern Abitibi subprovince, but are very similar to those of the late- to posttectonic S-type granites in the Pontiac subprovince and Lacorne block. This suggests that the Pb originated from a reservoir similar to that of the magmas which produced these granites, or alternatively, that it was leached from the latter. The Pb ratios yield a model age of 2.57 ± 0.07 Ga, which is interpreted to date the cooling of the hydrothermal system that introduced and/or remobilized gold into the C quartz-tourmaline vein. These results, when considered in the context of the evolution of the southern Abitibi, indicate that widespread hydrothermal circulation occurred between 2.64 and 2.55 Ga, after the collision of the Pontiac and Abitibi subprovinces, and was caused by dewatering and S-type magmatism in the thickened unstable continental crust. This long-lived hydrothermal system promoted remobilization of gold from earlier veins and possibly introduction of gold from deeper zones, enhancing gold resources in the Siscoe deposit.

Fluid evolution and large-scale gold metallogeny during Mesozoic tectonic transition in the Jiaodong Peninsula, eastern China

Abstract The Jiaodong Peninsula or eastern Shandong Province, the most important gold producing in region China, is located in the southeastern margin of the North China Craton. The gold deposits in the Jiaodong Peninsula are divided into three gold belts, from west to east, the Zhaoyuan–Laizhou, Penglai–Qixia and Muping–Rushan belts. The deposits occur as gold-bearing quartz veins and disseminated- and stockwork-style ores adjacent to fault zones. Most of the gold deposits can be classified in four stages: stage I, quartz–(minor) pyrite; stage II, pyrite–quartz–gold; stage III, quartz–base metal sulphide minerals; stage IV, quartz–carbonate. Ar–Ar ages, Rb–Sr isochrons, and hydrothermal zircon sensitive high-resolution ion microprobe U–Pb ages obtained from these deposits suggest a gold mineralization time of 120±10 Ma. The Sr–Nd isotopic compositions of pyrites and the associated rocks suggest that the ore-forming materials were probably derived from a mixed source. Fluid inclusion studies show that ore-forming fluids of gold deposits are consistent throughout the Jiaodong Peninsula, with similar mineralizing temperature and pressure conditions. Ore-forming fluids are characterized by H 2 O–CO 2 –NaCl±CH 4 . The optimal mineralizing temperature and pressure ranges are 170–335 °C and 0.7–2.5 kbar. Oxygen and hydrogen isotope data show that ore fluids are of magmatic origin. Gold deposits in the Jiaodong Peninsula formed in the same mineralizing–geodynamic conditions, and are related to the Mesozoic tectonic transition in the eastern North China Craton. Gold metallogeny is only one expression of the Mesozoic tectonic transition.

Progressive oxidation of pyrite in five bituminous coal samples: An As XANES and 57Fe Mössbauer spectroscopic study

Naturally occurring pyrite commonly contains minor substituted metals and metalloids (As, Se, Hg, Cu, Ni, etc.) that can be released to the environment as a result of its weathering. Arsenic, often the most abundant minor constituent in pyrite, is a sensitive monitor of progressive pyrite oxidation in coal. To test the effect of pyrite composition and environmental parameters on the rate and extent of pyrite oxidation in coal, splits of five bituminous coal samples having differing amounts of pyrite and extents of As substitution in the pyrite, were exposed to a range of simulated weathering conditions over a period of 17 months. Samples investigated include a Springfield coal from Indiana (whole coal pyritic S = 2.13 wt.%; As in pyrite = detection limit (d.l.) to 0.06 wt.%), two Pittsburgh coal samples from West Virginia (pyritic S = 1.32–1.58 wt.%; As in pyrite = d.l. to 0.34 wt.%), and two samples from the Warrior Basin, Alabama (pyritic S = 0.26–0.27 wt.%; As in pyrite = d.l. to 2.72 wt.%). Samples were collected from active mine faces, and expected differences in the concentration of As in pyrite were confirmed by electron microprobe analysis. Experimental weathering conditions in test chambers were maintained as follows: (1) dry Ar atmosphere; (2) dry O 2 atmosphere; (3) room atmosphere (relative humidity ∼20–60%); and (4) room atmosphere with samples wetted periodically with double-distilled water. Sample splits were removed after one month, nine months, and 17 months to monitor the extent of As and Fe oxidation using As X-ray absorption near-edge structure (XANES) spectroscopy and 57Fe Mössbauer spectroscopy, respectively. Arsenic XANES spectroscopy shows progressive oxidation of pyritic As to arsenate, with wetted samples showing the most rapid oxidation. 57Fe Mössbauer spectroscopy also shows a much greater proportion of Fe 3+ forms (jarosite, Fe 3+ sulfate, FeOOH) for samples stored under wet conditions, but much less difference among samples stored under dry conditions in different atmospheres. The air-wet experiments show evidence of pyrite re-precipitation from soluble ferric sulfates, with As retention in the jarosite phase. Extents of As and Fe oxidation were similar for samples having differing As substitution in pyrite, suggesting that environmental conditions outweigh the composition and amount of pyrite as factors influencing the oxidation rate of Fe sulfides in coal.

Research on Genesis of Pyrite near the Permian-Triassic Boundary in Meishan, Zhejiang, China

Abstract The content and crystal forms of pyrite and sulfur isotope composition of pyrite sulfur as well as its vertical distribution near the Permian-Triassic (P/T) boundary in the Meishan section, Changxing county, Zhejiang province, China were studied using geological, petrological, mineralogical and geochemical methods (techniques). The result showed that the genesis of abundant pyrites in bed 24e2 at the uppermost part of the Changxing Formation in the Meishan section may be related to volcanic activity. In bed 24e2 of the Meishan section, pyrite has its highest content of 1.84% and the sulfur isotope composition has the highest δ 34 S value at +2.2‰ which is very similar to that of the average value of volcanic gas. There are some volcanic products such as β-quartz, siliceous cylinders and siliceous spherules which coexisted with pyrites in beds 24e2 and 24f. It can be concluded that a large quantity of volcanic ash fell into the South China Sea and was incorporated into marine sediments during the formation of limestone at the uppermost part of the Changxing Formation. The volcanic eruption with massive amounts of H 2 S and SO 2 gas at the end of the Permian period resulted in the enrichment of H 2 S in the South China Sea areas. The reaction of H 2 S with reactive iron minerals formed the mass of abundant pyrites.

Metallogeny of the Mont-de-l’Aigle IOCG deposit, Gaspé Peninsula, Québec, Canada

The Mont-de-l’Aigle deposit is located in the northern part of Dome Lemieux, in the Connecticut Valley-Gaspe Synclinorium, Gaspe Peninsula, Quebec. The Dome Lemieux is a subcircular antiform of Siluro–Devonian sedimentary rocks that is cut by numerous mafic and felsic sills and dikes of Silurian to Late Devonian age. Plutonism occurred in a continental within-plate extensional setting typical of orogenic collapse. The Cu−Fe (± Au) mineralization of Mont-de-l’Aigle occurs in veins, stockworks, and breccias. Mineralization is located near or within N−S and NW−SE faults cutting sedimentary rocks. IOCG mineralization postdates intrusions, skarns, hornfels, and epithermal mineralization typical of the southern part of the Dome Lemieux. The paragenetic sequence comprises: (1) pervasive sodic, potassic, chlorite, and silica alteration, (2) hematite, quartz, pyrite, magnetite, and chalcopyrite veins, stockworks and breccias and, (3) dolomite ± hematite veins and veinlets cutting the earlier mineralization. Intrusions display proximal sodic and potassic alteration, whereas sedimentary rocks have proximal decalcification, silicification, and potassic alteration. Both intrusive and sedimentary rocks are affected by a pervasive distal chlorite (± silica) alteration. The sulfur isotope composition of pyrite and chalcopyrite (δ34S=−1.5 to 4.8‰) suggests that sulfur was derived mainly from igneous rocks. Fluid δ18O (−0.4 to 2.65‰) indicates meteoric or seawater that reacted with the country rocks. Mixing of hot magmatic fluids with a cooler fluid, perhaps meteoric or seawater is suggested for mineral deposition and alteration of the Mont-de-l’Aigle deposit. The mineralogy, alteration, and sulfur isotope composition of the Mont-de-l’Aigle deposit compare well with IOCG deposits worldwide, making the Mont-de-l’Aigle deposit a rare example of Paleozoic IOCG mineralization, formed at shallow depth, within a low metamorphic grade sedimentary rock sequence.