Native Sulfur Deposits Research Articles

Reply to the discussion, comment on “Lithological zoning and stable isotopes distribution in carbonates in the Polish native sulfur deposits. Implications for origin of the ores”

Reply to the discussion, comment on “Lithological zoning and stable isotopes distribution in carbonates in the Polish native sulfur deposits. Implications for origin of the ores”

“Lithological zoning and stable isotopes distribution in carbonates in the Polish native sulfur deposits. Implications for origin of the ores”. Discussion, comment

The paper of A. Gąsiewicz and P. Olchowy on lithological zoning and stable isotopes distribution in carbonates in the Polish native sulfur deposits and implications for origin of the ores as a result of sedimentary processes, presented there, are discussed. Steep contacts of sulfur-bearing limestones with gypsum and barren limestones contradict their supposed sedimentary origin and zonation. The arguments in favour of replacement of gypsum by sulfur-bearing limestone are presented as well for formation of barren limestones by sulfur leaching and reprecipitation in the neighbouring sulfur-bearing and surrounding rocks. The registered lithologic zonation of sulfur deposits is not a result of aerial changes of sedimentary environment, but may be explained by pH and Eh variation of connate formation water. The well documented variation of δ13C and δ18O may be explained by weathering processes. Karstification of sulfur-bearing limestones produced the intercalations of clays with crumbled limestone and sulfur, resembling the synsedimentary breccia. There are no strong arguments in favour of sedimentary origin of sulfur ores. The formation of sulfur-bearing limestone in sedimentary environment, however, cannot be totally excluded, but if occurred, may take place on a very limited area, concurrently with formation through epigenetic gypsum replacement.

Lithological zoning and stable O and C isotopes distribution in carbonates in the Polish native sulfur deposits: Implications for origin of the ores

The northern marginal part of the Polish Carpathian Foredeep hosts numerous native sulfur deposits associated with the Middle Miocene evaporite horizon. These deposits reveal lithological zoning, wherein both the barren and sulfur-bearing limestone zones are embedded within the gypsum basin area (zone). However, such zoning is incompatible with the bioepigenetic formation model of native sulfur deposits. Hence, their genesis remains enigmatic. Regional variations in stable oxygen and carbon isotope values of the limestones disclosed in the Osiek–Baranów Sandomierski native sulfur deposit are inconsistent with the molecular replacement of solid sulfate by calcium carbonate and native sulfur accumulations that expand from a fault zone into the gypsum basin. Instead, the distribution patterns of stable isotopes and sedimentological data suggest that a very shallow freshwater-dominated sedimentary–diagenetic environment developed in the hypersaline basin’s marginal zone, where the mixing of meteoric and highly saline water, as well as various bacterial processes, were responsible for lithological zoning and native sulfur distribution. The proposed results necessitate a reinterpretation of the epigenetic model of native sulfur ore formation.

Paleo‐thermal constraints on the origin of native diagenetic sulfur in the Messinian evaporites: The Northern Apennines foreland basin case study (Italy)

AbstractRecent studies on the genesis of sedimentary native sulfur deposits indicate diagenetic mid‐low temperature Bacterial Sulfate Reduction (BSR) as the main process, involving organic compounds (kerogen/hydrocarbons), bacterial colonies and gypsiferous rocks. In the peri‐Mediterranean area (Southern Spain, Sicily, Northern Apennines, Israel), the main sulfur accumulations are always associated with late Miocene sulfates and organic‐rich successions encompassing the Messinian salinity crisis (MSC). In particular, the Messinian successions of the Apennine‐Adriatic foreland basin system, due to a large amount of high‐resolution stratigraphic data, represent a perfect case study for understanding the diagenetic conditions controlling the development of the BSR process during sedimentary basin evolution. In this work, thermal models performed in three sub‐basins in a sector of the Northern Apennines comprised of the Sillaro and Marecchia rivers (Italy), calibrated by means of organic and inorganic geothermometers, indicate a general thermal immaturity of the studied successions attained as a result of a constant heat flow similar to the present day one (ca. 40 mW/m2) since Late Tortonian and lithostatic loads between 615 and 1,710 m depending on different sub‐basins. These results suggest that the MSC deposits experienced maximum temperatures between about 39°C and 65°C. Temperatures derived from thermal models have been used to constraint occurrence of the diagenetic BSR associated with evaporitic deposits providing thermal constraints in sulfur genesis as well as new useful thermal‐constraints for basin analysis studies.

Not Mining Sterilization of Explored Mineral Resources. The Example of Native Sulfur Deposits in Poland Case History

The sterilization of mineral resources makes considerable amounts inaccessible for future use and may be a barrier to the free supply of commodities. During the exploitation of mineral deposits, some parts of their resources become sterilized as inaccessible because of natural hazards or unfavorable economic conditions. Not mining land use and the social opposition against mining is the purpose of sterilization of considerable demonstrated mineral resources of deposits not yet engaged in exploitation. The native sulfur deposits in Poland are a good example of such “not mining” sterilization, which makes a considerable part of known resources inaccessible. On the northern border of the Carpathian Foredeep within the Miocene gypsum formation, the systematic exploration had demonstrated about 1 billion tons of sulfur resources located in the deposits of varied dimensions. The sulfur opencast mining and underground melting (the modified Frasch method) flourished from 1958 up to 1993. The increasing sulfur supply, recoverable from hydrocarbons, caused the closing down of sulfur mines, leaving a place with considerable untouched resources. About 67% of sulfur resources left by closed mines and of other explored but not exploited deposits are sterilized by the advancement of settlements, industrial plants, road construction, and by social opposition against mining.

Formation of Large Native Sulfur Deposits Does Not Require Molecular Oxygen.

Large native (i.e., elemental) sulfur deposits can be part of caprock assemblages found on top of or in lateral position to salt diapirs and as stratabound mineralization in gypsum and anhydrite lithologies. Native sulfur is formed when hydrocarbons come in contact with sulfate minerals in presence of liquid water. The prevailing model for native sulfur formation in such settings is that sulfide produced by sulfate-reducing bacteria is oxidized to zero-valent sulfur in presence of molecular oxygen (O2). Although possible, such a scenario is problematic because: (1) exposure to oxygen would drastically decrease growth of microbial sulfate-reducing organisms, thereby slowing down sulfide production; (2) on geologic timescales, excess supply with oxygen would convert sulfide into sulfate rather than native sulfur; and (3) to produce large native sulfur deposits, enormous amounts of oxygenated water would need to be brought in close proximity to environments in which ample hydrocarbon supply sustains sulfate reduction. However, sulfur stable isotope data from native sulfur deposits emplaced at a stage after the formation of the host rocks indicate that the sulfur was formed in a setting with little solute exchange with the ambient environment and little supply of dissolved oxygen. We deduce that there must be a process for the formation of native sulfur in absence of an external oxidant for sulfide. We hypothesize that in systems with little solute exchange, sulfate-reducing organisms, possibly in cooperation with other anaerobic microbial partners, drive the formation of native sulfur deposits. In order to cope with sulfide stress, microbes may shift from harmful sulfide production to non-hazardous native sulfur production. We propose four possible mechanisms as a means to form native sulfur: (1) a modified sulfate reduction process that produces sulfur compounds with an intermediate oxidation state, (2) coupling of sulfide oxidation to methanogenesis that utilizes methylated compounds, acetate or carbon dioxide, (3) ammonium oxidation coupled to sulfate reduction, and (4) sulfur comproportionation of sulfate and sulfide. We show these reactions are thermodynamically favorable and especially useful in environments with multiple stressors, such as salt and dissolved sulfide, and provide evidence that microbial species functioning in such environments produce native sulfur. Integrating these insights, we argue that microbes may form large native sulfur deposits in absence of light and external oxidants such as O2, nitrate, and metal oxides. The existence of such a process would not only explain enigmatic occurrences of native sulfur in the geologic record, but also provide an explanation for cryptic sulfur and carbon cycling beneath the seabed.

New insights on secondary minerals from Italian sulfuric acid caves

Sulfuric acid minerals are important clues to identify the speleogenetic phases of hypogene caves. Italy hosts ~25% of the known worldwide sulfuric acid speleogenetic (SAS) systems, including the famous well-studied Frasassi, Monte Cucco, and Acquasanta Terme caves. Nevertheless, other underground environments have been analyzed, and interesting mineralogical assemblages were found associated with peculiar geomorphological features such as cupolas, replacement pockets, feeders, sulfuric notches, and sub-horizontal levels. In this paper, we focused on 15 cave systems located along the Apennine Chain, in Apulia, in Sicily, and in Sardinia, where copious SAS minerals were observed. Some of the studied systems (e.g., Porretta Terme, Capo Palinuro, Cassano allo Ionio, Cerchiara di Calabria, Santa Cesarea Terme) are still active, and mainly used as spas for human treatments. The most interesting and diversified mineralogical associations have been documented in Monte Cucco (Umbria) and Cavallone-Bove (Abruzzo) caves, in which the common gypsum is associated with alunite-jarosite minerals, but also with baryte, celestine, fluorite, and authigenic rutile-ilmenite-titanite. In addition, the core of alunite and jarosite, from these two systems, results enriched in PO43-, clearly suggesting hypogene hydrothermal origin. Santa Cesarea Terme, Capo Palinuro, and Acqua Mintina caves show important native sulfur deposits, which abundantly cover walls, ceilings, and speleothems. Abundant copiapite, pickeringite, tamarugite, hexahydrate assemblages have been observed in the Calabrian systems; their association with pyrite and hematite would suggest they formed in very acidic conditions with pH ranging between 0 and 4.

Trace Elements and Minerals in Fumarolic Sulfur: The Case of Ebeko Volcano, Kuriles

Native sulfur deposits on fumarolic fields at Ebeko volcano (Northern Kuriles, Russia) are enriched in chalcophile elements (As-Sb-Se-Te-Hg-Cu) and contain rare heavy metal sulfides (Ag2S, HgS, and CuS), native metal alloys (Au2Pd), and some other low-solubility minerals (CaWO4, BaSO4). Sulfur incrustations are impregnated with numerous particles of fresh and altered andesite groundmass and phenocrysts (pyroxene, magnetite) as well as secondary minerals, such as opal, alunite, and abundant octahedral pyrite crystals. The comparison of elemental abundances in sulfur and unaltered rocks (andesite) demonstrated that rock-forming elements (Ca, K, Fe, Mn, and Ti) and other lithophile and chalcophile elements are mainly transported by fumarolic gas as aerosol particles, whereas semimetals (As, Sb, Se, and Te), halogens (Br and I), and Hg are likely transported as volatile species, even at temperatures slightly above 100°C. The presence of rare sulfides (Ag2S, CuS, and HgS) together with abundant FeS2 in low-temperature fumarolic environments can be explained by the hydrochloric leaching of rock particles followed by the precipitation of low-solubility sulfides induced by the reaction of acid solutions with H2S at ambient temperatures. The elemental composition of native sulfur can be used to qualitatively estimate elemental abundances in low-temperature fumarolic gases.

Organic-rich shales from internal Betic basins (SE Spain): potential source rocks analogs for the pre-Messinian Salt play in the Western Mediterranean

Southeastern Spain has a large number of Late Neogene basins with substantial evaporitic deposits that developed under an overall NNW-SSE compressional regime related to the African-European tectonic plates collision. Located in the Betic Cordillera, they can be considered as marginal Mediterranean basins that became gradually isolated during the Tortonian and Early Messinian due to tectonic uplift. Different evaporitic units accumulated in these basins during isolation and, in several cases, evaporitic conditions were associated to episodes of important organic matter accumulation. Results obtained from Late Tortonian to Early Messinian shales collected from boreholes, mines and outcrops in the internal Betic basins of Las Minas de Hellin, Cenajo and Socovos are presented. The organic matter was studied under fluorescence and scanning electron microscopy (SEM), and the main geochemical characteristics defined. They show a relation between organic-rich intervals with high potential of hydrocarbon generation, native sulfur, bio-induced dolomite and evaporitic deposits. These organicrich shales can be found before, during and after the evaporitic episodes. Results from the present study are compared with those previously obtained in the pre-evaporitic deposits of the Lorca Basin that showed high oil generation potential, a restricted-marine origin of the organic matter and a low degree of maturity. The occurrence of such potential source rocks in several basins points to a broad regional distribution. At a larger scale, in the Mediterranean Basin, organic-rich sediments were deposited before and during the Messinian Salinity Crisis. The studied examples could represent analogs for potential source rocks of the pre-Messinian salt play in the Western Mediterranean

Hydrothermal alteration, fumarolic deposits and fluids from Lastarria Volcanic Complex: A multidisciplinary study

A multidisciplinary study that includes processing of Landsat ETM+ satellite images, chemistry of gas condensed, mineralogy and chemistry of fumarolic deposits, and fluid inclusion data from native sulphur deposits, has been carried out in the Lastarria Volcanic Complex (LVC) with the objective to determine the distribution and characteristics of hydrothermal alteration zones and to establish the relations between gas chemistry and fumarolic deposits. Satellite image processing shows the presence of four hydrothermal alteration zones, characterized by a mineral assemblage constituted mainly by clay minerals, alunite, iron oxides, and more subordinated ferrous minerals and goethite. Hydrothermal alteration zones present in the Lastarria sensu stricto volcano are directly related to the recent fumarolic activity. Geochemistry of fumarolic gas condensed, obtained from two fumaroles at temperatures between 328 and 320 °C, has allowed detecting 37 diverse elements corresponding to halogens, chalcophiles, siderophiles, alkali metals, alkali earth metals and Rare Earth Elements (REE), with concentrations that vary widely between 5,620 ppm (chlorine) and 0.01 ppm (Mo, Ag, Sn, Pb, Se, Mg and Cr). Logarithm of Enrichment Factor (log EFi) for each element present values between 6.35 (iodine) and<1 (K, Na, Ca, Fe and Al). Those elements are originated primarily from a magmatic source, whereas at shallow level a hydrothermal source contributes typical rock-related elements, which are leached from the wall rock by a strong interaction with hyperacid fluids. Mostly of elements detected are transported to the surface in the fumarolic emissions as gaseous species, while very few elements (Mg, Ca and Al) are transported in silicate aerosols. A wide spectrum of minerals are present in the fumarolic deposits, which are constituted by sublimates and incrustations, and the main minerals phases are distributed in six mineral families, corresponding to sulphates, hydrated sulphates, sulphides, halides, carbonates, silicates and native element minerals. The sublimate/incrustation minerals are dominated by the presence of sulphate, sulphur, chlorine and diverse rock-related elements, which are formed by processes that include a. oxidation of gaseous phase; b. strong rock-fluid interaction; c. dissolution of silicate minerals and volcanic glass; d. gas-water interaction; e. deposition/precipitation of saline bearing minerals; f. oxidation of sublimates/incrustations to form secondary minerals and g. remobilization of sulphur deposits by meteoric water. Despite that sublimate/ incrustation minerals are dominated by rock-related elements, its chemistry shows high contents of high-volatile elements as As, Sb, Cd, among others. Fluid inclusions studies carried out in thin pseudobanded native sulphur from fumarolic deposits, by use of Raman and infrared spectroscopy combined with microthermometry analyses, provided evidence of H2O, CO2, H2S, SO4, COS bearing fluids, homogenization temperatures around 110 °C and salinities varying from ~11 to ~7 wt% NaCl. Fluid inclusions data show also evidences of a mixing (dilution) between hot and saline fluid with a cooler fluid (cold groundwater or a steam-heated water) as the main process.

A stable isotopic constraint on the origin of sulphur ore excavated from the exotic four‐lobe jars that prevailed during late medieval to early modern times in Sakai (Osaka), south‐western Japan

Stable sulphur isotope ratios were determined for native sulphur ore that was excavated from exotic four‐lobe jars in Sakai, south‐western Japan. The jars were buried after a fire event that occurred on 28 April 1615. The sulphur isotopic results (average δ34S = +0.5‰) were evaluated in terms of comparing ancient documents with a database from new sulphur collections. The origin of the sulphur ore is estimated to be transportation from native sulphur deposits formed around the solfataric fumaroles from Mts Garan and Kuju–Iwozan, in central‐eastern Kyushu. These analytical results support the validity of history based on the analysis of ancient documents.

Hydrogeochemical Indices for the Prospecting of Hydrocarbon and Native Sulphur Deposits

Two hydrogeochemical indices are presented namely: the balance of sulfate (B.S) and the index of aeration (I.A) and may be used as geochemical tools to give important information that indicate the presence of good prospects of oil and native sulphur deposits. The B.S and I.A are calculated from the hydrochemical data of natural waters (formation waters, oil field brines, sulphurous springs, …etc) that are associated with these deposits. For hydrocarbon deposits the B.S values were negative and ranged from few to several thousands, while I.A values were positive and ranged from zero to 10 for excellent prospects to 100 or to 1000 for less important prospects. For native sulphur deposits, both the B.S and I.A values were positive and ranged from few hundreds to thousands. Many examples of oil field waters and sulphurous springs from Iraq were examined and gave results of high positive significance.

Distribution, salinity and pH dependence of elements in surface waters of the catchment areas of the Salars of Coipasa and Uyuni, Bolivian Altiplano

The variation in concentrations of a wide variety of hydrochemical parameters in surface watercourses of the Bolivian Altiplano is statistically characterised. A variation of four to five orders of magnitude is characteristic for several parameters (Al, As, B, Cd, Cl −, Cu, Fe, Li, Mn, Na, S, and SO 4 2−), reflecting (i) evapoconcentration between mountainous watersheds and saline desert evaporative sinks, and (ii) geologically varied sources such as volcanic/thermal springs, fumarolic sulphur deposits and widespread sulphide mineralization. A tendency to increasing salinity from catchment headwaters to the salars is observed. pH values are generally rather high (median 8.3), and exhibit a similar, but weaker increasing trend. Arsenic concentrations are high (median=34 μg/l) and are probably largely derived from volcanogenic sources (fumarolic native sulphur deposits and thermal springs) on the Andean Cordillera Occidental. Arsenic exhibits positive correlations with pH and salinity, indicating its mobility as an oxy-anion under the generally high pH conditions and its susceptibility to evapoconcentration. Arsenic appears to be only weakly attenuated relative to chloride, probably by adsorption onto iron hydroxide precipitates or flocs.

Variation of Cl and SO3 Contents of Microphenocrystic Apatite in Intermediate to Silicic Igneous Rocks of Cenozoic Japanese Island Arcs: Implications for Porphyry Cu Metallogenesis in the Western Pacific Island Arcs

Abstract. Determinations of SO3 and Cl contents of igneous accessory apatite were carried out on Late Cenozoic intermediate to silicic intrusive and volcanic rocks in the Japanese island arcs of the western Pacific rim including the southwestern Kuril arc (eastern Hokkaido), Northeast Japan arc (southwestern Hokkaido through northeastern Honshu to central Honshu), Izu‐Bonin arc, Kyushu‐Palau ridge, Southwest Japan arc (northern Kyushu) and northern Ryukyu arc (southern Kyushu). These were compared to those from the Western Luzon arc, Philippines, to better understand the metallogenesis of porphyry Cu deposits in the western Pacific island arcs. In addition, SO3 and Cl contents of accessory apatite in the Cretaceous magnetite‐series granitic rocks in the Kitakami belt (northeastern Honshu) and the Miocene ilmenite‐series granitic rocks in the Outer Zone of Southwest Japan (southern Kyushu) were also examined.Microphenocrystic apatites in shallow intrusions associated with porphyry Cu deposits in the Western Luzon arc contain >0.1 wt% S as SO3. Such high SO3 contents of microphenocrystic apatite are a common characteristic of hydrous mag‐matism in the Western Luzon arc, from 15 Ma old tonalitic plutonic rocks of the Luzon Central Cordillera to present‐day volcanism at Mount Pinatubo. The accessory apatite in intrusive rocks associated with porphyry Cu deposits, especially those at the Santo Tomas II deposit, show significantly high Cl contents (>2 wt%).The SO3 contents of microphenocrystic apatite in most of the hydrous silicic rocks along the volcanic front, in andesites related to native sulfur deposits, and in Miocene and younger shallow granitic intrusions in northeastern Honshu, are generally <0.1 wt%. On the other hand, the SO3 contents of apatite in such rocks from eastern Hokkaido, southwestern Hokkaido, Izu, northern Kyushu and southern Kyushu are similar to those from the Western Luzon arc. The SO3 contents of accessory apatite in the Cretaceous magnetite‐series granitic rocks in the Kitakami belt are variable, whereas those of the Miocene ilmenite‐series granitic rocks in southern Kyushu are extremely low. The Cl contents of accessory apatite in some rocks of the Northeast Japan arc, Izu‐Bonin arc and Southwest Japan arc are significantly high.In terms of the Cl and SO3 contents of microphenocrystic apatite, Cenozoic Japanese arc magmatism show similarities with arc magmatism associated elsewhere with porphyry Cu mineralization, except for the most of northeastern Honshu of the Northeast Japan arc. Apatite commonly occurs as inclusions in other phenocrystic phases. Thus the variation in SO3 contents of apatite is a feature of early stage magmatic differentiation. The SO3 contents of microphenocrystic apatite are considered to reflect the redox state of the magma source region or fluids encountered during magma generation.

Occurrence of Halogen‐rich Phlogopite in Late Cenozoic Volcanic Rocks in the Japanese Arcs

Abstract. Halogen‐rich phlogopite occurs in the groundmass of andesite and dacite lavas from Late Tertiary to Quaternary volcanoes associated with native sulfur and limonite deposits (Shiretoko‐Iwozan, Hachimantai, Adatara, Omeshidake, Masaki) and hydrothermal ore deposits (Harukayama, Muineyama, Hishikari) in Japan. The F contents of the halogen‐rich phlogopite range from 3.6 to 5.7 wt%, corresponding to atomic F/(F+C1+OH) ratios ranging from 0.45 to 0.69. On the other hand, the Cl contents of the halogen‐rich phlogopite are around 0.2 wt%. The atomic Mg/(Mg+Fe) ratios range from 0.69 to 0.83.The fluorine intercept value [IV(F)] defined by Munoz (1984) of the phlogopites ranges from 0.79 to 3.17, and the chlorine intercept value [IV(Cl)] ranges from ‐7.11 to ‐7.77. The observed IV(F) of the phlogopites broadly overlap the range of the IV(F) for biotites from porphyry copper deposits. On the other hand, the observed IV(Cl) are significantly lower than the IV(Cl) for biotites from porphyry copper deposits. Whereas the F contents of the phlogopite appear more prominent compared to the Cl contents, the calculation of halogen intercept values revealed that the phlogopites are enriched in Cl with respect to the element distribution effect of Mg‐Fe substitution. Since the degree of Cl enrichment of the phlogopite is more significant compared to that of biotite in porphyry copper deposits, the phlogopites are considered to have formed under the condition of significantly high activity of halogens. Hydrothermal ore deposits may be formed in magmatic hydrothermal system associated with volcanoes where halogen‐rich phlogopite is formed by hypersaline fluid.

Distribution pattern of hydrogen sulphide-bearing gas in the former Soviet Union

H 2 S is an unwelcome accompaniment to natural hydrocarbon gas but, in sufficient volumes, it can provide an economic source of sulphur, termed a ‘gaseous sulphur’ accumulation. Such accumulations are an important component of the sulphur reserves of Russia and other countries. A comparative study of the distribution of economic gaseous sulphur accumulations, together with native sulphur deposits, in the Amu Dar’ya, Volga–Urals, North Caspian and other basins of the former Soviet Union and elsewhere shows that they occur only within large hydrocarbon basins and are restricted to thick and regionally persistent evaporite–carbonate successions. The lithological and geochemical controls and various types of sulphur paragenesis result in a zoned series of accumulations, from gaseous sulphur to sulphur-rich oils to native sulphur, which can be traced from the deep central regions of hydrocarbon-bearing basins with sulphate–evaporite successions towards the shallow basin margins.

PGE in fresh basalt, hydrothermal alteration products, and volcanic incrustations of Kilauea volcano, Hawaii

The concentrations of Os, Ir, Pd, and Au in fresh unaltered Kilauean tholeiite were determined by radiochemical neutron activation analysis. For a suite of 18 samples, averages were: Os = 0.38 ± 0.23, Ir = 0.38 ± 0.14, Pd = 2.40 ± 1.04, and Au = 1.78 ± 0.57 (in ppb with a 1σ SD). Correlations of these metals with Co, Cr, Cu, Ni, and MgO in fresh basalts, and petrographic observations, indicate that Os and Ir are carried mainly in chromite, much of which occurs as inclusions in olivine phenocrysts. Palladium correlations suggest its occurrence partly in olivine and partly in the matrix whereas Au seems to be predominantly a matrix constituent. Altered basalts were analyzed for Ir, Pd, and Au in a suite of 19 samples from five different locations. Minor changes only in either concentrations or element ratios were found for Ir and Pd when fresh and altered rock data were compared. However, Au was consistently enriched in altered relative to fresh rocks. These results imply that Pd and Ir, in contrast to Au, will likely retain their eruptive signatures upon burial in a subaerial eruptive setting. High-temperature sulfate-dominated condensates generate incrustations enriched in Ir, Os, Au, and Pd by approximately 50, 20, 10, and 3×, respectively, relative to fresh rocks. In contrast, low-temperature native sulfur deposits are the most depleted material found in the study with Ir, Pd, and Au lower by factors of 10, 4, and 5 compared with fresh rock averages. The strong enrichments of Os and Ir in the high-temperature suite are attributed mainly to enhanced volatility in highly oxygenated magmatic hydrothermal fluids contaminated by meteoric water near the structural top of volcanic conduits. The relatively smaller Pd enrichment, which is dependent on the chloride content of fluids, implies that PGE partitioning into volcanic fume may fractionate these metals (e.g., Pd versus Ir) relative to host basalt in the eruptive process.

Paleohydrology of the Delaware Basin, Western Texas: Overpressure Development, Hydrocarbon Migration, and Ore Genesis

This study integrates quantitative modeling techniques with field observations to establish a paleohydrologic framework of the Delaware basin, western Texas. The reconstructed paleohydrologic models allow for a better understanding of the development and maintenance of anomalous overpressures, hydro carbon generation and migration, and ore genesis in the basin. Results of numerical modeling show that disequilibrium compaction and oil generation might generate excess fluid pressures during the Late Permian in response to the rapid deposition of evaporite beds. The preservation of this overpressure to the present, however, requires the presence of an extremely low-permeability (<10-11 d) top seal. Most shaly sediments, with permeability ranging from 10-4 to 10-8 d, thus may be too permeable, by several orders of magnitude, to preserve overpressure for more than 250 m.y. The predicted present-day gas window is located within the overpressure zone, suggesting that the volume increase associated with the oil-to-gas conversion may be attributed to present overpressures. The native sulfur deposits likely formed in a fluid mixing zone resulting from the Laramide uplift of the western basin during the Tertiary. In our model, meteoric water recharged along the basin's uplifted western margin and discharged basinward. Hydrocarbons migrated landward by pressure gradients and buoyancy and discharged upward along faults in the western basin, where they mixed with meteoric water. Many oil and mineral reservoirs may have formed in the fluid mixing zone, where extensive chemical reactions take place. In the Culberson sulfur ore district, for example, fluids including hydrocarbons and meteoric water migrated upward through faults from underlying carrier beds, into the Permian Salado limestone. There, the mixture of fluid drives biochemical reactions that precipitate native sulfur.

Étude géologique et biologique in situ de deux zones hydrothermales du bassin de Manus (Papouasie Nouvelle-Guinée)

The aim of the BioAccess cruise was the study, with the submersible Shinkai 2000, of the Pacmanus and Desmos zones in the Manus basin. Due to their geodynamical setting, off axis and on a transverse fault, these two zones show a specific hydrothermal activity. Within the Desmos zone in particular, the hydrothermal activity is characterised by acidic fluids, native sulphur deposits, and a poor associated fauna highly dependent of its location and the andesitic nature of the outcropping rocks.

Sulfur redox reactions: Hydrocarbons, native sulfur, Mississippi Valley-type deposits, and sulfuric acid karst in the Delaware Basin, New Mexico and Texas

Hydrocarbons, native sulfur, Mississippi Valley-type (MVT) deposits, and sulfuric acid karst in the Delaware Basin, southeastern New Mexico, and west Texas, USA, are all genetically related through a series of sulfur redox reactions. The relationship began with hydrocarbons in the basin that reacted with sulfate ions from evaporite rock to produce isotopically light (δ34S = -22 to -12) H2S and bioepigenetic limestone (castiles). This light H2S was then oxidized at the redox interface to produce economic native sulfur deposits (δ34S = -15 to +9) in the castiles, paleokarst, and along graben-boundary faults. This isotopically light H2S also migrated from the basin into its margins to accumulate in structural (anticlinal) and stratigraphic (Yates siltstone) traps, where it formed MVT deposits within the zone of reduction (δ34S = -15 to +7). Later in time, in th zone of oxidation, this H2S reacted with oxygenated water to produce sulfuric acid, which dissolved the caves (e.g., Carlsbad Cavern and Lechuguilla Cave, Guadalupe Mountains). Massive gypsum blocks on the floors of the caves (δ34S = -25 to +4) were formed as a result of this reaction. The H2S also produced istopically light cave sulfur (δ34S = -24 to -15), which is now slowly oxidizing to gypsum in the presence of vadose drip water.