Sulphur Isotope Abundances Research Articles

Isotope indices of gas-condensate origin

The possibility of using isotopic studies for defining the gas-condensate genesis is shown. The method consists of comparative analysis of regular variations in the isotopic abundance of oils, condensates and gases, and the geological and geochemical conditions of their occurrence. Such an analysis was performed on samples from Timano-Pechora and other oil- and gas-bearing provinces. The analysis revealed the hydrocarbon sources of the liquid and gaseous components of gas-condensates from the sulphur and carbon isotope abundance, the relationship between them and the gas-condensate pools' origin, by means of studying the isotopic composition of methan which reflects the type and maturity of the gas-source material. Using isotope criteria and geologic-geochemical conditions of occurrence, some types of gas-condensates were identified in the areas under study.

Mineral deposits and sulfur isotope abundances in the Mount Read Volcanics between Que River and Mount Darwin, Tasmania

Most of the mineral deposits in the Mount Read Volcanics are of Cambrian age and are either stratiform exhalative bodies or epigenetic feeder systems (e.g., Rosebery, Mount Lyell, Que River). Others were formed at depth during the same or other phases of Cambrian seawater circulation (Lake Selina, Prince Darwin) and a few consist of probably remobilized veins in late Cambrian volcanics (Lake Dora, Jukes Proprietary). A number were formed from solutions circulating during Devonian deformation and metamorphism or derived directly from granitoid plutons.Sulfur in the stratiform deposits and feeder zones (-10 to + 19ppm but mostly 7-15ppm) and in the deep circulation systems exposed near granite at Murchison, Lake Selina, and Darwin (8-17ppm) is probably a mix of sulfur derived from the host volcanics and granites, and sulfate from reduced Cambrian seawater. A rock sulfur content declining with time is a more likely explanation for the upward increase of delta 34 S values in the Rosebery ore (8-17ppm; Green et al., 1981) than is an increasing water/rock ratio. No comparable zoning is apparent at Mount Lyell or Que River where the systems appears to be dominated by rock sulfur (6-10ppm). Late stratiform barite seen in the major deposits develops from systems containing only partially reduced Cambrian seawater sulfate (delta 34 S values [raquo] 30ppm), the process of sulfate removal during circulation having decreased in efficiency owing to destruction of reductants.Devonian fluid activity in the north of the region was dominated by magmatic solutions derived from shallow granite plutons. These reduced, sulfur-poor solutions commonly increased their sulfur content by dissolution of Cambrian sulfides having relatively high delta 34 S values (Rosebery pyrrhotite, North Mount Farrell). In the southern part of the region the Devonian fluids were relatively oxidized, resulting in precipitation of barite and barite + sulfide veins (19-31ppm), and at Mount Lyell, high-grade bornite-chalcopyrite-chalcocite assemblages (-10.5 to +3.5ppm).

δ34S variations in vegetation and soil exposed to intense biogenic sulphide emissions near Paige mountain, N.W.T., Canada

Sulphur isotope abundances demonstrate that natural emissions of biogenic H2S and its oxidation products from springs near Paige Mountain, N.W.T., Canada, can be incorporated into surrounding soil and vegetation. δ34S values as low as − 33‰ for soil and vegetation are the result of dominant uptake of biogenic atmospheric compounds. In contrast, vegetation on a gypsum outcrop remote from the springs, has δ34S values as high as + 26‰ indicating nearly exclusive derivation of S from the soil. Near the springs, soil with vegetative cover is less depleted in 34S than soil lacking cover. Lower needles on a Black Spruce were found to be less depleted in 34S than the upper needles. These observations suggest that upper foliage exerts a canopy effect on lower foliage and in turn, interception by vegetation reduces the flux of atmospheric S compounds to the soil. Clearly, natural emissions of S compounds can interfere in studies of long range transport of industrial emissions; S isotope analyses might identify such interferences and reduce the chance of misinterpretation.

Geographical trends of carbon and sulphur isotope abundances in human kidney stones

δ 13C values and δ 34S values in human kidney stones range from −24 to −10 and −10 to + 20 %., respectively, and depend upon geographical location. Although the distributions overlap, the mean δ 13C values in oxalate stones from North America become less negative with decreasing latitude. For Mexico and Hawaii, the distributions appear to be bimodal. Uric acid stones are generally enriched in 13C by up to 7%. in comparison to oxalates from the same location, whereas cystine stones tend to span the ranges of both stone types. The geographical trends can be explained by the relative proportions of dietary carbon derived ultimately from plants undergoing various established photosynthetic mechanisms (C 3, C 4, CAM). The differences among the various major stone types may reflect isotope fractionation during biochemical conversions. Exogenic oxalates and uric acid are considered to have little role in precipitating the respective minerals. Whereas, the currently available C isotope data support this contention, more data are desirable, particularly for ingested oxalates. In contrast, S isotope data provide strong evidence that cystine stones are derived from ingested organo-S compounds and bear no relation to inorganic sulphate consumed by the individual. In turn, these organic-S compounds were probably derived from sulphate in the hydrosphere at lower levels in the food chain, e.g., by bacterial assimilation.

Sulphur isotope abundances in Aphebian clastic rocks: implications for the coeval atmosphere

The evolution of the atmosphere has been of interest to many scientists because it relates to the history of the ocean, the sedimentary cycle, the geochemical cycle of volatile elements, and the development of life. It also has a key role in the genesis of iron formations and gold and uranium deposits. Although it is generally accepted that the primitive atmosphere was reducing, a debatable aspect is when and how the oxygen content increased. A rise of atmospheric oxygen pressure about 2,000 Myr BP is suggested by the appearance of redbeds and the banded iron formations1,2. On the other hand, high atmospheric oxygen in very early Precambrian time, as a result of photodissociation of water, has been proposed3. This is supported by occurrences in Precambrian rocks of sulphates4,5, volatile elements6, detrital minerals5,7 and palaeosols8, which are similar to those found in younger rocks. Because the change of sulphur valency is often accompanied by isotopic fractionation, sulphur isotope abundances in minerals have been used to infer the environment at the time of their formation. It occurred to us that additional sulphur isotope analyses of pyrite from continental sedimentary rocks might provide evidence relative to the question of oxygen development in the atmosphere. Accordingly, a major study of sulphur isotope abundances in pyrite from fluviatile sedimentary rocks in the Elliot Lake area- Canada, and for comparison, data from occurrences in Northwest Territories, Canada, Witwatersrand, South Africa, and Jacobina, Brazil, are now reported and implications respecting the coeval atmosphere discussed.

A method for the measurement of sulfur-34 abundance in bound cysteine and methionine

A technique is described for determining the abundance of sulfur-34 in bound cysteine and methionine. Samples to be assayed are first boiled with water to remove any nonbound cysteine and methionine, reduced with mercaptoethanol, and alkylated with methyl iodide in order to convert the cystine and cysteine residues into S-methylcysteine. Following hydrolysis with 6 m hydrochloric acid, the released amino acids are desalted in a Dowex 50W-8X column and converted into their N-trifluoroacetyl n-butyl esters for gas chromatographic-mass spectrometric analyses. Analysis of the sulfur isotope abundances in ions from the S-methylcysteine and methionine derivatives allows the determination of the atom% abundance of sulfur-34 in these molecules with a standard deviation of less than 1 atom%. Data are presented on the incorporation of 34S from sulfate by Escherichia coli under a variety of growth conditions.

Sulphur isotope compositions of sulphides and sulphates, DSDP Leg37

Sulphur isotope abundances were determined for 15 sedimentary and 9 basalt specimens from DSDP Leg 37 cores. Sedimentary sulphides had δ34S values as low as −54‰, which is consistent with isotopic selectivity during bacterial sulphate reduction. The δ34S values for soluble sedimentary sulphates were generally lower than ocean water sulphate. This is probably due to contributions of oxidized sedimentary sulphides. Pyrite in basalt fractures had δ34S values ranging from −33‰ to −5‰. An unique interpretation of these data is not possible at this time.

Sulphur isotope abundance elucidate uptake of atmospheric sulphur emissions by vegetation

THE sour gas wells of Alberta form the basis of its sulphur industry. The well known Claus process is used, whereby part of the H2S is oxidised to SO2 which is in turn reacted with more H2S to yield elemental sulphur. As a consequence, more than 1,200 t of sulphur per day are discharged into the atmosphere in Alberta, mostly as SO2. Using sulphur isotope abundances, I have assessed the uptake of these emissions by vegetation.

Carbon and sulfur isotope abundances in Archean iron-formations and early Precambrian life

The volcanically enclosed Michipicoten and Woman River iron-formations, both approximately 2.75 b.y. old, in Superior Province of the Canadian Shield lie at lithologically similar stratigraphic contacts between underlying felsic pyroclastics and overlying mafic lava flows. Both iron-formations display similar lateral transitions of, from west to east, oxide, carbonate, and sulfide facies, a common facies pattern attributed to chemical deposition of volcanically derived components upon eastward-inclined slopes forming parts of local volcano-tectonic basins of deposition. Both iron-formations contain numerous, thin graphitic units.Six samples of Michipicoten graphitic carbon give delta 13 C values ranging from --20.4ppm to --27.7ppm with a mean of -- 24.7ppm. A sample of Michipicoten inorganic carbon in the form of massive siderite gave a delta 13 C value of +2.4ppm, which is similar to Phanerozoic marine carbonates. These data indicate extensive biological activities in the Archean basin during deposition of iron-formation.Sulfur isotope abundances in 62 samples of Michipicoten iron-formation taken across live main stratigraphic sections have a mean delta 34 S value of +0.02ppm with a range of 20.6ppm (--10.5 to +10.1ppm) and in 33 samples of Woman River iron-formation taken across three sections have a mean delta 34 S value of --1.3ppm with a range of 15.0ppm (--6.8 to +8.2ppm). The delta 34 S distribution patterns, which show large fluctuations over short distances, in the sediments are essentially the same for the different iron ranges and for the different members, chert, siderite, and sulfide (pyrite), within the Michipicoten iron-formations. The results strongly indicate isotopic fractionation in the biological reduction of sulfate under anaerobic conditions from a restricted reservoir at low sulfate concentrations.The sulfur and carbon isotope data provide strong evidence for the existence of autotrophic organisms and reducing bacteria in Archean times, but taken together with geological considerations as to the physical and chemical environment of deposition, the evidence appears overwhelming.Further detailed sampling and isotope analysis of Archean iron-formation is under way in order to advance the understanding of biogenic activities and basin deposition during accumulation of these ancient Precambrian chemical sediments.

Sulfur isotopic evidence for the supergene origin of alunite deposits, Tolfa district, Italy

Sulfur isotope abundance data for minerals of the historically important alunite deposits of the Tolfa district indicate (1) compositional similarity between sulfates and sulfides (mean δS34 values of +5.54 and +6.34 permil respectively), (2) negligible fractionation factors (0.995 to 1.004) for sulfate-sulfide mineral pairs, (3) two distinct sulfide isotopic populations characterized by pyrite (+8.34 permil) and marcasite (−1.05 permil) and with associated alunite displaying a covariant isotopic shift, and (4) possible contamination of the hydrothermal system by evaporite sulfate (+25.1 permil) because hypogene pyrite, galena, and cinnabar are enriched in S34 (+6.1 to +10.3 permil). We suggest that alunite, barite, and possibly marcasite are of supergene origin and that the sulfate-sulfur was derived from the surficial oxidation of sulfides. Our conclusion is compatible with the geologic evidence and confirms the supergene hypothesis for the genesis of Tolfa alunites proposed by Fuchs and De Launay (1893) and De Launay (1906; 1913).

Sulfur Isotope Abundances and Genetic Relations of Oil Accumulations in Middle East Basin

A sulfur isotope study was made of sulfur in crude oils from various northern Iraq oil fields and of sulfate sulfur of gypsum and anhydrite deposits in the Arabian Gulf-Iraq-Iran basin. The sulfur isotope ratios (S34/S32) of 42 oil samples from Tertiary and Cretaceous reservoirs were found to be very uniform, the average ^dgrS34 value being --5.4 ^pmil, relative to Canyon Diablo troilite. By contrast, three oils from reservoir rocks of Triassic age showed a distinctly different S34/S32 ratio, the average ^dgrS34 being +2.4 ^pmil. The isotopic composition of oils from different depths--one above the other--is particularly uniform. In the Kirkuk field, oils from four levels--Tertiary and Upper, middle, and Lower Cretaceous--are identical within the reproducibility of the determinations (^dgrS34 = --5.5 ^pmil). In the Bai Hassan field, ^dgrS34 = --7.25 ^pmil for oils from the same four levels. These findings give strong support to Dunnington's view that the major oil accumulations in Cretaceous and Tertiary traps in northern Iraq originated from a common source. The sulfur isotopic composition of contemporaneous marine sulfates can be considered representative of the level from which isotope fractionation started. As a result of fractionation, reduced sulfur present as organic compounds in the oils is depleted in S34 relative to the sulfate from which it was formed. On the basis of ^dgrS34 values for Jurassic, Cretaceous, and Tertiary evaporites of the Middle East, a Jurassic origin for the oils is most favored, and a Tertiary origin is least likely.

Minor elements in sphalerite and galena from Binnatal

The trace element contents of 23 sphalerites and galenas from Binnatal, Switzerland, have been determined. Most of these samples have been previously studied in respect to lead and sulphur isotope abundances. Coloration of sphalerites — varying from yellow to black for nearly identical iron contents — seems to be strongly influenced by the manganese content. A linear relationship between sulphur isotope composition and copper content in sphalerites was found. Trace elements in galenas show a significant inverse relationship between silver and copper. With the determination of the bismuth content, it is possible to distinguish several galena types; a similar grouping has been found by lead isotope determinations. The results of the trace analyses are discussed in connection with the occurrence of a large number of very rare and special Pb-As-sulphosalt minerals in the Binnatal dolomites.

Sulfur isotope abundance data, Bingham District, Utah

Range in isotopic composition is small, with a mean close to that for meteorite sulfur, suggesting a magmatic hydrothermal origin and derivation from a deep-seated source, perhaps within the mantle. Pyrite samples show the entire range of compositions, from S-32/S-34 ratios of 22.151 to 22.306. Vein pyrite is richer in S-34 than disseminated pyrite. Sulfide minerals of individual samples show increasing mean S32/S34 ratios in the sequence molybdenite-pyrite-chalocopyrite-bornite. Weak zonation is shown by progressive depletion of S-34 outward from the central zone of the district.

The S32/S34ratio in troilite from the Bruderheim and Peace River meteorites

During the initial studies of sulphur isotope abundances, MacNamara and Thode [1950] reported that the S32/S34 ratio in meteorites was markedly constant, in contrast to the significant variations found in terrestrial samples. This constancy has been further confirmed [Vinogradov, 1958; Ault and Kulp, 1959; Thode et al., 1961; Shima and Thode, 1961; Jensen and Nakai, 1962]. Within the past four years, fragments of two chondritic meteorite showers, Bruderheim and Peace River, fell and were recovered in Alberta [Folinsbee and Bayrock, 1961, 1964].

Sulfur isotope abundances in basic sills, differentiated granites, and meteorites

Studies have been made of the S32/S34 ratios in four large basic sills presumably of deep-seated origin. The average ratio for these sills was determined by weighting each sample according to sulfur content and in accordance with the thickness of rock represented by each sample. These average ratios were within 1.0 per mil of the value for meteoritic sulfur. This is comparable with a spread of about 12.0 per mil for igneous rocks and an over-all spread of about 120.0 per mil for terrestrial samples. In the study of igneous rocks, both intrusive and extrusive, a number of granitic intrusives were found to have S32/S34 ratios completely outside the range of values for all other igneous rocks. The results suggest that these intruded granites are regenerated sediments rather than acidic differentiates that have risen from the subcrust or mantle.

Sulfur isotope abundances in rocks of the Sudbury District and their geological significance

A study has been made of the distribution of the S isotopes in the Precambrian rocks of the Sudbury district [Ontario]. The S isotope ratios obtained for the Ni irruptive including samples of the Cu-Ni ores, associated norite, and micropegmatite are consistent with the conventional picture of a single sheetlike intrusive of magma that underwent some gravity-controlled process of differentiation. The S isotope ratios obtained from Cu-Ni ore and associated norite samples from the Stillwater igneous complex in Montana, parallel those obtained for the corresponding Sudbury samples. The Cu-Zn-Pb deposits found in faults between igneous and sedimentary rocks in the center of the Sudbury basin, support the view that these ores are hydrothermal deposits derived from the micropegmatite possibly during the last stages in the differentiation of the irruptive. The sedimentary rocks S. of the Sudbury basin are found to be very uniform in S isotope content and to have a S isotope ratio almost identical with that of meteorites (delta S (super 349= 0). The sediments inside the basin, on the other hand, vary markedly in S isotope content and have isotope ratios which extend beyond the range usual for igneous rocks. These results are in agreement with other evidence that the ancient sediments inside and outside the basin were laid down under quite different conditions. The results suggest that the sediments inside the basin, in particular the graphite-rich slates, were formed in an environment in which extensive localized biological activity took place. The low C 13 content of these slates, delta C 13 = -36.9 permil with respect to standard limestone, also suggests life processes in Proterozoic times.

Sulphur isotope geochemistry

Sulphur isotope abundances of thirty-nine specimens of seventeen meteorites are reported. The results show again the remarkable constancy of the sulphur isotope ratios for meteorites of all types. However, differences in the S 32/S 34 ratios of 0.4%. would appear to be significant. The S 32/S 34 ratio for meteorites is discussed as a possible base level from which fractionation in the earth's crust began. The value is compared with estimates of average values found for terrestrial samples including some recent results of igneous intrusives. A large suite of sea water samples collected from widely separated points in three oceans at various depths have also been investigated and the S 32/S 34 ratios reported. The results show that the sulphate in the three oceans is exceedingly uniform in isotope ratio, with an enrichment of 20.1%. ± 0.3 in S 34 over that of the meteoritic standard. Sulphur isotope ratios of sulphur in a sea shell, sulphides in shallow ocean sediments, sulphate in rain water and in present-day formation of gypsum evaporites from the sea, have been measured and are compared to the sea water level. The geochemical sulphate cycle is discussed in the light of these results.

Sulphur Isotope Abundances in Petroleum and Associated Materials

A study has been made of the sulphur isotope ratios for petroleum from many different oil fields in the United States and Canada. The S34/S32 ratio for petroleum varies by about 4.5 per cent as compared with a total spread of about 9 per cent for terrestrial sulphur. The single large oil pools appear to be uniform in isotopic content. Also, oils from widely separated locations in Alberta, found in the same reservoir rock, have similar sulphur isotope ratios. On the other hand, the actual sulphur content of these latter oils may vary by a factor of 10. This result indicates that there is little or no fractionation of the sulphur isotopes in the maturation of the oil in which sulphur is lost. The fact that the H2S and its associated petroleu have similar sulphur isotope content is further evidence for this view. The sulphur isotope ratio for petroleum would seem, therefore, to give information concerning the isotopic content of the source sulphur at the time of petroleum formation. This in turn would reveal something about the environment in which the petroleum was formed. The very high S34 content of the petroleum in the recent sediments of the Uinta basin in Utah confirms the non-marine origin of these deposits. The decrease in S34 content with age and depth of petroleum deposit in the basin suggests a gradual S34 enrichment of the sulphate over a period of time in the enclosed lake, probably due to bacterial action.

Sulphur Isotope Abundances in Hydrocarbons and Source Rocks of Uinta Basin, Utah

The sulphur isotope abundances in the free asphalts, asphalts extracted from the supposed source rocks, and the inorganic sulphur compounds of the source rocks of the Uinta basin have been defermined. The results show that both the asphalts and inorganic sulphur compounds become more and more enriched in S34 with decreasing age and decreasing depth of the deposits, the youngest sediments being enriched 31 ^pmil as compared with 20 ^pmil for sea water sulphate. This one-to-one correspondence between S34/S32 ratio and age and depth of deposits is, in view of the changes in the nature of controlling environment which occurred, strong evidence in favor of a biological theory of S34 enrichment in inland lakes and seas. The free asphalt and asphalt extracted from the source rocks were found to have almost identical sulphur isotope ratios in the case of wurtzilite and albertite. However, in the case of the ozocerite, the asphalt extracted from the supposed source rock has quite a different S34/S32 ratio from that of free asphalt. These results confirm previously suggested relations except in the case of the ozocerite.

The origin of native sulphur deposits from isotope fractionation studies

Sulphur and carbon isotope abundance studies have been made on the sulphur well cores and adjacent formations of the Texas and Louisiana salt domes. The free sulphur was found to be depleted in S 34 with respect to associated sulphate by 3.9 per cent on the average. This compares to a 3.2 per cent fractionation of the sulphur isotopes in the formation of free sulphur from sulphate by bacterial action in North African lakes. Also, the associated sulphate was found to be enriched in S 34 as compared to adjacent anhydrite formations to various extents depending on the sulphur well investigated. Carbon isotope ratios obtained for the calcite matrix of the sulphur well cores showed that the carbon of the calcite was depleted by from 3.3 to 5.5 per cent in C 13 as compared to standard limestone. These results indicate that the calcite was formed simultaneously with the free sulphur from carbon of organic origin by a process resulting in some further fractionation of the carbon isotopes. All the isotope abundance data can be reconciled with the conclusion that the large sulphur deposits of the southwestern United States have been formed by living organisms.