Range Of δ34S Values Research Articles

A sulfur isotopic study of alunites from Latium and Tuscany, central Italy

Sulfur isotope analyses were made on 14 alunites from volcanic and sedimentary rocks widely different in chemistry and age from southern Tuscany and northern Latium, central Italy. The δ34S values range from +0.7 to +9.6‰, and appear not to be related to the nature of the host rock. Geological and isotopic evidence suggests that all the alunites formed by supergenic oxidation of sulfides. Sulfides occurring with alunites in the volcanic rocks of Latium can be divided into an isotopically light group of probably magmatic origin (δ34S=−1.5 to +3.4‰) and a heavy one with δ34S=+6.0 to +10.3‰, tentatively interpreted as deposited by hydrothermal fluids that leached sulfides of similar 34S/32S from the deep basement. Such an interpretation is consistent with recent studies indicating that in the perityrrhenian belt of Latium exists a continuation, at depth, of the Tuscan stratigraphic series, rich in sulfides with δ34 from +6 to +12‰.

Sulfur isotope stratigraphy in some Finnish ore deposits

Abstract Sulfur isotope stratigraphy involves the interpretation, on the basis of their sulfur isotope composition, of the features of rock strata in terms of their origin, palaeo-environment and geological history. Three, Finnish, strata-bound, ore deposits have been chosen as examples. At Outokumpu, there is an evolutionary series, which can be explained by changes in the chemical state of the ore-forming fluids controlled by a volcanic-exhalative mechanism. The δ34S values range from uniform but negative values in the quartzite outside the ore proper, through a regularly fluctuating, isotopic pattern on the negative side characteristic of the satellite ore body, and finally to values trending towards zero per mille in the main ore body. At Pahtavuoma, the δ34S values for sulfide sulfur are in principle divided into two categories. Negative values up to -15.5‰ characterize the ore proper, while positive values as high as +31.2‰ come from the low-grade ore at the hanging-wall side of the westernmost ore ...

Isotopic evidence on the origin of the Shamrocke copper mine, Rhodesia

The Shamrocke ore body is a stratiform deposit of disseminated copper-iron sulphides found within lenses of calcareous meta-arkose occurring in Lomagundi Group graphitic schist (Late Precambrian) at Karoi, Rhodesia. Both sulphides and sediments were subjected to high grades of regional metamorphism. Argon/argon isochron ages indicate a major metamorphic event at 550 m. y. (Damaran orogeny) with later minor argon losses. Ore sulphide δ34S values range from +3.0 to +14.8‰ CDT and a general decrease from footwall to hanging-wall reflects an original sedimentary environment where sulphides formed about the sea bed from hydrothermal fluids progressively mixing with sea water. Isotopically lighter sulphides formed syngenetically in the host rocks from bacterial reduction of sulphate. The pyrrhotite was probably formed from pyrite during metamorphism, and owing to reducing conditions maintained similar δ34S values to the original pyrite. Oxygen and carbon isotopic analyses of mineralised and unmineralised carbonate lenses are consistent with deposition as marine limestones in an evaporitic environment and/or near hot spring vents.

Sulphur and sulphate-oxygen isotopes and the origin of the silvermines deposits, Ireland

New sulphur and sulphate-oxygen isotope measurements for the main discordant and stratiform lead-zinc-barite orebodies at Silvermines Co. Tipperary, allow reappraisal of previously offered differing interpretations (Graham, 1970; Greig et al., 1971) of the bearing of sulphur isotopes on the genesis of this important Irish deposit. The following aspects of the data are confirmed: barite δ34 S-values range from 17–21‰, similar to lower Carboniferous seawater sulphate: stratiform sulphide lens pyrites have δ34 S-values ranging from −13 to −36‰; vein sulphide δ34 S-values range from −8 to 4‰; sulphide δ34 S-values increase upwards and outwards respectively in the related discordant and stratiform “G” orebodies; galena-sphalerite isotope palaeotemperatures are not too consistent, ranging from 40 to 430°C (using the calibration of Czamanske and Rye (1974). New facts are as follows: barite δ18O-values range from −13 to −17‰, stratiform barites ranging from 13 to 14.5‰; sulphides separated from a single stratiform ore lens hand specimen usually have δ34 Ssl > δ34 Sga > δ34 Spy; the outward decrease in δ34 S-values in the stratiform “G” orebody is confined to the first few hundred feet only; pyrite δ34 S-values progressively increase downwards through one stratiform sulphide orebody; yet variations of 13‰ occur within a single colloform pyrite structure from another stratiform orebody. It is concluded that there were at least two sources of sulphur, seawater sulphate and deep-seated sulphur. The former was the dominant source of all sulphate and, via biogenic reduction, of the sulphur in the bulk of the stratiform sulphide. The latter was the source of the sulphur in the vein sulphides. There was minimal isotopic interaction between the cool seawater sulphate and the warm unwelling ore fluid sulphur species, even though the latter precipitated under near isotopic equilibrium conditions when the temperature dropped and/or the pH and Eh increased. The lack of isotopic equilibrium between pyrite and ore sulphides in the stratiform ore lenses may result from the latter having precipitated slightly later than the former because of solubility relationships. Overall the present isotopic evidence supports considerable geological evidence favoring a syngenetic origin for the stratiform Silvermines orebodies.

Isotope studies on the Rosebery, Mount Farrell and Mount Lyell ores, Tasmania

Preliminary studies have been made on the distributions of oxygen and sulphur isotopes in the Rosebery, Mount Farrell, and Mount Lyell ores. These ores lie in Cambrian geosynclinal volcanic rocks in West Tasmania. At each locality the sulphur of the sulphide minerals has a distinctive degree of enrichment in δ34S in relation to sulphur in meteorites and a narrow range of δ34S values. The dominant ore at Mount Lyell (mainly pyrite-chalcopyrite) has an average δ34S value of +7.0‰, the main lode at Rosebery (pyrite-sphalerite-galenachalcopyrite) averages +10.9‰, and the Mount Farrell ore (galena-sphalerite) averages +14.1‰. The degree of enrichment does not appear to be related to local, near-surface geological factors. Other ores of geosynclinal volcanic type with similar mineralogy also show narrow ranges in δ34S and varying enrichments in 34S. Barite from a concordant sulphide-barite-carbonate lode at Rosebery has an average δ34S of +38.1‰ and an average δ18O of +10.7‰. Barite from veins at Mount Lyell has an average δ34S of +25.3‰ and an average δ18O of +10.6‰.