Sulphide isotopic composition

Kontak, D.J. Smith, P.K. 1989. Sulphur isotopic composition of sulphides from the Beaver Dam and other Meguma Group-hosted gold deposits, Nova Scotia implioations for genetic models. Canadian Journal of Earth Sciences, 26, 1617-1629. 

Bennett V. C., Norman M. N., and Garcia M. O. (2000) Correlated platinum group element and Re abundances with isotopic compositions in Hawaiian picrites the role of sulphides. Earth Planet. Sci. Lett. 183, 513—526. 

Strauss H. (2002) The isotopic composition of Precambrian sulphide—Seawater chemistry and biological evolution. In Precambrian Sedimentary Environments A Modern Approach to Ancient Depositional Systems. International Association of Sedimentologists Special Publication no. 33 (eds. W. Altermann and P. L. Corocoran). Blackwell, Oxford, pp. 67-105. 

Whereas conventional methods for analysing sulphur isotope compositions need >10 mg of physically separated sample and long analytical times, in contrast, the EA-IRMS technique uses small samples (1-2 mg) and has short analysis times. This achieves the high physical resolution and large sample populations needed for adequate study of biological variation in Archaean sulphide-rich organic sediments. 

There is another, very important and large repository of methane methane hydrates (also known as gas hydrates or clathrates Kvenvolden 1988).They comprise ice in which the interstices of the lattice house small molecules, such as methane, ethane, carbon dioxide and hydrogen sulphide. In fact, enough gas needs to be present to fill 90% of the interstices in order for the hydrate to form, and it has a different crystal structure from normal ice (Sloan 1990). If fully saturated, the most common crystalline structure can hold one molecule of methane for every 5.75 molecules of water, so lm3 of hydrate can contain 164 m3 of methane at STP (see Box 4.8).The solubility of methane in water is insufficient to account for hydrate formation, and a major nearby source is required, typically methanogenesis, based on the dominance of methane (99%) and its very light isotopic composition (813C generally <—60%o see Section 5.8.2). 

Naturally occurring sulphur-bearing species include native sulphur, the sulphate and sulphide minerals, gaseous H S and SO2 and a range of oxidized and reduced suphur ions in solution. A summary of the isotopic compositions of some major rock types is given in Figure 7.21. 

Sulphide mineral-pairs and sulphide-sulphate mineral-pairs are not always in equilibrium. This can arise when (1) the mineral-pair formed at low temperatures (7 < 200 °C) (2) the isotopic composition of a mineralizing fluid is variable (3) there was continued isotopic exchange following the formation of the mineral... 

Spooner E.T.C. and Gale N.H., 1982, Pb-isotopic composition of ophiolitic volcanogenic sulphide deposits, Troodos Complex, Cyprus. Nature, 296, 239-242. 

Betenekov et al. [39] used an isotopic tracer technique to show that, for then-range of solution compositions, the initial deposition involved adsorption of Cd(OH)2 on the glass substrate. At the beginning of the reaction, only Cd was observed to form on the substrate and this was interpreted to be due to Cd(OH)2, since any other insoluble Cd compounds that might be formed from the deposition solution (containing CdCl2, NaOH, NH4OH, and thiourea dissolved in water) were expected to contain either S or C. However, they concluded that the deposition proceeded, not by reaction between Cd(OH)2 and sulphide formed by decomposition of thiourea, but rather by decomposition of a Cd(OH)2-thiourea complex (see Sec. 3.3.3.1). 

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