Sulfur isotope

CDT. canyon diabolo troilite (a standard for sulfur isotopes see VCDT)... 

V. a term used to describe a voltage difference between one electrode and another VCDT. Vienna canyon diabolo troilite (actually silver sulfide used as a replacement standard for CDT [sulfur isotopes])... 

The only sulfur isotope with a nuclear spin is which is quadrupolar (/ = 3/2) and of low natural abundance (0.76%). In view of these inherent difficulties and the low symmetry around the sulfur nuclei in most S-N compounds, S NMR spectroscopy has found very limited application in S-N chemistry. However, it is likely that reasonably narrow resonances could be obtained for sulfur in a tetrahedral environment, e.g. [S(N Bu)4], cf. [S04] . On the other hand both selenium and tellurium have isotopes with I = Vi with significant natural abundances ( Se, 7.6% and Te, 7.0%). Consequently, NMR studies using these nuclei can provide useful information for Se-N and Te-N systems. 

R. W. FairbriiXjE, Encyclopedia of Geochemistry and Environmental Sciences, Van Nostrand, New York, 1972.. See sections on Geochemical Classification of the Elements Sulfates Sulfate Reduction-Microbial Sulfides Sulfosalts Sulfur Sulfur Cycle Sulfur Isotope Fractionation in Biological Processes, etc., pp. 1123 - 58. 

Isotope effects also play an important role in the distribution of sulfur isotopes. The common state of sulfur in the oceans is sulfate and the most prevalent sulfur isotopes are (95.0%) and (4.2%). Sulfur is involved in a wide range of biologically driven and abiotic processes that include at least three oxidation states, S(VI), S(0), and S(—II). Although sulfur isotope distributions are complex, it is possible to learn something of the processes that form sulfur compounds and the environment in which the compounds are formed by examining the isotopic ratios in sulfur compounds. 

What are the relative contributions of these two sources Two approaches have been taken. One is to establish the geology and hydrology of a basin in great detail. This has been carried out for the Amazon (Stallard and Edmond, 1981) with the result that evaporites contribute about twice as much sulfate as sulfide oxidation. The other approach is to apply sulfur isotope geochemistry. As mentioned earlier, there are two relatively abundant stable isotopes of S, and The mean 34/32 ratio is 0.0442. However, different source rocks have different ratios, which arise from slight differences in the reactivities of the isotopes. These deviations are expressed as a difference from a standard, in the case of sulfur the standard being a meteorite found at Canyon Diablo, Arizona. 

Evaporitic sulfur has a range of sulfur isotopic composition from +10%o to +30%o, while sedimentary sulfur is depleted in the heavy isotope and has a range of isotopic composition of about —40%o to +10%o. Most of this variation reflects systematic changes with geological age. The source fractions of a river water can be estimated from an isotopic mass balance ... 

Crowe, D.E., Valley, J.W. and Baker, K.L. 1990 Micro-analysis of sulfur-isotope ratios and zona-tion by laser microprobe. Geochimica et CosmochimicaActa 54 2075-2092. 

Smock AM, ME Bottcher, H Cypionka (1998) Fractionation of sulfur isotopes during thiosulfate reduction by Desulfovibrio desulfuricans. Arch Microbiol 169 460-463. 

Ore deposits associated with volcanic rocks generally exhibit polymetallic (Cu, Pb, Zn, Sn, W, Au, Ag, Mo, Bi, Sb, As and In) mineralization. Sulfur isotopic values of sulfides from these deposits are close to 0%o, suggesting a deep-seated origin of the sulfide sulfur. Clay deposits (pyrophyllite, sericite and kaolinite) are associated with both felsic volcanic rocks and ilmenite-series granitic rocks of late Cretaceous age in the San-yo Belt. 

Figure 1.4]. Sulfur isotopic compositions of sulfide minerals from Kuroko deposits (Shikazono, 1987b).

Figure 1.42. Sulfur isotopic variation and the vertical zonation of ores in the Shakanai No. 1 deposit (Kajiwara, 1971).

In individual deposits, S S of sulfides generally increases stratigraphically upwards (Fig. 1.42). (Kajiwara, 1971). Based on the sulfur isotope evidence, Kajiwara (1971) deduced that the ore solutions underwent a progressive cooling and oxidation due to mixing with seawater. 

Sulfur isotopic data of separated pyrite as the commonest sulfide mineral (Kajiwara, 1971 Kajiwara and Date, 1971) show different values for the three sub-types of Horikoshi and Shikazono (1978). The values of pyrite in the C sub-type deposits are higher than the values of pyrite from the Y and B sub-types. The values of pyrite from the Y sub-type seem to be slightly higher than those from the B sub-type. Kajiwara and Date (1971) are of a different opinion the values from the Kosaka district are higher than those in the Hanaoka district, because all sulfur isotopic data from the C sub-type were obtained in the Kosaka district. The sulfur isotopic data on the obtained Uwamuki deposits of the B sub-type in the Hanaoka district indicate systematic decrease in 8 S passing from the yellow ore (4-7%o) to the black siliceous ore (4-5%c) (Bryndzia et al., 1983). Kajiwara and Date s data (1971) include three values of pyrite in the Doyashiki deposit of C sub-type in the Hanaoka district. The main Doyashiki... 

If sulfur isotopic equilibrium between coexisting sulfates and sulfides was attained, using average values of sulfates and sulfides, -i-22%c and +5%c, respectively, we could estimate temperature using the equation by Ohmoto and Rye (1979). This temperature seems too high compared with temperature estimated from fluid inclusions and mineral assemblages (section 1.3.3). That means that sulfates and sulfides precipitated under the condition far from equilibrium. 

This estimate can be evaluated based on the strontium and sulfur isotopic studies... 

Se,o,s Sulfur isotopic composition of oxidized sulfur species. S S. r.s Sulfur isotopic composition of reduced sulfur species. 8 Stotaf Total sulfur isotopic composition of aqueous sulfur species. 

Figure 1.109. Sulfur isotopic compositions of Neogene Au-Ag vein-type and disseminated-type deposits. Sulfur isotopic compositions on the samples from the Yatani deposits (Sample No. YT26 from Zn-Pb vein S S = -)-3.3%o), and HS72050305-YT1, YT24 and NS-3 from Au-Ag vein (average S S = +3.3%c)) by Shikazono and Shimazaki (1985) are also plotted. Base-metal rich implies the sample containing abundant sulfide minerals but no Ag-Au minerals from base-metal rich deposits and also from Ginguro-type deposits (Shikazono, 1987b).

There is another explanation for the variations in values of sulfide sulfur. It was cited that oxidation state (/02) od pH of ore fluids are important factor controlling values of ore fluids (e.g., Kajiwara, 1971). According to the sulfur isotopic equilibrium model (Kajiwara, 1971 Ohmoto, 1972), of sulfides in predominance... 

Figure 1.112. Sulfur isotopic composition of pyrrhotite-bearing (solid) and hematite-bearing (open) samples from base-metal-rich deposits in Green tuff region (Shikazono, 1987b).

Sulfur isotopic compositions (S S) of sulfides and sulfate (barite) from the Se-type and Te-type are summarized in Fig. 1.122. Almost all S S values from the Se-type and Te-type fall in a range from —3%o to - -6%o (Fig. 1.122). In general, the 5 S values from the Se-type are similar to those of the Te-type. However, some S S values from the Se-type are lower than those from the Te-type. 

This mechanism as a main cause for epithermal-type Au deposition is supported by sulfur isotopic data on sulfides. Shikazono and Shimazaki (1985) determined sulfur isotopic compositions of sulfide minerals from the Zn-Pb and Au-Ag veins of the Yatani deposits which occur in the Green tuff region. The values for Zn-Pb veins and Au-Ag veins are ca. +0.5%o to -f4.5%o and ca. -l-3%o to - -6%c, respectively (Fig. 1.126). This difference in of Zn-Pb veins and Au-Ag veins is difficult to explain by the equilibrium isotopic fractionation between aqueous reduced sulfur species and oxidized sulfur species at the site of ore deposition. The non-equilibrium rapid mixing of H2S-rich fluid (deep fluid) with SO -rich acid fluid (shallow fluid) is the most likely process for the cause of this difference (Fig. 1.127). This fluids mixing can also explain the higher oxidation state of Au-Ag ore fluid and lower oxidation state of Zn-Pb ore fluid. Deposition of gold occurs by this mechanism but not by oxidation of H2S-rich fluid. 

Analytical results of sulfur isotope previously obtained are summarized in Fig. 1.151. 

Figure 1.151. Sulfur isotopic compositions of sulfides in the vein-type and Kuroko deposits. Solid box represents sulfur isotopic data from the ore deposits occurring in basement rocks (Shikazono and Shimizu, 1993).

Figure 1.178 represents a comparison between the stannite-sphalerite temperatures and homogenization temperatures of fluid inclusions or sulfur isotope temperatures. It can be seen in Fig. 1.178 that Nakamura and Shima s geothermometer would be rather consistent with the temperature estimated based on the fluid inclusions or sulfur isotope studies. It is notable that almost all stannite-sphalerite temperatures are within 30°C of average homogenization temperatures and sulfur isotope temperatures. 

Figure 1.178. Comparison between the stannite-sphalerite temperatures and filling temperatures of fluid inclusions or sulfur isotope temperatures. NT Nakatatsu, OB Obira, KN Kano, KG Kuga, TM Tsumo, KM Kamioka, OT Ohtani, KU Kaneuchi, Ak Akenobe, TT Takatori, YT Yatani (Shimizu and Shikazono, 1985).

The sulfur isotopic data are consistent with geologic environments of Hg and Sb deposits Sedimentary rocks are dominant and marine rocks are not present in Sb-Hg mineralization districts. However, a few samples of stibnite and cinnabar from the deposits in Green tuff region display high S S values. In contrast of this interpretation on the origin of sulfur, Ishihara and Sasaki (1994) thought that sulfur came from ilmenite-series granific rocks. However, these rocks are not found in the north Hokkaido. 

Factors in controlling chemical compositions of gold in equilibrium with the ore fluids are temperature, pH, concentration of aqueous H2S and Cl in the ore fluids, concentration ratio of Au and Ag species in the ore fluids, activity coefficient of Au and Ag components in gold, and so on (Shikazono, 1981). In the Yamizo Mountains, as a result, Ag/Au ratios of gold are correlated with a kind of the host rocks and sulfur isotopic compositions of the deposits. This correlation could be used to interpret Ag/Au ratios of gold. 

Hamada, M. and Imai, A. (2000) Sulfur isotopic study of the Toyoha deposit, Hokkaido, Japan — Comparison between the earlier-stage and the later-stage veins. Resource Geology, 50, 113-122. 

Ishihara, S. and Sasaki, A. (1994) Sulfur isotopic characteristics of late Cenozoic ore deposits at arc junction of Hokkaido, Japan. The Island Arc, 3, 122-130. 

Kajiwara, Y. (1971) Sulfur isotope study of the Kuroko-ores of the Shakanai No. 1 deposit, Akita Prefecture, Japan. Geochem. 7.,4, 157-181. 

Kawahata, H. and Shikazono (1988) Sulfur isotope and total sulfur studies of basalts and greenstones from Hole 504B, Costa Rica Rift Implications for hydrothermal alteration. Can. Min. 26, 555-565. 

Kiyosu, Y. (1977a) Sulfur isotopic compositions of epithermal vein type sulfides from the Toyoha mine, Hokkaido, Japan. J. Earth Sci. Nagoya U., 22, 23-32. 

Kiyosu, Y. (1977b) Sulfur isotope ratios of ores and chemical environment of ore deposition in the Taishu Pb-Zn sulfide deposits, Japan. Geochem. J., 11, 91-99. 

Komuro, K. and Sasaki, A. (1985) Sulfur isotope ratio of framboidal pyrite in Kuroko ores from the Ezuri mine, Akita Prefecture, Japan. Mining Geology, 35, 289-293. 

Kusakabe, M. and Chiba, H. (1983) Oxygen and sulfur isotopic composition of barite and anhydrite Irom the Fukazawa deposit, Japan. Econ. Geol. Mon. 5, 292-301. 

Shikazono, N. (1999b) Sulfur isotopic composition and origin of sulfide sulfur of epithermal Au-Ag veins. Resource Geology Special Is.sue, 20, 39-46. 

Shikazono, N. and Shimazaki, H. (1985) Sulfur isotopes study of the Yatani Zn-Pb-Au-Ag vein-type deposits in Japan. Geochem. J., 19, 259-267. 

Shimazaki, H. and Yamamoto, M. (1983) Sulfur isotope ratios for the Akatani, lide and Waga Sennin skam deposits, and their bearing on mineralization in the Green tuff region, Japan. Geochem. J., 17, 197-207. 

Ueda, A. and Sakai, H. (1984) Sulfur isotope study of Quaternary volcanic rocks from the Japanese islands arc. Geochim. Cosmochim. Acta, 48, 1837-1846. 

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