Minerals isotope data

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... 

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. 

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. 

Fig. 2.52. Histograms showing sulfur isotope data for sulfide minerals from the major volcanogenic Cu sulfide deposits within the Jurassic to Cretaceous accretionary terrains in Japan (Sato and Kase, 1996).

A representative sample of the isotopic data from terrestrial standards is given in Table 1 and plotted in figure 6 together with data from Mg-rich minerals (spinel and Ti-pyroxene) from Allende inclusions. Raw isotopic data are presented, corrected... 

Table 1. llnnormalized Mg Isotope Data from Terrestrial Samples and Mg-rich Minerals from Allende... 

At this point, nothing is known about Cu and Zn isotopic variability in seawater. Zn is very depleted in surface waters because it behaves as a nutrient. A substantial amormt of Zn isotope data is available for sediments. Marechal et al. (2000) found that the 5 Zn values of clay minerals from different environments (Paleozoic shales, including a black shale, Mediterranean sapropels. Pacific and Atlantic sediments, a eolian dust) fall within a narrow range (0.17-0.35%o) centered around the magmatic values and therefore reflect the Zn isotope composition... 

This report concerns the application of Pb isotope geochemistry in the exploration for unconformity-type uranium deposits in the Athabasca Basin of northern Saskatchewan (Fig. 1). 2006 Pb isotope data from a number of current projects, several with U mineralization, will be discussed (Cigar Lake East, Close Lake, Midwest A, Wolly/McClean Lake, Cree-Zimmer project, and Shea Creek). 

Many salt minerals have water of crystallization in their crystal structnre. Such water of hydration can provide information on the isotope compositions and/or temperatures of brines from which the minerals were deposited. To interpret snch isotope data, it is necessary to know the fractionation factors between the hydration water and the solntion from which they are deposited. Several experimental studies have been made to determine these fractionation factors (Matsno et al. 1972 Mat-subaya and Sakai 1973 Stewart 1974 Horita 1989). Becanse most saline minerals equilibrate only with highly saline solutions, the isotopic activity and isotopic concentration ratio of water in the solntion are not the same (Sofer and Gat 1972). Most studies determined the isotopic concentration ratios of the sonrce solntion and as Horita (1989) demonstrated, these fractionation factors have to be corrected using the salt effect coefficients when applied to natural settings (Table 3.2). 

The Mn- Cr system can be studied by TIMS, ICPMS, and SIMS techniques. For TIMS and ICPMS work, bulk samples or mineral separates are dissolved and the solutions are passed through ion-exchange columns to produce clean solutions of manganese and chromium. For minerals with high Mn/Cr ratios SIMS can obtain isotopic data while retaining the petrographic context of the measurements. The chromium isotopic compositions may have to be corrected for small additions of chromium from spallation reactions induced by cosmic rays. This is particularly important in iron-rich meteorites. 

Mass spectrometric investigations of isotopes in coal and coal minerals have also been very limited in scope. Rafter (25) published sulfur isotope data on 27 New Zealand coal samples but did not draw any conclusions from these data. Smith and Batts (26) determined the isotopic composition of sulfur in a number of Australian coals and concluded that, from this type of data, one might deduce the origin of the organically... 

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