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Scaling NIST SRM 3149 for Se isotope analysis and isotopic variations of natural samples
Goldschmidt Conference Abstract 2006
Trace element geochemistry of magnetite and pyrite in Fe oxide (±Cu–Au) mineralised systems: Insights into the geochemistry of ore-forming fluids M.J. CAREW1, G. MARK1,2, N.H.S. OLIVER1, N. PEARSON3 1
EGRU, School of Earth Sciences, James Cook University, Australia ([email protected]; [email protected]) 2 Monash Ore Geology Research and Exploration Group, School of Geosciences, Monash University, Australia (geordie.mark@ sci.monash.edu.au) 3 GEMOC, Macquarie University, Australia (norm.pearson@ mq.edu.au) LA-ICP–MS analyses of magnetite and pyrite from Fe oxide (Cu–Au) (e.g. Ernest Henry, Osborne, Starra and Mount Elliott) and related deposits in northwest Queensland, Australia shows that these minerals are enriched in a diverse suite of elements. Magnetite typically contains detectable Ti, Si, Al, Mg, Sc, Co, Ni, Cu, Zn, Ga, Sn, Pb, Mn, V, Cr and Mo, whereas co-genetic pyrite contains detectable Ti, Co, As, Si, Se and Ni. Comparison of ore-related and barren systems shows that magnetite and pyrite exhibit differences in relative trace element concentrations, where magnetite associated with ore typically contains lower Ti, V and Cr and higher Sc and Mo, while Co and As were higher in ore-related pyrite. These chemical differences are common for many Cu–Au ore systems in the district, and potentially indicate that magnetite and pyrite can be employed as geochemical mineral indicators toward ore-forming systems. The main factors considered important in controlling magnetite and pyrite geochemistry include: (i) fluid composition; (ii) process of ore formation (e.g. fluid mixing and fluid–rock interaction); and/or (iii) physicochemical conditions (e.g. T, foo) during mineral deposition. Given that the minerals in this study largely occur as open-space fill (e.g., veins), they were probably formed in fluid-buffered environments where contributions from the host rocks via element exchange were minimal. Consequently, we propose that the chemistry of magnetite and pyrite in the ore systems probably reflects the geochemistry of the precipitating fluid(s) which considered together with the stable isotope characteristics and complex chemistry of ore-forming fluids from the Ernest Henry and Starra Cu–Au deposits suggests a significant magmatic contribution to the metal budget of the ore deposits (1).
Reference Williams, P.J., Dong, G., Ryan, C.G, Pollard, P.J., Rotherham, J.F., Mernagh, T.P., Chapman, L.H., . Econ. Geol. 96, 875–883. doi:10.1016/j.gca.2006.06.078
A83
Scaling NIST SRM 3149 for Se isotope analysis and isotopic variations of natural samples J. CARIGNAN1, H. WEN1,2 1
CRPG-CNRS, 15, Rue Notre-Dame des Pauvres, B. P. 20, 54501, Vandoeuvre-le`s-Nancy Cedex, France (carignan@crpg. cnrs-nancy.fr) 2 KLODG, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China ([email protected]) There is actually no consensus on what material should be used as the ‘‘delta zero’’ reference for Se isotope analysis. Some concerned scientists suggested the use the NIST SRM 3149. Here we report its composition (lot 992106) relative to a MERCK Se solution which was already used as reference (Rouxel et al., 2002). The technique used is the on line, continuous flow hydride generation, coupled to a MC-ICP–MS Isoprobe, equipped with a collision cell, as described by Rouxel et al. (2002). The d82/ 76 SeMERCK measured for the NIST SRM 3149 is 1.53 ± 0.20 (± is 2 times the standard deviation from the mean, n = 31, 11 sessions). Recalculated d82/76Se relative to NIST for MERCK, CRPG and MH495 Se solutions are then respectively 1.53 ± 0.20&, 2.01 ± 0.2& (2.06 ± 0.11 measured, n = 3) and 3.04 ± 0.30&. Literature values (d82/76Se) may be recalculated in the NIST 3149 scale. Troilite from various iron meteorites and mafic terrestrial rocks yield an average composition of zero per mil with a small variation of ±0.39& and of ±0.72&, respectively. Sediments have a slightly larger range in composition (0.39 ± 1.11&). Sulfides from modern hydrothermal fields and from various black shales yield rather negative average values of 1.26 ± 2.6& and 0.57 ± 4.9% and relatively large range in compositions. New results obtained at CRPG laboratory on black shales revealed high variations of their d82/76SeNIST, from 12.9& to 4.9&. In these specific rocks, Se occurs as different chemical forms (Se 2 and Se0). Se isotopes are then sensitive to the alteration cycle of rocks and subsequent phase transformations related to redox conditions.
Reference Rouxel, O., Ludden, J., Carignan, J., Marin, L., Fouquet, Y., 2002. Geochim. Cosmochim. Acta 66, 3191–3199. doi:10.1016/j.gca.2006.06.079
Trace element geochemistry of magnetite and pyrite in Fe oxide (±Cu–Au) mineralised systems: Insights into the geochemistry of ore-forming fluids M.J. CAREW1, G. MARK1,2, N.H.S. OLIVER1, N. PEARSON3 1
EGRU, School of Earth Sciences, James Cook University, Australia ([email protected]; [email protected]) 2 Monash Ore Geology Research and Exploration Group, School of Geosciences, Monash University, Australia (geordie.mark@ sci.monash.edu.au) 3 GEMOC, Macquarie University, Australia (norm.pearson@ mq.edu.au) LA-ICP–MS analyses of magnetite and pyrite from Fe oxide (Cu–Au) (e.g. Ernest Henry, Osborne, Starra and Mount Elliott) and related deposits in northwest Queensland, Australia shows that these minerals are enriched in a diverse suite of elements. Magnetite typically contains detectable Ti, Si, Al, Mg, Sc, Co, Ni, Cu, Zn, Ga, Sn, Pb, Mn, V, Cr and Mo, whereas co-genetic pyrite contains detectable Ti, Co, As, Si, Se and Ni. Comparison of ore-related and barren systems shows that magnetite and pyrite exhibit differences in relative trace element concentrations, where magnetite associated with ore typically contains lower Ti, V and Cr and higher Sc and Mo, while Co and As were higher in ore-related pyrite. These chemical differences are common for many Cu–Au ore systems in the district, and potentially indicate that magnetite and pyrite can be employed as geochemical mineral indicators toward ore-forming systems. The main factors considered important in controlling magnetite and pyrite geochemistry include: (i) fluid composition; (ii) process of ore formation (e.g. fluid mixing and fluid–rock interaction); and/or (iii) physicochemical conditions (e.g. T, foo) during mineral deposition. Given that the minerals in this study largely occur as open-space fill (e.g., veins), they were probably formed in fluid-buffered environments where contributions from the host rocks via element exchange were minimal. Consequently, we propose that the chemistry of magnetite and pyrite in the ore systems probably reflects the geochemistry of the precipitating fluid(s) which considered together with the stable isotope characteristics and complex chemistry of ore-forming fluids from the Ernest Henry and Starra Cu–Au deposits suggests a significant magmatic contribution to the metal budget of the ore deposits (1).
Reference Williams, P.J., Dong, G., Ryan, C.G, Pollard, P.J., Rotherham, J.F., Mernagh, T.P., Chapman, L.H., . Econ. Geol. 96, 875–883. doi:10.1016/j.gca.2006.06.078
A83
Scaling NIST SRM 3149 for Se isotope analysis and isotopic variations of natural samples J. CARIGNAN1, H. WEN1,2 1
CRPG-CNRS, 15, Rue Notre-Dame des Pauvres, B. P. 20, 54501, Vandoeuvre-le`s-Nancy Cedex, France (carignan@crpg. cnrs-nancy.fr) 2 KLODG, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China ([email protected]) There is actually no consensus on what material should be used as the ‘‘delta zero’’ reference for Se isotope analysis. Some concerned scientists suggested the use the NIST SRM 3149. Here we report its composition (lot 992106) relative to a MERCK Se solution which was already used as reference (Rouxel et al., 2002). The technique used is the on line, continuous flow hydride generation, coupled to a MC-ICP–MS Isoprobe, equipped with a collision cell, as described by Rouxel et al. (2002). The d82/ 76 SeMERCK measured for the NIST SRM 3149 is 1.53 ± 0.20 (± is 2 times the standard deviation from the mean, n = 31, 11 sessions). Recalculated d82/76Se relative to NIST for MERCK, CRPG and MH495 Se solutions are then respectively 1.53 ± 0.20&, 2.01 ± 0.2& (2.06 ± 0.11 measured, n = 3) and 3.04 ± 0.30&. Literature values (d82/76Se) may be recalculated in the NIST 3149 scale. Troilite from various iron meteorites and mafic terrestrial rocks yield an average composition of zero per mil with a small variation of ±0.39& and of ±0.72&, respectively. Sediments have a slightly larger range in composition (0.39 ± 1.11&). Sulfides from modern hydrothermal fields and from various black shales yield rather negative average values of 1.26 ± 2.6& and 0.57 ± 4.9% and relatively large range in compositions. New results obtained at CRPG laboratory on black shales revealed high variations of their d82/76SeNIST, from 12.9& to 4.9&. In these specific rocks, Se occurs as different chemical forms (Se 2 and Se0). Se isotopes are then sensitive to the alteration cycle of rocks and subsequent phase transformations related to redox conditions.
Reference Rouxel, O., Ludden, J., Carignan, J., Marin, L., Fouquet, Y., 2002. Geochim. Cosmochim. Acta 66, 3191–3199. doi:10.1016/j.gca.2006.06.079