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Exploration applications of copper isotopes in the supergene environment / David Braxton in Economic geology, Vol. 106 N° 8 (Décembre 2011) 

Public ISBD [article]  in Economic geology > Vol. 106 N° 8 (Décembre 2011) . - pp. 1447-1463 Titre : Exploration applications of copper isotopes in the supergene environment : a case study of the bayugo porphyry copper-gold deposit, southern Philippines Type de document : texte imprimé Auteurs : David Braxton, Auteur ; Ryan Mathur, Auteur Année de publication : 2011 Article en page(s) : pp. 1447-1463 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Copper  isothrope  Copper  deposit  Gold  deposit  Philippines Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Copper isotope compositions of secondary phases from the supergene profile of the Bayugo porphyry copper-gold deposit (Philippines) show significant isotopic fractionation relative to hypogene sulfide phases and reveal systematic patterns of isotopic enrichment in the leached cap iron oxides and supergene copper sulfides. Thirty-nine iron oxide, copper oxide, and copper sulfide minerals yielded δ65Cu values between −3.4 and +6.9 per mil. Samples of hypogene sulfides have a narrow range of values near zero per mil (−0.6 to +1.0‰). In contrast, samples of supergene sulfides (chalcocite and djurleite) collected from the exotic and enriched copper zones define a trend of decreasing δ65Cu from the enriched source area and proximal exotic zone (>3‰) downgradient to the distal portions (<1‰) of the exotic zone. The higher isotopic values in the source area and proximal zones are consistent with Rayleigh fractionation models depicting multiple cycles of oxidation, leaching, and enrichment of copper. Large (1.8–2.7‰) copper isotope ratios measured for leached cap iron oxides provide evidence for a preexisting sulfide enrichment zone that was removed in subsequent cycles of oxidation, leaching, and enrichment. These findings are significant, because within exotic copper zones the copper isotope values of supergene sulfides can provide an indication both of proximity and direction to the source area. The technique could be applied in the search for unrecognized porphyry centers upgradient from headless exotic copper occurrences, by exploring for the supergene copper phases with the highest δ65Cu values. Independently, copper isotope ratios of iron oxides in surface samples or fossil leached caps might be used to rank prospects and to focus drilling in areas with the greatest potential for mature enrichment profiles, by mapping the distribution of isotopically enriched leached cap iron oxides. The leached cap screening and targeting tool could enhance the iron oxide mapping techniques traditionally applied in leached cap interpretation and exploration. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/106/8/1447.abstract [article] Exploration applications of copper isotopes in the supergene environment : a case study of the bayugo porphyry copper-gold deposit, southern Philippines [texte imprimé] / David Braxton, Auteur ; Ryan Mathur, Auteur . - 2011 . - pp. 1447-1463. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 106 N° 8 (Décembre 2011) . - pp. 1447-1463 Mots-clés : Copper  isothrope  Copper  deposit  Gold  deposit  Philippines Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Copper isotope compositions of secondary phases from the supergene profile of the Bayugo porphyry copper-gold deposit (Philippines) show significant isotopic fractionation relative to hypogene sulfide phases and reveal systematic patterns of isotopic enrichment in the leached cap iron oxides and supergene copper sulfides. Thirty-nine iron oxide, copper oxide, and copper sulfide minerals yielded δ65Cu values between −3.4 and +6.9 per mil. Samples of hypogene sulfides have a narrow range of values near zero per mil (−0.6 to +1.0‰). In contrast, samples of supergene sulfides (chalcocite and djurleite) collected from the exotic and enriched copper zones define a trend of decreasing δ65Cu from the enriched source area and proximal exotic zone (>3‰) downgradient to the distal portions (<1‰) of the exotic zone. The higher isotopic values in the source area and proximal zones are consistent with Rayleigh fractionation models depicting multiple cycles of oxidation, leaching, and enrichment of copper. Large (1.8–2.7‰) copper isotope ratios measured for leached cap iron oxides provide evidence for a preexisting sulfide enrichment zone that was removed in subsequent cycles of oxidation, leaching, and enrichment. These findings are significant, because within exotic copper zones the copper isotope values of supergene sulfides can provide an indication both of proximity and direction to the source area. The technique could be applied in the search for unrecognized porphyry centers upgradient from headless exotic copper occurrences, by exploring for the supergene copper phases with the highest δ65Cu values. Independently, copper isotope ratios of iron oxides in surface samples or fossil leached caps might be used to rank prospects and to focus drilling in areas with the greatest potential for mature enrichment profiles, by mapping the distribution of isotopically enriched leached cap iron oxides. The leached cap screening and targeting tool could enhance the iron oxide mapping techniques traditionally applied in leached cap interpretation and exploration. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/106/8/1447.abstract

Patterns in the copper isotope composition of minerals in porphyry copper deposits in southwestern United States / Ryan Mathur in Economic geology, Vol. 105 N° 8 (Décembre 2010) 

Public ISBD [article]  in Economic geology > Vol. 105 N° 8 (Décembre 2010) . - pp. 1457-1467 Titre : Patterns in the copper isotope composition of minerals in porphyry copper deposits in southwestern United States Type de document : texte imprimé Auteurs : Ryan Mathur, Auteur ; Molly Dendas, Auteur ; Spencer Titley, Auteur Année de publication : 2011 Article en page(s) : pp. 1457-1467 Note générale : Géologie économique Langues : Anglais (eng) Mots-clés : Porphyry  copper  deposits  Isotope  composition  United-States Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Cu isotope measurements of minerals from American southwest porphyry Cu deposits reveal a positive relationship with the grade of Cu and display spatial patterns. We measured the Cu isotope composition of 87 minerals contained within veins from drill core and hand specimen samples from three deposits (the Silver Bell, Ray, and Morenci mines). The overall range of Cu isotope ratios varies from −13.5 to +8.3 per mil. The deposits possess three different Cu reservoirs in which each has unique Cu isotope signatures, where δ65Cu for leach cap minerals < hypogene minerals < supergene enrichment minerals. The pattern exists in all three deposits and resulted from oxidative weathering of Cu at surface and reprecipitation of Cu at depth. A Rayleigh distillation model mimics the Cu isotope patterns found in the leach cap and quantifies the degree of leaching. A comparison of the isotopic composition of the three reservoirs among the three deposits reveals distinct differences—the Silver Bell mine possesses leach cap minerals that are more depleted in 65Cu and enrichment minerals that are more enriched in 65Cu than both the Morenci and Ray mines. A possible explanation for the difference among the deposits could indicate that the Silver Bell deposit experienced a greater degree of leaching than the Ray and Morenci deposits. The comparative analysis of the Cu isotope data reveals the exploration potential of using Cu isotope fractionation in the supergene environments. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/8/1457.abstract [article] Patterns in the copper isotope composition of minerals in porphyry copper deposits in southwestern United States [texte imprimé] / Ryan Mathur, Auteur ; Molly Dendas, Auteur ; Spencer Titley, Auteur . - 2011 . - pp. 1457-1467. Géologie économique Langues : Anglais (eng) in Economic geology > Vol. 105 N° 8 (Décembre 2010) . - pp. 1457-1467 Mots-clés : Porphyry  copper  deposits  Isotope  composition  United-States Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Cu isotope measurements of minerals from American southwest porphyry Cu deposits reveal a positive relationship with the grade of Cu and display spatial patterns. We measured the Cu isotope composition of 87 minerals contained within veins from drill core and hand specimen samples from three deposits (the Silver Bell, Ray, and Morenci mines). The overall range of Cu isotope ratios varies from −13.5 to +8.3 per mil. The deposits possess three different Cu reservoirs in which each has unique Cu isotope signatures, where δ65Cu for leach cap minerals < hypogene minerals < supergene enrichment minerals. The pattern exists in all three deposits and resulted from oxidative weathering of Cu at surface and reprecipitation of Cu at depth. A Rayleigh distillation model mimics the Cu isotope patterns found in the leach cap and quantifies the degree of leaching. A comparison of the isotopic composition of the three reservoirs among the three deposits reveals distinct differences—the Silver Bell mine possesses leach cap minerals that are more depleted in 65Cu and enrichment minerals that are more enriched in 65Cu than both the Morenci and Ray mines. A possible explanation for the difference among the deposits could indicate that the Silver Bell deposit experienced a greater degree of leaching than the Ray and Morenci deposits. The comparative analysis of the Cu isotope data reveals the exploration potential of using Cu isotope fractionation in the supergene environments. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/8/1457.abstract