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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