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Geology and intrusion-related affinity of the morila gold mine, Southeast Mali / Christopher R.M. McFarlane in Economic geology, Vol. 106 N° 5 (Août 2011) 

Public ISBD [article]  in Economic geology > Vol. 106 N° 5 (Août 2011) . - pp. 727-750 Titre : Geology and intrusion-related affinity of the morila gold mine, Southeast Mali Type de document : texte imprimé Auteurs : Christopher R.M. McFarlane, Auteur ; John Mavrogenes, Auteur ; Dave Lentz, Auteur Année de publication : 2011 Article en page(s) : pp. 727-750 Note générale : Géologie économique Langues : Anglais (eng) Mots-clés : Gold  deposits  Mali Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The ~8 Moz Morila gold mine, hosted within Paleoproterozoic Birimian volcano-sedimentary rocks of southeast Mali, is spatially and temporally associated with prolonged (2098–2065 Ma) arc magmatism during the late stages of the Eburnean orogeny. Visible gold at Morila is associated with variably deformed polymineralic veins containing native bismuth, maldonite, aurostibite, rare tellurobismuthite, and löllingite, suggesting a proximal intrusion-related source for this period of gold mineralization. This early formed mineralization is contained within a zone of hornblende hornfels contact metamorphism and is spatially associated with syn- to post-D2 emplacement of 2098 to 2091 Ma quartz-diorite, granodiorite, and leucogranite magmas. The occurrence of immiscible Au-Sb-Bi-Te blebs within sills or dikes associated with gold mineralization at the Morila deposit explicitly links granitic magmatism with gold mineralization This early intrusion-related gold system was over-printed by a younger post-D2 stage of hydrothermal alteration recorded by sulfidation along a north-north-east–trending zone characterized by disseminated idioblastic arsenopyrite porphyroblasts that contain polygonal gold blebs. Silicate alteration during this stage includes albitization of plagioclase and the growth of randomly distributed biotite and titanite, the latter typically surrounding ilmenite. Uranium-Pb dating of this generation of titanite yields a preliminary age for late-stage sulfidation of 2074 ± 14 Ma, which brackets mineralization to the interval 2098 ± 4 to 2074 ± 14 Ma. The geochemistry and isotope systematics of syn- to post-tectonic intermediate intrusions at the Morila deposit point to their derivation in a suprasubduction zone setting and emplacement into tectonically thickened crust. Based on these observations, it is suggested that the Morila gold deposit formed during late-stage collisional orogenesis involving the accretion of juvenile volcanic arc terranes against the Archean Man (Liberian) cratonic nucleus. This setting is analogous to younger Phanerozoic active continental margin settings which host the best-described examples of intrusion-related gold systems. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/106/5/727.abstract [article] Geology and intrusion-related affinity of the morila gold mine, Southeast Mali [texte imprimé] / Christopher R.M. McFarlane, Auteur ; John Mavrogenes, Auteur ; Dave Lentz, Auteur . - 2011 . - pp. 727-750. Géologie économique Langues : Anglais (eng) in Economic geology > Vol. 106 N° 5 (Août 2011) . - pp. 727-750 Mots-clés : Gold  deposits  Mali Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The ~8 Moz Morila gold mine, hosted within Paleoproterozoic Birimian volcano-sedimentary rocks of southeast Mali, is spatially and temporally associated with prolonged (2098–2065 Ma) arc magmatism during the late stages of the Eburnean orogeny. Visible gold at Morila is associated with variably deformed polymineralic veins containing native bismuth, maldonite, aurostibite, rare tellurobismuthite, and löllingite, suggesting a proximal intrusion-related source for this period of gold mineralization. This early formed mineralization is contained within a zone of hornblende hornfels contact metamorphism and is spatially associated with syn- to post-D2 emplacement of 2098 to 2091 Ma quartz-diorite, granodiorite, and leucogranite magmas. The occurrence of immiscible Au-Sb-Bi-Te blebs within sills or dikes associated with gold mineralization at the Morila deposit explicitly links granitic magmatism with gold mineralization This early intrusion-related gold system was over-printed by a younger post-D2 stage of hydrothermal alteration recorded by sulfidation along a north-north-east–trending zone characterized by disseminated idioblastic arsenopyrite porphyroblasts that contain polygonal gold blebs. Silicate alteration during this stage includes albitization of plagioclase and the growth of randomly distributed biotite and titanite, the latter typically surrounding ilmenite. Uranium-Pb dating of this generation of titanite yields a preliminary age for late-stage sulfidation of 2074 ± 14 Ma, which brackets mineralization to the interval 2098 ± 4 to 2074 ± 14 Ma. The geochemistry and isotope systematics of syn- to post-tectonic intermediate intrusions at the Morila deposit point to their derivation in a suprasubduction zone setting and emplacement into tectonically thickened crust. Based on these observations, it is suggested that the Morila gold deposit formed during late-stage collisional orogenesis involving the accretion of juvenile volcanic arc terranes against the Archean Man (Liberian) cratonic nucleus. This setting is analogous to younger Phanerozoic active continental margin settings which host the best-described examples of intrusion-related gold systems. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/106/5/727.abstract