Paleoproterozoic gold deposits at Alta Floresta Mineral Province, Brazil: two overprinted mineralizing events?
Posted on 2022-06-22 - 14:08
Large gold provinces commonly show complicated mineralization histories, and the Paleoproterozoic Alta Floresta, one of Brazil's most exciting Au–Cu mineral provinces, is a good example. The current models define four deposit types, all connected to a single (1.88–1.75 Ga) magmatic–hydrothermal event. However, long Province history, diverse geodynamic environment and older ages of type-1 mineralization weaken the single metallogenic event and enable the hypothesis of overprinted mineral events. By using scale-integrated analyses, we revise the tectonic–geological context, structural–hydrothermal alterations and chlorite–white mica geothermobarometer and propose the type-1 as an older, granitoid-hosted orogenic mineralization with subsequent overprinting by the magmatic–hydrothermal event. The older orogenic gold event developed orogenic gold deposits on WNW-trending shear zones in the Peixoto de Azevedo domain granitic–gneiss rocks. Phengite, biotite, chlorite–carbonate phyllonites (3.3–6.1 kbar, 300–420°C) host fault-fill quartz veins (pyrite–chalcopyrite–magnetite–pyrrhotite–gold–Bi–Ag tellurides). Mg-rich chlorite–phengite is the main alteration footprint for this mineralization type. A younger magmatic–hydrothermal event in the Juruena magmatic–arc rocks produced Ferich chlorite–white mica alteration zones (0.6–4.6 kbar, 120–380°C) and disseminated and stockwork–breccia ore (pyrite–chalcopyrite–gold–molybdenite– Ti minerals–allanite) in porphyry–epithermal deposits. Where the younger mineralization overprints the older, phyllic alteration destroyed the phengite orogenic gold phyllonite Sn+1 foliation. The ages of two pyrite populations (1979 and 1841 Ma) in the older fault-fill veins and molybdenite in late fractures (1805–1782 Ma) or disseminated in the ca. 1.79 Ga syenogranite porphyry suggest more than two episodes of mineralization. These two events differ in their alteration styles, P–T conditions, and structural, mineralogical and textural ore styles. The multi-scale approach enlightens the relationships between the various mineralization events, allowing a new explorational potential within the province.
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José Maluf de Mesquita, Maria; Gomes, Márcia Elisa Boscato; Moreira, Igor de Carvalho; Paes, Renata Augusta Sampaio; Martins, Hevelyn Eduarda da Silva; Matos, José Henrique da Silva Nogueira de; et al. (2022). Paleoproterozoic gold deposits at Alta Floresta Mineral Province, Brazil: two overprinted mineralizing events?. Geological Society of London. Collection. https://doi.org/10.6084/m9.figshare.c.6056324.v2
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Maria José Maluf de Mesquita
Márcia Elisa Boscato Gomes
Igor de Carvalho Moreira
Renata Augusta Sampaio Paes
Hevelyn Eduarda da Silva Martins
José Henrique da Silva Nogueira de Matos
Diego Fernando Ducart
Leonardo Zanchetta de Laurentis
André Massanobu Ueno Kunifoshita
trending shear zonespaleoproterozoic gold depositspaleoproterozoic alta florestaoverprinted mineral eventsdiverse geodynamic environment1805 – 1782two pyrite populationstwo events differphyllic alteration destroyedmain alteration footprintyounger mineralization overprintsvarious mineralization eventstextural ore stylesscale approach enlightenshosted orogenic mineralization6 – 4single metallogenic eventlong province historyfill quartz veins88 – 11 mineralization weaken3 – 6alteration stylesfill veinsp –two episodes6 kbarusing scale1 kbar1 foliationsubsequent overprintingmineralization typelate fracturesintegrated analyseshost faultgood example75 gaGeology