Exploration vectoring from the white mica spectral footprint in the atypical auriferous Lavra Velha deposit, San Francisco Craton, Brazil
Carlos Martín Medina, Diego Fernando Ducart, Josué Souza Passos, Leandro Rocha de Oliveira
ARTIGO
Inglês
Agradecimentos: Parts of this study were financed by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) - Finance Code 001. Yamana Gold, and especially their Ibitiara-based exploration staff, are thanked for financial-logistical support during fieldwork and analytical...
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Agradecimentos: Parts of this study were financed by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) - Finance Code 001. Yamana Gold, and especially their Ibitiara-based exploration staff, are thanked for financial-logistical support during fieldwork and analytical studies. The company granted access to drill cores and geochemical data and the permission to publish. We thank Prof. Celio Pasquini and Cristiane Vidal at the Institute of Chemistry of University of Campinas for assistance with SisuCHEMA device. Dr. João Motta at University of Campinas provided in-depth reviews of a draft manuscript. The authors would also like to thank Prof. Carlos Roberto de Souza Filho (University of Campinas) for providing helpful advice and technical feedback. Carlos Medina acknowledges the geologists Luciano Poggi and Simmon Viegas de Souza for technical help on the use of spectral analysis. Finally, we extend our gratitude to Doug Kirwin, who provided constructive formatting suggestions and technical comments in the final stages of this paper. Part of the data analysis for this paper was generated using Leapfrog Software. Copyright © Seequent Limited. Leapfrog and all other Seequent Limited product or service names are registered trademarks of Seequent Limited
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Abstract: The Lavra Velha deposit is a poorly understood gold deposit hosted by the 2.1 Ga Ibitiara Granitoid, within the São Francisco Craton (Brazil). Although not consensually agreed, Lavra Velha has been inserted into the Iron Oxide-Copper-Gold (IOCG) class. The major alteration footprint of the...
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Abstract: The Lavra Velha deposit is a poorly understood gold deposit hosted by the 2.1 Ga Ibitiara Granitoid, within the São Francisco Craton (Brazil). Although not consensually agreed, Lavra Velha has been inserted into the Iron Oxide-Copper-Gold (IOCG) class. The major alteration footprint of the deposit involves an upward mineralogical zoning from widespread chlorite-epidote-calcite (propylitic) to white mica-hematite-quartz association with an intervening magnetite-tourmaline-quartz-white mica realm. The ore occurs mostly as massive lenses composed of magnetite, hematite, pyrite, tennantite, bismuthinite, digenite and native gold. Gold is present as inclusion within hematite, pyrite, quartz and cassiterite, in association with white mica, but also with supergene jarosite-goethite. The proximal footwall and hanging walls of the mineralization are commonly anomalous in Cr-Ni-Co and, where weathered, a talc-nontronite association is documented. Such features are considered to represent ultramafic rocks closely associated with mineralization. Reflectance spectroscopy results show that white mica, hematite and Fe-tourmaline are closely and spatially associated with gold mineralization, thus representing a proximal alteration mineralogy. Notably, white mica becomes progressively more phengitic (>2210 nm) as higher Au grades are laterally approached, whereas it has muscovitic composition (<2198 nm) where gold grades are waning. This chemical gradient can be used as an exploratory guide to find zones of higher-grade mineralization. The crystallinity of white mica reveals a strong zonation from the top to the bottom of the deposit defined by the downward variation from muscovite to illite. The passage zone from muscovite to illite represents potential sites for gold deposition. In weathered profiles, the spectral mapping of talc-nontronite would be key in detecting gold-related ultramafic rocks. This work found that SWIR hyperspectral measurement of white mica features provides an efficient means for vectoring to gold mineralization, at least to district scale. The unusual mineralogical signature of Lavra Velha is not diagnostic of any specific style of known deposit and further in-depth studies are required to decipher what kind of deposit it belongs
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COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES
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Exploration vectoring from the white mica spectral footprint in the atypical auriferous Lavra Velha deposit, San Francisco Craton, Brazil
Carlos Martín Medina, Diego Fernando Ducart, Josué Souza Passos, Leandro Rocha de Oliveira
Exploration vectoring from the white mica spectral footprint in the atypical auriferous Lavra Velha deposit, San Francisco Craton, Brazil
Carlos Martín Medina, Diego Fernando Ducart, Josué Souza Passos, Leandro Rocha de Oliveira
Fontes
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Ore Geology Reviews Vol. 139 (Aug., 2021), n art. 104438 |