LATE CAMBRIAN Au-Pd MINERALIZATION AND Fe ENRICHMENT IN THE ITABIRA DISTRICT, MINAS GERAIS, BRAZIL, AT 496 Ma: CONSTRAINTS FROM U-Pb MONAZITE DATING OF A JACUTINGA LODE

Abstract

Bonanza-style mineralization of palladiferous gold in specular hematite-rich lodes engendered the most important gold rush in Brazilian history, which took place at the end of the seventeenth century in the province that became known as Minas Gerais. The timing of this itabirite-hosted vein mineralization, locally referred to as jacutinga, is controversial; different views have ascribed jacutinga to one of the two orogenic events recorded in the Quadrilátero Ferrífero of Minas Gerais, the ~2.0 Ga Transamazonian event and the ~0.6 Ga Brasiliano event. This controversy is due mainly to the absence of reliable age data for hydrothermal minerals. Here we report the first U-Pb age for a jacutinga lode, obtained by laser ablation-sector field-inductively coupled plasmamass spectrometry (LA-SF-ICP-MS) on monazite grains recovered from the Conceição Fe-ore deposit within the Itabira district. The monazite analyses yield a precise Late Cambrian age of 495.6 ± 2.2 Ma, which is well within the time period between ca. 524 and 444 Ma, suggested by recently published geochronologic data on regionally distributed similar hydrothermal systems. The age of 496 Ma for the jacutinga monazite corroborates an orogen-scale hydrothermal overprint at later stages of the Brasiliano event. This hydrothermal overprint also affected surrounding Neoarchean rocks of the Minas Supergroup, as well as younger rocks of the southern Serra do Espinhaço, along the platiniferous Au-Pd belt of Minas Gerais.

Trace-element composition of pyrite and its implications for hydrothermal process within the Mesoproterozoic metasedimentary sequences of the São Francisco Craton, northeastern Brazil

“…Regional fluid flow is presented as hydrothermal mineral deposits in the São Francisco Craton and adjacent orogenic belts (e.g., the Araçuaí orogen). It includes the Eastern Brazilian Pegmatite Province, Au-Pd deposits, amethyst and baryte hydrothermal deposits (Teixeira et al, 2010;Pedrosa-Soares et al, 2011;Guimarães et al, 2012;Cabral et al, 2015;Cruz et al, 2018). Furthermore, a large number of mineralized veins containing Au, barite-hematite and rutilated quartz are commonly observed in shear zones (Guimarães et al, 2005;Teixeira et al, 2010).…”

“…Previous geochronological studies have constrained the U-Pb and U-Th-4 He ages (ca. 524 -496 Ma) of hydrothermal systems and ore deposits in the São Francisco Craton (e.g., Cabral et al, 2013Cabral et al, , 2015. The Paramirim shear zone (see location in Figure 1) was dated at 486 ± 7 Ma using the Ar/Ar method (Guimarães et al, 2005).…”

A Contribuição Do Brasil Para a Descoberta De Um Novo Elemento Químico – O Paládio

“…Uma série de artigos [4][5][6][7] propõe a forma com que foi depositado o paládio, além de outros metais mais nobres como a platina e o ouro, em uma faixa do estado de Minas Gerais. Ela compreende um alinhamento de 120 km no sentido sul-norte que se inicia no Quadrilátero Ferrífero (QF), ou mais exatamente nas cidades de Ouro Preto e Ouro Branco, e se encerra em Diamantina no coração da Serra do Espinhaço (Figura 1).…”