Mineralização aurifera de Lages-Antonio Dias, Ouro Preto-MG controles lito-estratigraficos e estruturais

AUTOR(ES)
DATA DE PUBLICAÇÃO

1999

RESUMO

The Lages-Antônio Dias area is eomprised within the Ouro Preto mountain range, Minas Gerais. The area hosts a number of aneient, abandoned gold mines; Chieo Rei, Scliar and Duas Bocas being among the largest deposits. Detailed geologieal mapping of both the Lages-Antônio Dias area (1:2000) and these mines (1:250 se ale) showed that gold is associated with tourmaline- and -sulphide-rieh quartz veins. Sueh veins occur dominant1y along lithologie eontaets and struetural diseontinuities. The gold-bearing tourmalinites are assoeiated with quartz veins hosted within several litho-stratigraphie units that eompose the Ouro Preto ~ountain range. Their formation probably results from the interaetion between hydrothermal fluids and the host roeks. It is demonstrable that these fluids pervaded through fraeture systems regardless the local stratigraphy. The tourmalinites are found in four different circumstanees. They occur between the lithologieal contacts of (i) Nova Lima Group and Moeda Formation assemblages; (i i) Moeda Formation and Batata! Formation roeks; (iii) Batatal Formation and Cauê Formation roeks and, (iv) as eross-eutting veins within Moeda and Batatal Formations. The sulphide-rieh veins are akin to brittle structures to whieh later, ductile strains were superimposed. These quartz veins were emplaced along vertical and/or eonjugated extensional fraetures and are eomposed of (i) arsenopyrite, (ii) pyrite/calcopyrite and, (iii) pirrotite, besides minor tourmaline. The arsenopyrite-rich quartz veins occur in two different styles: (i) as diseordant veins within the Batatal Formation, where massive knots of arsenopyrite are found; (ii) as banded veins, enveloped by Moeda Formation quartzites, assoeiated with eonjugated normal faults that are part of an ubiquitous system of normal shear zones. The pirrotite-rieh veins are also banded and oceur along a normal shear zone, showing sense of movement to the south. They are mainly found emplaeed in the lower portions of the Cauê Formation. The pyrite-ealcopyrite-rieh veins are diseordant and cut only the Cauê Formation. Although the meehanisms of emplaeement are yet poorly constrained, the data gathered in this study suggests that the gold-mineralization was formed at least in two different stages, prior to regional deformation. The first stage was resposible for the emplaeement of tourmalinites and quartz-sulphidie veins, which are associate to fractures eutting thé Moeda quartzites, the Batatal earbonaeeous-phyllites and sehists and the Cauê itabirites. The tourmalinites assembled mainly between the interseetion of fraetures and sedimentary bedding. The seeond stage was marked only by the emplacement of sulphidic-rieh veins formed along conjugated fraetures that were developed within major normal-shear zones and faults. Field evidenees indicate that these two main stages of mineralization oceured prior to the formation of the Mariana anticline. The veins, formed along these two stages, were also later geometrieally modified by the antieline uplift

ASSUNTO(S)

ouro - ouro preto (mg) - quadrilatero ferrifero minas e recursos minerais - ouro preto (mg)

ACESSO AO ARTIGO

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