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Age constraints on felsic intrusions, metamorphism and gold mineralisation in the Palaeoproterozoic Rio Itapicuru greenstone belt, NE Bahia State, Brazil

Mineralium Deposita

By:
, , , , ,
DOI: 10.1007/s00126-005-0037-3

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Abstract

U-Pb sensitive high resolution ion microprobe mass spectrometer (SHRIMP) ages of zircon, monazite and xenotime crystals from felsic intrusive rocks from the Rio Itapicuru greenstone belt show two development stages between 2,152 and 2,130 Ma, and between 2,130 and 2,080 Ma. The older intrusions yielded ages of 2,152??6 Ma in monazite crystals and 2,155??9 Ma in zircon crystals derived from the Trilhado granodiorite, and ages of 2,130??7 Ma and 2,128??8 Ma in zircon crystals derived from the Teofila??ndia tonalite. The emplacement age of the syntectonic Ambro??sio dome as indicated by a 2,080??2-Ma xenotime age for a granite dyke probably marks the end of the felsic magmatism. This age shows good agreement with the Ar-Ar plateau age of 2,080??5 Ma obtained in hornblendes from an amphibolite and with a U-Pb SHRIMP age of 2,076??10 Ma in detrital zircon crystals from a quartzite, interpreted as the age of the peak of the metamorphism. The predominance of inherited zircons in the syntectonic Ambro??sio dome suggests that the basement of the supracrustal rocks was composed of Archaean continental crust with components of 2,937??16, 3,111??13 and 3,162??13 Ma. Ar-Ar plateau ages of 2,050??4 Ma and 2,054??2 Ma on hydrothermal muscovite samples from the Fazenda Brasileiro gold deposit are interpreted as minimum ages for gold mineralisation and close to the true age of gold deposition. The Ar-Ar data indicate that the mineralisation must have occurred less than 30 million years after the peak of the metamorphism, or episodically between 2,080 Ma and 2,050 Ma, during uplift and exhumation of the orogen. ?? Springer-Verlag 2006.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Age constraints on felsic intrusions, metamorphism and gold mineralisation in the Palaeoproterozoic Rio Itapicuru greenstone belt, NE Bahia State, Brazil
Series title:
Mineralium Deposita
DOI:
10.1007/s00126-005-0037-3
Volume
40
Issue:
8
Year Published:
2006
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Mineralium Deposita
First page:
849
Last page:
866
Number of Pages:
18