40Ar/39Ar geochronological constraints on the evolution of lateritic iron deposits in the Quadrilatero Ferrifero, Minas Gerais, Brazil

Spier, C. A., Vasconcelos, P. M. and Oliviera, S. M. B. (2006) 40Ar/39Ar geochronological constraints on the evolution of lateritic iron deposits in the Quadrilatero Ferrifero, Minas Gerais, Brazil. Chemical Geology, 234 1-2: 79-104. doi:10.1016/j.chemgeo.2006.04.006


Author Spier, C. A.
Vasconcelos, P. M.
Oliviera, S. M. B.
Title 40Ar/39Ar geochronological constraints on the evolution of lateritic iron deposits in the Quadrilatero Ferrifero, Minas Gerais, Brazil
Formatted title 40Ar/39Ar geochronological constraints on the evolution of lateritic iron deposits in the Quadrilátero Ferrífero, Minas Gerais, Brazil
Journal name Chemical Geology   Check publisher's open access policy
ISSN 0009-2541
Publication date 2006
Sub-type Article (original research)
DOI 10.1016/j.chemgeo.2006.04.006
Volume 234
Issue 1-2
Start page 79
End page 104
Total pages 26
Editor Deines, P.
Goldstein, S. L.
Gopel, C.
Place of publication Netherlands
Publisher Elsevier BV
Collection year 2006
Language eng
Subject C1
260109 Geochronology
780104 Earth sciences
040303 Geochronology
040307 Ore Deposit Petrology
Abstract Weathering profiles overlying the Sapecado, Pico and Andaime iron ore deposits, Quadrilátero Ferrífero (QF), Minas Gerais, Brazil, reach depths of 150–400 m and host world-class supergene iron orebodies. In addition to hosting supergene ore bodies of global economic significance, weathered banded iron-formations at the Quadrilátero Ferrífero and elsewhere (e.g., Carajás, Hamersley) are postulated to underlie some of the most ancient continuously exposed weathering profiles on earth. Laser incremental-heating 40Ar/39Ar results for 69 grains of hollandite-group manganese oxides extracted from 23 samples collected at depths ranging from 5 to 150 m at the Sapecado, Pico and Andaime deposits reveal ages ranging from ca. 62 to 14 Ma. Older Mn-oxides occur near the surface, while younger Mn-oxides occur at depth. However, many samples collected at the weathering–bedrock interface yield ages in the 51–41 Ma range, suggesting that the weathering profiles in the Quadrilátero Ferrífero had already reached their present depth in the Paleogene. The antiquity of the weathering profiles in the Quadrilátero Ferrífero is comparable to the antiquity of dated weathering profiles on banded iron-formations in the Carajás Region (Brazil) and the Hamersley Province, Western Australia. The age versus depth distributions obtained in this study, but not available for other regions containing similar supergene iron deposits, suggest that little further advance of the weathering front has occurred in the Quadrilátero Ferrífero lateritic profiles during the Neogene. The results suggest that weathering in some of these ancient landscapes is not controlled by the steady-state advance of weathering fronts through time, but may reflect climatic and geomorphological conditions prevailing in a remote past. The geochronological results also confirm that the ancient landsurfaces in the Quadrilátero Ferrífero probably remained immune to erosion for tens of millions of years. Deep weathering, mostly in the Paleogene, combined with low erosion rates, account for the abundance and widespread distribution of supergene iron, manganese, and aluminum orebodies in this region.
Keyword 40ar/39ar Dating
Geochronology
Quadrilátero Ferrífero
Weathering
Iron Ore
Sapecado
Paleoclimate
Geomorphology
Landscape Evolution
Geochemistry & Geophysics
Ar-40/ar-39 Dating
Quadrilatero Ferrifero
K-mn Oxides
Western-australia
Manganese Oxides
Queensland
Climate
Africa
Region
Craton
Rates
Age
Q-Index Code C1

 
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