Hematite and goethite from duricrusts developed by lateritic chemical weathering of Precambrian banded iron formations, Minas Gerais, Brazil

被引:37
作者
Ramanaidou, E
Nahon, D
Decarreau, A
Melfi, AJ
机构
[1] UNIV AIX MARSEILLE 3, FAC SCI ST JEROME, URA 132 CNRS, F-13397 MARSEILLE 20, FRANCE
[2] UNIV POITIERS, URA 721 CNRS, F-86000 POITIERS, FRANCE
[3] UNIV SAO PAULO, DEPT GEOFIS NUCL PESQUISA GEOQUIM & GEOFIS LITOSF, BR-05508 SAO PAULO, BRAZIL
关键词
hematite; goethite; laterite; Mossbauer spectrometry;
D O I
10.1346/CCMN.1996.0440102
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The upper 15-20 m of a 200 m thick lateritic weathering profile on Precambrian itabirites of Capanema, Brazil, reveals a genetic pathway for the formation of hematitic and goethitic nodules in the ferruginous crust through a very tine grain Al-hematite and Al-goethite mixture, called here the brick-red-material (brm). This evolution develops between the soft saprolite and a 10 m thick indurated ferruginous crust. The soft saprolite retains the original structures of the itabirite and is characterized by almost complete dissolution of quartz, the development of goethite septa, and the partial dissolution of primary hematite. Near the contact with the overlying ferruginous crust, the brm is gradually filling voids as well as replacing primary hematite and goethite in the saprolite. In the upper indurated crust, the brm transforms into coarse structureless ferruginous nodules (aluminous hematites and goethites) and is the precursor of the hematito-goethitic nodules of the crusts. Crystallization of newly-formed Al-goethite and Al-hematite within the brm occurs without detectable amounts of amorphous iron oxides of ferrihydrite precursors.
引用
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页码:22 / 31
页数:10
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