The Ribeira fluorite district,southern Brazil |
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Authors: | L H Ronchi J C Touray A Michard M A Dardenne |
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Institution: | 1. Université d'Orléans, ESEM, GdR 0969 et URA n°1366 du CNRS, Rue Leonard de Vinci, F-45072, Orleans Cedex 2, France 2. Faculté des Sciences et Techniques de St-Jér?me, Université d'Aix-Marseille III, Case 431, F-13397, Marseille Cedex 13, France 3. Instituto de Geociências, Universidade de Brasilia, 70.910, Brasilia, DF, Brasil
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Abstract: | The origin and evolution of different ore deposits grouped in the same district are often complex and may involve inheritance
from crustal or mantle geochemical anomalies, remobilization of former ore deposits and a polyphase hydrothermal history.
Localized in a Proterozoic basement in the Parana state, the Ribeira fluorite district is such an example composed of three
deposit types with distinct geological and geochemical characters. Emplaced at different periods from the late Proterozoic
to the Cretaceous, they are roughly aligned along a belt nearly 10 km in width and 50 km in length, the southern boundary
of which is a transcurrent fault. Two main ore facies are present: (1) microcrystalline ore (< 0.1 mm grains) and (2) macrocrystalline
ore (with a grain size of several millimetres). The former results from the replacement of metalimestones or internal karstic
sediments and the latter from microcrystalline ore dissolution and pore precipitation or recrystallization. At least two different
groups of source rocks can be proposed for the trapped REE in CaF2: (1) fluorite samples associated with the Mato Preto carbonatitic rocks display a slightly negative ɛNd compatible with a
mantle source and a REE pattern with the higher ΣREE and La/Yb ratio in the district; (2) other fluorites have a strongly
negative ɛNd (− 14 to − 20) which indicates a crustal source. That fluorine and REE have the same source is possible in strata-bound
and fracture-filling deposits, but is doubtful at Mato Preto, the only economic fluorite deposit associated with carbonatite
rocks in Brazil. This occurrence within a Precambrian fluorite belt suggests that remobilization of a former strata-bound
deposit was a more significant metallogenic process than magmatic differentiation.
Editorial handling: DR |
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