THE Barra do Itapirapua carbonatite belongs to a Cretaceous province related to the opening of the SouthAtlantic, and is emplaced in a Proterozoic granite. The carbonatite is mainly composed of plutonic magnesio-and f...THE Barra do Itapirapua carbonatite belongs to a Cretaceous province related to the opening of the SouthAtlantic, and is emplaced in a Proterozoic granite. The carbonatite is mainly composed of plutonic magnesio-and ferrocarbonatite and is mineralizing host of a REE mineralization related to late-to post-magmatic hydrothermal processes. The non-overprinted carbonatite has low bulk REE contents, andmagmatic pyrochlore is the major carrier of REE. In the altered mineralized carbonatite, corrosion cavitiesin primary ankerite are filled with a hydrothermal mineral assemblage of quartz, apatite, fluorite, RE-fluorocarbonates, barite, sulfides and Fe-oxides in variable proportions. Two types of hydrothermally overprinted carbonatites can be distinguished: type Ⅰ containing quartz and RE-fluorocarbonates, enriched inLREE and with ∑REE of up to 3% (weight percent), which is two orders of magnitude higher than thenon-overprinted carbonatite; and type Ⅱ containing apatite as the major hydrothermal mineral, and enriched in HREE. The END of the mineralized carbonatite reveals a nonradiogenic isotopic signature andsuggests a carbonatite-related source for the REE展开更多
文摘THE Barra do Itapirapua carbonatite belongs to a Cretaceous province related to the opening of the SouthAtlantic, and is emplaced in a Proterozoic granite. The carbonatite is mainly composed of plutonic magnesio-and ferrocarbonatite and is mineralizing host of a REE mineralization related to late-to post-magmatic hydrothermal processes. The non-overprinted carbonatite has low bulk REE contents, andmagmatic pyrochlore is the major carrier of REE. In the altered mineralized carbonatite, corrosion cavitiesin primary ankerite are filled with a hydrothermal mineral assemblage of quartz, apatite, fluorite, RE-fluorocarbonates, barite, sulfides and Fe-oxides in variable proportions. Two types of hydrothermally overprinted carbonatites can be distinguished: type Ⅰ containing quartz and RE-fluorocarbonates, enriched inLREE and with ∑REE of up to 3% (weight percent), which is two orders of magnitude higher than thenon-overprinted carbonatite; and type Ⅱ containing apatite as the major hydrothermal mineral, and enriched in HREE. The END of the mineralized carbonatite reveals a nonradiogenic isotopic signature andsuggests a carbonatite-related source for the REE
