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
The Wiborg rapakivi batholith (1.64 Ga) in southeastern Finland with documented occurrences of REE, indium and Zn-Cu-Pb sulphide mineralization was studied. Hydrothermal greisen and quartz vein type Fe-Sn and Zn-Cu-Pb...The Wiborg rapakivi batholith (1.64 Ga) in southeastern Finland with documented occurrences of REE, indium and Zn-Cu-Pb sulphide mineralization was studied. Hydrothermal greisen and quartz vein type Fe-Sn and Zn-Cu-Pb are found in the Kymi granite stock as intrusions. They are enriched with indium and rare earth elements, with roquesite (CuInS2) being a major indium- carrier, whereas monazite (Ce), allanite (Ce), bastnäesite (Ce), xenotime-(Y) and thorite are the main REE carriers. Combination of optical and field emission scanning electron microscopy (FE-SEM) and electron probe microanalysis (EPMA) were used to study the indium and REE-bearing mineral assemblages. EPMA of roquesite found in galena had a composition of 26.16% S, 0.02% Fe, 25.06% Cu, 0.03% Zn, 1.06% As, 0.31% Sb and 47.14% In. Substitution reaction Pb2+S2-Cu+In3+S2- is the cause of the incorporation of indium in the galena structure. The majority of the LREE are carried by monazite, bastnäesite and allanite, and the HREE by xenotime and zircon. There is a partial solid solution between monazite and xenotime with minor or trace amounts of LREE in xenotime grains (6.0 wt%). LREE (>95 mol% LREE) and less than 5 mol% HREE + Y reflects the enrichment of chondrite-normalized REE of the monazite grains of the Kymi granite stock. The xenotime grains (small and irregular) main composition contains 71 - 76 mol% YPO4, 16 - 27 mol% HREE, and 6 - 8 mol% LREE. It is believed that indium and REE-mineralization presence is due to the combination of magmatic and postmagmatic processes, particularly at later stages by fluid fractionation.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
文摘The Wiborg rapakivi batholith (1.64 Ga) in southeastern Finland with documented occurrences of REE, indium and Zn-Cu-Pb sulphide mineralization was studied. Hydrothermal greisen and quartz vein type Fe-Sn and Zn-Cu-Pb are found in the Kymi granite stock as intrusions. They are enriched with indium and rare earth elements, with roquesite (CuInS2) being a major indium- carrier, whereas monazite (Ce), allanite (Ce), bastnäesite (Ce), xenotime-(Y) and thorite are the main REE carriers. Combination of optical and field emission scanning electron microscopy (FE-SEM) and electron probe microanalysis (EPMA) were used to study the indium and REE-bearing mineral assemblages. EPMA of roquesite found in galena had a composition of 26.16% S, 0.02% Fe, 25.06% Cu, 0.03% Zn, 1.06% As, 0.31% Sb and 47.14% In. Substitution reaction Pb2+S2-Cu+In3+S2- is the cause of the incorporation of indium in the galena structure. The majority of the LREE are carried by monazite, bastnäesite and allanite, and the HREE by xenotime and zircon. There is a partial solid solution between monazite and xenotime with minor or trace amounts of LREE in xenotime grains (6.0 wt%). LREE (>95 mol% LREE) and less than 5 mol% HREE + Y reflects the enrichment of chondrite-normalized REE of the monazite grains of the Kymi granite stock. The xenotime grains (small and irregular) main composition contains 71 - 76 mol% YPO4, 16 - 27 mol% HREE, and 6 - 8 mol% LREE. It is believed that indium and REE-mineralization presence is due to the combination of magmatic and postmagmatic processes, particularly at later stages by fluid fractionation.
