In the Kenticha area,a series of barren to rare metal-bearing pegmatites intruded into the Neoproterozoic Adola Belt.The pegmatites host world-class Nb and Ta deposits and significant Li and Be reserves.In this contri...In the Kenticha area,a series of barren to rare metal-bearing pegmatites intruded into the Neoproterozoic Adola Belt.The pegmatites host world-class Nb and Ta deposits and significant Li and Be reserves.In this contribution,fluid inclusion data and feldspar geothermometry have been combined to define the crystallization condition of the Kenticha rare-metal pegmatite.Primary and complex assemblages of secondary fluid inclusions representing episodic fluid circulations have been identified in quartz and spodumene.A primary aqueous-carbonic fluid of low salinity aqueous solution with liquid and vapour CO_(2) phases,secondary carbonic fluid rich and carboniconly fluids,and multiple generations of secondary aqueous inclusions that represent sub-solidus hydrothermal circulation have been identified.All aqueous inclusions were homogenized into the liquid phase between 100 and 290℃.Aqueous-carbonic inclusions were homogenized,usually via a critical transition[T_(h)(LV→SCF)]between 241 and 397℃,or less commonly,via a dew-point transition[T_(h)(LV→V)]between 213 and 264℃.Crystallization of the rare-element pegmatite is certainly associated with the late-stage magmatic or early hydrothermal low-salinity aqueous-carbonic fluid that homogenizes to critical conditions.A combination of microthermometric data and existing experimentally determined solidus from flux and volatile bearing haplogranite suggests exsolution of fluids from hydrous silicate melt,perhaps during crystallization of the aplitic layer.The fluids were then trapped and isobarically cooled along a reasonable geothermal gradient within the pegmatite unit down to a temperature of around 397℃.展开更多
This work reviews the geology, geochemistry and geochronology and discusses the spatial and temporal relationship of the granite pegmatite and the rare metal mineralization of the Kenticha granite pegmatite, southern ...This work reviews the geology, geochemistry and geochronology and discusses the spatial and temporal relationship of the granite pegmatite and the rare metal mineralization of the Kenticha granite pegmatite, southern Ethiopia using published and unpublished works to give a comprehensive understanding about the formation of the mineral deposit. The Kenticha rare metal pegmatite belt comprises several groups of pegmatites which show a high magmatic fractionation, regional and compositional zoning, mineralogical assemblage, and secondary alterations. The internal zonation shows high degree of evolution from the border to the core zone during crystallization and solidification of the leucogranitic to pegmatitic melt. Tantalum mineralization at Kenticha includes zoned tantalite-(Mn) and columbite-(Mn), as well as microlite, pyrochlore, uranmicrolite, and rare tapiolite, ixiolite/wodginite and Ta-bearing rutile. The tectonic setting of the Kenticha granite pegmatite in the Within Plate Granite (WPG) to syn-Collisional Granite (syn-COLG) granite and probably sourced from extreme fractionation of syn-to late tectonic granites or anatexis process of the metasedimentary rocks in the area. The emplacement of the Kenticha pegmatite was at ca. 530 Ma and temporally related to the post-collisional phase of granitic magmatism at 570 - 520 Ma, after the last tectonic stage of east African orogeny during the late stage of Gondwana assembly.展开更多
文摘In the Kenticha area,a series of barren to rare metal-bearing pegmatites intruded into the Neoproterozoic Adola Belt.The pegmatites host world-class Nb and Ta deposits and significant Li and Be reserves.In this contribution,fluid inclusion data and feldspar geothermometry have been combined to define the crystallization condition of the Kenticha rare-metal pegmatite.Primary and complex assemblages of secondary fluid inclusions representing episodic fluid circulations have been identified in quartz and spodumene.A primary aqueous-carbonic fluid of low salinity aqueous solution with liquid and vapour CO_(2) phases,secondary carbonic fluid rich and carboniconly fluids,and multiple generations of secondary aqueous inclusions that represent sub-solidus hydrothermal circulation have been identified.All aqueous inclusions were homogenized into the liquid phase between 100 and 290℃.Aqueous-carbonic inclusions were homogenized,usually via a critical transition[T_(h)(LV→SCF)]between 241 and 397℃,or less commonly,via a dew-point transition[T_(h)(LV→V)]between 213 and 264℃.Crystallization of the rare-element pegmatite is certainly associated with the late-stage magmatic or early hydrothermal low-salinity aqueous-carbonic fluid that homogenizes to critical conditions.A combination of microthermometric data and existing experimentally determined solidus from flux and volatile bearing haplogranite suggests exsolution of fluids from hydrous silicate melt,perhaps during crystallization of the aplitic layer.The fluids were then trapped and isobarically cooled along a reasonable geothermal gradient within the pegmatite unit down to a temperature of around 397℃.
文摘This work reviews the geology, geochemistry and geochronology and discusses the spatial and temporal relationship of the granite pegmatite and the rare metal mineralization of the Kenticha granite pegmatite, southern Ethiopia using published and unpublished works to give a comprehensive understanding about the formation of the mineral deposit. The Kenticha rare metal pegmatite belt comprises several groups of pegmatites which show a high magmatic fractionation, regional and compositional zoning, mineralogical assemblage, and secondary alterations. The internal zonation shows high degree of evolution from the border to the core zone during crystallization and solidification of the leucogranitic to pegmatitic melt. Tantalum mineralization at Kenticha includes zoned tantalite-(Mn) and columbite-(Mn), as well as microlite, pyrochlore, uranmicrolite, and rare tapiolite, ixiolite/wodginite and Ta-bearing rutile. The tectonic setting of the Kenticha granite pegmatite in the Within Plate Granite (WPG) to syn-Collisional Granite (syn-COLG) granite and probably sourced from extreme fractionation of syn-to late tectonic granites or anatexis process of the metasedimentary rocks in the area. The emplacement of the Kenticha pegmatite was at ca. 530 Ma and temporally related to the post-collisional phase of granitic magmatism at 570 - 520 Ma, after the last tectonic stage of east African orogeny during the late stage of Gondwana assembly.
