Fluorite deposits occur in a variety of geologic environments throughout the globe. It may occur as the main or only economically recoverable ore mineral in deposits or may present as the accessory gangue minerals wit...Fluorite deposits occur in a variety of geologic environments throughout the globe. It may occur as the main or only economically recoverable ore mineral in deposits or may present as the accessory gangue minerals with other ores. It is therefore necessary to understand various genetic types of the fluorite deposit. The present paper synthesises the information of some of the known fluorite mineralisation from the world so that an understanding of them can help in establishing reliable criteria for further search of fluorite deposit. On the basis of a combination of geological background information and fluorite geochemistry, a new classification scheme is proposed.展开更多
The Gurupi Belt(together with the São Luís cratonic fragment),in north-northeastern Brazil,has been described in previous studies that used extensive field geology,structural analysis,airborne geophysics,zir...The Gurupi Belt(together with the São Luís cratonic fragment),in north-northeastern Brazil,has been described in previous studies that used extensive field geology,structural analysis,airborne geophysics,zircon U–Pb dating,and whole-rock Sm–Nd isotope and geochemical data as a polyphase orogenic belt,with the Rhyacian being the main period of crust formation.This was related to a 2240 Ma to 2140 Ma accretionary processes that produced juvenile crust,which has subsequently been reworked during a collisional event at 2100±20 Ma,with little evidence of Archean crust.In this study,we use Lu–Hf isotopic data in zircon from granitoids(including gneiss)of variable magmatic series,and amphibolite to improve the knowledge of this scenario,and investigate additional evidence of recycling of Archean basement.Pre-collisional high Ba-Sr and ferroan granitoids and amphibolite formed in island arc(2180–2145 Ma),show only zircons with suprachondriticεHf values(ca.+1 to+8)indicating the large predominance of juvenile magmas.Only 10%of the data show slightly negativeεHf values(0 to-4),which have been observed in granodiorite-gneiss formed in continental arc(2170–2140 Ma),and in strongly peraluminous collisional granites(2125–2070 Ma),indicating the rework of older Paleoproterozoic to Archean components(Hf_(TDM)=2.11–3.69 Ga).A two-component mixing model using both Hf and published Nd isotope data are in line with this interpretation and indicate more than 90%of juvenile material,and less influence of Archean materials.Comparing with other Rhyacian terranes that are interpreted to have been close to Gurupi in a pre-Columbia configuration(ca.2.0 Ga),our results differ from those of SEGuiana Shield,which show strong influence of Archean protoliths,and are very similar to those of the central-eastern portion of the Baoulé-Mossi Domain of the West African Craton,which has also been formed largely by juvenile magmas in an accretionary-collisional orogen.展开更多
文摘Fluorite deposits occur in a variety of geologic environments throughout the globe. It may occur as the main or only economically recoverable ore mineral in deposits or may present as the accessory gangue minerals with other ores. It is therefore necessary to understand various genetic types of the fluorite deposit. The present paper synthesises the information of some of the known fluorite mineralisation from the world so that an understanding of them can help in establishing reliable criteria for further search of fluorite deposit. On the basis of a combination of geological background information and fluorite geochemistry, a new classification scheme is proposed.
基金mostly an outcome of institutional projects developed by CPRM/Geological Survey of Brazil in the Gurupi Beltthe additional support of the Brazilian“Conselho Nacional de Desenvolvimento Científico e Tecnológico”(CNPq)to the first author(research grant 306798/2016-6)。
文摘The Gurupi Belt(together with the São Luís cratonic fragment),in north-northeastern Brazil,has been described in previous studies that used extensive field geology,structural analysis,airborne geophysics,zircon U–Pb dating,and whole-rock Sm–Nd isotope and geochemical data as a polyphase orogenic belt,with the Rhyacian being the main period of crust formation.This was related to a 2240 Ma to 2140 Ma accretionary processes that produced juvenile crust,which has subsequently been reworked during a collisional event at 2100±20 Ma,with little evidence of Archean crust.In this study,we use Lu–Hf isotopic data in zircon from granitoids(including gneiss)of variable magmatic series,and amphibolite to improve the knowledge of this scenario,and investigate additional evidence of recycling of Archean basement.Pre-collisional high Ba-Sr and ferroan granitoids and amphibolite formed in island arc(2180–2145 Ma),show only zircons with suprachondriticεHf values(ca.+1 to+8)indicating the large predominance of juvenile magmas.Only 10%of the data show slightly negativeεHf values(0 to-4),which have been observed in granodiorite-gneiss formed in continental arc(2170–2140 Ma),and in strongly peraluminous collisional granites(2125–2070 Ma),indicating the rework of older Paleoproterozoic to Archean components(Hf_(TDM)=2.11–3.69 Ga).A two-component mixing model using both Hf and published Nd isotope data are in line with this interpretation and indicate more than 90%of juvenile material,and less influence of Archean materials.Comparing with other Rhyacian terranes that are interpreted to have been close to Gurupi in a pre-Columbia configuration(ca.2.0 Ga),our results differ from those of SEGuiana Shield,which show strong influence of Archean protoliths,and are very similar to those of the central-eastern portion of the Baoulé-Mossi Domain of the West African Craton,which has also been formed largely by juvenile magmas in an accretionary-collisional orogen.
