Zircon chemistry and new laser ablation U–Pb ages for uraniferous granitoids in SW Cameroon  

作　　者：V.F.Embui C.E.Suh J.M.Cottle J.Etame J.Mendes C.M.Agyingi A.Vishiti E.M.Shemang B.Lehmann 

机构地区：[1]Department of Geology,University of Buea,P.O.Box 63,Buea,South West Region,Cameroon [2]Ore Treatment Laboratory,Institute of Geological and Mining Research(IRGM),P.O.Box 4110,Yaounde,Nlongkak,Cameroon [3]Department of Geology,Mining and Environmental Science,University of Bamenda,P.O.Box 39,Bambili,Cameroon [4]Department of Earth Sciences and Earth Research Institute,Webb Hall 2028,University of California,Santa Barbara,CA 93106-9630,USA [5]Laboratory of Geosciences Natural resources and Environment,Department of Earth Sciences,Faculty of Science,University of Douala,P.O.Box 24157,Douala,Cameroon [6]Department of Civil Engineering,University Institute of Technology,University of Douala,P.O.Box 8698,Douala,Cameroon [7]Departamento de Geologia,IGEO,Universidade Federal do Rio de Janeiro,Cidade Universitaria,Rio de Janeiro 21910-949,Brazil [8]Department of Earth and Environmental Sciences,Botswana International University of Science and Technology,Private Bag 16,Palapye,Botswana [9]Mineral Resources,Technical University of Clausthal,Clausihal-Zellerfeld,Germany

出　　处：《Acta Geochimica》2020年第1期43-66,共24页地球化学学报（英文）

基　　金：provided by Alexander von Humboldt-Stiftung(DE)

摘　　要：The Ekomedion two-mica granite,southwestern Cameroon,has potential for uranium and molybdenum mineralization.Here,we present LA-ICP-MS U-Pb ages,Lu-Hf isotope characteristics,trace element concentrations and Ti-geothermometry of zircon from this granite hosting U-Mo mineralization in pegmatitic pods.The majority of zircon are CL-dark though some CL-bright cores were also identified.U-Pb zircon age data range from 121±3 to743±11 Ma with only 5 of 34 ages being near concordant.The concordant mean age of 603±12 Ma is similar to ages of granitic intrusions along the Central African Shear Zone in Cameroon.Apparent ages with mean of261±6 Ma reveal open system behavior with respect to Pb and/or U.Zircon e Hfi values range from-20.3 to-0.3.This implies that U-Mo was remobilized during partial melting of the surrounding gneiss.Zircon Th/U>0.1 as well as an increasing Hf with decreasing Th/U indicates that fractional crystallization was the main factor that controlled U-Mo mineralization in pegmatitic pods.Y and Y/Ho ratios cluster from 29 to 33 close to the chondritic ratio of 28 and indicate fractionation of Y and Ho with low F contents during the earliest stages of crystallization.Late stage accumulation of F-rich magmatic-hydrothermal fluids impacted U-Mo mineralization as a ligand.Zircon contains a prominent negative Eu anomaly pointing to a fractionating system rich in plagioclase.Calculated Ti-in-zircon temperatures span 672℃to1232℃with the temperatures at the high end reflecting interference from mineral inclusions in the zircon grains while the lower temperature values are linked to crystallization.The Ekomedion two-mica granite, southwestern Cameroon, has potential for uranium and molybdenum mineralization. Here, we present LA-ICP-MS U–Pb ages,Lu–Hf isotope characteristics, trace element concentrations and Ti-geothermometry of zircon from this granite hosting U–Mo mineralization in pegmatitic pods. The majority of zircon are CL-dark though some CL-bright cores were also identified. U–Pb zircon age data range from 121 ± 3 to743 ± 11 Ma with only 5 of 34 ages being near concordant. The concordant mean age of 603 ± 12 Ma is similar to ages of granitic intrusions along the Central African Shear Zone in Cameroon. Apparent ages with mean of261 ± 6 Ma reveal open system behavior with respect to Pb and/or U. Zircon e Hfi values range from-20.3 to-0.3. This implies that U–Mo was remobilized during partial melting of the surrounding gneiss. Zircon Th/U [ 0.1 as well as an increasing Hf with decreasing Th/U indicates that fractional crystallization was the main factor that controlled U–Mo mineralization in pegmatitic pods. Y and Y/Ho ratios cluster from 29 to 33 close to the chondritic ratio of 28 and indicate fractionation of Y and Ho with low F contents during the earliest stages of crystallization. Late stage accumulation of F-rich magmatic-hydrothermal fluids impacted U–Mo mineralization as a ligand. Zircon contains a prominent negative Eu anomaly pointing to a fractionating system rich in plagioclase.Calculated Ti-in-zircon temperatures span 672 ℃ to1232 ℃ with the temperatures at the high end reflecting interference from mineral inclusions in the zircon grains while the lower temperature values are linked to crystallization.

关 键 词：ZIRCONS Uranium-molybdenum Cameroon 

分 类 号：P619.14[天文地球—矿床学] P597[天文地球—地质学]