Magnetite-fluorapatite geochemistry and monazite U-Pb geochronology of the Mohuldih uranium deposit, Singhbhum Shear Zone, eastern India

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中文题名印度东部Singhbhum剪切带Mohuldih铀矿床磁铁矿-氟磷灰石地球化学和独居石U-Pb年代学
作者Patel, Sarita
作者单位Indian Inst Technol IIT
刊名GEOLOGICAL JOURNAL
2023
58
05
摘要
In this study, textural relations coupled with mineral chemistry of hydrothermal magnetite, fluorapatite, monazite and allanite from the Mohuldih uranium deposit in the Singhbhum Shear Zone (SSZ) is used to characterize the nature of the fluid during various events of alteration and uranium precipitation. These minerals have two dis-tinct textural types, the earlier of which are coeval with the uraninite mineralization. The later type formed during subsequent hydrothermal overprint as a result of coupled dissolution-reprecipitation of earlier fluorapatite and mobilization of light rare earth ele-ments. Uranium-lead dating of texturally-constrained hydrothermal monazite grains yields two major concordant age clusters at 1855 +/- 7 Ma and 963 +/- 10 Ma and several discordant analyses. Two spot analyses furnish concordant ages of 1656 +/- 33 Ma and 1438 +/- 35 Ma that are identical within error of the 207Pb/206Pb ages (1628-1643 Ma and ca. 1392 Ma) of several discordant data points. Similar ages have been reported by other studies from the rocks of the SSZ and are therefore considered to be geologically meaningful. The oldest age of ca. 1855 Ma obtained from the texturally early core regions of monazite corresponds to the earliest stage of uraninite mineralization. The two main alteration types can be interpreted based on the known metamorphic events in the SSZ. A combination of high-temperature calcic iron +/- sodic and high-temperature potassic iron alteration accompanied the M1 metamorphic event and the low-temperature silicification/K-Al alteration during the M2 metamorphic event. A compar-ative study between our data on magnetite and fluorapatite compositions with those from global iron oxide-Cu-gold (IOCG) and iron oxide-apatite deposits classifies Mohul-dih as an IOCG-type deposit.

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