Dating of Columbite-tantalite and Monazite from Pegmatites of the Kawadgaon–Challanpara Area, Bastar Craton, Central India

Abstract

The results of geochronological studies on columbite-tantalite and monazite from the rare metal pegmatites of the Kawadgaon–Challanpara area in Bastar craton, central India are presented. Columbite-tantalite yielded U-Pb concordia upper intercept age of 1978±16 Ma (MSWD = 0.18). Radiogenic 207Pb*/206Pb* (T7/6) ages on 4 out of 5 columbite-tantalite vary in a narrow range of 1903 to 2077 Ma and are similar to U-Pb age, whereas, one sample shows younger 207Pb*/206Pb*(T7/6) age of 1728 Ma. Younger Pb-Pb age of 1744 ± 250 Ma (MSWD = 150) has also been indicated by these columbite-tantalite samples. Four out of five monazite samples define Pb-Pb errorchron age of 2050±370 Ma (MSWD = 165) and radiogenic 207Pb*/206Pb* (T7/6) ages on 3 out of 5 monazites show a narrow range of 1983 to 2083 Ma. Other two samples show younger 207Pb*/206Pb*(T7/6) ages as 1254 Ma and 1592Ma. Both monazite and columbite-tantalite indicate disturbance in Pb and U isotopic systematics as revealed by high MSWD. However, selected samples from both monazite and columbite-tantalite indicate age of their formation as c. 2000 Ma. Younger ages, i.e., 1254 to 1744 Ma are indicative of later geological disturbances. Reported age of c. 2000 Ma is comparable to Rb-Sr date of pegmatitic muscovite (1850-2330 Ma) from this area and is younger to intrusive granites of c. 2500 Ma. By analogy, therefore, it may be inferred that the age of the rare element mineralization may be ~2000 Ma old, and linked with younger granitic activity that spanned over the period from 2300 to 2100 Ma in the Bastar craton.