Pb isotopic assessment of Khetri Copper Belt, Rajasthan, India and its use as an exploratory tool for ore body extension

Abstract

A comprehensive lead isotopic database of the Khetri Copper Belt (KCB), Rajasthan, India has been constructed by analyzing the area's ore, minerals, mine water, plant parts, host and country rocks for the evaluation of the deposits in terms of its age of formation and using the database in a preliminary test case of mineral prospecting in neighbouring Haryana. KCB lies in the northeastern part of the Proterozoic Delhi Fold Belt and has been well researched because it houses India's largest copper repository in Madan Kudan, Kolihan and Chandmari mines in its northern part. The lead isotopic profiling conclusively proves repeated metamorphic occurrences in the study area and that Pb in the ore and other rock-forming minerals evolved in a high μ (238U/204Pb) environment of the upper crust. Whereas the 207Pb/206Pb and 208Pb/206Pb ratios of the sulphides of the Madan Kudan and Kolihan lodes of KCB are similar (0.8302–0.8372 and 2.0627–2.0646, respectively), the corresponding values for the Chandmari lode are 0.7209–0.7682 and 1.9463–2.1134. The evolution curves (207Pb/204Pb and 208Pb/204Pb against 206Pb/204 Pb) of KCB sulphides, country rocks, minerals and Indian galena samples, show two mixing lines and that the sulphides are younger (~800 Ma) to the older minerals like calcite, amphiboles and quartz. The first mixing line is formed from the clustering of Indian galena with the older minerals while sulphides and albitites cluster feebly in the second mixing line. There is no consistent correlation between Pb and U concentrations with the age of the different sulphides, country rocks, minerals. The sulphides of East Khetri Belt (EKCB), Muradpur, Bokri-Malwali and Papurna show exceeding variability in 206Pb/204Pb and 207Pb/204Pb ratios, indicating varying degrees of U enrichment of the source region. The mean 208Pb/204Pb, 207Pb/204Pb and 206Pb/204Pb values of the plant roots (37.489, 15.601, 17.614 respectively) are comparable with the corresponding values of mine water (37.138, 15.562, 17.230) indicating that these are isotopically similar. The 207Pb/204Pb and 208Pb/204Pb values of the leached soils from mineralized Golwa in Haryana cluster linearly with the East and North Khetri Copper Belt sulphides along with the soils of unmineralized Islampur-Sareli around 10 km away, thereby indicating the probability of a metallogenic zone in that area.