Nb–V-enriched sövites of the northeastern and eastern part of the Amba Dongar carbonatite ring dike, India – A reflection of post-emplacement hydrothermal overprint?

Evolution of pyrochlore in carbonatites of the Amba Dongar complex, India.

“…According to the nomenclature scheme of Atencio et al (2010), these minerals are oxycalciopyrochlore or fluorcalciopyrochlore. Fluorcalciopyrochlore, which contains high amounts of F and Na, was detected in the cores of fresh pyrochlore crystals in the calcite carbonatite (Magna et al, 2020).…”

“…Transitional and secondary alteration is characterised by leaching of Na and F from the A and the Y sites, respectively (Table 1). The contents of Na and F in pyrochlore from the calcite carbonatites decrease in its rim and within fractured zones, whereas the proportion of vacancies increases (Magna et al, 2020). Cation exchange involving Ba, Sr, REE, U, Th, Pb and Fe also occurs in the mineral and is accompanied by the removal of Na, Ca and F (Figs.…”

“…Fluorapatite, aegirine-augite, aegirine, phlogopite, magnetite, perovskite, titanite, pyrochlore, zirconolite, columbite, and zircon are common accessories, listed in decreasing order of abundance. Quartz, fluorite, strontianite, Sr-rich baryte, Ba-rich celestine, florencite-(Ce), bastnäsite-(Ce), parisite-(Ce), synchysite-(Ce), monazite-(Ce), ankerite, chalcopyrite, dickite, galena, pyrite, Fe and Mn oxides, ilmenite, vanadinite, wakefieldite-(Ce) and wakefieldite-(La) represent secondary minerals (Viladkar, 1981;Viladkar and Wimmenauer, 1992;Palmer and Williams-Jones, 1996;Srivastava, 1997;Doroshkevich et al, 2009;Magna et al, 2020). According to Doroshkevich et al (2009), the hydrothermal minerals at Amba Dongar were formed by re-equilibration and recrystallisation of the primary carbonatite minerals with a hydrothermal solution.…”

“…The zoning is very common in large crystals of pyrochlore; they consist of a dark core and a lighter margin. Sometimes pyrochlore in the calcite carbonatite overgrows magnetite (Magna et al, 2020), or occurs as inclusions in large crystals of phlogopite, together with apatite and zircon (Viladkar, 2000). Rarely, phlogopite composes thin bands in association with abundant pyrochlore and Nb-bearing zirconolite, which shows a parallel orientation (Viladkar and Wimmenauer, 1992).…”

“…Pyrochlore is a widespread accessory mineral in the calcite and ankerite carbonatites of the Amba Dongar complex (Viladkar and Wimmenauer, 1992;Ghose et al, 1997;Viladkar and Bismayer, 2010;Nanda et al, 2017;Magna et al, 2020). Pyrochlore from the Amba Dongar carbonatites is a primary magmatic mineral that occurs as an early crystallising phase in the carbonatite (Viladkar and Bismayer, 2010).…”