Evolution of pyrochlore in carbonatites of the Amba Dongar complex, India.
- 7 June 2021
- journal article
- research article
- Published by Mineralogical Society in Mineralogical Magazine
- Vol. 85 (4), 554-567
- https://doi.org/10.1180/mgm.2021.50
Abstract
Pyrochlore-group minerals are common accessory rare-metal bearing minerals in the calcite and ankerite carbonatites of the Amba Dongar complex (India). Pyrochlore from the Amba Dongar carbonatites differs from that in other Indian complexes in Ta, Zr, Ti, rare earth element (REE) and Pb contents, but is similar with respect to Ca, Ba and Sr abundances. The evolution of pyrochlore composition was studied to understand the alteration processes and the formation of late-stage pyrochlores enriched in REE and Pb. The early magmatic pyrochlore are calcio- and niobium-dominant types and were replaced by secondary cation-deficient varieties as a consequence of the action of hydrothermal fluids and supergene weathering. These processes produce changes mainly at theAsite, rarely at theBsite, and the original F is replaced by OH–groups. Calcium and Na can be extracted from the structure at the alteration stage and charge balance is achieved by the introduction of REE, Th, U, Ba or Sr. At the latest supergene stages, marginal and fractured zones of pyrochlore grains are altered to Pb-rich, Si-rich and cation-deficient hydrated varieties. The magmatic pyrochlore was crystallised in a highly alkaline environment at a high activity of Ca and at temperatures near 600°C, the alteration of pyrochlore began in a hydrothermal environment at temperatures below 350°C. The major compositional changes that are associated with the alteration are summarised by the following reactions: Ca2++ Nb5+→REE3++ Ti4+; Nb5++ Fe3+→ Ti4++ Zr4+; and 2Nb5++ Ca2+→ Ti4++ Si4++ U4+.Keywords
This publication has 51 references indexed in Scilit:
- Evolution of chemical composition of pyrochlore group minerals from phoscorites and carbonatites of the Khibina alkaline massifGeology of Ore Deposits, 2012
- MINERAL COMPOSITIONS AND PETROGENETIC EVOLUTION OF THE ULTRAMAFIC-ALKALINE - CARBONATITIC COMPLEX OF SUNG VALLEY, NORTHEASTERN INDIAThe Canadian Mineralogist, 2010
- Rare metal mineralization of calcite carbonatites from the Cape Verde ArchipelagoGeochemistry International, 2009
- Pyrochlore chemistry from the Sokli phoscorite-carbonatite complex, Finland: Implications for the genesis of phoscorite and carbonatite associationGEOCHEMICAL JOURNAL, 2006
- New data on pyrochlore- and perovskite-group minerals from the Lovozero alkaline complex, RussiaEuropean Journal of Mineralogy, 2002
- Primary zoning in pyrochlore group minerals from carbonatitesMineralogical Magazine, 2000
- Carbon and Oxygen Isotope Geochemistry of the Amba Dongar Carbonatite Complex, Gujarat, IndiaGondwana Research, 2000
- Petrology, geochemistry and genesis of rift-related carbonatites of Ambadungar, IndiaTschermaks Mineralogische und Petrographische Mitteilungen, 1997
- Alkaline rocks and carbonatites of Amba Dongar and adjacent areas, Deccan Igneous Province, Gujarat, India: 1. Geology, petrography and petrochemistryTschermaks Mineralogische und Petrographische Mitteilungen, 1992
- Compositional variation in pyrochlores from the Mt Weld carbonatite laterite, Western AustraliaTschermaks Mineralogische und Petrographische Mitteilungen, 1988