gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/002646199548916 Discussion on Le Bas et al. (1997) ‘Oxygen, Carbon and Strontium Isotope Study of the Carbonatitic Dolomite Host of the Bayan Obo Fe-Nb-REE Deposit, Inner Mongolia, China’, Mineralogical Magazine, 61, 531–41 Campbell L. S. * School of Geological Sciences, Centre for Earth and Environmental Science Research (CEESR), Kingston University, Penrhyn Road, Kingston upon Thames, Surrey, KT1 2EE, UK

Current address: Department of Environmental Resources, Telford Institute of Environmental Systems, The University of Salford, Frederick Road, Salford M6 6PU, UK

 12 1999 63 6 927 931 23 7 1998 14 4 1999 Copyright © 1999, The Mineralogical Society 1999 Abstract

Some important and interesting data on the O, C and Sr isotopic compositions of rocks associated with the Bayan Obo Fe-Nb-REE deposit have been reported by Le Bas et al. (1997). However, a number of points relating to the interpretation of these data, and also to the terminology adopted, are worthy of further discussion. The essence of this discussion is that some of the geochemical and isotopic signatures found at Bayan Obo are not exclusively consistent with an igneous origin. A replacement hypothesis involving deep-sourced fluids could also explain the pattern of data, if minor carbonatitic intrusions into a sedimentary sequence are considered.

 Keywords carbonatites stable isotopes rare earth mineralization replacement fluorite Bayan Obo