Pyrochlore, ideally (Ca,Na)2(Nb5O6)(OH,F), is a relatively common accessory mineral in many rock-types including carbonatites. In the Sokli carbonatite, N. Finland, pyrochlore concentrates to economically important amounts, where it forms the ore mineral of niobium. A large number and variety of cations can be accommodated in the pyrochlore structure, including, actinide elements (uranium and thorium). During radioactive decay of the unstable isotopes of the actinide elements, the pyrochlore structure can become partially or totally metamict. This will render the mineral susceptibility to further chemical reactions.
In this work the influence of metamictisation, hydrothermal alteration and weathering on the U-Th-Pb- isotopic distribution and the crystallographic order within single pyrochlore crystals and crystal domains should be quantified and correlated. It will reveal conclusions to the retention of pyrochlore group minerals for actinide in differently ordered crystal lattices and different chemical compositions. This will show the possibility to use pyrochlore minerals for age determination of carbonatite crystallisation and subsequent alteration stages.
Warnsloh, J.M. (2001) U- Th- Pb- elemental and isotopic distribution of pyrochlore minerals from the Sokli carbonatite complex, N- Finland. Res Terrae, Ser. A, No. 19, 14-15, Oulu.