INTRINSIC AND EXTERNAL CONTROLS ON THE INCORPORATION OF RARE-EARTH ELEMENTS IN CALC- SILICATE MINERALS
YUANMING PAN
Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2
MICHAEL E. FLEET
Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7
Abstract
The rare-earth elements (REE) in twenty nine calc-silicate minerals, mostly of metamorphic and hydrothermal origins, and catapleiite have
been analyzed by inductively coupled plasma - mass spectrometry (ICP-MS). Using pure mineral separates, very low detection limits for REE
in minerals (3 to 54 ppb) are achieved, and REE patterns for some minerals with low abundances of REE are reported for the first time. The
chondrite-normalized REE patterns of the calc-silicate minerals vary significantly. Although external geochemical factors are important in determining
the REE characteristics of metamorphic and hydrothermal calc-silicate minerals, crystal chemical effects are resolved also. A consideration of
stereochemical environments of the Ca site(s) allows the formulation of qualitative rules for selectivity of REE and site occupancy in calc-silicate
minerals. The selectivity of REE is controlled largely by the size of the Ca position, and, in calc- silicate minerals with multiple Ca sites,
bond-valence calculation is a powerful first-approximation technique for predicting the site preference of REE.