Acta Musei Moraviae

Secondary bastnäsite-(Ce), bastnäsite-(La) and parisite-(Ce) from the Cínovec deposit – products of interaction of primary REE minerals with late low-temperature fluids

The Cínovec/Zinnwald is a world-class greisen-type Li-Sn-W-Nb-Ta deposit. The REE minerals as common accessories are present there. Primary REE-bearing phases are represented by zircon, thorite, monazite, xenotime group minerals and fluorite. Secondary REE minerals include bastnäsite and synchysite group minerals, REE oxyfluorides, REE fluorides as well as dussertite group minerals. Magmatic monazite-(Ce) is a ubiquitous mineral with a distinct negative Eu anomaly. High contents of Th in monazite are characteristic for upper part of the granitic cupola (5.0–11.4 wt.% ThO₂). Within the deposit, replacement of monazite-(Ce) by bastnäsite-(Ce) was observed. Bastnäsite structure type is stable in mineral associations with elevated LREE concentrations which were formed by the reaction of primary monazite with relatively low temperature fluids rich in carbonate and fluoride ions. Different type of bastnäsite was formed by alteration of REE rich fluorite. However, the fluids responsible for both bastnäsite types formation were the most probably identical.