Rare earth element mobility during hydrothermal alteration in the footwall of the Waterloo VHMS deposit, Australia

摘要

The present study demonstrates that the REEs behaved mobile during hydrothermal alteration in the footwall of the Waterloo VHMS deposit, Australia. The REE patterns of weakly to moderately altered rocks from the outer alteration halo were apparently not significantly affected by the albitization, carbonatiza-tion, and saussuritization of primary plagioclase as well as incipient replacement of plagioclase by white mica and quartz. In contrast, intensely altered rocks from the inner alteration halo were found to show REE patterns that deviate substantially from those of least altered equivalents. The patterns of the intensely altered rocks can be related to the stability of the accessory minerals in the hydrothermal environment. In particular, the decomposition of primary apatite resulted in a mobilization of lanthanides whereas the formation of secondary monazite and xenotime led to a selective fixation of the light and heavy REEs, respectively.