Th and REE desposits in the Oaxaca complex in southern mexico

摘要

The Oaxaca Precambrian Complex contains several granitic pegmatite and carbonatite deposits with REE-Th-Zr mineralization. Based on mineralogical and textural criteria, the pematites are strongly zoned containing border, wall, first and second intermediate zones and quartz cores. The main Th-LREE mineralization occurs in the early formed zones and consits of allanite crystals and minor amounts of monazite and charalite. Late replacement units, produced as a result of subsolidus processes, are poorly developed and contain Nb-U-Y-REE minerals. The LREE-Th mineralization formed by reaction between the pegmatitic magma and the Ca-rich host rock. The HREE-Nb-Y-U mineralization was produced by enrichment of these elements in the late residual fluids.