Distribution of Rare Earth Metals in the South Nam Xe Carbonatites (Northwest Vietnam)

Abstract

Investigations on rare earth and trace element variation were conducted using ICP-MS on constituent minerals and bulk-rock from the South Nam Xe calcio- and ferrocarbonatites. The data show that the carbonatites are extremely high in light rare earth elements (3,400-6,100 ppm in calciocarbonatites; 43,200-163,900 ppm in ferrocarbonatites). Variations in rare earth element (REE) concentrations of the two carbonatites are closely along with the changes in mineral compositions. REE concentrations in calcite, biotite and aegirine from the calciocarbonatites are 5,500 ppm, 1,220 ppm and 320 ppm, respectively; whereas REE concentrations in ankerite, apatite-monazite, REE-carbonates and (Ba,Sr) sulfates are 830, 25,900 ppm, 262,600 ppm and 15.6 ppm, respectively. The calcite and the REE carbonates hold the highest REE levels suggesting their crucial roles in REE variations of the rocks.