Phosphorus in alkali feldspars as an indicator for prospecting for pegmatite-type rare-metal ore deposits in Altay, NW China

摘要

The phosphorus contents of alkali feldspars of 80 pegmatite veins from the Chinese Altay, NW China, were determined by electron microprobe in this study. The alkali feldspars of the barren pegmatites are poor in phosphorus and range from <0.01-0.05 wt% P_2O_5. Alkali feldspars from the fertile (rare-metal mineralized) LCT-class pegmatites are characterized by P_2O_5 in the range 0.10-0.40 wt% P_2O_5 for K-feldspars (Kfs), and 0.10-0.30 wt% P_2O_5 for albites (Ab). In the Qunkuer Be-Nb-Ta mineralized pegmatite, a value of 2.89 wt% P_2O_5 in K-feldspars was determined, the highest value of P_2O_5 in alkali feldspars reported. According to the statistical results, 0.1 wt% P_2O_5 in alkali feldspars separate the fertile pegmatites from the barren pegmatites, and more than 0.1 wt% P_2O_5 in the alkali feldspars, especially in K-feldspars, can be used as an indicator for prospecting for LCT-class pegmatite-type rare-metal ore deposits.