Albitization and amazonitization related to a Nb−Ta deposit in altered granite

A Nb- Ta- rare metal deposit has been discovered in an albitization-, amazonitization-granite by using amazonite as an indicator. The ore-bearing dyke, early Yenshanian in age, occurs in a Late Jurassic metamorphic sandstone and breccia. Three stages of albite can be distinguished, shewing regular variations in composition, optical property and structure with respective to different generations. Two generations of amazonite are noticed and studies are made on their composition and structure by using optical and X-ray diffraction methods. Amazonite is readily recognizable in the field by its colour. Its occurrence with albitization can be used as a prospecting indicator for Nb, Ta and other rare metals.