RARE EARTH ELEMENTS GEOCHEMISTRY OF FLUORITE FROM THE MATO PRETO CARBONATITE COMPLEX, SOUTHERN BRAZIL

Abstract

Fluorite deposits in Southern Brazil are usually associated to limestone and granitic rocks. The Mato Preto deposit fluorite is an exception because it occurs associated to carbonatite and alkaline silicate rocks. We discuss the origin of this deposit based on rare earth element (REE) geochemistry and show that fluorite from Mato Preto has an REE spectrum ranging from high to low (La/Lu) (sub n) ratios. We suggest that fluorite with high (La/Lu) (sub n) are related to the alkaline magmatism, whereas fluorite with intermediate to low (La/Lu) (sub n) did not derive from alkaline magmatism, but probably from the country rocks. This interpretation is supported by oxygen, carbon and strontium isotopes that show that the carbonatites are significantly contaminated by their country rocks.