GRANITIC ROCKS OF THE RIO DOS BUGRES MINE: HOST ROCKS OF FLUORITE DEPOSITS IN SOUTHERNMOST BRAZIL

Abstract

Most fluorite deposits in southernmost Brazil are hosted by Neoproterozoic granitic associations. Fluorite deposits are, nevertheless, much younger than granitic magmatism, and the only probable role of granitic rocks in fluorite genesis was as a source of F. This paper characterizes granitic-dioritic associations in which these fluorite lodes and veins are localized. The granitic suite includes quartz diorites, tonalites, biotite-bearing syenogranites, monzogranites, and rhyolite dikes. It is interpreted as formed by partial mixing of basic and granitic melts, generating hybrid products, such as the tonalitic rocks. The granitic magmatism is correlated with the late-transcurrent magmatism that characterizes the post-collisonal stages of the Brasiliano-Pan-African orogenic cycle in southernmost Brazil. Basic rocks have mildly alkaline or continental tholeiitic affinities. The associated granitic magmatism was probably produced by crustal melting or, alternatively, as a reaction product of mantle-derived basic melts with quartz-feldspathic gneissic crustal sequences. Trace-element and REE patterns of the basic rocks are consistent with melts produced from a mantle previously modified by subduction-related metasomatism. The granitic rocks show trace-element compositions compatible with comagmatic products derived from the basic magmatism, which can also be interpreted as an effect of mixing between two non cogenetic magmas. Hydrothermally altered granites exhibit HREE-enriched patterns that can be used as a prospective tool for fluorite deposits. Copyright © 2006 by V. H. Winston & Son, Inc. All rights reserved.