Abstract
The Mato Preto fluorite deposite are located in the Ribeira River valley 80 km NNE from Curitiba, Parana, Brazil. They consist of three known orebodies and numerous minor occurrences within an area of about 15 km 2 . Clugger, the largest deposit, is a hydrothermal replacement and fracture-filling type in a brecciated and sheared contact zone among carbonatite, nepheline syenite, phonolite, and tinguaite of the Cretaceous-Paleocene age Mato Preto Igneous Complex. Fluorite occurs four subparallel but coalescing ore lenses which form envelopes about dikes of phonolite-tinguaite and have strike lengths of 250 m, aggregate thickness up to 80 m, and extend to at least 120 m in depth . Dikes and lenses strike N50-55E and dip steeply to the northwest. Fluorite forms matrix replacemcnts and crosscutting veins in premineral and intermineral breccias adjacent to dikes. Fluorite mineralization has been introduced in at least two pulses and is associated with barite-celestite, apatite, rare earth minerals, and sulfides. Late explosive venting of the system has formed pipes of volcanic breccia with crackle breccia in ore adjacent. Fluorite along breakage planes is recrystallized into monomineralic veinlets. Mineralization is associated with fracture controlled epidote alteration, but major silicification apparently predates ore. The c1ugger deposit was probably forned at low pressures and temperatures, possibly within a vent of a now-eroded Mato Preto volcano.
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