Fluorite deposits in the Western United States are middle to late Tertiary in age, are associated with alkalic igneous rocks, and are situated above the deepest parts of two postulated early to middle Tertiary eastward-dipping subduction zones. Fluorine may have been concentrated in alkalic magmas generated along these subduction zones, carried through the crust as SiF4, and deposited as CaF2. Fluorite deposits and stockwork molybdenum deposits may be part of the same tectonic-magmatic setting and are distinct from porphyry copper deposits.

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