Strontium isotope geochemistry of fluorite mineralization associated with fluorine-rich igneous rocks from the Sierra Madre Occidental, Mexico: possible exploration significance

High-grade fluorite deposits occur as replacements and as veins mainly on the rims of calderas. The fluorite deposits are associated with and partly derived from F-rich, high-SiO₂ rhyolites that post-date the caldera-forming volcanism. Most of the Sr, and by inference the Ca, was obtained from the host rocks. Sr isotope composition of fluorite matches that of the wall rocks more closely, the larger the deposit. The closeness of this match is viewed as an assessment guide for exploration. -G.J.N.