Calcium-rich dravite from the Arignac Gypsum Mine, France: Implications for tourmaline development in a sulfate-rich, highly magnesian meta-evaporite

Abstract

Tourmaline occurs in a wide range of compositional environments, but its occurrence in meta-evaporites is less commonly investigated. Highly magnesian ( X Mg = 0.90–0.98), poikiloblastic tourmaline occurs in a sulfate-rich, anhydrite– gypsum-bearing meta-evaporite in the Arignac Gypsum Mine, France and preserves a petrologic record of this unusual geochemical environment. Originally a Triassic evaporite deposit, the sample is interpreted to have undergone high-temperature–low-pressure (HT–LP) metamorphism and subsequently experienced low-grade, highly deformed overprints. Poikiloblastic tourmaline preserves relicts of the HT–LP mineral assemblage, as inclusions of anhydrite, phlogopite, dolomite, tremolite, Cl-rich scapolite (71–85 % marialite component), rutile, zircon, and fluor-apatite. The low-grade deformational overprints are characterized by partial replacement of anhydrite by gypsum, phlogopite by clinochlore, dolomite by talc, and scapolite by mixtures of near end-member albite and K-feldspar with later crosscutting calcite and celestite. Tourmaline develops two textural zones – zone 1 with few mineral inclusions and zone 2 with abundant inclusions and/or complex chemical zoning. The tourmaline