Formational Conditions For the Binntal Emerald Occurrence, Valais, Switzerland: Fluid Inclusion, Chemical Composition, and Stable Isotope Studies

Abstract

Abstract Emerald from the Binntal occurrence in the Canton of Valais in Switzerland has been studied to determine its chemical zonation, stable isotopic signatures, depositional-fluid characteristics, pressure-temperature emplacement conditions, and formational model. The emerald is vanadium-rich, with optical and blue cathodoluminescence zoning related to chemical variations, primarily in V 2 O 3 concentrations. The hydrogen isotope signature of the emerald channel fluids is unique and in agreement with previously identified high-altitude (deuterium-depleted) Alpine-age meteoric fluids. Field studies, fluid inclusion analyses, and oxygen isotope thermometry are consistent with a metamorphic formational model for the Binntal emerald at temperatures and hydrostatic pressures ranging from 200 to 400 °C and 100 to 250 Mpa, respectively. This corresponds to formational depths on the order of 4 to 9 km and fluids consistent with a 10–20 Ma CO 2 -dominant fluid with approximate mole percentages of 84.0, 11.9, 1.5, 1.3, 0.3, and 0.5 for CO 2 , H 2 O, CH 4 , N 2 , H 2 S, and NaCl, respectively.