Characteristics of inclusions in topaz from Serrinha pegmatite (Medina granite, Minas Gerais State, SE Brazil) studied by Raman spectroscopy

Abstract

Eastern Brazilian Pegmatite Province includes many topaz-bearing pegmatitic bodies. Residual melts from the Fe–K-rich alkaline Medina granite (ca. 500Ma) formed the Serrinha pegmatite—a system of branched thin pegmatite veins hosted by pink facies of the parent granite. The colourless topaz from Serrinha pegmatite contains both mineral and fluid inclusions. Microcline (513, 476, 456cm−1), albite (507, 479, 457cm−1), topaz (926, 858, 267, 239cm−1), quartz (463cm−1), rutile (610, 444cm−1), wolframite (884cm−1) and uranophane (968, 788cm−1) represent solid inclusions formed by fluid-induced processes from the pneumatolytic (∼600–400°C) to hydrothermal (<400°C) stages of pegmatite crystallization. Fluid inclusions are mainly liquid or liquid-gas, which contain CO2 (marker bands ∼1388cm−1 and ∼1285cm−1) and traces of methane (2917cm−1). They are mainly of primary and pseudo-secondary origin, indicating tectonic quiescence during and after topaz crystallization (in agreement with the post-collisional nature of the parent granite). Topaz crystallized in high temperature conditions of the pneumatolytic stage at a depth around 8.5–10.0km.