Petrogenesis of the Platinova skarn in the Belmont domain (Composite Arc Belt, SE Ontario, Canada)

Abstract

The Platinova skarn is hosted by greenschist facies calcitic marble, contiguous to the hypersolvus Deloro pluton, in the Belmont domain, southeastern Ontario, Canada. The skarn is approximately 4 million tones grading 35% wollastonite. The contact between the pluton and the skarn is not exposed. The skarn is divided into wollastonite-rich and poor units. Garnet and pyroxene from the wollastonite-rich unit exhibit the composition Grs67–89Adr11–36Alm0–3Sps<2, and Di50–90Hd10–48Jo0–2, and from the wollastonite-poor unit Grs17–98Adr0–82Alm0–2Sps<1.5 and Di39–95Hd3–59Jo0.3–4, respectively. The skarn development is ascribed to the incursion of magmatogene, silica-rich, CO2-poor (<0.15) fluids at temperatures of approximately 580 °C, and at pressures of 200 MPa. The genetic model proposed for skarn development, based on field and mineralogical evidence indicates addition of many components relative to essentially pure calcitic marble precursor, including Si, Al, Fe, Mg, Mn, B, Na, and loss of CO2. Podiform fabrics of the wollastonite unit are interpreted as products of metasomatism rather than as relict sedimentary laminations or metamorphic structures.