Tale-Carbonate Alteration of some Serpentinized Ultramafic Rocks south of Timmins, Ontario

Serpentinized peridotites in an area south of Timmins, Ontario,have been extensively altered to tale and carbonate. In someplaces, rocks altered in this way have subsequently been decarbonatizedand converted back to a serpentine-magnetite assemblage. Chemicalanalyses of variably altered rocks indicate that the bulk chemicalchanges involved in the tale-carbonate alteration have beenthe addition of CO₂, and removal of H₂O and a very small amountof O₂. Little or no magnesium, silicon, iron, or nickel metasomatismhas occurred. Consequently the relative partial pressures ofH₂O and CO₂ in solutions passing through the rocks are likelyto have been controlling factors for the alteration and subsequentdecarbonatization.