Barite-celestine intergrowths in Archean plutons: the product of oxidizing hydrothermal activity related to alkaline intrusions

Fine sulfate grains are disseminated within feldspar porphyries of the late Archean Kirkland Lake alkaline igneous complex in the Abitibi greenstone belt. Some grains are completely enclosed within hydrothermal biotite. Bulk compositions of the sulfates are intermediate in the BaSO₄-SrSO₄ series, the majority containing 15 to 20 mol% BaSO₄. Optical properties and the result of acid-etching indicate that they are mechanical mixtures of fine barite and celestine. The consistent bulk chemical compositions, δ³⁴S values (~ +6‰), and high SO₄^2- contents in associated apatite indicate that they were formed as a barian celestine solid solution during oxidizing hydrothermal activity.

Lack of any major thermal events in post-Archean time and low ⁸⁷Sr/⁸⁶Sr alues of sulfates indicate the formation of sulfates in late Archean time. Low metamorphic grade of the area and the occurrenceo f sulfatesw ithin biotites suggesth at the sulfate formation was related to the intrusion of the alkaline complex.