Mineralogical and chemical variations in chrysotile veins and peridotite host-rocks from the asbestos belt of southern

Two types of serpentinites from the Thetford Mines-Black Lake area were studied: the first was selected from the Lake Asbestos mine and the second, from the Vimy Ridge deposit. The former, which has not undergone the oceanic episode of pervasive serpentinization, displays a complete transition from fresh peridotite to serpentinite associated with veins of chrysotile asbestos. The latter is tlpical ribbon-veined asbestos ore; the hosr peridotite has undergone serpentinization during both oceanic and con-tinental episodes. Samples were studied under the microscope and analyzed by X-ray diffraction and electron microprobe. In the Lake Asbestos sample the following variations can be seen as the chrysotile asbestos vein is ap-proached from the fresh peridotite: (l) Olivine is transform-ed into either lizardite or chrysotile in microveins in the fresh peridotite. (2) The peridotite host shows intense serpentinization in a narrow zone surrounding the asbestos vein. (3) The Mg/@e+Mg) and Mg/Si ratios vary as follows: a) they increase in the lizardite microveins of the fresh peridotite; b