The Sonapahar sillimanite-corundum deposit of Meghalaya, Northeast India occurs within high-grade metapelites and exhibits an unusual association of sillimanite-quartz, corundum-quartz, sapphirine-phlogopite-corundum-sillimanite rock. Pockets of sillimanite and corundum occur within the host quartz sillimanite schist with contrasting chemical signature, where the SiO₂/Al₂O₃ ratio is 2.5–3 for the host quartz sillimanite schist and 0.12–0.7 in sillimanite rocks. Earlier it was explained that the sillimanite-corundum rock was produced from metamorphosed paleosol, but the present study suggests that metasomatism had a major role to modify the host quartz-sillimanite schist into sillimanite-corundum rocks during post-peak metamorphism. Field disposition and structural control of the area show that pockets of sillimanite-corundum rock are restricted near the shear zones. Shear zones were the pathways for movement of hydrothermal fluids, conversion of host bulk chemistry by selective leaching and, finally, enrichment of sillimanite-quartz or corundum-quartz pockets within the quartz sillimanite schist.

印度东北部梅加拉亚邦的 Sonapahar 硅线石-刚玉矿床出现在高品位变泥质岩内，并表现出一种不同寻常的硅线石-石英、刚玉-石英、蓝宝石-金云母-刚玉-硅线石组合。硅线石和刚玉的口袋出现在主体石英硅线石片岩中，具有对比的化学特征，其中 SiO ₂ /Al ₂ O ₃主体石英硅线石片岩的比率为 2.5-3，硅线石岩石的比率为 0.12-0.7。早先有人解释说硅线石-刚玉岩是由变质的古土壤形成的，但目前的研究表明，交代作用在峰后变质作用期间将寄主石英-硅线石片岩改质为硅线石-刚玉岩。该地区的现场布置和结构控制表明，硅线石-刚玉岩的口袋在剪切带附近受到限制。剪切带是热液运动、通过选择性浸出转化主体化学物质以及最终富集石英硅线石片岩内的硅线石-石英或刚玉-石英袋的途径。