A new find of sapphire placer deposits on Nosy-Be, Madagascar

The north of Madagascar is rich in corundum occurrences. Late Mesozoic basaltic extrusions have brought with them many corundum xenocrysts, which can be found now in various types of placer deposits. A new deposit on Nosy-Be is described and compared with the occurrences on the Ambato peninsula and at Ambilobe, NE Madagascar. Sapphires are found mainly in the alluvium of small creeks. Searching and exploration is largely done by local villagers, who mine selectively in creek beds. Although up to 20 ct/m(3) are found, the size of the deposit does not appear to suffice for a large scale mining operation. The bulk of the corundum recovered is opaque. A minority of stones can be enhanced by heat treatment. Their gemmological characteristics correspond to those found in sapphires from basaltic-type deposits.