Yuanjiangite is the only auriferous and stanniferous new mineral ever discovered in nature and was approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association in August 1993. It occurs in the sandy gravel (rich in placer gold) of Middle Pleistocene (2.6-2 .5 Ma) moraine glaciofluvial deposition. Yuanjiangite occurs together with placer gold in the form of interlocking bodies, exhibiting irregular boundaries between them. Yuanjiangite occurs as crystalline granular aggregates and appear in the nodular-pseudobotryoidal forms; its crystal grains are smaller than 5 um, with somewhat larger hexagonal prisms and related combinations merely observed in a few drusy cavities of aggregates. Silver white in color; opaque; with metallic luster; streak black; slightly ductile; with obvious anisotropism. It is a gold-tin mutually-combined substance whose electron microprobe analytical result is Au 60.529%-64.580%，Sn 35.303 %-38.807%and small amounts of Ag and Pb impurities. Its chemical formula is AuSn，with the atomic ratio close to 1:1. X-ray powder diffraction analysis shows that Yuanjiangite has the structure of nickeline and the following unit cell parameters: a=4.316士0.001 A，c=5.510士0.002 A，V=88.88士0.005'A3, c/a=1.27, space group P63/mmc and Z=2. Based on the electrochemical principle combined with the mode of occurrence of yuanjiangite，it is considered that this mineral was formed by in-situ replacement of placer gold under the supergene condition.