Mumaya River, Mumaya, Shōgawa-cho, Takayama-city, Gifu, Japan

This beautiful mountain stream is popular among anglers, and is well-known of that gold dust is gathered.  This is sorted material from sand.  It consists of iron minerals 0.3-0.5mm in diameter (magnetite, ilmenite) with gold dust less than 1.5mm in diameter.  It shows the grains of gold dust in the picture below.