I found this interesting:

In the years 1991-1993, gold prospectors on the small river Narada, found unusual, mostly spiral-shaped objects. The size of these things ranges from a maximum of 3 cm (1.2 in.) down to an incredible 0.003 mm, about 1/10,000th of an inch! They have been found in the thousands at various sites mostly at depths between 3 and 12 meters (10 and 40 ft.)
The spiral-form objects are composed of various metals: copper, tungsten and molybdenum. All tests carried out to date them, give an age for the objects of between 20,000 and 318,000 years, depending on the depth and the situation of the site.