Pretty sure they meant Depleted Uranium by DU.
http://en.wikipedia.org/wiki/Depleted_uranium
Has a lower density than Tungsten, though so would make a poor counterfeiting material in both cost and physical properties.
Sorry yes, depleted uranium. Tugnsten also comes close, but not close enough to get it perfect. If you can accurately measure density you could still detect that.
The question I suppose is does anybody measure density carefully enough to detect tungsten, and if not, should they be?
EDIT: I think you meant Tungsten, also known as Wolfram (symbol W): http://en.wikipedia.org/wiki/Tungsten
Gold: 19.30 g/cm3 (http://en.wikipedia.org/wiki/Gold)
Wolfram: 19.25 g/cm3 (http://en.wikipedia.org/wiki/Tungsten)
EDIT2 (I can not reply to your reply): So you meant Depleted Uranium (http://en.wikipedia.org/wiki/Depleted_uranium)
Depleted Uranium: 19.1 g/cm3
So Wolfram is a better substitute for Gold, in terms of density. I do not know about prices or other physical properties.