Many years ago, I read The Belgariad by David Eddings. The dark races in his books, the Angoraks, used a special type of red gold in their foreign dealings, specifically bribery.
This Angorak Gold had a specific effect/curse regarding it, where once you had a little you wanted more. A good way to keep agents on the payroll. Recently, I’ve been thinking of something like this in relation to Chaos Dwarfs.
Fluff-wise, a material like this could explain a lot about the Chaos Dwarfs. Why they were determined to stay in the Dark Lands when things started to go bad, why they’d pave roads with (normal) gold, and how they could maintain a steady influx of slaves. Why put dangerous weapons in the hands of your neighbors when a little Dawi-Zharr Gold would do? Also, if a significant amount were to turn up in a foreign land, they would have a reason to venture forth and retrieve it.
As far as what it could be, I’ve considered the following:
1) Meteoric Gold- The same way that Gromril is Meteoric Iron. The Dark Lands could be the result of an impact millenia ago.
2)Natural gold tainted with Warpstone- Just as Rose Gold and White Gold are alloys with other materials
3)Natural gold corrupted by Hashut [My favorite]- During his imprisonment beneath the Dark Lands, the essence of Hashut seeped into the surrounding stone. Gold seams so tainted would have been mined relentlessly by Dark Lands Dwarfs and would eventually result in the breaching of his prison.
For those not so inclined, CD’s might mint normal gold coins and stamp them with runes that act to the same effect. Western Dwarfs use runes of Fortitude and Accuracy, why would their bretheren not have ones for Greed or Corruption?
All fluff ideas, of course. Take them or leave them for what they are.