Some two tonnes of gold from the Australian Gold Fields went down with her. Reckoning at a conservative $1000 per ounce, the wreck is now worth somewhere in the neighborhood of $70,548,000 dollars.
Read more here: http://en.wikipedia.org/wiki/Madagascar_(ship) and here: http://www.wrecksite.eu/wreck.aspx?56749.
Abundant more sites exist for the curious.