http://wiki.project1999.com/Minotaur_slaver
http://wiki.project1999.com/A_Minotaur_Slaver
Those look to drop gems on P99. Looks like peridots are the highest gems they drop and those sell to merchants for about 10pp iirc. The rest of the gems look to be in the few gold to 2pp range at most. Also don't look to have terriblely high drop rates (0.2-5%), but the chance for gems and battle axes (3pp resale to vendors) can make it an okay camp, especially if they give you exp (these minos are level 11).