I have to agree with dragonfel - it's not so much of an exploit when you realize you're giving up a sizeable percentage of all of your ore in order to generate iridium
Wait, what?
To generate rich slag, you run ore through an induction smelter and you get two ingots AND 20% of the time, rich slag. You lose nothing compared to a macerator and compared to a pulverizer you only lose the 5% chance at a bonus dust. Sand is no real cost, as anybody with a pick has an overabundance of cobble and that turns into sand easily enough
don't forget gregtech isn't the only mod with expensive ore costs. A turbine and boiler to run it are over 600 steel (600 iron and 600 coal coke) and nuclear reactors cost insane amounts of copper and tin and iron to make.
Anybody using rich slag to create extra iron in the FTB modpack has lost rationality and perspective. Tin maybe. Copper maybe. Iron? Never. I have over 30 stacks of iron ingots, and only 2 iridium. I have enough platinum to engage in this exploit, it only takes two to start, I just choose not to.
You're giving up reaching those 2 powerful energy generators anytime soon if you've been dumping all your ore in an induction furnace in the hopes of getting slag.
Probability is probability. There is no luck. There is no hope needed. If you want a stack of rich slag, you need only smelt 10 stacks of ores. That iis sufficient quantity to even out the probability. It takes time, but it is a guarantee.