I just bought a cast iron meat grinder; used it for the first time to grind a roast for hamburg. When finished there was some black residue around the handle and meant had some dark spots in it. Is this normal or should I throw away the meat?
If you did not clean and run an initial process through the grinder before using it for the first time, I recommend discarding the meat.
When the machine was packaged, oil was probably used to prevent sticking or corrosion during storage. Also, chemical residues from protectants and finishes may still be present in the machine. Before the first use, it is best to thoroughly clean the device and to put through a generous portion of raw meat fat to "sweep out" metal dust and filings and to clean up excess lubricant. Discard the raw meat fat where no animals will be able to scavenge it.
Sorry, but I can't imagine a food-processing piece of cast iron being coated with anything that is dangerous. I imagine the blackness you see is some remnant of cold seasoning. (Raw cast iron starts rusting immediately, within 30 seconds or less, if it does not have a protective coating of oil applied; in the case of kitchen equipment, it's food-safe oil. I suspect that not all the oil was cleaned off at the factory, given that the processes are automated now.) I don't think you should worry about it.
I refinish vintage and cast iron cookware as a hobby. I am well familiar with it.