Black sands
Excuse me Megan, but we are not crushing ORE here, just black SAND. Most black sand concentrates are already 16 mesh or finer to begin with. (mine are) The gold is merely bonded in the magnetite, hematite, limonite, or other iron minerals that make up the black sand. I have even milled dredge concentrates from one location, that was mostly gold coated with manganese. Fact. Simple crushing of the black sand (not ore from a lode) in a home-made mill WILL release 98 percent of it's gold! I even know one guy that would hand grind his black sands up in a meat grinder that was bolted to the table in his garage. Funny, sure, crude too, but it worked.
Again black sands are not ore. Ore comes from a hardrock lode mine. Black sands are the concentrates generated from placer mining. Compositions and hardness are different, ask any mining engineer. Also, it's a safe bet to mill all black sand concentrates that come from New Mexico, Arizona, or California. The rest of the country could be different, I don't know but, down here, it's a given. No testing to do, just recover the gold that's already in your hands or throw it away. Of course it would be fun to play with all those testing chemicals to assay a piece of ORE, if I happened to find one in the area, WHILE I was out placer mining, and recovering gold and black SAND.
I paid $30 for a used cement mixer, and paid a welder another $30 for the ten minutes it took him to take out the baffles with his cutting torch. As far as resurfacing, or replacing the balls; if you're running the daily TONNAGE that it would take to cause that much wear and tear, then you as an individual, must be serious competition to outfits like Phelps-Dodge, Asarco, and Newmont mining corporations. By the way, I bought my balls at a local foundry in Tempe (Marathon Steel) in the early eighties for $1 per pound. They're still rollin'! My ticker will probably wear out before they do. And costly? yes, I guess if you're not willing to give up the price of a round of golf, it could be. I have about $80 invested in my mill that has lasted many years. I'd say it was well spent.
If you'd like, I can post pictures of real gold ore, or of black sand concentrates for you. Best Regards, Hardpan