I remember back in the day when I was on an air leg drill...

I remember back in the day when I was on an air leg drill underground the engineer would tell me they required about 6 grams per ton of gold for underground to make a profit, and open pit moved more dirt, so could get by at about 2 grams of gold per ton. Years latter I found my self operating a 2 boom jumbo UG, drilling out a face in a couple of hours in a 5 x 5 meter drive. Sometimes getting 3 plus cuts a day with multiple headings. (May be the plus bit is a bit exaggerated) but my point is, they move a lot more dirt underground these days. So perhaps 3 grams upwards might be considered good, not sure. I'm still a bit old fashioned and like to see the 6 grams and more. I'm sure the milling process has improved over the years (something I know nothing about) and gold extraction improved.