RE:Size and gradeThe World Gold Council defines a high-quality underground mine as having a gold ore density between 8 and 10 g/t (grams per ton), while a low-quality underground mine has a gold ore density of 1 to 4 g/t. Open-pit mines tend to have a lower grade, but they can be considered very valuable because of the lower average operating costs necessary to obtain them. The council recommends using cost per ounce, not gold ore grading, to evaluate a gold mine.