A rule from the ultimate gold stock trader by Reg Ogden

A zone or intersection should be economic if grade (in ounces of gold) times width (in feet) exceeds the factor of three

22 meters = 72.18 feet

2.2 grams = 0.0707 troy ounce (0.0776 ounce)

72.18 x 0.0707 = 5.103