Grades / grams per ton

MGV/ Starlight has fantastic g/t and I feel this is really important when deciding where to invest , I have a question for the more informed on the grades topic .
What is the minimum g/t required before an open cast discovery should proceed to development , I recently sold out of a venture that produced a budget based on 1g/t , I felt that left no room for any problems , was I right or wrong to sell , the SP has risen 4c since then .