To make it economic guess you would need to get more than 4...

To make it economic guess you would need to get more than 4 times the price of putting a decline down 200 meters below a pit of say 100 meters in depth and assume the pit is economic so no overburden cost.
SO guess a 5*5 decline would cost $6000 a linear meter * 1/9 grade = $54000 a vertical meter
54000 * 4 = $21600 in revenue needed per meter or about 135 OVM.
135 * 200meters = $27 k oz
Never worked it out this way before so welcome to be shot down in flames.

footnote 5*5 =e 25 meters * 1 = 25 cubic meters * SG3 = 75tons per linear meter * $40 a ton = $3000 a linear meter plus add on some for ventilation shafts etc