5 to 7 years if all the permitting goes off without any problems. This is dead money!!!!!! The next time this will be worth anything is the next economic collapse. Gold sucks!!!!! Always has and always will. It's a fear trade.
Keep your eye open for the next permitting update from the ACOE. See my other responses to other posts. Also, NG should also should be providing an update on potential cost savings (gas pipeline update I would think as well) sometime soon. The last I heard is that part of the gas line will be realigned (and I believe should save construction cost). The result of this realignment will be fewer wetland impacts (fewer river crossings). Other challenges you can read up on in the ACOE newsletter 1 and 2 and public concerns. All these don't amount to very much IMO. Look up Pebble Project (THM) which has real opposition (which it probably should given the impact it would have on Alaska's fishery. The size and scope of Donlin is much smaller and Donlin is much more remote. Construction start date if everything goes well and NG is able to finance its half and if ABX is on board: Spring 2016. This is all very questionable right now. Many factors will play into this . Do your homework.