If the spread closes then the maximum gain is 21%.
The next step is to plot the ratio graph of these two (NEM/GDX) and make sure that is turning up.
I like the way NEM is acting here relative to the group and to the stock market.
Go long NEM and go short GDX. The profit is in the performance difference between the two. You only make money if NEM moves up more than GDX. The key is to put equal dollars into this trade.