I could be mistaken but I believe that sulphur compounds are more prevalent than oxides in mining. When assays are done they are mainly for the compound of interest. I do not believe that there will not be sulphur bearing compounds in the resulting tailings.
Just look at our Eagle's nickel deposit not too distant, plenty of sulphur there.
Sulphur is not the only element to be questioned.

Combine that with a very wet environment that may be subject to a heavy rainfall and it is waiting for an 'Accident' to happen.
I would be very picky about details before issuing an open pit permit in that area.

Note I'm no authority on the subject nor the area but this is from my past experience with other metal stocks. It is rarely easy.

Perhaps a geologist, or a chemist frequenting this forum might shed some light on the subject.