stockgreed,
The following can be found in "Ore Petrology" by Stanton, one of my old text books.
In the text there is a section that describes four major occurrances / environments in which sulphide nickle deposits can be found. One example obviously is the Sudbury deposit while the second is the Moak Lake - Settling Lake area in Manitoba or better known as Thompson Lake. "Substantial and extensive deposits of iron - nickel - copper sulphides occur in an area about 250 km southwest of Churchill on Hudson Bay".
"The principle ore-bearing formation is a group of beds of biotite schists and impure quartzite, sandwiched between metamorphosed iron formations and recrystalizred impure limestone, called scarn." The ore minerals, sulphides, actually fill fractures in the biotite schist and quartzite beds.
So the short answer is yes nickel sulphides can be associated with iron formations and in amounts that are minable. Hope this helps, will search further.
mh