The large area from Joma and Gjersvik in the NNE to Skiftesmyr and Godejord in the  SSW, comprising the Grong field, is approximately 120 km long and 50  km wide. Former mining clearly demonstrates  the geological potential of this field. Until 1958 a total  of 131 mineralized locations had been found. Furthermore, a number of significant mines have been in operation, including the three major deposits, Skorovass, Joma and Gjersvik.

Skiftesmyr and Godejord are situated in the Grong field, which covers an area of some 6,000 km².The sulphide deposits in  this area are strata-bound.