Genesis of the Foy (?) offset and its sulfide ores; the paleomagnetic evidence from a study in Hess Township, Sudbury, Ontario

A possible extension of the Foy offset, which outcrops to the north of the Sudbury basin, was examined at three localities in Hess Township. A specific geologic feature was examined at each locality: (1) a dike cutting the offset dike, (2) the contact between the country rock and a dike, and (3) a contact with a second dike and a sulfide zone. Analysis of these features yield the following results:Locality 1. Two older remanence directions of D = 346 degrees , I = 56 degrees (O1) and D = 287 degrees , I = 64 degrees (O8) occur in the offset, and a younger direction D = 056 degrees , I = 75 degrees (O6) occurs in the dike.Locality 2. A fully executed contact test was performed giving the dike direction of D = 051 degrees , I = 75 degrees (O6) in the offset.Locality 3. Magnetic susceptibility, remanence intensity, thermal demagnetization characteristics, and remanence directions provide evidence for five distinct zones in the offset at this locality. The fine-grained central portion of the offset marked by a crosscutting dike has a unique direction D = 040 degrees , I = 63 degrees and is geochemically distinct from the remainder of the offset at this locality. Two zones of sulfide mineralization on either side of this dike have distinct remanence directions. One of these is identical to the direction found in the barren diabase of both contact zones.From this data it may be concluded that in the area studied the Foy offset is a multiple intrusion. The remanence acquisition sequence, and therefore the sequence of intrusive events, is identical to that in the main irruptive. Hence the irruptive and the offsets have the same intrusive history. At least one phase of sulfide acquired its remanence direction at a time distinct from that related to the multiple intrusive events. Hydrothermal remobilization is the most probable mechanism.