The sulphide mineral deposits are associated with the ultramafic intrusions within the Pipe Formation, which is part of the Opswagan Group. The sulphide deposits occur as disseminated sulphides within the ultramafics, massive sulphide veins and lenses within the ultramafic and along the contact of the ultramafic with the Pipe Formation, and as massive sulphide veins and lenses within the Pipe Formation. All mineral reserves are contained within the latter two deposit types.

The stratigraphy at the Thompson Mine is overturned and dips 65 degrees to the west. The Archean Gneisses are located in the Thompson Mine hanging wall. Unconformably overlying the gneisses are quartzite, schist, nickel mineralization, calcareous marbles and iron formation. Amphibolite dykes and pegmatites crosscut all lithologies. Ultramafic bodies (locally called peridotite) are associated with the nickel mineralization in areas of Thompson Mine. The majority of sulphide mineralization at the Birchtree Mine is Ultramafic Associated Deposits.

Deposits are generally classified as to their spatial relationship of the mineralization to ultramafic bodies:

Metasedimentary Hosted Deposits
The structurally controlled dilation sulphide matrix mineralized zones are contained within the P2 Schist. Inclusions of wall rocks and ultramafics are common in the massive sulphide. The mineralization is linear and more predictable with widths ranging from 0.3 m to 60 m. Pinch and swe ........

Thompson is an underground mining operations with nickel sulfide ore bodies, which also contain some copper, cobalt, PGMs, gold and silver.

Mining methods primarily use Vertical Block Mining (VBM), a Slot-Slash Method, with vertical blocks averaging 100 ft in height, and Cut and Fill mining. The ore is crushed underground to -15 cm and shipped to the concentrator.

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