At the Thompson Mine zones of wide and high-grade mineralization are spatially correlated with dilation zones within multiple faulted/drag folded flatter lying stratigraphic sequences within P2. The ore occurs as distinct semi-massive sulphide breccias within these faulted zones as:

* Semi-conformable en echelon and anastamosing sub-vertical vein sets; and
* Flatter lying veins that have infilled dilatant drag folds.

These dilation zones occur at all types of scales, from true widths exceeding 300 feet (100 m) to microscopic scale. Massive sulphide occur locally and less frequently at varying orientations within tension gashes.

Late brittle structures do occur at Thompson Mine but are usually narrow and have limited strike length. Although they can have a negative affect on local ground conditions, they rarely affect the ore zone geometry. The exception is the large brittle 1D fault system that is locally referred to as the Davy’s Fault. It is prevalent within the Pipe formation in the 1D upper and portions of the 1D lower orebodies. In general, the fault crosses the ore zone at a very shallow angle from the south west or in several locations parallels the ore. Depending upon orientation and host rock type the fault can range from a vuggy quartz – carbonate breccia zone up to 100 ft (30 m) across down to graphitic shear zones on scale of a few millimetres. The fault zone affects the local rockmass stability and necessitates use of several ground control/support methods to allow for safe extraction of the ore.

At the Birchtree Mine two important fault structures occur:
* Strike- parallel faults in the structural footwall, including the 780 and 1080 Faults; and
* Shallow East - dipping faults including the 906 and 609 faults.
Minor splays associated with these fault structures also occur at the Birchtree Mine, one example is the 84 Shear.

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 swell structures are common. The majority of Thompson Mine orebodies fall in under this category.

Ultramafic Associated Deposits
The sulphide mineralized zones tends to concentrate between the footwall or hanging wall rocks and the ultramafic, although it is not uncommon for the ore to completely encompass the ultramafic. The Birchtree Mine 84 Orebody can generally be described as brecciated ultramafic within a sulphide matrix. The ultramafic inclusions, which are randomly distributed, range from centimetres to hundreds of metres in size.

At Pipe 2, mineralization consists of ultramafic associated disseminations, net textured sulphides, semi-massive segregations, and as semi-massive to massive veins and breccias. The sulphide zones extend along strike and dip from the ultramafic host into sediment hosted veins, pods and lenses of massive and breccia sulphide.

Sulphides
The massive sulphides contain inclusions of ultramafics and sediments. On average, massive sulphide consists of 90% pyrrhotite, 10% pentlandite and less than 1% chalcopyrite. Cobalt is contained within the pentlandite.

PGE Mineralization
Recent exploration data from the 1D Lower orebody at Thompson Mine indicates elevated platinum group element levels associated with remobilized, metasediment hosted, sulphide ores. The evaluation of the PGE potential of the TNB is now a part of Vale exploration approach. Several studies are currently underway to better understand PGE mineralization and distribution within ultramafic associated and metasediment hosted sulphide ores.

A positive Pd to Ni correlation exhibited in the 1D Lower data is beneficial in identifying and quantifying the potential PD resource within current ore zones. Data acquisition and evaluation of the PGE potential of metasediment hosted 108 and 109 Orebodies at Birchtree is currently underway.

Mine production is sourced from two underground mines: the Birchtree Mine and the Thompson Mine. 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.

Since the second half of 2018, Vale has started sending the majority of the nickel concentrate from Thompson to be processed in Sudbury. Since the second half of 2021, Vale has started sending most of the nickel concentrate from Thompson to be processed at the Long Harbour facility, however the material will sometimes be directed to Sudbury, pending the requirements of the operations.