Eric Bruce Mosley HBSc thesis abstract

Thesis Title: 
Geology and Mineralogy of the Rabbit Mountain Mine Mainland Belt Silver Region Thunder Bay District
Eric Bruce

The Rabbit Mountain Mine vein deposits occur in a fault controlled valley on the southern periphery of the northeast trending Mainland Belt of silver mines.  They were discovered about 12 miles southwest of Thunder Bay in 1882 and after 10 years of operation, mining operations closed.

A detailed surficial investigation was undertaken on the property through mapping and sampling.  Petrographic microscopy and x-ray diffraction was conducted on a number of rocks and minerals.

The hypogene deposits are dependent on the regional structures.  The deposits are confined to structural traps provided by post-diabase block faults which strike southwest, parallel to the Mainland Belt.  Post-diabase faulting was in response to sinking of the Lake Superior Basin.

The country rock is Precambrian Rove Argillite and semiconformable Logan diabase sills.  To the south of the Main Fault zone, the argillite dips southeast 5° and on the north side of 5° to the northwest.  Metamorphism of the argillite by the diabase is that of the albite-epidote hornfels facies.

Several types of veins occur:  simple veins, which are dominant in the diabase; and complex veins which are prevalent in the metasediments.  Emplacement of the veins occurred after a sufficient period of time for the diabase to cool to non-metamorphic temperature.  Heat from the cooling diabase sheets supplied the mobilizing forces to the metal rich complexes available in the argillite.

The metasedimentary derived deposits are largely gangue minerals; calcite, quartz and fluorite respectively.  Intermittent deposition, in order of abundance, of sphalerite, galena and pyrite, acanthite, native silver and chalcopyrite occurred in later stages.  Lattice parameter calculation of chalcopyrite crystals indicate the temperature of deposition to be at least below 600°C.  Throughout the veining history there was recurrent fault movement.