The Rabbit Mountain Mine hosts silver-bearing quartz-carbonate veins that are representative of the veins encompassing the Mainland Belt Silver Region near Thunder Bay, Ontario. These veins, which also contain base-metal sulphide mineralization, fill fractures within Rove Formation argillite and Logan diabase sills of the Proterozoic Southern Province of the Canadian Shield.
Silver and base-metals could have been derived from the diabase; however, a lack of differentiation within the sills and spatial relationships, which indicate that the veins occupy post-diabase faults, seem to preclude the diabase as the source of the metals.
The intruding diabase caused a contact metamorphic zone to be developed within the shale. Metamorphic reactions released calcium, carbon, and water from the shales, and these products migrated to low pressure zones centered on faults to form the gangue minerals.
To determine if silver, base-metals and arsenic accompanied this lateral secretion of gangue constituents, an outcrop of altered argillite cut by a vein (located at the Rabbit Mountain Mine) was sampled on lines perpendicular to the vein. The samples were analyzed by the Atomic Absorption method to determine the distribution pattern of silver, base-metals, arsenic and mercury in the argillite adjacent to the vein. Copper, zinc, lead, silver and possibly nickel are all depleted below their background levels indicating they have been removed from the shale during the heating event instigate by the diabase, and, like the gangue minerals, were deposited as vein constituents. Cobalt is elevated above background levels adjacent to the vein, indicating it was introduced to the argillite from the vein, ultimately being derived from the cooling diabase. Arsenic shows a slight depletion towards the vein. Mercury was above the lower detection limits only in samples taken immediately adjacent to the vein.