TAMARACK MAGMATIC NI-CU-PGE DEPOSIT, MIDCONTINENT RIFT LARGE IGNEOUS PROVINCE, MINNESOTA, USA

The Tamarack Ni-Cu-PGE prospect is a green field discovery made by Kennecott Exploration Company. The ~18km long by up to 3km wide Tamarack Intrusive Complex(TIC) is completely buried beneath 25-50m of glacial-fluvial sediments and up to 30m of Cretaceous sediments. The location and dimensions of the TIC did not become apparent until the completion of airborne magnetic surveys and follow up studies by the Minnesota Geological Survey in 1986. The Main Zone mineralization discovery hole in 2008 intersected a 138.4m interval of disseminated and matrix sulfides averaging 1.61%Ni, 1.06%Cu, 0.04%Co, 0.32ppm Pt, 0.22ppm Pd and 0.18ppm Au starting from a downhole depth of 325.6m (Rio Tinto press release, 2008). Exploration work at Tamarack is currently being funded by Talon Metals Corp. under a earn in agreement (Talon Metals press release June 2014).

The Tamarack Intrusive Complex is comprised of at least three separate intrusions referred to as; the Bowl intrusion, the FGO intrusion and the CGO intrusion. The CGO intrusion yielded a U-Pb baddelyite date of 1105+/-0.6Ma linking it to the ~1100Ma Midcontinent large igneous province. All three intrusions intrude into meta-sediments of the Paleoproterozoic Upper Thomson Formation. Sediments peripheral to the TIC intrusions are largely spotted hornfels, which locally show evidence of partial melting.

Where the ultramafic CGO intrusion is in close proximity to the base of the dominantly ultramafic FGO intrusion, the CGO intrusion contains disseminated and matrix sulfide mineralization (Main Zone mineralization). Highly, elongate lenses of massive sulfide are also located in the hornfelsed sediments beneath the FGO intrusion and above the CGO intrusion. A third type of mineralization occurs at the base of the FGO intrusion, mainly south of the Main Zone mineralization, where it appears that FGO and CGO like melts have mixed together.