The presence of widespread disseminated Ni-Cu sulfide mineralization in basal units of the Duluth Complex and the Mellen Complex, along with several other similar mineral occurrences around Lake Superior, shows that processes necessary for the formation of sulfide deposits were active in some intrusions locally in the Midcontinent rift. However, to determine the potential for significant undiscovered mineralization in a poorly exposed igneous province the size of the Midcontinent rift system requires a variety of geologic information collected through multidisciplinary investigations at both regional and detailed scales. Return to top of page Comparisons Between the Midcontinent Rift and the Voisey Bay and Noril'sk Regions Figure 3. The plume begins to melt due to decompression and may locally incorporate bits of lithospheric mantle into the magmas. These magmas follow fractures in the crust and may pond at various levels, creating magma chambers.
Some magma is erupted from the chambers, forming a thick package of overlying basalts.
Other magma solidifies in place, ultimately creating intrusions. Comparisons between the Midcontinent rift system and the Voisey Bay and Noril'sk settings point to several similarities that suggest that the Midcontinent rift is a likely setting for Ni-Cu mineralization. In the Midcontinent rift, melting of the plume produced more than 2 million cubic kilometers of mostly basalt lava flows and related intrusions. In all three regions, basalts derived from the mantle plume are enriched in trace elements, particularly in comparison to the most common basalts erupted on Earth, those formed at rifts in the oceans. Like basalts in the Noril'sk region, early basalts of the Midcontinent rift have compositions characterized by relatively high abundances of magnesium, chromium, nickel, and platinum, and relatively low abundances of sulfur.