Controls on the Stratiform Copper Mineralization in the Western Syncline, Upper Peninsula, Michigan

The Western Syncline hosts reduced-facies, or Kupferschiefer-type, sedimentary rock-hosted stratiform Cu deposits (SSC) in the lowermost meters of Nonesuch Formation, which is part a thick section clastic rocks that comprise upper fill Mesoproterozoic Midcontinent Rift North America. Located Porcupine Mountains district Upper Peninsula, Michigan, these blind were discovered 1956, but are not yet developed, although recent renewed interest may result near-term production. distinguished by their relatively undeformed nature and lack superposed hydrothermal events. Prior to lithification, chalcocite mineralization replaced diagenetic pyrite within two discrete tabular, albeit discontinuous, potential orebodies referred as lower Cu-bearing sequence (LCBS) (UCBS). Top Zone transgresses lithologic boundaries, suggesting limited volume fluids moved vertically upwards through unlithified stratigraphy, since reductant pyritic above this zone essentially barren Cu. total inventory has reasonable expectation economic extraction 3678 M lbs. with 15.3 oz. byproduct Ag. When cutoff grade 0.9% over minimum thickness 2 m applied justify an underground room-and-pillar mine, LCBS UCBS continuous Syncline. Sedimentology first-order control ore its continuity; dark-gray shales siltstones deposited under low-energy, anoxic conditions preferred host rocks, whose must be >2 host-rock determines viability extraction. Furthermore, stratigraphy influences time constraints on lithification process impedes vertical permeability thus flow upward section. Syn-sedimentary tectonic movements, likely along pre-existing buried faults, third-order enhanced such conditions. Therefore, understanding depositional history throughout fundamental limits possible exploitation optimizing