A new Cu-Mo-Ag Porphyry discovery and related Cu-Zn skarn at the Bahuerachi project, southwestern Chihuahua, Mexico

2006

Jean Pierre Jutras,

The Bahuerachi porphyry complex in southwest Chihuahua State contains a 4-kilometer long Laramide age intrusive complex composed of multiple phases of calc-alkaline feldspar-quartz-biotite ± hornblende porphyries (QFP). The mineralized complex has been dismembered and tilted by at least two generations of post-mineral normal faults. Porphyry-Cu style mineralization is spatially associated with an early coarse crowed QFP containing sheeted and multidirectional quartz vein stockworks. Pyrite-chalcopyrite ± bornite occur within quartz veins, disseminated, and along sulfide coated fractures. Late laminated quartz-molybdenite veins occur locally. Sericite, orthoclase, albite, biotite, anhydrite, and chlorite are the dominant alteration minerals. Mineralized porphyry (0.4 to 3.2% Cu) has been drilled over a strike length of 750 meters and to depths exceeding 400 meters, and the zone remains open in all directions. A supergene chalcocite blanket up to 100m thick overlies a large portion of the known mineralized system. Garnet dominated Cu-Zn-Ag-Au skarn developed at or near the contact between QFP and Cretaceous limestone. Skarn mineralization has been traced by drilling over a strike length exceeding 1600 meters with cumulative widths between 15 and 100 meters, and to depths exceeding 450 meters. Carbonate replacement style massive sulfides containing Zn-Pb-Cu-Ag occur in Cretaceous limestone distal to skarn.

Keywords: Carbonate Replacement, Mexico, Porphyry copper, Skarn