Unlike most Mesozoic MHIO deposits in Mexico, Guaynopa is found up to ~ 500 km inland from the continental paleo-edge. The Guaynopa IOCG and Guaynopita PCT deposits are likely to represent a previously unrecorded metallogenic event. δ18O and δ13C values suggest that ore-bearing fluids came from magmatic sources and interacted with host rocks. There is a minimum ~ 14 m.yr. period of metallogenic and magmatic activity in the area between IOCG and PCT deposits. The above renders new possibilities for exploration in NW Mexico for Cretaceous rocks. Chromian muscovite in Guaynopa as part of the potassic alteration is a previously undocumented mineral for IOCG deposits.