The metallogenic evolution in Mexico during the Mesozoic, and its bearing in the Cordillera of Western North America

Abstract

The Mesozoic ore and industrial mineral deposits in Mexico can be classified into four supergroups of deposits or ‘realms’: oceanic magmatic, continental magmatic, sedimentary-diagenetic, and orogenic-metamorphic. The oceanic magmatic realm comprises volcanogenic massive sulfide and sulfate deposits (VMS) and mineral deposits in ultramafic–mafic massifs that formed in oceanic arcs, largely between the Upper Jurassic and the early Upper Cretaceous. The continental magmatic realm comprises porphyry-type, non-iron oxide skarns, and magmatic-hydrothermal iron oxide deposits (MHIO) that formed in continental arcs, basically between the late Lower Cretaceous onward into the Cenozoic. Both magmatic realms are dominant along the Pacific margin of Mexico and extended up to several hundreds of km inland. The sedimentary-diagenetic realm comprises Mississippi Valley-type (MVT) and associated deposits, sedimentary-exhalative (SEDEX), red-bed or Kupferschiefer-type, and sedimentary phosphorite deposits that started forming in the basins of eastern Mexico since the latest Middle Jurassic, and formed mostly between the late Lower Cretaceous and the Eocene, although their ages remain largely undetermined. The orogenic-metamorphic realm is known only to comprise orogenic gold deposits, which formed between the Upper Cretaceous and the Eocene in western and southwestern Mexico.Three main metallogenic epochs for the Mesozoic are recognized in Mexico: (I) Triassic to Middle Jurassic, (II) Upper Jurassic to Lower Cretaceous, or Oxfordian to Albian-Cenomanian, and (III) Upper Cretaceous to the Cretaceous-Cenozoic limit, or Albian-Cenomanian to Maastrichtian, which connects with the Cenozoic epochs. The Triassic to Middle Jurassic epoch basically comprises deposits in ultramafic–mafic complexes and VMS deposits in the Vizcaíno terrane. The metallogenic belts or provinces for Upper Jurassic to Lower Cretaceous epoch occur mostly in the Guerrero composite terrane (GCT) and in the Baja California Peninsula. These are: (1) Late Jurassic to earliest Cretaceous province of sedimentary and sedimentary-exhalative deposits in the domain of the Gulf of Mexico, (2) Late Jurassic to earliest Cretaceous province of VMS deposits in the southern GCT, (3) Early Cretaceous province of VMS deposits in the Alisitos arc terrane, (4) Early Cretaceous province of deposits in ultramafic–mafic complexes on the southeastern border of the GCT, (5) Early Cretaceous province of generic MHIO deposits, and other deposits associated with calc-alkaline magmatism in the Peninsular Range batholithic belt (Baja California), along with (6) a few similar deposits in the coastal GCT, and (7) Cretaceous province of deposits in ultramafic–mafic complexes in the northern GCT. The Upper Cretaceous provinces are: (a) orogenic gold belts in NW Sonora and the southern Baja California Peninsula, which possibly constitute different belts, (b) the beginning of the metallogeny associated with the Sierra Madre Occidental silicic large igneous province (SLIP) during the Late Cretaceous to the Paleocene with generic MHIO deposits and deposits associated with calc-alkaline magmatism in Sonora and Chihuahua, (c) a trail of Late Cretaceous non-iron oxide skarn deposits along the northeastern and eastern (?) terrane boundaries of the GCT, (d) Late Cretaceous to Cenozoic province of magmatic-hydrothermal iron oxide deposits in the southern portion of the Pacific coast of Mexico, and (e) Late Cretaceous to Paleocene province of generic MHIO deposits and non-iron oxide skarn deposits in northern Baja California.The above configuration of metallogenic events and provinces occurred in response to drastic changes in the general tectonomagmatic regime: from magmatism associated with Jurassic to Albian synvolcanic extensional unroofing (magmatic oceanic realm for ore deposits) to a contractional continental volcanic arc thereafter (magmatic continental-subaerial realm for ore deposits). The transition from these metallogenic magmatic realms occurred between the mid-Aptian and mid-Cenomanian, and Mexico represents the last region in the Cordillera of western North America in which such transition occurred—it was predated by similar processes in Alaska and Canada between the Lower Jurassic and the Middle-Upper Jurassic, and in the southwestern USA between the Middle-Upper Jurassic and the Lower Cretaceous. Such southward and cratonward (eastward) progression was accompanied by orogenic pulses, which overlap in NE Mexico as thin-skinned Sevier structures were followed by thick-skinned Laramide structures, and were largely controlled by flattening of the subducted slabs. Laramide orogenic pulses played a key role in the formation of orogenic gold deposits, but are also responsible for the mobilization of basinal brines that ultimately led to the formation of MVT and red-bed deposits, although several of such deposits might have formed earlier, and others are post-orogenic.