In my previous post, a brief description on three of the most known Sediment-Hosted Copper Deposits (SHCD) in Mexico was provided: Las Vigas and Samalayuca in Chihuahua and El Jabalí, in the Cuatrociénegas area, Coahuila. However, the Triassic-Early Jurassic rift of eastern Mexico generated some basins with propitious structural and stratigraphic conditions where SHCD could develop. Several occurrences of this mineralization style have been observed in these rift basins and associated red-beds sequences, along the vicinity of regional structures that originally acted as normal faults in the edge of basement highs.
In Tamaulipas, the La Peregrina Anticline, is host to several occurrences of stratiform copper in La Boca-La Joya Formations, a red-beds sequence of Upper Triassic-Lower Jurassic age conformed by sandstones and conglomerates with some intercalations of calcareous shales.
In Central Coahuila at the Santa Teresa District, several occurrences of stratiform copper are hosted by the San Marcos red-beds sequence of Upper Jurassic-Early Cretaceous age composed of sandstones and conglomerates intercalated with carbonaceous shales and siltstones.
In Nuevo Leon, in the vicinity of La Popa structure, favourable stratigraphic and structural conditions exist to discover SHCD.
In the Huayacocotla Anticlinorium in Hidalgo, conglomerates and sandstones conform the red-beds sequence of the Huizachal Formation of Triassic age and is the host unit to some occurrences of stratiform copper.
In Chiapas, a red-beds sequence composed of sandstones, conglomerates, siltstones and scarce horizons of shales make the Todos Santos Formation, of Middle Jurassic age. Minor occurrences of stratiform copper have been identified in this red-beds sequence.
Other areas out of the rift of eastern Mexico with potential for SHCD exist in Guerrero in the Ciudad Altamirano area, and Baja California Sur around Loreto.
One of the main differences between the SHCD occurrences in eastern Mexico and those localities in Guerrero and Baja California is the thickness of the red-beds sequences in the basins and its sediment accumulation. In eastern Mexico, the red-beds sequences and the volume of sediments accumulations in rift basins are larger than those present in the areas of Guerrero and Baja California. If the red-beds were formed in hot dry climates they could produce evaporites, being this a very important factor for metal transporting. The presence of evaporite beds in the sequence and faults at high angles to bedding are particularly favorable for the formation of SHCD.
On the picture above, field assistant Juan Medina looking at rocks on a REDOX front (oxidation-reduction interface) in a red-beds sequence at Peregrina Canyon, Tamaulipas.