THE WEST MEXICAN METALWORKING ZONE

The west Mexican metalworking zone (figure 21.2), defined form the data described earlier, is where Mesoamerica's earliest, and some of its most innovative, metallurgical developments took place. This region includes western Guerrero, Michoacán, the southern portion of the state of Mexico, and Jalisco, Colima, Nayarit and Southern Sinaloa. Nearly all Mesoamerican metal artifacts dating to this period have been recovered within the metalworking zone. This particular area that offered unique combination of human and natural resources required for metal production. Here, largely hierarchically organized agricultural settlements existed in fairly close proximity to a rich and varied array of ore minerals and native metals. The Mexican copper belt runs through portions of this area (Michocán and Guerrero) and consists of a series of massive sulfide deposits and innumerable smaller copper outcrops. Other key ore minerals are also common in the metalworking zone; for example, native silver, argentite (the most abundant silver ore), silver sulfosalts, and arsenopyrite, the most abundant arsenic ore in Mexico. Small cassiterite deposits, the oxide ore of tin, occur sporadically along the northern boundary of this zone (Hosler 1994), and they also appear in the state of Mexico (Hosler 1986, 1994). Large copper deposits also occur in northern Mexico, but that area was sparsely inhabited, and principally by mobile desert foraging groups during the time period considered here. By contrast, large towns flourished in many areas of the metalworking zone. In the middle Balsas tierra caliente region of Guerrero and Michoaan, for example, these settlements are distinguished by extensive public and ceremonial architecture, including large pyramids and ball hours (Hosler n.d.). Large settlements also developed during the same period in Colima, Nayarit, highland Michoacán, and Jalisco.

The earliest evidence for metallurgy in the west Mexican metalworking zone consists of artifacts assemblages recovered at riverine or coastal sties: in Nayarit at Amapa; along the lower Balsas River between Michoacán and Guerrero; and at Tomatlan in Jalisco (figure 21.3). These date to between A.D. 600 and 900. Metal artifacts dating to a slightly later period (A.D. 800-900) occur at inland sites, for example in Jalisco's Lake Chapala basin. We assume that production activities likewise gradually moved inland. From the outset, metalworkers were particularly interested in the acoustical properties of metal, casting hundreds of small copper bells using the complex lost was method. They also hammered out various small implements and ornaments from cast copper blanks; for example, needles, tweezers, awls, and rings. Nearly all Epiclassic- and Early Postclassic-period artifacts were made from copper (Hosler 1988a, 1994), although archaeologists also occasionally have reported gold and silver items. Nonetheless, diagnostic trace elements in the artifact metal reveals that west Mexican smiths already had mastered fairly complex production (smelting) regimes. Tin, for example, sometimes appears in concentration between 0.10 and 0.40 weight percent in copper artifacts. Chalcopyrite, a copper sulfide ore, contains tin and these levels in disseminated from and is the only copper ore that does. When tin appears in copper artifacts in these trace concentrations, it signals the use of chalcopyrite and hence mastery of sulfide smelting regimes.