Another casual search on metallurgical technologies in ancient America puts metal working as early as 1500 B.C. Please see the following references. 
 6. D. Hosler and G. Stresser Pean, "The Huastec Region: A Second Locus for the Production of Bronze Alloys in Ancient Mesoamerica," Science, 257 (1992), pp. 1215-1220. 

 7. D. Hosler and Andrew MacFarlane, "Copper Sources, Metal Production and Metals Trade in Late Post-Classic Mesoamerica," Science, 273, (1996), pp. 1819-1824.  

 8. R. Brill and J. Wampler,"Isotope Studies ofAncient Lead," American of Archaeoloe, 71 (1967), p. 63.  

 9. E. Pemika, Archaeometry, 35 (1993), p. 259.  

 10. A.F. MacFarlane (Paper presented at the Har,ard Svmposium on Ancient Metallurgy, September 1997).  

 II G.L. Cummings, S.E. Kessler, and D. Kristic, Economic Geology 74 (1979), p. 1395.  

 12. D. Hosler, "Six Metal Production Sites in the Tierra Caliente of Guerrero" (unpublished research).  

 13. H. Ball and D. Brockinton, Mesoamerican Comlmunication Routes and Cultural Contacts, Papers of the New World Archaeological Foundation, 40, pp. 75-106.