Baja California, has also been Mexicanized and produces about 5,000 tons of blister copper annually. In 1969, Asarco Mexicana commenced construction of a concentrator at Inguaran, Michoacan. This underground mine-mill complex is designed initially to process 2,000 tons of ore per day and produce 12,000 tons annually of copper contained in concentrates. The Asarco smelter at San Luis Potosi is currently being expanded to absorb these concentrates. Asarco also is planning to construct a second electrolytic copper refinery, probably at the San Luis Potosi smelter site, to refine the Inguaran copper as well as that from La Caridad and other mines. The initial capacity of the smelter will be 45,000 tons of copper per year. In 1970, Mexico's copper production declined to 61,000 metric tons as compared with 66,167 metric tons in 1969. Cananea accounted for approximately 60 percent of this production from ore reserves estimated at 825 million tons, averaging 0.73 percent copper. The largest copper development under way in Mexico today is La Caridad (near Nacozari) approximately 100 miles south of the Arizona border. A new company called Mexicana de Cobre, S.A., which was organized to develop this deposit is a joint venture with Asarco Mexicana holding 49 percent, Comision de Fomento Minero 16 percent, and Mexican businessmen and institutions accounting for the balance. It is estimated that La Caridad will have a throughput of 30,000 tons of ore per day and 75,000 tons of blister copper per year. The published ore reserve figure for the development is 450 million tons containing 0.76 percent copper and 0.016 percent M02. An investment of at least $250 million is contemplated for the concentrator, smelter, township, and auxiliary facilities, including a railroad spur and water reservoirs. The exact amount of copper that has been produced in Mexico since colonial times is not known. But during the first half of this century, the nation produced 2.4 million metric tons and in the past 20 years an additional 1.2 million metric tons. Other than the United Nations' work in Sonora, there has been no highly organized, well-financed search for copper until the last few years. Consequently, it is possible that substantial new copper deposits will be located as major exploration companies direct their attention to Mexico. Silver and Gold The famous bonanza silver districts of Pachuca and Real del Monte are examples of shallow, low temperature vein type mineralization in Tertiary volcanic rocks. Metallization is related to an underlying magmatic source expressed at the surface in the form of rhyolite dikes and small stocks or plugs. Since about 1526, when the Pachuca - Real del Monte district was discovered, an estimated 40,000 tons of silver valued at almost $2 billion has been extracted from these deposits. About one ounce of gold is recovered for every 200 ounces of silver; thus, the district has supplied more than 2 million ounces of gold as well. At present, most of the production from Pachuca comes from the recovery of old stope fills left by the early miners. Traditionally, Mexico has been regarded as the largest silver producing nation of the world, with an annual production of about 43 million ounces or 20 percent of the world's total. However, in 1970, Mexico fell from first place to third, after Canada and the United States. The sharp decline in the price of silver from $2.48 in mid-1968 to $1.40 in 1971 probably accounts for the drop in production, as well as the deferral of plans to expand development or open new mines. 36