CUSI
[History]
The first mines, "San Miguel" and "La Candelaria", were discovered by a Spaniard, Antonio Rodríguez, in 1687. These mines are considered to be one of the most productive ones of Chihuahua during the colonial days.
The oldest mining production record in the Cusihuiriachic district goes back to the year 1687, when 500,000 tons of ore were mined and from which 1.5 tons of gold and 1,510 tons of silver were produced. The veins that were mined are the ones of the "Santa Maria" Group (San Antonio, Sta. Marina, San Bartolo, Santa Rosa y San Pedro) and "San Miguel". The "San Antonio" was the most important vein, developed by three shafts down to 150 m. At that time, thirteen (13) mills were in operation in the area. From 1881 to 1910, foreign investment was encouraged by the growth of the railway network linking Chihuahua City to Cuauhtémoc City.
The main companies that worked during those years were:
Don Enrique Mining Co. (1881-1896), exploited the "Santa Maria" mine where the "Sta Marina" and "San Bartolo" shafts were deepened to the 800-level (244 m) and installed a chlorine plant that was destroyed by fire in 1892.
Helena Mining Co. (1896-1911) bought the mines of "Santa Maria" and "San Miguel" and deepened the shafts of "Santa Maria" and "San Bartolo" to the 1000-level (305 m) and the San Miguel shaft to the 250-level (76m). The company used a chlorine plant that burned in 1902. Daily production was 60 tons of direct shipping ore obtained by manual selection grading 1,981 g/t Ag as well as 40 tons of second class ore treated at the local flotation plant and producing 4 tons of concentrate grading 3113 g/t Ag, with recovery of less than 50%. Between April 1900 and January 1903, they mined 16,416.4 tons of ore at 1347.08 g/t Ag, 18.62% Pb and 12.98% Zn. The total production for this period amounted to 150,000 tons of ore with recovery of 0.2 tons of gold and 150 tons of silver. During the years 1911 to 1937, the production was even more intense, favored by: 1) installation in 1908 of the "Avalos" smelting method, whereby the process of flotation was used; 2) a branch of the district railroad extended; and, 3) the discovery of bonanza ore at the "Promontorio" mine.
Cusi Mexicana Mining Co. (established in 1911) bought the "Santa Maria" and "San Miguel" mines, which were worked until 1923. The "Santa Marina" shaft was deepened to 366m to exploit sulfide ore grading more than 600 g/t Ag from the Sta Marina, San Antonio, San Miguel and San Nicolás veins. They also mined oxide ore at San Miguel. A flotation plant was installed with a capacity of 450 t/d, which was later increased to 600 tpd. The crash of 1929 caused silver prices to drop and the operations stopped in 1937. The company subsequently moved to Maguarichi where they discovered high grade gold ore. The total production during this period is estimated at approximately 710,000 tons of ore with recovered values of 0.3 tons of gold, 330 tons of silver, 18,000 tons of lead, 5,500 tons of zinc and 700 tons of copper.
The Cusi Mining Co. produced at the Promontorio mine 200 tpd of bonanza ore at grades no less than 750 g/t Ag. The concentrates from flotation assayed between 7.5 and 15 kg/t Ag, 6% Pb, 3% Cu and some Zn with 85% recovery. The mine produced 200,000 tons of ore that generated 300 tons of silver, 0.3 ton of gold, 450 tons of lead and 220 tons of copper.
Between 1938 and 1987, the San Miguel mine was mined by "gambusinos" who accessed old workings above the water table. The degree of activity followed the price of silver with long periods of inactivity. In 1970 they resumed work and during the following six years, they shipped 125,000 tons to the smelter in El Paso, Texas.