LOS JUAREZ MINE, QUERETARO, MEXICO
Part of the USAC Mexican property, including San Miguel I, II and part of San Juan III, was originally drilled by the Penoles Company in 1970, when antimony metal prices were high. They did not proceed with the property, due to the complex metallurgy of antimony. Subsequently, the Mexican Government did additional work and reported a deposit of 1,000,000 metric tons (mt) grading 1.8% antimony and 8.1 ounces of silver per metric ton (opmt) in Consejo de Recursos Minerales (Publicación M-4e). They neither assayed nor reported gold values probably due to the low price of gold. USAC determined that their antimony assays were high due to the oxidation/reduction method which also assays the iron content.
The deposit is regarded as a jasperoid type with all the elemental signatures of the Carlin Nevada type.
USAC has mapped and mined central parts of the mineralized zones at Los Juarez that appear to be vertical breccia pipes over a strike length of 3.5 kilometers with a maximum width of one kilometer. The mineralization is “open” on three sides and to depth. After milling 3,500 metric tons of rock from the Mina Grande pit, the feed grade was determined to be approximately 0.789% antimony, 6.11 ounces of silver (189 grams), and 0.049 ounces of gold (1.52 grams) per metric ton. A shallow but widespread drilling program was started in 2015 to identify the higher grade ore in the deposit. The global average based on these drill holes and rock chip samples was 0.057 ounces (1.77grams) gold, 2.43 ounces (75.24 grams) silver, and 0.343% antimony per metric ton. To date, less than 5% of the surface area of the property has been drilled. A caustic leach plant was built at Madero during 2015 and 2016 to treat flotation concentrates from Puerto Blanco. An application for a cyanide leach circuit to increase flotation recovery from the flotation tailings at Puerto Blanco is in process.
The anticipated recoveries without the cyanide circuit are as follows:
Following the successful operation of the 100 ton per day mill at Puerto Blanco and processing at Madero, an additional 400ton per day mill will be completed and dedicated to Los Juarez ore at either Puerto Blanco or adjacent to the open pit at Los Juarez.