The 1.8 million tonne Itos tailings deposit is the result of several years of processing by Comibol of ore from the San Jose and Itos Mines at Oruro, Bolivia. The historic flowsheet consisted of a flotation circuit in which silver-bearing galena (lead sulfide) was concentrated. Approximately half the silver in the ore could not be recovered, and the existing tailings contain 220 grams silver per tonne in the form of complex sulfides of silver, antimony, lead, and other metals coating grains of pyrite.
In 1992, Kappes, Cassiday & Associates undertook to develop a hot agitated chloride leach flowsheet, and subsequently became a principle partner in Baremsa along with Barex, a Connecticut-based metals trading company. Baremsa leased the tailings from Comibol and organized the necessary financing. In 1995 Baremsa constructed a 600 tonne/day (15,000 tonne per month) treatment plant. Using this chloride leach process, 81% of the remaining silver can be recovered with significant by-product credits from antimony, lead, copper, tin and sodium sulfate. Silver is recovered as 95% bullion metal.
The project is still a "work in progress". By-product facilities have not yet been installed. With by-product credits Itos can produce silver for a direct cash cost of $2.30 per ounce, but without them the production cost is about $6.00 per ounce (above the present market price).
This website describes the resources, technology, economics of, and plans for the Itos project.
Kappes, Cassiday & Associates is a metallurgical development firm based in Reno, Nevada. Our staff of 35 personnel works worldwide to develop the process metallurgy for recovery of metals from ores. At our Reno, Nevada office we maintain facilities for laboratory testing of ores, for preparation of feasibility studies and design/cost studies, and for equipment design and selection. We also fabricate mining equipment and have provided process plants to over 35 operating mines. For more about us, please visit our website.