- The initial cyanide leach recoveries of the Los Juarez gold and silver have been successful.
- Minor changes in the cyanide circuit have been made and will further enhance recoveries.
- The overall Los Juarez recovery involves utilizing caustic and cyanide leach circuits.
- The startup and use of the cyanide leach could result in gold values that are greater than the global average ore grades. More production this year will verify final global estimates.
Thompson Falls, Montana. United States Antimony Corporation (“USAC”, NYSE American “UAMY) reported that the initial production recoveries of the Los Juarez gold and silver cyanide leach plant are successful.
USAC began exploration, development, mining and milling of the Los Juarez deposit in 2006. Detailed mapping and sampling delineated jasperoid silica-rich mineralized pipes over an east-west strike length of 3.5 kilometers with a maximum width of 1 kilometer.
After years of metallurgical work, permitting, and construction, the Company has established the following processes to maximize recovery:
LOS JUAREZ MINE
Preliminary exploration indicates that it is a deep-seated silica-rich jasperoid with the following global assays and inferred recovered grades:
|Gold||0.035 opmt||90%||0.0315 oz||$1,600/oz||$49.60|
|Silver||3.27 opmt||85%||2.7795 oz||$18.00/oz||$49.86|
Global assay results and exhaustive metallurgical work have indicated a ratio of approximately1 ounce of gold to 90 to 130 ounces of silver. The bulk of the gold appears to be not homogenous or recoverable by flotation. The problem is that the gold may be coarse, not liberated from the gangue, or associated with oxide minerals that are not amenable to flotation. Accordingly, the gold may be of a higher grade. The variation in gold grades is illustrated in the following shallow drill holes:
The recovery of precious metals in the flotation concentrate was poor. The typical gold recovery was less than 25%, and the silver recovery was less than 70%. Antimony recoveries have generally been less than70%, but they are expected to increase when mining is below the surface oxidized zone. Since the silver is associated with the antimony, the silver flotation recovery is also expected to increase with depth.
FLOTATION MILL CONCENTRATES AND CAUSTIC LEACH
Generally only 30% to 40% of the gold and silver was recovered from the flotation mill concentrates by the USAC proprietary smelting process. This problem was solved by leaching the antimony out of the concentrates with a caustic leach and resulted in nearly a 100% recovery of gold and silver from the concentrates.
FLOTATION MILL TAILINGS AND CYANIDE LEACH
The flotation tailings that contained up to 75% of the gold and 30 to 40% of the silver are taken to a carbon in cyanide leach circuit (CIL). Some seven leaches have been completed. The gold recoveries have been in the 86% range, and the silver recoveries have been lower. Overall recoveries of gold and silver are being enhanced by circuit modifications to achieve a gold recovery of 90% or better and a silver recovery to 85%.
The precious metals are concentrated in the Montana refinery and sold in the United States.
ANTIMONY & ZEOLITE
Production during the month of February was as follows:
|Product||February 2020 sales|
|Zeolite short tons||942|
From the middle of January 2020, the Rotterdam price of antimony increased from $5,700.00 per metric ton or $2.585 per pound, to $6,400.00 per metric ton or $2.903 per pound. This is an increase of $0.318 per pound which should impact our sales in the future. Antimony prices have climbed in the past several weeks due to production curtailments and supply restrictions related to the ongoing Coronavirus (COVID-19) epidemic in China. The Company has been approached by several customers seeking new and diversified supplies of antimony products.
CEO John Lawrence said “The initial trials of the cyanide leach circuit for Los Juarez have been a success. We intend to have further details on estimated grades as production is ramped up. Proceeds from the 100 ton per day pilot will be used to complete the installation of the 400 ton per day mill.”