Analysis of valley-fill dump leach 2: Modeling and observations

Valley-Fill Dump Leach 2, located at a gold mine in the Great Basin region of the United States, began operation on My 3, 1986 and was operated for six years until July 3, 1995. Run-of-mine low grade gold ore, also termed "sub-ore," was placed in valley-fill dump (heap) leaches and processed for gold values with a cyanide lixiviant. Valley-fill dump leach 2 covered approximately 21 acres, and was comprised of 15 twelve-foot lifts containing a total of 4.5 million short tons of run-of-mine ore at an average grade of 0.037 ounces Au/short ton. Recovery was estimated at 50%, which accounts for more than 80,000 ounces of gold produced. Available precious metals leaching models were evaluated and a modified version of the simple diffusion leaching model was compared to column test data and operational data. Gold extraction curves from both the production lifts and the column tests compared reasonably well with the predicted gold extraction curves generated from the modified diffusion model. The major difficulty with modeling, however, was obtaining representative physiochemical characteristics of the ore. This circumstance would indicate that a sustained test program to determine these characteristics during the operation of the heap leach would be required if modeling is used as a technique to predict gold production.