Anglogold Ashanti’s scientific contributions

The La Colosa, Colombia porphyry gold deposit is currently in the pre-feasibility stage. This large deposit has many types of gold mineralization: native gold, electrum, and tellurides. These variations in the gold mineralization lead to variability in the gold recovery. The final process flowsheet may include gravity concentration with cyanide leaching. Metallurgical testwork is utilized to identify the zones of ore that may be problematic to recover. To help select the samples that represent the fluctuating variability zones, geometallurgical models are constructed using mineralogy and geology data. These zones are then wireframed and compared to the geological and structural models for spatial correlation. Samples for the variability testwork will be selected from these different zones to identify and analyse the effect the different gold mineralization types have on the recovery. By using geometallurgy to aid in the sample selection for metallurgical testwork, the variability in the ore body can be understood and constrained to aid in process optimization.

Gold distribution in vein-hosted hydrothermal ore deposits is commonly nuggety (i.e. occurs as very localised concentrations of gold). In these cases samples for gold assay from diamond drill core may be too small to model the underlying heterogeneity of gold distribution and result in poorly constrained ore body models and underestimated gold resources. Hence, it is common practice to use more spatially continuous proxies for mineralisation to help define the boundaries of mineralised regions. We present a method for automating the use of geochemical proxies for nuggety gold ore bodies.

A trial application of the Hydro-Jex © technology was deployed on the Valley Leach Facility at AngloGold Ashanti's Cripple Creek and Victor Gold Mine. Underperforming zones were identified within isolated areas of the heap. Surface-based remediation and recovery efforts were ineffectual because of the extreme depth of the targeted areas. The Hydro-Jex © application provided a direct means of delivering leaching reagents to the targeted areas. The project was supported by geophysical monitoring. Time lapsed electrical resistivity monitoring was conducted to help understand the fluid movement within the heap during the injections. The results of the monitoring are presented along with gold production estimates. INTRODUCTION AngloGold Ashanti's Cripple Creek and Victor Gold Mine (CC&V) is located in the historic mining district southeast of Cripple Creek, CO (Figure 1). Operations at CC&V consist of open-pit mining followed by heap leaching on a valley-fill-type heap that provides the sole means of gold production. Heap leaching operations at the Valley Leach Facility (VLF) have been in continuous operation since 1994. The VLF was originally designed with 0.7x10 6 m 2 of lined area and one internal pregnant solution storage area. A two-stage open-circuit crushing operation was used to process approximately 24,500 Mt of ore per day to a nominal P 80 of 3.8 cm. The ore was stacked on the heap in 15 m lifts under an ultimate height restriction of 91 m. Several expansion projects and permit amendments have since increased the scope of operations. Ultimately, the lined area has increased to over 66.5x10 6 m 2 . Additional solution storage areas were added in 1996 and 2003 and the crushing circuit was upgraded in 2002 to process 65,300 Mt per day to a P80 of 1.9 cm. The deepest point the VLF is currently over 183 m.