Atna Commences Optimization Study On Pinson Underground
GOLDEN, CO - Atna Resources Ltd. has retained Practical Mining LLC of Elko, Nevada, to commence a Technical Report to optimize underground mine design, costs, reserves and resources for the Pinson Underground Mine. Practical Mining is highly experienced in Carlin gold systems and is familiar with northern Nevada operating conditions and mining methods. Atna has been actively engaged in re-modeling geologic controls and grade shells for the Pinson underground based on experience gained during recent underground development operations at Pinson. The revised resource model will be the basis for the optimized mine plan.
"We gained valuable knowledge and experience in our development and initial production work at the Pinson Underground Mine. Most importantly, we determined that ground conditions were better than anticipated and that low cost screening of ore effectively reduces mining dilution, resulting in potentially lower operating cost and more productive mining.
Atna is convinced that Pinson is a valuable asset and we are excited to engage Practical Mining to optimize an underground mine plan and operation," states James Hesketh, President & CEO. The resources at the Pinson project are robust and justify further study.
The original development plan utilized underhand cut and fill mining with cemented rock fill ("CRF") to develop the ore stopes. This mining method was chosen for safety, anticipated variable geometry and poor ground conditions in the ore zones. Although effective, the method resulted in low productivity and high development and operating cost as implemented. Experience gained during development led to a number of conclusions about improvements that can be made to the mine design and mining methods that should increase productivity and significantly decrease costs. These conclusions include the following: 1. Ground conditions in development workings were generally good and posed no impediment to development operations. 2. Underhand cut and fill mining with CRF can be conducted safely in the ore zones. 3. Cuts were selectively increased in height during development from their original designs with a positive impact. Further work is required to determine optimal cut height. Increased cut height should reduce required access development costs. 4. Limestone clasts inherent in the ore combined with waste dilution from mining created excessive grade dilution. Grade distribution tests verified that larger rock fragments in the ore were mostly waste. Ore screening tests revealed that up to 20 percent of total material may be screened off using a 3-inch passing-screen-deck, and that the rejected material contained little or no gold, resulting in higher ore grades being shipped to third-party processing facilities. 5. Stope productivity can be improved by decreasing inefficiencies associated with geologically controlled "selective" mining practices and focusing instead on a bulk mining approach while removing waste dilution from the ore on surface by screening. 6. Engineers, on review of underground mining conditions, have recommended that modified long-hole stoping systems be considered for portions of the Pinson underground. 7. Actual mining results reconciled to within 20 percent of modeled reserve ounces. The reserve model generally performed well, but it is believed that further review of data and geologic controls used to model ore zones may significantly improve production design control and improve economic results.
Based on this experience, it is believed that improvements to the project design and plan can be made to optimize mine efficiencies and future project economics and that additional engineering, mine-design, and costing studies are well justified.
In addition to work on the underground, the Company is completing a pre-feasibility study to determine the economic feasibility of developing the section 33 open pit, which resides on private property, and is an extension to the existing Mag pit. The Mag pit previously produced over 300,000 ounces utilizing open pit, heap leach recovery methods. This study is expected to be completed by the end of the second quarter 2014. A second goal of this study is to develop information needed to produce a Mine Plan of Operations to be submitted to the regulatory authorities to commence the permitting process. The Mag pit project is currently unpermitted and will be subjected to the normal permitting process prior to the commencement of mining.