Arizona Gold & Silver Inc (TSX-V:AZS, OTCQB:AZASF) has provided an update on ongoing metallurgical testing and core drilling at its Philadelphia project in Arizona.
The company reported positive results from column leach tests on bulk samples, highlighting the benefits of high-pressure grinding rolls (HPGR) crushing for gold and silver recovery.
After 119 days of leaching, samples crushed to smaller than 6.3 mm (¼ inch) recovered 76% of the gold and 40% of the silver, which was 16% more gold and 12% more silver than conventional crushing methods.
Early-stage results also showed 51% gold and 26% silver recovery after four days, rising to 60% gold and 32% silver after 20 days.
Samples crushed to pieces smaller than 12.5 mm (½ inch) also showed higher gold and silver recoveries than traditional methods, suggesting the process works well even with coarser material.
Greg Hahn, Arizona Gold & Silver's vice president exploration, said the purpose of the metallurgical program is to demonstrate the potential viability of a heap leach operation alongside the underground development of the high-grade material.
“It is essential that a metallurgical program runs in parallel to our exploration drilling,” Hahn said.
“Drilling to date has established that there are substantial volumes of stockwork material above the high-grade zone. That material carries 0.4-1.5 gpt gold and is particularly valuable in today’s gold price environment.”
According to the company, the data illustrate the effectiveness of HPGR crushing in accessing fine-grained gold particles within microfractures of the near-surface stockwork zone, and confirm the material’s suitability for heap leach extraction.
“This now establishes the path forward for evaluating this material from a mining, processing, and economic perspective,” Hahn added.
“Several other open pit heap leach operations in the area crush to -6.3mm (-1/4”) and stack in multiple lifts up to +30 metres (100 feet). Permeability and compaction tests performed on the bulk sample prior to column leaching demonstrate the ability to stack this material to similar heights."
The column leach tests are scheduled to continue for up to 150 days or until gold extraction levels plateau, with the goal of achieving 80% total gold recovery at the -6.3mm crush size.
In addition, Arizona Gold & Silver has resumed core drilling at the project.
The next drill hole, PC25-157, is planned approximately 60 metres north along strike from the high-grade intercept in hole PC25-156, which reported 20.43 metres grading 9.04 grams per tonne (g/t) gold and 34 g/t silver.
Drilling will target the Perry Vein at the same elevation as the previous high-grade intercept.