Metallurgy and Gold Processing

Introduction to Metallurgy

• Importance of metallurgy in mining and gold recovery.
• Employing expert metallurgist assistance for clarity.
• Famous metallurgist: Georgius Agricola (wrote first book on metallurgy in the 1500s).
• Gascoigne's met results for the Never Never deposit.

Importance of Recovery

• High recovery percentage is crucial for profitability.
• Example: Gascoigne had low recovery from Ghibli pit (80% recovery).
• New results: Never Never deposit shows 92% for oxide ore and 94% for fresh rock.

Types of Ore

• Oxide Ore: Close to the surface, weathered, fewer sulfides.
• Fresh Rock: Solid, often contains sulfides and other elements.

Gold Extraction Processes

Gravity Circuit

• Uses physical properties (density, particle size) to extract free milling gold.
• Faster, environmentally friendly; no need for extensive chemical use.
• Initial gold bar from mine usually via gravity circuit.

CIL (Carbon in Leach)

• Uses cyanide to dissolve gold; cyanide is crucial as it is one of the few chemicals that can dissolve gold.
• Process: Gold-cyanide solution formed, gold attaches to activated carbon, then stripped and electro-won into dore bars.

Cyanide Circuit

• Cyclone Overflow: Material goes to cyanide circuit.
• Cyclone Underflow: Coarse, dense materials returned for further grinding.
• Cyanide leach process: high pH needed (adjusted with lime).
• Typical tank setup: two leach tanks with cyanide/oxygen, followed by adsorption tanks with carbon.

Recovery Results and Comparisons

• Gascoigne's Never Never results show strong recovery.
• Bellevue as a comparison: higher gravity recovery (73.6% - 91.7%) and overall recovery (97.8%).
• Bellevue's faster processing indicated by early recovery results.

Refractory Ore and Other Issues

• Refractory Ore: Gold that doesn't respond to cyanide treatment, often encapsulated in sulfides.
• Preg-robbing: Graphitic materials that interfere with carbon's ability to recover gold.
• No significant issues for Gascoigne's ore with deleterious elements.

Process Improvements

• Potential upgrades to existing plants to handle Never Never ore.
• Considerations for mine throughput and milling efficiency.
• Optimization studies for further recovery improvement.
• Importance of mineralogy in blending and regional consolidation strategies.

Conclusion

• Metallurgy is critical in determining mining viability and profitability.
• Gascoigne's results are promising but require careful analysis and potential upgrades for optimization.