Four-Acid vs Aqua Regia Digestions: Selecting the Defensible Geochemical Package

Near-Total vs Partial Chemical Extractions

A frequent decision in exploration planning is selecting the digestion method for drill samples. Aqua regia (3:1 HCl:HNO3) is a robust partial leach suitable for sulfides, carbonates, and epithermal gold, but fails to break down resistate silicate minerals.

The Power of Four-Acid Hydrofluoric Digestion

Four-acid digestion uses hydrofluoric (HF), nitric (HNO3), perchloric (HClO4), and hydrochloric (HCl) acids heated to near-dryness. This dissolves silicates, feldspars, and refractory oxides, releasing encapsulated metals into solution for true total geochemical analysis.

Selection Criteria

For early-stage regional soil mapping, aqua regia provides high signal-to-noise for mobile ions. For lithogeochemistry, alteration vectoring, and base metal resource estimation (Ni, Co, Cu, REEs), four-acid digestion is mandatory for regulatory compliance.