Rob Stevens

Sulfide vs. Oxide Deposits: What Every Copper & Gold Investor Must Know with Dr. Rob Stevens

• Top takeaway His central argument is that when a company presents an oxide deposit in a positive light as the better target, he broadly agrees. On average oxide deposits are cheaper to mine and process, with no grinders or flotation cells, usually heap leaching rather than a mill, and for copper the option to produce cathodes on site rather than send concentrate to a smelter.
• He is careful to limit that to copper and gold, pointing out that iron ore and uranium oxide deposits are primary rather than weathering products, so the same economics do not apply to them.
• He immediately qualifies his thesis with recovery, which he calls the downside. Oxide processing can recover as low as 60%, and he cites 65%, 70% gold recovery for some heap leach gold projects against over 90% from a conventional mill on the same deposit type. He argues the lower costs can still justify the lower recovery.
• His signature mechanism is supergene enrichment. Copper leached out of the upper deposit redeposits at what was historically the boundary between an oxygen-rich and an oxygen-poor environment, which builds a high-grade zone over the original deposit. He notes that if such a zone sits near the top it can be mined early in the mine life.
• His closing advice to investors is to always check the metallurgy, namely how the ore will be processed, the capital costs of the processing plant and the recoveries, plus the value of secondary minerals. He warns that the common junior story of oxides funding sulfide capex can be promotional, calling it "not a savior for a crappy deposit" and telling juniors to use a skeptical eye.

Oxide copper and gold deposits skip grinding and smelting, cutting the capital and operating costs a mine must carry. The trade-off is recovery: oxide heap leaching can return as little as 60% where a conventional mill can exceed 90%. Supergene enrichment zones gather leached copper near the surface, building high-grade ore that can be mined early in mine life. Refractory ore locks metal inside minerals conventional processing cannot break, often forcing a roaster or pressure oxidation step. The guest urges investors to demand standalone economics before crediting an oxide cap with funding a deeper sulfide mine.