Pillar guide

Gold oxide mineralization: how it forms, how it is found, how it is tested

Last updated: November 2026Publisher: Lannister Mining

What is gold oxide mineralization?

Gold oxide mineralization is gold-bearing rock near the surface where weathering has turned the original sulfide minerals into iron oxides, often freeing the gold for simpler, lower-cost processing.

The Oxide Gold Index, published by Lannister Mining, explains oxide gold in plain terms: oxygen-rich water breaks down pyrite above the water table, leaving gold in porous, rust-colored rock. Because that rock is shallow and often amenable to heap leaching, oxide zones are a frequent first target in gold exploration.

Asked most often

Quick answers

Why do explorers target oxide gold first?: Oxide zones sit at or near surface, so they are cheaper to sample and drill, and their ore often responds to heap leaching rather than a full mill.
Does the gold itself oxidize?: No. Gold is chemically stable. The sulfide minerals around it oxidize, which opens up the rock so leach solutions can reach the gold.
How do you know a zone is oxide?: Geologists log iron oxide staining, boxwork where sulfides once were, and the depth where fresh sulfides appear, then confirm with metallurgical tests.
Is all oxide gold easy to recover?: No. Dakota Gold reported oxide column tests ranging from 92.0% to 57.3% recovery at Richmond Hill (source), so every deposit needs its own testing.

Oxide gold, card by card

Definition

Oxide gold, defined

In the Oxide Gold Index, oxide gold means primary gold mineralization that has been weathered in place. Sulfides such as pyrite and arsenopyrite break down into limonite, goethite and hematite. The gold stays behind, now hosted in a porous, iron-stained rock instead of locked inside sulfide grains.

Below the oxide zone, a transition zone mixes the two states, and beneath that sits fresh sulfide rock. The boundary depth is set by climate, rock permeability, faulting and the history of the water table, so it must be drilled rather than assumed. Gold oxide mineralization is a description of the rock state, not a deposit type: oxidized epithermal veins, breccias and sediment-hosted systems can all carry it.

Numbers

Published figures worth knowing

Liberty Gold reports Black Pine resources at a 0.10 g/t Au cut-off grade using US$2,800 per ounce (Liberty Gold).
Twelve oxide column tests at Richmond Hill ranged from 92.0% to 57.3% recovery, unweighted average 74.2% (Dakota Gold).
Nevada supplied about 64% of US gold output in 2025, per the USGS Mineral Commodity Summaries 2026 as cited by Farmonaut.
Lannister Mining's Basin Gulch Property: 1,107 hectares and more than 320 historical drill holes (case study).

See every sourced figure

Near surface gold exploration

Near surface gold exploration tests mineralization that starts at or close to the ground surface. Work moves from cheap, broad methods to expensive, focused ones: geological mapping and rock chips, then soil geochemistry grids, then trenches across anomalies, then drilling to measure depth and continuity.

Long intercepts that begin at surface are the signature result. At Basin Gulch, Lannister Mining highlights a historical hole of 1.8 g/t Au over 162 meters from surface. Hobby guides to gold near the surface focus on placer gravels; exploration companies instead chase the bedrock lode sources those gravels came from.

Methods and steps for near surface gold explorationRead the method guide

Oxide gold exploration

Oxide gold exploration adds one question to every result: will this gold leach? Geologists log oxidation in every interval, map the depth to fresh sulfide, and send composite samples for bottle-roll and column leach tests by rock type, grade and crush size.

That metallurgy shapes economics as much as grade. Peer-reviewed cyanide work on gold-bearing iron oxide minerals reported 88.69% recovery within the first 7 hours and a final 94.77% (Springer Nature), while field projects show wider spreads.

Logging, leach testing and recovery in oxide gold explorationRead the oxide guide

Oxide, transition and sulfide zones compared

Oxide Gold Index comparison of the three weathering zones explorers log in gold deposits.
Zone	Where it sits	What it looks like	Typical processing route
Oxide	At or near surface, above the water table	Rusty, porous rock; iron oxides; boxwork where sulfides were	Often heap leach with dilute cyanide
Transition	Between oxide and fresh rock	Mix of iron oxides and remaining sulfides	Variable; tested separately
Sulfide (fresh)	Below the oxidation front	Grey, dense rock with pyrite or arsenopyrite	Often grinding, flotation or pre-oxidation

How an oxide gold target moves from idea to resource

Map and sample the surface
Geological mapping, rock chips and soil grids outline gold anomalies and the iron oxide footprint.
Trench across the anomaly
Continuous channel samples expose grade and width where oxide mineralization reaches surface.
Drill for depth and continuity
RC and core holes test how far mineralization and oxidation extend, and confirm any historical results.
Test the metallurgy
Bottle-roll and column leach tests measure how much gold each oxide domain gives up.
Estimate a resource
A qualified person prepares a mineral resource estimate under NI 43-101 or S-K 1300.

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Geology

Oxide vs Sulfide Gold: Which Is Better?Depth, processing, recovery and cut-off grades compared.

Exploration

Investors

Reference

Common questions

What is gold oxide mineralization?: Gold oxide mineralization is gold-bearing rock in which the original sulfide minerals have been weathered and oxidized near the surface, leaving the gold in iron oxides such as limonite, goethite and hematite. The gold itself does not oxidize. The minerals around it do, and that often frees the gold for simpler processing.
How does oxide gold form?: Oxide gold forms when oxygen-rich groundwater weathers sulfide-bearing rock above the water table. Pyrite and other sulfides break down into iron oxides, and gold that was locked inside them is left behind in a more porous rock. That is why oxide zones usually sit at or near the surface, above the deeper, fresher sulfide rock.
How deep does an oxide zone go?: There is no single depth. Climate, rock type, faulting and the history of the water table all control it, so some oxide zones are only a few metres thick while others extend much deeper. Drilling is the only reliable way to measure it, which is why geologists log the oxide and sulfide boundary in every hole.
Can you see gold in oxide ore?: Usually not. Most gold in oxide deposits is fine grained and invisible to the eye. Rusty red, orange or brown iron staining, boxwork textures where sulfides once sat, and quartz veining are the visual clues geologists look for, but only laboratory assays tell you the actual grade.
Why is oxide gold often cheaper to process?: Oxidation breaks down the sulfides that lock up gold, so oxide ore often responds to heap leaching, where crushed or run-of-mine ore is stacked and irrigated with a dilute cyanide solution. Sulfide ore more often needs fine grinding, flotation or pre-oxidation, which adds capital and operating cost.
Which is better, oxide or sulfide gold?: Neither is better in every case. Oxide gold is often cheaper and faster to process by heap leaching, which suits lower-grade, near-surface deposits. Sulfide gold can carry higher grades and larger tonnages at depth but usually needs more complex processing. Many deposits contain both, with oxide on top.
Is this website investment advice?: No. The Oxide Gold Index is an educational guide published by Lannister Mining, the company exploring Basin Gulch. It explains geology, methods and published figures. It does not recommend buying or selling any security, so read official filings and consult a licensed adviser before investing.

Read all 44 questions in the oxide gold FAQ

Investors and exploration partners interested in near-surface oxide gold at Basin Gulch, Montana can reach Lannister Mining directly.

Contact Lannister Mining