If you read news releases from gold exploration companies working in the Andes, two phrases come up constantly: "high-sulphidation epithermal" and "porphyry copper-gold". Both describe types of mineral deposits, but they form at different depths and produce very different exploration targets. This post explains the first one.
How a high-sulphidation epithermal deposit forms
Deep beneath a volcanic centre, a body of cooling magma releases hot, acidic, sulphur-rich fluids. Those fluids rise through fractures in the rock and react violently with everything they meet, stripping out original minerals and replacing them with silica, alunite and clays. Geologists call this alteration, and the zones it creates are visible from surface: bleached, silicified rock that stands out against its surroundings.
As the fluids cool (typically within about a kilometre of surface), gold, silver and copper precipitate out of solution and deposit in veins, vein swarms and breccias. Because the fluids are hot and acidic, sulphide minerals like pyrite and enargite dominate, which is where the "high-sulphidation" label comes from. The shallow depth gives the "epithermal" part.
What it looks like in the field
The surface expression can be dramatic: large zones of intense alteration, often measured in square kilometres rather than metres. At Carmona, for example, Kairos Gold has identified three gold-silver bearing high-sulphidation epithermal alteration systems covering an estimated 18 km². Those zones are what drew explorers to the area in the first place, and they are what modern geochemical sampling and geophysics programs are designed to map in detail.
Within the alteration, the highest gold grades tend to concentrate in veins and vein swarms. At Oro Brillante on the Las Garillas Project, surface and underground vein-swarm sampling returned 1.2 to 61.4 g/t gold, while rock samples across the wider property reached 61.0 g/t gold with 2.85% copper and 329 g/t silver.
Why it matters for exploration companies
High-sulphidation epithermal deposits are attractive for three reasons. First, the alteration is big and visible, so targets are identifiable before the first drill hole. Second, the grades can be very high over mineable widths, which changes project economics. Third, the epithermal veins at surface are often the top of a deeper porphyry system below, meaning a drill program that starts on the veins may discover something larger underneath.
This is exactly the interpretation Kairos Gold has laid out at Oro Brillante: drilling has defined a 200 to 600 metre wide hydrothermal alteration system with sulphides (pyrite, chalcopyrite, sphalerite, molybdenite) in stockwork, vein and breccia settings, and the Company interprets porphyry-style potential at depth. Phase Three infill drilling is designed to test that continuity.
Where to learn more
The geology and exploration page covers epithermal, porphyry and skarn deposits with a glossary. The Las Garillas project page carries the drill results and exploration history. The Investor FAQ answers the question "What type of gold deposits is Kairos Gold exploring for?" in a few sentences.
Qualified Person. The scientific and technical information on this page is drawn from Kairos Gold news releases and technical reports, each of which was reviewed and approved by a Qualified Person under National Instrument 43-101. Website review by a named Qualified Person is pending; direct technical questions to info@kairosgold.ca. Historical sampling and mining results are historical in nature and have not been independently verified by the Company unless stated in the source release. Surface and underground grab samples are selective by nature and may not represent average grades on the property.
Statements about planned programs, timing, budgets and geological potential are forward-looking and subject to permits, financing, contractor availability and results. See the disclaimer.