CH11 Exploration for Copper-Gold Porphyry – Afton/Ironmask Area, BC, Canada

GamX CH11 Afton-IronMask Area Alteration Types

The Ironmask Batholith is a northwest trending, late-Triassic, polyphase, alkalic intrusive complex which hosts at least 20 copper-gold prospects/past-producing mines, including New Afton (currently operating), Ajax East, Ajax West, Crescent, Pothook, Big Onion, DM, Python-Makaoo and Rainbow. Mineralization occurs within all phases of the batholith, primarily as fracture controlled chalcopyrite and bornite associated with magnetite. Pyrite and pyrrhotite occur peripherally. Hydrothermal alteration occurs as early magnetite (actinolite-apatite), intermediate potassic, and late albitic1 (right).  Not all alteration is mineralized.




In 1993, a GSC contracted, Teck-funded, gamma ray/mag helicopterborne survey was flown by Sander Geophysics Limited over the entire Ironmask Batholith using 400m line spacing. Results were surprising, as virtually all known occurrences/mines produced similar geophysical (geochemical) responses, appearing as eTh/K ratio LOWS located on the flanks of significant magnetic total field highs. The maps and stacked profiles below show this signature clearly.


GamX CH11 Afton-Ironmask Geology - Airborne Gamma Ray - Mag maps


GamX CH11 Afton-Ironmask Deposits Airborne Survey Profiles

Stacked profiles (Figure 2) show flight line responses (Mag, K, eU, eTh, eU/Th, eTh/K) over 6 of the “top 20” mines/prospects. All 20 display similar patterns. Although few occurrences produce an obvious airborne K anomaly, RELATIVE K indicated by the eTh/K ratio (again, this means K concentration in relation to the corresponding eTh concentration) is recognizable in all. In addition, all “top 20” occur on the flanks of prominent magnetic total field highs, as these examples show. Both signatures are required to define potential targets in this geological setting: many low eTh/K responses do not have a corresponding magnetic anomaly and do not overlie known occurrences; conversely, many high-magnetic flanks do not have corresponding eTh/K lows. The profiles in Figure 2F confirm the chemical response over the Ajax mine waste rock (low eTh/K signature of the altered, ore-enveloping rocks) with no corresponding mag-high (the waste rocks do not overlie a deposit!).



  1. Jim Logan, Mitch Mihalynuk, Tom Ullrich, Richard, Friedman, 2006. Geology and Mineralization of the Ironmask Batholith. GeoFile 2006-5. Poster.