Jack Halloran, MSc
J. Halloran1, J. Hedenquist1, K. Hattori1, T. Godoy2
1Department of Earth and Environmental Science, University of Ottawa, Ottawa, Ontario, Canada
2ATEX Resources, Toronto, Ontario, Canada
The Valeriano porphyry deposit is located at the northern extent of the El Indio belt in the Frontal Cordillera of Chile. ATEX Resources Inc. began exploration in 2021 and has now completed its sixth drilling campaign, totally over 50,000 m. The deposit is associated with Miocene porphyry and biotite-hornblende granodiorite stocks, hosted by Permian volcaniclastic rocks. A north-trending lithocap of advanced argillic alteration outcrops up to ~4500 m elevation. The intrusion-hosted porphyry mineralization is overlain by extensive polyphase, polymictic magmatic-hydrothermal breccia, with angular fragments of potassic-altered porphyry intrusions as well as A- and B-type quartz veins. The intermineral breccia hosts a high-grade zone, e.g., ATXD25C, 164 m of 1.69 wt% Cu, 0.97 g/t Au, 2.2 g/t Ag and 65 g/t Mo. The intermineral breccia is associated with a white mica-chlorite overprint of potassic alteration, with K-feldspar, biotite and magnetite replaced by illite, chlorite and hematite, associated with chalcopyrite, bornite and digenite and minor high-sulfidation sulphides. A second generation of inter-mineral breccia, inter-mineral breccia 2, was cemented by siderite and sulfides, responsible for the highest Cu and Au grades. Well-crystalline kaolinite + siderite cement and high sulfidation-state enargite/luzonite, chalcocite, digenite, bornite and covellite are intergrown, indicating syn-mineral formation. Earlier chalcopyrite + bornite fragments were replaced by digenite, chalcocite, and covellite, with enargite/luzonite on the rims of earlier sulphides. Enargite/luzonite, covellite and chalcocite also occur disseminated in the kaolinized inter-mineral breccia 2, replacing earlier disseminated sulphides.
Above the porphyry intrusions and overlying the inter-mineral breccia 2-hosted high-grade zone, a horizon of nodular pyrophyllite + alunite alteration (plus other aluminosilicate minerals, confirmed by shortwave infrared spectroscopy and X-ray diffraction) occurs near the base of the lithocap, as a replacement of white mica and quartz. Logging of 21 drillholes (15 in photographs) indicates that the nodular (previously referred to as patchy) alteration occurs ~600-1000 m above the intrusions, and <500 m above the 0.3% Cu grade shell, providing a shallow vector during porphyry exploration elsewhere.