Porfido

PORPHYRY Cu ± Mo ± Au
by Andre Panteleyev1
Modified for Yukon by A. Fonseca Refer to preface for general references and formatting significance. May 30, 2005

L04

IDENTIFICATION
SYNONYM: Calcalkaline porphyry Cu, Cu-Mo, Cu-Au. COMMODITIES (BYPRODUCTS): Cu. Mo and Au are generally present but quantities range from insufficient for economic recovery to major ore constituents. Minor Ag inmost deposits; rare recovery of Re from Island Copper mine. EXAMPLES (Yukon): Casino (115J 028), Revenue (115J 042), Nucleus (115I 107), Cash (115I 103), Stu (115I 011); (British Columbia - Canada/International): • Volcanic type deposits (Cu + Au ± Mo) - Fish Lake (092O041), Kemess (094E021,094), Hushamu (EXPO, 092L240), Red Dog (092L200), Poison Mountain (092O046), Bell (093M001), Morrison(093M007), Island Copper (092L158); Dos Pobres (USA); Far Southeast (Lepanto/Mankayan), Dizon, Guianaong, Taysan and Santo Thomas II (Philippines), Frieda River and Panguna (Papua New Guinea). • Classic deposits (Cu + Mo ± Au) - Brenda (092HNE047), Berg (093E046), Huckleberrry (093E037), Schaft Creek (104G015); Casino (Yukon, Canada), Inspiration, Morenci, Ray, Sierrita-Experanza, Twin Buttes, Kalamazooand Santa Rita (Arizona, USA), Bingham (Utah, USA),El Salvador, (Chile), Bajo de la Alumbrera (Argentina). • Plutonic deposits (Cu ± Mo) - Highland Valley Copper (092ISE001, 011, 012, 045), Gibraltar (093B012,007), Catface (092F120); Chuquicamata, La Escondida and Quebrada Blanca (Chile).

GEOLOGICAL CHARACTERISTICS
CAPSULE DESCRIPTION: Stockwork of quartz veinlets, quartz veins, closely spacedfractures and breccias containing pyrite and chalcopyrite with lesser molybdenite, bornite and magnetite occur in large zones of economically bulk-mineable mineralization in or adjoining porphyritic intrusions and related breccia bodies. Disseminated sulphide minerals are present, generally in subordinate amounts. The mineralization is spatially, temporally and genetically associated withhydrothermal alteration of the hostrock intrusions and wallrocks. TECTONIC SETTINGS: In orogenic belts at convergent plate boundaries, commonly linked to subduction-related magmatism. Also in association with emplacement of high-level stocks during

1

British Columbia Geological Survey, Victoria, B.C., Canada

extensional tectonism related to strike-slip faulting and back-arc spreading followingcontinent margin accretion. DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: High-level (epizonal) stock emplacement levels in volcano-plutonic arcs, commonly oceanic volcanic island and continentmargin arcs. Virtually any type of country rock can be mineralized, but commonly the high-level stocks and related dykes intrude their coeval and cogenetic volcanic piles. AGE OF MINERALIZATION: Two mainperiods in the Canadian Cordillera: the Triassic/Jurassic (210180 Ma) and Cretaceous/Tertiary (85-45 Ma). Elsewhere deposits are mainly Tertiary, but range from Archean to Quaternary. HOST/ASSOCIATED ROCK TYPES: Intrusions range from coarse-grained phaneritic to porphyritic stocks, batholiths and dyke swarms; rarely pegmatitic. Compositions range from calcalkaline quartz diorite to granodiorite andquartz monzonite. Commonly there is multiple emplacement of successive intrusive phases and a wide variety of breccias. Alkalic porphyry Cu-Au deposits are associated with syenitic and other alkalic rocks and are considered to be a distinct deposit type (see model L03). Jurassic intrusions host the majority of porphyry prospects in Yukon. The Casino and Cash deposits, however, are hosted in UpperCretaceous intrusive rocks; the Revenue deposit is hosted in mid-Cretaceous intrusive rocks; and the Stu deposit is hosted in Triassic intrusive rocks. DEPOSIT FORM: Large zones of hydrothermally altered rock contain quartz veins and stockworks, sulphide-bearing veinlets; fractures and lesser disseminations in areas up to 10 km2 in size, commonly coincident wholly or in part with hydrothermal or...