Spatial relationship between porphyritic Cu-Au mineral occurrences and magnetic signatures within the Iron Mask Batholith, south-central Cordillera, British Columbia

Abstract

Gold-rich porphyry copper deposits are commonly associated with magnetic highs related to high magnetite content - up to 10% volume - within potassium silicate alteration zones. This association promoted magnetic highs as exploration targets. The Iron Mask batholith (comprising Iron Mask and Cherry Creek plutons) contains more than 50 porphyry Cu-Au mineral occurrences, including the New Afton deposit. The batholith's strong positive magnetic signatures permit examining magnetic high correlations with porphyry-type mineralization and evaluating the significance of magnetic signatures for mineral exploration. Groups of prominent magnetic peaks were delineated, with six and two groups present in the Iron Mask pluton and Cherry Creek pluton, respectively. Mineral occurrences occur within the borders of two groups, but are peripheral to other groups, with the nearest occurrence an average of 500 m from the centre of a group. These close spatial relationships support magnetic exploration for porphyry-copper deposits that significantly narrows the search area. Magnetic exploration is also supported by the observation that porphyry (Cu±Mo±Au) and magnetite-apatite mineralization in the Iron Mask batholith are related to a single intrusive event, a characteristic shared by iron-oxide copper gold deposits, where magnetite-apatite mineralization is located laterally or deeper. The New Afton deposit is situated laterally to the Magnet magnetite-apatite deposit near the end of a linear magnetic high passing through the latter.