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Summary
• For alkalic porphyries, magnetic (oxidized) rocks are interesting, but
magnetite rich intrusives/alteration not as common in calc-alkalic settings
• Later phyllic alteration can destroy primary igneous and secondary
hydrothermal magnetite in host rocks in both alkalic and calc-alkalic settings
• Conductivity information can be very useful for detecting structures;
Intrusive bodies are usually resistive as a result of coherency
• IP surveys are very effective in detecting peripheral pyrite halos
• Scale important! At 5 km scale, magnetic and resistivity signatures likely
relate to rock type and structure, not mineralization; IP most effective
• There is no unifying geophysical model for porphyries - need to understand
typical background rocks and alteration, general structural orientations –
important for applying outside of BC!
– Host rocks (magnetic/non; brecciated/coherent)
– Depth of formation/erosion (related to alteration mineralogy/halos)
– Metal distribution (connected, disseminated Zoning)