Abstract
Many epithermal to mesothermal and porphyry-style Au ± Cu deposits worldwide occur associated with, or are hosted by, potassic igneous rocks and shoshonites. The host rocks are generally characterized by high halogens such as Cl and F, high LILE and low HFSE. Mineralization genetically associated with potassic igneous rock suites appears to be restricted to three tectonic settings: late oceanic arcs, continental arcs and postcollisional arcs. Examples of associations in late oceanic arcs include the Pleistocene Ladolam gold deposit, Lihir island, Papua New Guinea, the Pliocene Emperor gold mine, Viti Levu, Fiji and the Ordovician Goonumbla porphyry cooper-gold deposit, N.S.W., Australia. Examples from continental arcs include many epithermal gold and porphyry copper-gold deposits in the Mesozoic to Cenozoic Chilean Andes. An example of the association in a postcollisional-arc is the Miocene Porgera gold deposit, Papua New Guinea. For those potassic igneous rocks interpreted to be genetically related to gold-copper deposits in late oceanic arcs, continental and postcollisional arcs, the Cl contents of their mica phenocrysts are anomalously high with respect to Cl contents of barren high-K rocks from the same tectonic settings. Mineralized potassic igneous rocks from late oceanic arcs appear to be typified by both anomalously high Cl and F in mica phenocrysts.
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