Geochemical Characteristics of Intrusive Rocks, Southeastern Mindanao, Philippines: Implication to Metallogenesis of Porphyry Copper‐gold Deposits

Abstract

This paper describes petrologic and geochemical characteristics of intrusive rocks associated with porphyry copper deposits in south-eastern Mindanao, the Philippines, where the Kingking deposit is located. Intrusive rocks at the Kingking deposit, are classified into biotite-bearing diorite porphyry, hornblende diorite porphyry and diorite porphyry. Intrusive rocks in other areas in south-eastern Mindanao, including Batoto, Bukal, Maragusan, Masara, Amacan and Sumlog, are hornblende diorite porphyry and hornblende quartz diorite. They are adakitic in Sr/Y-Y diagram, but not in La/Yb-Yb diagram due to relatively low REE contents. The magmas are oxidizing as suggested by the high XMg of mafic silicate phenocrysts and SO3 contents of microphenocrystic apatite. An Oligocene-Miocene diorite intrusive complex formed by calc-alkaline, hydrous, oxidizing magma is considered to be associated with porphyry-type copper-gold mineralization.

Adakitic rocks in the Masara gold-silver mine, Compostela Valley, Mindanao, Philippines: Different places, varying mechanisms?

“…The Don Fernando adakitic diorites are believed to be Early to Late Miocene, as correlated with the intrusive rocks of Kingking and Amacan (e.g. Suerte et al, 2009). Some of these diorites have intruded into the Middle Miocene Agtuuganon Limestone.…”

“…slab melting) may not be very important, and that fractionation, water activity, sulfur fugacity and the state of oxidation of the melt are the more critical components that dictate whether mineralization is to be generated or not in a particular adakitic suite (e.g. Kay and Mpodozis, 2001;Richard and Kerrich, 2007;Imai et al, 2009;Suerte et al, 2009;Jenner et al, 2010;Tanaka et al, 2010;Richards, 2011a, b;Chiaradia et al, 2012;Hronsky et al, 2012;Loucks, 2014). More complications arise when the role of mantle oxygen fugacity on crust-derived fluids or melts is considered (Chen et al, 2015).…”

Origin of Bornite Pods in Intrusive Rocks at the Kingking Porphyry Copper‐gold Deposit, Southeastern Mindanao, Philippines

“…These rocks were intruded by mineralized and barren andesite, diorite and dacite porphyries in Miocene to Pliocene (Mitchell & Leach, 1991). Suerte et al (2009) report the characteristics of the intrusive rocks in south-eastern Mindanao including those at the Kingking porphyry copper-gold deposits, and discussed metallogenic implication.…”

“…2). Suerte et al (2009) described petrography, whole-rock chemistry and mineral chemistry of these intrusive rocks. Some portions of the diorites, probably along or near contact with the wall rock or with each other, exhibit brecciation.…”

“…It is also indicated in the geochemical data that the three diorites may be genetically related (Suerte et al, 2009). If the magmas which formed the three diorites are related and their copper values are not much different, why are the bornite pods occur only in the biotite diorite porphyry?…”