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

Abstract

At the Kingking porphyry copper-gold deposit, Compostela Valley, south-eastern Mindanao, Philippines, bornite pods occur in the brecciated parts in the biotite diorite porphyry, together with the volcanic rock and diorite fragments without associated stockworks of quartz veinlets. These pods are generally elongated in shape and measure several centimeters across their longest axes. They are composed of bornite and chalcopyrite with traces of calaverite. The d 34 S of bornite and subordinate chalcopyrite of bornite pods ranging from -2.2‰ to +0.1‰ are similar to the d 34 S of sulfides associated with quartz veinlets such as bornite and chalcopyrite ranging from -4.7‰ to Ϯ0.0‰. This suggests that the ultimate source of sulfur is identical for bornite pods and sulfides associated with quartz veinlets. Bornite pods are associated with volcanic rock and dioritic fragments in the brecciated portion of the biotite diorite porphyry. It was observed that some dioritic fragments contain quartz veinlets, which may indicate an earlier episode of mineralization. Fragments of the earlier dioritic intrusive rocks and the volcanic rocks, together with the sulfides were incorporated into the biotite diorite porphyry magma. A molten sulfide is possible for the composition between bornite and intermediate solid solution at~800°C. The sulfides from the earlier dioritic intrusive rocks in the molten state were segregated and then eventually coalesce to form the bornite pods in the brecciated section of the biotite diorite porphyry.

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

“…, 2003). Imai et al. (2009) discussed the origin of the bornite pods in the biotite diorite porphyry at the Kingking deposit.…”

Redistribution of Minor and Trace Elements During Roasting of Cu-Rich Complex Concentrate in Inert Atmosphere

“…In a strictly Cu-Fe-S system, Bor and iss-phase are known to form a low-melting eutectic below 800°C. [82,83] Inclusion of additional elements such as Zn, Pb, Ag, Sb, As (as in the presently investigated system of the Garpenberg concentrate) would likely reduce the melting point of this eutectic-phase combination further down. Interestingly, Bor exists primarily in the gaps between the solidified intergrowth phases in the microstructure in Figure 10(a).…”

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

“…Eastern Mindanao is host to several precious metal -base metal mines and prospects (e.g. Sillitoe, 1989;Suerte et al, 2007;Imai et al, 2009;Sonntag et al, 2011) (Figure 2). The general tectonic grain in the minesite is NW-SE consistent with the general direction of the Philippine Fault Zone.…”

“…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).…”