Late Miocene adakites associated with the Tangse porphyry Cu-Mo deposit within the Sunda arc, north Sumatra, Indonesia

Abstract

Porphyry deposits are generally found at convergent margins, especially above active subduction zones where adakite may be a great exploration target for porphyry-type Cu (-Mo and/or -Au) deposits. The Sunda arc is one of the recent island arcs in the world. The quartz diorite porphyry from the Tangse porphyry Cu-Mo deposit, west end of the Sunda arc, shows an emplacement age of 8.7 Ma and is characterized by high Sr/Y (23.9–32.9) and moderate Y (11.11–16.78), and obviously positive Eu anomalies (δEu = 1.10–1.35), which belongs to adakite with calc-alkaline affinities. This hypabyssal intrusion has the dominantly positive zircons εHf(t) values (+12.57 to +16.70) and whole-rock εNd(t) values (+3.8 to + 5.5). Slightly low 87Sr/86Sr values (0.70439 to 0.70449) and 143Nd/144Nd (0.512829 to 0.512914) of porphyries indicate that they have the sources similar to the Batu Hijau deposit in east end of the Sunda arc. Our study further displays that the mineralization of the Tangse Cu-Mo deposit is related to Indian ocean plate northward subduction during Late Miocene. The parental magma of the quartz diorite porphyry resulted from dehydration partial melting of subducted oceanic crust (including marine sediments) and subsequent contamination of mantle wedge material. The Tangse quartz diorite porphyry is characterized by high oxygen fugacities (ΔFMQ = +5.0 to +9.4), which has a good potential for the exploration of porphyry Cu-Mo deposit.