The origin of mafic–ultramafic rocks and felsic plutons along the Clarke River suture zone: implications for porphyry exploration in the northern Tasmanides

Abstract The Clarke River Fault in northeast Queensland records an early Paleozoic history of subduction, accretion and continental suturing. Samples of mafic–ultramafic rocks collected proximal to the Clarke River Fault record oceanic geochemical affinities and comprise alteration assemblages consistent with an ophiolitic origin. The ca 456 Ma Falls Creek Tonalite records a continental-arc geochemical signature and was formed in response to long-lived subduction beneath the Thomson Orogen. Ordovician subduction beneath the Thomson Orogen is broadly coeval with arc magmatism documented in the Lachlan Orogen, which has been associated with the formation of several large porphyry ore deposits. The Falls Creek Tonalite yields adakite-like geochemical signatures that reflect a fertile melt source conducive to the formation of porphyry ore deposits. The outcropping plutons record ductile deformation consistent with mid-crustal depths, and they were emplaced during late syntectonic activity. This implies that the Falls Creek Tonalite was emplaced at too great a depth to have formed porphyry ore deposits. The northern Charters Towers Province shares many geological similarities to the Greenvale Province, where the erosional level may be shallower, and the potential for porphyry deposit formation and preservation may be greater. KEY POINTS Mafic–ultramafic rocks situated along the Clarke River Fault are of ophiolitic origin. The Clarke River Fault is an early Paleozoic suture zone. The northern Tasmanides contain adakitic plutons formed from hydrous, fertile melts, conducive to the formation of porphyry ore deposits.