The plate tectonic setting of mineral deposits in the New England Orogen (Australia)

Continental arcs have produced some of the largest ore deposits on Earth. In eastern Australia, the New England Orogen (NEO) represents a long-lived continental arc, but the number of economically significant ore deposits hosted in this orogen is relatively small. Here I examine the spatiotemporal distribution of mineral deposits in the NEO, to assess whether metallogenic events, or the lack thereof, were ultimately controlled by plate tectonic processes. Integrating information on the style and timing of mineralisation with plate tectonic reconstructions allows identification of several metallogenic belts. A belt of epithermal Au Ag deposits, dated ~290 Ma, was developed in an extensional backarc setting during a period dominated by trench retreat. At ~250 Ma, a pulse of contractional deformation that coincided with the end of a magmatic cycle produced a porphyry Cu Mo belt and an intrusion-related Sn W belt in the northern and southern NEO, respectively. Importantly, the ~250 Ma porphyry belt is restricted to an arc sector that was underlain by a relatively shallowly dipping slab. A final phase of contraction, at 235–230, triggered Au Cu mineralisation within the contemporaneous arc, which is exposed only in the northern NEO. The results show that the NEO obtained favourable conditions for mineralisation, including shallowing of the slab dip angle, cyclic arc magmatism, and structural focusing by pulses of contractional deformation. Nevertheless, repeated periods of trench retreat that prevented crustal thickening may have undermined the mechanism for metal enrichment, thus explaining the lack of giant porphyry and epithermal systems in the NEO.