Tonian intra-oceanic magmatism as the source of the Goiás porphyry copper–gold system in the Brasília orogenic belt: petrogenesis and metallogenetic implications

In the Goiás Intra-Oceanic Arc System (Goiás IOAS), Brasília Orogen, Brazil, occurrences of porphyry-type mineral deposits have been identified. The most significant of these is the Chapada Cu–Au deposit (1056 Mt Cu @ 0.24% Au @ 0.12 g t –1 ). This deposit is related to metadiorites, orthogneisses and metavolcanic sedimentary rocks. This study aims to trace the igneous protolith source of the orthogneisses and to explore the impact of magmatism on the porphyry-type mineralization of the Goiás IOAS. The data obtained indicate that the orthogneisses represent two distinct magmatic series: one with a normal arc calc-alkaline (NCO) affinity, and the other with an adakitic (ADO) affinity. The NCO shows characteristics that suggest a source mantle metasomatized by slab-released fluids. They are geochemically and isotopically similar to metadiorites from the Chapada deposit, which suggests that they share a common mantle-derived magmatic origin. Evidence of mafic magma recharge suggests that the fertility of the system is related to addition of mantle-derived volatiles and incompatible elements. The ADO are distinct from the orthogneisses of the NCO and from the metadiorites of the Chapada deposits. They are not related to the Goiás IOAS mineralizing system.