Magmatic evolution of the Cerro Maricunga gold porphyry-epithermal system, Maricunga belt, N-Chile

Autor: Stephanie Lohmeier, Bernd Lehmann, Albrecht Schneider, B. Belyatsky
Rok vydání: 2019
Předmět:
Zdroj: Journal of South American Earth Sciences. 92:374-399
ISSN: 0895-9811
DOI: 10.1016/j.jsames.2019.03.003
Popis: The Cerro Maricunga gold project is located in the Maricunga gold belt in northern Chile, within the remnant edifice of the Tertiary Ojo de Maricunga volcano. The gold mineralization is hosted within a 23‒15 Ma old complex system of interwoven porphyry intrusions, flows, dikes and diverse breccia types, all forming part of a large diatreme system. In particular, phreatomagmatic and phreatic processes contributed to the formation of the synmineral diatreme complex. The rocks are calc-alkaline (daci)andesites and very rare dacites of the medium-K series with a high-K tendency and a conspicuous “adakitic” signature. Rare-earth element patterns reflect formation during a period of distinctly thickened continental crust with retention of heavy rare-earth elements by a garnet-bearing residue at a depth of ≥45 km. U-Pb zircon ages show a wide spectrum from Proterozoic, over Permian and Triassic ages to Paleocene, Oligocene, early and mid-Miocene ages. The Phanerozoic zircon ages indicate the assimilation of country rocks, whereas the Proterozoic age reflects the presence of a lower crustal Neoproterozoic basement that is also suggested by eNd values of −3.9 to −3.1 for bulk rock, i.e. mantle depletion model ages around 1 Ga. The last magmatic activity at the Ojo de Maricunga volcano was at ∼14.9 Ma. Stable isotope data on hydrothermal barite and supergene acanthite and gypsum (δ34Sacanthite: −0.6 to −0.4; δ34Ssulfate: 0.2 to 4.6; δ18Osulfate: 9.2 to 13.8) indicate an igneous origin of sulfur and arid conditions during mineral formation. The emplacement of the diatreme complex took place during the adjustment of the Chilean flat slab setting in a time of increased crustal thickness. Although the rocks at Ojo de Maricunga show a pronounced adakite-like signature, they formed in a common MASH zone or a deep hot zone within the lower crust. Gold mineralization took place at ∼17.9 Ma (Re-Os on molybdenite), syngenetic with diatreme formation and emplacement of hydrous magma. The thickening of continental crust was more advanced in the northern part of the Maricunga belt in the early to mid-Miocene than previously assumed, and then shifted south where several younger gold porphyries formed.
Databáze: OpenAIRE
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