Copper-mineralised porphyries sample the evolution of a large-volume silicic magma reservoir from rapid assembly to solidification

Volatile-rich intermediate to silicic magmatic systems can feed devastating volcanic eruptions but also generate valuable magmatic-hydrothermal ore deposits that supply most of the world's copper. Understanding geometry, dynamics and timescales these is critical in developing models for predicting occurrence future large eruptions. Here, we use zircon petrochronology from an equigranular monzonite successively emplaced porphyry dykes reconstruct time – temperature composition evolution magma sourced giant Cu-Mo-Au deposit at Bingham Canyon (USA). Combining high-precision CA-ID-TIMS geochronology with in-situ trace element analyses by LA-ICP-MS shows intra-grain, inter-sample temporal geochemical changes recording system over 817 ± 62 kyr. Systematic variation chemistry indicates crystallisation a coherent reservoir. After reservoir assembly its thermal chemical state was controlled protracted monotonous ∼650 kyr rapid cooling first 200 followed longer period approaching granite solidus. Porphyry Cu-Au formation occurred after early drop resulted large-scale fluid saturation expulsion into sub-volcanic environment main Mo-mineralisation low-temperature storage emplacement last porphyry. Zircons do not quantify depth this integrating independent geophysical evidence 2-D modelling recorded zircons consistent incremental pluton (magma rate ≳ 0.0065 km3/yr) initially zircon-undersaturated monzonitic pre-heated upper crust. Our results indicate massive rapidly-formed, reservoirs containing mobile mushy (>40 wt.% melt) occur crust, favouring copper deposits.