# Contrasting timescales of metal fluxes in porphyry copper systems from coupled physicochemical processes of magmas, rocks and fluids

## TL;DR

This paper explores how magmas release metals through different stages of degassing, influencing the formation of copper deposits.

## Contribution

A new numerical model was developed to simulate magma convection, degassing, and fluid flow with chemical partitioning effects.

## Key findings

- Magmas self-organize into distinct degassing stages with varying metal flux timescales.
- Initial tube-flow outbursts lead to shallow mineralization, while continuous fluid release affects deeper deposits.
- High water content and low distribution coefficients favor large porphyry deposit formation.

## Abstract

Volatile degassing from hydrous magma reservoirs controls the formation of porphyry copper deposits. Geochemical studies suggest that water-rich magmas may be more prone for ore formation, with fluid-melt partitioning potentially producing particularly metal-rich fluid stages. However, the coupled physicochemical processes at the magmatic-hydrothermal transition remain elusive, because they depend on non-linear properties of magmas, fluids and rocks. For this study, we further developed a numerical model for magma convection, volatile degassing, hydraulic fracturing and fluid flow by modifying its permeability response to brecciation and introducing chemical fluid-melt partitioning. We investigate the role of intrusion depth, water content and distribution coefficients on degassing and ore formation. The results show how magmas can self-organize into distinct degassing stages with contrasting timescales of metal fluxes. Depth and water content control the amount of fluids released by an initial short-lived tube-flow outburst event, leading to brecciation and a first mineralization event in shallow porphyry-epithermal levels for high distribution coefficients. Further cooling leads to continuous fluid release at lower rates, producing a second mineralization event at deeper levels. Our results suggest that near-saturated water contents of voluminous magma reservoirs in combination with low fluid-melt distribution coefficients support the formation of large porphyry deposits.