The economic potential of metalliferous sub-volcanic brines

Abstract

The transition to a low-carbon economy will increase demand for a wide range of metals, notably copper, which is used extensively in power generation and in electric vehicles. Increased demand will require new, sustainable approaches to copper exploration and extraction. Conventional copper mining entails energy-intensive extraction of relatively low-grade ore from large open pits or underground mines and subsequent ore refining. Most copper derives ultimately from hot, hydrous magmatic fluids. Ore formation involves phase separation of these fluids to form copper-rich hypersaline liquids (or ‘brines') and subsequent precipitation of copper sulfides. Geophysical surveys of many volcanoes reveal electrically conductive bodies at around 2 km depth, consistent with lenses of brine hosted in porous rock. Building upon emerging concepts in crustal magmatism, we explore the potential of sub-volcanic brines as an in situ source of copper and other metals. Using hydrodynamic simulations, we show that 10 000 years of magma degassing can generate a Cu-rich brine lens containing up to 1.4 Mt Cu in a rock volume of a few km 3 at approximately 2 km depth. Direct extraction of metal-rich brines represents a novel development in metal resource extraction that obviates the need for conventional mines, and generates geothermal power as a by-product.

Estimation of Spatial Distribution and Fluid Fraction of a Potential Supercritical Geothermal Reservoir by Magnetotelluric Data: A Case Study From Yuzawa Geothermal Field, NE Japan

“…Based on our resistivity model, we propose a mechanism for the evolution of a supercritical geothermal reservoir (Figure 10). The dacitic and andesitic melt below the supercritical geothermal reservoir may supply magmatic fluids to the supercritical geothermal reservoir (Blundy et al., 2021; Heinrich, 2005; Sillitoe, 2010). Upwelling supercritical fluids supplied from the melt are found to become trapped under a less‐permeable silica sealing, and supercritical fluids accumulated below the silica sealing as a result (Figure 10).…”

“…We consider magmatic supercritical fluids as NaCl‐H 2 O fluids because magmatic fluids mainly consist of water and chloride salts (Blundy et al., 2021; Heinrich, 2005; Monecke et al., 2018; Richards, 2011; Sillitoe, 2010). The electrical resistivity of NaCl‐H 2 O fluids has been studied extensively in the relationship between subsurface resistivity models and geological structures (Bannard, 1975; Nono et al., 2020; Quist & Marshall, 1968; Sakuma & Ichiki, 2016; Sinmyo & Keppler, 2016).…”

Ore-Forming Fluid Evolution of Shallow Polyhalite Deposits in the Kunteyi Playa in the North Qaidam Basin

“…Apparently, the fluid inclusions in these salt crystals are characterized by different high temperatures. The majority of nonferrous metals derive ultimately from igneous processes associated with magmatism (Blundy et al, 2021). This conclusion suggested that geothermal fluids provided both a circumstance of high temperature and Ca-rich brine for polyhalite formation.…”

Numerical Modeling of Structurally Controlled Ore Formation in Magmatic‐Hydrothermal Systems

“…Numerical simulations with models that can handle high‐temperature multiphase flow of NaCl‐H 2 O fluids in porous media can help quantify the dynamic behavior of mass and heat transfer in magma‐related hydrothermal systems (Ingebritsen et al., 2010). Previous studies focused on the physical hydrology of porphyry and epithermal deposits (Blundy et al., 2021; Weis et al., 2012) and active hydrothermal systems (Andersen et al., 2015; Coumou et al., 2008; Gruen et al., 2014; Hasenclever et al., 2014; Kissling et al., 2015). In these models, permeability values are typically used as bulk parameters, and where high‐permeability fault zones have been considered, they are resolved by fine mesh sizes, which is computationally expensive.…”