Failed eruptions lead to large copper deposits

the copperDue to its thermal and conductive properties, is one of the most used metals today, and therefore the most exploited. Its value should continue to increase in the future because it represents a key element in the energetic transition In progress. Indeed, all the electronic and electrical systems present in so-called “low carbon » require, for their manufacture, large quantities of copper, the resources of which are diminishingeye.

The transport sector is particularly copper-intensive, raising fears of a shortage by 2050, if no secondary production from the recycling is not implemented on a large scale. It is therefore becoming urgent to rethink the economy of copper but also to find new deposits.

The (very hot) genesis of copper deposits

Usually, copper is found naturally in deposits minerals called ” copper porphyries “. These deposits are formed by the circulation, within the Earth’s crusthot fluids produced during the cooling of the puddles. Copper precipitates from these fluids and is deposited in the form of porphyries between 1 and 6 km depth, near the magmatic reservoirs. This process, however, is not instantaneous. It takes tens of hundreds of thousands of years for these deposits to form!

Recent studies have made it possible to better define the mechanisms of the genesis of copper-bearing porphyries, but also the tectonic and magmatic environment in which they are set up. It appears that these deposits are generally associated with the production of calc-alkaline magmas, characteristic of volcanic arches developing in the continental crust in certain areas of subduction.

In this context, it appears that the importance of the deposit of copper-bearing porphyry will mainly depend on the quantity of fluid exsolved by the magma which will, itself, depend on the volume of magma cooling. However, the accumulation of large amounts of magma in the crust does not guarantee the formation of minerals of copper. Other parameters come into play.

Aborted eruptions allow the genesis of large copper deposits

In a new study, researchers set out to characterize more precisely the conditions allowing the formation of large copper deposits. Their results, published in Nature Communications Earth and Environment show that the formation of copper-bearing porphyries is indeed very dependent on the volume of magma, but also on its speed transfer to the upper crust and the magma reservoir. The formation of large deposits thus requires the injection of large volumes of magma with a fairly rapid ascent rate, at a debit greater than 0.001 km³/year.

This type of magmatic behavior is characteristic of large eruptions that are usually observed in rift environmentof hotspot or subduction. However, to guarantee the formation of large deposits, this magmatic system must not reach the stage of eruption. Indeed, when an eruption occurs, the fluids from the magma and from which the copper-bearing porphyries can form, will be rejected in theatmosphere instead of remaining within the continental crust.

The authors therefore conclude that the most abundant copper deposits form when these large eruptions fail. Large volumes of magma and fluids thus remain stored within the upper crust, allowing the genesis of copper-bearing porphyry. These new data will make it possible to better target prospecting sites to discover the new and vast copper deposits that will be necessary for our industry in the near future.

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