Key features of giant ore deposits.
Key features of giant ore deposits.

New computer simulations by geologists from ETH Zurich demonstrate how large copper and gold deposits are formed. The enrichment process of these metals follows physical principles that are similar to the extraction of deep geothermal energy by hydraulic fracturing of the rock.

 Porphyry-type ore deposits rank among the world’s most important sources of copper, molybdenum and gold. They meet around three quarters of today’s global copper demand and are thus of extreme economic importance. Finding new ore deposits in the Earth’s crust depends on our understanding how nature forms such gigantic metal accumulations that can be exploited at reasonable economic and environmental expense.

Until now, geologists have primarily studied these deposits using field observations and geochemical analyses, but were unable to fully understand the physical processes of ore formation. Using a computer model that simulates these dynamic processes, Philipp Weis, Thomas Driesner and Christoph Heinrich at the Institute of Geochemistry and Petrology of ETH Zurich have now found a clear answer to this question. Their study has just been published in Science.

 Volcano and magma chamber needed

Volcano and magma chamber
The deposits form above the roof of a magma chamber that lies beneath an active volcano. As the magma crystallises into granitic rock in the subsurface, metal- and salt-rich aqueous solutions are expelled from the chamber. These fluids make their way up through the volcanic vent, which has already solidified into porphyritic rock. At a certain height, the metals precipitate from the ascending fluids. The ore deposit has a typical, well-defined shape that resembles the cap of a mushroom. Its “stem” is the volcanic vent, which has solidified into porphyry and then cracked to form numerous veins through which the fluid pushed its way upwards.

With their numerical simulations, the researchers can now demonstrate which physical processes have to work together for the metals to accumulate. “The beauty of this model is that the volcanic system spontaneously organises itself in such a way that the metals accumulate locally until they reach the ore content observed in nature and are not scattered over the entire crustal depth from the magma chamber to the surface. The latter would never produce a mineable ore deposit,” says the first author of the Science study Philipp Weis. Using their model developed at the ETH-Zurich over many years, the researchers can now explain all the key information collected from geological field studies and chemical measurements.

 All down to temperature and pressure

The most important factors that determine ore deposition are the temperature and pressure of the fluid. If they drop, the solubility of the metals decreases. Moreover, the two factors also influence how brittle the rock is, which in turn governs the formation of veins and its permeability. Strong excess fluid pressures are required for vein formation in the host rock above the magma chamber and for the mineral- and salt-containing solutions to be pushed upwards through the rock as if through a sieve. However, because the hot fluids heat up the rock, it becomes ductile, which means it deforms in a plastic manner and becomes harder to break. As a result, the sieve’s mesh closes up.

At the same time, colder groundwater circulating in the Earth’s crust cools the system from the outside. As a consequence, a cylindrical ascent zone dominated by magmatic fluids forms above the magma chamber. Along a sharp boundary layer, this zone merges into a cooler area where surface water circulates. There, the rock is brittle and thus breaks more easily than deeper down.

This transition is crucial: here, the pressure and temperature change abruptly and drop dramatically in the space of 200 metres. As a result, the mechanical sieve becomes a chemical sieve where the ascending fluid drops its entire cargo of metals.

It takes around 50,000 years for the magma chamber to expel its fluid. During this period, the precipitation zone hardly shifts, enabling a substantial amount of copper to accumulate about two kilometres beneath the Earth’s surface.

Interaction between rock and fluid

“This interaction between rock behaviour and fluid dynamics is crucial for our model because the permeability of the rock strongly influences fluid flow and thus determines whether there will be a chemical enrichment to substantial economic ore grades at a particular point,” Weis stresses.

However, the significance of the model goes beyond the formation of ore deposits. The water pressed into the subsurface to exploit geothermal energy is also governed by similar principles – albeit the other way round.

Understanding deep geothermics better

In the crystalline subsurface, water injected artificially into a deep borehole exerts high pressure on the surrounding rock and changes its permeability. After fracturing the rock, water can flow through and heat up before being collected at a second drillhole, to be transported back to the Earth’s surface. “This interplay between fluid and rock is comparable to the ore system, even if the different temperature and pressure conditions call for different material descriptions,” explains co-author Thomas Driesner. He and a new doctoral student have now turned their attention to using the numerical model to tap into deep geothermics. The model is particularly suitable for applications on geothermal energy because the feedbacks between mechanical and chemical changes in the rock and the flow of water are essential. In practice, the key to efficient extraction of deep geothermal energy is to create a rock permeability that is high enough but not too high. If the water is allowed to flow through the fractured rock too fast, it cannot heat up sufficiently. On the other hand, if cracks and pores in the rock are too small, the flow is weak and ineffective for energy extraction.

“There is still a lot of research needed until deep geothermal systems can be controlled”, Philipp Weis says. Because it is difficult and costly to capture these processes in the deep subsurface by direct observations, numerical models are indispensable tools to gain new scientific insights and to eventually assist energy producers.

Note: The above post is reprinted from materials provided by ETH .
Online publication. DOI: 10.1126/science.1225009

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Геннадий Тарасенко said... March 6, 2016 at 7:47 AM

Магма образуется за счет электричества в земной коре! Электричество плавит горную породу и трансмутирует различные минералы. Этот процесс называется ХОЛОДНЫЙ ЯДЕРНЫЙ СИНТЕЗ! Магмы под нами нет! Планета "сухая" без магмы!

Геннадий Тарасенко said... March 6, 2016 at 7:49 AM

Cold fusion is not possible in atmospheric conditions but it is possible underground. Synthesis formation is connected with electricity in the entrails of the earth. Electricity is produced with the help of friction and geospheres speed differential from the core (20-40 m/s to the surface), the speed of which according to GPS data is 2-16 cm per year. Faraday has determined planet electric capacity with 1 farad. Continent drift takes place at the expense of geospheres rotation, leading to subduction of ocean and continental plates, abduction, spreading, rifting and collision. An example of planet formation is ball concretions. Their formation in the layers-collectors is connected with ball and linear lightning, formed with the help of electric discharge (short circuit) that attract various rocks from layers’ fluids. In this connection concretions consist of several geospheres with different chemical composition from the core to the surface and the core is usually hollow or very soft. This can be connected with the fact that lightning plasma loses energy and fluid rotation stops. The Earth has the same structure where there is plasm in the core and gas dust cloud from the moment of the Earth origin. Its rotation produces dynamo effect of the planet Earth that creates gravitation and magnetic field of the Earth and has been existing for 4,5 billion years already. Such point of view of the model of the planet Earth explains many natural processes in the Earth’s crust. It consists of natural electric condenser and heater, the cavities of which are filled with fluid formed in the zones of subduction with the help of the Earth electricity and cold fusion, oil is made of organic and water of non-organic. Various coal deposits are formed of those plates’ fluid which originated from oil with the help of cold fusion and iron ores, absorbed from plates’ waters. So electricity is necessary to produce oil, it produces pressure and temperature in subduction zones and their migration produces radiator effect for cooling and lubricating geospheres rotation.

Геннадий Тарасенко said... March 6, 2016 at 7:49 AM

Spheres rotation leads to plates’ friction with each other and produces millstone effect that grind the rock into powder. Rocks are dissolved in plates waters and are taken for tens of kilometers on laterals and verticals, filling karsts and forming basal benches of nonsoluble rocks (millstone, conglomerate, bennet) forming layers of collector and secondary deposits. Concretions formations take place in them with the help of lightning underground. Volcanos formation is connected with the Earth electricity (electrical furnace) that melts rocks and forms magma. Electricity availability in volcanos evidence is lightning above volcanos that spin eruption products and ball bombs-concretions. There is no magma under the continents and the planet Earth is cold with the temperature of 600 degrees in the core. Earthquakes are also caused by electric discharge in karsts filled with methane at different depths. Karsts formation increases with depth at the expense of great speed of geosphere, determined on listric snap in lithosphere and mantle, the speed of which increases up to 20 meter per year and more to the core. Spheres are torn and form karsts. That is why seismic reflecting horizons are less expressed and interrupted with depth. The evidence of hydrocarbon formation with the help of cold fusion is based on carrying out experiments with arc discharger at cathode at battery water solution adding titanium powder. After some time after burning arc discharger there was strong smell of acetylene. On the basis of this data, the planet Earth is a constantly functioning mechanism from the moment of “Big Bang”. “Big Bang” was formed with the help of electric discharge but not particles (substance) collision. Big hadronic collider is the model of the plant Earth appearance which is not proved by the experiments. For this I have created concretion model of the planet Earth which was formed with the help of electric discharge-explosion on the example of ball concretions formation. Tests on modelling the planet have led me to the design of electric generator, where ball and linear lightings is the rotor. Their rotation in the reactor will provide the stator with the electricity. Generator of the new type will save the planet Earth from destruction because fluids (oil, water) are the blood of the planet and their exhaustion leads to climate global change. Fluids serve the planet to cool and lubricate geospheres rotation. Lithosphere devastation is earth radiator and planet electric condenser destruction that serve for the planet vital activity. Sharp decrease of magnetic and gravitation filed of the Earth is the evidence of concretion model of the planet Earth and its actual model.