QUESTION: What causes ore (say copper) to be formed and in isolated areas? And can we find more ore deposits if we dig deep enough?
ANSWER: Dear Keith
There are not just one type of copper ore deposit. I can name Porphyry copper, Stratiform copper, and IOCG deposits, to name but a few.
The copper is a metal that when the conditions are oxidizing, it has lesser tendency to form minerals of its own. Instead it becomes concentrated in the melt or hydrothermal fluids. As a result copper is concentrated in magmatic melts over the process of fractional differentiation. Porphyry copper ores are formed in such conditions. In contrast when the magmatic melt is not oxidizing (it is reducing), copper sulfide minerals like chalcopyrite tend to form ealy in the melt and hence copper is removed from the melt without forming liable concentrations.
In Stratiform copper deposits, oxidizing formational waters leach the copper from the stata (especially red beds) and the metal is mobilized in fluids. When these oxidizing fluids come across reducing conditions, for example when there are organic matter in suitable sites for deposition, the copper is reduced by organic matter and copper sulfide minerals are formed.
Porphyry copper deposits and other kind of deposits are formed in certain levels in the crust. You have to know exact depth in which they are formed. You donít have to dig dipper nor shallower than required.
I hope my answer have helped you.
please feel free to ask more questions if needed.
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QUESTION: Many thanks Meisam for such a detailed response.
So is it the case that all ores are produced from the hydrothermal fluids and that different ores result from the process of fractional differentiation?
Moreover that the atomic properties of an ore determine whether there is a lot of it on this planet or very little.
Different names assigned to different fluids sometimes is arbitrary and the distinction between them is not always so straight forward.
Hydrothermal fluids are formed at the end of fractional crystalization processes of magma. During the crystalization of a magma body anhydrous (without water) minerals are crystalized at the early stages of cooling. As a consequence, magma which has meager amounts of water and other volatiles is enriched in volatiles. As a result of retention of water in the melt. Hence at the final states of magmatic differentiation, these volatiles effervesce from the magma and hydrothermal fluid (magmatic hot fluids) are formed. If the conditions are favorable, mineral deposits can form from this kind of fluid.
But not all fluids are hydrothermal in origin. For example, sea water can be an agent of mineralization. Salty water of the sea can dissolve some metals. MVT deposits are categorized as such. These deposits are formed when formational waters (salty brines derived originally from seawater) dissolve lead, and copper in oxidizing conditions and deposit them when reducing conditions are encountered.
Overall, the atomic abundance of elements on earth determines how big an ore deposit of that element would be. For example there arenít many big deposits of gold, because gold in one of the elements of lowest abundance in the universe. And that is because heavy elements are formed in nuclear reactions inside the stars and such nuclear reactions do not occur in all kinds of stars. In contrast, copper, iron, and lead deposits are much more common and form deposits are a much grander scale.
I hope this would help to clarify the matter.