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I find it very surprising that metal ore deposits are so separate, and unevenly separated on the Earth.

I do understand that there were various different conditions at some point in time in the places where ore deposits emerged, and the places were somewhat randomly distributed.

But how is it that there so many different conditions happening that all have fundamentally different effects? I would expect many different conditions, that can be grouped in much fewer types regarding the practical effect of the condition.

Or is exactly that the case, and what is surprising is only the numbers involved?

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    $\begingroup$ This question is simple but the answer is complex. Part of the answer involves the geological conditions during the various geological eras. For example, some nickle deposits are associated with komatiite volcanism, which largely occurred during the Archean period, in the Earth's very early history. Since then the Earth has cooled & komatiite no longer erupts, largely replaced by basaltic volcanism. Similarly, the age of gold deposits also varies between locations because of geological conditions at the times of formation. $\endgroup$
    – Fred
    Feb 6, 2020 at 13:30
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    $\begingroup$ Another part of the reason involves Plate Tectonics. Over the billions of years of Earth's history the continents have split, combined & moved. They all have undergone changes in geological conditions, weathering, being above or below oceans & experienced volcanism in various locations as various times. $\endgroup$
    – Fred
    Feb 6, 2020 at 14:09
  • $\begingroup$ Then there are things like iron ores, particular the banded iron formations en.wikipedia.org/wiki/Banded_iron_formation which are the result of long-ago biological activity. There's really no one simple (or even complex) answer. $\endgroup$
    – jamesqf
    Feb 7, 2020 at 18:52

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There are active geological processes that lead to separation of mineral constituents. A source material that contains specific primary minerals, with some transport mechanism (eg convection or liquid flows) to physically separate them and 'trapping' conditions that allow them to accumulate are all required. Processes that result in minerals being separated from the source material include -

Magmatic - (within molten and partly molten magmas). Differential melting will allow specific minerals to melt and be squeezed out separately. Differential crystallisation will allow some minerals in a mixture to crystallise within a molten mass and (with changing temperature and/or pressure) to separate and reform as crystals and precipitate separately in more concentrated form in sediments at the base of a molten mass (or to rise where they are lower density than the surrounding material). Some materials can separate in their molten state, because they are immiscible (they don't mix or dissolve within each other), with similar separation because of differing density or pressure squeezing them out and solidify in concentrated forms.

Hydrothermal - minerals dissolving (usually in association with salts), with different temperature and pressures dissolving minerals preferentially. As liquid they can travel and come into contact with other minerals, resulting in chemical reactions, with potential for further differentiation. Similar to differential crystallisation in magmas, specific minerals will crystallise and precipitate differentially out of concentrated water based solutions. Lots of sulphide mineral ore bodies were formed this way.

Physical process like erosion and sedimentation also separate and concentrate existing minerals.

(Answer in part from Wikipedia - Ore genesis).

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When the Earth was formed and was still in a molten or semi-molten state, the heavy metals, principally iron and nickel, were attracted by gravity to the Earth's deep interior, leaving only traces of them on the surface. However, the bombardment by comets, asteroids and mega-meteorites continued after a crust was formed. These were of varied composition and dumped their cargoes of metals randomly across the globe.

In addition to this, volcanoes spewed metal-rich magma into the upper layers of the crust, again rather randomly, and hydro-thermal seepages brought up metals from the depths and deposited them in the rocks on or near the surface. Magma plumes originating far down in the mantle can carry various elements, including metals, up to the surface. It often happens that metals which are close to each other in the periodic table and have similar properties are deposited in the same place.

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    $\begingroup$ This doesn't answer the question. $\endgroup$
    – jamesqf
    Feb 5, 2020 at 18:34
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    $\begingroup$ Michael, with all due respect, your answers often remind me of a student who, not quite understanding the question, write a long story with related stuff they know in the hope that the answer will be somewhere in there (this is why on many exam key sheets, points are subtracted for irrelevant information). $\endgroup$
    – gerrit ♦
    Feb 5, 2020 at 19:29
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    $\begingroup$ Michael the user is asking about metal enrichments and his distribution. I think you confused it with planetary elements differentiation, but the poster is not asking about it, he is asking about geochemistry differentiation process. $\endgroup$
    – user18590
    Feb 6, 2020 at 12:28
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    $\begingroup$ You provide a little introduction about it on second paragraph, but as jamesqf said you don't answer what poster is asking. $\endgroup$
    – user18590
    Feb 6, 2020 at 12:39
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    $\begingroup$ No I think he is asking about distribution of enrichments. It is true all starts in magmatic process, for that I tell you provide an introduction on second paragraph, but if a student fall in this question he is wondering about geodynamics concepts, touching geochemistry. Enrichment process as hydrothermal etc.... $\endgroup$
    – user18590
    Feb 6, 2020 at 12:49

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