As one begins to understand the manner in which mineralization and elemental concentration occurs as a result of terrestrial geology, it is only natural to wonder how this would occur on other worlds. On earth, the concentration of the elements in the form of mineral deposits is a partitioning phenomenon that benefits greatly from fractional crystallization, metamorphic modifications, and from a variety of transport mechanisms.

Fractional crystallization of magmas provides a condition whereby a mixture of simple and complex ions may associate to form mineral compositions that partition from the molten phase by virtue of high solidification temperature. In this way, solid, higher melting compositions precipitate from a melt sequentially, leading to the selective partition of certain combinations of elements into a new solid phase. The molten phase may be enriched in certain combinations of other elements by default- many of which may be relatively volatile.

The composition and cooling rate of the magma will determine the nature of the solid rock that is formed after cooling.  Over time, rock may be lifted toward the surface and subjected to modification by hydrothermal action or by erosion and redeposition by gravity. Cooled igneous rock may be subjected to crystalline modification by exposure to heat further down the timeline.

Hydrothermal water, superheated under high pressure, is a major force in the formation of mineral deposits. The sulfides (and hydrosulfides) of transition metals (i.e., Au) are thought to be transported from source rock through cracks, faults, and porous formations to be deposited in locations where transport can no longer be sustained. The accumulation of economic quantities of uranium are thought to be the result of hydrothermal or aqueous transport as well.

So here is the point of this essay–  If preconcentration of elements to viable deposits is critical for the success of value extraction on earth, what about mining on the moon or Mars? To what extent are we dependent on these mechanisms to make viable the mining and extraction of useful materials?  If lunar geology has not been quietly concentrating minerals in the manner to which we earthlings have been accustomed, how will we come to grips with using native materials on the moon for self-sustaining habitation?

It is one thing to find x ppm of oxygen or y ppm of titanium in the lunar regolith. It is quite another to enable extraction of critical elements from low-value (dilute) material. The chemical energy inputs for processing will be severely limited owing to the scarcity of reducing materials on the moon or Mars. Reducing materials are really just reservoirs of inexpensive and useful electrons. Reducing materials would include carbon or electropositive metals for the reductive winning of other metals. 

In the absence of an inexpensive supply of electrons, all phases of extraterrestrial mining and processing will be subject to large cost multipliers. Cheap electrons are required to energize machinery, move materials, or conduct refining. All of these familiar activities are energy intensive on earth and there is no reason to think it will be different on another world. On earth, cheap electrons come in the form of diesel and coal. On the moon and Mars, it seems likely that solar and nuclear will energize most work for those who try to set up camp there.