There is a rare earth exploration boom in progress at the present time. This boom is in response to the policy shift of the Chinese government toward greatly reduced export of crude rare earth feedstocks. This political phenomenon is the result of the grand geological lottery that has deposited mineral wealth around the world.
Billions of years ago the geological processes in play were causing the partitioning of the elements into minerals that afforded local concentrations of groups of elements. Over geological time magma rose and cooled, sequentially crystallizing out minerals that by virtue of the principles of chemistry, laid down zones of enrichment. Recrystallization, extraction, ion metathesis, hydrolysis, melting point depression, attrition, processing of melts, degassing- all processes recognizable to the chemist. These processes are responsible for the formation of mineral species as well as their transport and alteration.
But the earth is never finished processing its mineral horde. Land masses are subject to upheaval and erosion, geochemical synthesis and decomposition. Any given formation at any given time is an overprinting of frozen events separated in time.
Large zones of continent may be subject to forces that cause it to break in networks of fractures. The forces may be in the nature of shear where fracture faces slide past one another. Other forces may lead to an upthrust of rock on the continental scale leading to mountain building. The shear and bending applies forces that exceed the tensile strength of the rock, leading to fracturing. Over time these fractures may serve as channels for hydrothermal flows.
Hot, pressurized water over long periods will dissolve susceptible minerals in the rock faces and transport solutes and suspended solids throughout the fracture network. Established mineral species yield to the solvent effects of water and slough off part or all of their constituents. In doing so, the minerals are taken apart into anions and cations that will eventually reassemble elsewhere into different mineral species. Over time these fracture networks will fill with solids and self-seal. They are called veins.
Water is not innocent in its behavior. Water’s ever eager oxygen atom binds to oxophilic metals and metalloids, taking them down to the energy bargain basement of oxide or oxyanion formation. Water with dissolved acids can digest whole formations leading to cavernous voids in susceptible rock.
Over time, geological processes have left formations of elements in bodies of economically viable concentrations called ore bodies. In the case of rare earth ore bodies, these elements are found concentrated in veins and breccias, pegmatites, or dispersed at more dilute levels in many other kinds of minerals. It is a truism that the lanthanide set of the rare earths are all commonly found in the same formation, but emphasizing the lights (LREE) or heavies (HREE). Scandium and yttrium are the Group III elements grouped with the 15 lanthanides to form the rare earths. While yttrium is often found with the lanthanides, scandium is often scarce in deposits otherwise rich in the other rare earths (REE’s). It is not uncommon for REE deposits to contain significant levels of zirconium, hafnium, tantalum, niobium, thorium, and uranium.
China does not seek to deprive the world of products using REE’s. It has taken the position that the REE exports will be in the form of finished consumer products. The policy of China is that it will manage the output of rare earth-based products in a highly value added good as a means to extract the most value from it. China’s market has a central nervous system that has devised manufacturing policy. It is much like an octopus. In the US, the prevailing wisdom is that the market should seek it’s own equilibrium without government interference. Our system is a distributed in the manner of a coral reef.
Today, mining exploration firms principally from Canada, Australia, and South Africa are exploring Africa, Australia, and the Americas for deposits of REE’s- and finding them. In my survey of the field, it would seem that the US is poorly represented in the roster of rare earth exploration firms.
Lamentations on Chemistry 