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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.
The undersea volcano, El Hierro, in the Canary Islands has been in an eruptive phase since October 2011. The volcano is thought to vent approximately 70 meters below the surface. Surface events vary from jacuzzi-like roiling of turbid water to vigorous upwelling rising many meters above the ocean surface.
The blog Eruptions over on Wired is keeping close tabs on this event as it unwinds.
It is worth pointing out that a volcanic occurrence like this, in addition to land-form building, can also be viewed as a geochemical event. Subsurface eruption of magma comprises the extrusion of fluid rock as well as the injection of gases and solubles into seawater. In the process, water is flashed to steam which adds momentum to the upward convection of the water column from the eruption zone. This causes mixing to occur, tempering the water temperature and dispersing dissolved materials into the currents.
Th’ Gaussling drove to the southern border of Colorado to have an up close and personal view of an exposure of the K-T boundary. The coordinates are N 37º 7.335′, W 104° 36.248′. This exposure is perhaps 150 meters in length and is no more than a quarter mile hike from the parking area. The exposure is within Trinidad Lake State Park, so a $7 one day park pass is required for entry.
The term “K-T boundary” refers to both a layer of sediment and to a stepchange transition in paleoecology. The sediment layer was laid down at a time coincident with an extensive plant and animal extinction event. This period and the sediments put down then make up the boundary between the Cretaceous and Tertiary periods. Nomenclature alert: According to some sources, the use of Tertiary time or rock is discouraged in favor of Paleogene and Neogene. Under this terminology, it is referred to as the K-Pg boundary.
It is widely accepted that a large impactor collided with the earth forming the Chicxulub Crater approximately 65.5 MA. The Chicxulub (CHEEK sheh loob) crater was first observed from gravity mapping by Robert Baltosser in the 1960’s and later rediscovered by geophysicists Camargo and Penfield while doing geomagnetic work for Pemex in 1978. Pemex would not allow the disclosure of the data supporting the presence of the crater for several years. Eventually, Penfield was allowed to disclose their work at a conference.
The Chicxulub crater is found below the surface along the northern coast of the Yucatan Penninsula in Mexico. Gravity maps show evidence of a circular feature consistent with an impact crater. Sediment associated with the impact contains tektites, shocked quartz, vitrification and elevated levels of iridium. A common mistake propagated in the popular literature is that the layer consists of iridium. In fact the layer contains variously ppt or ppb levels of this platinum group element.
The theory of asteroid impact arose from the anomolous Ir content of the thin sediment layer found to have been deposited at the time of the K-T extinction. Geologist Walter Alvarez, son of non-other than Manhattan Project physicist Louis Alvarez, determined that significant iridium was found only in the K-T boundary layer and not in the layers above and below. The determination was had via neutron activation analysis and was carried out at Lawrence Berkeley Laboratories. After a variety of postulates were considered, the theory of asteroid impact ending the age of dinosaurs was born. The theory was disclosed in 1980, but was met mostly with derision. However, with the disclosure of the Chicxulub crater in the late 1980’s, the theory has since met with widespread acceptance.
Across the earth in what is now India and roughly contemporaneous (68 to 60 MA) with the Chicxulub event was a prolonged period of extensive vulcanism. The formation from that period that remains today is the Deccan Traps. According to one source, the word “trap” is a geological term from the Swedish word for “stairs”. This period of vulcanism is thought to have produced enough atmospheric pollutants to have raised the average atmospheric temperature by 2º C and enough lava to have covered half of present day India.
Whether or not the fullness of the transition from Cretaceous to Paleogene is due to the Chicxulub event or in combination with the Deccan vulcanism is unclear. What is clear is that the Chicxulub impactor delivered an estimated 4.0 E17 MJ jolt of energy to the planet, resulting in mega-tsunamis throughout what is now the Caribbean basin and the injection of vast amounts of dust and aerosols into the atmosphere.
An exposure of the K-T boundary can be found in an outcrop just west of Trinidad Lake in southern Colorado. The thin, off white layer lies within a seam of coal and under a cap of sandstone at this location. Note the rock hammer for scale.
The K-T layer at the Trinidad site is comprised of claystone which is weathered and crumbles easily. If the material contains parts per trillion quantities of iridium, then sending a sample out for GDMS is likely to be futile.
North of Trinidad are the Spanish Peaks. These peaks are of volcanic origin and are associated with a substantial array of dikes, a geat many of them visible from the road. The photo below was snapped from a roadcut during a recent rainstorm. To the west is the Sangre de Cristo Mountain range. This range is what is called a horst, which is an uplifted block of crust. Just west of this range is the San Luis Valley containing the Rio Grande rift formation.
Recently on an airplane I sat next to a 1948 chemistry graduate of UC Berkeley. We were enroute to John Wayne airport from Denver. As we both marveled at the majestic topography of the Grand Canyon below she told me of her experience of having both Luis Alvarez and Glenn Seaborg as professors. Alvarez, she said, gave an exam with 7 % as the high score. She shook her head, laughed, and asked, “can you imagine”?
Mount Etna in Italy has been in an eruptive phase since July 30 of this year. A good video clip taken from near the site of the eruption can be found at this link. Sadly, I was unable to plant the video clip into this post, \;-(. An excellent blog to keep up to date on global volcanism is Eruptions.
I have to wonder how much combustion of reduced magmatic components is occuring as the magma enters contact with the atmosphere. Certainly the sulfide components must combust at the surface.
Carbonates are prone to thermal decomposition as well, though from disproportionation to metal oxides and CO2. At some depth from the surface, the formation of CO2 must begin to produce at least some amount of PV work on the magma column.
It was suggested (tongue in cheek) that the volcano be renamed Mount Doom from the Lord of the Rings.
The Grimsvötn eruption in Iceland began its eruption on May 21, 2011 with the injection of considerable ash into the navigable airspace to the east. Excellent photographs can be found at the Icelandic Met Office. Grimsvötn is a very prolific basaltic volcano located on the southeast part of Iceland. Grimsvötn is the most frequently erupting volcano in Iceland, with the most recent eruption in 2004.
According to one source in Iceland, the eruptions have presently subsided to steam venting, though no one is prepared to say that the eruption is over. The safe distance for viewing is said to be 2 km.