REE Geology - This is a long page, and is intended as an introductory level text in REE geology. It will be 'in process' for some time. Please let me know if it is useful to you. It's more enjoyable to write when you know someone is out there reading.
An Introduction to the Geology of the Rare Earth Elements and Associated Mineral Ores
by Robert Beauford
Uncommon Minerals and The Economics of Science
One of the first things noted whenever rare earth elements are mentioned (and possibly the most overused phrase spoken in regards this suite of elements) is: 'The rare earth elements are not particularly rare.' This statement is basically true, but fails to communicate several very important concepts necessary to understanding these resources, their geological contexts, and the supply and demand issues that drive their mining and distribution. Authors generally point out that some of the rare earth elements are more common, in terms of overall crustal abundance, than several more heavily mined metals, such as tin, silver, gold, molybdinum, and mercury, and this is true. The most common rare earths, cerium, yttrium, and neodymium, are present in the earths crust in quantities that are meaningfully comparable to lead, nickel, and copper. This fact, however, completely fails to communicate anything about their availability as a mineable metal resource.
(Chart overall abundances of REEs and commonly mined metals.)
Copper, lead, tin, gold, silver, zinc, mercury, and other heavily mined metals, are naturally concentrated in relatively high percentages in abundantly available mineral ores. The mechanisms that sort these metals into mineable mineral ores, are a combination of dissolution and concentration by hot, subsurface water, physical sorting, and partial melting and crystallization of magmas. None of these mechanisms are particularly effective, however, at concentrating the rare earths. These elements start out widely distributed in igneous rocks. The igneous rocks form mountains, erode and wash to the sea, are buried deep in the earth, are boiled in hot, acidic groundwater, and are again melted and returned to their original state, all without significantly concentrating the rare earths they contain. Extraordinary (and infrequent) circumstances are required in order to concentrate these metals in mineable quantities.
What this means, is that while the REE's themselves may not be rare, the minerals from which they are mined are quite uncommon. This fact, like the overall crustal abundances of these metals, again fails to explain their current relative scarcity or their recently (last 20 years) limited (China) supply regions. These ores are not so uncommon that substantially higher quantities cannot be effectively mined. The largest factors contributing to global scarcity of rare earth metals and to the constriction of global supply lines to a very limited number of sources are:
In other words, rare earth elements are scarce, not because there are not enough of them on the planet, but because we haven't been digging them up. We haven't been digging them up because:
Understanding the geology of REEs, requires an understanding of the economic and social context within which the geology is developing. Science takes time and costs money.
(chart annual mined quantites, in tons, of each of the REEs compared to each other and to the major metals.)
Rocks, Minerals, and Frequently Substituting Atoms
Rock - a naturally occuring aggregate of minerals or mineral like substances.
Mineral - a naturally occuring, inorganic, crystalline solid that has a specific chemical composition and specific chemical and physical properties.
Rock Forming Minerals - common mineral types that constitute the bulk of most rocks, and that are often components of the definition of a rock type.
Several groups of the rare earth elements substitute for each other, in their host minerals, almost without preference. As a result, the elements are never found alone in naturally occuring minerals, and are never found in elemental form, or in anything close to it. The metals are found in mixes, bound up in minerals of often complex or variable chemistry. Sharing a common oxidation state and, in several cases, a similar ionic radius, the rare earth elements are, even once seperated from their phosphate, silicate, or carbonate host minerals, so similar in chemcial behaviour, that they are difficult to seperate from each other.
To someone without a substantial background in geology, the preceeding paragraph probably made little or no sense, so I'll try to explain more clearly. In order to do so, I need to dispell two common, but useful, misconceptions.
The first of these misconceptions regards rocks, minerals and their compositions. When geology is taught at a beginning level, minerals are presented as having uniform compositions, and mineral specimens are presented as representing these specific compositions. Limestone, for instance, we are taught is composed of calcite, or calcium carbonate (CaCO3), and this is more-or-less technically true... on paper. No individual specimen, however, of the naturally occuring mineral (rock), limestone, will ever actually entirely conform to this composition. Even crystals of relatively pure naturally occuring calcite, no matter how pure, will contain molecules of other minerals.
For the complex and highly variably sedimentary rock type that we know as limestone, composition will vary wildly, both within an individual rock mass, and from region to region. Limestone, a rock that is composed of many minerals, is described as being composed of calcite, a mineral species that exists, in pure form, only in a laboratory setting, because it is convenient and useful to do so. In order to talk about rocks and minerals, we must be able to talk about them as specific, real things of definable composition. The reality, however, is that rock names define ranges of composition and refer to assemblages of various minerals in varying proportions. A 'limestone' may contain less than 50% calcite (CaCO3), and be made up of much smaller percentages of dozens of other other minerals as well. It would (and does) take an entire book to describe the variations in composition of even a common and relatively simple rock type such as limestone.
The first misconception we are correcting, then, is that 'rocks' (outside of introductory books) are composed of individual minerals or of specific, well defined proportions of a combination of minerals. 'Rock' is a technical term in the geosciences. The image or idea that accompanies this term should be replaced with the conception of rock names (limestone, shale, granite) as approximations that capture a wide, but defined, range of possible compositions.
The second misconception that needs to be overcome, in order to understand rare earth element geology, concerns the unique individuality of minerals. Minerals are presented in introductory texts and in the common language as unique, unrelated substances. In reality, minerals are just named points on a map of vastly interchangeable chemical prefixes and suffixes. In other words, what starts out as calcium carbonate, the calcite from our previous example, can just as easily be magnesium carbonate, and can almost as easily be iron carbonate or manganese carbonate. In any specimen of calcite, some percentage of one or more of these other elements will 'substitute' for some of the calcite, leading to what is called a 'solid solution series.' This is an oversimplified explanation, but should provide some background to understand rare earth element substitution, or at least a jumping off point to start the reader on researching and understanding the necessary underpinning geological concepts.
An understanding that rocks are variable in composition, and that mineral names only define specific combinations of easily rearranged components, gives us a decent basis for beginning to understand the concepts of substitution in REE bearing minerals and of the natural processes that lead to their concentration in rocks, but that fail to effectively seperate the REEs from each other.
Substitution occurs readily when two or more elements, with similarly sized atoms (expressed as ionic radii) and the same charge (valence, or oxidation state) can take each other place within a crystal structure without substantially altering the crystal structure. The rare earth elements are found together in the same ores because they can easily substitute for each other in this manner. A good exampel of this is the common REE ore mineral monazite, (Ce, La, Pr, Nd, Th, Y)PO4. In the mineral, monazite, a simple phosphate ion attaches, with little preference, to cerium, lanthanum, praseodimium, and so on. In only slightly oversimplified terms, the group of rare earth metals that may substitute in monazite are limited only by their atomic size and their availability within the melted rock from which the monazite crystallizes.
This sort of easy substitution is true for a variety of the rare earth elements in most of the minerals in which they occur. It was not until very recently in history that anyone succeeded, even in a laboratory, in seperating some of these elements from each other. Even now, with modern mining, extraction, and chemical processing technologies, finding ways to effectively make these elements behave differently enough from each other to seperate them out of ores for use, presents one of the larger challenges to mining and production.
In summary, substitution is a key principle in understanding REE geology and REE bearing minerals. The ready substitutability of these elements, for each other, accounts for the fact that rare earth elements are never found in concentrations of only one element, but rather occur grouped together in ores. It also accounts for the odd fact that, unlike copper, nickel, iron, and so on, we refer to these metals by one common name, 'rare earth elements,' rather than by their 15 to 17 seperate names.
One more point should be added here, as an aside. All of the rare earth elements are capable of having a +3 valency or 'charge,' so they can interact in a similar manner, chemically, with other elements to form minerals. Because the size of the individual atoms of the elements, however, is different, and because some of the REEs can have other valencies as well, not all rare earth elements substitute for each other equally. There are two major groups of commonly associated REEs. The first of these groups is dominated by Cerium, and consists of the first half of the lanthanides, from lanthanum to europium. The second group is dominated by yttrium, and is made up of the second half of the lanthanides, from gadolinium to lutetium.
(chart the commonly affiliating REEs)
How Ores Form - The Natural Sorting Process
Sorting of elements in and on the earth:
Rare earth ores are the product of concentration of these elements in unusually high percentages, and in accessible rock or in sediments such as sand or clay. The mechanisms of concentration divide the rare earth ores into two large groups. These are:
Primary Ore Deposits
Rare earth elements are concentrated, in primary ore deposits, by exclusion rather than by inclusion. This means that minerals don't 'want' the REEs. They don't fit nicely into any of the dominant silicates or other minerals that form as magma cools and crystallizes. As a result, they get shoved aside repeatedly, until the last and only remaining melted material will contain these elements. When this material cools, the REEs are trapped. This is a relatively inefficient way to sort and concentrate an element, since it relies on negative pressures instead of chemical trapping. As an analogy, picture trying to 'heard' a flock of birds or a bunch of cats. Its easier to scare them away from the place you started, than it is to concentrate them in the place you were trying to get them to end up.
To understand the igneous portion of primary ore deposit formation, we have to understand 3 underlying principles that relate to the behaviour of magma and to the specific minerals formed by magma. These are partial melting, fractional crystallization, and incompatability.
Partial Melting (illustrate)
'Partial melting' is a geological process in which only some of the minerals that make up a rock are melted, and then generally, squeezed out of the rock in which they were originally situated. Rocks are typically made up of several different minerals, all of which have different melting temperatures. As the temperature or pressure of a rock mass rises, it will pass through a range in which the temperature is higher than the melting point of some of the minerals, but lower than the merlting point of other minerals. During this partially melted interval, the melted portion of the rock can get squeezed out of the rock like water from a sponge. This produces two different types of rock where there was previously only one. Because the sorting is temperature dependent, the newly produced rock may be dramatically different in composition than the 'parent' rock in which it originated. Partial melting occurs at all levels of the earth's crust and upper mantle, and is a major sorting mechanism for minerals at both large and small scales.
Alkaline igneous rocks, high in sodium and calcium, and peralkaline rocks, with large amounts of aluminum compared to silica, as well as carbonatites, uncommon igneous rocks composed of more than 50% carbonate minerals, are all produced as lower temperature melts, removed during partial melting of a previously existing igneous rocks source. Each of these three rock types is an important ore category for the rare earth elements. The rocks left behind, after these particular rocks are melted and squeezed out, will be higher in iron, magnesium, and silica.
Fractional Crystallization (illustrate)
Fractional crystallization is an opposite, but related, process to partial melting. When a mass of melted rock (magma) begins to cool below the earth's surface, solid minerals will begin to form within the magma, as well as on the walls and floor of the magma chamber. This is very similar to ice forming within a cooling dish of water, only the rocks sink rather than float like ice. Liquid rock doesn't give up all of its heat at once. It cools slowly. As a result, the newly formed minerals, which take the form of small cystals (usually less than 1cm) will often have time to sink to the bottom of the magma chamber or accumulate on its walls.
The minerals that form in a cooling magma will reflect two things. First, they will reflect the temperature of the magma. The reason for this is simple. You can't crystallize a mineral out of a magma while the magma is still hot enough to melt the crystal. (Imagine waiting for ice crystals to form in water that is 80 degrees.) Second, the minerals will reflect the composition of the magma. Iron rich magma will tend to produce specific iron rich minerals. The contrasting statement is true as well. You cannot crystallize iron rich minerals out of a magma that contains little or no iron. To use the water example again: If you cool water, you will get ice crystals. If the water contains salt, you will get salt crystals and water crystals (ice). You will not get sugar crystals by cooling salt water, no matter how you cool it.
As a mineral crystallizes (precipitates) out of a magma, it uses up some of the elements that are dissolved in the magma. One of the first minerals to precipitate out of cooling magma, since it crystallizes at high temperature, is olivine, a very iron rich mineral. This means that a cooling magma, in which olivine crystals are forming and removing iron, will become less and less rich in iron, and richer, by comparison, in other minerals as it cools. The hot, liquid magma may continue to cool in the same area at this point, or it may migrate to a different place underground. Either way, it leaves the iron behind, as a solid rock, and continues on with a different composition.
As the magma cools, the type of mineral being formed changes, and this change follows a particular sequence, known as the Bowen's Reaction Series. Fractional crystallization is a very important process in the differentiation of different rocks form an original rock type, and in the concentration of specific elements within those rock types.
(insert a section here on anomalous rapid 'fractionation' of a melt by liquid imiscability of melts in re some suggested possible carbonatite origins.)
Incompatability - Why Elements Are Included or Excluded.
Slow heating (partial melting) or slow cooling (fractional crystallization), both result in the sorting of elements within the earth, and by extension, in the formation of metal rich ore bodies. Both of these processes result in certain bodies of rock containing significant quantities of particular elements, and in other bodies of rock being rather depleted in these elements. Selection and sorting in this manner follows specific, predictable rules, and results from the physical and chemical aspects of individual elements that allow them to combine more or less easily with other elements into specific minerals. These rules, at the level of large, visible chunks of rock and minerals, can be broadly understood, at least in a general sense, with a study of Bowen's Reaction Series (worth looking up) and the concepts of partial melting and fractional crystallization.
To understand the details of why certain, very similar, minerals contain wildly different proportions of various elements, however, we have to look at a few distinctions at the atomic scale. These distinctions will answer the questions of why the rare earth elements, in specific, get shoved aside into the rock groups in which we find them, and why they substitute for each other so readily, and thus are always found mixed. Understanding these atomic scale distinctions (which drive larger scale sorting processes) will also clarify why the light rare earth elements and heavy rare earth elements are found in two distinct groups, and in seperate, but related, types fo host minerals.
Continue from here:
Ionic radius, valency, and objects that simply fit into crystal lattices, or don't.
Partition coefficients are numbers assigned to elements in order to describe and compare their behaviour in terms of sorting. An element's partition coefficient is specific to the elements behaviour in terms of a particular mineral. The individual REEs do not have a single partition coeffient, like they have mass or radius, instead, the partition coefficient is a number that results from calculating the probability of a particular element winding up trapped int he crystal lattice of a particular mineral as it forms. A high partition coefficient means the element will be trapped. A low partition coefficient means that the element doesn't fit in the lattice, and that it will be excluded, or pushed aside during the formation of the mineral.
(I need to understand partition coefficients and high field strength elements... better and explain it better - is this essentially a statistical expression of probability of behaviour? can the partition coefficient vary with temperature and pressure for the same element to mineral combination? does a low partition coefficient element in a mineral correspond to greater likelyhood of release during partial melting, as well as to probabibility of exclusion during fractional crystallization?)
A Second major class of primary ores: hydrothermal.
aggressive subsurface environments and deep time (thinking like a geologist: water and hydrothermal fluids as a magma)
Sedimentary concentration is primarily due to weight.
How the REEs move as groups, and what it takes to move them:
global scale sorting of incompatible elements, depleting of the mantle as it crystalized, and enrichment fo the crust. continuation of sorting in ongoing process of sorting by exclusion in fractional cooling and selective inclusion in low temp partial melts.
chemical grouping and migration
LREE (Lanthanum to Europium) (More effectively avoid capture in mafic igneous rocks, so more abundant in continental rocks.
HREE (Gadolinium to Lutetium)
Odd vs. Even Numbered REE (Even numbers more abundant)
How all of the above gives us two ore types:
The Primary Ore Groups
Alkaline Igneous Ores: Carbonatites and Peralkalines
Carbonatites are igneous rocks composed of more than 50% carbonate minerals, generally calcite or dolomite. They typically occur as localized cross cutting dikes, veins, or sills within larger masses of intrusive alkaline igneous rocks, and are often found in the context of a breccia formed during the event in which they were emplaced. The carbonatites represent, very nearly, an end member of the igneous sorting process, with the high-temperature crystallizing ultramafic rocks at one of the other extremes. Carbonatites are some of the lowest (if not the absolute lowest, 500-600 C.) temperature melts that are part of the igneous rock series on this planet. The combination of geological processes that lead to their formation are not entirely understood, and may vary from case to case. They represent either a late (extreme last) product of sorting by fractional crystallization from unusual (possibly upper mantle type) source rocks, the regional accumulation of low temperature minerals during partial melting, or a combination of both of these processes. Ironically, when silicates (generally less than 10%) are present in carbonatites, they tend to be the pyroxene and olivine, both of which have a very high melting (dissolution) temperature, and both of which are very exclusive of the various incompatable elements typically enriched in carbonatites. (And I have no idea why. Feel free to explain it to me... is it the inavailability of Al?)
(pie chart of 8 most common crustal elements beside chart of most common minerals)
Peralkaline Igneous Rocks
Peralkaline igneous rocks are igneous rocks in which aluminum is depleted relative to sodium and potassium. (More sodium and potassium oxides, combined, than aluminum oxides.)
To explain peralkaline igneous rocks, I'm going to start by summarizing earths crustal geology in 1 paragraph. This is an oversimplified, but essentially true, picture of the outer several miles of the planet.
Oxygen and silicon are the most common elements in the earth's crust. Together, they make up about 75% of crustal rock mass. The next most common element in the crust is aluminum, at about 8.3%. Iron and magnesium, combined, make up about another 8 percent. Sodium, calcium, and potassium, together, make up about another 8%. These 8 minerals, alone, make up just under 99% of the entire crustal mass of the planet. Silicon and oxygen are the backbone of every major crustal mineral. Quartz, just silicon and oxygen, is the single most common mineral. The remainder of the silicon and oxygen combine into one of two groups. They either attach to the iron and magnesium, forming simply structured minerals that we call olivine and pyroxene, or they form feldspars. Feldspars are silcon, oxygen, and aluminum, attached to one the other 3 common elements, potassium, calcium and sodium. Combined, the 3 feldspar types are the only crustal rock more common than quarts. These 4 mineral types: quartz, feldspar, olivine, and pyroxene, make up, at a first approximation, the entire crust of the planet. (So long as we ignore the fact that 70% of these rocks are covered by a giant ocean of hot molten lava that we call water.)
Now, to summarize peralkaline igneous rocks based on the above... In order to make normal continental earth rocks, liquid magma likes to have plenty of silicon, oxygen, and aluminum when it is cooling and crystallizing. Magma never runs out of silicon or oxygen, though content varies substabtially. It can, however, form feldspars until it runs out of aluminum, and wind up with an excess of left over sodium and potassium. At this point, it makes unusual minerals (still mostly silicates) that contain dense concentrations of incompatable elements. These last formed rocks are called peralkaline igneous rocks. The circumstances leading to their formation are similar to those for carbonatites, with which they are closely related. These circumstances are, more or less, repeated or extreme fractional melting of odd melts, concentration of low temperature partial melts, or a combination of the two.
We think of water and ice as something different from other types of rocks, and they are in a few ways, but not in a general sense. Water can be viewed as a type of liquid lava, or melted rock, that covers the majority of the planet earth, and that flows through gaps and cavities in the subsurface. We think of water as different because it is so pervasive, and because we perceive it as cold, relative to other types of molten rock. In the subsurface, where water is subjected to high pressures that prevent it from boiling away, it is found at very high temperatures.
Hydrothermal fluids, meaning mineral rich solutions of very hot and usually acidic water blend, more or less seamlessly, into the sequence of magmatic melts. At the lowest temperature end of the solidifying sequence of lavas, long after the various common iron rich rock forming silicates have crystallized, like ice, from magma chambers at over 1000 degrees C., and even after the relatively low temperature peralkaline siliocates and carbonatites have crystallized as 500 to 600 degrees C., hydrothermal fluids remain an active transporter of dissolved sulfur, silica, metals and non-metallic ions. Unlike other types of rock that we conventionally think of as magma, however, water does not crystallize into a rock when it drops below 500 degrees C., or even at earth surface temperatures. Instead, it either drops its dissolved load of metals and polyatomic ions in a manner equatable to fractional crystallization of the higher temperature silicate magmas, or exchanges these elements with surrounding rocks in a process called metasomatism. We refer to direct crystallization of minerals from the hot water as the precipitation of hydrothermally transported and deposited minerals.
All of the foregoing explanation, though slightly oversimplified, is meant to serve as a foundation to understand the following: As rare earth elements are excluded from silicate melts during fractional crystallization, they become concentrated in late forming peralkaline associated igneous rocks, whether silicates, phophates, or carbonates. As the process of exclusion continues, the rare earth elements, still not fitting nicely into the crystal lattices of many of the forming minerals, get pushed further aside, and wind up in solution in the even lower temperature 'melts' that we refer to as hydrothermal fluids. These water based fluids can either exchange their dissolved elements with surrounding rocks (forming skarns), or precipitate hydrothermal deposits of minerals crystallized directly out of solution. The rocks formed by this type of exchange or crystallization constitute the third major source of primary rare earth element ores.
It should also be pointed out that hydrothermal processes are not limited to shallow regions. They can occur at great depths in crust, where they play an important role in mineral sorting processes (especially in subduction zones).
Hydrothermal fluids don't have to originate during the original cooling of an intrusive pluton. Hot subsurface water can saturate a region of igneous rocks at any point, and add to or deplete the rare earth content of the rocks, either in overall REE content, or in distribution of REE content. There are a few limitations, however. Concentration of REEs to minable levels, by hydrothermal processes, is only going to occur in rock that is already rich in REEs through magmatic or other processes. Hydrothermal processes cannot accumulate mineable concentrations by dissolution of background levels of REE from regions of average igneous or metamorphic rocks. Hydrothermal and igneous processes work together in regions where REE are present, but this also only goes in one direction: Igneous processes can concentrate REE to mineable levels without the help of water, but the corrolary is not true. Magmatic concentration must preceed the action of water.
Also, solubility of REE in water is low, so depletion and enrichment are only likely to take place in the nearby vicinity of a magmatically enriched pluton. Long distance transport of REE by hydrothermal fluids is improbable. A third factor to consider is that LREE are more likely to be transported by hydrothermal fluids than HREE, so L/H group distinctions within or between ore locations may be enhanced by hydrothermal processes.
breccias, pegmatites, regions of concentration and examples.
It should be born in mind that, although the magmatic (partial melting and fractional crystallization) sorting processes and the hydrothermal concentration processes can be discerned as two seperate processes that lead to REE enriched areas,
Skarns and hydrothermally enriched ree zones
...are these second stage hydrothermal processes?
Fault Associated Enrichment
Hydrothermal fluid processes have led to the formation of REE and other incompatible element rich ores in some fault regions where a substantially magmatically enriched parent formation has not yet been discovered. It is possible that this represents an exception to the necessity of a precursor REE rich pluton, or it may be that the associated pluton(s) are not yet known. Hydrothermally facilitated pressure induced partial melting or ion liberation during recrystallization may act as a corrolary to end stage sorting of a plutonic environment in low concentration rocks in the faulting region, but I am hsitant to explain what I do not understand fully. Feel free to explain this to me if you know the answer, or I will get around to clarifying it when I spend more time studying the Lemhi Pass district and related areas. If I understand the geology of the region correctly, REE may have been introduced from low grade precursors by predominantly pressure induced partial melting (rather than from an actual body of hot magma) and then hydrothermally transported upward within fractures and breccias associated with the faulting.
Physical and chemical erosion and sorting processes, regions of concentration and examples.
bgs placer dep
How and where ore / element enriched zones are distributed phyiscally as opposed to chemically:
Regional Zones of Formation
Illustrate plutons, faults, hydrothermal skarns and breccias, and secondary depositional zones with related weathering sources, all graphically.
Explain batholiths and plutons, what they are, how they behave, late fracturing and intrusion of ree bearing dikes / dike swarms, enrichment of skarns, breccia pipes, and so on. Also, weathering products and such.
LREE vs HREE Sorting and Source
Devote a short chapter to the distinction of LREE and HREE, along with the zig-zag, from stellar nucleosynthesis and related solar abundances to large scale sorting processes, diffferences in compatibility, differential solubility, and on to why the different ores show differing distributions. Illustrate with an idealized curve for various predominant ore groups.
When discussing mineable ore deposits, rare earth elements are treated in terms of a quantity of profitably recoverable oxides. Mined oxides contain a percentage of each of the REEs that is variable and unique to specific deposits. I'm going to look at oxide to metal conversion, distribution of end metals in various ores, and how they relate to mineral source and market value, as well as at the sorting processes that are responsible for putting the oxides where they are in the earth. This page will develop the topic of rare earth elements in (more or less) real numbers, and I'm going to start at the beginning. This means that I will begin with rare earth element abundances in the solar system, and develop the topic through the processes of zoning within the solar disk, then move on to geological and geochemical sorting, and finally to the actual current distributions of REE oxides in various places on the planet earth, as well as in meteorites and on other moons and planets in the solar system.
The only thing I'm promising in terms of quality of output, is that I'll try to do a decent job, that I will learn in the process, and that I will try to make it a worthwhile learning resource when I am done.
Solar System Abundances
No rare earth element currently found on earth, or in any other nearby moon or planet, originated within this solar system. In fact, like most of the other elements that we breath, eat, walk on, and are made of, the rare earth elements are older than the sun itself. They are literally the remains of earlier generation(s) of stars. All of the heavy elements, including the rare earths, are generated late in the life span of a star. We know, from isotopic studies, that at least two stars, both of which are now long extinct, contributed to the stuff from which our sun and solar system formed. Our current understanding of the formation of the sun and solar system describes a process of condensation and clumping of dust and gas within a solar nebula. The nebula was the result of stellar explosions and other discharges from previous stars.
Rare Earth Elements in Chondrites
Chondrite meteorites are the most primitive objects in the solar system, meaning that they are the most unaltered in the last 4.56 billion years of solar and planetary processing. This type of comparatively common meteorite represents material that clumped together when the solar system formed, and which has floated around in space ever since. These meteorites were never heated, weather, melted, smashed, or otherwise disrupted in the manner that other materials in the solar system have experienced dozens to millions of times over. As such, the chondrites represent a snapshot of the early solar system, both in terms of its mineralogy and in terms of its original compsition before large scale processes began to sort elements into groups. The kinds of sorting processes that I am referring to, here, are very large scale, and affected the distribution of all of the other materials in the solar system tremendously. These processes include things such as the differentiation of planets into an iron nickel core, with an over riding iron, magnesium and silicate mantle, and a crust of the lightest materials flaoting on top. Because chondrites predate these events, they are very valuable to geologists and geochemists as a starting point against which to compare other processes.
Crustal Rare Earth Element abundances from MNDMF, Ontario Geological Survey, Kenora District, Recommndations for Exploration, untitled document, graphic attributed as unpublished report, Sinton, 2005. Crustal abundance numbers unatributes.
within the chondrites, very primitive subset
(Mass of Metal/Element) × (Conversion Factor) = (Mass of Oxide)
(Mass of Oxide) x (Conversion Factor) = (Mass of Metal/Element)
Remember to account for purity of starting products.
Do something like the following, but incorporate several bastnaesite and several monazite, develop and average, then graph as a 3 line graph to show the difference in how the REEs are distributed in ore type.
(% of total REO) of each rare earth element (modified from Sinton 2005).
Mountain Pass, CaliforniaBastnaesite
Mt. Weld, Australia Monazite
LongNan Jiangxi, China Iron Absorption Clays
Now make a conversion worksheet for taking a REO to a Metal ppm and the to a normalized ppm that can be geologically related to other numbers.
Quantifying in meaningful terms - normalizing to compare apples to apples
Quantifying against different constants and types of constants
Results against new constants
Pulling out sorting processes among elements and minerals using these tools.
Analyzing in terms of minerals, in terms of isotopes.
What was the composition of a parent body, when did sorting take place, how much of an end result has to do with compostion of a parent body vs later sorting
Tools for analysis: analytic instruments, resulting data sets
Simple math to understand and compare change processes: (ex birds, birds in two locations, Birds in two locations in terms of variation from a starting point, birds in two locations in terms fo a starting point against a constant speed,)
REE Geology Links