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Rare Earth Crystal Chemistry and Be-Si Disorder in Gadolinite from the White Cloud Pegmatite,
South Platte District, Colorado, USA.
By
RHIANA ELIZABETH HENRY
B. A. University of Colorado at Boulder, 2013
A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial
fulfillment of requirements for the degree of Master of Science Department of Geological
Sciences 2018
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This thesis entitled:
Rare Earth Crystal Chemistry and Be-Si Disorder in Gadolinite from the White Cloud Pegmatite, South Platte District, Colorado, USA. written by Rhiana Elizabeth Henry has been approved for the Department of Geological Sciences
Joseph Smyth
Markus Raschke
Date
The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline. iii
Henry, Rhiana Elizabeth (M. S., Geology, Department of Geological Sciences)
Rare Earth Crystal Chemistry and Be-Si Disorder of Gadolinite from the White Cloud Pegmatite,
South Platte Pegmatite District, Colorado, USA.
Thesis directed by Professor Joseph Smyth
Gadolinite is a monoclinic orthosilicate mineral that is part of the Gadolinite Supergroup of minerals. It occurs in beryllium and rare earth element (REE) bearing granites, pegmatites, and some metamorphic rocks (Baćík et al., 2014). The White Cloud Pegmatite is a small but rare earth element rich NYF (niobium-yttrium-fluorine) pegmatite located in the South Platte
Pegmatite district of Colorado, USA. It is associated with the 1.08Gy (Smith et al., 1999) granitic
Pikes Peak Batholith. The gadolinite in the White Cloud Pegmatite ranges from strong HREE
(heavy rare earth element) to LREE (light rare earth element) dominant species. The gadolinite occurs in close association with other REE minerals such as thalénite, fergusonite, allanite, yttrian fluorite, bastnäsite, synchysite. We explored the crystal chemistry and structure of two petrographically distinct samples by electron microprobe chemical analysis (EMPA), single crystal X-ray diffraction (XRD), and Raman spectroscopy. One sample (Z2A) shows nearly full occupancy of Fe, and partial substitution of Si for Be in the Q tetrahedral site with slight substitution of Be into the T-site. The second sample (SWC) has up to 15% vacancy in the Fe site and up to 15% disorder between Be and Si tetrahedral sites. The Be-Se partial disorder indicates that Be may substitute for Si in natural systems and be more abundant than previously thought. The different REE distributions indicate that gadolinite can accept a broad range of rare earth element cations.
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ACKNOWLEDGEMENTS
This research has been supported by the National Science Foundation grant NSF-EAR
14-16979, the Bolyard Scholarship from the Rocky Mountain Association of Geologists, and a donation from the Mile High Rock and Mineral Society.
My heartfelt thanks go to my adviser and mentor, Professor Joseph Smyth, for his support through my undergraduate and graduate careers. His academic brilliance and outstanding compassion make him a treasure among all scientists. More thanks go to Professors Lang Farmer who inspired me to keep studying geochemistry and Professor Craig Jones for his unique grumpy geophysics instruction and inspiring my interest in tectonic history. I would also like to thank
Professor Markus Raschke and Philip Persson for discovering field relations at the White Cloud pegmatite and initializing this project. Extra thanks go to Jason Van Fosson for preparing the thin sections and doing the preliminary investigations. Julien Allaz has my thanks for his thorough feedback and patience, guiding me on the microprobe, and being a beacon of logic to look up to.
My gratitude also extends to Kristine Johnson for her guidance throughout graduate school, and to Derek Weller for his advice and support. Ann-Marie Odasz has my thanks for always believing in me, and encouraging me to look for the beauty in everything.
Many extra thanks go to Bryan Barnhart for being at my side with many mugs of tea and plates of cheese as I wrote this thesis.
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CONTENTS
CHAPTER 1: INTRODUCTION…………………………………………………………………1
THE GADOLINITE SUPERGROUP OF MINERALS.………………………………….1
HISTORY AND OCCURRENCES OF GADOLINITE………………………………….6
CHEMISTRY AND OCCUPANCY OF STRUCTURAL SITES FOR GADOLINITE…………………………………………………………………….7
RARE EARTH ELEMENTS.……………………………………………………10
REE PEGMATITES.…………………………………………………….12
THE WHITE CLOUD PEGMATITE.…………………………………..14
GADOLINITE OF THE WHITE CLOUD PEGMATITE...…………………………….16
CHAPTER 2: SAMPLES AND METHODS….………………………………………………...17
SAMPLES AND DESCRIPTION.……………………………………………………...17
WHOLE ROCK ANALYSIS...………………………………………………………….21
X-RAY DIFFRACTION………………………………………………………………...21
ELECTRON MICROPROBE ANALYSIS.…………………………………………….22
RAMAN SPECTROSCOPY……………………………………………………………23
CHAPTER 3: RESULTS.……………………………………………………………………….24
WHOLE ROCK ANALYSIS…………………………………………………………...24
X-RAY DIFFRACTION.……………………………………………………………….26 vi
ELECTRON MICROPROBE ANALYSIS…………………………………………….31
RAMAN SPECTROSCOPY...…………………………………………………………37
CHAPTER 4: DISCUSSION…………………………………………………………………...38
CHEMICAL CONSTITUENTS.……………………………………………………….38
RARE EARTH ELEMENT DISTRIBUTION…………………………………………38
OCCUPANCY OF A AND M CATION SITES.……….………………………………44
PRESENCE OF HYDROXYL AT THE ϕ-SITE.……………………………………....47
BE-SI DISORDER...…….………………………………………………………………49
TETRAHEDRAL RINGS AND STRUCTURAL VARIABILITY…....……………….50
LACK OF METAMICTIZATION………………………………………………………54
BEST CHEMICAL FORMULA………………………………………………………...55
COMPARISON TO ALLANITE AND THALÉNITE………………………………….60
PHASES OF CRYSTALLIZATION……………………………………………………61
CHAPTER 5: CONCLUSIONS…………………………………………………………………63
THE SEARCH FOR BE…………………………………………………………………63
REE AND VARIABLE CHEMICAL AND STRUCTURAL PARAMETERS………...63
REFERENCES.………………………………………………………………………………….65
APPENDIX………………………………………………………………………………………70 vii
LIST OF TABLES
1. Gadolinite supergroup mineral classification diagram……………………………………2
2. a. Summarized whole rock elemental data for the White Cloud Pegmatite………...... 25 b. Summarized whole rock elemental data for the White Cloud Pegmatite continued….26
3. X-ray diffraction data and refinement parameters of gadolinite samples SWC and Z2A.27
4. a. Selected nearest neighbor distances of gadolinite samples SWC and Z2A…………...28 b. Selected nearest neighbor distances of gadolinite samples SWC and Z2A continued..29
5. Atomic position, displacement parameters, and electrostatic energy of sites for gadolinite SWC……………………………………………………………………………………...30
6. Atomic position, displacement parameters, and electrostatic energy of sites for gadolinite Z2A………………………………………………………………………………………30
7. Refined structural occupancy of cation sites of gadolinite samples SWC and Z2A…….31
8. Average elemental compositions from the electron microprobe for thin sections of gadolinite samples SWC and Z2A, and grain mount of SWC ……………………...... 35
9. Summary of selected average atoms per formula unit from the electron microprobe for thin sections of gadolinite samples SWC and Z2A, and grain mount of SWC …………36
10. Total cation charge with EMPA data…………………………………………………….49
11. Total cation charge with XRD data, with EMPA data for REE+Y in the A-site...……...49
12. Si-Si long and short distances in the tetrahedral rings for gadolinite SWC and Z2A…...52
13. Best chemical formulas for gadolinite samples SWC and Z2A, calculated from EMPA data……………………………………………………………………………………….59
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LIST OF FIGURES
1. The structure of gadolinite supergroup minerals.…………………………………………4
2. The structure of gadolinite supergroup minerals, displaying alternating layers.………….5
3. TO4QO4 tetrahedra in alternating rings…………………………………………………....5
4. Abundance of elements in Earth’s upper continental crust as a function of atomic number……………………………...... 11
5. Basic geologic map of the Pikes Peak Batholith and South Platte Pegmatite District.….15
6. Photomicrograph of thin section WhC3A………………………………………………..18
7. Photomicrograph of thin section WhC4A………………………………………………..18
8. Photomicrograph of sample SWC in thin section………………………………………..19
9. Photomicrograph of sample Z2A, bottom left gadolinite, in thin section……………….20
10. Photomicrograph of sample Z2A, top right gadolinite, in thin section………………….20
11. BEI of gadolinite sample SWC in thin section…………………………………………..32
12. BEI of gadolinite sample SWC in thin section…………………………………………..32
13. BEI of gadolinite sample Z2A in thin section ……...…………………………………...33
14. BEI of gadolinite sample Z2A in thin section…………………………………………...33
15. BEI of gadolinite grain mount SWC……...……………………………………………...34
16. Raman spectra of thin sections and grains of gadolinite samples SWC and Z2A……….37
17. a. Chondrite normalized REE distribution in gadolinite sample SWC via EMP data…...41 b. Chondrite normalized REE distribution in gadolinite sample Z2A via EMP data……41
18. Sum Y+HREE vs. Sum LREE…………………………………………………………...42
19. Whole rock chondrite normalized REE distribution.…………………………………….43
20. Y/(HREE+Y) vs. Y ……………………………………………………………………...44
21. Fe vs. total LREE………………....……………………………………………………...45 ix
22. Trace amounts of Ca vs. Fe ……………………………………...... 45
23. Trace amounts of Th vs Fe……………………………………………………………….46
24. M-site cation (Fe) vs. A-site cations (REE, Y, Th, Ca) ……………...... 47
25. b lattice parameter vs. Si-Si Short tetrahedral ring distance with XRD data…………….52
26. c lattice parameter vs. Si-Si Long tetrahedral ring distance with XRD data…………….53
27. Si-Si Long vs. Si-Si Short tetrahedral ring distances with XRD data...………………....53
28. Ce vs. Y…………………………………………………………………………………..57
29. Chondrite normalized REE distribution for allanite adjacent to gadolinite samples SWC and Z2A…………………………………………………..……………………………...60 1
Chapter 1: Introduction The Gadolinite Supergroup of Minerals
The gadolinite supergroup of minerals is a group of structurally similar minerals with a general chemical formula of A2MQ2T2O8ϕ2, and includes silicates, phosphates, and arsenates
(Baćík et al., 2017). The most common ions or vacancies within these sites are:
A: Ca, REE, Pb, Mn, Bi, Actinides; M: Fe, Vacancy, Mg, Mn, Zn, Cu, Al; Q: B, Be, Li; T: Si, P, As, B, Be, S; ϕ: O, OH, F. The site notation is that of Baćík et al., 2017, however, past studies will name the sites differently, with the general chemical formula of W2XZ2T2(O, OH)10 (Baćík et al., 2014), or
A2Z2XxT2O8[O2x(OH)2-2x] (Cámara et al., 2008). The gadolinite supergroup is first split chemically into the silicates (gadolinite group), and arsenates and phosphates (herderite group), by the primary occupant of the T-site. The subgroups are then divided by the dominant occupancy of the A and the Q-sites. The gadolinite group minerals are silicates, with Si4+ in the
T-site. This group includes the gadolinite and datolite subgroups. The gadolinite subgroup A-site has a charge of 3+, and a Q-site charge of 2+. Conversely, the datolite group has a 2+ charge in the A-site, usually Ca, and a 3+ charge, B, in the Q-site. Datolite is common as a secondary phase in altered mafic igneous rocks. The herderite group is defined by having an ion with a 5+ charge in the T site, instead of an Si4+, either As5+ or P5+. This group contains the herderite and drugmanite subgroups. The anions in the O2-4 sites contain oxygen ions, but ϕ can contain O2-,
(OH)-, or F-. While the O1 site is almost always oxygen too, in drugmanite it contains an (OH)- instead. The charge of the anions ranges from 16-20 negative charges total, per formula unit
(Baćík et al., 2017). The minerals of the supergroup are datolite, homilite, gadolinite, hingganite, 2 minasgeraisite, herderite, hydroxylherderite, bergslagite, and drugmanite (Table 1). The gadolinite subgroup minerals can be further broken into yttrium, cerium, and neodymium dominant subsets in the A-site; typically, specimens display a preference for HREEs or LREEs instead of incorporating all REEs. Subgroup minerals are likely to form in solid solution with each other. Miscibility between different subgroups (such as the datolite and gadolinite group) is limited, although most likely tied to variable geochemistry within their genetic environments, and/or structural factors. Gadolinite subgroup minerals have a greater ability to distort and have more variable occupancy than the less flexible datolite subgroup minerals, as seen in Table 1
(Baćík et al., 2014).
Table 1. Gadolinite supergroup mineral classification diagram. Site A M Q T O ϕ Gadolinite group Datolite subgroup A2+ Q3+ Datolite Ca2 Vacancy B2 Si2 O8 (OH)2 2+ Homilite Ca2 Fe B2 Si2 O8 O2 Gadolinite subgroup A3+ Q2+ 2+ Gadolinite REE2 Fe Be2 Si2 O8 O2 Hingganite REE2 Vacancy Be2 Si2 O8 (OH)2 2+ Minasgeraisite Y2 Ca Be2 Si2 O8 O2 Herderite group Herderite subgroup A2+ Q2+ Herderite Ca2 Vacancy Be2 P2 O8 F2 Hydroxylherderite Ca2 Vacancy Be2 P2 O8 (OH)2 Bergslagite Ca2 Vacancy Be2 As2 O8 (OH)2 Drugmanite subgroup A2+ Vacancy 3+ Drugmanite Pb2 Fe Vacancy2 P2 O7(OH) (OH)2 Nomenclature based off the occupancy of structural sites. Chart modified from Baćík et al., 2017. 3
Many samples of gadolinite and hingganite are metamict due to their ability to incorporate sufficient uranium and thorium into the A-site to damage the structure by alpha- decay which is exacerbated in older specimens.
The crystal structures of this group are based on a monoclinic unit cell with a = 4.6 –
o 4.9Å; b = 7.6 – 8.0Å; c = 9.6 – 11.1Å and β = 90.1 – 90.7 ; in space group P21/c (Baćík et al.,
2017 and references therein). Early studies described the structure in P21/a with a and c reversed
(Baćík et al., 2017). Gadolinite minerals demonstrate a wide variation in lattice parameters, accounting for both the largest unit cell volume (gadolinite-(Nd)) and the smallest (gadolinite-
(Y)).
The A-site has 8-fold coordination with O and ϕ. It can contain ions with a charge of 2+,
3+, and potentially 4+ for trace elements such as U and Th. There is no evidence of significant vacancies or 1+ ions in the A site. The AO6ϕ2 polyhedra are distorted tetragonal antiprisms
(Cámara et al., 2008). The M-site is in 6-fold coordination with O and ϕ, creating MO4ϕ2 octahedra. These polyhedra occur in layers, sharing edges with the M site polyhedra. Together, the A and M polyhedra form irregular 6-member rings, with 4 A-site antiprisms and 2 M-site octahedra, seen in Figure 1 (also including Q and T site tetrahedra). This layer of AO6ϕ2MO4ϕ2 polyhedra is parallel to (1 0 0), alternating on the [1 0 0] direction (Baćík et al., 2017). These layers alternate with layers of TO4QO4 tetrahedra (Figure 2). The T and Q-sites form linked tetrahedral that create 4 and 8-member oblong and tilted rings (Figure 3). These rings have distorted lengths and widths depending on the occupancy of both the Q and T-site tetrahedra, and the occupancy of the A-site (Baćík et al., 2014). 4
If the ϕ-site is occupied by an oxygen ion, the location is as depicted in Figures 1 and 2.
In the case of datolite, hingganite, hydroxylherderite, and bergslagite, ϕ becomes a hydroxyl when the M-site becomes vacant. This vacancy is not fully empty, as the hydrogen portion of the hydroxyl leans towards the vacant M-site, while the oxygen remains in the ϕ-site.
Figure 1. The structure of gadolinite supergroup minerals. Structure from gadolinite-(Y) from Cámara et al., 2008. Sites in colors: Purple, A; Red, M; Blue, Q; Yellow, T; Orange, O1-4; Pink, ϕ. Viewed perpendicular to (1 0 0). A and M sites as ball-and-stick for sake of viewing whole structure unobstructed. Graphics obtained from XTALDRAW 2003.
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Figure 2. The structure of gadolinite supergroup minerals, displaying alternating layers. Structure from gadolinite-(Y) from Cámara et al., 2008. View parallel to [0 1 0] depicting the alternating TO4QO4 tetrahedral layer and AO6ϕ2MO4ϕ2 layer. Graphics obtained from XTALDRAW 2003.
Figure 3. TO4QO4 tetrahedra in alternating rings. Red line: T-T site long ring axis. Orange line: T-T site short ring axis. View perpendicular to (1 0 0). Graphics obtained from XTALDRAW 2003. 6
History and Occurrences of Gadolinite The discovery of gadolinite is intertwined with the discovery of yttrium and several rare earth elements. Swedish artillery officer Carl Arrhenius originally found an interesting heavy black mass of minerals near Ytterby, Sweden. Later, Sir Johann Gadolin, a professor of chemistry at the University of Åbo, investigated this mineral and over the course of several years discovered the element yttrium (Weeks, 1932). He published his findings in 1794, but it took 34 more years to isolate yttrium from its original mineral (Chakmouradian and Wall, 2012). While yttrium was discovered and named for the town (as were ytterbium, terbium, and erbium), the heavy black mass studied was named gadolinite in honor of Sir Gadolin by mineralogists many years later. Ytterby is a type locality for many rare earth elements and rare earth minerals due to the works of Sir Gadolin and many researchers since. The element gadolinium, another REE, was also named for Sir Gadolin, but was discovered by Swiss chemist Jean Charles Galissard de
Marignac (Weeks, 1932). The earliest structural studies on gadolinite were conducted in the
1974 by Jun Ito and Stefan Hafner, paving the way for future research on this mineral group.
Gadolinite is found as an accessory phase in REE and Be-rich granites and pegmatites, and some metamorphic rocks (Baćík et al., 2017). Specimens studied by Cámara et al., 2008 were discovered in volcanic ejecta. When it occurs in pegmatites, it is associated with the niobium-yttrium-fluorine (NYF) type, which include the REE enriched subtypes. Gadolinite is found in both yttrium and cerium dominant members, as gadolinite-(Ce) and gadolinite-(Y).
There has been at least one case of a neodymium dominant member, gadolinite-(Nd) (Škoda et al., 2017). Commonly it is found as a partial solid solution with hingganite, up to 50% vacancy in the M-site (with a corresponding substitution of hydroxyl at the ϕ-sites). 7
Originally identified in Ytterby, Sweden, gadolinite-(Y) has since been found in numerous locations around the world, as had its analogue, gadolinite-(Ce). The gadolinite-(Nd) specimen was found in a bastnas-type skarn in Sweden. Gadolinite-(Y) is known for its occurrences in the Heftetjern pegmatite in Norway (Chukanov et al., 2017), various parts of the
Alps in fissures and pegmatites (DeMartin et al., 1993), pegmatites in the Kola peninsula
(Lyalina et al., 2014), Rode Ranch, Texas (Gibson and Ehlmann, 1970), Vico Lake, Italy
(Cámara et al., 2008), the White Cloud Pegmatite (this study), and multiple others. Gadolinite-
(Ce) is known for occurring in Skien Norway (Segalstad and Larsen, 1978), and multiple regions of Sweden (Holtstam and Andersson, 2007). Among REE-bearing minerals, gadolinite is unusual in having both HREE and LREE varieties, sometimes in the same locality such as the studied area in the South Platte district. Individual specimens of gadolinite favor HREE or LREE typically, although may have variable zonation within them.
Commonly, gadolinite is found with varied proportions of REE, changing slightly by region, or by core to rim as is the case for gadolinites analyzed from Baveno and Cuasso al
Monte (Pezzotta et al., 1999). However, it is less common for samples from the same locality to display drastically different compositions, as much as subtle changes; or two species exist with very little mixing. This makes the South Platte region and ideal location to study gadolinite, due to the presence of both LREE and HREE rich species.
Chemistry and Occupancy of Structural Sites for Gadolinite
Ideally, with the supergroup formula of A2MQ2T2O8ϕ2, gadolinite has the overall formula of REE2FeBe2Si2O8O2, sometimes written as REE2FeBe2Si2O10 or specifying the dominant REE present, with two formula units per unit cell. The rare earth elements occur in highest coordination, 8-fold, in the A-site. Iron occurs in the octahedral M-site. The Be and Si 8 create the alternating rings of tetrahedra, with the Si tetrahedra at the vertices of the rings.
However, since it can be in solid solution with hingganite and potentially datolite, it can display a range of different occupancies in specific sites. In solid solution with hingganite, the Fe in the
M-site becomes partially vacant. In order to compensate for the lost divalent cation, the ϕ site becomes occupied by a hydroxyl instead, lowering the total negative anion charge with the exchange: Fe+2 + 2O-2 ↔ □ + 2OH-1.
This is further complicated when a specimen is also in solid solution with datolite, although this only can happen with B in the system. The transformation of hingganite to datolite comes from the coupled exchange of (Y, REE+3) + Be+2 ↔ Ca+2 + B+3. Additionally, depending on geochemical environment, F-1 can enter the ϕ-site serving the same charge balance purpose as a hydroxyl anion.
When datolite subgroup substitutions are present, the tetrahedral rings (Figure 3) widen, increasing the Si-Si short distance, as Ca tends to have a larger ionic radius than the REE
(exceptions of La, Ce, and Pr). However, the gadolinite subgroup minerals tend to have a longer
Si-Si long distance to the tetrahedral rings. The tetrahedral rings display a negative correlation between short and long Si-Si distances for gadolinite group minerals. The long Si-Si distance is correlated to the occupancy of the T-site, while the occupancy of the A and the M-sites is correlated to the short Si-Si distance (Baćík et al., 2014).
Gadolinite subgroup minerals are commonly metamict, as U and Th can substitute into the A-site (Ito and Hafner, 1974; Segalstad and Larsen, 1978; DeMartin et al., 2001). In the case of the gadolinite-(Y) from Vico Lake, there was a significant amount of Li counterbalancing the increased charge of the U and Th, by substituting in the Q and T-sites via the substitution MFe+2 9
+ AY+3 ↔ MLi+1 + A(Th + U)+4 and QBe2+ + MFe2+ ↔ QLi+ + MFe3+ (Cámara et al., 2008).
Lacking Li, U and Th could be charge balanced by M-site vacancies, or by an exchange such as
2REE3+ ↔ Ca2+ + U, Th4+. Metamictization can cause problems with structure analysis, diminishing X-ray signals, but can potentially be resolved by annealing specimens (Gibson and
Ehlmann, 1970).
Due to the great possibility for substitutions within the gadolinite group minerals, extra care must be taken in analysis to account for all potential compositions and occupancies. It also makes calculating the appropriate chemical formula challenging, as there are rarely fixed variables for normalization. Knowing potential elements in a mineral using geologic constraints can help, but usually will not take into account all possibilities. Unless thorough chemistry is available, it is incorrect to normalize to 10 anions (Baćík et al, 2017). Since electron microprobe analysis (EMPA) cannot account for Be, B, Li, or the H in a hydroxyl, these elements cannot be used for normalization. And due to the potential vacancy of the M-site, one cannot use cations from this site. Baćík et al., 2017 proposes three different methods to calculate appropriate chemical formulas for gadolinite supergroup minerals, although all of them have potential pitfalls.
The first suggestion for chemical analysis normalization is to use a basis of four (A + T) cations. In the case of gadolinite, the assumption is that there are two REE in the A-site, and two
Si in the T-site. The drawback of this is the potential to have Ca substituting into the A-site or the
M-site (meaning there could be over 2 apfu, if Ca is counted in the A-site), B and Si substitutions at T, or Al and Si substitutions at T. Similarly, if the T-site cation is over 2 apfu, the total of four
(A + T) cations cannot be assured by the standard cations in these sites. However, neither of 10 these sites are likely to be vacant, so this could be used if there is a way to verify that there are not excess cations from these sites in the Q or T-sites.
If the T-site has multiple potential cations present, the second idea should be implemented: normalize on the basis of two A-site cations. This assumes that the contents of the
A-site are uniformly two cations. While vacancy is rare in this site, it is common to have multiple elements within it. Such is the case for gadolinite, with a slew of REE elements (and possibly Ca, U, Th, and Pb).
Lastly, should the A-site show variability, and the T-site have a sole occupant, normalize on the basis of two T cations. For gadolinite, this means assuming that there are two Si cations per formula unit, which may not be necessarily true.
Although these are strong methods to deal with the convoluted chemical formulas, there are drawbacks and other considerations which are encountered in this study. These methods cannot take into account variability in both the A and the T-site cations. Structural X-ray diffraction data on occupancy, and Raman or infrared spectroscopy can prove to be a boon in knowing what normalization factor to use.
Rare Earth Elements
The rare earth elements (REE) constitute the lanthanide row of the periodic table, with atomic numbers 57-71. Yttrium (atomic number 39) is commonly included in the REE, as it behaves geochemically as a REE due to chemical similarities (Van Gosen et al., 2014). With only a few exceptions, all of the REE occur in a trivalent state. Europium can behave differently than other REE, as it can be reduced to a divalent state and fractionate into Ca-rich plagioclase, thus it is less prevalent in granitic continental crust; it may already be consumed into more mafic 11 rocks earlier in a magmatic fluid’s history. Ce can also exist outside of a trivalent state, as it can oxidize to +4 charge, which can potentially indicate alteration after crystallization.
The REE are separated into the light rare earth elements (LREE) and heavy rare earth elements (HREE) based on atomic weight and ionic radius; La through Gd are classified as
LREE, while Y and Tb through Lu are classified as HREE. The REE also experience lanthanide contraction: as the atomic number increases along the lanthanides, the atomic radius decreases linearly from 1.160Å (La) to 0.977Å (Lu), with 1.019Å (Y) (coordination number 8 assumed)
(Shannon, 1976). This trend occurs due to increasing attraction between the nuclei and 6s electrons which are poorly shielded by the 4f electrons (Chakmouradian and Wall, 2012).
Figure 4. Abundance of elements in Earth’s upper continental crust as a function of atomic number. Abundance is normalized to 106 atoms of Si, modified from Haxel et al., 2002. Note that the REE and Y are in similar overall abundance to Cu, an element considered to be a common metal. 12
It is misleading to call the REE rare, as they occur at abundances similar to copper in the continental crust (Figure 4). While copper forms hydrothermal ore deposits and can more readily be mined, REE deposits are few and far between, as REE are not frequently concentrated. They are more prevalent as trace elements within major minerals of the crust. Forming a concentration of REE requires specific conditions, each involving a form of extreme fractionation or chemical separation. REEs can concentrate in carbonatite magmas, alkaline igneous rocks, ion-adsorption clay deposits, and monazite-xenotime-bearing placer deposits for economic deposits (Van Gosen et al., 2014) and granitic NYF type pegmatites. The pegmatites have a plethora of REE minerals, although often are not large enough in scale to be considered economically viable
(Chakhmouradian and Wall, 2012).
Rare Earth Element Pegmatites
Rare earth element pegmatites are among the rarest of pegmatite subtypes. The majority of pegmatites are simple compositions, forming similarly to veins and dikes. Less than 1% of pegmatites are deemed “rare-element pegmatites” which contain appreciable quantities of rare elements at all (Li, Be, Cs, B, P, Ta), let alone rare earth elements (London and Kontak, 2012).
Rare-element pegmatites are a small but diverse class of pegmatites that can be broken down into two families: LCT (lithium, cesium, tantalum) and NYF (niobium, yttrium, fluorine). Within the
NYF family, there is the rare-earth type, with the allanite-monazite subtype and the gadolinite subtype (Černy, 1991). Despite their overall rarity, several major fields of REE-pegmatites are known around the world: SW Grenville Province, ON-QC, Canada; Pikes Peak batholith, CO,
USA; Spruce Pine and Amelia districts, VA-NC, USA; southern Norway and Sweden; Kola-
Karelia region, Russia; Pribaikal region, Russia; Aldan Shield, Russia; southern Japan; and
Antsirabe-Kitsamby and Ankazobe districts, Madagascar (Ercit, 2005). The NYF family of 13 pegmatites is typically correlated with anorogenic A-type granites (Černy, 1991). This is prominently seen in the South Platte district, as the Pikes Peak batholith is a classic A-type granite and hosts dozens of small NYF pegmatites within the South Platte at its northern extent.
Pegmatites are derived from highly fractionated magmas, from igneous sources or anatexis of appropriate composition metamorphic rock. These fractionated melts could be residual from the crystallization of (usually) granitic plutons, and they are enriched in incompatible elements, fluxes, volatiles, and rare elements (Simmons and Webber, 2008). These intrusive bodies are known for their coarse sized crystals, but actually have a wide range of grain sizes, from sub-millimeter to many meters. Fractionation continues during the crystallization of the pegmatite body. The fluxing elements and volatiles prevent crystal nucleation until the fluid is super cooled, forcing crystallization to occur suddenly and sequentially. An alternative theory for the derivation of magmas, to the fractionation theory, is that the overall composition of a pegmatite is similar to that of an original granitic magma, except that it includes fluxes such as
H2O, F, CO2, and B. This causes the magma to enter an undercooled state which delays crystallization then causes a crystallization front in a constitutional zone refinement process
(London and Morgan, 2012). This also would lead to zonation and fractionation processes within the pegmatite. The NYF subtype pegmatites such as those in the Pikes Peak Batholith fractionate in an onion-like sequence of zones, from the host granite, inward to a quartz-microcline-biotite wall zone, a quartz-microcline core, a core-margin zone, and then fluorite-rare-earth replacement units (Simmons and Heinrich, 1980). What that study describes as “replacement units” may not in fact be replacement minerals, however, is undoubtedly REE-enriched. This layer could be derived from a magmatic source, or a hydrothermal phase at the end of the crystallization 14 process. Mineral replacement could be part of the formation of this zone, but is unlikely to be the only derivation of these REE minerals.
The White Cloud Pegmatite
The White Cloud Pegmatite is within the South Platte Pegmatite District of the Pikes
Peak Batholith, in one of the northern most plutons (Figure 5). The Pikes Peak Batholith is a classic A-type batholith, with subsolidus two-feldspar quartz monzonite which is surrounded by one-feldspar hypersolvus granite (Haynes, 1965; Simmons and Heinrich, 1975; Simmons and
Heinrich, 1980; Smith et al., 1999; Frost and Frost, 1997; Simmons and Heinrich, 1972). This pegmatite district spans 80 km2 and contains over 50 complex, concentrically zoned pegmatites.
They are some of the most well-known pegmatites of the NYF subtype, and follow roughly concentric zonation as described by Simmons and Heinrich, 1980. These pegmatites occur distinctly within the pluton, not at the margins (Simmons et al., 1987). South Platte pegmatites are well known for their enrichment in rare-earth and iron minerals, and depletion in tourmaline and beryl. These pegmatites have been mined for the feldspar in their cores, exposing the REE enriched zones (Haynes, 1965). The White Cloud Pegmatite is a small body, ~100 x 40 meters across and displays geochemically complex concentric zoning. It is possible that the White
Cloud Pegmatite produced a “carload” of gadolinite-rich ore in the 1950s (Simmons and
Heinrich, 1980). Other pegmatites of this district include (but are not limited to) the Big Bear
No. 2, the Dazie Bell, and The Big Bertha; they have similar REE mineral assemblages, although they are not identical. White Cloud Pegmatite specifically is known for having the largest concentration of a REE-rich fluorite in this pegmatite district (Simmons and Heinrich, 1980).
Bastnäsite, (REE)CO3F, occurs in the White Cloud Pegmatite in both cerium and yttrium end 15 members. Although it is often associated closely with allanite, it also occurs as a dark reddish brown alteration of gadolinite (Simmons and Heinrich, 1980).
Figure 5. Basic geologic map of the Pikes Peak Batholith and South Platte Pegmatite District. The South Platte Pegmatite District and the White Cloud Pegmatite are enhanced in the upper right. Map created by Julien Allaz, adapted from Simmons et al., 1987.
2+ 3+ Allanite ((Ca, Ce)2(Al, Fe , Fe )3(SiO4)(Si2O7)O(OH)), bastnäsite ((Ce, Y)(CO3)F), synchysite (Ca(Ce, Y)(CO3)2F), thalénite ((Y, HREE)3Si3O10F), and gadolinite
(REE2FeBe2Si2O10) are prevalent REE-rich minerals within the fluorite-REE-iron rich zone.
Cerite ((Ce, Ca)9(Mg, Fe)(SiO4)(HSiO4)4(OH)3), fergusonite ((Ce, Y, Nd)NbO4), fluocerite
((LREE)F3), yttrofluorite ((Ca1-xYx)F2+x), monazite ((LREE)PO4), xenotime ((Y, HREE)PO4), uraninite (UO2), thorite (Th(SiO4)), and zircon (Zr(SiO4)) are also present in small quantities.
Most of the REE-rich minerals are found in an aggregate of small crystals within a fluorite 16 matrix, although some occur at the boundary of this zone and are in contact with quartz and feldspars.
Gadolinite of the White Cloud Pegmatite
The gadolinite of the White Cloud Pegmatite is unusual due to having a range of compositions from LREE rich to HREE rich, while many of the other minerals in the pegmatite exist with LREE or HREE dominant species (such as allanite and thalénite). In this study, we analyze chemical and structural trends of gadolinite at the White Cloud Pegmatite. We discovered that the gadolinite here has abnormalities regarding crystal structure which have not been previously documented in any locality; Be and Si are partially disordered. Additionally, we find that the M site with iron is potentially partially vacant, without evidence of corresponding hydroxyl substitution in the ϕ-site. Lastly, chemical analyses of the gadolinite revealed that there could have been multiple stages of fluid evolution within the REE zone of the pegmatite.
17
Chapter 2: Samples and Methods
Samples and Description
Six rock samples were crushed into powder for whole rock analyses. WhC3A and
WhC4A are the REE-rich zone. These samples are visually quite different, and are both prominent assemblages within the REE-rich zone; they have overlapping assemblages but not identical (photomicrographs in Figures 6, 7). WhC3A is brick red aggregate of fine grain crystals, surrounded on two sides by the feldspar and quartz zone. At the boundary of the red
REE-zone and the feldspar and quartz zone is a fine (~1 mm) rim of pale green fluorite.
Gadolinite crystals < 1 mm across exist within this sample, almost always with a proportionally thick alteration rim of red-brown bastnäsite. Allanite and thalénite also exist within this sample, but the bastnäsite is most prominent. REE minerals are surrounded by a matrix of fluorite.
WhC4A is an aggregate of gray, purple, and brown fine grain crystals, and is almost entirely
REE-rich minerals in a fluorite matrix. Allanite, thalénite, and synchysite dominate the REE minerals of the thin section, but some gadolinite and bastnäsite exist as noteworthy accessory minerals. Gadolinite in this sample do not have an alteration rim of bastnäsite. The majority of the feldspar and quartz was ground off the sides of WhC3A and WhC4A before crushing them into powder to analyze as close to pure REE-zone rock as possible. 18
Figure 6. Photomicrograph of thin section WhC3A. Left: Viewed in plane polarized light. Right: Viewed in cross polarized light.
Figure 7. Photomicrograph of thin section WhC4A. Left: Viewed in plane polarized light. Right:
Viewed in cross polarized light. WhC1B is a fine graphic granite, quartz and potassium feldspar, with the graphic texture on a roughly 5mm scale. WhC2A is the margin of graphic granite with exceptionally iron rich biotite that has likely been altered at the surface. WhC1A1 and WhC1A2 are the host Pikes Peak
Granite from the immediate vicinity of the White Cloud Pegmatite. The Pikes Peak Granite is an amphibole and biotite granite with a high amount of microcline feldspar (Smith et al., 1999). 19
Thin sections of each sample were made for use in a petrographic microscope. WhC3A and
WhC4A were polished for use in the electron microprobe.
Two additional thin sections were used for electron microprobe analysis and Raman spectroscopic analysis; these thin sections contain the crystals that the chips for X-ray diffraction were taken from. Photomicrographs of these thin sections are seen in Figures 8, 9, 10. The gadolinite is an olive green crystal, roughly 1 cm in diameter. It is surrounded by, and has two large inclusions of feldspar, quartz, and fluorite. The gadolinite is also partially included by allanite, and has a thin rim of brownish red alteration on the edges (bastnäsite). Z2A gadolinite crystals are 1-4 mm across; they’re in a matrix of fluorite and surrounded by allanite, thalénite, and more REE-minerals. They do not have significant bastnäsite around the rim of the crystals.
Two prominent green grains of gadolinite are within this thin section (one at the top right, one at the bottom left) and were used in the electron microprobe and Raman spectrometer.
Figure 8. Photomicrograph of sample SWC in thin section. Left: Viewed in plane polarized light. Right: Viewed in cross polarized light. Zonation banding is evident in the bottom of the main crystal, far right, and at the top. 20
Figure 9. Photomicrograph of sample Z2A, bottom left gadolinite, in thin section. Left: Viewed in plane polarized light. Right: Viewed in cross polarized light. Gadolinite is the olive color mineral on the left edge of the thin section. Dark brown allanite is adjacent to it.
Figure 10. Photomicrograph of sample Z2A, top right gadolinite, in thin section. Left: Viewed in plane polarized light. Right: Viewed in cross polarized light. Gadolinite is the olive-beige color mineral on the right side of the thin section, at the margin of the white fluorite and the REE-rich brown minerals. We chipped a ~100µm fragment out of the gadolinite from both SWC and Z2A for use in single crystal X-ray diffraction analyses. They were placed unglued on a slide for analysis in the
Raman spectrometer after X-ray diffraction. After analysis in the X-ray diffractometer and 21
Raman spectrometer, the grains were remounted onto 24mm round glass to be analyzed by the electron microprobe. However, in the process of remounting, only the SWC shard successfully was glued to the grain mount and polished.
Whole Rock Analysis
The powdered rock samples were sent to the Bureau Veritas Minerals in Vancouver,
Canada, for analysis in the ACME Labs inductively-coupled-plasma mass spectrometer.
Significant elements were analyzed to ppm level precision: Si, Al, Fe, Mg, Ca, Na, K, Ti, P, Mn,
Ni, Cr, Sc, Ba, Be, Co, Cs, Ga, Hf, Nb, Rb, Sn, Sr, Ta, Th, U, V, W, Zr, Y, La, Ce, Pr, Nd, Sm,
Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. Some of the REE of the WhC3A and WhC4A samples were over detection boundaries; the Y of WhC3A was >50000 ppm, and the Nd was >10000 for both WhC3A and WhC4A.
X-Ray Diffraction
The X-ray diffraction (XRD) analyses on fragments of SWC and Z2A were conducted using a Bruker P4 four circle diffractometer with an APEX II CCD detector and a rotating Mo- anode generator. The Mo-anode generator was operated at 50 kV and 250mA with a graphite monochromator. Sample SWC was analyzed through 2θ of 55o, and Z2A was analyzed through
2θ of 65o. Atom positions, anisotropic displacement parameters, and site occupancy were refined for each specimen using SHELX-97 (Sheldrick, 1997) in the WinGX-2014 software package
(Farrugia, L. J., 2014). Ionized-atom scattering factors were used for these refinements (Cromer and Mann, 1968; Azavant and Lichanot, 1993). The A-site cations were refined using ytterbium scattering factors, as it has the highest atomic number we expected in abundance. Therefore, the structural occupancy appears low, since most of the REE within gadolinite are not ytterbium, but 22 by number of electrons found during refinement, will be reasonable for a mix of REE and yttrium. The M-site was refined using the Fe2+ scattering factors. The Si and Be sites in the T and
Q-sites were allowed to disorder. The oxygen sites were fixed to full occupancy (5 O, Z = 2), but allowed to vary spatially. Twinning instructions were included in the SHELX refinement on the recommendations of Cámara et al., 2008. The R-factor improved slightly with the twin matrix applied to the refinement.
Electron Microprobe Analyzer (EMPA)
EMPA data was collected on a new JEOL-8230 electron microprobe (EMP) at the
University of Colorado-Boulder for quantitative elemental analysis. Before gathering quantitative analyses, we used energy dispersive X-rays to identify major mineral trends in samples WhC3A and WhC4A. Backscatter electron images (BEI) were taken of the analyzed regions in SWC and Z2A to identify zonation within the gadolinite crystals. We used wavelength dispersive spectroscopy point analyses for quantitative analysis, choosing points based on the observed variation of the BSE signal in order to capture most of the composition variability. All analyses were performed at an acceleration voltage of 15 keV. Points were generally taken with
50 nA current and 5 µm beam size, but narrow regions were analyzed with 30 nA and 2 µm.
Peak interference corrections were applied to improve the accuracy. The analyses of SWC and
Z2A done with a conductive carbon coating on the thin sections and grain mount of SWC.
Analyzed elements are summarized in Table 8. Full analyses of the element weight percentages, standards and settings used, and interference correction information is contained in the appendix.
It was not possible to analyze fluorine due to the low content expected, and complications arising from numerous peak and background interferences from M-lines of the REE. The gadolinite formula was normalized to 10 oxygen anions (seen in the summary tables) and later constrained 23
to have Si + Be = 4 apfu, as per the ideal formula of REE2FeBe2Si2O10, and for consistency with our XRD analysis.
Allanite adjacent to the gadolinite specimens in SWC and Z2A was analyzed during a separate set of data collection using a ca. 17 nm aluminum conductive coating with a ca. 6 nm overcoat of carbon to permit the use of a high beam current (100 nA) without risking damage to the minerals with even a focused beam (ca. 0.5 µm); some analyses were acquired at 20 nA or with a defocused beam to confirm the absence of beam damage This data set was done in part to test the analysis of REE elements with an aluminum coating on the new instrument. This set of data is less reliable and accurate due to technical difficulties during the analysis, and less accurate due to incomplete peak interference corrections. However, general REE trends can still be interpreted. Results of this analysis are included in the appendix.
Raman Spectroscopy
The Raman spectra of samples SWC and Z2A, both in thin section and the crystals used for XRD, were collected with a Horiba LabRAM HR Evolution Raman spectrometer at the
Raman Microspectroscopy Laboratory, University of Colorado-Boulder. A 535 nm laser beam was focused through a 50x objective lens with power at the sample surface of 7mW. Spectral resolution of 4.5 cm-1 (full width at half maximum) was achieved with a 600lines/mm grating and a 100µm confocal pinhole. Before analysis the spectrometer was calibrated with the 520cm-1
Raman peak of Si. The spectra were collected by averaging 3-8 spectra that were each collected with a 10s counting time. This measurement was repeated for overlapping spectral ranges from
200cm-1 to 4000cm-1.
24
Chapter 3: Results
Whole Rock Analysis
ACME Labs returned the whole rock analyses in the form of weight percent oxides for the elements analyzed and are summarized in Tables 2a and 2b. The totals for the REE Zone rocks are well below 100% as fluorine and carbon were not analyzed.
25
Table 2a. Summarized whole rock elemental data for each zone of the White Cloud Pegmatite. WhC1B: WhC2A: WhC 1A1: WhC1A2: WhC3A: WhC4A: Element/Oxide Units Graphic Border Granite Granite REE Zone REE Zone Granite Zone SiO2 % 74.4 74.27 75.35 70.74 15.5 16.55
Al2O3 % 12.59 12.93 13.26 14.8 3.17 5.17
Fe2O3 % 2.11 2.22 0.1 1.74 2.06 7.39
MgO % 0.11 0.14 <0.01 0.03 0.44 0.32
CaO % 0.57 0.21 0.04 1.14 33.25 28.97
Na2O % 3.26 4.18 2.14 3.73 0.68 0.03
K2O % 5.77 4.73 8.85 6.67 0.81 1.07
TiO2 % 0.21 0.29 <0.01 0.13 0.01 0.05
P2O5 % 0.03 0.03 <0.01 <0.01 <0.01 <0.01
MnO % 0.03 0.08 <0.01 <0.01 0.02 0.17
Cr2O3 % 0.002 <0.002 <0.002 <0.002 0.038 0.039
Ni ppm <20 <20 <20 <20 <20 <20
Sc ppm 5 9 <1 1 11 18
Ba ppm 607 614 110 459 17 20
Be ppm 4 3 2 5 2116 3718
Co ppm 14.3 20 29.4 12.6 0.8 1.2
Cs ppm 4.5 0.6 0.9 0.6 1.6 1.7
Ga ppm 22.8 21.7 24.4 27.8 40.7 60.3
Hf ppm 12.9 14.2 0.5 3.3 <0.1 42.1
Nb ppm 62.7 83.9 4.7 34.2 36.4 209.6
Rb ppm 194.2 167.6 439 244.8 86.1 107.6
Sn ppm 4 9 <1 6 27 108
Sr ppm 55.1 80.5 13.4 42.3 641.5 92.9
Ta ppm 3.5 5.6 1.2 2.3 4.2 25.3
Th ppm 14.6 31.3 1.4 14.7 412 577.4
U ppm 2.7 3.6 0.6 3.5 48.8 78.1
V ppm <8 <8 <8 <8 <8 <8
W ppm 167.3 202.6 286.8 128.3 12.4 27.8 26
Table 2b. Summarized whole rock elemental data for each zone of the White Cloud Pegmatite, continued. WhC1B: WhC2A: WhC1A1: WhC1A2: WhC3A: WhC4A: Element/Oxide Unit Graphic Border Granite Granite REE Zone REE Zone Granite Zone Zr ppm 436.9 478.8 5.6 55.2 5.9 524.4
Y ppm 94.5 146.4 3.7 58.2 >50000 43845.1
La ppm 54.8 152.6 2.3 7.1 13197.5 15211.4
Ce ppm 136.6 330.4 3.6 39.6 38019.7 42410.5
Pr ppm 17.91 40.18 0.53 2.32 5668.46 6279.28
Nd ppm 74 151.4 1.9 10.4 >10000 >10000
Sm ppm 15.52 28.14 0.37 3.23 7298.91 7461.95
Eu ppm 1.86 1.96 0.39 1.16 15.41 17.27
Gd ppm 14.62 25.27 0.48 4.66 7213.96 6539.1
Tb ppm 2.62 4.01 0.1 0.9 1396.25 1280.41
Dy ppm 17.34 26.58 0.73 6.32 9162.41 8421.44
Ho ppm 3.52 5.24 0.17 1.54 1906.02 1721.18
Er ppm 10.53 15.52 0.58 4.94 6580.19 5880.65
Tm ppm 1.55 2.38 0.1 0.8 1257.42 1120.41
Yb ppm 9.75 15.2 0.78 5.72 9298.55 8349.14
Lu ppm 1.48 2.11 0.12 0.91 1454.17 1272.58
Total % 99.78 99.71 99.96 99.60 67.25 68.91
Totals for the REE zone are low since C and F were not analyzed, however, there are significant quantities of REE carbonate minerals, REE fluoride minerals, and fluorite.
X-Ray Diffraction
The crystal structure refinement yielded a monoclinic unit cell with space group P21/c, with parameters displayed in Table 3. The cell parameters of SWC are significantly larger than those of Z2A. Selected nearest neighbor distances for these gadolinite samples are displayed in
Table 4. The ϕ-site is included in the nearest neighbor distances as an oxygen, on the assumption that the samples have 10 oxygen per formula unit. The refined atomic positions and displacement parameters for SWC are listed in Table 5, and for Z2A in Table 6. A-site preference, such as 27
“gadolinite-(Y)” is not yet stated as this is covered in the Discussion section. The refined occupancies of various sites are given in Table 7. The A-site was refined as a single very heavy
REE (Yb), but accounts for all the electrons that can represent a range of REE. The oxygen sites were refined using the O2- scattering factor curve of Azavant and Lichanot (1992) assuming full occupancy.
Electrostatic energy potentials were calculated using the code ELEN (Smyth, 1988), based on a nominal point charge model with charges of +3 for A, +2 for M and Q, +4 for T, and -
2 for O1, O2, O3, O4, and ϕ. These are presented in Table 5 and 6 as potential in volts.
Table 3. X-ray diffraction data and refinement parameters for gadolinite samples SWC and Z2A. Parameter SWC Z2A
a (Å) 4.8391(18) 4.7770(9)
b (Å) 7.7313(22) 7.5604(21)
c (Å) 10.1822(23) 10.0166(24)
β (o) 90.160(23) 90.402(12)
Volume (Å3) 380.94 361.75
2θ Max (o) 55 65
# Reflections 3124 5752
#Unique Reflections 840 1292
R(int) 0.048 0.063
R 0.049 0.053
28
Table 4a. Selected nearest neighbor distances for gadolinite samples SWC and Z2A. A-site SWC Z2A
A-O1 (Å) 2.400(8) 2.356(5)
A-O1 (Å) 2.407(7) 2.323(5)
A-O2 (Å) 2.471(7) 2.409(5)
A-O3 (Å) 2.753(8) 2.477(5)
A-O3 (Å) 2.560(8) 2.705(5)
A-O4 (Å) 2.461(7) 2.413(5)
A-ϕ (Å) 2.547(8) 2.384(5)
A-ϕ (Å) 2.436(8) 2.498(6)
Polyhedral Volume (Å3) 26.7(4) 24.8(2)
Electrons in Site 45.3 44.8
M-site SWC Z2A
M-O2(2) (Å) 2.347(8) 2.287(5)
M-O4(2) (Å) 2.241(8) 2.208(5)
M-ϕ(2) (Å) 2.069(8) 2.048(5)
Polyhedral Volume (Å3) 13.5(2) 12.9(1)
O. Q. E. 1.053 1.049
Angle Variance 166.7 157.2
Electrons in Site 20.9 23.2
29
Table 4b. Selected nearest neighbor distances for gadolinite samples SWC and Z2A, continued.
Q-site SWC Z2A
Q-O2 (Å) 1.665(14) 1.660(10)
Q-O3 (Å) 1.698(13) 1.673(9)
Q-O4 (Å) 1.654(14) 1.648(11)
Q-O5 (Å) 1.607(14) 1.577(10)
Polyhedral Volume (Å3) 2.30(5) 2.22(4)
T. Q. E. 1.0084 1.0121
Angle Variance 37.71 56.04
Electrons in Site 2.96 2.77
T-site SWC Z2A
T-O1 (Å) 1.599(9) 1.588(6)
T-O2 (Å) 1.652(8) 1.654(5)
T-O3 (Å) 1.622(9) 1.612(5)
T-O4 (Å) 1.671(8) 1.653(6)
Polyhedral Volume (Å3) 2.24(3) 2.20(2)
T. Q. E. 1.0027 1.0045
Angle Variance 11.01 17.91
Electrons in Site 8.81 9.88
30
Table 5. Atomic position, displacement parameters, and electrostatic energy of sites for gadolinite SWC.
Site x/a y/b z/c U11 U22 U33 U23 U13 U12 Electrostatic Energy (V) A (REE) 0.9983(2) 0.10774(9) 0.32780(7) 0.0197(5) 0.0132(5) 0.0161(5) -0.0023(4) 0.0028(3) -0.0004(4) -29.261
M (Fe) 0.0 0.0 0.0 0.0153(17) 0.0423(20) 0.0118(16) 0.0095(13) 0.0005(12) -0.0006(14) -29.386
Q (Be) 0.533(2) 0.413(2) 0.3364(11) 0.022(8) 0.038(8) 0.018(6) -0.001(5) -0.003(5) 0.004(6) -48.236
T (Si) 0.4792(8) 0.2758(4) 0.0786(4) 0.013(2) 0.018(2) 0.010(2) -0.0005(14) -0.0005(14) 0.0002(15) -30.807
O1 0.2443(16) 0.4082(10) 0.0325(7) 0.021(5) 0.028(4) 0.019(5) -0.001(4) -0.001(4) -0.0005(39) 25.652
O2 0.6685(16) 0.2873(10) 0.4527(7) 0.023(5) 0.024(4) 0.018(5) 0.006(3) 0.008(4) 0.008(4) 27.457
O3 0.6813(16) 0.3459(10) 0.1943(8) 0.022(5) 0.035(5) 0.014(4) -0.005(4) 0.004(3) -0.007(4) 26.457
O4 0.3176(16) 0.1029(10) 0.1402(8) 0.025(5) 0.020(4) 0.028(5) 0.001(4) 0.005(4) -0.005(4) 27.324
ϕ (O5) 0.2010(16) 0.4117(10) 0.3340(8) 0.016(5) 0.040(6) 0.021(5) -0.001(4) -0.003(4) 0.002(4) 22.686
Table 6. Atomic position, displacement parameters, and electrostatic energy of sites for gadolinite Z2A. Site x/a y/b z/c U11 U22 U33 U23 U13 U12 Electrostatic Energy (V) A (REE) 0.00029(11) 0.10717(8) 0.32859(5) 0.0161(3) 0.0179(3) 0.0161(3) -0.0014(3) 0.0014(2) -0.0003(3) -30.064
M (Fe) 0.0 0.0 0.0 0.0132(9) 0.0240(12) 0.0122(8) 0.0052(7) 0.0097(63) -0.0004(8) -23.878
Q (Be) 0.5310(18) 0.4145(12) 0.3347(8) 0.024(5) 0.028(6) 0.022(4) 0.0004(40) -0.0035(33) 0.0030(42) -48.564
T (Si) 0.4805(5) 0.2791(3) 0.0778(2) 0.0135(12) 0.0153(15) 0.0133(11) -0.0009(9) -0.0003(8) 0.0002(10) -30.989
O1 0.2422(10) 0.4117(7) 0.0302(5) 0.022(3) 0.014(3) 0.016(3) -0.001(3) 0.004(2) -0.001(3) 26.189
O2 0.6750(10) 0.2871(7) 0.4513(5) 0.013(3) 0.016(3) 0.016(3) 0.003(2) 0.002(2) -0.0004(23) 27.158
O3 0.6873(10) 0.3477(7) 0.1946(4) 0.018(3) 0.021(3) 0.009(2) -0.006(2) 0.002(2) -0.003(2) 26.846
O4 0.3145(10) 0.1068(7) 0.1410(4) 0.017(3) 0.012(3) 0.014(2) -0.000(2) 0.002(2) -0.001(2) 27.574
ϕ (O5) 0.2009(10) 0.4122(7) 0.3327(5) 0.019(3) 0.022(3) 0.015(3) -0.001(3) 0.004(2) 0.002(3) 23.107 31
Table 7. Refined structural occupancy of cation sites of gadolinite samples SWC and Z2A.
Structural Site SWC Z2A (Refined as, ideal apfu) A (Yb3+, 2) 45.3 electrons 44.8 electrons
M (Fe2+, 1) 87(1)% 97(1)%
Q (Be2+, 2) 88(2)% 90(1)%
Q (Si4+, 2) 12(2)% 10(1)%
T (Si4+, 2) 85(2)% 98(1)%
T (Be2+, 2) 15(2)% 2(1)%
A-site occupancy is in number of electrons. It was refined assuming Yb, so it can account for total electrons but not specific rare earth elements. Electron Microprobe Analysis
The EMPA data set included 73 points from the thin section of SWC, 67 points from the thin section of Z2A, and 25 points from the grain mount of SWC. The analysis included the
Mean Atomic Number (MAN) background correction (Donovan and Tingle, 1996). The average elemental weight percent of the points, and average high density and average low density regions for each SWC, Z2A, and the grain mount of SWC are displayed in Table 8. Examples of high and low density regions are shown in the backscattered electron images in Figures 11, 12, 13, 14, and 15. Low density regions correspond to darker tones, and conversely, higher density regions correspond to brighter tones. In Table 8, Be, is not displayed as Be is not directly analyzed.
Table 8 includes oxide weight percent totals, with Be assumed to be stoichiometric with 10 O.
Full composition data are contained within the appendix. The average atoms per formula unit for
SWC and Z2A are summarized in Table 9. Table 9 includes separation of high and low density regions, and the grain mount, as seen by BEI to display the range of compositions seen in each 32 sample. The atoms per formula unit are normalized on the basis of 10 oxygen atoms per formula unit.
Figure 11. BEI of a portion of gadolinite sample SWC in thin section. Area is from the bottom part of the thin section photo and has been rotated 180o. Dark regions are lower density, bright is higher density. The black and pure white seconds are not gadolinite.
Figure 12. BEI of a portion of gadolinite sample SWC in thin section. Area is from the top part of the thin section photo and has been rotated 180o. Dark regions are lower density, bright is higher density. The black and pure white seconds are not gadolinite.
33
Figure 13 BEI of a portion of gadolinite sample Z2A in thin section. Lower left crystal in thin section. Dark regions are lower density, bright is higher density. The black and pure white sections are not gadolinite.
Figure 14. BEI of a portion of gadolinite sample Z2A in thin section. Upper right crystal in thin section. Dark regions are lower density, bright is higher density. The black and pure white sections are not gadolinite. 34
, Figure 15. BEI of gadolinite sample SWC grain mount. Dark regions are lower density, bright is higher density. The black and pure white seconds are not gadolinite.
35
Table 8. Average elemental compositions from the electron microprobe for thin sections of gadolinite samples SWC and Z2A, and grain mount of SWC. Element SWC SWC SWC SWC SWC Z2A Z2A Z2A Average Average Average Grain Grain Average Average Average Low High Weight Average High Low High Weight Density Density Percent Weight Density Density Density Percent Weight Weight Percent Average Weight Weight Percent Percent Weight Percent Percent Percent Y 13.25 9.17 8.95 8.25 5.4 21.34 15.78 17.75 Si 10.24 10.27 10.09 10.20 10.18 10.78 10.29 10.46 Th 0.12 0.20 0.23 0.30 0.31 0.04 0.01 0.02 U <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 Ca 0.13 0.09 0.13 0.15 0.17 0.08 0.07 0.07 Pb <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 La 3.03 2.86 2.28 1.84 3.64 0.23 0.18 0.19 Ce 9.01 11.85 11.09 10.89 15.58 1.81 1.62 1.67 Nd 5.49 7.32 7.88 8.74 8.90 3.58 4.51 4.17 Pr 1.33 1.80 1.86 1.98 2.29 0.47 0.49 0.48 Sm 1.54 2.05 2.29 2.60 2.31 1.82 3.11 2.67 Tb 0.33 0.39 0.42 0.47 0.40 0.46 0.81 0.69 Eu 0.07 0.05 0.06 0.06 0.05 0.07 0.06 0.06 Dy 2.41 2.84 3.02 3.22 2.59 3.36 5.66 4.86 Gd 1.37 1.71 1.85 2.05 1.77 2.14 3.72 3.17 Er 2.07 2.15 2.20 2.19 1.64 2.77 3.69 3.36 Yb 4.35 3.17 3.74 3.54 2.45 4.13 4.17 4.16 Ho 0.46 0.50 0.53 0.55 0.40 0.68 1.04 0.92 Tm 0.46 0.43 0.43 0.42 0.30 0.50 0.60 0.56 Fe 9.28 8.93 8.92 8.87 7.90 10.00 9.54 9.72 Mg <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 Al <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 Lu 0.66 0.50 0.49 0.44 0.25 0.60 0.49 0.53 Total 98.04 98.89 98.25 98.57 97.93 98.84 98.43 98.58 Weight % U, Pb, Mg, and Al were at detection limits and yielded imprecise results. Eu was often at or near detection limits (0.05-0.06 weight % Eu) and should be regarded skeptically. Full results are in the supplementary material.
36
Table 9. Summary of selected average atoms per formula unit from the electron microprobe for thin sections of gadolinite samples SWC and Z2A, and grain mount of SWC.
Element SWC SWC SWC SWC SWC Z2A Z2A Z2A Average Average Average Grain Grain Average Average Average Low High Average High Low High Density Density Density Density Density APFU Average ΣLREE 0.793 1.016 1.004 1.027 1.313 0.290 0.376 0.343
ΣHREE+Y 1.217 0.982 0.994 0.955 0.982 1.718 1.639 1.669
ΣREE +Y 2.011 1.998 1.998 1.982 1.998 2.008 2.015 2.012
Y 0.819 0.574 0.565 0.520 0.345 1.257 0.970 1.075
La 0.120 0.114 0.092 0.074 0.149 0.009 0.007 0.007
Ce 0.353 0.470 0.444 0.436 0.632 0.068 0.063 0.064
Nd 0.209 0.282 0.307 0.339 0.351 0.130 0.171 0.156
Pr 0.052 0.071 0.074 0.079 0.092 0.018 0.019 0.018
Sm 0.056 0.076 0.085 0.097 0.087 0.063 0.113 0.095
Tb 0.011 0.014 0.015 0.016 0.014 0.015 0.028 0.023
Eu 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.002
Dy 0.082 0.097 0.104 0.111 0.056 0.108 0.190 0.161
Gd 0.048 0.061 0.066 0.073 0.064 0.071 0.129 0.108
Er 0.068 0.071 0.074 0.074 0.056 0.087 0.120 0.108
Yb 0.138 0.119 0.121 0.115 0.081 0.125 0.132 0.129
Ho 0.015 0.017 0.018 0.019 0.014 0.022 0.035 0.030
Tm 0.015 0.014 0.014 0.014 0.010 0.015 0.019 0.018
Lu 0.021 0.016 0.016 0.014 0.008 0.018 0.015 0.016
Ca 0.018 0.013 0.018 0.021 0.024 0.011 0.009 0.010
Fe 0.914 0.889 0.896 0.890 0.804 0.938 0.934 0.937
Si 2.004 2.034 2.018 2.035 2.034 2.009 2.003 2.004
Th 0.003 0.005 0.006 0.007 0.008 0.001 0.000 0.000
Normalized on the assumption of 10 O per formula unit.
37
Raman Spectroscopy
The resulting Raman spectra for samples SWC and Z2A, thin section crystals and the crystals used for XRD, are displayed in Figure 16. The spectra were analyzed from 200 cm-1 to
4000 cm-1. There are spectra lines from the epoxy roughly around 1500 and 3000 cm-1. Bands between 200-750 cm-1 are due to banding modes of Si-O and Be-O, stretching vibrations of
REE-O and Fe-O (Škoda et al., 2017). Sample Z2A has its most prominent peak at 904 cm-1 and a minor peak at 980 cm-1, while SWC has weak peaks in this region. These peaks are attributed to stretching vibrations of Be-O and Si-O in tetrahedral coordination (Škoda et al., 2017). All samples have weak peaks at approximately 2200 cm-1. Similar peaks are also displayed in phenakite (Be2SiO4).
Figure 16. Raman spectra of thin sections and grains of gadolinite samples SWC and Z2A. Red: Spectra of sample SWC crystal used in XRD analysis. Blue: Spectra of sample SWC in thin section. Orange: Spectra of sample Z2A crystal used in XRD analysis. Purple: Spectra of sample Z2A in thin section.
38
Chapter 4: Discussion Chemical Constituents
The chemistry of each sample is distinctly that of gadolinite, however, there is compositional variability in the REE content of each sample and of the Fe content. Both samples
SWC and Z2A have trace quantities of U, Th, Ca, and Pb. However, the U and Pb are frequently at detection limits (0.02 weight % U, 0.01 weight % Pb). The Mg and Al contents are minimal; they’re at detection limits of the EMP (0.005 weight % Mg or Al). Similarly, the Eu contents are low, to the point of being near the detection limits of the EMP (0.06 weight % Eu), contrary to the other REE. The Ca content is not significant enough to indicate a major solid solution with datolite, but enough to be of note. Including Ca and Th, into the total atoms for the A-site yields a total that is in slight excess of 2 apfu. For this to be possible, some of the ions must be present in another structural site, potentially the M-site substituting for Fe. There is indication that there is a slight excess of silica in the gadolinite, especially in sample Z2A (considering the XRD data). Although the EMP is unable to analyze Be, the XRD shows variation in the Be contents of the gadolinite between samples SWC and Z2A. In the EMP data, a total of four Be + Si per formula unit seems most likely and is consistent with the XRD data.
Rare Earth Element Distribution
Sample SWC displays a larger range of REE compositions than sample Z2A, and is more enriched in LREE. The low density regions seen in BEI tend to be enriched in HREE and Y, while the higher density regions are enriched in LREE. Although HREE are denser than LREE, the Y content brings the overall density below that of the LREE rich areas. There is only very minor overlap in REE distribution between the two samples; they are overall quite different.
When chondrite normalized, the REE contents of the gadolinite have slight slopes seen in Figure 39
17 (chondrite values from McDonough and Sun, 1995). Chondrite normalized values may vary by a single order of magnitude between LREE and HREE in a single specimen, as opposed to two to three orders of magnitude variation as is seen in thalénite (Raschke et al., 2017).
The REE distribution in sample SWC is remarkably similar to that of the REE rich zone in the whole rock (Figure 17a, 19). The whole rock data in Figure 19 depicts the REE evolution of the White Cloud Pegmatite, from the Pikes Peak granite with low REE values and a moderate negative Eu anomaly, through the REE enriched zone with orders of magnitude more REE than the granite. However, unlike traditional fractionation patterns, in which each phase of crystallization becomes more enriched in incompatible elements such as REE, the transition zone and the graphic granite are depleted in REE compared to the granite. This is not out of the ordinary for a highly fractionated pegmatite however; the REE partitioned further into the final fluid, and the quartz, feldspar, and mica rich zones excluded the REE. The graphic granite has a slight positive Eu anomaly, expected for rocks rich in feldspars. Similarly, the transition zone has no Eu anomaly, as it has only moderate amounts of feldspar to hold Eu, but not enough other minerals that exclude it. There is a slight increase in Ce, which could indicate that this zone has experienced an oxidizing alteration event at some point in its history.
The majority of the REE got concentrated in the final stages: the REE zone. This is the section that has a similar enrichment pattern to gadolinite SWC on average (Figure 11a). The
LREE are fairly flat-lined, with a negative Eu anomaly, and a nearly flat pattern in the HREE with a minor dip in Y. The similarity between the REE rich zone and sample SWC could indicate that SWC crystallized early from the REE rich fluid, and was able to take proportionate quantities of REE. Z2A however shows a depletion in the LREE compared to the HREE (Figure
11b). Although SWC may have been controlled by the original fluid, Z2A shows that there could 40 be a later stage of crystallization, in which LREE have been crystallized previously, enriching the remaining fluid in HREE. Another possible cause for the different compositions is variability in available resources due to the coexistence and crystallization of other REE minerals such as allanite or monazite, which would cause partitioning of the REE.
Another anomaly of this pegmatite is that there are two distinct members of the gadolinite series at a single locality. Other localities, such as gadolinite-(Y) from the Alps (DeMartin et al.,
1993), gadolinite-(Y) from Vico Italy (Cámara et al., 2008), gadolinite-(Nd) from the Malmkärra mine in Sweden (Škoda et al., 2017), and gadolinite-(Ce) from Skien Norway (Segalstad and
Larsen, 1978), do not display significant variation in a single location. However, these locations are also quite different than that of the White Cloud Pegmatite. Of those locations, only the gadolinite-(Ce) from Norway is within a pegmatite, but it is a syenite pegmatite emplaced as a vein within basalt. The samples from Vico Italy are volcanic in origin, with drastically different chemistry (high Li, U, Th, Ca, B, F, and even Mn). The gadolinite-(Nd) is derived from a
Bastnäs-type skarn deposit, formed with felsic metavolcanic rocks and interlayered marble
(Škoda et al., 2017). Some of the samples from the Alps were from fissures, and others from pegmatites (although the study was not specific about type of granite). The White Cloud
Pegmatite on the other hand, is emplaced within the A-type granite of the Pikes Peak Batholith, and almost certainly derived from the granitic magma (either by a fractionation process, or a subset of the magma with excess fluxing agents such as fluorine). Therefore, due to their geochemical environments, it reasonable to expect that the gadolinite from previous studies would have different chemistry than that of the White Cloud Pegmatite.
The REE exchange easily with the substitution of LREE ↔ HREE, Y; SWC is clearly
LREE rich compared to Z2A, although is variable in composition. Sample Z2A is consistently 41
HREE rich (Figure 17b, 18). Additionally, the gadolinite of the White Cloud Pegmatite follows trends regarding the yttrium and REE distribution, separating the yttrium from the REE.
1000000
100000
Sample/Chondrite 10000
17a 1000 La Ce Pr Nd Sm Eu Gd Tb Dy Y Ho Er Tm Yb Lu 1000000
100000
Sample/Chondrite 10000
17b 1000 La Ce Pr Nd Sm Eu Gd Tb Dy Y Ho Er Tm Yb Lu
Figure 17. Chondrite normalized REE distribution for samples SWC and Z2A with EMP data. Figure 11a displays SWC data. Figure 11b displays Z2A data. Lines selected for minimum Ce, maximum Ce, and average values. Weight% Sample/Weight% Chondrite. Chondrite values from McDonough and Sun 1995. SWC points are blue; Z2A points are orange. Minimum Ce lines are light, maximum Ce lines are medium, average lines are dark. 42
2
1.8
1.6
1.4
1.2
1
0.8 SUM SUM + Y HREE(apfu)
0.6
0.4
0.2
0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 SUM LREE (apfu)
Figure 18. Sum Y + HREE vs Sum LREE. There is a clear 1:1 linear correlation, as all cations occupy the A-site. SWC points are in blue. Z2A points are in orange. 43
100000
10000
1000
100 Sample/Chondrite
10
1 La Ce Pr Nd Sm Eu Gd Tb Dy Y Ho Er Tm Yb Lu
Figure 19. Whole rock chondrite normalized REE distribution. Weight% Sample/Weight% Chondrite. Chondrite values from McDonough and Sun 1995. Blue: REE rich zones. Reds: host Pikes Peak granite. Gold: graphic granite-pegmatite transition zone. Green: graphic granite. Yttrium increases alongside the HREE, and against the LREE, and increases as a percentage of the HREE + Y total, seen in Figure 20. This ratio increases at approximately the same rate for both samples SWC and Z2A, but each sample has a different starting point; they do not grade into each other like what is seen for overall Y+REE distribution. If the crystals formed sequentially from the same fluid, a smooth transition from SWC points to Z2A points would be expected; this is not seen. This may be evidence that the crystals started forming within different fluids, and/or alongside a different set of minerals, but with the similar Y and HREE distribution patterns.
44
0.85
0.8
0.75
0.7
0.65 Y/(HREE+Y) 0.6
0.55
0.5
0.45 0.2 0.4 0.6 0.8 1 1.2 1.4 Y (apfu) . Figure 20. Y/(HREE+Y) vs. Y. SWC points are blue; Z2A points are orange. Two parallel but discontinuous trends are observed for the two samples. Occupancy of A and M Cation Sites
From the EMPA data, sample SWC contains between 0.804 and 0.914 apfu iron, and
Z2A contains between 0.934-0.938 apfu iron (Table 11). The XRD data confirms this: SWC has
0.871 apfu iron, and Z2A has 0.966 apfu of iron (Table 7). Baćík et al., 2014 noticed a similar trend; smaller cations (such as HREE) in the A-site preferentially take Fe in the M-site, but samples with larger cations (LREE) in the A-site are more prone to M-site vacancies. In sample
SWC, the regions with more LREE are also the regions with lower Fe per formula unit (Table 9,
Figure 21). Additionally, there is a slight increase in Ca and Th with a decrease in Fe (Figures
22, 23), indicating that these cations may be able to substitute into the M-site in small quantities. 45
1
0.95
0.9
0.85 Fe Fe (apfu)
0.8
0.75 0 0.15 0.3 0.45 0.6 0.75 0.9 1.05 1.2 1.35 1.5 Sum LREE (apfu) Figure 21. Fe vs. total LREE. SWC points are blue; Z2A points are orange. Although one point is errant, the overall trends are consistent. Less iron correlates with greater LREE.
0.03
0.025
0.02
0.015 Ca (apfu) Ca
0.01
0.005
0 0.75 0.8 0.85 0.9 0.95 1 Fe (apfu)
Figure 22. Trace amounts of Ca vs. Fe. There is a generic, but not ideal trend of Ca increasing as Fe decreases. SWC points are blue; Z2A points are orange. 46
0.012
0.01
0.008
0.006 Th (apfu) Th
0.004
0.002
0 0.75 0.8 0.85 0.9 0.95 1 Fe (apfu)
Figure 23. Trace amounts of Th vs. Fe. There is a generic, but not ideal trend of Th increasing as Fe decreases. SWC points are blue; Z2A points are orange. When plausible A-site cations are summed (REE, Y, Ca, Th), the total is frequently greater than 2 apfu. There could be limited substitution of cations that belong in the larger A-site into the M-site vacancies, since the volume of the M-site increases with lower Fe, and higher
LREE content. SWC has an A-site polyhedral volume of 26.7(4) Å3, and Z2A has an A-site polyhedral size of 24.9(2) Å3; SWC has an M-site polyhedral size of 13.5(2) Å3, and Z2A has an
M-site polyhedral size of 12.9(1) Å3 (Table 4a). The majority of points have approximately 0.05
- 0.15 apfu M-site vacancy (0.85 – 0.95 apfu Fe), and 2.00 - 2.05 apfu excess A-site cations
(Figure 24). There are likely limited substitutions of A-site cations that prefer 8-fold coordination in the 6-fold coordinated M-site, such as Ca and Th. This is true in the case of minasgeraisite,
M 2+ M 2+ REE2CaBe2Si2O8, where Ca can occupy the M-site, via the exchange Fe ↔ Ca , although this mineral is contentious in structure refinements of its pure form (Baćík et al., 2017). 47
1
0.95
0.9 Fe Fe (apfu) 0.85
0.8
0.75 1.96 1.98 2 2.02 2.04 2.06 2.08 2.1
REE+Th+Ca (apfu) Figure 24. M-site cation (Fe) vs. A-site cations (REE, Y, Th, Ca). SWC points are blue; Z2A points are orange.
Presence of Hydroxyl at the ϕ-Site In the absence of iron (and presence of hydroxyl at the ϕ-site), a solid solution with hingganite is formed via the exchange MFe+2 + ϕ2O-2 ↔ M□ + ϕ2OH-1. However, there is evidence against this for samples SWC and Z2A. Significantly, the Raman spectra (Figure 9). do not indicate any OH stretching bands at 3500 cm-1 for either SWC or Z2A. If OH was present, the spectra should show some sharp peaks near 3500 cm-1, similar to that seen in the infrared spectroscopy of Cámara et al., 2008 for which OH bands are distinctly present, and OH comprises 0.29 apfu of the ϕ-site. Škoda et al., 2017 documented a small OH peak at 3500 cm -1 in gadolinite-(Nd) with 0.337 apfu of OH in their specimen Instead, our spectra are nearly flat in that region. The XRD refinement was successfully modeled by assuming 10 O per formula unit. 48
Although our Raman spectra is indistinct, it is as good as others on the RRUFF database for gadolinite, and it should be trusted in regards to OH. This poses a dilemma, as vacancy in the M- site decreasing the cation charge must be balanced with hydroxyl (or fluorine) in the ϕ-site, or the structure must accommodate additional charge into the A, Q, or T-sites. One possible exchange for this to occur could be MFe2+ + QBe2+ ↔ M□ + QSi4+, in which case Be is removed from the Q-site in favor of Si; this is seen in the XRD refinement of sample Z2A.
The total cation charges for the average sample values were calculated under two different conditions: EMPA data only (assuming Be + Si = 4 apfu, after normalizing to 10 O), and XRD data with REE from the EMPA (Tables 10, 11). The total cations are near +20, indicating that if there is hydroxyl present, it is in low quantities. The best charge balance method available to this study, with our methods, comes from the EMPA data, assuming 4 apfu total of Be and Si; each calculation is below 3% difference from the +20 total cation charge needed to balance -20 total anion charge from 10 O. The combination of the charge balance, strong XRD structure refinement, and the lack of an OH band in the Raman spectra leads to the conclusion that the gadolinite of the White Cloud Pegmatite has minimal, if any, hydroxyl in the
ϕ-site.
The total cation charge of sample SWC tends to be slightly lower than that for Z2A; sample SWC is the one with lower Fe per formula unit, more M-site vacancies, therefore should ideally have some hydroxyl (or fluorine) ions to counter the loss of the +2 cations. However, the
Raman spectroscopy rules out significant hydroxyl. Another option potentially is that some of the Fe in the M-site is actually Fe3+, although this is unlikely considering past studies have disproven significant Fe3+ for gadolinite; the closest mineral from the supergroup with a Fe3+ charge in the M-site is drugmanite (Baćík et al., 2017). To charge balance these, approximately 49
0.21 apfu of F or OH would be required in the ϕ-site for sample SWC, in the high density region.
This quantity of OH would show up in a Raman spectrum, and we do not have the means to analyze for fluorine in this study.
Table 10. Total cation charge with EMPA data. Sample Set Cation Charge from EMPA data, Be + Si = 4 apfu SWC Low Density Average +19.91
SWC High Density Average +19.79 SWC Average +19.88 SWC Grain Mount Average +19.94 SWC High Density Grain +19.82 Mount Average Z2A Low Density Average +19.94 Z2A High Density Average +19.94 Z2A Average +19.94 SWC and Z2A high and low density averages, and overall averages are included to show the possible range of compositions. REE and Y calculated with +3 charge, U and Th with +4, Fe and Ca and Be with +2, and Si with +4. Table 11. Total cation charge with XRD data Sample Cation Charge from XRD SWC +19.6 ± 0.4 Z2A +20.3 ± 0.5
EMPA data used for REE+Y in the A-site. Errors estimated using refined occupancy.
Be-Si Disorder Sample SWC is, to our knowledge, the first significant documented case of Be-Si disorder in a mineral from XRD structural refinement. Sample Z2A may have Be-Si disorder, however the error margins make this unassured. The Q-site of sample SWC has 88(2)% Be and
12(2)% Si, while the T-site has 86(2)% Si and 15(2)% Be. Sample Z2A only has significant disorder in Si; the Q-site has 90(1)% Be and 10(1)% Si, and the T-site has 99(1)% Si but 2(1)%
Be (Table 7); this puts sample Z2A over 2 apfu Si. At minimum, sample SWC has 13% 50 occupancy of Be in the T-site, which should be occupied fully by Si, proving that Be can exist in an Si tetrahedra.
The Q and T-site tetrahedra are nearly identical in size, therefore by volume and bond lengths they are fit for ionic substitutions (Tables 4b). The Q-site of sample SWC has a tetrahedral volume of 2.30 Å3, and 2.22 Å3 for sample Z2A; The T-site of sample SWC has a volume of 2.24 Å3 and 2.20 Å3 for Z2A.
The Raman spectra of our samples (Figure 16) shows another line of evidence. Sample
Z2A displays sharp peaks for the Be-O and Si-O bonds; SWC does not, and is the sample with disorder. The shallower and broader peaks displayed by sample SWC at 904 and 981 cm-1 could be due to the disorder between Si and Be.
There may be slight excess Si in both samples according to the EMPA and XRD data.
From the EMPA data (Table 9), SWC has a range of Si from 2.004 to 2.035 apfu, and Z2A ranges from 2.003 to 2.009 apfu. From the XRD data (Table 7), sample Z2A has 2.16 apfu Si, and 1.84 apfu Be (the extra Si is in the Q-site instead of Be). Sample SWC however has 2.06 Be, and 1.96 apfu Si. This would benefit from further analysis, such as by a comparison with a measurement using mass spectroscopy.
Tetrahedral Rings and Structural Variability
The Q-site with Be, and T-site with Si, form oval rings of alternating Q and T tetrahedra, seen in Figure 3. In these oval rings there are four Q-site tetrahedra occupied primarily by Be, alternating with four T-site tetrahedra containing mostly Si, with Si at the far ends of the rings and across from each other widthwise. These oval rings connect to form smaller rings of two Q- 51 site and two T-site tetrahedra. Depending on the contents of each site in the gadolinite group, the
8-member oval rings can distort relative to the unit cell parameters (Table 3).
The Si-Si long and short distances in the tetrahedral rings are calculated from the unit cell parameters and atomic coordinates (Tables 3, 5, 6), as done by Baćík et al., 2014 (Table 12). The findings of Baćík et al., 2014 indicate that the long Si-Si distance is correlated to the occupancy of the T-site, but the short Si-Si distance correlates most with the occupancy of the A and M- sites.
Our findings for sample Z2A are similar to the results of Baćík et al., 2014; there is an expansion of the tetrahedral ring width with variation in the b lattice parameter (Figure 25). We expect the sample with higher LREE content and more M-site vacancies, such as sample SWC to have more tetrahedral ring width expansion, which is seen, but not to the trend of Baćík et al.,
2014. Sample SWC has an Si-Si Short ring length more similar to those of their hingganite samples (longer than gadolinite), and a drastically larger b length than predicted. This large b length could be due to the high LREE content, as suggested by Baćík et al., 2014, but perhaps also in part due to the structural disorder between Si and Be in the Q and T-sites.
When comparing the c-axis length to the Si-Si Long ring length, our results show that both parameters are considerably longer than any of the samples from Baćík et al., 2014, but do fall along their trendline (Figure 26). The LREE rich SWC is larger, as is expected, but sample
Z2A is also of relatively large size. Neither are distorted significantly in regards to the c axis and the Si-Si Long ring length.
A comparison of the tetrahedral rings long and short distances reveals that the rings of
SWC are perturbed (Figure 27), but sample Z2A is consistently similar to the gadolinite-(Y) 52 sample from Baćík et al., 2014. This could be due to the Be-Si disorder in SWC, or due to excess
A-site cations extending the short Si-Si ring distance and b-axis length. Since these are the primary differences between sample SWC and previously documented gadolinite, it is plausible that the Be-Si disorder and/or excess A-site cations cause the enlarged tetrahedral ring width.
Variations in sample Z2A from those studied by Baćík et al., 2014 can likely be attributed to the mixed REE content or excess silica; it is extremely similar to their gadolinite-(Y) samples, but with slightly large cell parameters. The excess Si in the Q-site of Z2A is less likely to be the cause of distortion of the tetrahedral rings as the disordering of both Si and Be between the Q and T-sites.
The layered nature of the structure allows a variety of REE to enter into the A-site.
However, LREEs contribute to the expansion of the unit cell, and the M-site. The larger M-site is more prone to vacancies than smaller HREE end members. Additionally, the layer expansion is reflected in the b-axis and tetrahedral ring width expansion.
Table 12. Si-Si long and short distances in the tetrahedral rings for gadolinite SWC and Z2A. Sample Si-Si Long (Å) Si-Si Short (Å) SWC 9.59(3) 3.82(1) Z2A 9.45(2) 3.69(1) Errors estimated from the uncertainty in unit cell axes and the atomic coordinates.
53
7.75 SWC
7.7 Z2A
7.65 Bacik
Å Gadolinite-(Y) b 7.6 Bacik Hingganite-(Y)
7.55 Bacik Hingganite- (Ce) 7.5 3.65 3.7 3.75 3.8 3.85 3.9 3.95 4 Si-Si Short Å Figure 25. b lattice parameter vs. Si-Si Short tetrahedral ring distance. This is compared to gadolinite subgroup minerals and trend from Baćík et al., 2014.
10.2 SWC 10.1
10 Z2A
9.9
Å Bacik c Gadolinite-(Y) 9.8
Bacik 9.7 Hingganite-(Y)
9.6 Bacik Hingganite-(Ce) 9.5 8.8 8.9 9 9.1 9.2 9.3 9.4 9.5 9.6 9.7 Si-Si long Å Figure 26. c lattice parameter vs. Si-Si Long tetrahedral ring distance. This is compared to gadolinite subgroup minerals and trend from Baćík et al., 2014. 54
9.7 SWC 9.6
9.5 Z2A 9.4
Å 9.3 Bacik Gadolinite-(Y)
9.2
Si Si Long
- Si 9.1 Bacik Hingganite-(Y) 9 Bacik 8.9 Hingganite-(Ce)
8.8 3.65 3.7 3.75 3.8 3.85 3.9 3.95 4 Si-Si Short Å Figure 27. Si-Si Long vs. Si-Si Short tetrahedral ring distances. This is compared to gadolinite subgroup minerals and trend from Baćík et al., 2014.
In addition to the enlargement of the tetrahedral ring width, Be-Si disorder, higher LREE content, and partial M-site vacancies, sample SWC also has the largest unit cell volume of documented gadolinite at 380.94 Å3 (Table 3, 10). The previous record holder is a gadolinite-
(Nd) with a unit cell volume of 376.2 Å3, studied by Škoda et al., 2016. LREE dominant gadolinite is expected to have the largest unit cell volume, however, based on sample SWC and the gadolinite-(Nd) studied by Škoda et al., 2016, a variable or mid-size REE likely causes the largest unit cell size instead. Škoda et al., 2016 also noted up to ~5% disorder between Be and Si in the Q and T-sites. The structural disorder could contribute to the enlarged unit cell volume in addition to the expansion of the width of the tetrahedral rings, explaining the large unit cell volumes. Sample Z2A has a large unit cell, but not anomalously so like sample SWC; the unit cell volume of Z2A is 361.751Å3, which is comparable the gadolinite-(Ce) documented by 55
Segalstad & Larsen, 1978 (360.7 Å3), and similar to the gadolinite-(Y) documented by Cámara et al., 2008 from Vico, Italy (360.0 Å3).
Lack of Metamictization
Due to the possible inclusion of radioactive elements U and Th into the A-site, gadolinite can become metamict as they decay over time. Therefore, the U, Th, and Pb content of gadolinite must be analyzed; at sufficient quantities and older ages, they damage the structure of the host mineral. Pezzota et al., 1999 reported metamict gadolinite-(Y) from Baveno, Italy, with up to
0.04 apfu Th, in a 277 ± 8 Ma pluton. These specimens are both more radioactive and younger than specimens at the White Cloud Pegmatite. However, samples from Vico, Italy, analyzed by
Cámara et al., 2008, have a significant quantity of U and Th (0.132 apfu Th, and 0.024 apfu U).
These samples are young at ~150 k.y so they have not yet become metamict.
The specimens from the White Cloud Pegmatite are old; 1.08 Ga assuming they are of the same age as the Pikes Peak Batholith. They have very low concentrations of U, Th, and their decay product, Pb (U and Pb near detection limits, Th up to 0.009 apfu, Table 9). This is an order of magnitude lower than quantities found at Baveno, and two orders of magnitude less than at
Vico. These radioactive elements are insufficient to create significant metamictization. In addition, the XRD structural refinements were a success to an R of 0.049 for SWC and 0.053 for
Z2A. These are excellent refinements for a chemically complex structure, and far better than would occur for a metamict sample.
A comparison of powder diffraction analyses of metamict samples to annealed and recrystallized samples of gadolinite by Gibson and Ehlmann (1970) demonstrates that the metamict samples have poor diffraction patterns, while crystallized forms show defined peaks. 56
Typically, poor Raman spectra are also an indication of metamictization. However, based on the available spectra from the RRUFF database, gadolinite does not have strong spectra even while
XRD structure refinements are strong. A Raman spectrum without many sharp peaks is not indicative of a metamict sample of gadolinite. Therefore, the gadolinite of the White Cloud
Pegmatite does not appear to have sufficient radiation damage to affect the refinements.
Best Chemical Formula
Due to the complex chemistry of gadolinite, attention must be paid to the complete chemical formula. This study normalized the chemical formula to 10 O per formula unit. The
XRD refinement successfully used 10 O per formula unit. The Raman spectra (Figure 9) yields no indication of hydroxyl anions in the ϕ-site. The cations are very close to charge balanced
(Table 10), assuming 4 Be + Si per formula unit. Additionally, it is wrong to normalize based off the assumption that there are 2 Si per formula unit, as this is disproven by the XRD refinement of
Z2A which has excess Si. It is also incorrect for our analysis to normalize to 2 Be per formula unit, as they may be depleted, and we are unable to directly analyze this cation with EMPA. The total of Si and Be is most likely 4 apfu due to structural constraints, but this assumption is not ideal for normalization unless the Be content is proven by another method. One cannot normalize to 1 M-site cation as the M-site is commonly vacant.
There is a chance that there is F in the ϕ-site, but high quantities of F are unlikely here due to the charge balance to +20 within error estimates. Hydroxyl is unlikely due to the lack of an OH band in the Raman spectra. The gadolinite group and subgroup minerals do not typically
-1 involve F in the ϕ-site, however, herderite subgroup minerals do (herderite: Ca2□Be2P2O8F2).
This is most plausible for sample SWC, which has a calculated cation charge below +20 (EMPA 57 data, Table 12) per 10 anions. Further analysis (such as by laser ablation mass spectrometry, or secondary ion mass spectrometry) would be needed to discover if the error margins in the charge balance are due to small amounts of hydroxyl or F-1 ions.
With strong charge balance, the inability to normalize on the basis of A or M-site cations, structural refinements negative normalization to Q or T-site cations, and strong refinements with
10 O, 10 O are used for normalization. The best chemical formula available to this study is given by the EMPA, normalizing to 10 oxygen per formula unit, followed by assuming 4 Be + Si per formula unit (Table 9). By atoms per formula unit, sample SWC should be called gadolinite-(Y) typically, as it has 0.564 apfu Y which is greater than the Ce (0.444 apfu). However, the sample on average is also just barely LREE dominant, with 1.004 apfu total of LREE, versus 0.980 apfu
HREE + Y. However, it does have regions which are Ce dominant, such as the dense zones of the grain mount (0.63 apfu Ce, and 0.345 apfu Y; 0.682 apfu HREE + Y, 1.313 apfu LREE).
Sample Z2A is clearly a gadolinite-(Y) as it is consistently Y dominant (1.072 apfu Y average), and has more HREE (1.647 apfu HREE average) than LREE (0.344 apfu LREE average). REE variability in Z2A is much more minor than that in SWC, although it does have variable Y content. To demonstrate Ce vs Y dominance in the two samples, Ce has been plotted against Y in
Figure 28. SWC is typically Y dominant, despite the LREE content, but there is a distinct portion with Ce dominance. Z2A is always Y dominant. 58
0.7
0.6
0.5
0.4
Ce Ce (apfu) 0.3
0.2
0.1
0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 Y (apfu)
Figure 28. Ce vs. Y in samples SWC and Z2A. SWC has both Ce and Y dominant zones. Z2A is always Y dominant. EMP data used. SWC in blue; Z2A in orange.
59
Table 13. Best chemical formulas for gadolinite samples SWC and Z2A. SWC Gadolinite-(Y) (Low Density Average)
(Y0.819, La0.120, Ce0.353, Pr0.052, Nd0.209, Sm0.056, Eu0.002, Gd0.048, Tb0.011, Dy0.082, Ho0.015, Er0.068, Tm0.015, Yb0.138,
Lu0.021, Ca0.018, Th0.003)2.031 Fe0.914 Be1.996 Si2.004 O10
SWC Gadolinite-(Y) (High Density Average)
(Y0.574, La0.114, Ce0.470, Pr0.071, Nd0.282, Sm0.076, Eu0.002, Gd0.061, Tb0.014, Dy0.097, Ho0.017, Er0.071, Tm0.014, Yb0.119,
Lu0.016, Ca0.013, Th0.005)2.015 Fe0.889 Be1.966 Si2.034 O10
SWC Gadolinite-(Y) (Grain Mount Average)
(Y0.520, La0.092, Ce0.436, Pr0.079, Nd0.339, Sm0.097, Eu0.002, Gd0.073, Tb0.016, Dy0.111, Ho0.019, Er0.074, Tm0.014, Yb0.115,
Lu0.014, Ca0.018, Th0.006)2.010 Fe0.890 Be1.965 Si2.035 O10
SWC Gadolinite-(Ce) (High Density Grain Mount Average)
(Y0.345, La0.149, Ce0.632, Pr0.092, Nd0.351, Sm0.087, Eu0.002, Gd0.064, Tb0.014, Dy0.090, Ho0.014, Er0.056, Tm0.010, Yb0.081,
Lu0.008, Ca0.024, Th0.008)2.026 Fe0.804 Be1.940 Si2.060 O10
SWC Gadolinite Average
(Y0.564, La0.092, Ce0.444, Pr0.074, Nd0.307, Sm0.086, Eu0.002, Gd0.066, Tb0.015, Dy0.105, Ho0.018, Er0.074, Tm0.014, Yb0.121,
Lu0.016, Ca0.019, Th0.006)2.022 Fe0.894 Be1.982 Si2.018 O10
Z2A Gadolinite-(Y) (Low Density Average)
(Y1.257, La0.009, Ce0.068, Pr0.018, Nd0.130, Sm0.063, Eu0.002, Gd0.071, Tb0.015, Dy0.108, Ho0.022, Er0.087, Tm0.015, Yb0.125,
Lu0.018, Ca0.011, Th0.001)2.02 Fe0.938 Be1.991 Si2.009 O10
Z2A Gadolinite-(Y) (High Density Average)
(Y0.970, La0.007, Ce0.063, Pr0.019, Nd0.171, Sm0.113, Eu0.002, Gd0.129, Tb0.028, Dy0.190, Ho0.035, Er0.120, Tm0.019, Yb0.132,
Lu0.015, Ca0.009)2.02 Fe0.934 Be1.997 Si2.003 O10
Z2A Gadolinite-(Y) Average
(Y1.072, La0.007, Ce0.064, Pr0.018, Nd0.156, Sm0.096, Eu0.002, Gd0.109, Tb0.023, Dy0.162, Ho0.030, Er0.108, Tm0.018, Yb0.129,
Lu0.016, Ca0.010)2.02 Fe0.937 Be1.996 Si2.004 O10
This is calculated from EMPA data set collected with a carbon coating. This was normalized to 10 O per formula unit, and assumes Be + Si = 4 apfu. Multiple compositions are given to demonstrate the range in each specimen. 60
Comparison with Allanite and Thalénite
Allanite and thalénite are both prominent REE minerals coexisting with gadolinite in the
White Cloud Pegmatite. The allanite is enriched in LREE compared to both gadolinite specimens, and only displays minor variation between samples SWC and Z2A (Figure 29). In a chondrite normalized plot, both samples display a minimum at Y, and then a minor increase through the HREE after the minimum at Y (Figure 29). The allanite has a strong preference for the LREE, while the gadolinite displays variability in its REE distribution at the White Cloud
Pegmatite. The allanite is likely to be one of the minerals that took LREE out of the crystallizing fluid, and since gadolinite has more structural flexibility, it could form with a range of mixes of
LREE and HREE that are left over.
1000000
100000
10000
1000 Sample/Chondrite 100
10
1 La Ce Pr Nd Sm Eu Gd Tb Dy Y Ho Er Tm Yb
Figure 29. Chondrite normalized REE distribution for allanite adjacent to gadolinite in samples SWC and Z2A. EMP data used, average values displayed. Weight% Sample/Weight% Chondrite. Chondrite values from McDonough and Sun 1995. SWC in blue; Z2A in orange. While the allanite is enriched in LREE, the thalénite from the White Cloud Pegmatite analyzed by Raschke et al., 2018 is strongly enriched in HREE, it does not have an Eu anomaly 61 like the gadolinite and allanite. It is more strongly enriched in HREE than sample Z2A, and much more enriched than sample SWC. Raschke et al., 2018 postulate that the thalénite formed under multiple generations of crystallization, ranging from late-magmatic to hydrothermal phases in the pegmatite, with fluid driven alteration and localized REE remobilization and after the Be was depleted (thus ending formation of gadolinite). This is consistent with Z2A crystallizing later than SWC, and before the formation of thalénite. Sample SWC is LREE enriched and would have formed before sample Z2A, perhaps with the LREE enriched allanite, before the thalénite.
Phases of Crystallization
Based on the different chemistries of samples SWC and Z2A, it is clear that gadolinite can form with extremely variable REE content, unlike allanite or thalénite which are preferential to LREE and HREE respectively. This indicates that gadolinite chemistry is at the mercy of the fluid it forms from and the minerals forming in conjunction with it, which may have more rigid structures than the flexible gadolinite structure.
Since the chondrite normalized plots of the whole rock REE zone and sample SWC are similar (Figures 18a, 19), sample SWC likely formed from the bulk fluid early in the crystallization of the zone, taking an assortment of REE as they were available. Sample Z2A likely formed after the LREE were consumed by other minerals. This is consistent with EDS analyses and BEI images of multiple minerals in these thin sections; LREE dominant minerals tended to make up the cores of grains, but HREE dominant minerals are usually observed on the rims of grains, indicating that LREE minerals formed before HREE minerals. 62
Once all Be is consumed, crystallization of gadolinite should halt. From the XRD analysis, the HREE enriched sample Z2A likely has excess Si and a depletion in Be. The depletion in Be seen in sample Z2A could be due to formation with very little Be remaining, coinciding with HREE enrichment. Since it is possible to have Si in the Q-site, crystallization could have continued beyond total Be consumption to a limited degree.
Figure 20 shows that the fluid in the White Cloud Pegmatite has likely undergone multiple stages of evolution that changed the Y/HREE proportions of the fluid, along with the
LREE vs HREE proportions. The comparison of Y to HREE is not a continuous transition from sample SWC to sample Z2A, which would be expected for continuous fluid evolution. It is entirely logical for Y/HREE to increase with Y, which is observed.
The combination of evidence from variable chemistry, Be depletion with HREE enrichment, and discontinuous Y/HREE distribution leads to the conclusion that the White Cloud
Pegmatite experienced at minimum two episodes of gadolinite crystallization, and three episodes of fluids and crystallization of non-gadolinite minerals (two of which occurred with gadolinite: the original fluid which formed SWC which had a mixture of LREE and HREE and crystallized more LREE, an episode of fluid and crystallization without gadolinite that lowered the Y/HREE, and an episode depleted in LREE and Be but enriched in HREE which formed sample Z2A.
63
Chapter 5: Conclusion
The Search for Be
The disorder of Be into the T-site site indicates that Be can substitute into Si tetrahedra, and could be present in more than only gadolinite minerals, due to the prevalence of Si in tetrahedral coordination in minerals of the crust and upper mantle. As silicates make up the vast majority of Earth’s crust, this opens up a world of potential hiding spots for Be. If Be is capable of substituting into common Si, or even potentially Al, tetrahedra, it could be present in most rock forming minerals. Additionally, disorder could be found in other Be-silicates, such as phenakite, beryl, and euclase (euclase specifically shares a space group with gadolinite). Since
Be is an uncommon element, and one that is not commonly analyzed, its geochemical significance and overall abundance may not be fully recognized. This presents an opportunity for future research.
REE and Variable Chemical and Structural Parameters
The gadolinite of the White Cloud Pegmatite is chemically variable and structurally flexible. The variability in REE content between the two samples is drastic, reflecting the changing chemistry during REE crystallization. The gadolinite in the White Cloud Pegmatite ranges from gadolinite-(Ce) which likely formed earlier in the crystallization of the REE zone, and gadolinite-(Y) which likely formed after the LREE were consumed by other minerals.
These specimens are also unique in that they have M-site vacancies without significant evidence of hydroxyl in the ϕ-site, indicating that the structure can possibly accommodate cations that prefer the 8-fold coordination of the A-site in the 6-fold coordinated M-site to maintain charge balance. Higher abundance of LREE contributes to the stretching of the 64 structure, stretching the unit cell and the A and M-site polyhedral layer, expanding the tetrahedral rings. The disordering of Be and Si in the Q and T-sites could contribute to the tetrahedral ring width expansion. This, combined with high LREE content and M-site vacancies could explain the enlarged unit cell of sample SWC compared to previously studied gadolinite.
Lastly, the overabundance of Si in Z2A sheds doubt on the assumption that gadolinite minerals are restricted to 2 Si per formula unit.
65
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70
Appendix
Appendix 1a. Elemental weight percentages from EMP. SWC Region 1, central midgray; SWC grain top right; SWC grain left edge bright. Rows continued in 1b.
SA M P LE Y WT% Si WT% Th WT% U WT% Ca WT% Pb WT% La WT% Ce WT% Nd WT% Pr WT% Sm WT% Tb WT% Eu WT% SWC001 region 1 central midgray run 1 8.695 9.925 0.306 0.032 0.175 0.004 1.301 9.845 8.993 1.983 2.686 0.475 0.090 SWC001 region 1 central midgray run 1 9.438 9.925 0.312 0.045 0.149 0.003 1.113 9.038 8.630 1.881 2.715 0.538 0.034 SWC001 region 1 central midgray run 1 9.416 9.917 0.227 0.029 0.143 0.005 1.147 8.990 8.410 1.805 2.566 0.477 0.040 SWC001 region 1 central midgray run 1 9.482 9.982 0.241 0.023 0.133 0.006 1.098 8.887 8.316 1.876 2.685 0.474 0.061 SWC001 region 1 central midgray run 1 10.189 10.122 0.236 0.076 0.140 0.004 1.058 8.474 8.166 1.790 2.577 0.497 0.119 SWC001 region 1 central midgray run 2 8.653 10.116 0.306 0.039 0.169 0.002 1.251 10.050 9.056 2.077 2.807 0.464 0.049 SWC001 region 1 central midgray run 2 9.750 10.008 0.277 0.048 0.151 0.000 1.054 8.497 8.381 1.815 2.683 0.491 0.035 SWC001 region 1 central midgray run 2 9.458 9.989 0.235 0.049 0.139 0.001 1.138 8.680 8.548 1.776 2.689 0.479 0.074 SWC001 region 1 central midgray run 2 9.481 10.023 0.270 0.031 0.137 -0.004 1.152 9.149 8.252 1.849 2.490 0.478 0.017 SWC001 region 1 central midgray run 2 9.901 9.971 0.222 0.083 0.140 0.013 1.053 8.671 8.239 1.788 2.554 0.486 0.077
SWC001 grain top right 7.365 10.102 0.321 0.021 0.092 0.000 2.654 13.359 8.800 2.190 2.348 0.360 0.064
SWC001 grain top right 7.978 10.004 0.277 0.011 0.099 0.000 1.982 11.754 9.073 2.106 2.629 0.431 0.024
SWC001 grain top right 8.993 9.937 0.374 0.022 0.152 0.000 0.811 7.915 8.626 1.743 2.987 0.599 0.044 SWC001 grain left edge bright 5.481 10.183 0.261 0.003 0.168 -0.004 3.710 15.892 8.772 2.320 2.299 0.398 0.020 SWC001 grain left edge bright 2 5.543 10.080 0.285 -0.025 0.163 0.005 3.815 15.686 8.694 2.321 2.127 0.357 0.049 SWC001 grain left edge bright 3 5.494 10.133 0.286 -0.004 0.178 -0.017 3.719 15.637 8.764 2.221 2.206 0.414 0.068 SWC001 grain far left edge bright 1 5.292 10.206 0.314 -0.011 0.166 0.007 3.647 15.629 9.027 2.290 2.370 0.420 0.054 SWC001 grain far left edge bright 2 5.167 10.305 0.417 -0.018 0.175 -0.004 3.289 15.045 9.268 2.314 2.551 0.413 0.037
71
Appendix 1b. Elemental weight percentages from EMP. SWC Region 1, central midgray; SWC grain top right; SWC grain left edge bright. Rows continued from 1a.
SA M P LE Dy WT% Gd WT% Er WT% Yb WT% Ho WT% Tm WT% Fe WT% Mg WT% Al WT% Lu WT% Be WT% O WT% TOTAL SWC001 region 1 central midgray run 1 3.329 2.214 2.296 3.627 0.552 0.443 9.014 0.004 -0.005 0.429 3.250 28.246 97.910 SWC001 region 1 central midgray run 1 3.448 2.241 2.344 4.024 0.574 0.494 9.197 0.001 -0.005 0.535 3.250 28.356 98.278 SWC001 region 1 central midgray run 1 3.539 2.195 2.467 4.115 0.559 0.518 9.197 0.002 -0.007 0.562 3.256 28.291 97.865 SWC001 region 1 central midgray run 1 3.572 2.129 2.523 4.145 0.596 0.504 9.281 0.003 -0.008 0.524 3.259 28.406 98.199 SWC001 region 1 central midgray run 1 3.514 2.019 2.506 4.323 0.696 0.491 9.127 0.002 -0.002 0.516 3.273 28.639 98.550 SWC001 region 1 central midgray run 2 3.315 2.212 2.251 3.633 0.546 0.400 9.087 0.005 -0.006 0.427 3.256 28.534 98.702 SWC001 region 1 central midgray run 2 3.579 2.124 2.509 4.192 0.654 0.489 9.176 0.004 -0.007 0.559 3.264 28.444 98.178 SWC001 region 1 central midgray run 2 3.584 2.179 2.464 4.170 0.624 0.475 9.203 0.001 -0.005 0.540 3.259 28.395 98.143 SWC001 region 1 central midgray run 2 3.512 2.131 2.520 4.201 0.598 0.483 9.187 0.001 -0.002 0.536 3.263 28.441 98.196 SWC001 region 1 central midgray run 2 3.537 2.278 2.538 4.174 0.583 0.483 9.224 -0.001 -0.009 0.565 3.259 28.434 98.265
SWC001 grain top right 2.726 1.769 1.865 3.003 0.448 0.380 8.575 0.011 -0.003 0.339 3.246 28.351 98.385
SWC001 grain top right 3.085 2.024 2.017 3.272 0.458 0.390 8.822 0.008 0.000 0.392 3.242 28.315 98.390
SWC001 grain top right 4.055 2.496 2.759 4.194 0.745 0.523 9.130 0.007 -0.004 0.486 3.244 28.251 98.091 SWC001 grain left edge bright 2.519 1.715 1.617 2.520 0.406 0.247 7.880 0.008 0.016 0.248 3.238 28.202 98.118 SWC001 grain left edge bright 2 2.548 1.687 1.630 2.496 0.405 0.309 7.842 0.013 -0.003 0.249 3.236 28.021 97.533 SWC001 grain left edge bright 3 2.513 1.813 1.620 2.437 0.347 0.304 7.893 0.008 0.010 0.253 3.242 28.098 97.638 SWC001 grain far left edge bright 1 2.674 1.820 1.655 2.418 0.447 0.311 7.925 0.014 -0.002 0.228 3.232 28.216 98.345 SWC001 grain far left edge bright 2 2.679 1.819 1.679 2.395 0.418 0.316 7.954 0.012 0.009 0.251 3.249 28.267 98.007
72
Appendix 2a. Elemental weight percentages from EMP. SWC BL bright edge; SWC bright dark edge; SWC top right vdark zone; SWC top right vbright zone; SWC grain lower left; SWC grain central. Rows continued in 2b.
SA M P LE Y WT% Si WT% Th WT% U WT% Ca WT% Pb WT% La WT% Ce WT% Nd WT% Pr WT% Sm WT% Tb WT% Eu WT% SWC BL bright edge 30nA 2um 6.506 10.301 0.204 -0.002 0.076 -0.003 3.130 14.018 8.297 2.021 2.287 0.439 0.062 SWC BL bright edge 30nA 2um 6.441 10.246 0.217 0.003 0.077 -0.011 3.341 14.222 8.256 2.022 2.279 0.420 0.006 SWC BL bright edge 30nA 2um 7.064 10.207 0.218 0.001 0.093 0.012 3.210 13.534 7.815 1.982 2.071 0.394 0.041 SWC BL bright edge 30nA 2um 7.200 10.314 0.215 0.002 0.097 0.004 3.427 13.437 7.676 1.991 2.050 0.391 0.042 SWC BL bright dark edge 30nA 2um 9.321 10.231 0.361 0.027 0.824 0.005 0.983 7.530 7.522 1.636 2.455 0.435 0.014 SWC top right vdark zone 30nA 2um 15.351 10.273 0.042 -0.019 0.091 -0.026 4.954 9.990 3.485 1.038 0.773 0.192 0.089 SWC top right vdark zone 30nA 2um 15.617 10.294 0.027 -0.029 0.097 -0.021 4.922 9.578 3.476 0.994 0.803 0.171 0.077 SWC top right vdark zone 30nA 2um 16.026 10.377 0.040 -0.007 0.108 -0.023 4.744 9.303 3.382 0.985 0.765 0.184 0.130 SWC top right vbright zone 30nA 2um 11.839 10.254 0.195 0.031 0.098 0.009 1.692 9.050 7.091 1.588 2.031 0.395 0.065 SWC top right vbright zone 30nA 2um 11.506 10.643 0.191 0.053 0.102 -0.005 1.626 8.929 7.238 1.651 2.131 0.411 0.046 SWC top right vbright zone 30nA 2um 11.497 10.543 0.228 0.043 0.101 0.003 1.569 9.161 7.232 1.685 2.269 0.411 0.058 SWC top right vbright zone 30nA 2um 11.663 10.578 0.203 0.050 0.099 0.014 1.754 9.179 7.180 1.606 2.090 0.399 0.095 SWC001 grain lower left 50nA 5um 9.229 10.393 0.279 0.030 0.144 -0.003 1.357 9.645 8.558 1.866 2.548 0.456 0.060 SWC001 grain lower left 50nA 5um 9.155 10.244 0.317 0.022 0.170 0.002 1.376 9.680 8.623 1.949 2.601 0.458 0.094 SWC001 grain lower left 50nA 5um 9.254 10.223 0.263 0.012 0.149 -0.003 1.346 9.454 8.546 1.871 2.574 0.446 0.039 SWC001 grain lower left 50nA 5um 9.204 10.241 0.291 0.012 0.160 0.006 1.430 9.981 8.568 1.934 2.488 0.424 0.054 SWC001 grain lower left 50nA 5um 9.231 10.210 0.328 0.021 0.142 0.005 1.479 9.944 8.710 1.858 2.611 0.455 0.080 SWC001 grain lower left 50nA 5um 9.204 10.270 0.264 0.014 0.149 -0.010 1.369 9.790 8.386 1.804 2.566 0.452 0.041 SWC001 grain central 50nA 5um 8.692 10.181 0.314 0.015 0.130 0.001 1.559 10.565 9.065 2.007 2.601 0.481 0.043 SWC001 grain central 50nA 5um 8.978 10.286 0.321 0.017 0.138 0.002 1.529 10.391 8.771 1.963 2.544 0.431 0.041 SWC001 grain central 50nA 5um 8.847 10.281 0.282 0.015 0.148 -0.007 1.508 10.389 8.977 1.998 2.622 0.437 0.070 SWC001 grain central 50nA 5um 9.355 10.310 0.221 0.009 0.158 -0.010 1.457 9.705 8.700 1.969 2.561 0.464 0.013
73
Appendix 2b. Elemental weight percentages from EMP. SWC BL bright edge; SWC bright dark edge; SWC top right vdark zone; SWC top right vbright zone; SWC grain lower left; SWC grain central. Continued from 2a.
SA M P LE Dy WT% Gd WT% Er WT% Yb WT% Ho WT% Tm WT% Fe WT% Mg WT% Al WT% Lu WT% Be WT% O WT% TOTAL SWC BL bright edge 30nA 2um 2.954 1.824 2.074 3.252 0.502 0.420 8.695 0.009 -0.005 0.370 3.242 28.553 99.224 SWC BL bright edge 30nA 2um 2.973 1.711 2.055 3.133 0.532 0.390 8.674 0.016 -0.009 0.410 3.237 28.487 99.129 SWC BL bright edge 30nA 2um 2.988 1.866 2.154 3.496 0.454 0.439 8.762 0.010 -0.005 0.427 3.243 28.487 98.962 SWC BL bright edge 30nA 2um 2.946 1.822 2.159 3.609 0.512 0.449 8.789 0.009 -0.008 0.461 3.246 28.671 99.511 SWC BL bright dark edge 30nA 2um 3.474 2.053 2.508 4.319 0.568 0.459 6.782 0.043 0.039 0.553 3.374 28.010 93.525 SWC top right vdark zone 30nA 2um 1.442 0.728 1.581 4.144 0.323 0.385 9.319 0.002 -0.008 0.684 3.391 29.382 97.608 SWC top right vdark zone 30nA 2um 1.471 0.729 1.578 4.201 0.288 0.390 9.365 0.000 -0.010 0.723 3.397 29.426 97.564 SWC top right vdark zone 30nA 2um 1.445 0.768 1.701 4.460 0.297 0.417 9.383 0.002 -0.011 0.748 3.396 29.616 98.237 SWC top right vbright zone 30nA 2um 2.971 1.781 2.368 4.197 0.485 0.491 9.210 0.004 -0.008 0.567 3.309 28.996 98.707 SWC top right vbright zone 30nA 2um 3.060 1.701 2.352 4.194 0.658 0.477 9.238 0.001 -0.007 0.581 3.331 29.442 99.551 SWC top right vbright zone 30nA 2um 3.019 1.831 2.353 4.156 0.562 0.462 9.262 0.000 -0.003 0.616 3.317 29.369 99.745 SWC top right vbright zone 30nA 2um 2.929 1.869 2.297 4.126 0.521 0.462 9.194 0.001 -0.005 0.583 3.325 29.402 99.613 SWC001 grain lower left 50nA 5um 3.304 2.066 2.318 3.913 0.606 0.475 9.114 0.005 -0.002 0.536 3.286 28.900 99.081 SWC001 grain lower left 50nA 5um 3.304 2.000 2.313 3.871 0.588 0.448 9.101 -0.001 0.003 0.521 3.274 28.724 98.837 SWC001 grain lower left 50nA 5um 3.323 2.164 2.323 3.892 0.560 0.441 9.109 0.008 0.002 0.508 3.280 28.669 98.452 SWC001 grain lower left 50nA 5um 3.130 1.950 2.194 3.686 0.517 0.398 9.092 0.007 0.002 0.519 3.288 28.678 98.254 SWC001 grain lower left 50nA 5um 3.109 1.978 2.202 3.730 0.534 0.396 9.156 0.003 0.003 0.498 3.276 28.694 98.654 SWC001 grain lower left 50nA 5um 3.275 1.992 2.349 3.961 0.577 0.445 9.056 0.004 -0.004 0.532 3.283 28.700 98.472 SWC001 grain central 50nA 5um 3.040 2.035 2.099 3.450 0.471 0.402 9.095 0.005 0.000 0.468 3.269 28.609 98.596 SWC001 grain central 50nA 5um 3.135 2.015 2.137 3.645 0.547 0.461 9.138 0.001 -0.001 0.474 3.274 28.785 99.026 SWC001 grain central 50nA 5um 3.112 2.072 2.151 3.583 0.520 0.407 9.093 0.007 -0.001 0.456 3.273 28.769 99.009 SWC001 grain central 50nA 5um 3.241 2.079 2.257 3.876 0.543 0.473 9.123 0.006 -0.001 0.541 3.277 28.857 99.186
74
Appendix 3a. Elemental weight percentages from EMP. SWC grain far top right; SWC BL; SWC BL2. Continued in 3b.
SA M P LE Y WT% Si WT% Th WT% U WT% Ca WT% Pb WT% La WT% Ce WT% Nd WT% Pr WT% Sm WT% Tb WT% Eu WT% SWC001 grain far top right 50nA 5um 8.613 10.128 0.307 -0.003 0.156 -0.004 0.965 8.555 9.159 1.837 3.009 0.571 0.095 SWC001 grain far top right 50nA 5um 9.542 10.283 0.308 0.003 0.159 -0.001 0.799 6.997 8.484 1.612 3.214 0.636 0.118 SWC001 grain far top right 50nA 5um 8.904 10.101 0.373 0.049 0.156 0.005 0.942 8.519 8.689 1.803 2.870 0.555 0.064 SWC001 grain far top right 50nA 5um 9.642 10.250 0.378 0.015 0.170 0.009 0.848 6.961 8.067 1.526 3.065 0.605 0.090 SWC001 grain far top right 50nA 5um 8.667 10.199 0.261 0.005 0.121 0.003 1.786 11.253 8.167 1.971 2.396 0.426 -0.018 SWC001 grain central 2 50nA 5um 8.694 10.096 0.237 0.027 0.125 0.004 1.391 10.239 9.074 2.060 2.620 0.465 0.101 SWC001 grain central 2 50nA 5um 9.247 10.289 0.236 0.024 0.157 -0.007 1.483 9.781 8.721 1.953 2.573 0.482 0.111 SWC001 grain central 2 50nA 5um 8.766 10.218 0.270 0.020 0.141 0.004 1.503 10.427 8.839 1.982 2.603 0.482 0.008
SWC001 BL2 50nA 5um 6.334 9.182 0.215 -0.019 0.084 -0.011 3.121 13.733 8.031 2.092 2.238 0.405 0.058
SWC001 BL2 50nA 5um 6.797 10.152 0.260 -0.022 0.085 -0.007 3.262 13.776 7.950 2.083 2.270 0.414 0.021
SWC001 BL2 50nA 5um 6.791 9.865 0.215 0.002 0.097 -0.003 3.218 13.296 7.753 1.963 2.128 0.436 0.044
SWC001 BL2 50nA 5um 6.582 10.084 0.299 0.005 0.095 -0.009 2.948 13.309 8.250 2.027 2.369 0.441 0.072
SWC001 BL2 50nA 5um 6.304 9.943 0.338 0.009 0.090 0.009 2.773 13.351 8.462 2.071 2.476 0.453 0.031
SWC001 BL2 50nA 5um 7.023 10.049 0.228 -0.002 0.086 -0.008 3.330 13.814 7.818 2.000 2.118 0.402 0.085
SWC001 BL2 50nA 5um 7.019 10.115 0.253 0.007 0.088 0.003 3.370 13.906 7.780 1.939 2.094 0.382 0.045
SWC001 BL2 50nA 5um 6.862 10.057 0.216 0.008 0.092 0.003 3.262 13.537 7.904 2.066 2.225 0.434 0.024
SWC001 BL2 50nA 5um 6.850 10.101 0.275 -0.008 0.097 0.009 3.143 13.390 7.988 2.024 2.290 0.423 0.061
SWC001 BL2 50nA 5um 9.857 10.226 0.213 0.018 0.152 0.001 1.260 9.235 8.378 1.837 2.561 0.470 0.100
SWC001 BL 50nA 5um 11.253 10.232 0.261 0.038 0.171 -0.011 1.115 8.034 7.387 1.512 2.294 0.460 0.062
SWC001 BL 50nA 5um 11.156 10.328 0.186 0.042 0.182 -0.003 1.058 7.859 7.609 1.576 2.399 0.466 0.091
SWC001 BL 50nA 5um 9.446 10.079 0.300 0.038 0.133 0.008 1.278 9.480 8.528 1.866 2.657 0.462 0.064
SWC001 BL 50nA 5um 9.677 10.077 0.289 0.052 0.137 0.006 1.186 9.199 8.414 1.909 2.674 0.441 0.105
SWC001 BL 50nA 5um 9.620 10.026 0.248 0.036 0.127 0.005 1.164 9.035 8.592 1.859 2.676 0.488 0.118
SWC001 BL 50nA 5um 11.261 9.983 0.249 0.042 0.142 0.002 1.123 8.082 7.176 1.663 2.217 0.434 0.095
SWC001 BL 50nA 5um 11.262 10.159 0.272 0.049 0.146 -0.004 1.109 8.218 7.229 1.589 2.224 0.426 0.051 SWC001 BL 50nA 5um 9.802 10.090 0.209 0.013 0.151 -0.007 1.140 8.947 8.365 1.739 2.548 0.478 0.107 75
Appendix 3b. Elemental weight percentages from EMP. SWC grain far top right; SWC BL; SWC BL2. Continued from 3a.
SA M P LE Dy WT% Gd WT% Er WT% Yb WT% Ho WT% Tm WT% Fe WT% Mg WT% Al WT% Lu WT% Be WT% O WT% TOTAL SWC001 grain far top right 50nA 5um 3.941 2.323 2.569 3.920 0.719 0.502 9.289 0.003 0.004 0.493 3.250 28.548 98.949 SWC001 grain far top right 50nA 5um 4.204 2.562 2.865 4.431 0.754 0.515 9.192 0.004 0.002 0.546 3.266 28.780 99.273 SWC001 grain far top right 50nA 5um 3.846 2.347 2.686 4.105 0.623 0.503 9.209 0.002 0.000 0.509 3.255 28.490 98.604 SWC001 grain far top right 50nA 5um 4.360 2.522 2.914 4.526 0.743 0.567 9.270 0.006 0.000 0.552 3.267 28.739 99.091 SWC001 grain far top right 50nA 5um 3.176 1.875 2.234 3.670 0.526 0.405 8.987 0.005 0.001 0.474 3.271 28.590 98.451 SWC001 grain central 2 50nA 5um 3.171 2.006 2.204 3.604 0.579 0.440 9.110 0.002 0.002 0.458 3.260 28.497 98.466 SWC001 grain central 2 50nA 5um 3.123 1.941 2.201 3.825 0.565 0.448 9.177 0.005 -0.002 0.503 3.280 28.807 98.923 SWC001 grain central 2 50nA 5um 3.163 2.131 2.204 3.596 0.527 0.410 9.160 0.005 0.003 0.465 3.268 28.686 98.879
SWC001 BL2 50nA 5um 2.969 1.782 2.050 3.200 0.506 0.351 8.623 0.006 0.000 0.380 3.184 26.993 95.508
SWC001 BL2 50nA 5um 2.917 1.702 2.069 3.320 0.540 0.409 8.751 0.010 -0.002 0.422 3.237 28.398 98.814
SWC001 BL2 50nA 5um 2.881 1.735 2.087 3.384 0.492 0.403 8.577 0.004 1.533 0.444 3.306 29.354 100.005
SWC001 BL2 50nA 5um 3.061 1.837 2.190 3.331 0.534 0.390 8.757 0.011 -0.001 0.407 3.232 28.261 98.485
SWC001 BL2 50nA 5um 3.169 1.887 2.192 3.246 0.552 0.387 8.784 0.010 -0.001 0.375 3.219 28.054 98.183
SWC001 BL2 50nA 5um 2.807 1.737 2.085 3.396 0.485 0.351 8.744 0.007 -0.007 0.423 3.235 28.281 98.488
SWC001 BL2 50nA 5um 2.802 1.772 2.092 3.375 0.442 0.395 8.776 0.006 -0.005 0.381 3.239 28.368 98.645
SWC001 BL2 50nA 5um 2.928 1.767 2.105 3.428 0.507 0.385 8.805 0.006 -0.001 0.426 3.233 28.284 98.559
SWC001 BL2 50nA 5um 2.952 1.835 2.111 3.424 0.518 0.394 8.727 0.011 -0.004 0.418 3.235 28.314 98.577
SWC001 BL2 50nA 5um 3.278 1.908 2.410 4.091 0.608 0.479 9.146 -0.002 -0.003 0.541 3.279 28.764 98.806
SWC001 BL 50nA 5um 3.360 1.950 2.566 4.587 0.618 0.529 9.250 0.004 -0.005 0.629 3.302 28.866 98.464
SWC001 BL 50nA 5um 3.373 1.924 2.582 4.555 0.614 0.526 9.321 0.002 -0.003 0.587 3.308 28.994 98.731
SWC001 BL 50nA 5um 3.290 2.098 2.399 3.867 0.575 0.452 9.180 0.002 -0.003 0.542 3.263 28.550 98.555
SWC001 BL 50nA 5um 3.387 1.970 2.430 3.971 0.624 0.451 9.199 0.002 -0.002 0.507 3.266 28.569 98.540
SWC001 BL 50nA 5um 3.341 2.036 2.419 3.985 0.594 0.450 9.161 0.004 -0.004 0.513 3.265 28.469 98.227
SWC001 BL 50nA 5um 3.241 1.870 2.623 4.686 0.633 0.517 9.191 0.001 -0.008 0.635 3.288 28.508 97.652
SWC001 BL 50nA 5um 3.313 1.854 2.576 4.626 0.624 0.544 9.233 0.003 -0.008 0.673 3.298 28.757 98.221 SWC001 BL 50nA 5um 3.436 2.056 2.446 4.135 0.652 0.470 9.220 0.006 -0.003 0.502 3.273 28.576 98.350 76
Appendix 4a. Elemental weight percentages from EMP. SWC BL edge bright; SWC edge middark, SWC BL abundant gray. Rows continued in 4b.
SA M P LE Y WT% Si WT% Th WT% U WT% Ca WT% Pb WT% La WT% Ce WT% Nd WT% Pr WT% Sm WT% Tb WT% Eu WT% SWC001 BL edge bright 50nA 5um 6.771 9.828 0.250 0.001 0.082 -0.010 3.232 13.728 7.891 1.974 2.232 0.418 0.032 SWC001 BL edge bright 50nA 5um 6.716 10.015 0.236 -0.001 0.082 -0.008 3.303 13.670 7.935 2.013 2.232 0.408 0.048 SWC001 BL edge bright 50nA 5um 6.807 9.994 0.236 -0.011 0.073 -0.001 3.245 13.959 7.874 2.089 2.219 0.406 0.018 SWC001 BL edge middark 50nA 5um 11.279 10.257 0.237 0.062 0.151 0.001 1.085 7.921 7.249 1.575 2.225 0.485 0.076 SWC001 BL edge middark 50nA 5um 10.764 10.126 0.193 0.028 0.175 -0.009 1.172 8.535 7.745 1.706 2.362 0.460 0.034 SWC001 BL adundant gray 50nA 5um 9.830 9.995 0.302 0.037 0.159 0.001 1.336 9.271 8.235 1.804 2.459 0.447 0.114 SWC001 BL adundant gray 50nA 5um 9.420 10.039 0.171 0.037 0.176 -0.002 1.311 9.497 8.739 1.879 2.603 0.497 0.065 SWC001 BL adundant gray 50nA 5um 9.787 9.894 0.266 0.061 0.150 0.007 1.319 9.068 8.336 1.849 2.594 0.460 0.138 SWC001 BL adundant gray 50nA 5um 9.773 9.854 0.266 0.074 0.152 0.004 1.252 9.007 8.371 1.838 2.598 0.461 0.083 SWC001 BL adundant gray 50nA 5um 9.785 9.930 0.289 0.036 0.160 -0.002 1.346 9.220 8.306 1.845 2.454 0.459 0.064 SWC001 BL adundant gray 50nA 5um 10.614 9.999 0.207 0.022 0.201 -0.005 1.376 8.990 7.867 1.700 2.335 0.458 0.066 SWC001 BL adundant gray 50nA 5um 10.307 9.950 0.255 0.057 0.156 0.013 1.202 8.951 8.103 1.791 2.476 0.439 0.086 SWC001 BL adundant gray 50nA 5um 9.878 9.906 0.189 0.018 0.142 0.004 1.500 9.551 8.003 1.821 2.383 0.441 0.073
77
Appendix 4b. Elemental weight percentages from EMP. SWC BL edge bright; SWC edge middark, SWC BL abundant gray. Rows continued from 4a.
SA M P LE Dy WT% Gd WT% Er WT% Yb WT% Ho WT% Tm WT% Fe WT% Mg WT% Al WT% Lu WT% Be WT% O WT% TOTAL SWC001 BL edge bright 50nA 5um 2.947 1.756 2.126 3.318 0.516 0.382 8.697 0.003 -0.001 0.423 3.220 27.939 97.753 SWC001 BL edge bright 50nA 5um 2.956 1.846 2.094 3.313 0.469 0.373 8.609 0.009 -0.002 0.410 3.232 28.156 98.117 SWC001 BL edge bright 50nA 5um 2.889 1.794 2.048 3.251 0.456 0.367 8.649 0.007 -0.007 0.386 3.231 28.152 98.135 SWC001 BL edge middark 50nA 5um 3.480 2.000 2.647 4.687 0.638 0.556 9.249 0.002 -0.001 0.642 3.299 28.908 98.712 SWC001 BL edge middark 50nA 5um 3.252 2.012 2.466 4.387 0.597 0.504 9.195 0.005 -0.004 0.583 3.290 28.700 98.278 SWC001 BL adundant gray 50nA 5um 3.207 1.932 2.340 4.087 0.590 0.461 9.114 0.002 -0.004 0.547 3.270 28.437 97.973 SWC001 BL adundant gray 50nA 5um 3.270 2.134 2.255 3.858 0.547 0.427 9.081 0.004 -0.005 0.492 3.266 28.481 98.242 SWC001 BL adundant gray 50nA 5um 3.209 2.005 2.280 3.962 0.554 0.437 9.125 0.002 -0.009 0.533 3.265 28.285 97.578 SWC001 BL adundant gray 50nA 5um 3.229 2.044 2.335 3.998 0.550 0.454 9.169 0.005 -0.004 0.560 3.261 28.252 97.587 SWC001 BL adundant gray 50nA 5um 3.246 1.969 2.324 4.049 0.569 0.449 9.150 0.007 -0.004 0.554 3.265 28.361 97.831 SWC001 BL adundant gray 50nA 5um 3.042 1.872 2.311 4.062 0.534 0.464 9.093 0.002 -0.008 0.573 3.290 28.490 97.554 SWC001 BL adundant gray 50nA 5um 3.167 1.910 2.321 3.842 0.577 0.413 9.216 0.001 -0.006 0.529 3.283 28.399 97.436 SWC001 BL adundant gray 50nA 5um 3.166 1.914 2.312 3.904 0.586 0.455 9.109 0.005 -0.003 0.535 3.271 28.309 97.476
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Appendix 5a. Elemental weight percentages from EMP. SWC central light abundant gray; SWC top abundant gray; SWC center right. Rows continued in 5b.
SA M P LE Y WT% Si WT% Th WT% U WT% Ca WT% Pb WT% La WT% Ce WT% Nd WT% Pr WT% Sm WT% Tb WT% Eu WT% SWC001 central light abundant gray 50nA 5um 6.390 9.891 0.244 -0.040 0.165 -0.012 3.205 14.206 8.457 2.157 2.177 0.387 0.023 SWC001 central light abundant gray 50nA 5um 6.666 9.950 0.225 -0.032 0.166 -0.004 3.207 13.952 8.189 2.100 2.245 0.377 0.024 SWC001 central light abundant gray 50nA 5um 6.671 9.999 0.221 -0.025 0.174 -0.014 3.107 13.827 8.316 2.116 2.252 0.431 0.082 SWC001 central light abundant gray 50nA 5um 6.401 9.924 0.217 -0.038 0.175 -0.008 3.228 14.228 8.466 2.163 2.277 0.389 0.063 SWC001 central light abundant gray 50nA 5um 6.443 9.898 0.255 -0.013 0.181 -0.013 3.274 14.322 8.398 2.188 2.247 0.372 0.065 SWC001 central light abundant gray 50nA 5um 6.353 9.949 0.240 -0.015 0.175 -0.007 3.294 14.243 8.453 2.102 2.264 0.388 0.071 SWC001 central light abundant gray 50nA 5um 6.532 9.938 0.214 -0.009 0.174 -0.013 3.272 14.322 8.247 2.110 2.254 0.413 0.071 SWC001 central light abundant gray 50nA 5um 6.432 9.977 0.242 -0.026 0.174 -0.015 3.257 14.308 8.264 2.089 2.231 0.393 0.046 SWC001 top abundant gray 50nA 5um 13.524 10.234 0.092 0.052 0.118 -0.014 2.897 9.483 4.898 1.284 1.281 0.283 0.089 SWC001 top abundant gray 50nA 5um 13.473 10.194 0.127 0.054 0.111 -0.002 2.941 9.531 4.892 1.291 1.295 0.259 0.063 SWC001 top abundant gray 50nA 5um 13.221 10.146 0.104 0.026 0.117 0.000 3.065 9.759 4.982 1.296 1.262 0.295 0.084 SWC001 top abundant gray 50nA 5um 13.351 10.069 0.098 0.042 0.121 -0.006 2.958 9.560 4.938 1.256 1.292 0.244 0.012 SWC001 top abundant gray 50nA 5um 13.481 10.116 0.105 0.032 0.111 -0.008 2.773 9.455 4.964 1.251 1.343 0.284 0.046 SWC001 center right 50nA 5um 7.981 9.917 0.083 -0.030 0.067 -0.023 4.214 14.348 6.630 1.842 1.591 0.293 0.065 SWC001 center right 50nA 5um 7.706 9.870 0.087 -0.023 0.066 -0.008 4.047 14.429 6.883 1.832 1.700 0.354 0.093 SWC001 center right 50nA 5um 7.488 9.902 0.078 -0.017 0.062 -0.012 4.041 14.463 7.151 1.947 1.763 0.327 0.016 SWC001 center right 50nA 5um 8.149 10.008 0.077 -0.030 0.073 -0.017 4.086 14.271 6.508 1.721 1.660 0.317 0.057 SWC001 center right 50nA 5um 7.134 9.953 0.124 -0.028 0.068 -0.009 3.641 14.099 7.501 1.992 2.089 0.392 0.065 SWC001 center right 50nA 5um 7.760 9.856 0.112 -0.026 0.072 -0.003 3.897 13.981 6.917 1.830 1.816 0.324 0.018 SWC001 center right 50nA 5um 6.926 9.730 0.149 -0.027 0.064 -0.013 3.619 14.208 7.673 1.957 2.033 0.367 0.029
79
Appendix 5b. Elemental weight percentages from EMP. SWC central light abundant gray; SWC top abundant gray; SWC center right. Rows continued from 5a.
SA M P LE Dy WT% Gd WT% Er WT% Yb WT% Ho WT% Tm WT% Fe WT% Mg WT% Al WT% Lu WT% Be WT% O WT% TOTAL SWC001 central light abundant gray 50nA 5um 2.819 1.762 1.941 3.057 0.463 0.369 8.213 0.007 -0.002 0.349 3.228 27.902 97.361 SWC001 central light abundant gray 50nA 5um 2.880 1.723 2.013 3.177 0.489 0.357 8.263 0.007 -0.003 0.359 3.234 28.011 97.573 SWC001 central light abundant gray 50nA 5um 2.916 1.751 2.027 3.167 0.504 0.394 8.167 0.005 -0.003 0.330 3.235 28.062 97.714 SWC001 central light abundant gray 50nA 5um 2.829 1.711 1.947 3.047 0.506 0.371 8.196 0.003 -0.006 0.348 3.226 27.961 97.625 SWC001 central light abundant gray 50nA 5um 2.798 1.826 1.936 3.057 0.443 0.340 8.189 0.007 -0.004 0.351 3.222 27.958 97.741 SWC001 central light abundant gray 50nA 5um 2.843 1.824 1.955 2.943 0.429 0.331 8.199 0.009 -0.001 0.359 3.230 27.990 97.622 SWC001 central light abundant gray 50nA 5um 2.776 1.823 1.962 3.061 0.469 0.356 8.122 0.011 -0.006 0.368 3.228 27.989 97.684 SWC001 central light abundant gray 50nA 5um 2.794 1.757 1.949 3.053 0.456 0.378 8.143 0.001 0.000 0.337 3.236 27.998 97.476 SWC001 top abundant gray 50nA 5um 2.215 1.247 2.192 4.571 0.415 0.486 9.145 -0.001 -0.007 0.712 3.353 29.057 97.606 SWC001 top abundant gray 50nA 5um 2.226 1.212 2.185 4.557 0.493 0.441 9.213 -0.002 -0.002 0.704 3.349 29.024 97.631 SWC001 top abundant gray 50nA 5um 2.259 1.258 2.187 4.511 0.443 0.456 9.208 0.001 -0.004 0.673 3.340 28.955 97.644 SWC001 top abundant gray 50nA 5um 2.259 1.167 2.231 4.536 0.438 0.446 9.175 0.001 -0.005 0.707 3.345 28.821 97.056 SWC001 top abundant gray 50nA 5um 2.288 1.258 2.177 4.559 0.421 0.468 9.255 0.000 -0.006 0.697 3.346 28.916 97.335 SWC001 center right 50nA 5um 2.389 1.384 1.958 3.516 0.446 0.408 8.740 0.004 -0.005 0.452 3.249 28.186 97.707 SWC001 center right 50nA 5um 2.471 1.468 1.963 3.370 0.443 0.365 8.837 0.005 -0.002 0.448 3.241 28.131 97.776 SWC001 center right 50nA 5um 2.512 1.386 1.945 3.265 0.494 0.376 8.800 0.004 -0.002 0.434 3.241 28.141 97.805 SWC001 center right 50nA 5um 2.461 1.357 1.990 3.599 0.461 0.384 8.857 0.010 0.000 0.447 3.257 28.349 98.053 SWC001 center right 50nA 5um 2.726 1.594 1.963 3.251 0.492 0.370 8.767 0.010 0.000 0.398 3.237 28.163 97.991 SWC001 center right 50nA 5um 2.518 1.520 2.062 3.589 0.456 0.395 8.741 0.006 -0.002 0.437 3.241 28.078 97.597 SWC001 center right 50nA 5um 2.758 1.688 1.976 3.287 0.479 0.404 8.756 0.009 -0.003 0.401 3.217 27.861 97.549
80
Appendix 6a. Elemental weight percentages from EMP. Z2A Lower Left 1 mixed grayrun 1; Z2A Lower Left 1 mixed grayrun 2; Z2A far top right vdark; Z2A bottom left inner bright; Z2A bottom left dark. Rows continued in 6b.
SA M P LE Y WT% Si WT% Th WT% U WT% Ca WT% Pb WT% La WT% Ce WT% Nd WT% Pr WT% Sm WT% Tb WT% Eu WT% Z2A Lower Left 1 mixed gray run 1 22.287 10.852 0.089 0.000 0.077 -0.001 0.275 2.352 4.661 0.663 1.929 0.304 0.067 Z2A Lower Left 1 mixed gray run 1 16.280 10.318 0.015 -0.016 0.044 -0.017 0.182 1.525 4.220 0.476 3.057 0.829 0.078 Z2A Lower Left 1 mixed gray run 1 15.045 10.264 -0.008 -0.001 0.051 -0.018 0.213 1.836 5.253 0.585 3.396 0.812 -0.027 Z2A Lower Left 1 mixed gray run 1 16.868 10.426 0.004 -0.024 0.049 -0.010 0.136 1.449 4.119 0.446 2.857 0.768 0.008 Z2A Lower Left 1 mixed gray run 1 21.703 10.780 0.057 -0.024 0.068 -0.019 0.275 2.079 4.121 0.529 1.993 0.400 0.053 Z2A Lower Left 1 mixed gray run 2 22.465 10.948 0.064 -0.013 0.078 -0.015 0.272 2.373 4.830 0.646 2.055 0.322 0.098 Z2A Lower Left 1 mixed gray run 2 15.624 10.468 -0.001 -0.017 0.046 -0.026 0.185 1.590 4.682 0.520 3.184 0.822 0.048 Z2A Lower Left 1 mixed gray run 2 14.947 10.377 0.010 -0.022 0.042 -0.013 0.204 1.987 5.354 0.635 3.414 0.853 0.018 Z2A Lower Left 1 mixed gray run 2 17.033 10.569 0.019 -0.011 0.050 -0.020 0.138 1.355 3.947 0.391 3.030 0.828 0.100 Z2A Lower Left 1 mixed gray run 2 16.959 10.513 0.005 -0.012 0.058 -0.028 0.150 1.363 4.005 0.423 3.005 0.791 0.007 Z2A far top right vdark 30nA 2um 22.920 11.484 0.015 -0.013 0.125 -0.019 0.192 1.518 2.604 0.376 1.295 0.411 0.110 Z2A far top right vdark 30nA 2um 22.725 11.469 0.030 -0.025 0.121 -0.002 0.234 1.664 2.715 0.368 1.266 0.400 0.117 Z2A far top right vdark 30nA 2um 22.732 11.527 0.030 -0.003 0.145 -0.025 0.235 1.705 2.764 0.432 1.302 0.435 0.063 Z2A far top right vdark 30nA 2um 22.923 11.419 0.033 0.006 0.121 -0.022 0.223 1.604 2.792 0.380 1.392 0.415 0.054 Z2A bottom left inner bright 30nA 2um 15.882 10.729 -0.006 0.002 0.044 -0.015 0.134 1.514 4.590 0.558 3.208 0.814 0.073 Z2A bottom left inner bright 30nA 2um 15.582 10.746 0.018 0.002 0.050 -0.019 0.196 1.603 4.725 0.504 3.388 0.847 0.072 Z2A bottom left inner bright 30nA 2um 15.651 10.717 0.021 0.003 0.051 -0.014 0.192 1.655 4.815 0.527 3.242 0.814 0.009 Z2A bottom left inner bright 30nA 2um 16.011 10.681 0.029 -0.019 0.046 -0.004 0.185 1.457 4.458 0.462 3.135 0.885 0.017 Z2A bottom left dark 50nA 5um 21.906 10.663 0.043 -0.018 0.073 -0.021 0.280 2.274 4.178 0.581 1.787 0.402 0.025 Z2A bottom left dark 50nA 5um 21.459 10.554 0.073 -0.015 0.076 -0.004 0.236 2.122 4.136 0.511 1.929 0.408 0.049 Z2A bottom left dark 50nA 5um 21.466 10.629 0.059 -0.003 0.075 -0.021 0.272 2.141 4.213 0.523 1.933 0.391 0.058 Z2A bottom left dark 50nA 5um 21.549 10.562 0.084 -0.016 0.076 -0.021 0.291 2.119 4.103 0.514 1.889 0.401 0.047 Z2A bottom left dark 50nA 5um 21.744 10.792 0.080 -0.019 0.068 -0.020 0.293 2.174 4.085 0.586 1.911 0.402 0.021 Z2A bottom left dark 50nA 5um 21.539 10.681 0.055 -0.018 0.074 -0.016 0.236 2.011 4.091 0.554 1.929 0.433 0.083
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Appendix 6b. Elemental weight percentages from EMP. Z2A Lower Left 1 mixed grayrun 1; Z2A Lower Left 1 mixed grayrun 2; Z2A far top right vdark; Z2A bottom left inner bright; Z2A bottom left dark. Rows continued from 6a.
SA M P LE Dy WT% Gd WT% Er WT% Yb WT% Ho WT% Tm WT% Fe WT% Mg WT% Al WT% Lu WT% Be WT% O WT% TOTAL Z2A Lower Left 1 mixed gray run 1 2.317 1.781 1.927 3.464 0.399 0.393 10.143 0.001 -0.011 0.526 3.513 30.817 98.823 Z2A Lower Left 1 mixed gray run 1 5.619 3.668 3.617 4.114 1.129 0.606 9.796 -0.002 -0.006 0.454 3.355 29.418 98.760 Z2A Lower Left 1 mixed gray run 1 5.645 3.797 3.577 4.079 0.980 0.587 9.666 0.000 -0.001 0.478 3.334 29.229 98.770 Z2A Lower Left 1 mixed gray run 1 5.580 3.594 3.598 4.213 1.016 0.556 9.690 -0.008 -0.006 0.468 3.374 29.575 98.746 Z2A Lower Left 1 mixed gray run 1 2.966 1.963 2.384 3.742 0.649 0.422 10.049 -0.002 -0.011 0.576 3.490 30.633 98.875 Z2A Lower Left 1 mixed gray run 2 2.181 1.722 1.845 3.361 0.371 0.345 10.086 -0.005 -0.005 0.585 3.520 30.964 99.091 Z2A Lower Left 1 mixed gray run 2 5.712 3.672 3.723 4.246 1.077 0.623 9.772 -0.004 -0.008 0.481 3.351 29.549 99.320 Z2A Lower Left 1 mixed gray run 2 5.583 3.745 3.547 4.051 1.029 0.608 9.654 -0.003 -0.008 0.463 3.336 29.369 99.178 Z2A Lower Left 1 mixed gray run 2 5.570 3.596 3.637 4.236 1.056 0.592 9.762 -0.002 -0.007 0.503 3.375 29.832 99.579 Z2A Lower Left 1 mixed gray run 2 5.581 3.606 3.645 4.237 1.080 0.594 9.745 -0.003 -0.008 0.536 3.372 29.743 99.366 Z2A far top right vdark 30nA 2um 3.042 1.758 2.936 4.701 0.747 0.541 10.215 -0.008 -0.008 0.700 3.537 31.663 100.840 Z2A far top right vdark 30nA 2um 3.094 1.815 2.883 4.697 0.618 0.571 10.162 -0.006 -0.008 0.754 3.533 31.617 100.812 Z2A far top right vdark 30nA 2um 3.250 1.836 2.910 4.643 0.672 0.560 10.002 -0.005 -0.011 0.714 3.530 31.697 101.140 Z2A far top right vdark 30nA 2um 3.177 1.837 2.916 4.558 0.695 0.507 10.094 -0.008 -0.009 0.700 3.526 31.594 100.929 Z2A bottom left inner bright 30nA 2um 5.737 3.850 3.643 4.180 1.045 0.585 9.758 -0.001 -0.006 0.504 3.367 29.924 100.113 Z2A bottom left inner bright 30nA 2um 5.816 3.731 3.728 4.168 1.085 0.557 9.658 -0.001 -0.007 0.468 3.362 29.904 100.183 Z2A bottom left inner bright 30nA 2um 5.704 3.723 3.678 4.112 1.084 0.600 9.638 -0.002 -0.004 0.516 3.365 29.860 99.957 Z2A bottom left inner bright 30nA 2um 5.824 3.760 3.746 4.211 1.040 0.594 9.741 -0.004 -0.004 0.511 3.365 29.870 99.997 Z2A bottom left dark 50nA 5um 2.659 1.832 2.298 3.682 0.518 0.425 9.985 -0.005 -0.008 0.565 3.498 30.462 98.086 Z2A bottom left dark 50nA 5um 2.976 1.984 2.432 3.774 0.520 0.445 10.010 -0.005 -0.006 0.578 3.481 30.284 98.005 Z2A bottom left dark 50nA 5um 2.934 2.051 2.406 3.684 0.553 0.448 10.003 -0.005 -0.007 0.563 3.484 30.388 98.239 Z2A bottom left dark 50nA 5um 2.916 1.882 2.410 3.752 0.594 0.448 9.954 -0.003 -0.005 0.498 3.487 30.281 97.813 Z2A bottom left dark 50nA 5um 2.878 1.852 2.344 3.744 0.585 0.433 9.989 -0.006 -0.008 0.562 3.498 30.619 98.610 Z2A bottom left dark 50nA 5um 2.909 1.932 2.357 3.654 0.582 0.420 10.035 -0.001 -0.003 0.569 3.497 30.435 98.037
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Appendix 7a. Elemental weight percentages from the EMP. Z2A bottom left abundant lightgray; Z2A bottom left dark 2; Z2A bottom left light 2; Z2A far top right midgray. Rows continued in 7b.
SA M P LE Y WT% Si WT% Th WT% U WT% Ca WT% Pb WT% La WT% Ce WT% Nd WT% Pr WT% Sm WT% Tb WT% Eu WT% Z2A bottom left abundant lightgray 50nA 5um 16.270 10.260 -0.009 -0.017 0.042 -0.022 0.157 1.397 4.381 0.434 3.090 0.842 -0.005 Z2A bottom left abundant lightgray 50nA 5um 15.777 10.215 0.022 -0.010 0.045 -0.017 0.159 1.542 4.502 0.511 3.197 0.797 0.051 Z2A bottom left abundant lightgray 50nA 5um 16.222 10.305 0.002 -0.028 0.050 -0.023 0.155 1.414 4.230 0.446 3.113 0.783 0.092 Z2A bottom left abundant lightgray 50nA 5um 16.460 10.226 -0.020 -0.005 0.054 -0.031 0.142 1.364 4.116 0.443 2.968 0.809 0.090 Z2A bottom left abundant lightgray 50nA 5um 17.305 10.355 0.013 -0.013 0.056 -0.024 0.178 1.409 3.953 0.419 2.856 0.742 0.072 Z2A bottom left abundant lightgray 50nA 5um 15.958 10.013 -0.003 -0.004 0.050 -0.016 0.143 1.417 4.454 0.472 3.201 0.822 0.080 Z2A bottom left abundant lightgray 50nA 5um 16.148 10.099 0.022 -0.008 0.047 -0.027 0.157 1.403 4.346 0.449 3.065 0.807 0.074 Z2A bottom left abundant lightgray 50nA 5um 15.419 10.099 0.007 -0.023 0.049 -0.016 0.160 1.585 4.691 0.453 3.162 0.845 0.072 Z2A bottom left abundant lightgray 50nA 5um 15.370 10.177 -0.005 -0.011 0.056 -0.022 0.195 1.565 4.778 0.529 3.324 0.826 0.077 Z2A bottom left abundant lightgray 50nA 5um 16.085 10.256 -0.016 -0.013 0.051 -0.022 0.151 1.450 4.230 0.484 3.078 0.817 0.079 Z2A bottom left abundant lightgray 50nA 5um 16.505 10.295 -0.022 -0.041 0.052 -0.021 0.132 1.367 3.976 0.400 2.957 0.809 0.047 Z2A bottom left dark 2 50nA 5um 21.698 10.573 0.027 -0.025 0.063 -0.021 0.238 2.011 4.021 0.552 1.870 0.389 0.112 Z2A bottom left dark 2 50nA 5um 21.494 10.608 0.032 -0.016 0.060 -0.018 0.217 2.024 4.122 0.591 1.918 0.417 0.102 Z2A bottom left dark 2 50nA 5um 22.441 10.639 0.013 -0.021 0.064 -0.019 0.294 2.104 3.749 0.556 1.566 0.320 0.083 Z2A bottom left light 2 50nA 5um 15.833 10.308 0.003 -0.004 0.045 -0.021 0.164 1.509 4.518 0.464 3.110 0.829 0.037 Z2A bottom left light 2 50nA 5um 15.912 10.220 0.023 -0.008 0.050 -0.025 0.148 1.531 4.391 0.450 3.158 0.806 0.094 Z2A bottom left light 2 50nA 5um 15.731 10.263 0.015 -0.006 0.052 -0.023 0.192 1.610 4.601 0.455 3.212 0.840 0.109 Z2A bottom left light 2 50nA 5um 15.632 10.116 0.021 -0.009 0.050 -0.026 0.132 1.578 4.587 0.424 3.191 0.814 0.046 Z2A far top right midgray 50nA 5um 17.459 10.201 -0.013 -0.008 0.110 -0.037 0.144 1.338 3.495 0.365 2.524 0.750 0.107 Z2A far top right midgray 50nA 5um 17.741 10.334 0.033 -0.009 0.105 -0.023 0.179 1.341 3.277 0.340 2.352 0.667 0.040 Z2A far top right midgray 50nA 5um 17.882 10.321 0.006 -0.018 0.109 -0.024 0.144 1.369 3.424 0.377 2.370 0.696 0.082 Z2A far top right midgray 50nA 5um 17.414 10.356 -0.006 -0.001 0.127 -0.019 0.165 1.436 3.678 0.426 2.557 0.725 0.066 Z2A far top right midgray 50nA 5um 17.346 10.296 -0.004 -0.018 0.112 -0.021 0.157 1.342 3.713 0.423 2.622 0.738 0.013 Z2A far top right midgray 50nA 5um 17.648 10.335 0.013 -0.020 0.118 -0.017 0.154 1.328 3.484 0.389 2.492 0.779 0.068
83
Appendix 7b. Elemental weight percentages from the EMP. Z2A bottom left abundant lightgray; Z2A bottom left dark 2; Z2A bottom left light 2; Z2A far top right midgray. Rows continued from 7a.
SA M P LE Dy WT% Gd WT% Er WT% Yb WT% Ho WT% Tm WT% Fe WT% Mg WT% Al WT% Lu WT% Be WT% O WT% TOTAL Z2A bottom left abundant lightgray 50nA 5um 5.613 3.792 3.646 4.120 0.993 0.573 9.603 -0.004 -0.003 0.486 3.356 29.281 98.275 Z2A bottom left abundant lightgray 50nA 5um 5.710 3.733 3.706 4.135 1.034 0.597 9.545 0.000 -0.006 0.492 3.344 29.170 98.251 Z2A bottom left abundant lightgray 50nA 5um 5.656 3.692 3.741 4.281 1.010 0.589 9.647 -0.002 -0.002 0.506 3.354 29.359 98.592 Z2A bottom left abundant lightgray 50nA 5um 5.591 3.607 3.671 4.143 1.028 0.603 9.616 -0.006 -0.005 0.476 3.362 29.233 97.934 Z2A bottom left abundant lightgray 50nA 5um 5.351 3.454 3.562 4.142 0.997 0.571 9.664 -0.001 -0.004 0.505 3.378 29.531 98.470 Z2A bottom left abundant lightgray 50nA 5um 5.713 3.654 3.704 4.138 1.078 0.618 9.526 -0.001 -0.005 0.492 3.333 28.931 97.767 Z2A bottom left abundant lightgray 50nA 5um 5.726 3.792 3.682 4.074 1.041 0.580 9.584 -0.006 -0.004 0.434 3.344 29.060 97.890 Z2A bottom left abundant lightgray 50nA 5um 5.701 3.713 3.710 4.192 1.051 0.612 9.587 -0.001 -0.003 0.462 3.336 28.977 97.840 Z2A bottom left abundant lightgray 50nA 5um 5.716 3.898 3.672 4.125 0.999 0.579 9.555 -0.001 -0.006 0.459 3.335 29.098 98.288 Z2A bottom left abundant lightgray 50nA 5um 5.664 3.638 3.706 4.156 1.083 0.614 9.638 -0.002 -0.005 0.512 3.354 29.255 98.243 Z2A bottom left abundant lightgray 50nA 5um 5.548 3.712 3.702 4.276 1.017 0.614 9.697 -0.007 -0.009 0.505 3.365 29.338 98.213 Z2A bottom left dark 2 50nA 5um 2.830 1.942 2.409 3.820 0.575 0.420 10.095 -0.004 -0.008 0.581 3.487 30.338 97.992 Z2A bottom left dark 2 50nA 5um 2.983 2.118 2.443 3.764 0.562 0.419 10.023 -0.006 -0.008 0.598 3.480 30.368 98.296 Z2A bottom left dark 2 50nA 5um 2.645 1.764 2.354 3.819 0.517 0.422 10.021 -0.005 -0.008 0.602 3.506 30.475 97.903 Z2A bottom left light 2 50nA 5um 5.769 3.763 3.660 4.116 1.072 0.566 9.658 0.000 -0.003 0.472 3.352 29.318 98.537 Z2A bottom left light 2 50nA 5um 5.626 3.816 3.644 4.162 0.980 0.562 9.547 0.003 -0.005 0.467 3.351 29.177 98.079 Z2A bottom left light 2 50nA 5um 5.726 3.914 3.660 4.123 0.993 0.591 9.681 -0.003 -0.001 0.463 3.339 29.300 98.838 Z2A bottom left light 2 50nA 5um 5.693 3.704 3.683 4.089 1.021 0.578 9.631 -0.001 -0.004 0.453 3.344 29.020 97.768 Z2A far top right midgray 50nA 5um 5.268 3.355 3.680 4.369 1.017 0.608 9.578 -0.004 -0.006 0.528 3.383 29.277 97.489 Z2A far top right midgray 50nA 5um 5.136 3.103 3.744 4.951 1.012 0.634 9.704 -0.002 -0.007 0.622 3.387 29.518 98.179 Z2A far top right midgray 50nA 5um 5.071 3.074 3.632 4.749 1.016 0.642 9.663 -0.007 -0.007 0.568 3.390 29.508 98.037 Z2A far top right midgray 50nA 5um 5.284 3.341 3.686 4.321 1.004 0.624 9.544 -0.005 -0.008 0.547 3.386 29.500 98.148 Z2A far top right midgray 50nA 5um 5.321 3.369 3.629 4.321 1.006 0.576 9.552 -0.006 -0.008 0.570 3.385 29.392 97.824 Z2A far top right midgray 50nA 5um 5.300 3.273 3.611 4.363 1.008 0.607 9.587 -0.006 -0.009 0.534 3.391 29.478 97.909
84
Appendix 8a. Elemental weight percentages from the EMP. Z2A far top right light gray abundant; Z2A far top center dark. Rows continued in 8b.
SA M P LE Y WT% Si WT% Th WT% U WT% Ca WT% Pb WT% La WT% Ce WT% Nd WT% Pr WT% Sm WT% Tb WT% Eu WT% Z2A far top right light gray abundant 50nA 5um 15.604 10.321 0.013 -0.010 0.084 -0.021 0.201 1.738 4.572 0.502 3.082 0.798 0.081 Z2A far top right light gray abundant 50nA 5um 15.549 10.202 0.012 0.008 0.085 -0.022 0.195 1.740 4.515 0.459 3.061 0.772 0.062 Z2A far top right light gray abundant 50nA 5um 15.647 10.220 0.014 0.005 0.086 -0.024 0.206 1.794 4.516 0.500 3.062 0.789 0.085 Z2A far top right light gray abundant 50nA 5um 15.670 10.250 0.013 -0.002 0.088 -0.012 0.192 1.725 4.519 0.526 3.063 0.821 0.063 Z2A far top right light gray abundant 50nA 5um 15.629 10.263 0.019 -0.022 0.087 -0.028 0.181 1.755 4.499 0.477 3.060 0.813 0.104 Z2A far top right light gray abundant 50nA 5um 15.805 10.240 0.007 -0.011 0.088 -0.019 0.179 1.643 4.478 0.511 3.031 0.783 0.087 Z2A far top right light gray abundant 50nA 5um 15.726 10.244 0.013 -0.022 0.092 -0.026 0.189 1.656 4.420 0.472 2.993 0.782 0.074 Z2A far top right light gray abundant 50nA 5um 15.747 10.221 -0.009 -0.015 0.091 -0.018 0.215 1.676 4.315 0.464 2.986 0.818 0.092 Z2A far top right light gray abundant 50nA 5um 15.730 10.184 0.013 -0.013 0.089 -0.019 0.179 1.710 4.270 0.487 2.930 0.804 0.064 Z2A far top right light gray abundant 50nA 5um 15.737 10.186 0.027 -0.008 0.099 -0.009 0.183 1.670 4.348 0.466 2.971 0.776 0.026 Z2A far top right light gray abundant 50nA 5um 15.360 10.221 0.028 -0.018 0.095 -0.032 0.184 1.665 4.637 0.554 3.151 0.850 0.067 Z2A far top right light gray abundant 50nA 5um 14.919 10.222 0.054 0.000 0.072 -0.019 0.207 1.920 5.045 0.598 3.241 0.784 -0.009 Z2A far top right light gray abundant 50nA 5um 14.699 10.283 0.021 -0.015 0.063 -0.021 0.232 2.167 5.365 0.642 3.434 0.814 0.047 Z2A far top right light gray abundant 50nA 5um 15.046 10.214 0.017 -0.022 0.079 -0.018 0.176 1.931 5.012 0.592 3.276 0.833 0.090 Z2A far top center dark 50nA 5um 19.254 10.477 0.040 -0.007 0.069 -0.025 0.195 1.541 3.640 0.433 2.218 0.634 0.041 Z2A far top center dark 50nA 5um 19.392 10.434 0.001 -0.025 0.079 -0.032 0.152 1.419 3.361 0.401 2.214 0.610 0.073 Z2A far top center dark 50nA 5um 19.601 10.483 0.002 -0.011 0.082 -0.019 0.183 1.345 3.231 0.407 2.088 0.609 0.052 Z2A far top center dark 50nA 5um 19.597 10.476 0.036 -0.031 0.074 -0.021 0.183 1.457 3.347 0.381 2.176 0.572 0.091 Z2A far top center dark 50nA 5um 19.722 10.515 0.002 -0.028 0.073 -0.026 0.156 1.380 3.233 0.365 2.101 0.579 0.088
85
Appendix 8b. Elemental weight percentages from the EMP. Z2A far top right light gray abundant; Z2A far top center dark. Rows continued from 8a.
SA M P LE Dy WT% Gd WT% Er WT% Yb WT% Ho WT% Tm WT% Fe WT% Mg WT% Al WT% Lu WT% Be WT% O WT% TOTAL Z2A far top right light gray abundant 50nA 5um 5.731 3.798 3.707 4.186 1.030 0.623 9.517 0.001 -0.005 0.443 3.347 29.311 98.655 Z2A far top right light gray abundant 50nA 5um 5.671 3.737 3.663 4.197 1.069 0.607 9.401 -0.003 -0.009 0.487 3.347 29.081 97.886 Z2A far top right light gray abundant 50nA 5um 5.651 3.759 3.689 4.123 1.074 0.588 9.411 -0.007 -0.005 0.464 3.345 29.144 98.136 Z2A far top right light gray abundant 50nA 5um 5.574 3.676 3.688 4.208 1.069 0.623 9.410 0.000 -0.007 0.475 3.348 29.179 98.161 Z2A far top right light gray abundant 50nA 5um 5.536 3.741 3.703 4.216 0.985 0.584 9.450 0.000 -0.002 0.506 3.352 29.191 98.099 Z2A far top right light gray abundant 50nA 5um 5.601 3.810 3.690 4.263 0.985 0.584 9.539 0.002 -0.006 0.523 3.346 29.225 98.387 Z2A far top right light gray abundant 50nA 5um 5.651 3.666 3.701 4.274 1.098 0.596 9.522 0.000 -0.009 0.501 3.350 29.188 98.151 Z2A far top right light gray abundant 50nA 5um 5.730 3.683 3.687 4.213 1.037 0.603 9.517 -0.004 -0.005 0.490 3.350 29.156 98.039 Z2A far top right light gray abundant 50nA 5um 5.618 3.612 3.740 4.220 1.079 0.655 9.523 -0.006 -0.010 0.459 3.351 29.081 97.749 Z2A far top right light gray abundant 50nA 5um 5.676 3.694 3.737 4.207 1.090 0.638 9.472 -0.001 -0.009 0.489 3.348 29.099 97.913 Z2A far top right light gray abundant 50nA 5um 5.778 3.900 3.695 4.106 1.019 0.625 9.407 0.000 -0.007 0.489 3.340 29.124 98.237 Z2A far top right light gray abundant 50nA 5um 5.712 3.745 3.662 4.120 1.042 0.543 9.398 -0.001 -0.003 0.517 3.336 29.073 98.179 Z2A far top right light gray abundant 50nA 5um 5.611 3.708 3.577 3.985 1.048 0.595 9.420 -0.001 -0.004 0.486 3.331 29.173 98.659 Z2A far top right light gray abundant 50nA 5um 5.638 3.651 3.649 4.099 1.076 0.614 9.339 -0.002 -0.007 0.467 3.336 29.069 98.156 Z2A far top center dark 50nA 5um 4.460 2.836 3.320 4.272 0.880 0.575 9.854 -0.005 -0.007 0.568 3.419 29.930 98.612 Z2A far top center dark 50nA 5um 4.381 2.857 3.358 4.406 0.877 0.580 9.847 -0.005 -0.008 0.565 3.424 29.856 98.218 Z2A far top center dark 50nA 5um 4.465 2.682 3.406 4.489 0.936 0.572 9.958 -0.003 -0.008 0.586 3.426 29.972 98.534 Z2A far top center dark 50nA 5um 4.359 2.751 3.314 4.439 0.904 0.564 9.880 -0.009 -0.005 0.558 3.426 29.953 98.474 Z2A far top center dark 50nA 5um 4.459 2.787 3.352 4.449 0.858 0.594 9.887 -0.002 -0.007 0.567 3.431 30.013 98.545
86
Appendix 9. Settings and standards on the JEOL JXA-8230 Superprobe during analyses of gadolinite samples SWC and Z2A. C-coating (15 nm) Element X-ray line Crystal Peak Time Bkg Time Standard Detection Limit (99%) Spectro. Peak Position Bkg Type Bkg Correction Hi-bkg Position Lo-bkg Position Correction for interference from... Y La TAP 60 0 YPO4 (Harlov GFZ) 0.016296 1 70.14 MAN ------Si Si Ka TAP 30 0 Albite Amelia 0.006745 1 77.4488 MAN ------Ho, Tm, Yb, Y Mg Ka TAP 90 0 Diopside 0.003778 1 107.481 MAN ------Tb, Eu, Nd, Dy Al Ka TAP 90 0 Almandine NY 0.003723 1 90.6307 MAN ------Tm, Ho, Yb, Er Th Ma PETL 90 0 ThO2 (Ian Steele) 0.021179 2 132.405 MAN ------U Mb PETL 90 0 UO2 (Ian Steele) 0.017306 2 118.88 MAN ------Th Ca Ka PETL 90 0 F-Apatite (Harlov GFZ) 0.002778 2 107.478 MAN ------Yb, Dy Pb Mb PETL 300 0 Pyromorphite (MJJ) 0.010189 3 162.548 MAN ------Ce La La LIFL 40 0 LaPO4 (Harlov GFZ) 0.028127 4 185.378 MAN ------Nd Ce La LIFL 40 0 CePO4 (Harlov GFZ) 0.024787 4 178.138 MAN ------Nd La LIFL 40 0 NdPO4 (Harlov GFZ) 0.022958 4 164.84 MAN ------Ce Pr Lb LIFL 40 0 PrPO4 (Harlov GFZ) 0.041982 4 157.094 MAN ------Sm Lb LIFL 40 0 SmPO4 (Harlov GFZ) 0.043295 4 138.984 MAN ------Tb, Er Tb La LIFL 40 0 TbPO4 (Harlov GFZ) 0.025426 4 137.42 MAN ------Sm, Pr, Tm, Fe Eu Lb LIFL 40 0 EuPO4 (Harlov GFZ) 0.044309 4 133.581 MAN ------Dy, Fe Dy La LIFL 30 0 DyPO4 (Harlov GFZ) 0.026664 5 132.675 MAN ------Eu, Yb, Sm, Fe Gd Lb LIFL 30 0 GdPO4 (Harlov GFZ) 0.048545 5 128.335 MAN ------Ho Er La LIFL 40 0 ErPO4 (Harlov GFZ) 0.024483 5 124.005 MAN ------Tb, Eu Yb La LIFL 40 0 YbPO4 (Harlov GFZ) 0.027014 5 116.142 MAN ------Dy, Eu, Tb, Sm Ho Lb LIFL 40 0 HoPO4 (Harlov GFZ) 0.048641 5 114.436 MAN ------Eu, Sm, Dy Tm La LIFL 40 0 TmPO4 (Harlov GFZ) 0.026317 5 119.965 MAN ------Sm, Dy, Tb Fe Ka LIFL 20 0 Almandine NY 0.012125 5 134.556 MAN ------Eu, Dy, Nd, Sm Lu La LIFL 40 0 LuPO4 (Harlov GFZ) 0.029432 5 112.469 MAN ------Dy, Ho MAN = Mean Atomic Number background correction (Donovan and Tingle, 1996)
87
Appendix 10a. Elemental weight percentages from the EMP for allanite, adjacent to gadolinite in SWC and Z2A. Analyzed with an Al coating instead of C coating. Rows continued in 10b. SAMPLE Y WT% Si WT% Th WT% U WT% Ca WT% Pb WT% La WT% Ce WT% Nd WT% Pr WT% Sm WT% Tb WT% Eu WT% SWC001 allanite5 0.19 14.02 0.13 0.00 6.04 0.01 3.62 12.47 3.64 1.35 0.38 -0.15 -0.11 SWC001 allanite5 0.21 14.08 0.15 -0.01 6.14 0.02 3.50 12.17 3.73 1.36 0.36 -0.16 -0.19 SWC001 allanite5 0.21 14.10 0.15 -0.01 6.07 0.01 3.62 12.34 3.79 1.36 0.43 -0.16 -0.13 SWC001 allanite5 0.10 14.24 0.12 0.00 6.15 0.01 4.09 13.26 3.74 1.41 0.41 -0.15 -0.13 SWC001 allanite5 0.11 14.17 0.18 0.01 6.02 0.01 4.18 13.20 3.60 1.40 0.35 -0.17 -0.15 SWC001 allanite5 0.17 14.14 0.16 0.00 6.05 0.00 4.23 12.98 3.59 1.44 0.41 -0.15 -0.11 SWC001 allanite5 0.13 14.20 0.17 0.01 6.05 0.00 4.21 13.22 3.58 1.40 0.28 -0.18 -0.15 SWC001 allanite5 0.08 14.18 0.10 0.00 6.30 0.00 4.02 13.11 3.59 1.37 0.31 -0.16 -0.11 SWC001 allanite5 0.13 14.14 0.19 0.01 6.14 0.01 4.08 12.61 3.72 1.39 0.38 -0.16 -0.12 Z2A allanite1 0.20 14.82 0.04 0.00 7.38 0.00 4.89 11.05 4.86 1.34 0.56 -0.13 -0.10 Z2A allanite1 0.29 14.92 0.05 0.00 7.54 0.00 4.44 10.47 5.00 1.31 0.61 -0.11 -0.10 Z2A allanite1 0.54 14.89 0.04 0.00 7.37 -0.01 3.79 9.94 5.13 1.28 0.80 -0.12 -0.13 Z2A allanite1 0.62 14.54 0.14 -0.01 6.30 0.01 3.23 9.77 4.79 1.37 0.80 -0.12 -0.23 Z2A allanite1 0.17 14.39 0.08 0.01 6.46 0.01 3.73 10.88 5.46 1.55 0.77 -0.12 -0.17 Z2A allanite1 0.12 14.46 0.10 0.02 5.87 0.01 4.47 11.83 4.85 1.43 0.49 -0.16 -0.14 Z2A allanite1 0.22 14.38 0.10 0.01 5.67 0.01 4.68 11.93 4.72 1.39 0.54 -0.18 -0.16 Z2A allanite1 0.20 14.60 0.09 0.00 6.68 0.01 3.08 10.28 6.11 1.64 0.82 -0.16 -0.15 Z2A allanite1 0.11 14.47 0.08 0.01 6.13 0.00 4.58 11.89 4.63 1.37 0.53 -0.18 -0.18 Z2A allanite1 0.17 14.49 0.09 0.01 6.32 0.01 3.97 11.27 5.22 1.45 0.64 -0.16 -0.16 Z2A allanite1 0.18 14.45 0.13 0.02 5.74 0.01 4.78 12.01 4.70 1.50 0.45 -0.13 -0.13 Z2A allanite1 0.21 14.47 0.12 0.01 5.75 0.00 4.80 12.07 4.50 1.41 0.42 -0.18 -0.19
88
Appendix 10b. Elemental weight percentages from the EMP for allanite, adjacent to gadolinite in SWC and Z2A. Analyzed with an Al coating instead of C coating. Rows continued from 10a. SAMPLE Dy WT% Gd WT% Er WT% Yb WT% Ho WT% Tm WT% Fe WT% Mg WT% Al WT% O WT% TOTAL SWC001 allanite5 0.18 0.13 0.12 0.19 0.00 0.01 12.06 0.06 5.12 30.20 89.65 SWC001 allanite5 0.18 0.16 0.13 0.21 0.01 0.02 11.54 0.06 5.20 30.19 89.06 SWC001 allanite5 0.17 0.13 0.12 0.15 -0.06 0.01 12.16 0.05 5.21 30.42 90.13 SWC001 allanite5 0.07 0.12 0.09 0.09 0.01 -0.01 12.77 0.04 5.56 31.28 93.27 SWC001 allanite5 0.09 0.10 0.09 0.13 0.02 0.02 13.14 0.03 5.35 31.04 92.94 SWC001 allanite5 0.09 0.15 0.11 0.11 -0.04 -0.02 13.40 0.04 5.24 31.00 92.97 SWC001 allanite5 0.07 0.13 0.11 0.13 0.01 0.02 13.23 0.04 5.39 31.15 93.20 SWC001 allanite5 0.04 0.12 0.11 0.12 0.08 0.03 12.81 0.03 5.46 31.10 92.68 SWC001 allanite5 0.10 0.12 0.08 0.10 0.05 0.00 12.88 0.03 5.50 31.04 92.44 Z2A allanite1 -0.08 0.18 0.09 0.05 -0.05 -0.01 9.14 0.07 7.29 32.89 94.49 Z2A allanite1 -0.07 0.21 0.08 0.00 -0.01 0.00 9.84 0.05 7.03 32.91 94.45 Z2A allanite1 0.07 0.32 0.12 0.04 -0.01 -0.02 10.25 0.03 6.84 32.70 93.87 Z2A allanite1 0.54 0.34 0.17 0.24 0.00 0.01 10.88 0.03 6.15 31.41 91.00 Z2A allanite1 0.10 0.24 0.09 0.02 -0.03 -0.01 12.71 0.01 5.78 31.64 93.77 Z2A allanite1 0.14 0.13 0.08 0.00 -0.03 0.00 12.60 0.02 5.99 31.74 94.01 Z2A allanite1 0.18 0.11 0.09 0.05 0.01 0.00 12.56 0.01 6.09 31.71 94.12 Z2A allanite1 0.11 0.30 0.08 0.00 -0.02 -0.01 12.62 0.01 5.83 31.92 94.04 Z2A allanite1 0.13 0.16 0.09 0.02 -0.01 0.01 12.67 0.01 5.84 31.73 94.10 Z2A allanite1 0.05 0.18 0.07 0.01 -0.04 0.00 12.61 0.02 5.81 31.71 93.75 Z2A allanite1 0.12 0.12 0.05 0.02 -0.01 -0.03 12.50 0.02 5.95 31.71 94.16 Z2A allanite1 0.16 0.10 0.04 0.02 0.01 0.00 12.56 0.02 5.98 31.73 94.02
89
Appendix 11. Settings and standards on the JEOL JXA-8230 Superprobe during analyses of allanite adjacent to gadolinite in samples SWC and Z2A. Al-coating (17 nm) + C-coating (6 nm) Detection Peak Bkg Hi-bkg Lo-bkg Correction for Element X-ray line Crystal Peak Time Bkg Time Standard Limit (99%) Spectro. Position Bkg Type Correction Position Position interference from... Y La TAP 120 0 YPO4 (Harlov GFZ) 0.007406 1 69.9 MAN ------Si Si Ka TAP 120 0 Garnet NMNH 87375 0.002171 1 77.2722 MAN ------Mg Ka TAP 60 0 Johnstown Hypersthene 0.002707 1 107.462 MAN ------Th Ma PETL 60 60 ThO2 (Ian Steele) 0.029581 2 132.391 MULT ------U Mb PETL 60 90 UO2 (Ian Steele) 0.019265 2 118.874 MULT ------Th Ca Ka PETL 50 0 F-Apatite (Harlov GFZ) 0.002563 2 107.477 MAN ------Pb Ma PETL 180 157.5 Pyromorphite (MJJ) 0.011306 3 169.242 MULT ------Th, Y, La La La LIFL 30 20 LaPO4 (Harlov GFZ) 0.040475 4 185.376 OFF Multi-Point 188.376 181.176 Ce La LIFL 30 20 CePO4 (Harlov GFZ) 0.035261 4 178.12 OFF Multi-Point 181.12 173.92 Nd La LIFL 30 20 NdPO4 (Harlov GFZ) 0.033209 4 164.819 OFF Multi-Point 168.819 161.819 Ce Pr Lb LIFL 30 20 PrPO4 (Harlov GFZ) 0.061134 4 157.083 OFF Multi-Point 161.783 155.583 Sm Lb LIFL 30 20 SmPO4 (Harlov GFZ) 0.063008 4 138.967 OFF Multi-Point 144.467 134.517 Tb, Er Tb La LIFL 30 20 TbPO4 (Harlov GFZ) 0.036259 4 137.411 OFF Multi-Point 140.011 134.511 Sm, Pr, Fe Eu Lb LIFL 30 20 EuPO4 (Harlov GFZ) 0.065265 4 133.577 OFF Multi-Point 134.477 129.277 Dy, Fe Dy La LIFL 30 20 DyPO4 (Harlov GFZ) 0.034881 5 132.664 OFF Multi-Point 139.914 129.264 Eu, Yb, Sm, Fe Gd Lb LIFL 30 20 GdPO4 (Harlov GFZ) 0.063963 5 128.323 OFF Multi-Point 129.253 127.023 Er La LIFL 30 20 ErPO4 (Harlov GFZ) 0.036153 5 123.981 OFF Multi-Point 126.981 122.481 Tb, Eu Yb La LIFL 30 20 YbPO4 (Harlov GFZ) 0.03975 5 116.126 OFF Multi-Point 117.876 113.826 Dy, Eu, Tb, Sm, Ho Ho Lb LIFL 30 20 HoPO4 (Harlov GFZ) 0.072545 5 114.398 OFF Multi-Point 111.798 107.998 Yb, Dy, Sm Tm La LIFL 30 20 TmPO4 (Harlov GFZ) 0.037331 5 119.963 OFF Multi-Point 122.463 117.863 Dy, Sm, Tb Fe Ka LIFL 30 20 Johnstown Hypersthene 0.013276 5 134.542 OFF Multi-Point 139.942 129.242 Dy, Eu, Nd MAN = Mean Atomic Number background correction (Donovan and Tingle, 1996). MULT = multipoint correction (Allaz et al. 2018, in review). OFF / Multi-point = shared background correction (Allaz et al. 2018, in review)