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An Introduction to the Palermo Pegmatites

Steven McCaw

on 18 December 2012

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Transcript of Pegmatites

The Palermo Pegmatites So, what is a pegmatite, exactly? A pegmatite is technically any rock with crystals larger than 2.5 centimeters across. Jahns & Burnham 1969 The Palermo Pegmatites are complex REE/LCT beryl-phospate pegmatites in the Grafton Pegmatite Field of New Hampshire. Type Temperature Pressure Elements Abyssal Muscovite Rare Element
LCT Rare Element
NYF Miarolitic High High Low Low Very Low High Low Low Very Low Low U, Th, Zr, Nb, Ti, Y, REE, Mo Li, Be, Y, REE, Ti, U, TH, Nb > Ta Li, Rb, Cs, Be, Ga, Sn, Hf, Nb, Ta, B, P, F Y, REE, Ti, U, Th, Zr, Nb > Ta, F Be, Y, REE, Ti, U, Th, Zr, Nb > Ta, F This is rather unusual behavior for a rock. It takes some special conditions for it to happen. Volatiles Enrichment: Decreases polymerization Decreases viscosity Decreases solidus temperature Decreases nucleation rate Increases rate of diffusion Increases solubility (Simmons, Webber, Falster & Nizamoff, 2003) Incompatible Elements: Large Ion Lithophiles High Field Strength Elements Pegmatophile Elements (Small Size, Low Charge) Cesium (I), rubidium (I), barium (II), lead (II), strontium (II) Tantalum (V), niobium (V), phosphate (V), zirconium (IV), uranium (IV),
thorium (IV), hafnium (IV), titanium (IV), various rare earth elements Lithium (I), beryllium (II), boron (III) Zoning Simple Zoned Complex Uniform texture and composition Characterized by a core surrounded with one or more concentric outer zones. They appear to grow from the wall inwards. Zoned Pegmatites with further alteration. A Brief History of the Palermo Mine *125 years of mining history

-Operations began in 1863 When Charles E. Kellog began mining muscovite

-1883- Palermo Mining Company purchases all mineral rights, changing the name to the Palermo Mine. With the change in ownership came a drastic change in mining technique – hand drills were replaced with steam power, and black powder was replaced by the use of dynamite, providing a more economic means of extraction.

-1914- General Electric Company bought mineral rights and continued underground mica operations.

-1944- GE leases the mine to Ashley Mining Company, locally based in Rumney, NH. The Ashley Mining Company would go on to produce 4,222 tons of feldspar, 495 tons of mica, and 49 tons of beryl in its opening year of operations. The facing of the Prudential Insurance Company building in Boston was also taken from the Palermo mine. A Brief History Continued -1973- Peter Samuelson leases Palermo for the production of gem quality beryl and other mineral specimens. At this time, Paul B. Moore from the University of Chicago Department of Geophysical Sciences discovers a new mineral, Bjarebyite.

-1974- Robert Whitmore and Forest Fogg purchase all mineral rights to Palermo, titling their endeavor ‘Palermo Mine Enterprises’. Five new phosphate minerals were subsequently found, including Foggite, Goodhenite, Samuelsonite, Shoonerite, and Whitmoreite.

Present day – Robert Whitmore is the sole owner of the property, which contains 110 mineral species, including eleven with a specific type locality at this location. Heres a peek at some of the rare minerals found exclusively at the Palermo Mines - -Bjarebyite BaMn(2+)2Al2(PO4)3(OH)3 Falsterite - CA2MgMn(2+)2(Fe2+0.5Fe3+0.5)4Zn4(PO4)8(OH)4(H2O)14 Foggite - CaAl(PO4)(OH)2-H2O Palermoite with Geodkenite
SrLi2Al4(PO4)4(OH)4 ///Sr2Al(PO4)4,2(OH) Samuelsonite (Ca,Ba)Ca8Mn(2+)2Fe(2+)(PO4)10(OH)2 Schoonerite ZnMn(2+)Fe(2+)2Fe(3+)(PO4)3(OH)2-9H2O Wolfeite - Fe2+2(PO4)(OH) Whitelockite - Ca9Mg(PO4)6(HPO4) Xanthoxenite - Ca4Fe3+2(PO4)4(OH)2-3H2Orft6 Bowen's Reaction Series Quartz, muscovite and k-spar are at the bottom of the series, and they're the three most common minerals in pegmatite Economic Purposes of Mining the Palermo Pegmatites Beryl
-Often alloyed with copper
-2nd lightest element, 5x lighter than steel
-Non-magnetic, so ideal for computers
-Doesn’t expand with heat
-Used in many components of spaceships and aerospace engineering
-X-ray equipment generally uses beryllium
-Used for tweeters in high end sound systems
-First member of alkaline earth elements
-Non-gem beryl is considered semi precious
-NH’s state mineral Uses of Mica - Formerly used in the production of furnace windows

-Used in makeup and paints to add shimmer

- Also used to add decorative finish to pottery

- Found at Teotihuacan 'Pyramid of the Sun' in layers up to 12 inches thick, again, for decorative purposes Pegmatites typically form from the 'dregs' of a melt, the things that they have too much of, and the materials no other rock wants to crystallize with. This is usually quartz, volatiles, and incompatible elements. These alter the characteristics of the remaining melt. These guys are usually present in very low concentrations, but they concentrate in melts because nothing wants to crystallize with them. For the purposes of pegmatology, a pegmatite is often not just a texture, but also the structures hosting that texture. Industrial Applications of Feldspars - Glass/Ceramics - Feldspar is commonly used to lower the melting point of quartz, allowing a reduction in production costs

- Commonly used as a filler in paints, plastics, and rubber

- Used in enamels, reducing defects in finished products

- A common road aggregate

- Used in mild abrasives Why smoky quartz? Smoky quartz is common in the Grafton
pegmatites due to gamma ray bombardment
of nearby uranium mineralization.
The quartz itself is not radioactive, however
the color change is due to an alteration in
crystal structure. Smoky Quartz - Palermo #1 (drained) The Groton Pegmatite Fields How are pegmatites distributed? As we saw before, pegmatites occur in 'pods' coming off of a pluton. When they are all are very similar chemically and emplaced in the same unit, it's a pegmatite field. Pegmatite Fields Like So This distribution mirrors the growth of mineral pods along the core margin zone. Himalaya Dike, CA Bibliography Simmons, W., Webber, K., Falster, A., & Nizamoff, J. (2003). Pegmatology: Pegmatite mineralogy, petrology, and petrogenesis. New Orleans: Rubellite Press. Graphic Granite One rock found at the interface between the k-spar hood and the quartz core is graphic granite Kartashov, Pavel. Graphic Granite. 2009. www.mindat.org Web. <http://www.mindat.org/photo-231952.html> (Kartashov, 2009) Symplectite/Micrographic Texture Symplectite comes from an interface between two minerals of very different grain energies, especially right after a sudden drop in pressure. Micrographic texture comes about as the last phase crystallization between k-spar and quartz. Both of these textures can resemble the largescale textures of pegmatite with respect to a pluton, and they're caused at the same time, and often for the same reasons! Fractal Nature It goes farther than that. Rare Earth Pegmatite Classifications Conclusions/Further Research There is a lot more work to be done on the Palermo pegmatites! Rare Earth Beryl Complex Albite-Spudomene Albite Allanite-Monzanite Gadolinite Pegmatite Type Pegmatite Subtype Beryl-Colmubite Beryl-Columbite-Phospate Spudomene Petalite Lepidolite Amblygonite Geochemical Signature (L), Ree, U, Th Y, (H)REE, Be, Nb > Ta, F (U, Th, Ti) Zr Be, Nb > Ta, +/- Sn, B Be, Nb > Ta, P (Li, F +/- Sn, B) Li, Rb, Cs, Be, Ta > Nb (Sn, P, F +/- B) Li, Rb, Cs, Be, Ta > Nb (Sn, Ga, P, F, +/- B) F, Li, Rb, Cs, Be, Ta > Nb (Sn, P +/- B) P, F, Li, Rb, Cs, Be, Ta > Nb (Sn +/- B) Li, (Sn, Be Ta > Nb +/- B) Ta > Nb, Be, (Li +/- Sn, B) Typical Minerals Allanite, monzanite (topaz) Gadolinite, fergusonite, euxenite, beryl Beryl, columbite-tantalite Beryl, columbite-tantalite, triplite, triphylite Spodumene, beryl, tantalite, (amblugonite, lepidolite, pollucite) Petalite, tantalite, beryl, (amblygonite, lepidolite) Lepidolite, beryl, topaz, microlite, (pollucite) Amblygonite, beryl, tantalite, (lepidolite, pollucite) Spodumene, (beryl, cassiterite, tantalite) Tantalite, beryl, (cassiterite) You'll note: the Palermo is Beryl-Phosphate, with no significant columbite, it doesn't fit onto this chart! Adapted from Cerny 1991 Cerny, P. (1991). Rare-element granitic pegmatites, part 1: Anatomy and internal evolution of pegmatite deposits. part 2. Geoscience Canada, 49-81. Jahns, R. H., & Burnham, W. C. (1969). Experimental studies of pegmatite genesis. 1. a model for the derivation and crystallization of granitic pegmatites. Economic Geology, 843-864 What was the heat source for the pegmatites? When were they emplaced? What is the parent melt? The Palermo pegmatites are probably related to the nearby Esty pegmatites, which crosscut the Concord granite.

Pb/ Pb in uraninite dates the Palermo pegmatites at 342 Ma, though this aging method is notably unreliable. (Foord et al. 1997) Pegmatite Field What does that mean? What makes it a field? Pegmatite field Pegmatite province Pegmatite belt Pegmatite district Pegmatite group A geographic rather than geologic term. Describes all of the pegmatites within a geological province. Related to large linear structures, like deep faults, that are all related to a single geologic structure. A territory with pegmatites in a single formation, with a similar age, source, and structural environment. Another geographic term. A part of a province. A member of a district. Tourmaline is found in great abundance Palermo #2, but is completely absent from Palermo #1. Why is that? The farther they get from their magma source, the more fractionated they become, the more concentrated they are in incompatible elements and volatiles, and the more zoning we see. If they are younger than the Concord granite, there had to be another source. Maybe there is another unexposed pluton. The fluids responsible for hydrothermal alteration are thought to be post crystallization and aqueous (Moore, 1973), and probably came from dehydration of micas (Dorais, personal communication). Quartz With all of these volatiles running around, quartz becomes very fluid, gets a very high diffusion rate, and a very low nucleation rate. Not only that, but it becomes much more adept at holding onto incompatible elements in its fluid and vapor state. It also makes it crystallize at a lower temperature. With all those factors put together, pegmatites can crystallize in a matter of days. How does this relate to Tourmaline? Major Minerals Before anything else, and this might be review. Our biggest minerals are quartz and k-spar 207 206 When were these Emplaced? Like the Concord Granites, the Palermo Pegmatites show no signs of deformation. Moore, P. B. (1973). Pegmatite phosphates; descriptive mineralogy and crystal chemistry. Mineralogical Record, 103-130. Quartz is found in high amounts because there is just so much of it, recall that silicon and oxygen are the two most abundant elements in the crust. After that, in terms of abundance, we have aluminum, iron, calcium, sodium, and magnesium, and finally potassium. Iron, calcium, and magnesium all crystallize very early in mafic rocks, leaving us with sodium, aluminum, and potassium. Perthite By the time we get to Pegmatite, we have silicon, aluminum, potassium, and some sodium left over. Most of the sodium has already crystallized into albite, but just a little bit is left over. Perkins, D. (2012). Kalsi3o8-naalsi3o8 system at 0.1 mpa. [ [Print Photo]]. Retrieved from http://serc.carleton.edu/images/research_education/equilibria/abor_hypersolvus.jpg First k-spar will crystallize, and then little tiny bits of albite (NaAlSi O ) will crystallize as little lines after the system has passed its solidus. This is called "perthite" and it is the second most common mineral at the Palermos. If it were closer to the parent, or there were more sodium, we might see anti-perthite, where small lines of k-spar exsolve into albite. perthite Quartz By far the most common mineral in pegmatite is quartz. At Palermo, it forms the core, with crystals as big as 10 meters across. Compounding the fact that nobody wants to crystallize with the incompatible elements and volatiles, the more felsic a melt, the better it is at holding onto them. As the quartz content gets higher, so does the volatile content. Granite, the most common parent rock of pegmatite, already has at least 20% Quartz, and by the time it's fractionated to pegmatite, it's much higher. Incompatible Elements Quartz and k-spar can't crystallize with them either, so they get pushed out the two crystallize. The quartz crystallizes from the core outwards, and from the wall inwards, and both sides push the incompatible elements away. When they finally cool into pods, it's as giant clusters of incompatible elements forced to crystallize into whatever configuration they can come up with. Often times, this mineral is Quartz, and they form very sharp veins. Anyone who came to Maine saw one of them near the first stop. There is a very beautiful zoned pegmatite on Andrew's Point in Rockport. Palermo is one of these. It was zoned, but it was cracked and has significant hydrothermal alteration. quartz core Core margin zone The diffusion rate means that elements can move freely through the melt, the nucleation rate means it's very hard to form new crystals. You can actually tell a lot about the pegmatite from its geochemistry. Adapted from Cerny 1991 Zoning also occurs from one pegmatite pod to the next. Li, Cs, Be, Ta, Nb Li, Ba, Ta, Nb Be, Nb, Ta Be Barren Because tourmaline is a mineralogical trash can! Exactly which elements are more enriched is a matter needing further study (if I had to guess, I'd say boron). Either way, one of them is in a zone with tourmaline, the other is not. You see these variations throughout the Grafton Pegmatite Field We also get a little bit of biotite and sodium rich feldspar (albite). So. What does the Palermo have to do with any of that? Glad You Asked! How does the Palermo fit in? The Palermo is an LCT Type pegmatite. Specifically a beryl phosphate one. Having a beryl phosphate pegmatite that doesn't have significant columbite is so rare, it isn't even on the chart. It's complex, it started off zoned, but took some hydrothermal alteration which made most of its phosphate minerals. The hydrothermal alteration took place a long time after it crystallized, and at a pretty high temperature. Hydrothermal Alteration Before we're done, you'll understand what all of that means! Scorzalite-lazulite (Fe,Mg, Al (PO ) (OH) : This is produced from montebrasite-amblygonite (LiAlPO (OH,F)) 2 2 4 2 4 o High temperature: 500-300 C The Palermo shows a textbook example of hydrothermal alteration. Phosphate paragenesis ~600-500 C High temperature metasomatic alteration, hydroxilation and cation exchange ~500-300 C Low temperature metasomatic alteration hydration, hydroxylation and cation exchange ~300-100 C Minerals in Palermo Examples Phosphate paragenesis: Triphylite-lithiophylite: Li(Fe,Mn)PO , montebrasite-amblygonite (LiAlPO (OH,F)) 4 4 Scorzalite also forms from triphylite with the addition of hydrothermal Al (III) at this temperature. Low temperature: ~300-100 C o Palermoite forms from montebrasite-amblygonite with the addition of strontium. Nizamoff, James W., Whitmore, Robert W. (2012) The Palermo Pegmatites, North Groton, New Hampshire. Guidebook to Field Trips in Western New Hampshire and adjacent Vermont and Massachusetts, 2012 NEIGC confrence. pp 165-181 Samuelsonite forms from montebrasite-amblygonite with barium This is a very short list, there are probably hundreds of secondary phosphates, and most of them are found at Palermo! What brought about that heat? Unfortunately, most of the research that needs to be done is quite expensive. No detailed geochemical and field studies to determine the petrogenetic origin of the pegmatites have been undertaken in the Grafton field. Nizamoff (2006) Several Acadian to post-Acadian orogeny granitoids of the New Hampshire Plutonic suite outcrop within 10 km of the Palermo #2 pegmatite and may have served as the parental source for the pegmatites of the Grafton field. (Page 1937) Bibliography Continued Page, L.R. (1937) The geology of the Rumney quadrangle, New Hampshire. Unpublished Ph.D. thesis, University of Minnesota. Nizamoff, James. (2006).The Mineralogy, Geochemistry and Phosphate Paragenesis of the Palermo #2 Pegmatite, North Groton, New Hampshire. University of New Orleans Theses and Dissertations http://webmineral.com/specimens/picshow.php?id=146&target=Bjarebyite http://mindatnh.org/Falsterite%20Gallery.html http://webmineral.com/specimens/picshow.php?id=422&target=Foggite http://www.mindat.org/photo-135370.html http://mindatnh.org/Samuelsonite%20Gallery.html http://www.mindat.org/photo-14808.html http://mindatnh.org/Whitlockite%20Gallery.html http://mindatnh.org/Wolfeite%20sheet.html http://www.mindat.org/photo-75161.html 3 8 Caption Reads: Increasing fractionation, volatile enrichment. Complexity of zoning. Extent of replacements. By 'textbook' I mean: it's actually featured in textbooks!
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