Sample records for euxenite
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NASA Astrophysics Data System (ADS)
Škoda, Radek; Novák, Milan
2007-04-01
Aeschynite-group minerals (AGM) and euxenite-group minerals (EGM) occur in REL-REE euxenite-subtype pegmatites from the Třebíč Pluton, Czech Republic. They form strongly metamictized, light brown to black, equigranular to needle-like, subhedral to anhedral grains enclosed in blocky K-feldspar and less commonly in albite, and blocky quartz, and in the graphic unit (quartz and K-feldspar). Both AGM and EGM are homogeneous to slightly heterogeneous in BSE images. They are not commonly associated with the other primary Y,REE,Ti,Nb-bearing minerals, i.e. allanite-(Ce), monazite-(Ce), titanite, and ilmenite, which occur within the same textural-paragenetic unit. Aeschynite-(Y), aeschynite-(Ce), aeschynite-(Nd), nioboaeschynite-(Ce), tantalaeschynite-(Ce), vigezzite and polycrase-(Y) were identified using EMP and canonical discrimination analysis [Ercit, T.S., 2005a. Identification and alteration trends of granitic-pegmatite-hosted (Y,REE,U,Th)-(Nb,Ta,Ti) oxide minerals: a statistical approach. Can. Mineral. 43, 4 1291-1303.]. The exchange vector ACa B(Nb,Ta) A(Y,REE) - 1 BTi - 1 or its combination with the exchange vector ACa 2B(Nb,Ta) 3A(U,Th) - 1 A(Y,REE) - 1 BTi - 3 have been elucidated for the AGM. The exchange vector ACa A(U,Th) A(Y,REE) - 2 is predominant in the EGM. The AGM are enriched in HREE, whereas LREE are concentrated in the EGM. Weak to none-existent geochemical fractionations, as expressed by the U/(U + Th), Y/(Y + REE), Ta/(Ta + Nb) and (Nb + Ta)/(Ti + Nb + Ta) ratios, were noted for single grains from both the AGM and EGM, as well as in grains of polycrase-(Y) from four different textural-paragenetic units located in the Vladislav pegmatite. Simultaneous increase of U/(U + Th) and Y/(Y + REE) in the AGM during fractionation is typical. The Ta/(Ta + Nb) fractionation is usually weak and contradicts the Y/(Y + REE) and U/(U + Th) fractionation trends. This unusual behavior of Nb and Ta may be controlled by associated Ti-rich minerals (titanite, ilmenite, rutile), the composition of parental melt and/or by elevated F activity. The AGM and EGM from pegmatites of the Třebíč Pluton are quite similar in composition to those from REL-REE euxenite-subtype pegmatites in the Trout Creek Pass, Chaffee County, Colorado, USA, which are generally Ca,U,Th-depleted, show lower Ta/(Ta+Nb), and lower variation in HREE/LREE.
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Grimaldi, F.S.
1957-01-01
This paper presents a selective iodate separation of thorium from nitric acid medium containing d-tartaric acid and hydrogen peroxide. The catalytic decomposition of hydrogen peroxide is prevented by the use of 8quinolinol. A few micrograms of thorium are separated sufficiently clean from 30 mg. of such oxides as cerium, zirconium, titanium, niobium, tantalum, scandium, or iron with one iodate precipitation to allow an accurate determination of thorium with the thoronmesotartaric acid spectrophotometric method. The method is successful for the determination of 0.001% or more of thorium dioxide in silicate rocks and for 0.01% or more in black sand, monazite, thorite, thorianite, eschynite, euxenite, and zircon.
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Beryl-bearing pegmatites in the Ruby Mountains and other areas in Nevada and northwestern Arizona
Olson, Jerry C.; Hinrichs, E. Neal
1960-01-01
Pegmatite occurs widely in Nevada and northwestern Arizona, but little mining has been done for such pegmatite minerals as mica, feldspar, beryl, and lepidolite. Reconnaissance for beryl-bearing pegmatite in Nevada and in part of Mohave County, Ariz., and detailed studies in the Dawley Canyon area, Elko County, Nev., have shown that beryl occurs in at least 11 districts in the region. Muscovite has been prospected or mined in the Ruby and Virgin Mountains, Nev., and in Mohave County, Ariz. Feldspar has been mined in the southern part of the region near Kingman, Ariz., and in Clark County, Nev. The pegmatites in the region range in age from Precambrian to late Mesozoic or Tertiary. Among the pegmatite minerals found or reported in the districts studied are beryl, chrysoberyl, scheelite, wolframite, garnet, tourmaline, fluorite, apatite, sphene, allanite, samarskite, euxenite, gadolinite, monazite, autunite, columbite-tantalite, lepidolite, molybdenite, and pyrite and other sulflde minerals. The principal beryl-bearing pegmatites examined are in the Oreana and Lakeview (Humboldt Canyon) areas, Pershing County; the Dawley Canyon area in the Ruby Mountains, Elko County, Nev.; and on the Hummingbird claims in the Virgin Mountains, Mohave County, Ariz. Beryl has also been reported in the Marietta district, Mineral County; the Sylvania district, Esmeralda County; near Crescent Peak and near Searchlight, Clark County, Nev.; and in the Painted Desert near Hoover Dam, Mohave County, Ariz. Pegmatites are abundant in the Ruby Mountains, chiefly north of the granite stock at Harrison Pass. In the Dawley Canyon area of 2.6 square miles at least 350 pegmatite dikes more than 1 foot thick were mapped, and beryl was found in small quantities in at least 100 of these dikes. Four of these dikes exceed 20 feet in thickness, and 1 is 55 feet thick. A few pegmatites were also examined in the Corral Creek, Gilbert Canyon, and Hankins Canyon areas in the Ruby Mountains.The pegmatite dikes in the Dawley Canyon area intrude granite and metamorphic rocks which consist chiefly of quartzite and schist of probable Early Cambrian age. The granite is of two types: a biotite-muscovite granite that forms the main mass of the stock and albite granite that occurs in the metamorphic rocks near the borders of the stock. The pegmatites were emplaced chiefly along fractures in the granite and along schistosity or bedding planes in the metamorphic rocks.Many of the Dawley Canyon pegmatite dikes are zoned, having several rock units of contrasting mineralogy or grain size formed successively from the walls inward. Aplitic units occur either as zones or in irregular positions in the pegmatite dikes and are a distinctive feature of the Dawley Canyon pegmatites. Some of the aplitic and fine-grained pegmatite units are characterized by thin layers of garnet crystals, forming many parallel bands on outcrop surfaces. The occurrence of aplitic and pegmatitic textures in the same dike presumably indicates abrupt changes in physical-chemical conditions during crystallization, such as changes in viscosity and in content of volatile constituents. Concentrations of 0.1 percent or more beryl, locally more than 1 percent, occur in certain zones in the Dawley Canyon pegmatites. Spectrographic analyses of 23 samples indicate that the BeO content ranges from 0.0017 to 0.003 percent in the albite granite, from ,0.0013 to 0.039 percent in aplitic units in pegmatite, from 0.0005 to 0.10 percent in coarse-grained pegmatite, and from less than 0.0001 to 0.0004 percent in massive quartz veins. The scheelite-beryl deposits at Oreana and in Humboldt Canyon, Pershing County, are rich in beryllium. Twelve samples from the Lakeview (Humboldt Canyon) deposit range from 0.018 to 0.11 percent BeO, but underground crosscuts have failed to intersect similar rock at depth. Beryl locally constitutes as much as 10 percent of the pegmatitic ore at Oreana. The beryl was not recovered during tungsten mining at Oreana and is now in the tailings of the mill at Toulon, Nev. The percentage of beryl is lower than the Oreana ore because of dilution by tailings from other ores milled at Toulon. Beryl has been found in many pegmatite dikes in the Virgin Mountains. Both beryl and chrysoberyl occur in dikes on the Hummingbird claims, north of Virgin Peak, in Mohave County, Ariz. Spectrographic analyses of 5 representative samples of the principal dike on the Hummingbird claims range from 0.055 to 0.11 percent BeO.
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Thorium resources of selected regions in the United States
Staatz, Mortimer Hay; Hall, R.B.; Macke, D.L.; Armbrustmacher, T.J.; Brownfield, I.K.
1980-01-01
Thorium resources have been assessed in a previous report entitled 'Principal thorium resources in the United States' (Staatz and others, 1979) for (1) veins in the larger districts, {2) massive carbonatites, {3) disseminated deposits, and {4) stream placers of North and South Carolina. This report is a sequel to that report and assesses thorium resources in {1) Florida beach placers, (2) Idaho stream placers, (3) veins and pipes in the Bokan Mountain district, Alaska, (4) carbonatite dikes, and {5) apatite-bearing iron deposits near Mineville, New York. Thorium resources for each of these categories are divided into reserves and probable potential resources. When data are available, each of these is then divided into the following cost categories: (1) the amount of ThO2 producible at a cost of less than $15/lb (per pound), (2) the amount producible at a cost of between $15 and $30/lb, and (3) the amount producible at a cost of between $30 and $50/1b. Beach placers of northern Florida have reserves of 16,200 short tons of ThO2 and probable potential resources of 5,120 tons of ThO2. These deposits are heavy-mineral placers that are mined for a variety of minerals--principally titanium minerals and zircon. The thorium-bearing mineral in these placers, monazite, makes up only a minor part of the heavy minerals. Therefore, production of ThO2 from these placers is dependent on the markets for other heavy minerals. Assuming the market for other heavy minerals to be the same as in 1978, then 98 percent of the ThO2 could be produced for less than $15/lb. If, however, no other coproducts were produced, then the cost of producing ThO2 would be greater than $50/1b. Stream placers containing thorium are found along many streams that drain the Idaho batholith, but most are too small to add significantly to the thorium resources. The resources of the five largest districts, each of which consists of at least several individual placers, have been tabulated. These districts are (1) Long Valley, (2) Bear Valley, (3) Burgdorf-Warren area, (4) Boise Basin, and (5) Ell City-Newsome area. These five areas have reserves of 10,100 short tons of ThO2 and probable potential resources of 10,300 tons. Long Valley contains about half the reserves--5,680 tons of ThO2--and all the probable potential resources. Monazite is the most important heavy mineral in all except the Bear Valley deposit. Here euxenite, although not quite as abundant as monazite, is a more important mineral, because it contains approximately 14.5 percent U3O8 in addition to 5 percent ThO2. Reserves in this placer amount to 1,605 short tons of ThO2 and 1,475 tons of U3O8. Eighty-two percent of the reserves and all of the probable potential resources can be produced at less than $30/1b of ThO2. The lower cost reserves are concentrated in the Long and Bear Valley areas. Here 64 percent of the ThO2 can be produced for less than $15/1b and another 29 percent of the ThO2 at between $15 and $30/lb. Sixteen veins and pipelike bodies are evaluated in the Bokan Mountain area of southeastern Alaska. The district contains other deposits that are too poorly exposed to make meaningful resource estimates. Reserves estimated in this district are 1,440 short tons of ThO2; probable potential resources amount to 2,320 tons of ThO2. About 99 percent of these resources are in deposits whose grade is at least 0.2 percent ThO2. In addition, these deposits contain reserves of 420 tons of U3O8 and probable potential resources of 820 tons of U3O8. Eighty-two percent of the reserves and probable potential resources can be produced at less than $15/lb. The average grade of this ore is 0.54 percent ThO2 and 0 15 percent U3O8. Some carbonatite dikes, although generally not as high grade as the veins, contain resources of thorium. Carbonatite dikes in the following six districts were investigated: (1) Wet Mountains, Colo.; (2) Powderhorn district, Colorado; (3) Mountain Pass area, California; (4) Bearpaw