Note on the Occurrence of Thorite at Alter Pedroso (Portugal). Report No. 29; NOTA SOBRE UMA OCORRENCIA DE TORITE EM ALTER PEDROSO. Memoria No. 29

Technical Report · Fri Jan 01 00:00:00 EST 1960

OSTI ID:4099835

Pacheco, J T; Gomes, R A.D.

The first known occurrence of thorite in Portugal is reported. The mineral was found as small dark reddishbrown euhedral grains scattered in a soil sample from the hyper-alkaline syerdte region of Alter Pedroso, in prospecting for radioactive materials. Zircon, riebeckite, aegirine, feldspar, biotite, magnetite (all of these common minerals of the hyper-alkaline syenite), and a few other urddentified minerals were found in the soil associated with thorite. This suggests the weathering of a local pegmatitic differentiation of the syenite as the origin of the thorite. Microscopic examination shows the mineral to be only partially metumict, and it is probably altered to a variable degree. Euhedral grains are constituted by several nearly colorless anisotropic nuclei (n/sub p/ near 1.69, n/sub g/ near 1.71, and sometimes anomalous B+ with variable 2V averaging 10/sup 0/) surrounded by a golden-brown isotropic material (n about 1.67). Specific gravity determinations were somewhat impaired by zircon inclusions and led to a value of 4.79. The chemical composition was determined by emission and x-ray fluorescence spectrography and shows a high yttrium content. A partial semiquantitative analysis gave the following results: ThO/sub 2/ (58.0%), SiO/sub 2/ (14.5%), Fe/sub 2/O/sub 3/ (2.5%), Y/sub 2/O/sub / 3>i (2.5%), CaO (l.1%), U/sub 3/O/sub 8/ (0.5%), and PbO (0.2%). The elements Be, Mg, Al, Mn, and P were also detected. X-raypowder patterns obtained before and after heating the sample to 1000 ts C for 1 hr in air confirmed the mineral to be only slightly metamict and showed that the tetragonal phase still prevails above 950 ts C. Calculations based on these patterns led to a tetragonal unit cell with a/sub 0/ = 7.05 0.01 A, c/sub 0/ = 6.27 0.01 A, and c/sub 0//a/sub 0/ = 0.889. (auth).

• Research Organization: Portugal. Junta de Investigacoes do Ultramar, Lisbon
• NSA Number: NSA-15-009180
• OSTI ID: 4099835
• Report Number(s): NP-9826
• Resource Relation: Other Information: Orig. Receipt Date: 31-DEC-61
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

GEOLOGY, MINERALOGY, AND METEOROLOGY
AEGIRINE
ALUMINUM
ALUMINUM SILICATES
AMPHIBOLES
ANISOTROPY
BERYLLIUM
BIOTITE
CALCIUM SILICATES
COLOR
CRYSTALS
DENSITY
EUROPE
FELDSPARS
FLUORESCENCE
GRAIN SIZE
HORNBLENDE
IGNEOUS ROCKS
IMPURITIES
IRON OXIDES
IRON SILICATES
LATTICES
MAGNESIUM
MAGNESIUM SILICATES
MAGNETITE
MANGANESE
MICA
MICROSCOPY
MINERALS
OXIDES
PHOSPHORUS
PORTUGAL
POTASSIUM SILICATES
POWDERS
PROSPECTING
QUALITATIVE ANALYSIS
QUANTITY RATIO
RIEBECKITE
SILICATES
SODIUM SILICATES
SPECTROSCOPY
SPINELS
SYENITES
THORITE
THORIUM OXIDES
THORIUM SILICATES
URANIUM OXIDES
X RADIATION
YTTRIUM
YTTRIUM OXIDES
ZIRCON
ZIRCONIUM SILICATES