The study of ore mineralization is difficult for the size of mineral phases (in μm), gel nature of components etc. Application of traditional geological instruments (EPMA, SEM, XRD) is often limited due to the low-grade ore, particle size or colloidal nature of uranium and uranium-bearing phases.
Dear Mr. Mikysek,
The identification of the element content of micro grains smaller than 5 microns should not be a big problem.
The bottom line for the use of SEM and EPMA is the surface quality of the samples. The highest surface quality can be achieved with an ion beam cross section polisher. Latest SEM and EPMA analyzers can measure even element profiles in the nanometer range in very sensitive materials.
As an example, I show you here attached a SEM image of an arsenic sulfide surface which has been prepared with an ion beam cross section polisher and was analyzed by an SEM or EPMA quantitatively along a profile line. The tiny spherule (approx. 100 nanometers in diameter) is embedded in a matrix of arsenic sulfide.
Best regards,
Guenter Grundmann
Dear Mr. Mikysek,
the problem will be to a lesser extent aggravated by the size than by the type of U black ore minerals which you might expect. I suspect it is of a "Hamr-type" environment where organic matter (not detectable neither by SEM nor by EMPA), and U minerals of poor crystallinity may be present. I found in an environment like that lots of U compounds where a proper identification failed and only constraining of the mineral phases seemed possible. XRD reaches its limits but sometimes may be helpful, particularly when the remobilization of the U is of Cenozoic age and metamictization is not in full swing. This is especially true in case of U-Ti-Si compounds. I avoid the mineralogically well-defined names coffinite and brannerite.
I wish you much success
Best regards
H.G.Dill
Dear Mr. Mikysek
EPMA technique is a good tool for a well-polished surface, at least for semi-quantitative (qualitative) analysis of fine-grained minerals (even < 1 microns). Field emission scanning electron microscope (FESEM) is more powerful than EPMA for ultra-high magnification and accurate quantitative-semi-quantitative analysis of fine mineral particles.
Have a good luck.
Ahmed
Dear colleagues,
Many thanks for useful advice! I will try to briefly elaborate some of these points and append a few comments and questions.
Indeed it is uranium mineralization situated within geological structure called Stráž block (in the area of northern part of the Bohemian Cretaceous Basin) with unique association of elements U-Zr-P-Ti, which characterizes the ore fields. Besides the presence of organic matter (especially in freshwater sediments) is crucial anomalous occurrence of Zr.
In the first step, I used XRF-mapping for localization the largest possible surface of ore samples to determine the most abundant spheres of occurrence the elements of interest (U, Zr, Nb, etc.). Based on these results (elemental maps) is considerably simpler to prepare polished sections of region of interest. Their quality is not always perfect (due to the friability of material). Ion beam polishing is certainly a useful solution. But, I have two questions - Is it possible to use this technique for preparing of thin or rock sections? For my investigation, it is more attractive idea, than doing the cross section of samples. Combination of the highest surface quality and SEM/EPMA can be successful. However, is it suitable for determination of mineralogically poorly defined phases?
As an example, I show you here three SEM images (as an attachment) of sample, where quartz grains are cemented by zirconium matrix and clay minerals. U-minerals are not visible in BSE. But uranium (M-lines) is diffused in the micro-grains form within the matrix. Third image shows Zr-matrix in secondary electrons. I think that Zr-matrix (known as hydrozircon) conceals micro-grains or inclusions of “true” U-minerals (uraninite, coffinite). This theory is necessary to confirm or refute instrumentally.
Best regards
Petr Mikysek
Hello Petr, fine-grained mineralisation can indeed be a problem in characterising uranium ores. Many of the answers provided above regarding EPMA or SEM techniques are correct. Please see the attached document for issues regarding identification of fine-grained U-mineralisation via electron beam techniques.
Article The application of automated electron beam mapping technique...
- Badges
- Science topic