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Guelph Scanning Proton Microprobe

SULFIDE MINERAL ANALYSIS

Evaluation of ore bodies and subsequent exploitation to recover silver, gold, platinum-group, and other elements, demand knowledge of the distribution of minor and trace elements in the various sulfide mineral species of the ore. The need to analyze well-characterized individual grains demands an in-situ microprobe technique. Analysis of co-existing minerals e.g. silicates may also be necessary in arriving at a complete understanding of elemental distribution.

Micro-PIXE provides this analysis, with detection limits of a few ppm. Micro-PIXE has already proved its value in measurements of Ag concentration in minor carriers such as chalcopyrite and sphalerite. It has had extensive use in the study of PGE elements in pentlandites from various massive sulfide deposits.

Proton Energy: 3 MeV
Beam Current: 14 nA
Spot Size: 5 x 10 µm
Measuring Time: 10 minutes

Detection Limits in ppm. (wt.):

Pyrrhotite Chalcopyrite
Se 4 6
Mo 4 5
Rh 4 5
Pd 5 6
Ag 6 7
Sn 9 10

GARNETS, CHROMITES, ETC. AND DIAMOND EXPLORATION

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Considerable experience has been built-up at Guelph in the micro-PIXE analysis of garnets, chromites and ilmenites, whose trace element content may help to distinguish diamondiferous from barren rock types. The trace nickel content of garnets is of special interest, in view of the well-defined inverse correlation between nickel content and formation temperature reported in the geochemical literature. The nickel range of interest, 10-100 ppm, which is below electron probe detection limits, is easily handled by micro-PIXE.

Results from a typical garnet analysis:

Proton energy: 3 MeV
Beam current: 7.5 nA
Spot size: 10 x 10 µm
Measuring time: 4.5 minutes

 

Detection limits in ppm (wt.)

Element Ni Cu Zn Ga As Zr Mo
LOD ppm 5 4 3 3 2.5 4 5

Click here to see BHVO-1 results

Micro-PIXE measurements for major elements (Cr, Fe) agree well with electron probe results; measurements for trace nickel agree with those for reference standards. A variety of reference materials have been investigated, e.g. BHVO-1 (basalt).






SR ZONING IN FISH OTOLITHS


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Click here to zoomFish otoliths are composed of calcium carbonate. In the case of anadromous fish, which migrate between fresh and salt-water, there are significant differences in the concentration of strontium that is incorporated in the calcite, reflecting the low Sr content of inland lakes and the high Sr content of ocean water. The growth bands are visible in optical microscopy, and their Sr content can be measured by micro-PIXE, whose limit of detection for Sr is about 1-2 ppm. Linescans conducted across a series of zones reveal an oscillatory behaviour in the Sr concentration for fish that migrate annually to the ocean. Comparison of the Sr banding to the optical banding can reveal in which particular years since birth a fish has migrated, and in which particular years it remained in spawning grounds. Absolute levels of Sr in the primordium assist in the identification of fish with particular lakes.

Click here to zoomMicro-PIXE imaging and analysis of Sr in otoliths thus provides a new quantitative tool for studies of fish migration and for population discrimination. It may prove useful in the context of aboriginal land claims in Canada. The method is also relevant to long-term studies of aquatic pollution by mining operations, since the otoliths incorporate other trace elements.
 

Sample preparation methodology has been developed by a collaboration involving fisheries scientists from DFO, earth scientists from the University of Manitoba and physicists from the University of Guelph. To provide statistically useful data, many otoliths should be examined in any particular study. A large number of specially sectioned otoliths are "potted" in particular orientations in a standard mineral mount, and optically imaged to provide photographs of the band structure. A complete micro-PIXE study of these otoliths is then pre-programmed at the GSPM and the analysis is conducted with minimal operator intervention.

Three posters dealing with specific otolith projects are available for download in PDF format that can be viewed with Acrobat. They are listed below:

Validation of the use of otolith strontium distribution for determing migratory behaviour of Arctic Char (Salvinus alpinus)z

To sea or not to sea, evidence for non-anadromous behaviour of Artic Char (Salvlinus alpinus) from Lake Hazen, Ellesmere Island, Northwest Territories

Preliminary results of stock discrimination of Dolly Varden Char, Salvelinus malma and Arctic Char, S. alpinus from Ivvavik National Park, Yukon Territory using micro-PIXE analysis of otolith strontium