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Cleuson, Val de Nendaz, Wallis, Switzerland

The Cleuson locality is a small radioactive anomaly with several ore veins in finely layered host rock. One of the veins is the type locality for Cleusonite, see the literature list at the bottom. The dump, created by building a small road, was screened with a scintillation counter. Samples showing an activity above base level were cut and polished. The main ore mineral found was arsenopyrite (Asp). The entire sample shows strong flow patterns, even visible in the polished slabs. The sample contains are larger amount of rutile, either as clusters of small crystals, as rounded and partly fractured or dissolved blebs or as entirely scattered fragments within the flow patterns. Euhedral zircon is also present. An other sample from the banded wall rock contained small grains of chalcopyrite with a gray rim showing brown internal reflections, which most likely is goethite. The matrix consists of quartz, muscovite and albite as determined by Raman spectroscopy.

Polished slab with a quarz-arsenopyrite vein. Width at the base: 7 cm

Unbenannt-126

Enlarged part from the upper picture. The arsenopyrite crystals can easily be seen:

Unbenannt-225

The polished section with Nic //, Obj. 10x, air. Arsenopyrite in quarz, with a twin crystal (100 µm bar):

image_0000437

Same with Nic +:

image_0000638

Clusters of rutile needles, Nic //, Obj. 50x, air.

image_0001031

Same with Nic +, Obj. 50x, air

image_0001132

Rutile in state of fracturing and dissolution. Nic //, Obj. 20x, air, 100 µm scale bar

Rutile_1a_100um

Rutile in state of fracturing and dissolution. Flow structures are dominating in the sample. Nic //, Obj. 20x, air, 100 µm scale bar

Rutile_2_100um 1

Euhedral zircon in quartz matrix (with internal reflections). Nic //, Obj. 50x, air, 50 µm scale bar

Zircon_50um_1

Zircon (right) and rutile (left). Nic //, Obj. 50x, air, 50 µm scale bar

Zircon_50um_2

View of the second sample with finely distributed chalcopyrite (width: 3.5 cm):

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Chalcopyrite from the second sample, with a rim most likely goethite, Nic //, Obj. 50x, air

image_0001719_50x

Same with Nic +, Obj. 50x, air

image_0001620_50x

Micro raman spectroscopy

Several cavities with the size of about 100-500 µm were found in the sample and analysed. The spots marked in red all contained native sulfur, probably as a weathering product of arsenopyrite. Nic //, Obj. 20x, air, 100 µm scale bar

Cleuson

Rruff reference for sulfur at 532 nm (blue), results from this study (black). The first peak at about 85 cm-1 is confirmed as a sulfur peak by the McCreery group standard raman spectra page (http://www.chem.ualberta.ca/~mccreery/ramanmaterials.html).

Cleuson Rruff


For further informations on the region this article might be interesting:

Wülser, P.-A., Meisser, N., Brugger, J., Schenk, K., Ansermet, S., Bonin, M., Bussy, F.: Cleusonite, (Pb,Sr)(U4+,U6+)(Fe2+,Zn)2(Ti,Fe2+,Fe3+)18(O,OH)38, a new mineral species of the crichtonite group from the western Swiss Alps. European Journal of Mineralogy.17.(2005).933-942.