Unusual organic matter associated with uranium from the Claude Deposit, Cluff Lake, Canada

Abstract

Blebs and pods of organic matter (0.2-7.0 cm in diam) are associated with uranium mineralization in all the major deposits (D, N-R-F, Claude, OP, and Dominique-Peter zones) of the Cluff Lake area in northwestern Saskatchewan. These deposits are hosted in strongly altered quartzofeldspathic, graphitic pelitic, and granitoid gneisses of suspected Archcan age and locally, as in the D zone, in the basal section of the unmetamorphosed middle Proterozoic Athabasca Group sediments, which comprise conglomerate, sandstone, and siltstone. Samples of the organic matter from the Claude deposit contain up to 12 percent uranium, principally as small uraninite grains (10-40 mu m in diam) and minor coffinite. Associated mineral grains include pyrite, marcasite, chalcopyrite, galena, molybdenite, jordisite, gersdorffite, and altaite.The uranium and its daughters have caused massive radiation damage that is expressed as complexly zoned halos approximately 50 mu m wide in the surrounding organic material. Stable isotope determinations of the bulk organic matter give a delta 13 C value of -44 per mil vs. PDB, whereas occluded gases CH 4 and CO 2 , produced by irradiation, show delta 13 C values of -48 and -32 per mil vs. PDB, respectively. Pyrolysis-gas chromatography-mass spectrometry of the sample yields mainly one- and fused-ring aromatic molecules from the organic matter that are out of range of the alpha particles from the uraninite grains.The presence of possible flow structures in the organic matter and the angular nature of the mineral inclusions suggest that most of the minerals were broken from vein walls and mixed into the organic matter as it filled the veins. Thus, their presence in the organic matter is the result of mechanical processes that occurred after the minerals were originally precipitated.