Oxidation state of iron in alteration minerals associated with sandstone-hosted unconformity-related uranium deposits and apparently barren alteration systems in the Athabasca Basin, Canada: Implications for exploration

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• 作者：Ronald Ng^a ; ^{ng@geoladm.geol.queensu.ca} ; Paul Alexandre^a ; Kurt Kyser^a ; Jonathan Cloutier^b ; Yassir A. Abdu^c ; Frank C. Hawthorne^c
• 关键词：Athabasca Basin ; Sandstone-hosted unconformity-related uranium ; Iron oxidation state ; Illite ; Chlorite
• 刊名：Journal of Geochemical Exploration
• 出版年：2013
• 出版时间：July, 2013
• 年：2013
• 卷：130
• 期：Complete
• 页码：22-43
• 全文大小：12076 K

文摘

Sandstone-hosted unconformity-related U deposits in the Athabasca Basin at McArthur River Zone 4 and Maurice Bay as well as barren alteration systems at Wheeler River Zone ¡°K¡± and Spring Point are surrounded by an outer, peripheral zone of illite and an inner, central zone of chlorite alteration. The oxidation state of Fe determined by ⁵⁷Fe M?ssbauer spectroscopy of illite, sudoite, and clinochlore from these systems indicates that pre-ore illite contains mostly Fe^3 + (Fe^3 +/¦²Fe = 0.77-1.00), reflecting formation from a predominantly oxidizing basinal fluid. Lower Fe^3 +/¦²Fe ratios are recorded by late pre-ore sudoite and clinochlore occurring near faulted unconformities, consistent with the contribution to the chlorites from reducing basement-derived fluids. Sudoite and clinochlore in the alteration halo of barren systems are more reduced (Fe^3 +/¦²Fe median = 0.3-0.4) than sudoite from mineralized systems (Fe^3 +/¦²Fe median = 0.45-0.55). Sudoite from both systems becomes broadly more oxidized with increasing distance from the fault zone. Variations in the Fe^3 +/¦²Fe ratios of sudoite and clinochlore support a mechanism in which Fe^2 + transported by reducing basement-derived fluids is partially oxidized to Fe^3 + by basinal fluids prior to incorporation into the chlorite. Thus, scarcity of oxidizing U-bearing basinal fluids available for interaction with reducing basement fluids is a critical factor precluding U mineralization in barren systems. Trends of decreasing Fe^3 +/¦²Fe ratios in sudoite coupled with decreasing ²⁰⁷Pb/²⁰⁶Pb ratios of leachable Pb can be used as geochemical vectors to the sites of potential U mineralization.