Geochemical alteration of pyrochlore group minerals; betafite subgroup

Abstract

Other| October 01, 1996 Geochemical alteration of pyrochlore group minerals; betafite subgroup Gregory R. Lumpkin; Gregory R. Lumpkin Australian Nuclear Science and Technology Organisation, Materials Division, Menai, N.S.W., Australia Search for other works by this author on: GSW Google Scholar Rodney C. Ewing Rodney C. Ewing University of New Mexico, United States Search for other works by this author on: GSW Google Scholar American Mineralogist (1996) 81 (9-10): 1237–1248. https://doi.org/10.2138/am-1996-9-1022 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Gregory R. Lumpkin, Rodney C. Ewing; Geochemical alteration of pyrochlore group minerals; betafite subgroup. American Mineralogist 1996;; 81 (9-10): 1237–1248. doi: https://doi.org/10.2138/am-1996-9-1022 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Relatively low-temperature, secondary alteration is common in samples of metamict betafite and initially proceeds by the substitution mechanisms ANaYF → A□Y□, ACaYO → A□Y□, and ACaxO → A□X□ Alteration is usually accompanied by hydration (∼10-15 wt% H2O) together with minor increases in Al, K, Mn, Fe, Sr, and Ba. At this stage, U and Th remain relatively unaffected by the alteration process. Once Na and F are removed and the Ca content drops below about 0.2-0.3 atoms per formula unit (∼2.5-3.5 wt% CaO), betafite bulk compositions fall within the stability field of liandratite + uranpyrochlore + rutile (or anatase), thus promoting major element mobility (including Th, U, Pb, and B-site cations), incipient recrystallization, and partial dehydration. New phase assemblages occur as a function of decreasing bulk U content in the order liandratite + rutile, liandratite + uranpyrochlore + rutile, and uranpyrochlore + rutile. The same phase assemblages also occur in laboratory heating experiments performed in an inert atmosphere at 1000 °C. Up to 20-30% of the original amount of U may be lost during severe secondary alteration and recrystallization of betafite. Part of this U is retained by liandratite crystallized in the adjacent host rock. Loss of radiogenic Pb results from both long-term diffusion and secondary alteration, aided by radiation damage-induced volume expansion and microfrac-turing. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.