• journal_title：Geology
• Contributor：Julien Mercadier ; Antonin Richard ; Michel Cathelineau
• Publisher：Geological Society of America
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.1130/G32509.1
• journal_abbrev：Geology
• issn：0091-7613
• volume：40
• issue：3
• firstpage：231
• section：Articles

In giant unconformity-related U deposits from the Athabasca Basin (Canada), the origin of the ore fluids and the source of elements typically associated with U ore, such as Mg and B, are highly controversial. This paper presents a petrographic and boron isotopic study of Mg-tourmalines (dravites) coeval with U oxides and of primary tourmalines from basement rocks. The heavy B isotopic compositions of dravites (δ¹¹B = 19.6‰–36.5‰) contrast with the light composition of basement tourmalines (δ¹¹B = –8.1‰–3.3‰) and clearly show that most of the B was brought to the ore system by basinal brines of marine origin. Because the latter are also typically Mg-rich, a similar origin for Mg is proposed. These results support the idea that marine-derived brines were the only fluids involved in the formation of the deposits, and therefore challenge the previous models in which the B and Mg were leached from sedimentary and/or basement rocks, or carried by a basement-derived fluid.