U/Pb age and origin of supergene uranophane-beta from the Borborema Pegmatite Mineral Province, Brazil

• U/Pb age dating of supergene alteration.
• Physical-chemical constraints of supergene alteration.
• Identification of uranophane-beta in field samples.

Uranophane-beta of supergene origin formed in the Borborema Pegmatite Mineral.Province, which is situated in the north-easternmost part of Brazil. The sampling site lies in the topmost parts of the Quintos Pegmatite, about ten kilometers north of the town of Equador. The uranyl silicate was investigated for its age and physical chemical regime of formation. Age dating yielded a U/Pb age of 6.77 ± 0.61 Ma. Uranophane has been derived together with autunite from weathering of brannerite in a tropical climate under alternating wet and dry seasons, when the pH was below 8. This canary-yellow well-crystallized uranyl silicate can be used as a physical chemical marker as well as a clock for supergene alteration.