Mineralogy and chemistry of a new halloysite deposit from the Rio de Janeiro pegmatite province, south-eastern Brazil

Abstract

Halloysite is a 1:1 dioctahedral clay mineral that has been studied widely for applications in nanotechnology and as a mineral exploration guide for recognizing regolith-hosted heavy rare earth element (HREE) deposits. In Brazil, pegmatites from the state of Rio de Janeiro have been catalogued, but their potential to host halloysite deposits has never been studied. After a mineral exploration programme, one pegmatite with considerable halloysite contents and economic potential was discovered. This study reports the mineralogical and chemical characterization of the halloysite of this pegmatite and evaluates the possibility of clay-adsorbedHREEdeposits, like that in the Zudong (China) regolith-hostedHREEdeposit. Seven samples were collected in horizontal channels. Bulk samples and clay fractions (2, 36.10 wt.% Al₂O₃, 14.62 wt.% loss on ignition and 1.04 wt.% Fe₂O₃, as well as technological properties close to those observed in world-class halloysite deposits such as Dragon Mine (USA) and Matauri Bay (New Zealand). The clay minerals did not present significantHREEcontents.