Ar/³⁹Ar and (U–Th)/He – ⁴He/³He geochronology of landscape evolution and channel iron deposit genesis at Lynn Peak, Western Australia

(U–Th)/He geochronology of authigenic goethite cements from the Lynn Peak channel iron deposit (CID), Hamersley Province, Western Australia, reveals a history of mineral precipitation ranging from ca. 33 to 14Ma. Massive goethites from nearby weathering profiles at Roy Hill North, a possible source of detrital material during the aggradation of the Lynn Peak channels, yield (U–Th)/He results as old as ca. 64Ma. The combination of (U–Th)/He geochronology with incremental outgassing ⁴He/³He studies on proton-irradiated samples reveals that Lynn Peak goethites host radiogenic ⁴He in low retentivity (LRD) and high retentivity (HRD) domains and that the HRDs account for most of the sample mass and have lost very little of their original ⁴He over geologic time. Such high retentivity is especially notable given the goethites were collected from the surface, where they were subject to significant heating by solar irradiation. Minor contamination by detrital fragments of potentially ⁴He-rich primary phases (e.g., rutile, ilmenite, zircon) occurs in some samples. Fortunately, the ⁴He/³He method permits characterization of this extraneous ⁴He component, which is small (