REE-bearing phosphate mineral chemistry for iron sulfide‑copper‑gold exploration: A study at Jericho, NW Queensland, Australia

We present mineral chemistry data from the rare-earth element (REE) bearing phosphates monazite and rhabdophane sampled from the Jericho iron sulfide‑copper‑gold (ISCG) deposit in the Cloncurry District, north-west Queensland. REE-bearing phosphates sampled from within the narrow mineralised sequence have a characteristic mineralogy and chemical signature compared to REE-bearing phosphates sampled from the unmineralised metamorphic host sequences only meters away. The mineralised samples contain the hydrated REE-bearing phosphate rhabdophane (REEPO₄ · n H₂O) which occurs as veins and ‘spongy’ textured grains in association with sulfide minerals and commonly replacing apatite. In contrast, the metamorphic host rocks contain monazite (REEPO₄) with metamorphic textures and are rarely associated with sulfide minerals. Rhabdophane and monazite have comparable ΣREE and REE profiles, however the rhabdophane grains are characterised by lower Th contents and higher Ca, S and water contents. Molar ratios of S/Th and Ca/Th, determined by electron probe microanalyser (EPMA), can be used to discriminate between REE phosphates from within the Jericho mineralisation from those not associated with mineralisation. The presence of hydrated rhabdophane also indicates the temperature of mineralisation is at or below 200–250 °C.