Rare earth elements (REE) are commonly enriched in alkaline magmatic systems and may be further redistributed by late-stage hydrothermal processes. This study focuses on REE-bearing mineralization in post-orogenic alkaline rocks and hydrothermal veins of the Amram Massif and Ramat Yotam volcanic complex, at the northernmost Arabian-Nubian Shield (Eilat area, southern Israel). These late Neoproterozoic (600-580 Ma) rocks record shallow emplacement of alkaline magmas followed by prolonged, possibly multi-stage, hydrothermal activity.
Fieldwork targeted late-stage silicic alkaline rocks, which often show intense alteration, and associated calcite, barite, and manganese-oxide veins. Whole-rock REE concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS) and mineralogical assemblages were defined using X-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive spectroscopy (SEM-EDS). Oxygen and hydrogen isotope ratios of calcite-hosted fluid-inclusions and oxygen and carbon isotope ratios of host vein calcite were measured using cavity ring-down spectroscopy (CRDS) and isotope-ratio mass spectrometry (IRMS).
Total REE concentrations in Amram alkaline rocks range from 100 to 700 ppm and are generally higher than those of other basement rocks in Israel (≤300 ppm). The LREE are enriched over HREE in all the magmatic rocks studied. Primary magmatic monazite is locally replaced by REE-F carbonates, recording remobilization of REE from phosphates into secondary phases during hydrothermal alteration.
Calcite veins provide an additional REE reservoir, with total REE ranging from 100 to 800 ppm, comparable to the host magmatic rocks, yet significantly higher than any other calcite veins recorded in Israel. Most calcite veins are LREE-enriched while some, from Amram Massif, are equally enriched in LREE and HREE. Stable isotope ratios of calcite and hosted fluid-inclusions indicate relatively high temperature (120-150°C) calcite precipitation from fluids of meteoric-origin, suggesting that REE were first concentrated in shallow alkaline magmas and subsequently redistributed into veins by later hydrothermal circulation in post-orogenic setting.