Hydrothermal Rare Earth Element (Xenotime) Mineralization at Maw Zone, Athabasca Basin, Canada, and Its Relationship to Unconformity-Related Uranium Deposits

Hydrothermal formation of heavy rare earth element (HREE)–xenotime deposits at 100 °C in a sedimentary basin

“…The vast majority of rare earth element (REE) deposits are known to form at high temperatures in association with carbonatitic and peralkaline magmatism (e.g., Migdisov et al, 2016). However, lesser-known hydrothermal deposits of heavy REE (HREE)-enriched xenotime (YPO 4 ) also occur within sedimentary basins (e.g., Rabiei et al, 2017). Given the low aqueous solubility of xenotime, it has been unclear if REEs are in fact transported in large quantities at basinal temperatures or if hightemperature magmatic-hydrothermal fluids are required to explain the deposits.…”

Common Problems and Pitfalls in Fluid Inclusion Study: A Review and Discussion

“…A 'fluid inclusion assemblage' (FIA) [22] is defined by Goldstein and Reynolds (1994) [14] and Goldstein (2001) [15] as the most finely discriminated, petrographically distinguishable group of fluid inclusions formed by a single event of fluid inclusion entrapment. Since its emergence, the fluid inclusion assemblage (FIA) concept has been increasingly appreciated and used in the fluid inclusion community (e.g., [23][24][25]). This is largely due to its usefulness in validating fluid inclusion data as imposed by Roedder's rules [19]: (1) the individual inclusions trapped a single (i.e., homogeneous) phase; (2) the inclusions represent an isochoric (constant volume) system; and (3) after trapping, nothing has been added to, or removed from, the inclusions.…”

“…For example, for a fluid with a salinity of 20 wt% NaCl To make the estimation of depth from fluid pressure even more complicated, fluid pressure may be below hydrostatic (subhydrostatic) or above lithostatic (supralithostatic) (Figure 8a) in some geologic conditions or processes [21,51]. For example, if fluid immiscibility is indicated by fluid inclusions that yield relatively low T h (e.g., <200 • C) and extremely low P h (e.g., <10 bars) due to negligible non-aqueous volatile contents, such as in some hydrothermal uranium and REE mineralization in sedimentary basins [23,25,53], it is difficult to explain how this can happen at such P-T conditions. This is because for the given P-T conditions, the aqueous fluid would be located in the liquid field and no fluid unmixing can happen under normal geothermal gradients (Figure 8b).…”

“…In a histogram displaying results from many FIAs, each FIA is best represented by one data point regardless how many fluid inclusions were measured in the FIA [14]. If both FIA and non-FIA data are presented in the same diagram, they should be distinguished [23,25].…”

Fluid inclusion and stable isotope constraints on the heavy rare earth element mineralisation in the Browns Range Dome, Tanami Region, Western Australia

“…Nonetheless, the mechanisms whereby the REE -particularly the highly-sought after heavy (H)REE -are mobilised and precipitated by hydrothermal fluids, remain poorly understood. Available data on natural samples of REE-bearing hydrothermal fluids are restricted mostly to high temperature magmatic systems (e.g., Campbell et al, 1995;Williams-Jones et al, 2000), with only few recently-published studies on REE transport in low temperature environments (Richard et al, 2013;Rabiei et al, 2017; Richter et al, 2018). A detailed understanding of hydrothermally-formed REE deposits can, therefore, enhance our knowledge of hydrothermal REE mobility and deposition.…”