The Nature and Origin of the REE Mineralization in the Wicheeda Carbonatite, British Columbia, Canada

Abstract

In response to rising demand of the rare earth elements (REE), recent exploration of the British Columbia alkaline province has identified the Wicheeda Carbonatite, which contains an estimated 11.3 million tons of light REE-enriched ore grading 1.95 wt.% TREO, to be the highest-grade prospect known in British Columbia. However, research of the deposit is restricted to one paper describing mineralization in carbonatite dikes adjacent to the main plug. This study describes the nature and origin of REEmineralization in the Wicheeda plug.The carbonatite was emplaced in metasedimentary limestone and argillaceous limestone belonging to the Kechika Group, which has been altered to potassic fenite immediately adjacent to the carbonatite and to sodic fenite at greater distances from it. The carbonatite comprises a ferroan dolomite core, which passes outwards gradationally into calcite carbonatite. Three texturally distinct varieties of dolomite have been recognized. Un modèle est proposé dans lequel la carbonatite calcitique est la phase magmatique la plus précoce. Cette phase a atteint la saturation en niobium très tôt, entrainant la précipitation du pyrochlore. Le magma a évolué plus tardivement vers une composition de carbonatite dolomitique qui, lors de son refroidissement, a exsolvé un fluide aquocarbonique altérant les métasédiments de Kechika en fénite potassique et se mélangeant avec les eaux formationelles, plus distales, pour produire les fénites sodiques.Le fluide aquo-carbonique a mobilisé et transporté les ETR sous la forme de complexes chlorurés, au sein de la porosité et des fractures de la carbonatite dolomitique. A la suite des interactions fluide-roche prolongées, les ETR ont précipité du fait du refroidissement et de l'augmentation du pH ; la présence d'apatite a entrainé la formation de monazite-(Ce). La concentration hydrothermale a permis une répartition homogène des teneurs, avec la carbonatite dolomitique contenant dans son ensemble plus de 1 % TREO, faisant de Wicheeda un gisement très attrayant. Contributions of AuthorsThis thesis has been written in manuscript format in accordance with the regulations put

The origin of secondary heavy rare earth element enrichment in carbonatites: Constraints from the evolution of the Huanglongpu district, China

“…Equally, sulphate-rich fluids within carbonatite-related hydrothermal systems are widespread, with barite and celestine as common accessories in carbonatite systems (e.g. Nikiforov et al, 2014;Trofanenko et al, 2016;Xie et al, 2015). The key factor for the genesis of sulphide-or sulphate-bearing carbonatite systems is the redox state of the melt or fluid.…”

Deducing the source and composition of rare earth mineralising fluids in carbonatites: insights from isotopic (C, O, 87Sr/86Sr) data from Kangankunde, Malawi

“…Khibina) and Vuoriyarvi, Zaitsev et al (2002) suggested burbankite replacement occurred through open-system, post-magmatic isotopic exchange with a low-temperature, water-rich, fluid. REE redistribution occurs in rocks where associated carbonates exhibit a trend toward 18 O-and 13 C-enrichment (e.g., Andrade et al 1999;Downes et al 2014;Trofanenko et al 2016). In a single bastnäsite-(Ce) analysis from Belaya Zima, this enrichment has also been shown in REE mineralisation (Doroshkevich et al 2016 (Deines 1970(Deines , 1989Ray and Ramesh 2000)] or through alteration from successive generations of hydrothermal fluid (Santos and Clayton 1995;Ray and Ramesh 1999).…”

“…It is, therefore, difficult to envisage any fractionation or hydrothermal process which relates these rock types as both would increase the O and C isotope ratios (e.g. Deines 1970Deines , 1989Santos and Clayton 1995;Ramesh 1999, 2000;Trofanenko et al 2016). This interpretation is supported by the size of the two carbonatite bodies exposed; the earlier apatite-bearing dolomite carbonatite being much smaller than the later REE-rich carbonatites (Fig.…”

“…Chloride is currently commonly favoured as the most important ligand for transporting the REE (e.g. WilliamsJones et al 2012;Downes et al 2014;Trofanenko et al 2016;Broom-Fendley et al 2016a, 2017a) but there is not yet any fluid inclusion evidence at Kangankunde to support this. Given the circumstantial nature of the evidence for different fluid compositions, it is difficult to conclude how the REE are transported at Kangankunde.…”

Ti-Nb Mineralization of Late Carbonatites and Role of Fluids in Its Formation: Petyayan-Vara Rare-Earth Carbonatites (Vuoriyarvi Massif, Russia)

“…REE enrichment is "most commonly found only in the latest and most highly evolved parts of a carbonatite intrusion" [6]. The accumulation of REE in late carbonatites is assumed to be controlled by fluid activity [7][8][9][10][11][12][13][14][15][16]. Such a surplus in articles reflects a keen interest in REE occurring in late carbonatites.…”