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

The Petyayan-Vara Carbonatite-Hosted Rare Earth Deposit (Vuoriyarvi, NW Russia): Mineralogy and Geochemistry

“…Therefore, rare earth carbonatites are a major focus of critical metal research. Over the past five years, several dozens of papers have been published on the subject of rare earth carbonatites (RE carbonatites) in Angola [5,6], Australia [7][8][9], Brazil [10,11], Canada [12][13][14][15][16][17], China [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37], Finland [38], India [39][40][41][42], Italy [43,44], Malawi [45][46][47][48][49][50][51], Mongolia [52,53], Namibia…”

Magmatic-Hydrothermal Processes Associated with Rare Earth Element Enrichment in the Kangankunde Carbonatite Complex, Malawi

“…The central core lithology which consists of carbonatite agglomerate is cut by carbonatite dykes and surrounded by a ring of feldspathic breccia and agglomerate [16]. The first intrusion stage comprises apatite-dolomite characteristics and followed by the intrusion of dolomitic to ferroan-dolomitic carbonatite [5]. The apatite-dolomite carbonatite was named beforehand by Garson [15], but the samples that exhibit similar characteristics in our study are named apatite-rich carbonatites because they were not collected from the main apatite body, but most likely from dykes that were too small to map.…”

“…Among the main types of REE deposits, carbonatites are important exploration targets because of their enrichment in these elements as well as their size and, generally, amenable mineralogy for extraction [3,4]. Although carbonatites exhibit notable enrichments in REE [5], the concentrations vary significantly, depending on the evolutional processes that they underwent, thereby allowing some carbonatites to be (potential) REE resources (e.g., Barra do Itapirapuã, Brazil [6]; the Mianning-Dechang and Qinling belts, China [7]; Kangankunde, Tundulu, and Songwe, Malawi [8,9]).…”

“…Processes that govern the enrichment of REE in carbonatites include fractional crystallization of a carbonatitic melt [10], enrichment by orthomagmatic fluids during late magmatic stages i.e. the magmatic-hydrothermal phase [5], dissolution and re-crystallization of primary to secondary carbonatitic minerals, resulting in the REE being concentrated in the latter [8], and supergene enrichment in weathered zones [11]. Although some studies report that magmatic processes play significant roles in concentrating the critical elements [4,12], Chakhmouradian and Wall [2] suggest that REE enrichment in carbonatites typically occurs during the final stages of the carbonatite's evolution.…”

“…Previous work carried out on the Kangankunde carbonatite includes (i) a detailed geological description of the lithologies present in the complex, highlighting that the REE are mainly concentrated at the centre of the complex [15]; (ii) a description of Mn-rich ankerite along with exotic REE hosting minerals occurring in cavities and vugs, suggesting the precipitation of REE-bearing minerals from orthomagmatic fluids [16]; and (iii) Sr, C, and O isotope compositions of carbonate and phosphate minerals, that suggest that REE mineralization was associated with multi-phase processes occurring at near-magmatic temperatures [5]. Consequently, the processes that were reported on the complex in previous studies may highlight important stages through the evolution of the carbonatite because they play significant roles in concentration of the critical elements [4,12,17].…”