Geology of the Ngualla carbonatite complex, Tanzania, and origin of the Weathered Bastnaesite Zone REE ore

Witt, W. K.; Hammond, D.P.; Hughes, Martin J.

doi:10.1016/j.oregeorev.2018.12.002

Cited by 30 publications

(12 citation statements)

References 25 publications

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“…12 have been previously noted by workers at several different deposits. In cases where work has focussed on different aspects of a deposit, information on the order of crystallisation is limited to noting the presence of residual apatite hosted in a secondary apatite groundmass (Cargill, Canada, [Sage 1991]; Ngualla, Tanzania, [Witt et al 2019]; Araxá, Brazil [Mariano 1989]), the formation of secondary apatite on the rim of a primary apatite grain (Dorowa, Zimbabwe [Fernandes 1978]; Mt Weld, Australia [Lottermoser 1990]), or the formation of fibrous apatite in fractures (Anitapolis, Brazil, [Girard et al 1993]). However, paragenetic descriptions of secondary apatite are available for the Mabounié, Matongo and Juquiá complexes (Walter et al 1995a, b;Boulingui 1997;Decrée et al 2016), and sufficiently detailed descriptions of apatite textures are reported for the Eppawala, Salitre I and Martison deposits such that a crystallisation sequence can be inferred (Tazaki et al 1986(Tazaki et al , 1987Subasinghe 1988, 1989a, b;Potapoff 1989;Sage 1991;Araújo 2015).…”

Section: Interpretation and Discussionmentioning

confidence: 99%

“…1 Locations of carbonatites where secondary carbonate-bearing fluorapatite has been described, grouped by genetic interpretation. Key references for each locality are as follows: 1 McConnell and Gruner (1940), 2 Burton (1986), 3 Fletcher and Litherland (1981), 4 Litherland et al (1986), 5 Walter et al (1995a, 6 b), 7 Girard et al (1993), 8 Sage (1988bSage ( , 9 1991, 10 Potapoff (1989), 11 Horner et al (2016), 12 Sage (1988a), 13 Sandvik and Erdosh (1977), 14 Pressacco (2001), 15 Erdosh (1979), 16 Laval et al (1988), 17 Boulingui (1997), 18 Brasseur et al (1961, 19 Decrée et al (2015, 20 2016), 21 Witt et al (2019), 22 Verwoerd (1986), 23 Graupner et al 2018, 24 Prins (1973), 25 Fernandes (1978, 26 1989), 27 Mgonde (1994), 28 Egerov (1991), 29…”

Section: Introductionmentioning

confidence: 99%

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The origin and composition of carbonatite-derived carbonate-bearing fluorapatite deposits

et al. 2020

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Carbonate-bearing fluorapatite rocks occur at over 30 globally distributed carbonatite complexes and represent a substantial potential supply of phosphorus for the fertiliser industry. However, the process(es) involved in forming carbonate-bearing fluorapatite at some carbonatites remain equivocal, with both hydrothermal and weathering mechanisms inferred. In this contribution, we compare the paragenesis and trace element contents of carbonate-bearing fluorapatite rocks from the Kovdor, Sokli, Bukusu, Catalão I and Glenover carbonatites in order to further understand their origin, as well as to comment upon the concentration of elements that may be deleterious to fertiliser production. The paragenesis of apatite from each deposit is broadly equivalent, comprising residual magmatic grains overgrown by several different stages of carbonate-bearing fluorapatite. The first forms epitactic overgrowths on residual magmatic grains, followed by the formation of massive apatite which, in turn, is cross-cut by late euhedral and colloform apatite generations. Compositionally, the paragenetic sequence corresponds to a substantial decrease in the concentration of rare earth elements (REE), Sr, Na and Th, with an increase in U and Cd. The carbonate-bearing fluorapatite exhibits a negative Ce anomaly, attributed to oxic conditions in a surficial environment and, in combination with the textural and compositional commonality, supports a weathering origin for these rocks. Carbonate-bearing fluorapatite has Th contents which are several orders of magnitude lower than magmatic apatite grains, potentially making such apatite a more environmentally attractive feedstock for the fertiliser industry. Uranium and cadmium contents are higher in carbonate-bearing fluorapatite than magmatic carbonatite apatite, but are much lower than most marine phosphorites.

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Section: Interpretation and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The origin and composition of carbonatite-derived carbonate-bearing fluorapatite deposits

et al. 2020

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“…Folded apatitite similar to the Good Hope clasts are apparently rare as most accumulations of apatite in carbonatites consist of subhedral crystals with allotriomorpic granular rather than prismatic textures, although when present prisms tend to be large (0.1–15 mm) isolated euhedral to subhedral crystals. An apatite carbonatite with folded bands of apatite has been noted from the Ngualla carbonatite (Tanzania) by Witt et al (2019). This carbonatite has not been metamorphosed or deformed tectonically.…”

Section: Pyrochlore Apatititementioning

confidence: 91%

“…This carbonatite has not been metamorphosed or deformed tectonically. Unfortunately, only a macroscopic description was presented by Witt et al (2019) without accompanying textural or mineralogical data. Deformed apatitite clasts have been recognised (this work) from the St. Honoré (Québec) carbonatite which are analogous to the Good Hope folded clasts.…”

Section: Pyrochlore Apatititementioning

confidence: 99%

Mineralogy and genesis of pyrochlore apatitite from The Good Hope Carbonatite, Ontario: A potential niobium deposit

Mitchell

Wahl

Cohen³

2019

MinMag

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The Good Hope carbonatite is located adjacent to the Prairie Lake alkaline rock and carbonatite complex in northwestern Ontario. The occurrence is a heterolithic breccia consisting of diverse calcite, dolomite and ferrodolomite carbonatites containing clasts of magnesio-arfvedsonite + potassium feldspar, phlogopite + potassium feldspar together with pyrochlore-bearing apatitite clasts. The apatitite occurs as angular, boudinaged and schlieren clasts up to 5 cm in maximum dimensions. In these pyrochlore occurs principally as euhedral single crystals (0.1–1.5 cm) and can comprise up to 25 vol.% of the clasts. Individual clasts contain compositionally- and texturally-distinct suites of pyrochlore. The pyrochlores are hosted by small prismatic crystals of apatite (~100–500 μm × 10–25 μm) that are commonly flow-aligned and in some instances occur as folds. Allotriogranular cumulate textures are not evident in the apatitites. The fluorapatite does not exhibit compositional zonation under back-scattered electron spectroscopy, although ultraviolet and cathodoluminescence imagery shows distinct cores with thin (<50 μm) overgrowths. Apatite lacks fluid or solid inclusions of other minerals. The apatite is rich in Sr (7030–13,000 ppm) and rare earth elements and exhibits depletions in La, Ce, Pr and Nd (La/NdCN ratios (0.73–1.14) relative to apatite in cumulate apatitites (La/NdCN > 1.5) in the adjacent Prairie Lake complex. The pyrochlore are primarily Na–Ca pyrochlore of relatively uniform composition and minor Sr contents (<2 wt.% SrO). Irregular resorbed cores of some pyrochlores are A-site deficient (>50%) and enriched in Sr (6–10 wt.% SrO), BaO (0.5–3.5 wt.%), Ta2O5 (1–2 wt.%) and UO2 (0.5–2 wt.%). Many of the pyrochlores exhibit oscillatory zoning. Experimental data on the phase relationships of haplocarbonatite melts predicts the formation of apatite and pyrochlore as the initial liquidus phases in such systems. However, the texture of the clasts indicates that pyrochlore and apatite did not crystallise together and it is concluded that pyrochlores formed in one magma have been mechanically mixed with a different apatite-rich magma. Segregation of the apatite–pyrochlore assemblage followed by lithification resulted in the apatitites, which were disrupted and fragmented by subsequent batches of diverse carbonatites. The genesis of the pyrochlore apatitites is considered to be a process of magma mixing and not simple in situ crystallisation.

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“…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.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

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Carbonatites undergo various magmatic-hydrothermal processes during their evolution that are important for the enrichment of rare earth elements (REE). This geochemical, petrographic, and multi-isotope study on the Kangankunde carbonatite, the largest light REE resource in the Chilwa Alkaline Province in Malawi, clarifies the critical stages of REE mineralization in this deposit. The δ56Fe values of most of the carbonatite lies within the magmatic field despite variations in the proportions of monazite, ankerite, and ferroan dolomite. Exsolution of a hydrothermal fluid from the carbonatite melts is evident based on the higher δ56Fe of the fenites, as well as the textural and compositional zoning in monazite. Field and petrographic observations, combined with geochemical data (REE patterns, and Fe, C, and O isotopes), suggest that the key stage of REE mineralization in the Kangankunde carbonatite was the late magmatic stage with an influence of carbothermal fluids i.e. magmatic–hydrothermal stage, when large (~200 µm), well-developed monazite crystals grew. The C and O isotope compositions of the carbonatite suggest a post-magmatic alteration by hydrothermal fluids, probably after the main REE mineralization stage, as the alteration occurs throughout the carbonatite but particularly in the dark carbonatites.

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Geology of the Ngualla carbonatite complex, Tanzania, and origin of the Weathered Bastnaesite Zone REE ore

Cited by 30 publications

References 25 publications

The origin and composition of carbonatite-derived carbonate-bearing fluorapatite deposits

The origin and composition of carbonatite-derived carbonate-bearing fluorapatite deposits

Mineralogy and genesis of pyrochlore apatitite from The Good Hope Carbonatite, Ontario: A potential niobium deposit

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

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