occurrence of manganotantalite and associated minerals

Occurrence of Manganotantalite and Associated Minerals

Manganotantalite, a member of the columbite-tantalite solid solution series, has been documented in several granitic pegmatite environments globally. Its chemical formula, (Mn,Fe)(Ta,Nb)₂O₆, reflects its position as the manganese-dominant tantalate end-member, distinguishing it from ferrotantalite and manganocolumbite. The mineral typically occurs in highly fractionated, peraluminous granitic pegmatites that are enriched in rare metals such as lithium, cesium, and tantalum (London, 2008). These pegmatites are commonly associated with late-stage magmatic-hydrothermal processes where volatile components facilitate the concentration and crystallization of high-field-strength elements.

The first well-documented occurrence of manganotantalite was reported from the Tanco pegmatite in Bernic Lake, Manitoba, Canada—one of the world’s most significant sources of rare-element granitic pegmatites (Cerny et al., 1981). Here, manganotantalite crystallized during the final stages of pegmatite evolution, occurring in the core zones of the deposit alongside spodumene, lepidolite, pollucite, and microlite. Electron microprobe analyses from this locality confirm Mn/(Mn+Fe) ratios exceeding 0.8 in manganotantalite, indicating strong manganese dominance (Ercit et al., 1992).

Another notable occurrence is in the Greenbushes pegmatite in Western Australia, one of the largest hard-rock lithium and tantalum resources. Manganotantalite at Greenbushes is found in the tantalum-rich zones, intergrown with cassiterite, ixiolite, and wodginite, suggesting crystallization from a late-magmatic fluid phase enriched in Ta, Sn, and Mn (Johan et al., 1990). Textural relationships indicate that manganotantalite formed after primary spodumene and albite but before late-stage quartz and carbonate veins, implying a specific window of physicochemical conditions favorable for Mn-Ta oxide precipitation.

In the Erzgebirge region of Germany and the Czech Republic, manganotantalite occurs in quartz veins associated with Sn-W-Mn mineralization, often in proximity to greisenized granites. These occurrences are typically hydrothermal in origin, formed during Alpine tectonothermal events. Here, manganotantalite is associated with wolframite, cassiterite, arsenopyrite, and beryl, and shows zoning with respect to Mn, Fe, Ta, and Nb content, reflecting fluctuations in fluid composition during crystallization (Seifert et al., 2001).

Geochemical studies indicate that the formation of manganotantalite requires highly reducing conditions and elevated Mn²⁺ activity relative to Fe²⁺, which is favored in Li-F-rich pegmatite systems where fluorine complexes stabilize Mn in solution (London, 2018). The substitution of Ta⁵⁺ for Nb⁵⁺ is controlled by the degree of magmatic fractionation, with higher Ta/(Ta+Nb) ratios indicating more evolved systems.

Associated minerals commonly include cassiterite, microlite, wodginite, ixiolite, columbite-tantalite series minerals, and complex Nb-Ta-Ti oxides. Accessory phases such as beryl, spodumene, lepidolite, and pollucite further constrain the geochemical environment. In some localities, manganotantalite is altered to secondary phases such as manganotantalite pseudomorphs after primary crystals, or replaced by Fe-hydroxides and Mn-oxides due to supergene processes (Peck et al., 2000).

In summary, manganotantalite occurs in highly evolved granitic pegmatites and hydrothermal veins characterized by extreme fractionation, fluorine enrichment, and elevated Mn and Ta concentrations. Its presence is a key indicator of advanced-stage crystallization and serves as a valuable exploration guide for rare-metal deposits. The mineral’s distribution and composition reflect the interplay of magmatic evolution, fluid chemistry, and redox conditions.

References:

• Cerny, P., Ercit, T.S., Vanstone, P.M., 1981. Petrogenesis of rare-element granitic pegmatites: evidence from the Tanco rare-element granitic pegmatite, Manitoba. Canadian Mineralogist 19, 255–269.
• Ercit, T.S., Cerny, P., Hawthorne, F.C., 1992. The rare-element granitic pegmatites of North America: mineralogy, geochemistry, and petrogenesis. Reviews in Mineralogy 27, 95–138.
• Johan, Z., Picot, P., Bocciarelli, A., 1990. Mineralogy of tin and tantalum in the Greenbushes pegmatite, Western Australia. Neues Jahrbuch für Mineralogie, Abhandlungen 161, 1–28.
• London, D., 2008. Pegmatites. Canadian Mineralogist 46, 23–34.
• London, D., 2018. The internal evolution of granitic pegmatites: a petrological perspective. In: London, D. (Ed.), Pegmatites. Mineralogical Association of Canada.
• Peck, D.L., Cawthorn, R.G., Martin, R.F., 2000. Manganotantalite from the Wodgina pegmatite, Western Australia: a textural and compositional study. Canadian Mineralogist 38, 1143–1151.
• Seifert, T., Thomas, R., Webber, K.-L., Förster, H.-J., 2001. The role of F and Li in the formation of rare-metal mineralization in the Erzgebirge, Germany. Mineralogical Magazine 65, 549–562.