Alekseev and Marin reported in 2022 on studies of accessory cassiterite from rare metal granites, pegmatites, and accompanying greisens in 1990–2021. The earlier and newest data on the morphology, physical and chemical features of accessory cassiterite, and its economic facility are summarized. The consolidated database includes 1759 cassiterite compositions from more than 100 publications.
The authors have confirmed previous and have identified new indicator features of cassiterite from rare metal granites, pegmatites, and greisens: concentrations of isomorphous components (Ta, Nb, Fe, Ti, Mn, W, Sc, In, Zr, Hf, U), informative ratios (Nb/Ta, Zr/Hf, Fe/Mn), and main substitution schemes (“tapiolite” and “hydrothermal”).
The average trace element content in cassiterite from granites, pegmatites, and greisens is 6.68, 4.87, and 1.18 wt %, respectively. Based on the published data, the solubility limit of tapiolite (Fe,Mn)(Ta,Nb)2O6 in the structure of cassiterite is calculated. These limit is 0.1–11, 0.7–12.8, and 0.1–3.3% in granites, pegmatites, and greisens, respectively. The tapiolite endmember proportion in cassiterite ranges from 0.1 to 12.8%. It is noted that tantalum-bearing cassiterite is predominantly observed in Li–F plumasite granites and LCT lepidolite pegmatites with the high phosphorus concentration over the range of 0.12–2.50 wt % P2O5. The Ta2O5 content in accessory cassiterite reaches 17.9–18.4 wt % and promises additional economic prospects for rare metal pegmatites and granites.
Cassiterite can be used as an alternative source of tantalum, indium, niobium, and scandium. Typical occurrences of accessory cassiterite have been identified in granites of the Beauvoir massif (France), in pegmatites of the Peerless (USA) and Varuträsk (Sweden) deposits, and in greisens of the Kester
and Polyarnoe deposits (Yakutia). Accessory cassiterite is an advanced mineral geochronometer for rare metal granites and pegmatites, since it is not susceptible to radiation damage and disruption of the U–Pb isotope system.
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