Accessory cassiterite as an indicator of the rare metal petrogenesis and ore-genesis

Alekseev V. I., Marin Yu. B.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2021. V. 150. N 4. P. 1-37

https://doi.org/10.31857/S0869605521040031

Language: Russian

Abstract

The paper is a scientific review of studies of accessory cassiterite from rare metal granites, pegmatites, and accompanying greisens, that were published the period 1990–2021. Previously known and the newest information on morphology, physical and chemical features of accessory cassiterite and the possibility of its commercial use is systematized. The consolidated database includes currently quantitative data of 1759 analyses from more than 100 published sources. There are confirmed known and determined new typomorphic features of cassiterite in rare metal granites, pegmatites, and greisens: concentrations of isomorphic components (Ta, Nb, Fe, Ti, Mn, W, Sc, In, Zr, Hf, U), indicator ratios (Nb/Ta, Zr/Hf, Fe/Mn), the main isomorphic schemes (“tapiolite” and “hydrothermal”). The average total contents of trace elements in cassiterite are as following: 6.68 wt % in granites, 4.87 wt % in pegmatites, 1.18 wt % in greisens. Based on published data, solubility limits of tapiolite (Fe,Mn)(Ta,Nb)₂O₆ in the structure of cassiterite are calculated. These limits are 0.1–11 wt% in granites, 0.7–12.8 wt% in pegmatites, and 0.1–3.3 wt % in greisens. The limit of the isomorphic saturation of cassiterite is in the range 0.1–12.8 wt % of the tapiolite component. It is noted that tantalum-bearing cassiterite is found mainly in plumasite granites of Li-F type and lepidolite pegmatites of LCT-type with the high phosphorus concentration in the range 0.12–2.50 wt % P₂O₅. The Ta₂O₅ content in the accessory cassiterite can reach 17.9–18.4 wt % and determinate the additional economic prospects for rare-metal pegmatites and granites. Cassiterite can be used as an alternative source of several rare metals – tantalum, indium, niobium, and scandium. Typical occurrences of accessory cassiterite are highlighted in granites of the Beauvoir massif (France), in pegmatites of the Peerless (USA) and Varuträsk (Sweden) deposits, in greisens of Kester and Polar fields (Yakutia). Accessory cassiterite is an advanced mineral geochronometer of rare-metal granites and pegmatites, since it is not susceptible to radiation damage and violation of the U-Pb isotopic system.

Keywords: cassiterite, typomorphism, typochemistry, plumasite rare-metal granite, raremetal pegmatite, greisen, rare-metal ore deposits, petrogenesis, ore-genesis, tantalum, isomorphism