The Lanthanide “Tetrad Effect” as an Exploration Tool for Granite-Related Rare Metal Ore Systems: Examples from the Iberian Variscan Belt

Abstract

Highly fractionated granites and related magmatic-hydrothermal ore-forming processes can be traced by elemental ratios such as Nb/Ta, K/Rb, Y/Ho, Sr/Eu, Eu/Eu*, Zr/Hf, and Rb/Sr. The lanthanide “tetrad effect” parameter (TE1,3) can also be a useful geochemical fingerprint of highly fractionated granites. This work assesses its application as an exploration vector for granite-related mineralization in the Central Iberian Zone by examining TE1,3 variations with different elemental ratios and with the concentrations of rare metals and fluxing elements (such as F, P, and B). The multi-elemental whole-rock characterization of the main Cambrian–Ordovician and Carboniferous–Permian granite plutons and late aplite–pegmatite dykes exposed across the Segura–Panasqueira Sn-W-Li belt show that the increase in TE1,3 values co-vary with magmatic differentiation and metal-enrichment, being the Carboniferous–Permian granite rocks the most differentiated, and metal specialized. The Argemela Li-Sn-bearing rare metal granite and the Segura Li-phosphate-bearing aplite–pegmatite dykes deviate from this geochemical trend, displaying TE1,3 < 1.1, but high P2O5 contents. The results suggest that mineralized rocks related to peraluminous-high-phosphorus Li-Sn granite systems are typified by TE1,3 < 1.1, whereas those associated with peraluminous-high-phosphorus Sn-W-Li (lepidolite) and peraluminous-low-phosphorus Sn-Ta-Nb granite systems display TE1,3 > 1.1, reaching values as high as 1.4 and 2.1, respectively.

Lithium-, Phosphorus-, and Fluorine-Rich Intrusions and the Phosphate Sequence at Segura (Portugal): A Comparison with Other Hyper-Differentiated Magmas

“…The CIZ is characterised by the high volume of peraluminous granitic rocks [20] that are syn-to-post kinematic [21][22][23], and it includes strongly peraluminous, Ca-poor, and variably P-enriched two-mica leucogranites, which are interpreted as being derived from the melting of a metasedimentary source along with several series of metaluminous to weakly peraluminous granites [23,24]. In the Góis-Panasqueira-Argemela-Segura strip, many granite intrusions are peraluminous, like those of Segura, Penamacor, Panasqueira, Orca, and Castelo Branco (Figure 1a).…”

Petrogenesis of Shihuiyao Rare-Metal Granites in the Southern Great Xing’an Range, NE China

“…Therefore, it is proposed that the tetrad effect was likely controlled by fractional crystallization rather than melt-fluid interactions. The lanthanide "tetrad effect" parameter (TE 1,3 ) can also be a useful geochemical fingerprint of highly fractionated granites, and the increase in TE 1,3 values varies with magmatic differentiation [54]. The Shihuiyao muscovite-zinnwaldite granite and amazonite-bearing granite show slightly higher TE 1,3 values but comparable K/Rb and Nb/Ta ratios to those of the zinnwaldite granite (Figure 7b,c), indicating the increasing degree of magma differentiation.…”