Geochemical criteria for distinguishing magmatic and metasomatic albite-enrichment in granitoids ? examples from the Ta-Li granite Yichun (China) and the Sn-W deposit Tikus (Indonesia)

Abstract

Two examples ofalbite-rich granitoids of different genesis are discussed: the Ta-Li granite at Yichun (China) exhibits dominantly igneous textures, and the sodium-enrichment zone in biotite granite of the Sn-W deposit at Tikus is characterized by metasomatic textures. The Yichun stock shows a magmatic evolution from biotite-muscovite granite to lepidolite granite with an increase of Na20 and F concentrations and a decrease of CaO and Sr concentrations. The composition of the different granite phases is close to pseudoternary minima in the haplogranite-H20(-Li-F) system. The composition of the F-rich albitization zone at Tikus deviates strongly from the pseudoternary minima and shows a tendency to become monomineralic (nearly pure albitite). CaO and Sr concentrations are increased or remain unchanged with respect to the unaltered biotite granite at Tikus. Albitization produced by fluid-rock interaction in F-rich systems is characterized by that CaO or Sr released by the breakdown of plagioclase in the granite protolith, are fixed in newly formed fluorite or albite, respectively. aluminous granitoids) as well as REE, Y, Nb and Zr (peralkaline granitoids).Apart from textural studies, the geochemical characterization of the granitoids is crucial for distinguishing sodium-enrichment in the magmatic stage from metasomatic sodium-enrichment. This can be demonstrated with two examples: the rare-metal granite at Yichun (China) crystallized from a sodium-rich magma, and the albitized granite associated with Sn-W greisen at Tikus (Indonesia) which is an example of albite deposition by the interaction of sodium-bearing fluids within a consolidated granite along a tectonized zone.

Origin and hydrothermal alteration of rare-metal granites in the Al-Hamra area, northeastern Arabian Shield, Saudi Arabia

“…Economic or potentially economic HFSE concentrations hosted in alkaline igneous rocks have been interpreted either due to fractional crystallization or hydrothermal alteration (Schwartz 1992). The Arabian Shield contains one of the largest fields of alkali granites in the world.…”

Mineral-deposit model for lithium-cesium-tantalum pegmatites

“…Rare-element-enriched parts of these granites are typically zones within a larger granite body. Examples include the Yichun Li-F granite of China (Schwartz, 1992) and the Beauvoir granite of the Massif Central, France (Raimbault, 1998). Such granites are only known from the Phanerozoic (Tkachev, 2011).…”

Chemistry of cassiterite in rare metal granitoids and the associated rocks in the Eastern Desert, Egypt

“…They are both petrographically and geochemically specialized, particularly their anomalous concentrations of elements such as F, Li, B, Sn, and Rb (Tischendorf, 1977). Formation of rare -metal granitoids in general and stanniferous ones in particular can be attributed to magmatic or post -magmatic, metasomatic processes (Schwartz, 1992;Abdalla et al, 1998;Abdalla and Mohamed, 1999).…”

“…Meanwhile, cassiterite belong to the second types of association is related to lithium -albite granites which are formed as ultimate differentiates from haplogranitic melt by simultaneous crystallization of minerals from melt and fluid under conditions of high a F, Li ; the activities of lithium and fluorine; (Pollard, 1983; Chemistry of cassiterite in rare metal granitoids and the associated rocks Kovalenko and Kovalenko, 1984;Schwartz, 1992).…”

“…The metasomatic nature of the investigated metasomatized granitoids and the magmatic characters of the lithium albite granite stocks were based on the criteria cited by Pollard (1983), Schwartz (1992), Abdalla (1996), Abdalla et al (1996) and Abdalla et al (1998). Detailed geochemical characteristics of the investigated tin -bearing granitoids can be found elsewhere (e.g., Abdalla et al, 2008;Abdalla, 2008).…”