Elemental and boron isotopic variations in tourmaline in two-mica granite from the Cuona area, Tibet: Insights into the evolution of leucogranitic melt

Hydrothermal fluid evolution in the Cuonadong Sn–W–Be polymetallic deposit, southern Tibet: indicated by the in–situ element and boron isotope compositions of tourmaline

“…In addition, the δ 11 B values of the tourmaline grains in this study from the core to the rim are similar (Figure 9). Compared to the hydrothermal tourmalines in this study, magmatic tourmalines from the leucogranite (GT Group) in the Xianglin area in the Cuonadong dome have δ 11 B values ranging from −8.7 to −8.0‰ (an average of −8.3‰) (Xie et al, 2022) (Figures 8, 9). Frontiers in Earth Science frontiersin.org…”

“…There is little B isotope fractionation between the melt and exsolution fluid in the granitic magma system (Meyer et al, 2008;Zhao et al, 2019). The δ 11 B fluid values of Tur-1 from −10.1 to −9.6‰ are close to the tourmaline δ 11 B values (−8.7 to −8.0‰) of leucogranite in the Xianglin area (Xie et al, 2022), which suggest their closely genetic relationship (Figure 7). The B isotope characteristics of the granitoid in the Cuonadong polymetallic deposit indicate that it was mainly derived from partial melting of a metasediment source.…”

“…Furthermore, the whole Tur-1 from the rim to the core shows constant Mg/(Mg + Fe) and δ 11 B values, Frontiers in Earth Science frontiersin.org which indicates that the fluid composition was stable during Tur-1 formation (Figures 8, 9). Boron isotope signatures of Tur-2 (δ 11 B =−11.1 to −9.3‰; calculated δ 11 B fluid =−7.9 to −6.1‰), higher than those in the leucogranitic melt, preclude the possibility of a single boron source of the leucogranite (average δ 11 B = −8.3‰) (Xie et al, 2022) and suggest that the other sources with high δ 11 B values were needed. The possible high δ 11 B sources involved in the fluid of Tur-2 included seawater, evaporite, and marine carbonate (Marschall and Jiang, 2011;Trumbull and Slack, 2018).…”

“…With hydrothermal fluid invasion, it has been observed that the partial major element Frontiers in Earth Science frontiersin.org compositions of hydrothermal tourmaline may be influenced by the surrounding rock composition depending on the water-rock ratio (Yang et al, 2015b;. Tur-1 displays semblable Al, Ca, and Na + K contents with magmatic tourmalines in the leucogranite from Xie et al (2022) (Figure 4). Tur-1 has different geochemical compositions with higher Mg/(Mg + Fe) (0.39-0.48) and lower Ca values (0.18-0.46 wt%) and Na/(Na + Ca) values (0.91-0.96) than the surrounding granitic gneiss (Mg/(Mg + Fe): 0.05-0.08; Ca: 0.92-1.22 wt%; and Na/(Na + Ca): 0.82-0.85) from Xia et al (2019b), which show that the granitic gneiss was less mixed into the magmatichydrothermal fluid from the geochemical perspective.…”

“…The preliminary drilling exploration of only the W-Sn-Be orebody in the skarn around the mantle of the gneiss dome found that the average grade of WO 3 , Sn, and BeO is 0.21%, 0.36%, and 0.08%, respectively, and the their resource quantities are more than 50,000 tons, 80,000 tons, and 170,000 tons, respectively (Li et al, 2017;Cao et al, 2020). Previous detailed studies mainly focused on the regional geological evolution (Zhang et al, 2017;Fu et al, 2018;, ore Frontiers in Earth Science frontiersin.org geology (Li et al, 2017;Cao et al, 2020;Cao et al, 2021), petrology (Huang et al, 2018;Xie et al, 2018;Xia et al, 2019a;Xie et al, 2020;Cao et al, 2022), geochronology (Dong et al, 2017;Xie et al, 2018;Xia et al, 2019a;Xie et al, 2020), mineralogy (Dai et al, 2019;Han et al, 2020;Xie et al, 2020;Dai et al, 2022;Wang et al, 2022;Xie et al, 2022), and evolution of the related leucogranitic magma (Xie et al, 2020;Cao et al, 2022;Xie et al, 2022). However, the hydrothermal activities for the minerogenetic region are complex, and the understanding of the source and evolution of ore-forming fluids for the orebody is still limited.…”