Chemical Evolution of Nb-Ta Oxides and Cassiterite in Phosphorus-Rich Albite-Spodumene Pegmatites in the Kangxiwa–Dahongliutan Pegmatite Field, Western Kunlun Orogen, China

Abstract

The Kangxiwa–Dahongliutan pegmatite field in the Western Kunlun Orogen, China contains numerous granitic pegmatites around a large granitic pluton (the Dahongliutan Granite with an age of ca. 220 to 217 Ma), mainly including barren garnet-, tourmaline-bearing pegmatites, Be-rich beryl-muscovite pegmatites, and Li-, P-rich albite-spodumene pegmatites. The textures, major element contents, and trace element concentrations of columbite-group minerals (CGM) and cassiterite from three albite-spodumene pegmatites in the region were investigated using a combination of optical microscopy, SEM, EPMA and LA-ICP-MS. The CGM can be broadly classified into four types: (1) inclusions in cassiterite; (2) euhedral to subhedral crystals (commonly exhibiting oscillatory and/or sector zoning and coexisting with magmatic cassiterite); (3) anhedral aggregates; (4) tantalite-(Fe)-ferrowodginite (FeSnTa2O8) intergrowths. The compositional variations of CGM and cassiterite are investigated on the mineral scale, in individual pegmatites and within the pegmatite group. The evolution of the pegmatites is also discussed. The variation of Nb/Ta and Zr/Hf ratios of the cassiterite mimics the Nb-Ta and Zr-Hf fractionation trends in many LCT pegmatites, indicating that these two ratios of cassiterite may bear meanings regarding the pegmatite evolution.

Barren and Li–Sn–Ta Mineralized Pegmatites from NW Spain (Central Galicia): A Comparative Study of Their Mineralogy, Geochemistry, and Wallrock Metasomatism

“…In this case, the lithium aluminosilicate often develops a narrow rim consisting of a fine-grained vermicular quartz-spodumene symplectitic intergrowth (Figure 6c). This texture has also been described in other pegmatites in this pegmatitic field [36] and also in the bodies of the Kangxiwa-Dahongliutan pegmatite field in the Western Kunlun Orogen of China [37]. Note the presence of spodumene between the albite crystal and the petalite aggregates; (b) spodumene+quartz replacement (SQI) of petalite; (c) spodumene crystals with a fine-grained symplectitic quartz-spodumene intergrowth at the contact with neoformed albite.…”

Columbite U-Pb Geochronology of Kalu’an Lithium Pegmatites in Northern Xinjiang, China: Implications for Genesis and Emplacement History of Rare-Element Pegmatites

“…The dated CGM grains exhibit oscillatory zoning and/or sector zoning (e.g., Figure 5), similar to typical magmatic CGMs in many granitic pegmatites [25,40,[44][45][46]. Petrographic observations also reveal that columbite is associated with the primary mineral assemblage spodumene + albite + quartz + muscovite in the Li pegmatites (Figure 4).…”

“…For each analysis, signals on the gas background and sample were collected for 10 s and 40 s, respectively. The analytical procedure and the method for the precision test were described in Feng et al [40]. NIST SRM 610 and NIST SRM 612 were used as the primary and secondary external standards.…”

The Tres Arroyos Granitic Aplite-Pegmatite Field (Central Iberian Zone, Spain): Petrogenetic Constraints from Evolution of Nb-Ta-Sn Oxides, Whole-Rock Geochemistry and U-Pb Geochronology

“…This model of the genetic linkage between granite plutons and pegmatites, as residual melts derived from fractional crystallization in large-scale granitic plutons (e.g., [19]), is supported by field relationships and petrographic observations, combined with mineralogical, geochemical, and geochronological data in some pegmatite provinces (e.g., [20][21][22]). However, a number of recent geochronological studies revealed large age differences (>10 Ma) between pegmatites and spatially related granites, making their genetic relationship difficult to identify (e.g., [23][24][25]). In these cases, the pegmatites are interpreted to be of anatectic origin, meaning that they crystallized directly from melts formed by a low-degree of partial melting of high-grade metamorphic rocks (e.g., [23][24][25]).…”

“…However, a number of recent geochronological studies revealed large age differences (>10 Ma) between pegmatites and spatially related granites, making their genetic relationship difficult to identify (e.g., [23][24][25]). In these cases, the pegmatites are interpreted to be of anatectic origin, meaning that they crystallized directly from melts formed by a low-degree of partial melting of high-grade metamorphic rocks (e.g., [23][24][25]). Likewise, in other regions, the observations and data are not conclusive, particularly in pegmatite provinces with overlapping magmatic events, which cannot be resolved by geochronology or where granite plutons are absent (e.g., [26][27][28]).…”