Trace element composition of quartz from different types of pegmatites: A case study from the Moldanubian Zone of the Bohemian Massif (Czech Republic)

Abstract

The evolution of the trace-element patterns of quartz during crystallization of pegmatite melt was investigated using laser ablation inductively coupled plasma mass spectrometry. The contents of Al, B, Ba, Be, Cr, Fe, Ge, Li, Mn, P, Rb, Sn, Sr and Ti were analysed in quartz from the border, intermediate and core zones of four granitic pegmatites differing in degree of fractionation and origin. The material investigated originates from the pegmatite district of the Strážek Unit, Moldanubian Zone, Bohemian Massif, Czech Republic and includes: lepidolite LCT (Li-Cs-Ta) pegmatite from Rožná; berylcolumbite LCT pegmatite from Věžná; anatectic pegmatite from Znětínek; and intragranitic NYF (Nb-Y-F) pegmatite Vladislav from the Třebíč Pluton. The abundances of the elements analysed varied over wide intervals: <1 to 32 ppm Li, 0.5 to 6 ppm B, <1 to 10 ppm Ge, 1 to 10 ppm P, 10 to 450 ppm Al, 1 to 45 ppm Ti and <1 to 40 ppm Fe (average sample contents). Concentrations of Be, Rb, Sr, Sn, Ba, Cr and Mn are usually <1 ppm. Quartz from LCT pegmatites exhibits a distinct evolutionary trend with a decrease in Ti and an increase in Al, Li and Ge from the pegmatite border to the core. In comparison with the most fractionated rare-metal granites, pegmatitic quartz is relatively depleted in Al and Li, but strongly enriched in Ge. Quartz from simple anatectic and NYF pegmatites is poor in all trace elements with their evolution marked by a decrease in Ti and a small increase in Ge. There is little Al or Li and neither shows any systematic change with pegmatite evolution. Using the Ti-in-quartz thermobarometer, the outer zones of the Znětínek and Vladislav pegmatites crystallized at ∼670°C, whereas the border zone in the Rožná pegmatite yields a temperature near 610°C.

Trace-element chemistry of barren and ore-bearing quartz of selected Au, Au-Ag and Sb-Au deposits from the Bohemian Massif

“…This behavior resembles the fractionation trend common in silica-rich melts (i.e., from granite to evolved pegmatite; e.g. Breiter et al 2014). Therefore, this points to the formation of Q1 veins from a hydrothermal fluid (with a significant contribution of the magmatic component) directly derived from the magma of the host granodiorite (see also ).…”

“…The Al/Ti and Ge/Ti ratios have been widely used to study the fractionation of granitic and pegmatitic systems (e.g. Müller et al 2002;Jacamon and Larsen 2009;Breiter and Müller 2009;Breiter et al 2013Breiter et al , 2014Garate-Olave et al 2017). Variations of Ti and Al in individual growth zones can be easily visualized by cathodoluminescence.…”

Extreme fractionation in a granite–pegmatite system documented by quartz chemistry: The case study of Tres Arroyos (Central Iberian Zone, Spain)

“…5), as it was described for some pegmatites from the Bohemian Massif by Breiter et al (2014). Lithium contents in quartz have been related to the peraluminosity of the melt (Jacamon and Larsen, 2009), as well as to the fractionation degree and coexisting Li-bearing minerals (Breiter et al, 2013(Breiter et al, , 2014. However, none of these reasons seems easy to apply in this case, as discussed above for Al.…”

“…Studies on the variation of the trace elements contents in quartz during the crystallization of single pegmatites are scarce: e.g. strong variations have been observed in some LCT pegmatites from the Borborema Pegmatite Province (Beurlen et al, 2011); similar evolutionary trends from fractioned granites to LCT pegmatites are described in the Bohemian Massif, (Breiter et al, 2014); noticeable variations are also described for the NYF pegmatites in Evje-Iveland (Müller et al, 2015). In contrast, almost no variation is found in quartz chemistry across the internally zoned abyssal pegmatites from Froland (Müller et al, 2015).…”

Titanium

“…2007) to develop petrogenetic models that include the pressure and temperature of crystallization (e.g., Wark et al, 2007;Thomas and Watson, 2012;Breiter et al, 2014), temperature of deformation (Nachlas et al, 2014, and references therein), the time scales of thermobarometric events (Spear et al, 2012), and the provenance of quartz crystals (Ackerson et al, 2015). Ti in zircon (ppmw)…”