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Titanium contents of both vein and magmatic quartz from five Bohemian gold deposits with known P-T history were used to calculate/discuss the titanium oxide activities (aTiO2) of natural quartz formed in the absence of Ti-buffering phases at 250-550 °C and 0.1-4 kbar. Data suggest significant variations in aTiO2 during vein quartz formation, due to variation of P, T and growth rate. Negative correlation between aTiO2 and quartz formation temperature was documented for intrusion-related gold deposits, implying quartz precipitation under closed-system conditions (i.e., without substantial equilibration of the ascending fluid with surrounding rocks). We propose a relationship for quantifying disequilibrium quartz formation that can be readily applied to quartz with known P-T history. The relationship was tested on natural samples exhibiting both rapid and slow crystallization. An example of extreme Ti enrichment (up to ~30 ×) in quartz, associated with its rapid growth, is described and discussed. [ABSTRACT FROM AUTHOR]

The trace-element contents in gold-bearing and barren quartz veins from eight Au, Au-Ag and Sb-Au Variscan deposits in the Bohemian Massif have been determined in situ in order to evaluate the differences between the various types of gold deposits and discuss trace-element variations in the successive generations of quartz veins. The variability of Ti, Al, Ge, Li and Sb abundances obtained by Laser-Ablation Inductively-Coupled Plasma Mass Spectrometry (LA-ICP-MS) roughly correlates with the origin and the temperature of the mineralizing fluids. The Al content ranges up to 4020 ppm (median value 230 ppm), while the Li content is generally low (< 4 ppm). The elevated Sb content (30-360 ppm Sb) is only related to quartz that immediately preceded deposition of Sb-rich phases. The titanium content of the ore-bearing vein quartz follows bimodal distribution: gold deposits with assumed higher temperature (> 450 °C) formation exhibit higher median values (~10 ppm Ti) than medium-to-low (< 300 °C) temperature deposits (~2 ppm Ti). A statistically significant threshold value (8 ppm Ti) has been recognized as an empirical tool for discriminating between them. In terms of the Ti and Al contents, the studied Bohemian gold deposits fall within and in between fields of orogenic gold and porphyry deposit types. [ABSTRACT FROM AUTHOR]

Primary fluid inclusion in quartz crystals from barren subvertical quartz veins that crosscut the Upper Carboniferous (Upper Asturian) coarse-grained clastics at Butov near Stíbro were found to have almost the same microthermometric characteristics (salinity, temperature of homogenization and variability of filling) as fluid inclusions from mineralized veins of the Stíbro Ag-Pb-Zn ore district. The mineralization at Stříbro should be therefore Upper Asturian in age, or younger. It is notably, that fluid salinities and temperatures of veins from Butov, and also of the Stříbro district, are very similar to that of Triasic to Jurasic fluorite-barite mineralization from the Erzgebirge Mts. (Moldava, Vrchoslav deposits). [ABSTRACT FROM AUTHOR]

Abstract: Unusual paleofluid composition is reported for the Libčice orogenic-type gold deposit located in the Central Bohemian Plutonic Complex (CBPC), Czech Republic. Unexpected bicarbonate-rich fluids and their complex chemistry variations characterize primary fluid inclusions from the main gold-bearing quartz vein. A detailed microthermometry, Laser Raman Micro Spectroscopy (LRMS) and SEM cathodoluminescence study was used to understand the complex chemistry and P–T–X history. The results indicate the presence of H2O and H2O–CO2–CH4 (±N2; H2S) fluids, the latter displaying variations of the CO2/CH4 ratio in the gaseous phase from 6.8 to 0.06. Variation of the CH4 content across single grains and between different levels of the mine was recorded. The presence of nahcolite, H2 (up to 6mol%) and ethane (0–0.2mol%) in the fluids were also discovered by LRMS. Potential models for the formation of different types of fluids present in the deposit are discussed, including the genesis of HCO3 − rich fluids as well as H2 and C2H6 presence in the primary fluid inclusions. The potential influence of organic matter-bearing sediments, as well as the impact of the intrusion of CBPC, re-equilibration and/or re-speciation of fluid inclusions during the post-entrapment history is considered to have the main impact on the complex paleofluid chemistry. Based on the thermodynamic modeling, H2 diffusion into the fluid inclusions was shown to be the main reason for the CH4 variation on the scale of a single grain, as well as across the whole vein. Although the exact processes of production/formation of HCO3 − and H2 at the Libčice deposit remain open to discussion, reactions in the C–O–H system are considered to be a possible formation mechanism. This work also contributes to our understanding of the importance of post-entrapment modifications and reactions in the C–O–H system on interpretation/deciphering the processes in orogenic-type deposits. [Copyright &y& Elsevier]