Bicarbonate-rich fluid inclusions and hydrogen diffusion in quartz from the Libčice orogenic gold deposit, Bohemian Massif

0358377 - GLÚ 2012 RIV NL eng J - Článek v odborném periodiku
Hrstka, Tomáš - Dubessy, J. - Zachariáš, J.
Bicarbonate-rich fluid inclusions and hydrogen diffusion in quartz from the Libčice orogenic gold deposit, Bohemian Massif.
Chemical Geology. Roč. 281, 3-4 (2011), s. 317-332. ISSN 0009-2541. E-ISSN 1872-6836
Výzkumný záměr: CEZ:AV0Z30130516
Klíčová slova: bicarbonate * fluid inclusions * hydrogen diffusion * orogenic gold deposits * raman spectroscopy
Kód oboru RIV: DB - Geologie a mineralogie
Impakt faktor: 3.518, rok: 2011

Unusual paleofluid composition is reported for the Lib̌ice 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.
Trvalý link: http://hdl.handle.net/11104/0196441