Geochemical characteristics of surface waters and groundwaters in the Velenje Basin, Slovenia

The geochemical and isotopic composition of surface water and groundwaters in the Velenje Basin, Slovenia,were investigated to gain a better understanding of the origin of surface and groundwaters. Surface waters andgroundwaters from the Triassic aquifer are dominated by HCO3-, Ca2+, and Mg2+ from dissolution of carbonate minerals,while groundwaters from the Pliocene and Lithotamnium aquifers have distinct geochemical signatures,enriched in Na+ and K+. Surface waters are controlled by calcite dissolution, while groundwaters from the Triassicaquifer are controlled by dolomite dissolution. The partial pressure of CO2 in surface waters and groundwaters iswell above atmospheric concentrations, indicating that these waters are a potential source of CO2 to the atmosphere.The δ13CDIC values of surface waters are shown to be controlled by biogeochemical processes in the terrestrial environment,such as dissolution of carbonates, degradation of organic matter, and exchange with atmospheric CO2,which is more pronounced in the lake waters. The δ13CDIC values of groundwater from the Triassic aquifer are consistentwith degradation of CO2 and dissolution of dolomite. Groundwaters from the Pliocene and Lithotamniumaquifers have δ13CDIC values suggestive of biogenic CO2 reduction and degradation of organic matter

Spatial distribution and origin of coalbed gases at the working faces of the Velenje Coal Basin, Slovenia, since the year 2000

Geochemical and isotopic monitoring of coalbed gases at the excavation fields of mining areas in Velenje Coal Basin, Slovenia, has been ongoing since the year 2000 with the aim of obtaining better insights into the distribution and origin of coalbed gases. Results from the mining areas Pesje and Preloge (active excavation fields) are presented here from the year 2000 up to the present. Composition and origin of coalbed gases were determined using mass spectrometry at the Jožef Stefan Institute. From a larger database of geochemical samples, 119 samples were used for analysis and spatial presentation in a geographical information system (GIS) environment. We have used geochemical (CH4, CO2 and N2) and isotopic (δ13CCO2 and δ13CCH4) tracers for geochemical and isotopic characterisation of coalbed gases from the active excavation fields. Concentrations of CO2 and the carbon dioxide–methane indices in the southern part of the basin are higher than in the northern part of the basin due to the vicinity of the active Šoštanj Fault. The value of δ13CCH4 at the active excavation field indicates a bacterial origin, with values greater than –50‰, and only some boreholes show elevated δ13CCH4 quantities as a consequence of the CO2 reduction process in Velenje Coal Basin. The value of δ13CCO2 indicates the bacterial and endogenic origin of carbon

Exploring the 2013-2018 degassing mechanism from the Pesje and Preloge excavation fields in the Velenje coal basin, Slovenia

Gas samples were collected from 25 m long horizontal boreholes drilled into the excavation field at 10° inclination to the longwall face in two mining areas, Pesje and Preloge, in the Velenje Coal Mine, Slovenia, from 2013 to 2018. The degassing mechanism of coalbed gas and its stable isotopic composition (δ$^{13}$C$_{CO2}$, δ$^{13}$C$_{CH4}$, and δ$^2$H$_{CH4}$) were investigated in boreholes in advance of eight working faces. The major coalbed gas constituents were CO$_2$ and methane. Gas concentrations and isotope values revealed that the methane is biogenic in origin with δ$^{13}$C$_{CH4}$ values of −69.4 to −29.5 ‰, δ$^2$H$_{CH4}$ values of −301 to −222 ‰, and a fractionation factor (α$_{CO2^-CH4}$) of 0.998–1.073, suggesting that methane derives from microbial acetate fermentation and CO$_2$ reduction. The carbon dioxide methane index values ranged from 50.0–98.3 vol.% and δ$^{13}$C$_{CO2}$ values from −11.8 to −0.5 ‰, indicating that CO$_2$ is biogenic and endogenic in origin. The degassing mechanism results in isotope fractionation of methane and CO$_2$ for carbon isotopes up to 39.9 ‰ and up to 8.5 ‰, respectively, depending on the position of the excavation fields in space, e.g. under pre-mined coal area, fresh overburden

The effect of geochemical processes on groundwater in the Velenje coal basin, Slovenia: insights from mineralogy, trace elements and isotopes signatures

This study investigated the mineralogical and isotopic composition of groundwater and precipitation to identify and constrain geochemical processes within stacked Pliocene and Triassic aquifers in the Velenje coal basin. Scanning electron microscopy combined with energy-dispersive X-ray spectroscopic analysis revealed that suspended matter in the Pliocene aquifer consists of feldspars and quartz, while dolomite, calcite and feldspars are present in the aquifer dewatering Triassic strata. The concentrations of trace elements in Triassic and Pliocene aquifers range from highest to lowest Zn > Fe > Ni > Al > Ba > Mn > B > Li > Mo > As with the majority of trace element concentrations below international drinking water health guidelines. Multivariate principal component analysis indicated that concentrations of Mn, Ba, Eu, Cs, Y, Li and T, pH, conductivity and dissolved oxygen in samples were the best chemical parameter for distinguishing the two aquifers. A significant positive correlation (p < 0.05) was found between Ni, Mn, Co, Zn, As and Mo. Groundwater in the Pliocene aquifer likely has an external source of carbon based on the delta C-13(CO2) values (- 12.3 to - 3.6%). The groundwater also has detectable levels of dissolved methane with isotopic values (-77.7 to - 51.4 parts per thousand delta C-13(CH4); -247 to -162 parts per thousand delta H-2(CH4)) consistent with microbial methanogenesis. The groundwater in the Triassic aquifer has tritium values (up to 4.1 TU H-3) characteristic of modern recharge (< 50 years), while the lack of detectable H-3 (0TU) in the Pliocene aquifer is consistent with longer residence times.6 month embargo; published online: 31 October 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]