| Title | Active fault delineation studies using soil gas survey in the North-Ghoubbet geothermal prospect |
|---|---|
| Authors | Y. Samod, K. Yonezu, M. Kayad, M. Hassan |
| Year | 2024 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Mercury, radon, carbon dioxide, skewness, Quantile plot |
| Abstract | Soil gas surveying (carbon dioxide, Radon and mercury soil sample) are important assets for geothermal resource exploration. Several surface manifestations, in particular, fumaroles occur in the North-Ghoubbet geothermal field and have not yet been examined by those techniques. Therefore, this study aims to determine the flow of geothermal fluids by examining the soil CO2 flux, radon and mercury distribution to detect buried structures that may infer permeability for the Nord-Ghoubbet geothermal area as a preliminary investigation. Anomalous distribution of the following soil gas (Radon (Rn), dioxide carbon (CO2), mercury (Hg) etc…) should be the “halos” of underground geothermal system and frequently used for the first phase of geothermal. Soil gas samples were obtained by hammering steel pipes in the ground to penetrate the ground to a depth of 0.6~1.0 meter. In total, 86 points were measured by CO2 (using a Kitakawa Gas detector), and mercury (The samples were analysed by a mercury analyser, NIC, MA 3000 at Kyushu University) at the same points. And 76 points for radon (using radon detector “RD-200”). In this study area, they are no background values measured for radon and CO2 concentration, for that statistic analysis were applied to determine the threshold value (the anomalous concentration). According to the calculated descriptive statistics , the skewness must be close to zero and doesn’t exceed 0.1 but in the data, the skewness is very high which means the data are not a normal distribution, the data is either log-normally or exponentially distributed. Quantile plot (The quantile-quantile (q-q)) plot were used to analyse the data and data appear as a lognormal distributed. The cumulative probability plots were used also to perform statistical analyses and classify the anomalies distribution. The anomaly distribution highlighted the lowest value is located in the Moudououd horst with a significantly lower concentration, 0.01% of CO2, 1.3071 ppb of mercury and a relatively low-value anomaly of 1 cpm for the radon gas survey. The highest CO2 and mercury anomalous concentrations were located at the Afay, Anale and Qeridaba areas with 2.5% CO2 and 1000 ppb of mercury, and the anomalous concentration of radon (for the thorium 220Rn with more than 100 cpm, and the radon 222Rn more than 10 cpm) concentrate to the Afay area. In the central part of the study area, the fumaroles and altered ground were distributed, and also the soil gas sampling was concentrated in this area. The NNW and NW structures are dominant and coincide with structures already exist in the study are by soil gas analysis. The buried structures can be estimated as active faults, which may be a conduit path of gas emanations. |