The relationship between light hydrocarbons and carbonate petrology―a study from the Mendip hills

Anomalously high values of light hydrocarbons (C1–C4) have been detected in carbonate rocks hosting base metal mineralization, and have a potential use in mineral exploration. Development of an exploration method based on such anomalies requires an understanding of the controls on the hydrocarbon content of the rocks, other than by mineralization, i.e. the hydrocarbons present in background areas. This study uses gas chromatography to investigate the light hydrocarbons present in rocks from such a background area, the Carboniferous Limestone of the Mendip Hills, in order to determine the extent to which different carbonate lithologies affect the quantity and nature of hydrocarbons present. It appears that the lithological effects are minimal when compared to the anomalous values from mineralized areas. The limited effects are due to variations in the depositional and diagenetic regimes of the original sediments.