Silicate weathering contributed to arsenic enrichment in geotherm-affected groundwater in Pliocene aquifers of the Guide basin, China

•High arsenic in groundwater was generally related to high Na+ and low Ca2+.•The middle-Pliocene aquifer sediments had low contents of water-soluble Ca and SIC.•Endogenic CO2 was responsible for silicate weathering in middle-Pliocene aquifer.•Silicates weathering in middle-Pliocene aquifer released arsenic into groundwater.•High temperature promoted arsenic desorption and weathering of silicates.