Lithium in fluids from Paleozoic-aged reservoirs, Appalachian Plateau region, USA

• Li in produced waters from western PA and eastern OH shows systematic patterns.
• Li content in Appalachian Plateau Silurian–Devonian fluids is up to 40 mmol/kg.
• Li concentrations increase from west to east and with increasing depth.
• Areas of anomalously high Li overlie NW-trending salients of vitrinite reflectance.
• Li may indicate paleo-flowpaths of fluid expulsed from the Appalachian Basin.

This study presents the spatial distribution of a compilation of lithium (Li) and selected other dissolved species concentrations in saline fluids from oil and gas wells in western Pennsylvanian and eastern Ohio that are producing from Silurian- to Devonian-age formations. Lithium concentrations in the data set range from about 40 to 40,000 μmol kg−1 indicating water–rock reactions that added Li to the saline fluids. Chloride (Cl) concentrations range from about 160 to 5300 mmol kg−1, likely the result of different burial fluids (seawater or evaporated seawater), variable dilution with meteoric water and variable interaction with marine evaporites. The Li/Cl in these fluids is not constant, potentially indicating multiple sources of Li in addition to multiple origins of Cl. Lithium and the Li/Cl ratio generally decrease from east to west across the study area in four or five bands of similar Li or Li/Cl. Lithium and Li/Cl are not correlated with petroleum-production formation and are only generally correlated with depth. A few of the fluid samples have anomalously high Li and Li/Cl. These anomalous samples coincide in location with northwesterly trending salients of high vitrinite reflectance, suggesting that Li in this segment of the Appalachian Plateau Province may provide insight into paleoflow pathways in the region, indicating where hot, chemically evolved, saline fluids might have been driven to the northwest, upwards and out of the basin, during tectonism.