Data of shale samples from the Dawuba Formation

Instrument reference standards (501‑506 and 501‑679) were inserted after every 20 samples. The analytical error was controlled within ±5%.Major Element AnalysisMajor element analysis was carried out on the shale samples. The analysis was performed with an inductively coupled plasma optical emission spectrometer (ICP‑OES, PerkinElmer Optima 8300V).

The shale samples were crushed to pass 300 mesh (<50 μm) and dried at a temperature of 24 °C and a relative humidity of 55%. An accurately weighed portion of about 0.05 g of sample was placed in a PTFE digestion vessel, and a mixed acid (HF:HNO₃:HClO₄ = 10:5:3) was added. Digestion was performed at 180 °C for approximately 12 hours.

After complete digestion, the solution was made up to 50 mL with 1% HNO₃. The measurement conditions were: RF power 1200 W, plasma gas (Ar) flow 15 L/min, auxiliary gas (Ar) flow 0.2 L/min, nebulizer gas (Ar) flow 0.8 L/min, peristaltic pump speed 1.5 mL/min, and each measurement was repeated three times. The analytical error was controlled within ±5%.Trace and Rare Earth Element AnalysisTrace and rare earth element analysis was performed on the shale samples.

The analysis was carried out using an inductively coupled plasma mass spectrometer (ICP‑MS, Agilent 7700 series). The sample pretreatment was the same as that used for major element analysis: the sample solution was prepared by mixed‑acid digestion (HF:HNO₃:HClO₄ = 10:5:3). The measurement conditions were: RF power 1300 W, carrier gas (Ar) flow 0.9 L/min, auxiliary gas (Ar) flow 1.2 L/min, plasma gas (Ar) flow 15 L/min, lens voltage 6 V, pulse stage voltage 850 V, quadrupole offset 0, detector chamber vacuum 1×10⁻⁶ Pa, and sample uptake rate 1.0 mL/min.

The analytical error was controlled within ±5%.