Dataset: Radiochemistry data for rocks and deposits from the Lost City Hydrothermal Field at the Atlantis Massif from 2018-2020

Solid samples were obtained from the 2018 Return to Lost City and four previous expeditions in 2015, 2005, 2003, and 2000 (Kelley et al., 2001; Kelley et al., 2005; Früh-Green et al., 2018). In all years except 2015, chimney and local rock materials were gathered as grab samples by the manipulators of either the ROV or Human Occupied Vehicle (HOV) Alvin and stowed in rock boxes. In 2015, rock samples were recovered with seabed rock drills as part of International Ocean Discovery Program (IODP) Expedition 357, which drilled a series of shallow boreholes across the Atlantis Massif (Früh-Green et al., 2018). In 2015 and 2018, samples were wrapped in Teflon sheeting and stored at -20°C. In previous years, samples were dried and stored at room temperature. 

The solid rock samples were analyzed for uranium (Ur) and thorium (Thr) concentrations by a Thermo Element 2 inductively coupled plasma mass spectrometer (ICP-MS). Approximately 40 mg of sample and approximately 80 mg of an Sm-Nd (145Nd) spike were weighed into a Teflon vial. The samples were digested for four days in a 4 mL dissolution mixture (3:1 concentrated HF: concentrated HNO3) in a closed beaker at 100°C. The digest was dried, 1 mL of concentrated HNO3 added, and the sample dried again. This was repeated three times. The digestion was brought into solution with 2.2 mL of 7N HNO3 and 4.8 mL of water and stored overnight. The contents were transferred to a 50 mL tube and diluted with an additional 33 mL of water. A 1:1 dilution (1 mL of sample and 1 ml of 2% HNO3) was distributed into 4 mL omnivials, and the samples were analyzed by ICP-MS.

Analyses of Ra in the solid samples (Rar) were conducted on seven carbonates, 19 serpentinites, four gabbro. The carbonates were crushed with a mortar and pestle while the other rocks were crushed with an impact mortar. An aliquot of dry, crushed sample (2 – 10 g) was then measured for 227Ac, 226Ra, 228Ra and 228Th via gamma spectrometry.