Authigenic pyrite plays a vital role in understanding diagenetic processes, growth mechanisms within marine gas hydrate-bearing sediments, and the global sulfur cycle. This study investigates the elemental and sulfur isotopic composition of authigenic pyrites within the gas hydrate-bearing layer of a drilling core retrieved from the Shenhu region, northern South China Sea. A suite of in-situ analytical techniques, including electron microprobe analysis (EMPA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS), were employed to characterize the pyrites. Two distinct pyrite groups were identified based on their morphology and geochemical signatures: (1) framboidal pyrite and (2) subhedral pyrite. Group 1 framboidal pyrites exhibit negative δ³⁴S_V-CDT values (-24.5‰ to -7.1‰) and elevated concentrations of Cr, Mn, Co, Zn, As, Mo, Sb, Ba, and Pb. Conversely, Group 2 subhedral pyrites display positive δ³⁴S_V-CDT values (2.7‰ to 41.4‰) and lower concentrations of the aforementioned trace elements. Integrating the textural and geochemical variations observed in the two pyrite groups, we propose a growth model for authigenic pyrite within a closed system influenced by gas hydrates. The transition from framboidal to subhedral pyrite morphology likely reflects evolving sediment geochemical conditions. The high abundance and variable sulfur isotopic and elemental compositions of the pyrites suggest elevated reaction rates associated with sulfate-driven anaerobic oxidation of methane (SD-AOM) and pyritization within the gas hydrate-bearing layers. The elevated abundance and unique geochemical feature of pyrites within the gas hydrate-bearing layer could potentially serve as an indicator of pre-existing gas hydrate. This study provides valuable insights into the growth processes of authigenic pyrite within a gas hydrate-driven closed system and elucidates the relationship between authigenic pyrite formation and gas hydrate occurrence, which will be beneficial to the prospecting for the gas hydrate reservoir.

The latest and ongoing sample return missions from extraterrestrial objects present an opportunity to expand our knowledge of the chemical composition and subsequent evolution of the Solar System, beyond the information that can be obtained from the study of meteorites. Nevertheless, a potential limitation of such missions, at least in the foreseeable future, would be the recovery of a limited amount of sample. In light of these considerations, we have developed a multi-element chemical separation protocol utilizing a sample amount of approximately 25 mg. With this sample amount (and less), we can successfully separate elements including Mg, K, Ca, Ti, Cr, Fe, Ni, Zn, Sr, Zr, Mo, Ba, REEs, Hf, W, Pb, and U. This includes the crucial elements Ti and Cr, whose isotopic compositions are used for the latest classification of meteorites, and in turn the parent asteroidal materials. The new method achieved chemical yields for these elements after separation of greater than 90% for both major and trace elements in the Murchison meteorite (with an exception for Pb with 85%). The corresponding total procedural blanks were negligible, representing less than 0.1% for the majority of the elements. This method was specifically designed for the analysis of small samples (< 30 mg) of extraterrestrial materials from sample return missions, such as Hayabusa2 and OSIRIS-REx. It will be of significant application in future missions such as MMX and Artemis where limited quantities of asteroidal, cometary, planetary, and other primitive Solar System solids will be returned.