Geochemical Characteristics of the Volcanic Rocks Associated with Boron-Rich Deposits from the Xiongba Basin, Qinghai–Tibet Plateau

The Qinghai–Tibet Plateau (QTP) hosts significant lacustrine sedimentary boron-rich deposits, with the Xiongba Basin being a prominent region housing two large sedimentary boron-rich deposits. These deposits are closely associated with extensive Neogene volcanic rocks. This study investigates the origin and boron sources of Miocene volcanic rocks in the Xiangqu River area, located within the Xiongba Basin. The volcanic rocks in the basin comprise ultrapotassic andesites, ultrapotassic trachyte, potassic trachyte, and potassic trachyandeiste. The trace element content and the active/inert elements ratios of the studied volcanic rocks have indicated that they were generated in a subduction environment and were influenced by enrichment fluids derived from deep-sea sediments or altered oceanic crust during their formation. Accordingly, the studied volcanic rocks exhibit significant boron enrichment. The eruption of magma and subsequent hydrothermal activity released boron, which became the primary source for the lacustrine sedimentary boron-rich deposits within the basin. The arc-like trace element features (e.g., Nb-Ta depletion relative to La and K) and high B concentrations in these rocks were inherited from the mantle source, which had been enriched by melt/fluid of the subducted sediments. A two-stage evolutionary model is proposed to explain the enrichment of B in subduction environments, as well as the subsequent melting of the B-enriched source during a post-collisional setting. These findings highlight the potential for boron and lithium mineralization in similar volcanic rock-bearing regions across the QTP. Future exploration efforts in such areas could provide valuable insights into the formation processes of lacustrine sedimentary boron-rich deposits and contribute to the understanding of boron and lithium resource potential.