Enrichment conditions and metallogenic model of potassium and lithium resources in the Lower–Middle Triassic, northeastern Sichuan Basin, SW China

Abstract

Wells CXD1 and CX2 have uncovered high-concentration potassium- and lithium- containing brines and substantial layers of halite-type polyhalite potash deposits within the 4th and 5th members of the Triassic Jialingjiang Formation and the 1st Member of Leikoupo Formation (Jia 4 Member, Jia 5 Member, and Lei 1 Member) in the Puguang area, Sichuan Basin. These discoveries mark significant breakthroughs in the exploration of deep marine potassium and lithium resources within the Sichuan Basin. Utilizing the concept of “gas-potassium-lithium integrated exploration” and incorporating drilling, logging, seismic, and geochemical data, we have investigated the geological and enrichment conditions, as well as the metallogenic model of potassium-rich and lithium-rich brines and halite-type polyhalite. First, the sedimentary systems of gypsum-dolomite flats, salt lakes and evaporated flats were developed in Jia 4 Member, Jia 5 Member, and the 1st member of Leikoupo Formation (Lei 1 Member) in northeastern Sichuan Basin, forming three large-scale salt-gathering and potassium formation centers in Puguang, Tongnanba and Yuanba, and developing reservoirs with potassium-rich and lithium-rich brines, which are favorable for the deposition of potassium and lithium resources in both solid or liquid phases. Second, the soluble halite-type polyhalite has a large thickness and wide distribution, and the reservoir brine has a high content of K⁺ and Li⁺. A solid-liquid superimposed “three-story structure” (with the lower thin-layer of brine reservoir in lower part of Jia 4 Member and Jia 5 Member, middle layer of halite-type polyhalite potash depositS, upper layer of potassium-rich and lithium-rich brine reservoir in Lei 1 Member) is formed. Third, the ternary enrichment and mineralization patterns for potassium and lithium resources were determined. Vertical superposition of polyhalite and green bean rocks is the mineral material basis of potassium-lithium resources featuring “dual-source replenishment and proximal-source release”, with primary seawater and gypsum dehydration as the main sources of deep brines, while multi-stage tectonic modification is the key to the enrichment of halite-type polyhalite and potassium- lithium brines. Fourth, the ore-forming process has gone through four stages: salt-gathering and potassium-lithium accumulation period, initial water-rock reaction period, transformation and aggregation period, and enrichment and finalization period. During this process, the halite-type polyhalite layer in Jia 4 Member and Jia 5 Member is the main target for potassium solution mining, while the brine layer in Lei 1 Member is the focus of comprehensive potassium-lithium exploration and development.