Carbonate-hosted clay-type lithium deposit and its prospecting significance

In recent years, the clay-type lithium resources have attracted increasing attention due to their large scale, stable distribution, low cost of mining and utilization. Comparing with the traditional pegmatite-type and brine-type lithium deposits, it has become an important direction of exploration of new type lithium resources. The clay-type lithium resources reported have genetic relationship to volcanic materials. Through systematic research and review, this paper first proposed the genetic concept of carbonate-hosted clay-type lithium deposit, which was related to carbonate weathering-sedimentation. Li-rich clay rocks found at present mainly include the Jiujialu formation (C(1)jj) of lower carboniferous in Guizhou Province and Daoshitou formation (P1d) of the lower Permian in central Yunnan Province. Although the different formation ages of the two sets of Li-rich strata in this study, their lithology is relatively similar to the section upward, including: (1) Aluminized clay rocks, local iron bearing; (2) compact aluminaceous clay rocks; (3) bean oolitic aluminaceous clay rocks; (4) loose soil-like clay rocks, among which the dense aluminaceous clay rocks and pisolitic aluminaceous clay rocks are the most favorable lithology for lithium enrichment. The results of XRD analysis show that the major minerals of clay rocks are hydralite, bomberite, montmorillonite, illite, kaolinite, anatase, rutile, zircon and pyrite. According to the analysis of more than 1000 samples from more than 30 profiles, it is shown that most of the samples from two sets of Li-rich strata have reached the comprehensive utilization index of lithium in bauxite (Li2O >= 500 mu g/g), and the average Li2O content in the clay rocks is about 0.3%, and the highest is 1.1%. The detailed micro-analysis using Tof-SIMS technique has shown that lithium was mainly distributed in clay minerals, and mainly occurred in amorphous clay minerals identified as montmorillonite. The trace and major elements suggest that the weathering of underlying carbonate rocks provides a source of Li-rich clay rocks. Detailed field observations in combination with trace element geochemical analysis (such as high lithium samples of Sr/Ba ratio is generally less than 0.5, MgO/Al2O3 ratio less than 1, Rb/K ratio is less than 0.003, Ni/Co ratio greater than 5), indicate that oxygen-poor and low-energy coastal marshes, lagoons and limited and closed ancient bay (basin) in the transitional environment may be ideal places for Li enrichment to form high-grade deposits. Therefore, the main geological and geochemical characteristics of this new type can be summarized as: (1) The ore-forming material is derived from the underlying carbonate formation; (2) lithium mainly exists in the smectite phase by adsorption; (3) the sedimentary environment plays an important role in the enrichment of lithium, the limnic basin in coastal plain was an ideal place for lithium accumulation; (4) in addition to Li, there may be Ga and REE enrichment occurring in this type clay. According to this new metallogenic model, it has obtained 340000 tons of lithium oxide resources in Dianzhong basin by geological exploration, reaching a super-large class deposit. Due to the numerous regions with similar ore-forming conditions of these type lithium resources, it can be expected that carbonate-hosted clay-type lithium deposit will become an important source of lithium resources in China.