Critical metals in sediment-hosted Pb-Zn deposits in China

<p indent=0mm>Sediment-hosted Pb-Zn deposits are mainly comprised of Mississippi Valley-type (MVT) deposits situated in carbonate-dominated sedimentary rocks and clastic-dominated (CD) deposits located in siliciclastic-dominated sequences. They are significant sources of critical metals such as cadmium, gallium, and germanium, as well as indium, cobalt, and thallium. In China, sediment-hosted Pb-Zn deposits are found in 5 metallogenic belts/districts, namely the Sanjiang belt, the Yangtze Block district, the Tarim Craton district, the Changba belt, and the Langshan belt. They provide 54% of China’s Pb-Zn resources, but their resource endowment and the metallogenic characteristics of these associated critical metals remain unclear. After briefly reviewing the main critical metals in sediment-hosted Pb-Zn deposits and sediment-hosted Pb-Zn deposits in China, this review summarizes the distribution and enrichment mechanisms of critical metals in sediment-hosted Pb-Zn deposits in China and recommends future research. These critical metals are unevenly enriched in sediment-hosted Pb-Zn deposits in China. Compared to the crustal elemental abundances, Cd, Ge, and In are the most enriched, Tl and Co have lower enrichment degrees, and Ga has the lowest enrichment degree. Cd, Ga, Ge, and Tl are rich in MVT deposits, while In and Co are rich in CD deposits. In all five sediment-hosted Pb-Zn belts/districts, Cd is relatively abundant. However, other critical metals are enriched to a different degree in each belt/district. In terms of distribution, Cd is well enriched in all five sediment-hosted Pb-Zn belts/districts, particularly in the Sanjiang belt of the Qinghai-Tibet Plateau, and the Yangtze Block district; Ge is most abundant in the Yangtze Block district, followed by the Changba belt in the Qinling orogenic belt, and Sanjiang belt; In and Co are enriched in the Sanjiang belt, followed by the Yangtze Block district and the Changba belt; Tl is enriched in the Sanjiang belt, the Yangtze Block district, and the Changba belt; and, Ga is most enriched in the Changba belt and Yangtze Block, followed by the Sanjiang belt. Based on these characteristics, two enrichment mechanisms are occurring in sediment-hosted Pb-Zn deposits. First, sediment-hosted Pb-Zn deposits are selective for the enrichment of critical metals, and second, the degrees of enrichment of critical metals in these deposits are different. The first enrichment mechanism results from the similarity in physicochemical properties between the critical metal elements and dominant elements (such as Zn and Fe) in the ore and gangue sulfides (such as sphalerite and pyrite). The second mechanism is associated with substitution forms of critical metal elements and host minerals, as well as physicochemical conditions and tectonic conditions of the deposits and tectonomagmatic processes throughout geological history. Research into critical metals in sediment-hosted Pb-Zn deposits in China abounds in the Yangtze platform Pb-Zn metallogenic belt and MVT Pb-Zn deposits; however, this research is still in the pipeline. A database of critical metal resources hosted by sediment-hosted Pb-Zn deposits in China is urgently needed, as is comprehensive research into the metallogenic mechanism of different critical metals, and the determination of the regional metallogenic regularity of these critical metals.