Enrichment mechanisms and occurrence regularity of critical minerals resources in the Yaojialing Zn skarn polymetallic deposit, Tongling district, eastern China

Abstract

Critical minerals resources are widely used in emerging industries, and their mineralization characteristics and metallogenic regularity are of high importance. Skarn deposits are one of the important sources of critical minerals resources. Yaojialing deposit is a typical large skarn zinc polymetallic deposit in Tongling district of the Middle and Lower Yangtze River metallogenic belt. The ore bodies are mainly lenticular and veined occurrence along the proximal skarn zone and structural or lithologic contacts, respectively. We recognize five hydrothermal stages in the deposit: skarn stage, oxide stage, early sulfide stage, late sulfide stage and carbonate stage. The early and late sulfide stages are the main ore-forming stages. In addition to the production of zinc, gold and copper, the deposit also contains critical element resources such as cadmium, cobalt, selenium, and tellurium. Taking the Yaojialing deposit as an example, this paper shows the occurrence and distribution of critical minerals resources in a typical skarn deposit by using scanning electron microscope, TESCAN integrated mineral analyzer (TIMA), and sulfide LA-ICP MS analysis. Although there are no cadmium minerals in Yaojialing deposit, cadmium can incorporated in the sphalerite lattice, and sphalerite in veins has elevated cadmium content (average 5478.78 ppm). Tellurium content in various sulfides is very low, and it does not enter into the sulfide lattice. It mainly forms tellurobismuthite, hessite and tetradymite, which occur in Cu-Zn ore formed in the early sulfide stage, there are 227 tetradymite grains in a single rock section. Selenium occurs as naumannite in vein ore in the distal of the deposit; selenium can also incorporated the lattice of chalcopyrite and sphalerite, and the selenium content is elevated in sphalerite formed in the early sulfide stage (average 226.80 ppm). The cobalt mineral glaucodot is only found in skarn ore; cobalt easily incorporated the lattice of pyrite and sphalerite, and pyrite and sphalerite formed in the early sulfide stage are enriched in cobalt (average 1962.18 ppm). The characteristics of trace elements in pyrite and sphalerite show that temperature is the main factor affecting the distribution of critical minerals resources, high temperature is conducive to the enrichment of cobalt, selenium and tellurium, while low temperature is conducive to the enrichment of cadmium. Cadmium, cobalt, selenium, and tellurium have high content in specific parts of the deposit, which makes them potentially amenable to recovery.