Geology and genesis of the newly identified Early-Devonian Hatuzhongyou REE deposit, NW China: Insights from petrology, geochemistry, and isotopes

The East Kunlun Orogenic Belt (EKOB) is an important Cu-Co-Ni-Au-Fe metallogenic belt in China, but the degree of exploration for rare earth elements (REE) mineralization remains very limited. Following the identification of the Dagelegouxi carbonatite-associated REE-Nb deposit (2022) and the Hatuzhongyou (HT) REE deposit (2017), the researchers have paid increasing attention to the REE mineralization potential in the EKOB. The former has been systematically studied in terms of the metallogenic processes. However, no systematic studies have been conducted on the HT deposit, resulting in a research gap. Therefore, this study applies petrology, whole-rock and in-situ mineral geochemistry, geochronology and Sr-Nd-Pb-Hf isotopes to investigate tectonic setting and metallogenic processes of the HT deposit.The HT deposit represents an alkaline silicate complex (ASC)-hosted mineralization system. The ASC comprises hornblende gabbro (HG), clinopyroxene syenite (CS), hornblende-clinopyroxene syenite (HCS), and quartz-hornblende-clinopyroxene syenite (QS), displaying brecciated, stockwork, and disseminated REE ores. REE mineralization is dominated by allanite, xenotime, monazite, and bastnäesite. The zircon U-Pb concordant age of the HCS suggests that the HT ASC formed in an extensional setting induced by slab detachment and asthenospheric upwelling at ca. 413 Ma, marking a flare-up stage of magmatism and mineralization from ca. 430 Ma to 359 Ma in the EKOB. All rocks in the HT deposit are enriched in large ion lithophile elements (LILEs) and REE, but depleted in Nb, Ta, Ti, and Eu. Petrology, mineral compositions, geochemical data, and Hf-Sr-Nd-Pb isotopic compositions suggest that the source of the HT deposit originated from low-degree partial melting of a metasomatized enriched lithospheric mantle, followed by fractional crystallization, magmatic-hydrothermal metasomatism, and fluid boiling.