Objective The Qimantag metallogenic belt is an important porphyry−skarn polymetallic metallogenic belt in China, and the Niukutou deposit is a large−scale Pb−Zn polymetallic deposit discovered in this metallogenic belt in recent years. However, there is a lack of research on the relationship between the age of the ore−forming rock mass, skarn formation, and Pb−Zn mineralization. Additionally, the relationship between the physicochemical conditions for skarn formation and mineralization in this deposit has not been thoroughly explored, which restricts our understanding of the metallogeny. Methoods Through the zircon LA−ICP−MS dating and electron probe technology analysis methods, this paper provide detailed information on the mineralization age, skarn zoning, and mineral composition characteristics.
Results The results indicate that the monzogranite closely related to skarn was formed at 389.9 ± 2.2 Ma, indicating that the Niukutou mineralization occurred in the Middle Devonian. The skarn rocks of the Niukutou deposit exhibit obvious alteration zones, and overall belong to the calcium−magnesium series skarn rock formation. Near the ore−forming rock mass, there is a set of andradite and hedenbergite mineral assemblages, while far away from the ore−forming rock mass, there is a set of grossularite and Mn−hedenbergite mineral assemblages. The main skarn minerals in the retrograde metamorphic stage are ilvaite, tremolite, actinolite, etc. The MnO content is low near the ore−forming rock mass, and gradually increases away from the ore−forming rock mass. This suggests that the chemical composition of the skarn minerals in the retrograde metamorphic stage has a certain inheritance from the skarn minerals in the prograde metamorphic stage. The ore−forming hydrothermal fluid migrates from the proximal to distal end of the ore−forming rock mass (southwest to northeast), during which temperature, f_\mathrmO_2 , and pH gradually decrease. Mineralization changes from the high−temperature metal mineralization assemblage near the ore−forming rock mass to the Pb−Zn mineralization assemblage distal from the ore−forming rock mass.
Conclusions Based on previous research, this article believes that the calcium−magnesium skarn formation related to Middle−Late Devonian magmatic rocks in the Qimantag may be a prospecting indicator for skarn Pb−Zn deposits in this region. The temperature, f_\mathrmO_2 , and pH gradually decrease during the migration of ore−forming hydrothermal fluids from the proximal to distal end (southwest to northeast) of the ore−forming rock mass. This change in physical and chemical conditions is the reason for the enrichment of manganese rich skarn minerals and Pb−Zn mineralization in the distal end of the ore−forming rock mass.
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