Geochemistry and Geochronology of the Causative Intrusion and a New Genetic Model Study of the Yaojialing Polymetallic Skarn Deposit, Tongling District, China

Abstract

AbstractThe Yaojialing deposit is the first large‐scale Zn–Au–Cu polymetallic skarn deposit located in the Shatanjiao ore field of the Tongling area in the Middle–Lower Yangtze belt. It has distinct metallogenic characteristics and is clearly different from the known skarn Cu–Au deposits in the Tongling area and the Middle–Lower Yangtze belt. Previous studies of the Yaojialing deposit have included rock geochemistry, alteration and mineralization characteristics, as well as metallogenesis and metallogenic models. However, there are still numerous problems concerning the coexistence of multiple elements, metallogenetic specialization of the magma and the metallogenic model. In this study, using the latest production exploration work on the deposit, we investigated the Yaojialing deposit including its geological characteristics, petrography, LA–ICP MS zircon U–Pb dating and whole rock geochemistry. Two kinds of magmatic rocks have been distinguished for the first time in the deposit, amongst which the granodiorite porphyry exposed on the surface of the mining area, which is the host rock of the veined lead–zinc ore body, is the wall‐rock intrusion; and the deep concealed quartz monzonite porphyry is the causative intrusion, the distribution of orebodies and wall‐rock alteration characteristics showing regular zoning around the quartz monzonite porphyry. The 206Pb/238U weighted average age of the granodiorite porphyry is 140.2 ± 1.0 Ma (MSWD = 0.85, n = 13) by LA–ICP MS zircon U–Pb dating, while the quartz monzonite porphyry is 138.9 ± 1.2 Ma (MSWD = 0.60, n = 16), which is consistent with petrographic evidence. The geochemical characteristics show that the quartz monzonite porphyry is a high‐K calc‐alkaline series peraluminous rock. The trace element characteristics show that the quartz monzonite porphyry is enriched in LILE such as K, Rb, Sr, Ba and LREE, yet depleted in HFSE such as Nb, Ta, P and Ti. The Yaojialing deposit shows the mineralization characteristics of proximal skarn and distal skarn, having the common characteristics of ‘multi‐storey’ and ‘Trinity’ metallogenic models.