Abstract
Volcanic rocks, as the extrusive counterparts of the mineralized intrusions, can provide important information on the magma source, petrogenesis, and metallogenic conditions of the coeval porphyry-epithermal system. Shanghang Basin volcanic rocks are spatially and temporally related to a series of adjacent porphyry-epithermal Cu–Au deposits, and they can be used as a window to study the related deposits. Two laser-ablation–inductively coupled plasma–mass spectrometry zircon U–Pb analyses of the volcanic rocks yield weighted mean ages of ~105 Ma, identical to the age of the coeval porphyry-epithermal mineralization. Rocks have SiO2 contents of 55.4 to 74.8 wt % and belong to the high-K to shoshonitic series, characterized by strong differentiation of light rare-earth elements (REEs) relative to heavy REEs (mean LaN/YbN = 16.88); enrichment in light REEs, Rb, Th, and U; and depletion in Nb, Ta, Zr, Hf, and Ti. The volcanic rocks display (87Sr/86Sr)i values of 0.709341 to 0.711610, εNd(t) values of −6.9 to −3.3 εHf(t) values of −3.95 to −0.30, and δ18O values of 6.07‰–6.79‰, suggesting that the parental magmas were derived from a mantle source enriched by subduction-related progress. SiO2 content shows a strong negative correlation with the contents of some major and trace elements, indicating that fractional crystallization played an important role in the generation of these rocks. A binary mixing model of Hf–O isotopes gives an estimated degree of crustal contamination of 30%. In addition, magnetite crystallized early, and the samples showed high zircon EuN/EuN* values (0.48–0.68), indicating that the parental magma had a high oxygen fugacity. The inferred suppression of plagioclase crystallization and increasing hornblende crystallization during magma evolution suggest that the magma was water rich. The high-water content and high oxygen fugacity of the magma promoted the dissolving of sulfides containing Cu and Au in the source area and contributed to the migration of ore-forming elements.
Highlights
The Zijinshan ore district is located in southwestern Fujian Province, southeastern China (Figure 1)and is one of the most important copper, gold, and molybdenum-producing areas in the country.Proven reserves of gold, silver, copper, and molybdenum exceed 400 tons, 6000 tons, 4.1 million tons, and 0.11 million tons, respectively [1]
The Zijinshan ore district is widely regarded as a typical porphyry-epithermal metallogenic system [6–9]
Understanding the relationship of the volcanism in the Shanghang Basin to porphyry-epithermal mineralization at Zijinshan can help to understand the nature of the metallogenic magma source area and the controls on metallogenesis
Summary
The Zijinshan ore district is located in southwestern Fujian Province, southeastern China (Figure 1)and is one of the most important copper-, gold-, and molybdenum-producing areas in the country.Proven reserves of gold, silver, copper, and molybdenum exceed 400 tons, 6000 tons, 4.1 million tons, and 0.11 million tons, respectively [1]. The Zijinshan ore district is located in southwestern Fujian Province, southeastern China (Figure 1). Is one of the most important copper-, gold-, and molybdenum-producing areas in the country. Silver, copper, and molybdenum exceed 400 tons, 6000 tons, 4.1 million tons, and 0.11 million tons, respectively [1]. It is generally considered that the copper-gold-molybdenum mineralization was associated with large-scale magmatic and hydrothermal activities during the Late. With most of these deposits having formed during the Cretaceous [2–5]. The Zijinshan ore district is widely regarded as a typical porphyry-epithermal metallogenic system [6–9]. Minerals 2020, 10, 200 includes the Zijinshan high-sulfur epithermal copper-gold deposit, the Yueyang low-sulfur epithermal silver-gold-dominated polymetallic deposit, and the Luoboling porphyry copper-molybdenum deposit (Figure 2). (b) Geological map depicting the distribution of Cretaceous magmatism in Fujian Province, modified from [11]
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