Fluid Evolution and Ore Genesis of the Qibaoshan Polymetallic Ore Field, Shandong Province, China: Constraints from Fluid Inclusions and H–O–S Isotopic Compositions

• Main Authors: Guang-Yuan Yu, Shun-Da Li, Yi-Cun Wang, Ke-Yong Wang
• Format: Article
• Language: English
• Published: MDPI AG 2019-06-01
• Series: Minerals
• Subjects: stable isotopes; fluid inclusions; Qibaoshan polymetallic ore field; Jiaodong Peninsula
• Online Access: https://www.mdpi.com/2075-163X/9/7/394

The Qibaoshan polymetallic ore field is located in the Wulian area, Shandong Province, China. Four ore deposits occur in this ore field: the Jinxiantou Au−Cu, Changgou Cu−Pb−Zn, Xingshanyu Pb−Zn, and Hongshigang Pb−Zn deposits. In the Jinxiantou deposit, three paragenetic stages were identified: quartz−pyrite−specularite−gold (Stage 1), quartz−pyrite−chalcopyrite (Stage 2), and quartz−calcite−pyrite (Stage 3). Liquid-rich aqueous (LV type), vapor-rich aqueous (V type), and halite-bearing (S type) fluid inclusions (FIs) are present in the quartz from stages 1−3. Microthermometry indicates that the initial ore-forming fluids had temperatures of 351−397 °C and salinities of 42.9−45.8 mas. % NaCl equivalent. The measured hydrogen and calculated oxygen isotopic data for fluid inclusion water (δ¹⁸O_FI = 11.1 to 12.3‰; δD_FI = −106.3 to −88.6‰) indicates that the ore-forming fluids were derived from magmatic water; then, they were mixed with meteoric water. In the Changgou deposit, three paragenetic stages were identified: quartz−pyrite−specularite (Stage 1), quartz−pyrite−chalcopyrite (Stage 2), and quartz−galena−sphalerite (Stage 3). LV, V, and S-type FIs are present in the quartz from stages 1−3. Microthermometry indicates that the initial ore-forming fluids had temperatures of 286−328 °C and salinities of 36.7−40.2 mas. % NaCl equivalent. The measured hydrogen and calculated oxygen isotopic data for fluid inclusion water (δD_FI = −115.6 to −101.2‰; δ¹⁸O_FI = 12.2 to 13.4‰) indicates that the ore-forming fluids were derived from magmatic water mixed with meteoric water. The characteristics of the Xingshanyu and Hongshigang deposits are similar. Two paragenetic stages were identified in these two deposits: quartz−galena−sphalerite (Stage 1) and quartz−calcite−poor sulfide (Stage 2). Only LV-type FIs are present in the quartz in stages 1−2. The ore-forming fluids had temperatures of 155−289 °C and salinities of 5.6−10.5 mas. % NaCl equivalent. The measured hydrogen and calculated oxygen isotopic data for fluid inclusion water (δD_FI = −109.8 to −100.2‰; δ¹⁸O_FI = 10.2 to 12.1‰) indicates that the ore-forming fluids were derived from circulating meteoric waters. The sulfur isotopes (δ³⁴S_sulfide = 0.6 to 4.3‰) of the four deposits are similar, indicating a magmatic source for the sulfur with minor contributions from the wall rocks. The ore field underwent at least two phases of mineralization according to the chronology results of previous studies. Based on the mineral assemblage and fluid characteristics, we suggest that the late Pb−Zn mineralization was superimposed on the early Cu (−Au) mineralizaton in the Changgou deposit.