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

Abstract

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 (δ18OFI = 11.1 to 12.3‰; δDFI = −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 (δDFI = −115.6 to −101.2‰; δ18OFI = 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 (δDFI = −109.8 to −100.2‰; δ18OFI = 10.2 to 12.1‰) indicates that the ore-forming fluids were derived from circulating meteoric waters. The sulfur isotopes (δ34Ssulfide = 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.

Ore Geology, Fluid Inclusions, and (H-O-S-Pb) Isotope Geochemistry of the Sediment-Hosted Antimony Mineralization, Lyhamyar Sb Deposit, Southern Shan Plateau, Eastern Myanmar: Implications for Ore Genesis

“…A useful tool to constrain the origin of sulfur is offered by the stable isotopes of sulfur [77][78][79][80][81][82][83][84][85][86][87][88], although temperature, pH value, oxygen fugacity, and ion activity often influence the total sulfur isotopic composition. The average δ 34 S of minerals would correspond to that of the total sulfur in the hydrothermal fluid when the sulfides from different sources have all reached sulfur isotopic equilibrium [80][81][82][83][84].…”

“…On this basis, circulating meteoric water dominated in the initial ore-forming fluid in the Lyhamyar deposit. In general, meteoric water has low δD and δ 18 O values [31,49,77]. At high temperatures, it was driven by a hot magma source and the meteoric water constantly exchanged oxygen isotopes with the surrounding silicate-and carbonate-containing rocks.…”

“…The bulk sulfur isotopic composition of the fluids can be interpreted to represent the δ 34 S values of sulfides. There are three major sulfur reservoirs on earth, with different sulfur isotopic compositions: (a) mantle or magmatic (0% ± 3%, [80,84]); (b) marine-seawater (+20%, present as SO 4 2− , [80]), and (c) reduced sulfur or biogenic sulfur in sedimentary rocks, characterized by δ 34 S < 0 [77,80,85].…”

“…Our δ 34 S values of the Lyhamyar stibnite are distinctly different from sulfur originating from biogenic sulfur in sedimentary rocks and falls in between the sulfur isotope compositions of the magmatic and metamorphic sources. It is suggested that a possible mechanism for formation of reduced sulfur is thermochemical sulfate reduction (TSR) or bacterial sulfate reduction (BSR) [77,87] by the sulfur isotopic composition from the hydrothermal stage. The high temperatures can have TSR while BSR can only occur at low temperatures of <100 • C [77,88].…”

“…It is suggested that a possible mechanism for formation of reduced sulfur is thermochemical sulfate reduction (TSR) or bacterial sulfate reduction (BSR) [77,87] by the sulfur isotopic composition from the hydrothermal stage. The high temperatures can have TSR while BSR can only occur at low temperatures of <100 • C [77,88]. The mineralization temperatures of the Lyhamyar deposit (typically 143.8-260.4 • C) ( Figure 14) lend support to the mechanism for formation of reduced sulfur and thus it is the most likely from thermochemical sulfate reduction (TSR).…”