Fluid inclusion and thermodynamic studies of the Dalingkou Ag, Pb, and Zn ore deposit, Peoples Republic of China.

摘要

The Dalingkou ore deposit is a very important Ag, Pb, and Zn ore deposit in southeastern China and is being mined from seven levels. The ore bodies occur as vein type in faults. Ore body #1-1 is the most important with mineralization divided into three stages: (I) quartz-sulfide; (II) sulfide; and (III) fluorite. Sulfide stage is the most important with the main ore minerals: galena, sphalerite, and argentite. The three mineralization stages have different averages of homogenization temperature, salinity, and density. They are: 289.1{dollar}spcirc{dollar}C, 4.95 wt.% NaCl, and 0.781 g/cm{dollar}sp3{dollar} for stage I; 202.2{dollar}spcirc{dollar}C, 2.67 wt.% NaCl, and 0.884 g/cm{dollar}sp3{dollar} for stage II; and 151.7{dollar}spcirc{dollar}C, 1.44 wt.% NaCl, and 0.927 g/cm{dollar}sp3{dollar} for stage III, respectively. From mining level 7 (surface) to mining level 1 (deepest, 600 meters), the homogenization temperature, salinity, and density increase in stage III and decrease in the stages I and II.; The main species in the liquid phase of primary fluid inclusions are Na{dollar}sp+{dollar}, K{dollar}sp+{dollar}, Ca{dollar}sp{lcub}2+{rcub}{dollar}, Mg{dollar}sp{lcub}2+{rcub}{dollar}, F{dollar}sp-{dollar}, Cl{dollar}sp-{dollar}, and SO{dollar}sb4sp2-{dollar} and in the gaseous phase are CO{dollar}sb2{dollar}, CH{dollar}sb4{dollar}, CO, and H{dollar}sb2{dollar}O. The average pressure in stage II is 127 bars and in stage III, 121 bars, representing ore-forming depths of 480 meters and 457 meters, respectively. The average log fs{dollar}sb2{dollar} and log fo{dollar}sb2{dollar} are {dollar}-{dollar}7.77 and {dollar}-{dollar}32.52 for stage I and {dollar}-{dollar}12.49 and {dollar}-{dollar}45.46 for stage II, respectively. The ionic strengths are 0.888, 0.566, and 0.068 for stages I, II, and III, respectively. Total concentration of sulfur is 0.034 m for stage I and 0.083 m for stage II. pH is 4.36 for stage I and 4.98 for stage II.; The solubilities of the three main ore minerals, galena, sphalerite, and argentite, were controlled mainly by T, pH, m{dollar}sb{lcub}Sigmasb{lcub}rm s{rcub}{rcub}{dollar}, and m{dollar}sb{lcub}rm Clsp-{rcub}.{dollar} Temperature is the most important. Hydrogen and oxygen isotopes reveal that the ore-forming fluids essentially are a mixture of magmatic and meteoric water. Lead isotope results suggest that the ore-forming lead came from the upper cratonized crust. Sulfur isotopic and REE analyses suggest that sulfur and other ore-forming substances are related primarily to the rhyolite porphyry host rock.; Based on lead isotopic compositions, the ore deposit-forming age is between 84 and 99 m.y. with an average of 91.5 m.y.; The Dalingkou ore deposit is a typical vein-type, hydrothermal, sulfide ore deposit.