Re-Os Isotope Ages of Molybdenum Deposits in East Qinling and Their Significance

Dating of metallic ore deposits has been one of the problems concerned with by ore geologists for many years. The establishment of the Re-Os Isotope Laboratory at the Institute of Rock and Mineral Analysis, Chinese Academy of Geological Sciences, has provided us with a new technique to carry out geochronological studies of molybdenum ores. As one of the most important Re-bearing minerals, molybdenite contains almost no common osmium, but 187Os was derived completely from decay of 187Re, with 187Os content as the function of Re content in the mineral. An ID-ICP-MS technique has been used in this study, and Re-Os isotopic ages of several large molybdenum deposits of different types from the East Qinling molybdenum belt have been determined. It is indicated that the Huanglongpu carbonatite vein-type molybdenum-(lead) deposit has a Re-Os age corresponding to Indosinian, while tbe rest porphyry-type molybdenum deposits and porphyry-skarn-type molybdenum-(tungsten) deposits have Re-Os ages corresponding to Yen