Geological Characteristics of the Furong Tin Orefield, Hunan,40Ar-39Ar Dating of Tin Ores and Related Granite and Its Geodynamic Significance for Rock and Ore Formation

摘要

Furong, Hunan, is a large tin orefield discovered in China in recent years, which is mainly of the skarn-greisenchlorite type. On the basis of the geological characteristics of the orefield, 40Ar-39Ar dating was performed on muscovite from greisen-type tin ore and biotite from related amphibole-biotite granite, which yielded three sets of age data, i.e., a plateau age of 157.5±0.3 Ma and an i sochron age of 156.9±3 Ma for amphibole-biotite granite; a plateau age of 156.1 ±0.4Ma and an isochron age of 155.7±1.7 Ma for the Sanmen greisen-type tin ore; and a plateau age of 160.1±0.9 Ma and an isochron age of 157.5±1.5 Ma for the Taoxiwo greisen-type tin ore. The three sets of age data coincide well with each other They not only accurately reflect the timing of rock and ore formation but also indicate close relations between granite and tin deposits. In addition, the plateau ages of all three sets suggest that no subsequent thermal perturbation event occurred after the formation of granite and tin deposits. The Furong tin orefield is a component part of the southern Hunan large tungsten-tin polymetallic deposit concentration area and also a representative deposit formed in the time interval of 160-135 Ma in four peaks of Mesozoic tungsten-tin mineralization in the South China region. They might still correspond to the middle and late stages of the major geodynamic transition from a N-S- to an E-W-direction in eastern China.