Thus, calcite mineral should have similar potential for Sm-Nd isotope dating.
Tianjin Institute of Geology & Mineral Resources, Chinese Academy of Geological Sciences, Tianjin 300170, China Correspondence should be addressed to Peng Jiantang (e-mail: [email protected] chinese.com) Abstract The research on Samarium-Neodymium iso- tope systematics of hydrothermal calcites from the Xi- kuangshan antimony deposit, Central Hunan, places precise timing constraints on the Sb mineralization in this area.It is revealed that the Xikuangshan deposit formed during the late Jurassic-early Cretaceous Period, the early- and late- stage mineralization took place at (155.5 ± 1.1) Ma and (124.1 ±3.7) Ma, respectively.The mineral assemblage for ores are dominated by quartz stibnite, quartz calcite stib- nite and calcite stibnite.The wall-rock alterations are 1134 Chinese Science Bulletin Vol. 13 July 2002 predominated by silicification and subordinately by car- bonatization and, to a lesser extent, baritization and fluori- tization.Therefore, the Sm-Nd isotope dating is an effective method for precisely determining the time of ore forma- tion.
In recent years, some hydrothermal Ca-bearing min- erals were used for Sm-Nd isotope dating such as scheelite [6ü9] , fluorite [10ü13] and tourmaline [8,14] .
Sm and Nd are similar in chemical character, so the daughter 143 Nd decayed from the parent 147 Sm is easy to be preserved in mineral lattice, i.e.
the Sm-Nd isotope systmatics is liable to be kept closed, and capable of re- sisting weathering and/or alteration to some degree.
Ore bodies dominantly occur in the Devonian Shetianqiao Formation (D3s) and subordinately in the Qiziqiao Formation (D2q), and usually appear stratiform and stratoid, locally irregular in shape.
The ores are simple in composition, the metallic mineral is stibnite, and the gangue minerals mainly in- clude quartz and calcite.
2 Sampling and analytical methods All the analyzed specimens coevally with stibnite in this study were collected from underground exposures.