Abstract:

     Titanite  is a common accessory mineral  in calc-alkailine granites, and may contain  tin  to various extents owing  to similar crystal-chemical  features between Ti4+and Sn4+.  It  thus may be considered as a useful mineral  in studying  tin granites (particularly oxidized tin granites). This paper deals with a systematic study on titanite from three granites with known extensive tin mineralization  (Qitianling, Huashan and Guposhan)   and other  three granites currently unknown  for important  tin mineralization (Lianyang, Dadongshan and Jiufeng). Titanite  from all  these granites can  form both at early-magmatic stage and during biotite chloritization at hydrothermal stage; late-magmatitc titanite is also found in Qitianling, Huashan and Jiufeng. Electron-microprobe results  reveal distinct compositions among  three  types of  titanite. Early-magmatic  titanite contains  trace of  tin  (generally < 1%  SnO2), whereas  late-magmatic  titanite with 3  to 26 % SnO2 can be  found  in Qitianling, Huashan and Jiufeng. Hydrothermal titanite is typified by high Al and F contents. Comparison of SnO2 contents for titanite from six granites shows that titanite, either magmatic or hydrothermal,  from  three  tin granites  (Qitianling, Huashan and Guposhan)  is  rich  in SnO2 with averages > 0.4 %,revealing  their strong  tin mineralizing potential;  titanite of Lianyang and Dadongshan granites  is very poor  in SnO2  (< 0.1 %), consistent with their barren feature. However, similar to Huashan titanite, the magmatic titanite from Jiufeng granite contains up to 3 % SnO2, and hydrothermal one up to 2 % SnO2. Such tin enrichment in titanite might imply higher tin potential of the Jiufeng granite, possibly favorable for further tin exploration. The present results demonstrate that titanite may act as a simple, but useful mineral criterion of tin mineralizing potential in granites.

Key words:  titanite, accessory mineral, tin-bearing granite, tin potential, Nanling Range