Mineralogy and titanite geochronology of the Caojiaba W deposit, Xiangzhong metallogenic province, southern China: implications for a distal reduced skarn W formation

摘要

The Caojiaba tungsten deposit (19.03 Mt@ 0.37wt% WO3) is hosted by skarn along the contact between clastic and carbonate rocks in the Xiangzhong Metallogenic Province of southern China. The deposit is characterized by an early prograde skarn containing low andraditic garnet (Ad(0.7-21.9)) and hedenbergitic pyroxene (Hd(52.9-77.3)) overprinted by a retrograde biotite-chlorite assemblage and then by quartz-scheelite veins, similar to well-studied reduced tungsten skarns worldwide. Scheelite has low MoO3 (0.01-0.16wt%), and ore commonly contains up to 1.5ppm Au and up to 0.33wt% Sb. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb analyses of hydrothermal titanite coexisting with scheelite in three skarn ore samples provide ages between 206 +/- 5Ma and 196 +/- 3Ma (2 sigma). Our new ages demonstrate that the tungsten mineralization took place at Caojiaba between 206 and 196Ma, overlapping the 228-201Ma emplacement age of granitic rocks in the Xiangzhong Metallogenic Province. Mineralogical and geochronological evidence collectively indicates that Caojiaba is a distal reduced W skarn deposit. The 226-196Ma granite-related W mineralization recognized throughout the province has a possible link with the widespread Sb-Au mineralization in the region.