The Chechang-Betai granite is located in the northern part of the Wutai Complex and occupies an area of approximately 300 km2 (Fig. 5). It is composed of several phases. Sample 95-PC-6B [Lat. 39° 04' 31"; Long. 113° 39' 53"] was collected from this location, just south of Taipinguo. It is a hornblende-biotite granodiorite. Data for 15 tightly concordant analyses from 14 zircon grains are presented on a concordia plot in Fig. 48, defining a weighted mean 207Pb/206Pb age of 2552±5 Ma.
Such ages are similar to those recorded previously from the Lanzhishan and Ekou granites (Wilde et al., 1997). Slightly younger ages from the Chechang-Betai granite (Wilde et al., in review) of 2546±3Ma and 2542±7 Ma (WC7) are nonetheless within error of this result and were obtained from fine- and coarse-grained fractions, respectively. The youngest age of 2538±6 Ma (WC5 - see below) is also from a coarse-grained fraction and overlaps the younger dates within error.