A suite of low-grade metamorphic sedimentary rocks, exposed in Huashikoujing area of eastern Longshoushan, was originally regarded as the Paleoproterozoic "Longshoushan Group". Detrital zircons from two low-grade metamorphic sedimentary rocks yielded ages ranging from 0.52 Ga to 3.56 Ga, similar to the age spectrum of the rock from neighboring Cambrian Dahuangshan Group. Thus, the metamorphic sedimentary rocks were probably deposited in the middle-late Cambrian period. A total of 129 concordant data were obtained from two sandstone samples from Huashikoujing area and a sandstone sample from Dahuangshan Group, whose ages predominately range between 0.7 Ga and 1.2 Ga (47%, peaks at around 0.8 Ga, 0.94 Ga, 1.0 Ga) and between 2.5 Ga and 2.8 Ga (31%, peaks at around 2.5 Ga, 2.7 Ga). Two smaller age groups range from 0.5 Ga to 0.6 Ga (7%, peaks at around 0.56 Ga) and from 1.4 Ga to 1.8 Ga (10%, peaks at around 1.5 Ga). The other zircons have sporadic ages ranging from 1.8 Ga to 2.4 Ga, with a few zircons older than 3.0 Ga. Provenance analysis shows that detrital matters of Dahuangshan Group were mainly derived from Qilian Block. Late-Neoproterozoic to early-Paleozoic grains were probably derived from related igneous rock in north Qilian orogen, Neoproterozoic grains were derived from magmatic rock distributed widely in Qilian Block, and Mesoproterozoic to Archean grains were probably derived from recycled meta-basement rocks in Qilian Block. Based on regional geological information, the authors consider that the low-grade metamorphic sedimentary rocks and Cambrian Dahuangshan Group, which were probably deposited in continental margin of Qilian Block, belong to the Qilian orogen rather than the Alxa Terrane.