Geochemical analyses of the placer anomaly with high content of pyrope and chrome-spinel in Xiawengshao area, Shibing County, Guizhou Province

Existing data reveal that there exists the placer anomaly with high content of pyrope and chrome-spinel in Xiawengshao area, Shibing County, Guizhou Province. It is distributed in the gravel-clay rock from the Neogene Wengshao Formation in Duimenpo area on the northern side of the Xiawengshao basin, and the "unexplained" deposits of sand-gravel in the slope zone, 2km south side of the Xiawengshao basin. Such a phenomenon constitutes the high content of placer anomalies, which is prominent among lots of information related to diamond prospecting in Guizhou Provence. The source of these minerals and its significance to the exploration of diamonds have remained unsolved for a long time. Based on the analysis of the "unexplained" deposits of sandgravel in the slope zone, 2km south side of the Xiawengshao basin, it is found that the 2.7grains/L and Chrome-spinel>5.0 grains/L of original magnesia-alumina pyrope prove the existence of the anomaly. Results from electron microprobe analysis revealed that the pyrope is classified as G9-pyrope, and the picotite as S5-chromite that is poor in titanium but abundant in aluminum and magnesium. Their source has little relation with kimberlite.