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226 Handbook on the Physics and Chemistry of Rare Earths 4.2.7 Denudation or Preservation of Ore Body Depth of REE ore bodies is variable at different deposits (Figs. 42 and 43), because weathered crusts on granites have been removed by erosion. If a denudation rate is high, an ore body is rarely preserved or crops out on the surface. In contrast, if a denudation rate is low, an ore body is buried deep in a weathering profile. A moderate denudation rate may lead to ore formation in a moderate depth, and this is probably typical in ion-adsorption type depos- its in southern China (Bao and Zhao, 2008; Zhang, 1990). The weathered crusts on the Zudong intrusion in the Longnan deposits have a thin REE- leached zone with a positive Ce anomaly up to only 0.7 m deep and a thick REE-accumulation zone (ore body) with a negative Ce anomaly is developed from 0.7 to 19 m deep (Wu et al., 1990). In other deposits of Heiling, Guposhan, and Huashan, the REE-leached zone with a positive Ce anomaly is thin as well (Bao and Zhao, 2008). The thin REE-leached zones suggest that they have been mostly eroded after supplying REEs to the REE- accumulation zone in the lower part of the profile. Chemical weathering is promoted by the temperate and tropical climate conditions because the chemical weathering rate increases with the increase in annual precipitation and temperature (both are climatic parameters) (Gislason et al., 2009; Oliva et al., 2004; Sanematsu and Watanabe, 2016; Viers et al., 2014; White and Blum, 1995). The ion-adsorption type deposits and prospects were found in the temperate (C) and tropical (A) areas, see Fig. 34 (K€oppen, 1936; Peel et al., 2007), because chemical weathering and degradation of REE-bearing minerals are promoted by moderate to high tem- peratures and high annual precipitation rates. Not only chemical weathering but also moderate mechanical erosion is required to preserve REE ore bodies. Elevations of granite areas appear to have important roles to preserve the ore bodies as well as climate because they are closely related to denudation (erosion) of weathered rocks (Einsele, 2000). A moderate denudation rate of southern China is preferable for the preservation of weathering profiles including ion-adsorption ore bodies. Ion-adsorption type deposits in southern China were found in low hill areas (Bao and Zhao, 2008), and they are mostly present below an elevation of 550 m (Zhang, 1990). On the other hand, Wang et al. (2013) summarized that the elevation ranges mostly from 160 to 400 m with some exceptions of higher hills in Dingnan (Wang et al., 2013), Guposhan (Li and Shen, 2013), and Long’an as summarized in Table 13. Denudation rate of low hills is compared to that of high mountains (Einsele, 2000; Milliman and Syvitski, 1992), and this likely helps to preserve thick weathering profiles of ion-adsorption ores in southern China (Table 13). Since the denudation rate is controlled by both weathering and transport rates of weathered materials, and thick weathering profiles can be preserved where more weathered rocks can be developed by weathering than can be removed by transport processes (Einsele, 2000). Because the most important transport processes consist of rainfall, surface runoff, and river flow (Einsele, 2000),PDF Image | HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS
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