3.2. Zhou'an Cu–Ni deposit—covered by sedimentary rocks and alluvial soils
The Zhou'an Cu–Ni deposit is located 29 km south of Tanghe County,
Henan province. The ore-bearing ultramafic complex with extensive alteration has been intruded into Mesoproterozoic and Neoproterozoic
metamorphic strata. The stratiform ore bodies, mainly at the top and
bottom of the complex, were formed by post-magmatic hydrothermal
processes (Mi et al., 2009). The complex and its ore bodies are buried
under Cenozoic strata and Quaternary alluvial soils at a depth of more
than 400 m (Fig. 7). Traditional geochemical surveys are useless under
these circumstances. However, airborne magnetic anomalies contributed
largely to the discovery of the Zhou'an Cu–Ni deposit. It is an ideal
area for a deep-penetrating geochemistry study as there have been no
signs of any exploitation and contamination (Zhang et al., 2013).