Abstract:

The strategic value of nickel (Ni) continues to rise with the increase in demand for nickel from China’s new energy industries and infrastructure projects. Quantitative evaluation of nickel content and distribution is critical for nickel prospecting and for alleviating nickel shortage in China. The China Geochemical Baselines project (CGB) has established the geochemical baseline of Ni in China from 3382 top and 3380 deep catchment sediment/alluvial soil samples and 11602 rock samples. The Ni baseline (median value) and background levels in rock were 12.1×10^-6 and 22.2×10^-6, respectively, comparable to the Ni abundance level in exposed crust in eastern China, where ultrabasic and basic rocks had respectively baseline levels of 1317×10^-6 and 63.4×10^-6, much higher than intermediate (17.5×10^-6) and felsic (3.19×10^-6) rocks. In surface and deep layers of catchment sediment/alluvial soil the Ni baseline levels were 23.6×10^-6 and 22.4×10^-6, respectively, slightly lower compared to other continents (countries) and close to the average Ni level obtained from the Regional Geochemistry National Reconnaissance project (RGNR). Parent rock types, especially ultrabasic-basic rocks, predominantly controlled the distribution of Ni-enriched catchment sediments/alluvial soils. Nickel-enrichment areas (> 85th percentile) were mainly in regions with widespread ultrabasic-basic outcrops, such as ophiolite belts, large igneous provinces, and black shales along the middle-lower Yangtze River. Nickel anomalies correlated well with magmatic Ni deposits. The geological setting mainly controlled Ni geochemical baselines in the sampled environments, whereas strong chemical weathering and well developed carbonate rocks could also contribute to Ni enrichment. The geochemical baseline of nickel provide a reference and data basis for further quantitative resource evaluation and establishment of environmental baselines.

Key words: nickel (Ni), geochemical baselines, rocks, catchment sediment, alluvial soil