Mineralization zoning of coal-metal deposits in China

Substantive progress has been made in extracting germanium, gallium, rare earth elements (REEs), lithium, and other metals from coal. Coal deposits are becoming important sources of many strategic metal resources. However, ore deposit theory study for coal-metal resources has not been systematic. This paper summarizes the mineralization characteristics of germanium, gallium, lithium, and REEs in coal on the basis of previous research results and field investigations, including those on seven metallogenic zones of coal metal deposits in China. Coal-germanium deposits, products of magmatic hydrothermal activity, mainly occur in low rank coal in the areas of Erlian, the Hailaer Basin, Inner Mongolia, and the Sanjiang district in the Yunnan Province. Occasionally, rich-germanium-coal can be found in other areas. Coal-gallium deposits are mainly in the Permian coal of North China, Jurassic coal of Northwest China, and late-Permian coal of South China. The accumulation of gallium in coal is closely related to aluminum-containing minerals. Coal-lithium deposits mainly occur in the Zhungeer coal field, Inner Mongolia, the Pingshuo coal field, and the Jingcheng coal field in the Shanxi Province, and some coal fields in South China. Similarly to gallium, the accumulation of lithium in coal is also closely related to aluminum-containing minerals. Coal-REE deposits mainly occur in the Early Jurassic coal of the Erlian Basin and Inner Mongolia, and Late Permian coal in South China. REEs of Erlian basin coal likely entered in ionic forms in early stages of coal or peat bog formation. REEs of South China coal are likely associated with REE-rich trass volcanic ash which deposited synchronously with peat bog accumulation. Abundant abnormal metal elements in coal are important for classification of metallogenic zones. Regional tectonic background and evolution, characteristics of stratigraphic sedimentary environment, and coal quality are also important factors. (1) Delineation of germanium metallogenic zones in the coal follows the principles that: coal in the coal area should be low-metamorphic bituminous (long-flame) coal; the basement of the coal-bearing basin was broken and faults developed in the region; and there are obvious traces of hydrothermal intrusion in or around the coal measures in the zone. (2) Delineation of gallium metallogenic zones in coal is based on these traits: an obvious gallium source should exist in the region; the provenance area has favorable weathering and denudation conditions; and an aluminum-gallium formation under strong leaching is contained within. (3) Delineation of lithium metallogenic zones in coal requires: relatively clear sources of lithium in the zones; favorable weathering and denudation conditions in the provenance area; and aluminum-lithium containing rocks under strong leaching. (4) Delineation of rare earth mineralization zones in coal is based on: large scale volcanic eruptions in or near peat bogs during the accumulation period, with tuff in the coal-bearing strata; and hydrothermal intrusion into coal-measure strata during the peat bog period or early coal-forming period. According to the principles above, seven coal-metal metallogenic zones were identified, including: (1) the Erlian Basin-Hailaer Basin coal-germanium and REE deposit zone; (2) the Tianshan coal-gallium deposit zone; (3) the South-Yinshan coal-gallium-lithium deposit zone; (4) the East-Taihang Mountain coal-gallium deposit zone; (5) the Qilian-Qinling coal-gallium-lithium deposit zone; (6) the Sichuan-Yunnan-Guangxi coal-gallium-lithium and REE deposit zone; and (7) the Sanjiang (west Yunnan Province) germanium deposit zone.