Gold is a kind of rare precious metal and has a wide-range use. Gold price has been rising since the 80's of the last century. The great demand for gold has not only stimulated gold exploration but also led to the need of understanding the genesis of gold deposits. A number of models have been advanced to explain how gold deposits were formed, and several types of gold deposits are accordingly established, such as the Witwatersrand-type, porphyry-type, Carlin-type, epithermal (low and high sulphidation), and orogenic gold deposits. These popular models, however, can hardly apply to the Early Cretaceous giant gold enrichment and mineralization in the North China craton (NCC), and the controversy has been continuing over the genesis of the NCC gold deposits.
A research group, led by Professor Rixiang Zhu at Institute of Geology and Geophysics, Chinese Academy of Sciences, recently conducted an investigation of the Early Cretaceous gold deposits in the NCC based on geological, geophysical and geochemical data, trying to unravel the multiple controls of both crustal deformation and deep geodynamic processes related to craton destruction on the giant and explosive enrichment of gold deposits. It is demonstrated that the gold mineralization in the NCC was closely related to the mantle-derived melts/fluids that was largely sourced from the Early Cretaceous magma generated as a result of decratonization. This idea is brand new for Au mineralization, and thus a new type of gold deposits is put forward, the decratonic gold deposits. The results were published in the Issue 9, 2015 of Science China: Earth Sciences.
Gold is of strategic significance and plays an important role in maintaining currency stability, dealing with financial crisis, curbing inflation and protecting national economic security. China is still faced with the shortage of gold resource with the guarantee period of gold resource being less than 10 years. This situation apparently necessitates the in-depth studies of gold mineralization so as to provide theoretical basis for the effective explorations of new large gold concentration and to safeguard state economic system.
This study systematically summarizes the space-time distributions of the Early Cretaceous gold deposits in the NCC, and identifies two gold belts, the Western and Eastern Belts. It is argued that the distribution pattern of gold belts was controlled by subduction, rollback, and retreat of the western Pacific plate as well as slab stagnation at the mantle transition zone. These tectonic processes led to the destruction of original thick, refractory mantle lithosphere, changing it into an oxidized and highly enriched mantle. Ore-forming fluids were sourced from partial melting of the enriched mantle and the overlying crust.
Zhu et al. argued that the decratonic gold deposits should have widely existed because some cratons are shown to have experienced various-degree destruction, such as the North America craton. It is suggested that the so-called Carlin-type Au deposits in Nevada of the United States must have pertained to decratonization processes, and thus should be classified as the decratonic gold deposits. They emphasized that the pivotal process in the formation of the Decratonic gold deposits is the generation of magma and resultant gold-bearing fluids/melts, which are in practice the consequence of lithospheric stretching and unstable mantle flows.
The model could help to look for new gold concentration regions in the NCC. It is postulated that the two gold belts of the NCC might continue north-northeastward, and thus the potential areas for large and super-large gold deposits could exist along the eastern and western edges of the eastern NCC.
This research was funded by National Natural Science Foundation of China (Grant No. 91414301) and Project of the State Key Laboratory of Lithospheric Evolution (Grant No.1303).
See the article:
Zhu R X, Fan H R, Li J W, Meng Q R, Li S R, Zeng Q D. 2015. Decratonic gold deposits. Science China: Earth Sciences, doi: 10.1007/s11430-015-5139-x