Gallium(Ga)is a critical mineral that plays an irreplaceable role in consumer electronics,clean energy technologies and the aerospace industry.Nowadays competition for gallium resources at the national strategic level has begun to emerge,but gallium resources are unevenly distributed globally,and their presence is not guaranteed.New discoveries revealed an average gallium concentration of thirty-one samples from M_(1),M_(2),M_(3) and M_(4) stone coal-bearing seams of the Cambrian strata on South Qinling Orogenic Belt in central China is 157 mg/kg(9.98–747 mg/kg),which is 27.6-fold higher than the global hard coal average,as well as the existing association of Mo–V–U–Cd–Zn–Ba–Se–Mg–Ni–Cu enrichment.Ga average of these coal seams are 344 mg/kg(M_(3),44.5–747 mg/kg,n=11),270 mg/kg(M_(4),14.3–270 mg/kg,n=5),53.8 mg/kg(M_(2),22.6–75.4 mg/kg,n=8)and 19.8 mg/kg(M_(1),9.98–34.9 mg/kg,n=7)respectively,as well as the thickness of approximately 6,12,8,and 20 m,which be close to or exceed to the boundary grade standard(30 mg/kg)and minimum recoverable thickness(0.7 m)of gal-lium resources exploration.These findings indicate that the Cambrian stone coal deposits,especially in the middle and late Cambrian period,should be considered as promising alternative sources of gallium.The anomalous gallium-enriched sediments originated from a complex combination of hydrothermal flu-ids,original biomass and terrigenous materials.For the M_(1) stone coal-bearing seams,gallium most likely occurred in the mode of GaAs,Ga_(x)In_(1-x)As and GaO(OH),while modes of gallium in the M_(2) to M_(4) seams is interrelated with the organic affinity and clay minerals.The crude reserve estimate of gallium resources in central China is approximately 10.06?104 tons,corresponding to a super-large coal-hosted gallium ore deposit.The unique paleogeographic location and geological structure in central China resulted that this newly discovered deposit is a unique type of gallium-enriched deposit that has been discovered worldwide.T
The Ediacaran and early Cambrian black shales are widespread across the South China Craton(Yangtze and Cathaysia blocks). However, the trace element distribution patterns of the Ediacaran and early Cambrian black shales in the Cathaysia Block are still unclear. In this study, thirtyfour black shale samples in the Lechangxia Group(Ediacaran) and thirteen black shale samples in the lower Bacun Group(early Cambrian) from Guangning area, western Guangdong Province, South China, were analyzed for major and trace elements concentrations. Compared to the upper continental crust, the Ediacaran black shales exhibit strongly enriched Se, Ga, and As with enrichment factor values(EF) higher than 10, significantly enriched Bi and Rb(10>EF>5), weakly enriched Mo, Ba, Cs, V, In, Be, Tl, and Th(5>EF>2), normal U, Cr, Cd, Sc, Pb, Cu, and Li(2>EF>0.5), and depleted Ni, Zn, Sr, and Co. Early Cambrian black shales display strongly enriched Se, Ga, and As, significantly enriched Ba, Bi, and Rb, weakly enriched Mo, Cs, Cd, V, U, Be, In, and Tl, normal Sc, Th, Cr, Li, Cu, Ni, and Pb and depleted Co, Zn, and Sr. Moreover, Se is the most enriched trace element in the Ediacaran and early Cambrian black shales: concentrations vary from 0.25 to 30.09 ppm and 0.54 to 5.01 ppm, and averaging 4.84 and 1.72 ppm, with average EF values of 96.87 and 34.32, for the Ediacaran and early Cambrian shales respectively. The average concentration of Se in the Ediacaran black shales is 2.8 times higher than that of early Cambrian black shales. Se contents in the Ediacaran and early Cambrian black shales exhibit significant variation(P = 0.03). Provenance analysis showed that Se contents of both the Ediacaran and early Cambrian black shales were without detrital provenance and volcanoclastic sources, but of hydrothermal origin. The deep sources of Se and the presence of pyrite may explain the higher Se contents in the Ediacaran black shales. Similar with the Se-rich characteristics of the contemporaneous black shales in the south Qingling Mountain and Yang
