Abstract
A significant linear correlation between Ba and Eu contents has been observed in a set of mudrock formations in the lower Cambrian Hetang Formation in South China. Combined with petrographic features and reinvestigation of published data obtained from the same laboratory, the analytical interference of Ba can be excluded as a main factor of this correlation. Electron microprobe analyses (EMPA) have indicated that Ba-rich minerals (hyalophane and cymrite) precipitated from hydrothermal fluids account for the total Ba content. It is evident that significant contribution of both Ba and Eu from hydrothermal fluids is the cause of this linear relationship, while this coexistence is ultimately controlled by their similar chemical properties and abundances in rock sequences along the fluid path. This interpretation was supported by similar linear Ba-Eu correlations retrieved from barite-bearing chert in another area of the Yangtze platform during the same geological period. Therefore, linear Ba-Eu correlations may be more common than previously thought in this area, where hydrothermal activities were active during the specific time interval.
Highlights
The rare earth elements (REEs) include lanthanum (La) and the f-block elements in the periodic table, whose atomic number ranges from 57 to 71
The REEs are insoluble in most geological settings and resistant to remobilization beyond the mineralogical scale during weathering, diagenetic, and metamorphic processes
For each sample analyzed by Electron microprobe analyses (EMPA), the occurrence of Ba-rich minerals, in hydrothermal veins and/or in matrix, is specified (Figure 2)
Summary
The rare earth elements (REEs) include lanthanum (La) and the f-block elements (cerium through lutetium) in the periodic table, whose atomic number ranges from 57 to 71. The distinctive redox chemistries of Eu and Ce are of considerable importance to understanding geochemical conditions with unique insights into magmatic, aqueous, and sedimentary processes ([1, 2, 4,5,6]; Murray et al, 1990; Atwood, 2012). Europium occurs in the form of Eu2+ under highly reducing conditions. It exists only within certain magmatic and/or hydrothermal environments that are rarely found at the surface of the Earth. Positive Eu anomalies have been widely reported in modern deep-sea hydrothermal systems [7,8,9] and in massive deposits of submarine hydrothermal exhalative origin [10,11,12].
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