Petrological and Mineralogical Characteristics of Jingao Jade and Its Color Genesis

The Jingao jade produced in Luonan County, Shaanxi Province, is named for its distinctive golden color. Currently, the research on the color and genesis of the Jingao jade deposit is still in its infancy and has not yet reached a consensus. The lack of completeness in the research on the origin of color restricts the non-destructive detection of Jingao jade as a gemstone. In order to further clarify the color origin and genesis of Jingao jade, different colored samples were selected and studied by polarized light microscopy, X-ray diffraction (XRD), inductively coupled plasma-optical emission spectrometry/mass spectrometry (ICP-OES/ICP-MS), electron probe microanalysis (EPMA), scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS), laser Raman spectroscopy (LRS), diffuse reflectance spectroscopy (DRS), and stable isotope mass spectrometry. Data demonstrate that Jingao jade mainly consists of dolomite. The unit cell parameters and chemical composition of the dolomite are very close to those of the ideal dolomite. Whole-rock geochemistry and EPMA spot analyses of dolomite both reveal that the Fe content in the yellow jade is significantly higher than that in the white one. First-derivative diffuse reflectance spectra of Jingao jade exhibit characteristic goethite absorptions at 526–538nm and 435–437nm, and the intensity of the yellow hue increases linearly with goethite content. The regular shift of the main peak of dolomite in Raman spectroscopy also indicates that the Fe in dolomite might also contribute to the yellow color. Whole-rock chemical analysis indicates that Jingao jade has not been significantly influenced by terrestrial components and can reflect the environment during the formation period. The average values of δEu and δCe of Jingao jade are 0.956 and 0.818, respectively, indicating a weakly oxidized sedimentary environment. Based on the results of the isotopic analysis of carbon and oxygen (with the average δ¹³C value of Jingao jade being −0.1896‰ and the average δ¹⁸O value being −4.2107‰), the formation model analysis indicates that Jingao jade may belong to burial-origin dolomite. Based on the carbon and oxygen isotope values, the Z value is calculated using empirical formulas to determine the source of the limestone. The average Z value of Jingao jade is 142.746, which is far beyond the discrimination threshold for marine limestone (Z>120 indicates marine limestone, while Z<120 indicates freshwater limestone). This supports the conclusion that Jingao jade was formed by the transformation of limestone with distinct marine origin characteristics, and did not undergo any geological events that might have significantly reduced the carbon and oxygen isotopes (such as sea level drop or freshwater environment) after diagenesis, reflecting a stable marine sedimentary environment. The BRIEF REPORT is available for this paper athttp://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202503100040.