Combining Rare Earth Element Analysis and Chemometric Method to Determine the Geographical Origin of Nephrite

Abstract

Nephrite is a high-valued gem material, whose geographical origin determination is a topic of interest to both consumers and producers since the geographic origin determines its price and reputation. In the present study, we suggest a two-step method for discriminating geographical origins of nephrite based on the rare earth element (REE) contents combined with chemometrics. In the first step, the REE contents of nephrite samples were determined by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), combined with previously reported data—the chondrite-normalized REE distribution pattern; the REE parameters of nephrite samples from six origins, namely Xinjiang, Qinghai, Russia, Guangxi, Guizhou, and Liaoning were then compared. In the second step, origin discriminant models were established by linear discriminant analysis (LDA), and the accuracy of the model was evaluated by leave-one-out cross-validation (LOOCV). The results showed that the REE contents were significantly different among the six nephrite origins with regional characteristics, which makes it possible to trace the origin. Using chondrite-normalized REE distribution patterns, the six nephrite origins can be divided into three separate groups: Xinjiang−Qinghai−Russia, Luodian−Dahua, and Xiuyan. Xiuyan nephrite can be directly distinguished from the other origins due to its unique REE distribution pattern. In the second step, the LDA discrimination models were performed on the remaining two groups. For the Luodian−Dahua group, the accuracy of the original classification and LOOCV were 97.9% and 85.4%, which indicated REE combined with LDA could effectively identify Luodian nephrite and Dahua nephrite. For the Xinjiang−Qinghai−Russia group, the accuracy of the original classification and LOOCV was 74.1% and 63.9%, respectively. Overall, this work proves that a combination of REE analysis and chemometrics has a certain feasibility and broad application prospects for geographical origin, and the same methodology can be applied to study the origin of other gem materials.

Nephrite from Xinjiang Qiemo Margou Deposit: Gemological and Geochemical Insights

“…Previous studies have indicated that the magmatic rocks in magnesian marble-type skarn Hetian nephrite deposits show high rare earth element contents, Eu-negative anomalies, an LREE right deviation, and an HREE flat rare earth distribution pattern, while magnesian marble is characterized by a relatively stable rare earth distribution pattern and low rare earth content [25]. The REE distribution patterns and contents in the black cyan and black nephrite of Qiemo Margou show that these nephrites mainly inherited the geochemical characteristics of the surrounding magmatic rocks and magnesium marble, indicating that the Qiemo Margou black and black cyan nephrites belong to the magnesian marble skarn-type Xinjiang nephrite deposit.…”

“…The REE distribution patterns and contents in the black cyan and black nephrite of Qiemo Margou show that these nephrites mainly inherited the geochemical characteristics of the surrounding magmatic rocks and magnesium marble, indicating that the Qiemo Margou black and black cyan nephrites belong to the magnesian marble skarn-type Xinjiang nephrite deposit. Previous studies have indicated that the magmatic rocks in magnesian marble-type skarn Hetian nephrite deposits show high rare earth element contents, Eu-negative anomalies, an LREE right deviation, and an HREE flat rare earth distribution pattern, while magnesian marble is characterized by a relatively stable rare earth distribution pattern and low rare earth content [25]. The REE distribution patterns and contents in the black cyan and black nephrite of Qiemo Margou show that these nephrites mainly inherited the geochemical characteristics of the surrounding magmatic rocks and magnesium marble, indicating that the Qiemo Margou black and black cyan nephrites belong to the magnesian marble skarn-type Xinjiang nephrite deposit.…”

Comparative analysis of LDA, PLS-DA, SVM, RF, and voting ensemble for discrimination origin in greenish-white to white nephrites using LIBS

“…For instance, with chemical compositions, rare Earth elements, and isotopes, we can successfully distinguish between a few origins of nephrite; however, when faced with more diverse origins of samples, they may fall short. 28 In such cases, it becomes essential to explore a robust discrimination method to differentiate certain origins of nephrite that have similar tones accurately.…”

A multi-strategy linear discriminant analysis (LDA) method coupled with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for discriminating the geographical origin of nephrite

“…23 In the case of multivariate statistical methods, linear discrimination analysis (LDA) is the most widely used for tracing the origins of various gemstones. [24][25][26][27][28] In addition to gemology, the combination of LA-ICP-MS and LDA can also be used as an effective tool in the eld of provenance study in archaeology, 29 food origin classication in foodstuffs, 30 counterfeit identication in commercial trade, 31 habitat discrimination in speciology, 32 forensic investigation in forensic pathology, 33 and mineral exploration in mineralogy. 34 Despite that the LDA method has proven effective in differentiating a material and identifying its origin, the mechanism of origin determination from different origins has not been studied in great depth and the chemometric methods (especially for LDA) applied to the discriminant model and their application context have not been compared and explored.…”