Formation of the Nephrite Deposit With Five Mineral Assemblage Zones in the Central Western Kunlun Mountains, China

Abstract

The Saidikulam nephrite deposit, which is famous for its high-quality white nephrite in history and nowadays, is located in the eastern part of the Western Kunlun Orogen, in the northwestern margin of the Tibetan Plateau, Yutian County, Xinjiang, China. Field investigations and petrographic observations revealed the presence of five mineral assemblage zones from granodiorite to dolomitic marble in the Saidikulam nephrite deposit: slightly epidote-altered granodiorite → epidote-altered diopsidite → nephrite → calcite tremolitite → calcite-bearing dolomitic marble. However, little is known about the relationships among these five zones or the formation age of the deposit. The slightly epidote-altered granodiorite consists of plagioclase, orthoclase, quartz, biotite, and epidote, with accessory apatite, zircon, and allanite. They exhibit slightly negative Eu anomalies (0.69–0.72), with declined LREE and flat HREE patterns. They are also strongly enriched in Rb, Zr, U, and Sm, and depleted in Hf, Ti, P, and Nb. The epidote-altered diopsidite close to the granodiorite intrusions is a relatively high-temperature metasomatic rock composed of Fe-rich diopside and actinolite, while the calcite tremolitite adjacent to the dolomitic marble is a relatively low-temperature rock composed of prismatic tremolite and calcite. The main mineral component of the nephrite is tremolite, with minor epidote, chlorite, apatite, calcite, graphite, and allanite. The nephrites have low ∑REE contents (4.38–18.53 ppm), with declined LREE and flat HREE patterns. All of the analyzed nephrite exhibits pronounced negative Eu anomalies (δEu = 0.20–0.82), and they are strongly enriched in Rb, U, and Ti and relatively depleted in Ba and HFSEs. SHRIMP U-Pb dating of zircons from the granodiorite yielded a Concordia age of 453.8 ± 3.7 Ma, which is interpreted as the upper limit of the Saidikulam nephrite formation age. The zircons in the epidotized syenite in the deposit yielded a SHRIMP Concordia U-Pb age of 489.2 ± 4.2 Ma. These two ages indicate that the dolomitic marble experienced at least two thermal events. The approximate ages of the nephrite deposits along the giant Kunlun-Altyn Tagh belt indicate that the closure of the Proto-Tethys may have been the predominant driving force for the formation of the whole nephrite deposits. The multistage metasomatism and the Fe absorption of epidote-altered diopsidite had a positive impact on the formation of high-quality nephrite.

A New Nephrite Occurrence in Jiangxi Province, China: Its Characterization and Gemological Significance

“…During multiple mineral metasomatisms, the texture of tremolite became finer, resulting in a higher-quality of nephrite. This texture has been observed in various origins of high-quality nephrite [12,44].…”

“…Nephrite deposits are common worldwide, such as in China [3], Russia [4], Korea [5,6], Canada [7,8], and Somaliland in Africa [9], which has important economic implications. In China, the culture of nephrite has a long history [10,11], and the origin of nephrite is widely distributed, such as in Xinjiang [12][13][14], Qinghai [15,16], Dahua, Guangxi [17], Xiuyan, Liaoning [18,19], Panshi, Jilin [20], Tieli, Heilongjiang [21], etc.…”

Nephrite from Xinjiang Qiemo Margou Deposit: Gemological and Geochemical Insights

“…The Qiemo Margou black cyan and black nephrite show relatively high FeO (3.97-5.09wt.%) and TFe 2 O 3 (4.68-6.11wt.%) contents. For comparison, the FeO content of Gobi nephrite is between 0.36 and 1.83 wt.% [6,31], that of Alamas white nephrite and of green nephrite is between 0.41 wt.% and 1.96 wt.% [3], that of Karakax River green nephrite is between 0.67 wt.% and 3.18 wt.%, and that of black nephrite is between 0.48 wt.% and 9.55 wt.%. White nephrite has TFe 2 O 3 content ranging from 0.33 wt.% to 1.42 wt.%, bluish-white nephrite has TFe 2 O 3 content ranging from 0.43 wt.% to 0.96 wt.%, and green nephrite has TFe 2 O 3 content ranging from 0.77 wt.% to 3.97 wt.%.…”

“…Nephrite has a characteristic tangled fibrous texture [1]. The predominant mineral in nephrite is tremolite, accompanied by minor minerals such as actinolite, diopside, talc, serpentine, epidote, clinozoisite, forsterite, coarse-grained tremolite, dolomite, quartz, magnetite, and pyrite [2][3][4][5]. Globally, nephrite deposits are found in various countries, including China, Canada, Russia, South Korea, Australia, New Zealand, Pakistan, and Poland [6][7][8][9].…”

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

“…Nephrite, a rock primarily composed of nearly monomineralic tremolite-actinolite (Ca 2 (Mg, Fe) 5 Si 8 O 22 (OH) 2 ), is distributed worldwide. [1][2][3][4][5][6][7][8] It is classied into dolomite-related and serpentine-related types based on the parent and host rocks associated with ore formation. Both types of nephrites are formed through a process known as metasomatism.…”