A New Type of White Nephrite from Limestone Replacement along the Kunlun–Altyn Tagh Mountains: A Case from the Mida Deposit, Qiemo County, Xinjiang, China

Abstract

The recently discovered Mida nephrite deposit, located in the East Kunlun Mountains, Qiemo County, Xinjiang, Northwest China, contains new types of white and greenish white nephrite formed by limestone replacement, which shows microstructures, macroscopic features and country rocks typologies that are quite different from those of the other deposits along the Kunlun–Altyn Tagh Mountains. The gemological and mineralogical characteristics of Mida nephrite are presented here. These nephrites show an ivory white color and a porcelain-like appearance, with semitranslucent-to-opaque transparency and a porcelain-to-greasy luster. Petrographic study, electron probe microanalysis (EPMA) data and scanning electron microscopy (SEM) images have indicated that the nephrite is composed of tremolite, accompanied by minor quartz, calcite and diopside. Tremolite aggregates have shown different textures, like flaky, granular, fibrous–felted, bundle, radial and metasomatic relict textures. Quartz has appeared in granular or disseminated form, dispersed in the tremolite matrix. Calcite has shown a metasomatic relict texture in the white nephrite samples. Diopside has shown euhedral grains, with some distributed with a certain geometric appearance. Based on our observations, it is suggested that the quartz in the nephrite originated from Si-rich hydrothermal fluids. We propose that the substantial size difference of mineral grains, together with uncompacted grains with inter-particle pores, are the main reasons for the internal reflection and refraction under transmitted light, which allow less transmitted light to pass through the nephrite body and generate the appearance of a semitranslucent-to-opaque transparency, ivory white color and porcelain luster. Our study has unveiled that the Mida nephrite is not typical of the two known types (D-type: dolomite-related; S-type: serpentinite-related) and is overlapped by quartz grains dispersed throughout the less compact tremolite matrix. These observations would help set it apart from the majority of nephrite jades found in the Kunlun Mountains region and provide valuable insights for enhancing comprehension of the diversity of the nephrite deposits.

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

“…For example, black nephrite from Dahua, Guangxi, is located at the boundary zone between diabase and limestonebearing siliceous rock [49]; nephrite in Luodian, Guizhou was found to be produced in the contact metamorphic zone between basic diabase and calcic carbonate rock [50]. Recently, the white nephrite from the Mida deposit in Qiemo County, Xinjiang, was also reported to be related to limestone replacement [51]. These nephrites, including Xinyu nephrite, are all closely related to limestone, not dolomite.…”

Nephrite from Xinjiang Qiemo Margou Deposit: Gemological and Geochemical Insights

“…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].…”