LA-ICP-MS U–Pb Dating of Cenozoic Rutile Inclusions in the Yuanjiang Marble-Hosted Ruby Deposit, Ailao Shan Complex, Southwest China

Tianjian Yang,Ying Liu,Xiaoming Sun,Guiyong Shi

doi:10.3390/min11040433

Tianjian Yang, Ying Liu + Show 2 more

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https://doi.org/10.3390/min11040433

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Abstract

Among the marble-hosted ruby deposits in the Himalayan tectonic belt, which yields the highest-quality rubies in the world, the Yuanjiang deposit is the only economically viable one located in China. More attempts are necessary to put constraints on the ore-forming age of these marble-hosted ruby deposits. Here, we dated rutile inclusions in the Yuanjiang rubies using the LA-ICP-MS U–Pb method, which yielded a lower intercept 206Pb/238U age of 20.2 ± 1.2 Ma on the Tera-Wasserburg plot, close to the 22.5–22.2 Ma 40Ar/39Ar ages of phlogopite from the ruby host matrix assemblage. Our U–Pb rutile age put a constraint on the cooling history of the Yuanjiang rubies deposit. The new rutile age is consistent with our previous model that shows the ca. 28–22 Ma left lateral shearing plays an important role in transporting the ruby deposit toward the surface. This study provides the first example of in-situ U–Pb dating of rutile in the Himalayan tectonic belt, demonstrating the great potential of U–Pb rutile geochronology for Cenozoic mineral deposits.

Highlights

The marble-hosted ruby deposits in Central and Southeast Asia produce rubies of the highest quality [1]
Limited geochronological tools have been used to date the ore-forming age of the ruby deposit, such as 40Ar–39Ar dating of micas from the ruby host matrix assemblage and U–Pb dating of zircon inclusions in rubies
Interpretation of Rutile Inclusion U–Pb Dating Results Our results reveal that rutile inclusions contain high U

Summary

Introduction

The marble-hosted ruby deposits in Central and Southeast Asia produce rubies of the highest quality [1]. Limited geochronological tools have been used to date the ore-forming age of the ruby deposit, such as 40Ar–39Ar dating of micas from the ruby host matrix assemblage and U–Pb dating of zircon inclusions in rubies. For the Yuanjiang ruby deposit, a previous study obtained the 40Ar–39Ar ages of phlogopites and U–Pb age of zircon inclusions, which are 22.5–22.2 Ma and 36.2 Ma, respectively [5]. The U–Pb system closure temperature of zircon is close to ruby formation, and zircon inclusions are protected by hosted rubies from later interaction of permeating fluids and U–Pb resetting, making zircon inclusions as potential candidates for constraining the crystallization age of gem ruby and sapphire deposits [1,5,8,9,10,11,12]. To better define the ore-forming age of the Minerals 2021, 11, x FOR PEER REVIEmWarble-hosted ruby deposits, geochronological constraints from other minerals syng2enoef t1ic0 to rubies are warranted

Results

Discussion

Conclusion