The Geochronology and Geochemistry of Zircon as Evidence for the Reconcentration of REE in the Triassic Period in the Chungju Area, South Korea

Sang-Gun No,Maeng-Eon Park

doi:10.3390/min10010049

Abstract

The Chungju rare-earth element (REE) deposit is located in the central part of the Okcheon Metamorphic Belt (OMB) in the Southern Korean Peninsula and research on REE mineralization in the Gyemyeongsan Formation has been continuous since the first report in 1989. The genesis of the REE mineralization that occurred in the Gyemyeongsan Formation has been reported by previous researchers; theories include the fractional crystallization of alkali magma, magmatic hydrothermal alteration, and recurrent mineralization during metamorphism. In the Gyemyeongsan Formation, we discovered an allanite-rich vein that displays the paragenetic relationship of quartz, allanite, and zircon, and we investigated the chemistry and chronology of zircon obtained from this vein. We analyzed the zircon’s chemistry with an electron probe X-ray micro analyzer (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The grain size of the zircon is as large as 50 µm and has an inherited core (up to 15 µm) and micrometer-sized sector zoning (up to several micrometers in size). In a previous study, the zircon ages were not obtained because the grain size was too small to analyze. In this study, we analyzed the zircon with laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) for dating purposes. The REE patterns and occurrence of zircon in the quartz–allanite vein match well with previous reported recrystallized zircon, while the behavior of the trace elements shows differences with magmatic and hydrothermal zircon. The 206Pb/238U ages obtained from the zircon in the quartz–allanite vein are from 240.1 ± 2.9 to 257.1 ± 3.5 Ma and this age is included in the tectonic evolution period of the study area. Therefore, we suggest that the quartz–allanite veins in the Gyemyeongsan Formation were formed during the late Permian to early Triassic metamorphic period and the zircon was recrystallized at that time. The Triassic age is the first reported age with zircon dating in the Gyemyeongsan Formation and will be an important data-point for the study of the tectonic evolution of the OMB.

Highlights

Rare-earth elements (REE) are of great importance and are used in a wide range of applications, especially in high-tech consumer products, such as cellular telephones, computer hard drives, lasers, magnets, batteries, radar and sonar systems, electric and hybrid vehicles, and flat-screen monitors and televisions
We focus on zircon geochronology and chemistry with an electron probe X-ray micro analyzer (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and Laser Ablation Multi-Collector (LA-MC)-ICP-MS in the quartz–allanite vein to clarify the mineralization history and the origin of the REE and high-field-strength element (HFSE) mineralization in the Gyemyeongsan Formation
The quartz–allanite were emplaced along the foliation in the metavolcanic rocks (Gyemyeongsan Formation) and crosscut veins were emplaced along the foliation in the metavolcanic rocks (Gyemyeongsan Formation) and thecrosscut

Summary

Introduction

Rare-earth elements (REE) are of great importance and are used in a wide range of applications, especially in high-tech consumer products, such as cellular telephones, computer hard drives, lasers, magnets, batteries, radar and sonar systems, electric and hybrid vehicles, and flat-screen monitors and televisions. Global REE production has been dominated by China. China forced mines in the USA and other countries out of operation. Minerals 2020, 10, 49 exports and the dramatic increase in prices in 2009 and 2010, mines in worldwide exploration became active again. Since REE and high-field-strength element (HFSE) mineralization was first reported in 1989 in the Chungju area in the central part of the Southern Korean Peninsula [1], a steady stream of studies has been carried out [2,3,4,5,6,7,8,9,10]. Constraining the age of the REE and HFSE mineralization at the Chungju area is important to understand the genesis and complicated history of mineralization

Methods

Results

Conclusion