Ore genesis and tectonic implication of the Daeheung-Ryongyang magnesite deposits in the East Jiao-Liao-Ji Belt, North Korea

Abstract

The Daeheung and Ryongyang magnesite deposits in the Dancheon Mineralized Belt (DMB) of South Hamgyong Province, North Korea, have attracted wide attention because of their large reserves and geological similarity with a number of magnesite deposits in the Dashiqiao magnesite belt of Liaoning Province, China. The study of the magnesite deposits in the DMB was performed to analyze and compare the genetic and geotectonic implications between the two districts. The Daeheung and Ryongyang deposits comprise sedimentary and metamorphic rocks of the Paleoproterozoic Bugdaecheon Series and intrusive and extrusive rocks of diverse ages. Magnesite ores comprise magnesite, talc, chlorite, quartz, calcite, and apatite, and based on the mineralogy, ores can be divided into four groups: pure magnesite, chlorite-magnesite, talc-magnesite, and chlorite-talc-magnesite. Rare earth element (REE) patterns can be classified into three types: middle REE-enriched, heavy REE-enriched, and light REE-enriched, implying multiple events in the formation of magnesite deposits in the DMB. The carbon and oxygen isotope compositions of magnesite ores and dolostones in the DMB range from −1.0 to 1.0‰ and from 8.7 to 23.0‰, respectively. The results suggest that the mineralization proceeded under low fluid/rock ratios at low XCO2 or large input of freshwater into hydrothermal fluids. Salinity and homogenization temperature of fluid inclusions in magnesites range from 0.5 to 34.1 wt% NaCl eq. and from 112 to 290 °C, respectively, which are similar to those of the Dashiqiao magnesite belt. Considering the ore mineralogy, REE patterns, stable isotope composition, and fluid inclusion characteristics, magnesite ores may have been formed by various processes involving the inflow of Mg-enriched brines into carbonate rocks and then hydrothermal fluid infiltration related to granitoid intrusions. These results indicate that the Daeheung and Ryongyang magnesite deposits in the DMB belong to the Veitsch-type sedimentary-metamorphic deposits and are genetically correlated with mineralization in the Dashiqiao magnesite belt of Liaoning Province in China.