A new orogenic gold belt in Southeast Asia: Geology, mineralogy and genesis of the Vangtat gold deposit, Southeastern Laos

Abstract

The Vangtat deposit is the major gold deposit in a new orogenic gold belt discovered and developed in southeastern Laos in the past two decades. Our study of the Vangtat orogenic gold deposit shows that it formed within a convergent margin along the western segment of the Poko suture zone, which marks the collision between the Indochina Terrane and the Kontum Massif. Shear structure and greenschist facies metamorphic rocks are the main hosts for gold mineralization in the Vangtat deposit. High-grade gold-bearing quartz-sulfide veins and wall rock hydrothermal alteration are genetically related, and alteration minerals consist of quartz, carbonate, graphite, white mica, chlorite, and pyrite. The study of fluid inclusions and wall rock alteration assemblages indicate that the Vangtat gold deposit was formed by an aqueous-carbonic, low salinity, reduced, weakly alkaline to near-neutral pH fluid, mainly composed

Large Amount of Excess Argon in Hydrothermal Quartz from the Vangtat Orogenic Gold Belt, Southern Laos: New In-Sight from K-Ar and Noble Gas Isotope Analyses

“…The Vangtat shear zone is the structural host for the Vangtat orogenic Au belt in southern Laos (Figure 1) [8]. The Vangtat shear zone is the main subsidiary structure of the Poko suture zone (PKSZ, Figure 1), which resulted from the collision between the Indochina Terrane and the Kontum Massif during the Permo-Triassic [17][18][19][20].…”

“…The Thongkai-Ok Au deposit is one of several actively mined deposits in the newly discovered Vangtat orogenic Au belt of southern Laos [9]. The major orebodies within the high-grade belt are found in quartz-sulfide-carbonate-graphite-white mica-chlorite veins in which Au is commonly present as inclusions within sulfides, mainly pyrite [8]. The quartz veins and silicified zones have a thickness of up to 10 m and are hosted by strongly deformed and sheared pelitic schist [8].…”

“…The major orebodies within the high-grade belt are found in quartz-sulfide-carbonate-graphite-white mica-chlorite veins in which Au is commonly present as inclusions within sulfides, mainly pyrite [8]. The quartz veins and silicified zones have a thickness of up to 10 m and are hosted by strongly deformed and sheared pelitic schist [8]. Lower-grade Au mineralization occurs in a graphite-carbonate-quartz-sulfide alteration envelope that grades into sub-economic to barren altered pelitic schist [8].…”

“…The quartz veins and silicified zones have a thickness of up to 10 m and are hosted by strongly deformed and sheared pelitic schist [8]. Lower-grade Au mineralization occurs in a graphite-carbonate-quartz-sulfide alteration envelope that grades into sub-economic to barren altered pelitic schist [8].…”

“…In a recent study of Au mineralization in the Vangtat orogenic Au belt of southern Laos [8], Bounliyong et al (2021) [9] dated samples of hydrothermal muscovite from the shear-zone hosted quartz veins of the Thongkai-Ok Au deposit. The K-Ar ages of four size fractions (<2, 2-4, 4-10, and 10-40 µm) separated from three hydrothermal muscovite samples revealed a large range of calculated ages, from 348 to 206 Ma [9].…”