Evolution of Ore-Forming Fluids and Gold Deposition of the Sanakham Lode Gold Deposit, SW Laos: Constrains from Fluid Inclusions Study

Shusheng Liu,Linnan Guo,Meifeng Shi,Xiaoyu Cui,Siwei Xu,Jun Ding,Fei Nie,Lin Hou,Huimin Liang

doi:10.3390/min12020259

Shusheng Liu, Linnan Guo + Show 7 more

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https://doi.org/10.3390/min12020259

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Abstract

The Sanakham gold deposit is a newly discovered gold deposit in the Luang Prabang (Laos)–Loei (Thailand) metallogenic belt. It consists of a series of auriferous quartz-sulfide veins, which is distinguished from the regional known porphyry-related skarn and epithermal gold deposits. There are four mineralization stages identified in Sanakham, with native gold grains mainly occurring in stages II and III. Evolution of ore-forming fluids and gold deposition mechanisms in Sanakham are discussed based on fluid inclusion petrography, microthermometry, and Laser Raman spectroscopy. The original ore-forming fluids belong to a medium-high temperature (>345 °C) CH4-rich CH4–CO2–NaCl–H2O system. In stages II and III, the ore fluids evolve into a NaCl–H2O–CO2 ± CH4 system characterized by medium temperature (~300 °C), medium salinity (~10 wt% NaCl eq.), and CO2-rich (~10% mol). They might finally evolve into a NaCl–H2O system with temperature decreasing and salinity increasing in stage IV. Two fluid immiscibility processes occurred in stages II and III, which created high-CH4 & low-CO2 and low-CH4 & high-CO2 end-members, and CO2-poor and CO2-rich endmembers, respectively. Gold-deposition events are suggested to be associated with the fluid immiscibility processes, with P–T conditions and depth of 236–65 MPa, 337–272 °C, and 8.7–6.5 km, respectively.

Highlights

The mainland of Southeast Asia consists of a series of continental blocks or terranes together with related sutures and volcanic arcs (Figure 1a)
This study aims to discuss the evolution of ore-forming fluids and gold deposition mechanisms in Sanakham, and to provide basic data for further study on regional gold metallogenic regularity
Laser Raman spectroscopy indicates that both type M and type C fluid inclusions have carbonic component-dominate vapor phase (Figure 7)

Summary

Introduction

The mainland of Southeast Asia consists of a series of continental blocks or terranes together with related sutures and volcanic arcs (Figure 1a). It is endowed with a diversity of mineral resources distributed in several important metallogenetic belts, such as the Truong. The Luang Prabang (Laos)–Loei (Thailand) metallogenic belt lies along the western periphery of the Indochina Block, to the east of Changning–Menglian–Chieng Mai Suture zone (Figure 1a). Paleo-Tethys Ocean and the subsequent collisional orogeny between the Sibumasu Block and the Indochina Block, is traditionally recognized as a metallogenic belt dominated by porphyry-related skarn and epithermal deposits [2,3] (Figure 1b). The gold orebodies consist of a series of quartz-sulfide veins that are controlled by secondary structures of the regional NNE-trending brittle-ductile shear zone, which is different from the regional porphyry-related skarn and epithermal

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