Where Ancient Continents Converge: Laos – A Nexus of Rich Geological Heritage

During the Carboniferous to Permian time, shallow seas opened between three continental blocks. Large volumes of limestone and related carbonate rocks were deposited in these seas.

In early Permian time, the continental blocks moved together, producing subduction zones accompanied by magmatic arcs. Numerous porphyry-style mineralization systems were generated in these magmatic arcs. The interaction between these porphyry systems and the carbonate rocks gave rise to skarn-style mineral deposits, such as Phu Kham Cu-Au and Sepon Carlin-style Au and manto-style Cu. Clusters of granitoid intrusions associated with tin and polymetallic mineralization systems may have also occurred during this period. Additionally, several examples of Michigan-style (native copper) mineralization were identified in intermediate to mafic volcanics of these magmatic arcs, although this style has attracted minimal exploration.

Several Mississippi Valley-style lead-zinc deposits were identified within the Permo-Carboniferous limestones. While a few of these deposits have been exploited on a small scale for oxide zinc minerals, the sulphide zones remain largely unexplored.

During the Permian time, the continental blocks collided, forming the Truongson and Loei fold belts. Several orogenic quartz-gold vein-style deposits, known in Laos, probably formed during this time. Previously formed deposits were also deformed due to the collision.

Several significant ultramafic complexes with platinum (Pt), nickel (Ni), chromium (Cr), and copper (Cu) mineralization occur along crustal-scale structures in Laos. While the age of these rocks remains unknown, radiometric dating of the Nan-Uttaradit ultramafic complex in Thailand suggests a Carboniferous age.

A second episode of extension during early Triassic time led to another period of shallow marine carbonate sedimentation and acid magmatism. This period resulted in epithermal and porphyry mineralization styles, including Chatree low-sulfidation vein Au.

From Jurassic to Cretaceous time, a vast inland basin covered much of Laos, filling with oxidized “redbed” style sediments. Though this basin has since been dissected, remnants contain thick evaporite sequences, including halite, gypsum, and potassium-rich salts, which have been exploited for industrial purposes. The lower parts of this sequence have also developed some “redbed style” sedimentary copper-silver deposits, though these remain minimally explored.