Study On Tectonic Evolution And Metallogenesis In Laos And Its Adjacent Regions

Laos lies in north-eastern Indochina and stays at a relatively low level of geological study compared to neighbouring China, Thailand and Vietnam. Based on the geological and mineral information collection and adjacent area’s field geological survey, aiming at present-research status and existed problems, and under the guidance of plate tectonics and modern metallogenic theories, the study was carried out by the author on regional tectonic-diagenesis-metallogenesis, the temporal-spatial distribution and characteristics of the main mineral deposits were summarized, and the regional tectonic-metallogenic evolution model was established.Based on the predecessors of study, the author further summarized the extension trends of tectonic units and their interrelations, and divided the study area into7sub-tectonic units, i.e., Jinghong-Sukhothai arc, Nam-Uttaradit suture, Simao-Phitsanulok block, DienBienPhu-Loei suture, Vientiane-Kontum block, Sepon-TamKy suture, Truong Son block.Regional metallogenic dynamics analysis shows that Laos and adjacent regions have multiple tectonic characteristics during different geologic stages. On the whole, it can be divided into three important tectonic evolution stages. Firstly, the Precambrian continental formation stage, in which the Kontom and Truongson blocks basement were formed, which appear the affinity to the South China block; Secondly, the Early Paleozoic to Middle Triassic active plate tectonic stage, in which the Paleotethys evolution of Dienbienphu-Loei ocean, Sepon-TamKy ocean, Nam-Uttaradit arc-back ocean and Song Ma ocean and interaction of oceans and terranes were experienced; Thirdly, the Later Triassic-Cenozoic intracontinental stage, which was characterised by intraplate extension, strike-slipping, and associated basining and coeval alkaline magmatic activities.The author analyzed the regional metallogenic characteristics comprehensively, including division of metallogenic units, typical ore deposits study, ore-forming epoch, ore-forming background and so on. Some typical deposits are selected for genetic analysis in this paper, i.e., Sepon copper-gold deposit, PhuKham copper-gold deposit, PhaLek iron deposit, Vientiane potash deposit and Boloven bauxite deposit. In addition, the control factors of regional mineralization are discussed in three contexts:regional structure, magmatism and sedimentary formation, and regional metallogenetic regularity is also summaried.On the basis of the above study, the author further discussed the relationship between geotectonic evolution and metallogenesis, and constructed three tectono-metallogenic evolution stages. First, Precambrian basement evolution and mineralization stage, the mineralization was weak and there are no important ore deposits discovered, but it might be important for mineral source rock formation. Second, the Early Paleozoic to Middle Triassic plate activity-metallogenesis evolution stage, in which the metallogenic evolution was subject to the ocean-terrane transform system, the arc-magmatic hydrothermal cooper-gold-molybdenum-iron polymetallic mineralization related to subduction and syncollision-magmatic hydrothennal tungsten-tin-rare metals mineralization related to continental collision were developed. Third, the Later Triassic-Cenozoic intracontinental tectonic-metallogenesis evolution stage, intracontinental orogenic magmatic hydrothennal tin-iron-lead-zinc-gold mineralization, continental basin sedimentary (transformation) potash-cooper-lead-zinc mineralization, continental rifting eruptive mafic-magmatic sapphire mineralization and supergene weathering-sedimentary placer gold-tin-chromium mineralization.Finally, the reginional tectonic-metallogenesis evolutionary event was summaried and the evolutionary model was established for the first time.The study shows that Laos is presently located in the junction region of several ancient continental blocks and disppeared oceans, where has experienced long-historic and multistages geological-mineralization evolution, several important mineral types such as copper, gold, bauxite, potash, etc., were formed, it can be believed that Laos has great potential for mineral exploration and development.