Late Paleozoic Tectonic‐Magmatic Development in Southern Mongolia: Constraints From U–Pb Zircon Dating and Gold Mineralisation of the Hoid Burged Deposit

ABSTRACT The Hoid Burged gold deposit is located in a Paleozoic island arc terrane of southern Mongolia. Based on primary geological relationships, the age of the plutonic complex has been determined as Carboniferous; however, the Hoid Burged gold deposit (~50 t Au) in the Kharmagtai‐Hoid Burged area of the region is still unclear on the precise age and origin. We present integrated results of new U–Pb zircon ages, geochemical characteristics and other detailed studies for the Late Paleozoic intrusions containing Au mineralisation, based on surface samples and HB16 borehole data of the deposit. Three new U–Pb ages for diorite porphyry, altered diorite and monzogranite are 318.8 ± 7.6, 324.3 ± 4 and 336.5 ± 3.7 Ma, respectively, coinciding with the period of Paleo‐Asian Ocean subduction. Volcanic rocks are the high‐K to shoshonite series and exhibit peraluminous compositions (ASI > 1). They represent S‐type granitoids with island arc affinity, emplaced in a subduction setting. The ore‐forming fluids were magmatic in origin. Gold occurs as pseudomorphs of amphibole (hornblende) and very fine‐grained, 2–12 μm, and is associated with Ag, Te, Fe, Se and Bi minerals. Gold grades range up to 5.78 ppm in continuous core samples, and 3.31 ppm by sieve analysis where the Au is associated with Ag, Te, Cu and As. We suggest that the porphyry system of the Hoid Burged gold deposit was overprinted with epithermal vein/veinlets, and formed by extension of the Carboniferous arc maturation, which began in the Devonian period in southern Mongolia.