Gold mineralization of the Thone Myae Song area, Sagaing Region, northern Myanmar

Abstract

• Central Magmatic-Volcanic Belt (CMVB) hosts several Au-Cu ore types and Thone Myae Song deposit. • Formation of CMVB is related to the eastward subduction of Indian Ocean floor during the Cretaceous. • Sericite-carbonate alteration is important as confines to the margins of mineralized veins. • Fluid immiscibility was a major trigger to the precipitation of gold and base metals at EE3 deposit. Several gold deposits are found in the Central Magmatic-Volcanic Belt (CMVB) of Myanmar, which forms a nearly N–S-trending, 1500-km-long arc extending from the Andaman Sea to northern Myanmar. The CMVB consists of Cretaceous granitoids intruded into folded andesites and pillow basalts (Mawgyi Andesite) which rest on cherts, talc-schists, mudstones and phyllites. The EE3 gold deposit is part of gold mineralization in the Thone Myae Song area, located in the Kawlin–Wuntho block in the northern part of the CMVB. The orebodies occur as sulfide-bearing massive quartz veins hosted by Mawgyi Andesite. Based on the mineral assemblages and cross-cutting relationships, three mineralization stages are identified in the EE3 gold deposit: Stage-I quartz-carbonate-sulfide veins; Stage-II quartz-carbonate veins intersecting the Stage-I veins; and Stage-III quartz-carbonate-sulfide veins parallel to the Stage-I veins. The main hydrothermal alteration minerals are sericite, epidote, chlorite and calcite. Three main types of fluid inclusions were distinguished from the mineralized quartz veins hosted by Mawgyi Andesite: liquid-rich aqueous fluid inclusions (Type A), vapor-rich aqueous inclusions (Type B), and H₂O-CO₂-NaCl inclusions (Type C). The latter occurs only in the Stage-I veins. The ore-forming conditions are estimated from fluid inclusions in the Stage-I, Stage-II and Stage-III veins to be at 180 °C and 28 bars, 176 °C and 26 bars, and 158 °C and 21 bars, respectively. The formation pressures of the Stage-I, Stage-II and Stage-III mineralization correspond to a shallow depth of 300 m, 280 m, and 225 m, respectively. Based on the ore and alteration mineral assemblages, and estimated temperature and pressure conditions of the mineralization, the EE3 gold deposit was formed in an epithermal condition.