Abstract
The Kyaukmyet prospect is one of the principal epithermal gold prospects in the Monywa District, Central Myanmar; its gold- and base metal-bearing quartz veins contain around 3 g/t gold. Ore minerals are mainly hosted by volcanic and volcaniclastic rocks of the Late Oligocene to Middle Miocene Magyigon Formation. The distribution of magmatic intrusions in the area is controlled by ENE-WSW trending faults; these faults are likely related to ore mineralization. Common ore minerals at the Kyaukmyet prospect include pyrite, sphalerite, galena, chalcopyrite, and electrum. They occur in mineralized crustiform-textured brecciated quartz veins and banded (colloform) and massive quartz veins. Mineralized rock is accompanied by silicification and propylitic and argillic alterations. The alteration mineral assemblages include quartz, adularia, calcite, chlorite, illite/smectite, sericite, and illite. Fluid inclusions in the quartz veins have homogenization temperatures ranging from 148 °C to 304 °C and salinities from 0.35 wt % to 2.75 wt % NaCl equiv. The quartz in the mineralized quartz veins was most likely precipitated at a depth ranges165-256 m below the paleosurface. The precipitation of gold at the Kyaukmyet prospect may have been formed by mixing large amounts of meteoric fluid with small amounts of magmatic fluid. The coexistence of liquid-rich and vapor-rich inclusions and presence of adularia and bladed calcite indicate that fluid boiling is caused the main mechanism of ore formation. The vein textures, ore mineral assemblages, alteration minerals and fluid inclusion data suggest that the Kyaukmyet prospect is a polymetallic low-sulfidation epithermal gold deposit.
Highlights
The Monywa District is an important copper-gold district in Myanmar (Zaw, 2017; Zaw et al 2017) and the district lies within the N-S trending Inner Volcanic Magmatic Arc (Zaw, 1989; Zaw, 1990; Chhibber, 1934) which is an important metallogenic province in Myanmar Fig
We focus on a detailed description and characteristics of the gold-base metal veins and mineralized rocks including alteration minerals, ore mineral assemblages and paragenesis, together with fluid inclusion petrography and microthermometry to constrain the evolution of the ore-forming fluids and the depth of ore formation
In addition to the fluid inclusion data, the presence of adularia, lattice bladed calcite, lattice-bladed calcite replaced by quartz, crustiform, banded, colloform, and plumose/feathery textured quartz all suggest that fluid boiling occurred
Summary
The Monywa District is an important copper-gold district in Myanmar (Zaw, 2017; Zaw et al 2017) and the district lies within the N-S trending Inner Volcanic Magmatic Arc (Zaw, 1989; Zaw, 1990; Chhibber, 1934) which is an important metallogenic province in Myanmar Fig.. There are four well-known, very large high-sulfidation copper-gold ore deposits in the Monywa District: the Sebataung, Sebetaung South, Kyisintaung, and Letpadaung deposits Fig.. The district hosts low-sulfidation style Au-Ag mineralized prospects in the outcrops of hypabyssal. Oligocene rhyolitic volcanics formed at 27-24 Ma and host low-sulfidation mineralized rock and a Miocene andesite porphyry at Letpadaung with an emplacement age of 19 Ma (Knight and Zaw, 2015) has been associated by a high-sulfidation mineralizing event. The Kyaukmyet prospect is approximately 5 km NE of the high-sulfidation Kyisintaung copper-gold deposit. The host rocks the Kyaukmyet prospect are members of the Late Oligocene to Middle Miocene aged Magyigon Formation consisting of volcanic and volcaniclastic rocks Fig. (Mitchell et al 2011). Vein textures and minor adularia documented by Kirwin (1994) (unpublished data) suggests a low-sulfidation epithermal system
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