Geochemical Characteristics of Metamorphic Rock-Hosted Gold
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E-ISSN : 2541-5794 P-ISSN :2503-216X Journal of Geoscience, Engineering, Environment, and Technology Vol 02 No 03 2017 Geochemical Characteristics of Metamorphic Rock-Hosted Gold Deposit At Onzon-Kanbani Area, Central Myanmar Aung Tay Zar 1,3,*, I Wayan Warmada1, Lucas Donny Setijadji1, Koichiro Watanabe2 1Department of Geological Engineering, Faculty of Engineering, Gadjah Mada University, Yogyakarta, Indonesia 2 Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan 3Department of Geology, Pyay University, Pyay, Myanmar * Corresponding author : [email protected] Tel.:+62-81-329-747-974 Received: June 16, 2017. Revised : July 1, 2017, Accepted: Aug 20, 2017, Published: 1 Sept 2017 DOI : 10.24273/jgeet.2017.2.3.410 Abstract Onzon-Kabani area is located on the western border of generally N-S trending Mogoke Metamorphic Belt. Many artisanal and small-scale gold mines were noted sincelast three decades. Gold mineralization is mainly hosted in marble and occasionally observed in gneiss.Host rocks chemistry is mainly controlled by hydrothermal activities and regional metamorphism. The compatible elements of host rocks are relatively more mobile than incompatible elements during alteration and deformation. Variety of plutonic rocks such as leucogranite, syenite and biotite granite are intruded into older metamorphic rocks. In ACF diagram, leucogranite and syenite are placed in S-type granite field and biotite granite occupied in I-type granite field. Mineralization is observed as fracture filling vein and less amount of disseminated nature in marble unit. Mineralogically, gold areassociated with other base metal such as pyrite, galena, sphalerite, and chalcopyrite. Hydrothermal alteration halos are developed as a narrow zone in the peripheral of hydrothermal conduits from proximal to distal; 1) silicic, 2) sericite-illite, and 3) propylitic alteration. In place, silicic altered zone is rich in SiO2, Al2O3, and K2O. Moreover, concentrations of S, Cu, Zn, and Pb are more than any other alteration zones. The CaO is gradually increase to least altered zone where wt% of loss of ignition (LOI)also increase significantly to least-altered samples (marble). Some fluid boiling characteristics of vein textures and fluid inclusion petrography are also observed in hydrothermal system of research area. The homogenization temperature (Th) of quartz vein samples are 159°C to 315°C and salinity are 0.88 to 12.51 wt% of NaCl equivalent. This research focused to describe the geochemical characteristics of metamorphic rock-hosted gold deposit in Onzon-Kanbani area. Keywords: Mogok Metamorphic Belt, Fracture filling vein, Hydrothermal alteration, Fluid boiling metamorphic rock-hosted gold deposit but also to 1. Introduction understand the deposit genesis of research area. Gold and associated base metal mineralization at Onzon-Kanbani areais located in Thabeikkyin 2. Methods of study Township, Mandalay region, central Myanmar. This area is west 85km faraway from well known Mogok Totally, fifty ofthin and polished sections of Township (ruby land), Myanmar. Small scale local altered rocks and ore sampleswere conducted for gold rush and abundant artisanal working were mineralogical study by optical microscope and started since last thirty years ago. This area is alsoa confirmed again by scanning electron microscopy part of Mogok Metamorphic Belt(Searle and Haq, with energy-dispersive X-ray (SEM-EDX). 1964)which famous for their precious and semi- Additionally, X-ray Diffraction (XRD) analysis for precious gem stones production and distinct the hydrothermal alteration minerals that were geological feature. Mineralization is mostly hosted done for both bulk rock (random powder) and clay in marble unit and occasionally in gneiss.It is fraction. Major and trace elements analyses were observed as fracture filling veins and minor carried out on representative samples using XRF disseminated nature in marble. Generally, gold and inductively coupled plasma optical emission mineralization in Mogok Metamorphic Belt is spectroscopy (ICP-OES).Moreover, quartz samples inferred as orogenic gold (Mitchell et al., 2004) but were collected from mineralization veins to locally epithermal and skarn gold mineralization conduct fluid inclusion study. Double polished are also spread along this belt (Myint et al., 2014). quartz wafers were prepared for these quartz veins The main objective of this paper writing is not where the thickness of wafers varied between 150 onlyto describethe geochemical characteristics of and 300µm. Microthermometric measurements were done using Linkam THMSG600 combined Zar A.T. et al./ JGEET Vol 02 No 03/2017 191 heating and freezing stage, attached to Nikon Plateau (Sibumasu) is a topographic high with petrographic microscope with Axiovision software. anaverage elevation of about 1000m and mainly All of these laboratory analyses were made in composed of a series of Ordovician-Triassic Department of Earth Resource Engineering, Mineral carbonate rocks and continental sedimentary rocks Resource lab, Kyushu University, Japan. (Jurassic?). The western margin of Mogok Metamorphic Belt is juxtaposed with Central low- land (West Burma) which is filled by Eocene to Plio- 3. Regional geologic setting Quaternary sediments. Myanmar is tectonically complex region and 4. Geology of Onzon-Kanbani area composed with micro plates such as Sibumasu, West Burma, and India. Along a tectonic history is Onzon-Kanbani area is a part of Mogok built by repeatedly occurring subduction, accretion Metamorphic Belt. Therefore, mainly composed and collision events. These events chiseled the with metamorphic and igneous rocks which are geological landform and metallogenic provinces in exposed with differing areal coverage Myanmar. Traditionally, the territory of Myanmar is (Fig.2).Metamorphic rocks of research area such as subdivided into (1) the India plate to the west, (2) avariety of marbles, calc-silicate rocks and gneiss Burma microplate (West Burma) in the central part are widely distributed in eastern and western part. and (3) Shan- The age of the protolith of metasedimentary was originally considered Precambrian (Bender, 1983), Mogok Metamorphic Belt is one of the distinct but Permian fossils in marble near Kyaukse (Thein geological and metallogenic province in Myanmar and Win, 1969)indicate that Carboniferous to and located between Central low-land (West Triassic ageis more likely. Alternatively, igneous Burma) and Shan-Thai block (Sibumasu). It is units are generally covered the middle part of the believed that southern continuation of Himalaya research area and found as fitful. The older (Searle and Haq, 1964)and formed by either metamorphic rocks are intruded by granite and collision (Mitchell, 1979) or strike-slip movement syenite. The main igneous intrusion of the research (Metcalfe, 2009). In this place, well-known right area is biotite granite lateral strike-slip fault, Sagaing Fault (Swe, 1972)is served as awestern boundary. Alternatively, Metamorphic Belt ranged that magmatism of thestructural configuration of this area is closely leucogranite and syenite melt took place in Eocene related to this fault.Mogok Metamorphic Belt is time during the regional metamorphism and then composed of Paleozoic to Mesozoic meta-carbonate Kabaing granite intruded the country rocks of the rocks andmetapelite where avariety of Cretaceous- study area in Miocene after regional metamorphism Palaeogene plutonic igneous rocks(Barley et al., (Barley et al., 2003). 2003; Mitchell, 1979; Mitchell et al., 2012)are intruded to older rocks. East of this belt, Shan Fig.1. Map showing geologic setting of Mogok Metamorphic Belt and its environ. Modify after(Barley et al., 2003) 192 Zar A.T. et al./ JGEET Vol 02 No 03/2017 intruded to marble units. Light to pinkish color 5. Petrography appearance of outcrops arecharacteristic feature. The dominant metamorphic rocks in Onzon- Biotite granite is a one of important plutonic rock in Kanbani area which is composed of meta-carbonate research area. It has dark grey to yellowish color rocks (marbles and calc-silicate rock) and biotite weathered surface and light grey offresh surface. gneiss. Heterogeneous igneous intrusions are The exfoliation nature is common textural feature. observed the middle part of the area where diopside Microscopic observation shows a variety of calc-silicate rock occur along the margin of igneous minerals in marble and gneiss. In marble unit, intrusions (Fig. 2). diopside, phlogopite, calcite are main constituents Marble unit appears white (fresh) and dark gray whereas biotite, plagioclase and quartz are to pale greenish (weathered) in color. The foliated dominant in gneiss. Some of the minerals are nature also occurs in some marbles (thin foliated believed that the products of regional marble and diopside marble) and calc-silicate rock. metamorphism related with India-Asia collision. In Gneiss unit is medium-crystalline, banded and syenite and leucogranite, felsic color minerals are gneissose with finer and coarser portion. mainly observed such as quartz, plagioclase, Weathered color light grayand dark gray of fresh muscovite and nepheline. The common minerals of surface indicate that abundance of biotite and biotite granite are quartz, biotite, plagioclase and hornblende in gneiss. In igneous rocks, leucogranite orthoclase. and syenite are observed as small intrusive bodies Fig. 2. Simplify geological map of research area with sample location.