Xplore.Global

Xplore.Global is a UK-based mineral exploration consultancy whose specialty is to provide companies with technical and logistical support during operations around the globe, across a wide range of commodities.

In August 2016, soon after graduating from the University of Birmingham, I was invited by Benedikt Steiner to assist on a comprehensive multi-disciplinary desktop study on the geology and mineral resource potential of Myanmar.

Beautiful photo over an unknown region of Myanmar, a previously overlooked jurisdiction in terms of its mineral wealth. credit

Recent democratic elections (2015) have lifted the veil on a previously politically, economically and socially unstable nation, fuelled by international isolation by a military government. Consequent governmental and mining reforms have begun to foster increased interest from international exploration and mining companies.

Myanmar was a challenging country to assess. Sparse detailed geological mapping, coupled with plenty of conflicting literature by numerous academics and field geologists alike, made regional geological interpretation tough to get my head around. Soon though, I was able to report a fascinating geological history.

The complex geology of Myanmar, and the rest of Southeast Asia, is a product of 400+ million years of Gondwana rifting, terrane divergence and basin development, succeeded by northward drift of numerous structural terranes in three episodes, marking the opening and closing of three intervening sub-Tethyan oceans:

• Palaeo-Tethys (Devonian-Triassic)
• Neo-Tethys (Early Permian-Late Cretaceous)
• Ceno-Tethys (Late Triassic-Late Cretaceous

The tectonic evolution of Myanmar, a continuous series of accretion and subduction events, has resulted in the genesis of four major and 2 minor geological provinces:

• Indo-Burman Ranges
• Wuntho-Popa Arc
• Mogok-Mandalay-Mergui Belt
• Shan Plateau

and:

• Granite Provinces
• Ophiolite Belts

Within some of these are a number of sub-provincial geological belts, in particular, the:

• Mogok Metamorphic Belt (in the Mogok-Mandalay-Mergui Belt)
• Jade Mines Belt (in the Wuntho-Popa Arc)

Geological map of Myanmar, notice the four distinct geological provinces trend north-south, corresponding with the tectonic evolution of the country.

Given such geological history, it goes without saying that Myanmar is subsequently endowed with a diverse range of metallic and gemstone deposits. These can be categorised into 9 distinct mineral deposit styles:

• Orogenic Au
• Porphyry Cu-Au
• Epithermal Cu-Au
• Skarn Au-Ag (+Pb-Zn)
• Magmatic-hydrothermal/pegmatite/granitoid Sn-W
• Irish-Type and VMS-Type Pb-Zn
• Ultramafic ophiolite Ni-Cr-Cu + PGE
• Retrograde metamorphic calcite vein-hosted corundum
• High-grade regional metasomatic jadeite

As part of the study, I was able to produce a large geodatabase in ArcGIS and generate detailed commodity maps thus delineating a number of mineral provinces within Myanmar. Through further literature searching, I was able to produce a really detailed analysis of the mineral resource potential of Myanmar. A few of the many examples studied are outlined briefly below.

Porphyry and epithermal Cu-Au province of the Wuntho-Popa Arc linked to the Early Cenozoic (mostly Miocene) emplacement of shallow metaluminous I-type granitoids during the highly-oblique subduction phase. These deposits are principally centered around two major inliers, the Wuntho Massif and the Monywa Segment. One of the most significant discoveries to date within this province is the Monywa Copper District (MCD). Here, Miocene I-type plutons and quartz-andesite porphyries intrude a series of basic igneous and gneissic basement, overlain by Late Miocene marine sediments, volcanics and volcaniclastics. The MCD encompasses four distinct deposits with reported resources totaling 1.7Bt @ 0.37% Cu (6.3Mt contained Cu).

A man working the tailings of the Letpadaung deposit, within the MCD. credit

Hi-sulfidation epithermal and orogenic Au provinces of the Wuntho-Popa Arc and the Mergui Slate Belt, respectively. Much like the epithermal copper deposits mentioned above, the epithermal Au deposits are also genetically attributed to the shallow emplacement of I-type granitoids during the Miocene. The difference in economically viable gold deposits is that mineralisation occurs within silicified Lower-Mid Eocene sandstones. This manifests as quartz-vein stockworks associated with dilational fault-jogs and en-echelon transtensional faulting. In particular, the Oligocene-Miocene Sagaing fault zone is critical in the control of epithermal gold mineralisation. Conversely, orogenic Au deposits appear to be genetically independent of Late Cretaceous-Miocene magmatism. Very little literature discusses mineralisation pathways in Myanmar, however, the majority of orogenic Au deposits are within eastward dipping, Mergui Slate Belt-hosted mesothermal quartz veins, centralised along regional north-south structures.

Gold mining activity within the Mergui Slate Belt, Mon State. credit

Sediment-hosted VMS and Irish-Type Pb-Zn (+Ag) provinces are scattered within Precambrian-Lower Palaeozoic sedimentary sequences of the Shan Plateau. The largest and most well-studied of these deposits is the Bawdwin Mine, northern Shan State. Cambro-Ordovician volcanism in the rifting continental arc terrane (Sibumasu Terrane) associated with an Andean-Type subduction zone along the Proto-Tethyan margin of Gondwana is deemed responsible for the genesis of VMS-Type Pb-Zn-Ag deposits. At Bawdwin specifically, three sub-parallel massive sulphide lodes are hosted within Cambro-Ordovician tuffaceous rocks, volcaniclastics and turbidite sequences. Ore reserves were calculated at 10.8 Mt @ 22.8% Pb, 13.9% Zn, 1.1% Cu, 670 g/t Ag. Pb-Zn Irish-Type deposits, such as the Theingon Deposit, are principally located within Ordovician limestones and dolomites, manifesting as epigenetic hydrothermal calcite veins. These mineralised systems are found most commonly associated with structural fissure systems.

Company offices and railway stop at the Bawdwin Mine site, northern Shan State. credit

Sn-W province, that extends from Naypyitaw in the north, along the Mogok-Mandalay-Mergui Belt, to Victoria Point in southernmost Myanmar. These Sn-W deposits are considered analogous with those in Cornwall. Cretaceous late-stage orogenic emplacement of S-type granitoids acts as a source of metals, which are mobilised by later fracturing of country rock. Mineralisation is in the form of W-Sn-Qtz veins, as well as metasomatic Sn greisens. The majority of historic exploitation in Myanmar is from alluvial, colluvial and eluvial deposits. For example, the Heinda Deposit, free cassiterite is enriched in silty horizons within 12-13 Late Tertiary sedimentary cycles. Cassiterite content of the Heinda placers ranges from 0.06 – 3.9 kg SnO₂ m^-3 (UNDP, 1996). Alternatively, at the Mawchi deposit 64 parallel/sheeted, N-S striking, sub-vertical Sn-W-quartz veins cross-cut the apical portions of the granitoid and country rock. These veins are 2.5m in width and 570m along strike (Chhibber, 1934; Khin Zaw, 1990, UNDP, 1996). In the 1970s, annual tin-tungsten concentrate production was approx. 400t @ 38% cassiterite and 32.5% wolframite (UNDP, 1996).

Workers in a tin mine exploiting Late Tertiary placer deposits. credit

Finally, to accompany the report, we compiled a literature database using Microsoft Access. I had the chance at that point to develop some new IT and computing skills. I had never used MS Access before, but I quickly got a grasp of the technicalities and was able to produce a perfectly functioning database, complete with forms and reports.

During this process, I developed a strong set of basic technical skills for using ArcGIS (georeferencing, generating shapefiles, geodatabases, etc.), as well as cartography. On top of this, my general IT skills improved significantly alongside report writing, literature search and review, and my general scientific/academic outlook.

Here is a short list of valuable references:

• Chhibber, H.L., 1934. The Geology of Burma. University of Michigan, MacMillan. 538p.
• Gardiner, N. J., Robb, L. J., Morley, C. K., Searle, M. P., Cawood, P. A., Whitehouse, M. J., Kirkland, C. L., Roberts, N. M.W., Myint, T. A., 2016. The tectonic and metallogenic framework of Myanmar: A Tethyan mineral system. Ore Geology Reviews, 79, 26-45.
• Gardiner, N. J., Robb, L. J., Searle, M. P., 2014. The metallogenic provinces of Myanmar. Applied Earth Science, 123 (1), 25-38.
• Gardiner, N. J., Searle, M. P., Morley, C. K., Whitehouse, M. P., Spencer, C. J., Robb, L. J., 2015a. The closure of Palaeo-Tethys in Eastern Myanmar and Northern Thailand: new insights from zircon U-Pb and Hf isotope data. Gondwana Research, In press.
• Gardiner, N. J., Searle, C. K., Robb, L. J., Morley, C. K., 2015b. Neo-Tethyan magmatism and metallogeny in Myanmar – An Andean analogue?. Journal of Asian Earth Sciences, 106, 197-215.
• Khin Zaw, 1990. Geological, petrological and geochemical characteristics of granitoid rocks in Burma: with special reference to the associated W-Sn mineralization and their tectonic setting. Journal of Southeast Asia Earth Sciences, 4 (4), 293-335.
• Metcalfe, I., 2013. Gondwana dispersion and Asian accretion: Tectonic and palaeogeographic evolution of the Eastern Tethys. Journal of Asian Earth Sciences, 66, 1-33.
• UNDP, 1996. Atlas and Mineral Resources of the ESCAP Region, Volume 12: Geology and Mineral Resources of Myanmar, United Nations Publication, 12, 1-193.

 

Thanks go to Benedikt Steiner for taking me under his wing for the duration of this project and developing my ArcGIS skillset as well as funding my acquisition of an ArcGIS package and my trip to the Mineral Deposits Study Group conference.