Bawdwin (from the Shan for Silver Mine) is a lead-zinc-silver deposit that also produced accessory nickel and cobalt. It is hosted in an isolated late Cambrian to early Ordovician volcanic centre in the northern Shan State of Myanmar.
Bawdwin is located about 60 km from Lashio, the capital of the northern Shan State. Lashio is about 150 km from the Chinese border on the highway that links Yunnan to Mandalay.
Mineralisation at Bawdwin is structurally controlled within steeply-dipping, cross-cutting lodes. It has generally considered to be a VHMS (volcanic-hosted massive sulphide) deposit that has been strongly structurally modified, however an alternative structurally-controlled magmatic-hydrothermal genesis is possible.
Before WW2, Bawdwin was one of the richest mines in the British Empire. In 1938, the Bawdwin reserve was quoted at 10.8 Mt at 22.8% Pb, 13.9% Zn, 1.05% Cu and 670 g/t Ag, which is unusually high Pb:Zn ratio for a VHMS deposit.
Historical Exploration and Production
Mining of silver at Bawdwin dates at least to the 15th Century and estimated historical production is estimated at c.10M oz of Ag.
The British mining era commenced c.1906 when Great Eastern Mining Company started exploiting old mine slags. Burma Corporation was established in 1914 (by Herbert Hoover), and developed the Dead Chinaman Tunnel, Marmion Shaft and Tiger Tunnel to access deeper sulphide ore. Peak production occurred from 1919 to 1940 with total production reported as 12.68M tonnes. Grades mined in the 1930’s were typically c.20% Pb, 15% Zn, 0.3% Cu, and 500g/t Ag. Significant Ni and Co was also present in parts of the mine but resource and production figures are not available. A ROM (run-of-mine) sample reported by Dunn (1973) had grades of 21% Pb, 15% Zn, 0.3% Cu, 0.23% Ni, 0.08% Co, 550 g/t Ag, and 1.2% Sb.
The plant and smelter were worked by the Japanese after invasion but were destroyed during the war. The operation was re-opened in 1951 and continued under British ownership until 1965 when the mine was nationalised. Following nationalisation, the mine was run down and starved of capital investment. To illustrate the progressive decline, refined lead metal production fell from 77,700 tonnes in 1938 to 16,518 tonnes in 1960 and 4,843 t in 1974/75.
The first documented exploration programme occurred from 1955-57 when Hunting completed geophysical and geochemical exploration around Bawdwin. They were engaged by Burma Corporation to discover new deposits motivated by declining grades and production from the main lodes.
Historical Resources and Reseves
In 1962-1964, UNSFP completed drilling and estimated ‘ore reserves’ and provided exploration consulting. The UN created polygonal “reserve” boundaries in 1963 (underground) and 1980 (open pit).
In 1973-74, the Canadian International Development Agency (CIDA) completed a significant drilling programme.
In 1973-76, the German Geological Mission completed geochemical and geophysical exploration and geological mapping. A total of 22 drillholes were completed at this time.
In 1976, a polygonal “reserve” (long tons) for the main lodes was reported based on a mining cut-off grade of 5% Pb:
Underground 6.69 Mt at 7.59% Pb, 3.54% Zn, 151 g/t Ag, 0.15% Cu
Open Pit 9.69 Mt at 5.37% Pb, 2.54% Zn, 0.25% Cu (no Ag reported)
In 1987, AMDEL working for the Australian International Development Assistance Bureau (AIDAB) completed assessments of Bawdwin and Namtu slags focused on metallurgy and processing options. The programme also reviewed the Bawdwin mine potential (Hopwood, 1985).
In 1997, RSG (for Mandalay Mining) reported (under JORC guidelines, although the terminology is not presently JORC-compliant) a mineral resource that included the lower grade halo mineralisation outside the main lodes:
Total Resource 104.3 Mt at 5.61% Pb, 2.34% Zn, 0.21% Cu, 71 g/t Ag
(at 2% Pb cut-off)
Indicated Resource 23.81 Mt at 6.49% Pb, 2.84 % Zn, 0.26% Cu, 177 g/t Ag (at 4% Pb cut-off)
“Recoverable resource” 94.5 Mt at 6.49% Pb, 2.84% Zn, 0.26% Cu, 118 g/t Ag
Estimates were based on limited drilling and extensive underground sampling. A total of 65 diamond drill holes were completed from 1956-88, mostly in the period 1973-75 (CIDA). Most holes were shallow (80- 150m) and recoveries were poor.
Mining appears to have been guided by underground visual control and channel sampling for grade control. Resources and reserves were not drilled out in advance of mining. It was reported that 66% of ore mined from 1962-1973 came from outside reserve boundaries.
Underground mining cut-off in the 1990’s was 5% Pb. Mining and processing cost for ore was US$32/t, and for waste US$1.7/t.
The recent, sustained increase in the international price for zinc metal and strong underlying demand for zinc supply reinforces the Board’s positive outlook for zinc production. The Company therefore seeks to establish itself as a significant regional metals producer based in Myanmarwith a focus on base metals and accompanying silver, copper, cobalt, nickel, gold and other by-products.
Upon exercise of the “Bawdwin Option”, Myanmar Metals Limited could ultimately be established as a producer of zinc metal in Myanmar.
This can be achieved in the short-medium-term by producing metals concentrates (principally lead/zinc/silver) from a potential open pit at Bawdwin and in the longer term by producing metals concentrates from the Great Bawdwin Mine if successful modern exploration shows that Bawdwin can be reopened as a safe, modern, high-productivity underground mine.
Accordingly, the Board remains focused on progressing both the “Bawdwin Option” – for a controlling interest in the Bawdwin zinc/lead/silver/copper polymetallic mine lease held by Win Myint Mo Industries Co Ltd.