Captain's Flat mining ventures now depended on the government's decision whether to build a railway line from Bungendore. This had been approved in principal, as early as 1930 without further action, but in late 1937 the bill was finally ratified. On 10 January 1939, the first ore rattled its way out of Captain's Flat by rail.

The outbreak of war threatened the sales of lead and zinc, with German, French and Belgian markets being closed. Britain took the zinc for the production of brass while the lead went to the United States for smelting. The government gave considerable concessions in power and freight charges to the mining company, to ensure the continuation of overseas funds into Australia.

By 1940 Lake George Mines employed 550 people and the population increased in three years to 1,700. The Yarrowlumla Shire Council, apart from making 2 seats available on the council for Captain's Flat representatives, did not spend much money on improving the town. Therefore, the mining company built 190 fibro cottages for married miners and a large hostel-type building for single men, while others lived in tents until more permanent accommodation was built.

A new theatre, hospital, swimming pool, ambulance service, doctors, nurses, even football players were all paid for by the company, as were street lighting, electricity and domestic water. It is said that men came to work in the mines just to get an opportunity to play on the local football team! Meanwhile, the job of sanitation, street and road improvements and upgrading and garbage disposal fell to the Shire Council.

By 1956, they had sealed the major streets, built a playground, swimming pool and tennis courts and constructed kerbing and gutters. In 1955, local residents had loudly criticised the Council for the lack of money being attributed to the town and for the poor state of disrepair of local roads.

Old buildings, relics of the old days suddenly became obsolete. The hotel was demolished in 1939, after construction began on a new, two-storey hotel was begun in 1938. This building was fitted with a bar which stretched 32 metres in length, which was the longest bar in Australia at the time. Patrons guzzled down some 102 thirty six gallon kegs of beer every week, had 20 rooms for accommodation, two dining rooms, a saloon bar and large fireplaces for warmth.

Other businesses soon sprang up, with a garage and service centre, five taxi companies and a bus service catering for transport needs. Domestic services such as a supermarket, dry-cleaner, chemist, butcher shops, bakers, greengrocers, a dress shop, milk bars and cafes all began trading.

The first bank in Captain's Flat was the Government Savings Bank of NSW opened in 1889. This was later changed to the Commonwealth Savings Bank which continues to trade from the Post Office to this day. The Union Bank opened its doors in a new building on the corner of Foxlow and Kurrajong Streets in 1937. In 1951, this bank was merged with the Bank of Australasia and became the ANZ bank. Captain's Flat was a boisterous, prosperous town built solely on the back of the mines.

But the relationship between the company and the miners was not always a happy one. In 1948, one strike lasted seven months, resulting in huge losses in pay and production. It began in October when 430 miners asked the company for an increase in their lead bonuses. Instead, Lake George Mines offered them 20 percent share in company profits. The miners refused and so began "The Big Strike".

Both sides showed little animosity toward the other, but neither would they back down. Miners who fell behind in their rents were guaranteed that they would not be evicted from their company houses. Money became extremely scarce and strike funds were issued to miners at the rates of £2 to single men, £2/5/- to married men and 2/6 per child dependant.

Then again in 1954, another protracted strike began. The mining company had been going through a time of hardship, during which the miners agreed to forego their lead bonus to help out. The company then asked the miners to work longer hours and this triggered a walkout. The miners also banned the company from bringing in outside contractors to sink the main shaft deeper.

Lake George Mines ceased operations and sacked some 300 men. The Australian Workers Union agreed with mine management to allow outside contractors access to work on the main shaft, but the miners on strike refused to comply with the agreement until all men sacked were reinstated. Other unions supported the striking miners with strike funds paid as food stamps.

This strike cost the company £750,000 in unmined ore and the workers £350,000 in lost wages. Miners began turning back their electricity meters to save money, some being so adept at this that the company actually paid them refunds. Though the strike cost both sides dearly, conditions at the mines became among the best in the country. Management told the miners that if this kind of actions were continued, the mines would eventually close. But it was simply a lack of viable ore to be mined that finally forced the mines' closure in 1962.