From a series of articles that appeared in the Pottsville Republican and Herald in 1997:
The Gilberton Colliery was locate on the north side of the Mahanoy Creek in the borough for which it was named.
On June 28, 1862, Kendrick and Tyson were granted a lease on the property and drove a water-level tunnel 250 feet north to the south dip Mammoth Vein and later sank a slope on that vein 300 feet to the first level.
In 1864, Kendrick and Tyson sold the colliery to the Gilberton Coal Company, H. K. Smith & Company, for $200,000.
Gilberton Coal sank a tender slope adjoining the hoisting slope and drove gangways east and west.
in 1867, the gangways had been advanced 1,500 feet when they failed. The colliery was placed in the hands of receivers, who continued mining until January 1870, when the company re-organized.
With new capital, it resumed operations by extending the two slopes 330 feet to the second level and making $300,000 in improvements.
Miners drove the east and west gangways until 1875, when they reached their boundaries. Mining continues until 1879, when the operation failed and the Philadelphia & Reading Coal & Iron Company purchased the colliery at a sheriff’s sale.
In 1884, the Philadelphia & Reading Coal Company drove a tunnel north from the second level Mammoth gangway 195 feet to the Buck Mountain Vein, and gangways were driven east and west. A breast was driven in line with the old Buck Mountain Furnace colliery slope with the intention of extending the slope to a lower level.
The first level of Gilberton Colliery and the Furnace Colliery were then consolidated.
In 1877, the Gilberton Buck Mountain slope was sunk to a third level — a distance of 1,239 feet — and in 1894, the tender slope was sunk to the same level.
In 1889, the tender slope on the Mammoth Vein was extended to the third level for drainage purposes.
In 1896, the Gilberton water shaft was sunk, 1,070 feet to a vein underlying Buck Mountain. A tunnel was driven south 767 feet across the basin connecting the Draper Colliery works with the water shaft, which began to operate March 30, 1898.
In 1910, the Buck Mountain slopes were sunk to the sixth level.
In 1911, the old abandoned Laurel Ridge Colliery slopes were reopened and made a section of Gilberton Colliery as the No. 1 and No. 2 Skidmore slopes.
In 1913, a new breaker was put into operation and the No. 1 slope was sunk 480 feet to the second level.
The total amount of coal from the Gilberton Colliery up to 1928 was 8,243,296 tons.
The colliery was closed November 10, 1938.
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Article by Frank Blase, Historian, Reading Anthracite Company Historical Library, Pottsville Republican & Herald, October 8, 1997.
Corrections and additional information should be added as comments to this post.