Hard Rock Milling Interpretation Sign Juneau-Douglas City Museum ~ Juneau, Alaska
Excuse the photo...had to take from side due to glares.
There are many mines & prospects in the Juneau Gold Belt. The hard rock miners working in those mines extracted ore from underground tunnels.
The ore was collected in carts & transported above ground to be processed. The ore was sorted to separate the host quartz & diorite rocks containing gold from the schist & basalt waste rock. The remaining large boulders & rocks were grounded into fine particles. Gold, Silver, & other metals could then be separated using extraction methods such as gravity separation, chlorination, & cyanidation.
Every operating mine had a mill, tailored to the character of its ore & to the available technology. Two of the largest & most profitable were the Treadwell, located on Douglas Island, & the Alaska-Juneau, located in Juneau on the mainland. They used different methods of grinding the ore & are described below.
Four mines operated within the Treadwell Mine Complex on Douglas Island: the Treadwell Mine, the 700-Foot Mine, the Alaska Mexican Mine & the Ready Bullion Mine. A test mill with 5 stamps was used to determine the quality of the ore in the Paris Lode which would become what we refer to as the Glory Hole today. Treadwell's original 5-stamp can still be viewed at the entrance to the Treadwell Historic Trail on Douglas Island.
Each of the mines within the complex had their own stamp mills. At the Alaska Mexican Mine, the first 60-stamp mill was built & began operation in 1893. By 1896 the mill was expanded to operate 120 stamps. In 1898, the Foot Mine built a mill with 100 stamps & the a 120-stamp was built at Ready Bullion Site.
The largest of them all, & in its day the largest in the world, was the 300-stamp mill constructed at the Treadwell Mine site. The mill was 3040 feet long & 85 feet wide. Treadwell's 300=stamp mill could handle 2,700 tons of ore each day.
Initially, each mill ran seasonally, running on waterpower using Pelton water wheels. Later, steam plants were introduced into the mills so they could operate year-round. In 1898, hydroelectric plant, called the 240Plant, was constructed to power the mills. It was fed by water in the Treadwell Ditch which was initially constructed to feed water into the water wheels. The series of ditch lines ran approximately 18 miles from the backside of Mount Anderson, near the Eaglecrest Ski Area, to Treadwell, collecting water from various creeks, including: Fish, Eagle, Cowee, Lawson, Paris, Ready Bullion, & Bullion.
By 1900 there were 880 stamps running at the Treadwell Mine Complex 24 hours a day, 363 days a year.
Stamp mills are large & complex pieces of machinery. However, their job is simple. Stamp mills crush rock into sand, finer than beach sand, allowing gold, silver, & any other metal to drop free. Each of the 880 stamps at Treadwell were powered by hydropower, weighed approximately 1,050 pounds (476 kg), & dropped about 95 times per minute, pulverizing the stone. In 1911, the Treadwell Mine along milled, 1.3 million tons of ore. The stamps were used until the complex ceased operation in 1921.
Ball Mill at Alaska-Juneau Mine
Early in its operation, the Alaska-Juneau (AJ) Mine used stamp mills to crush ore. Its original 3-stamp mill in the Silver Bow Basin operated between 1896-1912. Between 1913 & 1914, the president of the mine Frederick W. Bradley constructed a 50-stamp pilot mill above South Franklin Street to test different recovery & sorting methods. The pilot mill took advantage of the mountainside & gravity to create a step-down processing line.
In 1915, plans for a new mill were begun under the advisement of J.H. Mackenzie, the AJ's consultant engineer. The design for the mill was completed by George O. Bradly of the Utah Copper Company. The AJ Ball Mill began operation in 1917. Initially the ball mill was unsuccessful, only averaging 1,200 tons of ore daily instead of the expected 8,000 tons per day.
Over the next 14 years the process was improved & adapted for the low grade ore being taken out of Mount Roberts & transported almost two miles from the inland AJ Mine site to AJ Mill. A course crushing floor was added at the beginning of the process to help reduce the load on the fine grinding units. The mill also reintroduced hand sorting so that the only white quartz ore was sent into the mills & the black schist waste rock was discarded .Though not exclusively, the rock sorters were often Filipino decent. The mill did not operate at a profit until 1928.
The AJ continued to be a successful operation through the 1940s until labor shortages due to World War 11 & union disputes closed the mine in 1944. The mill was an iconic Juneau Landmark on the side of Mount Roberts until it burned down in the 1960s, though remnants of the mill can still be seen on the mountain.
Like stamp mills, ball mills have the same simple goal of grinding the ore. Ball mills vary in size from large-scale operation to small table-top tumblers. No mater their size, ball mills utilize a rotational motion to move the mill balls & rock within a cylinder. As the mill balls & ore circulate within the cylinder the rock is crushed & ground into smaller & smaller pieces. This process is much quieter than stamp mills & their implementation dramatically changed the audio-landscape of Juneau.
Hard Rock Milling Interpretation Sign Juneau-Douglas City Museum ~ Juneau, Alaska
Excuse the photo...had to take from side due to glares.
There are many mines & prospects in the Juneau Gold Belt. The hard rock miners working in those mines extracted ore from underground tunnels.
The ore was collected in carts & transported above ground to be processed. The ore was sorted to separate the host quartz & diorite rocks containing gold from the schist & basalt waste rock. The remaining large boulders & rocks were grounded into fine particles. Gold, Silver, & other metals could then be separated using extraction methods such as gravity separation, chlorination, & cyanidation.
Every operating mine had a mill, tailored to the character of its ore & to the available technology. Two of the largest & most profitable were the Treadwell, located on Douglas Island, & the Alaska-Juneau, located in Juneau on the mainland. They used different methods of grinding the ore & are described below.
Four mines operated within the Treadwell Mine Complex on Douglas Island: the Treadwell Mine, the 700-Foot Mine, the Alaska Mexican Mine & the Ready Bullion Mine. A test mill with 5 stamps was used to determine the quality of the ore in the Paris Lode which would become what we refer to as the Glory Hole today. Treadwell's original 5-stamp can still be viewed at the entrance to the Treadwell Historic Trail on Douglas Island.
Each of the mines within the complex had their own stamp mills. At the Alaska Mexican Mine, the first 60-stamp mill was built & began operation in 1893. By 1896 the mill was expanded to operate 120 stamps. In 1898, the Foot Mine built a mill with 100 stamps & the a 120-stamp was built at Ready Bullion Site.
The largest of them all, & in its day the largest in the world, was the 300-stamp mill constructed at the Treadwell Mine site. The mill was 3040 feet long & 85 feet wide. Treadwell's 300=stamp mill could handle 2,700 tons of ore each day.
Initially, each mill ran seasonally, running on waterpower using Pelton water wheels. Later, steam plants were introduced into the mills so they could operate year-round. In 1898, hydroelectric plant, called the 240Plant, was constructed to power the mills. It was fed by water in the Treadwell Ditch which was initially constructed to feed water into the water wheels. The series of ditch lines ran approximately 18 miles from the backside of Mount Anderson, near the Eaglecrest Ski Area, to Treadwell, collecting water from various creeks, including: Fish, Eagle, Cowee, Lawson, Paris, Ready Bullion, & Bullion.
By 1900 there were 880 stamps running at the Treadwell Mine Complex 24 hours a day, 363 days a year.
Stamp mills are large & complex pieces of machinery. However, their job is simple. Stamp mills crush rock into sand, finer than beach sand, allowing gold, silver, & any other metal to drop free. Each of the 880 stamps at Treadwell were powered by hydropower, weighed approximately 1,050 pounds (476 kg), & dropped about 95 times per minute, pulverizing the stone. In 1911, the Treadwell Mine along milled, 1.3 million tons of ore. The stamps were used until the complex ceased operation in 1921.
Ball Mill at Alaska-Juneau Mine
Early in its operation, the Alaska-Juneau (AJ) Mine used stamp mills to crush ore. Its original 3-stamp mill in the Silver Bow Basin operated between 1896-1912. Between 1913 & 1914, the president of the mine Frederick W. Bradley constructed a 50-stamp pilot mill above South Franklin Street to test different recovery & sorting methods. The pilot mill took advantage of the mountainside & gravity to create a step-down processing line.
In 1915, plans for a new mill were begun under the advisement of J.H. Mackenzie, the AJ's consultant engineer. The design for the mill was completed by George O. Bradly of the Utah Copper Company. The AJ Ball Mill began operation in 1917. Initially the ball mill was unsuccessful, only averaging 1,200 tons of ore daily instead of the expected 8,000 tons per day.
Over the next 14 years the process was improved & adapted for the low grade ore being taken out of Mount Roberts & transported almost two miles from the inland AJ Mine site to AJ Mill. A course crushing floor was added at the beginning of the process to help reduce the load on the fine grinding units. The mill also reintroduced hand sorting so that the only white quartz ore was sent into the mills & the black schist waste rock was discarded .Though not exclusively, the rock sorters were often Filipino decent. The mill did not operate at a profit until 1928.
The AJ continued to be a successful operation through the 1940s until labor shortages due to World War 11 & union disputes closed the mine in 1944. The mill was an iconic Juneau Landmark on the side of Mount Roberts until it burned down in the 1960s, though remnants of the mill can still be seen on the mountain.
Like stamp mills, ball mills have the same simple goal of grinding the ore. Ball mills vary in size from large-scale operation to small table-top tumblers. No mater their size, ball mills utilize a rotational motion to move the mill balls & rock within a cylinder. As the mill balls & ore circulate within the cylinder the rock is crushed & ground into smaller & smaller pieces. This process is much quieter than stamp mills & their implementation dramatically changed the audio-landscape of Juneau.