The mill was known as the Horwood Lumber Co Pulp Mill.
It was built between 1911 and 1913 by the Horwood Lumber Company because of an increase in price for pulp in American markets. In the spring of 1915 and again in 1916 the dam had broke. After the 2nd time the Horwood Lumber Co, closed the mill due to the low price of pulp.
The concrete builting is the powerhouse which is the only thing remaining. It was built reinforced concrete walls and structural supports, and would have had a roof made from wooden slabs. Connected to the powerhouse was a large 100 meter long, 3 meter wide circular penstock that directed water into a large room causing two turbines to rotate inside. The turbines were directly connected to three turbines in the mill next door via a long horizontal shaft that remains there today.
This information and more can be found at http://www.hiddennewfoundland.ca/campbellton-pulp-mill