Northwestern Fissure Mine

Northwestern Fissure mine, Keweenaw, MIKeweenaw County, Michigan - In 1845 the Northwestern Mining Company was organized, and work began on a fissure vein south of the greenstone, bearing N 23 degrees W and dipping slightly to the west. 1 A second vein was discovered 100 feet west of the main Slawson vein.

Copper mining continued in a small way for two years, with the vein widening to an average 1.5 feet in width (and later to 4 feet) the deeper they went.

Northwestern Fissure Mine PDF slideshow by PNGincIn 1845 the company was reorganized as the Northwestern Mining Company, and work at the mine shifted to high gear. A 1,250-foot adit was driven in from the south all the way to the greenstone. Over a four-year period, a workforce of 60 miners deepened four shafts to a maximum depth of 215 feet.

A stamp mill was built in 1852, using both pumped mine water & a branch of the Eagle River for washing. At the northernmost shaft #4 there was a hoisting engine with winding machinery.

By 1853 the company had their own sawmill & employed 80 miners. The mineral mined yielded 72.2 per cent or 44,166 pounds of refined copper.

In 1854 the mine produced 139 barrels of stamp copper, 96 barrels of barrel rock, 99 masses (129,794 pounds) for a total mineral amount of 250,763 pounds. After smelting, copper ingots weighed 154,900 pounds. At 25 cents per pound, this brought in around $39,000.

However, expenses outweighed copper sold, so the company ended the year with a $16,500 debt. And no matter what the subsequent improvements in technical capacity, or the amount of assessments made to stockholders, the company just couldn’t continue. In 1857 all work was suspended.

A brief period of activity aimed at exploration of the Central vein on the property ended with deeper debt & operations were again suspended in 1865.

Total recorded production amounted to 313,000 pounds.  Total assessments were listed as $228,000.

Northwestern Mine Workings


Depth/Length (feet)

No. 1


No. 2


No. 3


No. 4


Adit level



 1 Annual Report of the Commissioner of Mineral Statistics for 1880 – Page 20 of 133

 2 USGS Professional Paper 144 Butler & Burbank pp 223-233,  FISSURE DEPOSITS


Northwestern fissure, abandoned mine, Keweenaw copper, district heating, geothermal storage, solar turbogenerator, renewable energy, Ken Rieli

Phoenix Navigation & Guidance Inc.

[Copper Country Mines]