Keweenaw Peninsula EarthCaches 

Delaware Copper Mine EarthCache 

Connection to the Earth Science Curriculum

Essential Lessons:

Why is there copper in the Keweenaw Peninsula?

Earth Science Literacy Principles

Big Idea number 3 – Earth is a complex system of interacting rock, water, air, and life.

Common misconceptions

The Earth has always been pretty much the way it is now.

All rocks are more or less the same (a rock is a rock!).

All bedrock is non-porous material.

Michigan State Science Content Expectations Addressed:

6th grade learning outcomes.

E. SE. 06.12 – Explain how waves, wind, water, and glacier movement, shape and reshape the land surface of the Earth by eroding rock in some areas and depositing sediments in other areas.

Key Geology Vocabulary

Ore - a material that can be economically mined. If you remove the material from the ground you can make a profit.

Mining - removing the ore from the non-ore rock.

Stamp mill - a machine for stamping ore.

Waste rock (poor rock) - all of the material that is left over after you remove the metal from the ore. It has no economic value at this time and so is dumped on a waste pile away from the ore bearing rock.

Fissures vein - a crack in the earth's surface filled with mineral matter.

Amygdaloidal - top layer of a lava flow generally rich in minerals.

Conglomerate - rocks of stone fragments cemented together by a mineral or other substance.

Located in the town of Delaware 12 miles south of Copper Harbor lays a mine that operated from 1847 to 1887 mining the Allouez conglomerate. Eight million pounds of copper were removed from this mine. The mine had 5 shafts that reached a depth of 1400 ft with 10 different levels. As you walk the ground level area of the mine evidence remains of waste discarded by the mine.

Materials needed for your visit:
    GPS and local rock/mineral guide for Michigan

Coordinates: 47° 25.410′N 88° 6.121′W

A Precambrian Midcontinent rift formed around 1.1 billion years ago. Over the next 100 million years layers of volcanic and sedimentary rocks were deposited into the rift valley. Then hot water moved through the rocks filling the open pore spaces with native copper and other minerals. (Hydrothermal mineralization) The copper is commonly found in the permeable layers of conglomerate between the sand and pebbles.

The Keweenaw Peninsula has two types of copper deposits-Lode deposits and fissure deposits. The lode deposits comprise of conglomerate lodes (rocks held together by copper), and amygdaloidal lodes (almond-shaped deposits in the top layer of lava flows)

The fissure deposits are veins along fractures that parallel or cross the beds.

Originally the Delaware mine started by mining a fissure vein. The ground was poor but there was enough copper to continue mining that site. Mining fissures was difficult for the miners to remove the large pieces of copper. Later miners started to mine conglomerate loads because the copper was easier to remove and more consistently found than in the fissure copper lodes. The conglomerate loads could be mined more efficiently with the ore blasted out, taken to the surface and then railroaded to stamp mills.

Even though the conglomerates were rich in copper only about 2% of the ore/ rock hauled to the surface was copper. The remaining rock was called poor rock and set in piles near the mine or hauled away and put to other uses. Another waste product of mining was stamp sand. Stamp sand is still a problem plaguing the Keweenaw Peninsula.


Figure 1 – Tailing pile at the Delaware mine. Waste rock pile at the Delaware mine.

Source: © Paul T. Brandes – Photo ID: 248417


Figure 2 – Bedrock Geology.
This map illustrates where copper conglomerates are located

Logging Question

Describe the types of rock found in the waste rock pile, include color, texture and shape.

What are some possible uses for this type of rock?

Access Information

Owner of site – Tom & Lani Poynter – private

National Park Preserving natural history

References and citations

Brandes, P. (2008) Geology of the Keweenaw Peninsula, Michigan.
Retrieved July 28th, 2011 from Geology of the Keweenaw Peninsula

Brandes, P. (Photographer). (2009) Photo of waste rock piles at Delaware mine.
Retrieved July 28th, 2011 from:

Rose, B. (2011) MiTep ESI.
Retrieved July 28th, 2011 from MiTEP ESI-1

Schaetzl, R. (n.d.) Michigan's Copper Deposits and Mining.
Retrieved July 28th, 2011 from Michigan State University