Delaware Mine EarthCache

Figure 1. Waste rock pile at the Delaware mine. Photo by Paul T. Brandes
 

Cache Coordinates: N 47° 25.410 W 088° 06.121

EarthCache Lesson: 

Why is there copper in the Keweenaw Peninsula?
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, geologist call this 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).
 

Figure 2. Bedrock Geology Map. This map illustrates where copper conglomerates are located. Source: http://www.dnr.state.mi.us/spacialdatalibrary
 

The fissure deposits are veins along fractures that parallel or cross the beds.
Originally the Delaware mine started as a fissure vein mine.  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.

What are the properties of copper?
Copper is an element and a mineral. Copper would appear red in color on a polished fresh surface and
it would appear dull brown on a tarnished surface due to oxidation. If you were to scrape copper on
a streak plate the streak color would be red. Copper has a metallic luster. Copper is not a hard metal,
ranked 2.5-3 on Mohs hardness scale. Copper could be scraped by a nail, piece of metal or quartz.
However, copper is hard enough that you will not be able to scrape it with your finger nail. If you find
copper in the rock pile it would most likely be irregularly shaped and less than three inches in size.
 
Logging Your Visit: 
To obtain credit for visiting this EarthCache, please email me a brief response to the following questions:
1. Left over from mining are piles of rocks with little mineral value called poor rocks. Look through
the poor rock pile and describe the rocks you find there. Include the size range and color of the
rocks.
2. See you if can find copper in the pile using the information about copper’s properties. How will
you know if you have found copper?
3. Find another mineral from the rock pile that is not copper. How do you know it’s not copper?
How are its properties different from copper?

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Earth Science 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

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Earth Science Literacy Principles Big Ideas
Big Idea number 3- Earth is a complex system of interacting rock, water, air, and life.
 Visit http://www.earthscienceliteracy.org/es_literacy_22may09.pdf  for more information on the Big Ideas.
 

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Common Earth Science Misconceptions:  A common misconception is that the Earth has always been pretty much the way it is now. This site gives evidence that the Keweenaw Peninsula was drastically different in the past and is changing till this day. Visit http://hub.mspnet.org/media/data/MiTEP_List_of_Common_Geoscience_Misconceptions.pdf?media_000000007297.pdf for more information on Common Earth Science Misconceptions.
 

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The owner of this cache is a participant in the Michigan Teaching Excellence Program (MITEP) through Michigan Technological University, which teams with science teachers to improve science teaching and learning.

This work was supported by the National Science Foundation award # 0831948
 

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References:
Brandes, P. (2008) Geology of the Keweenaw Peninsula, Michigan.   Retrieved July 28^th ,2011 from http://www.mindat.org/article.php/255/GeologyoftheKeweenawPeninsula
 
 Brandes, P. (Photographer). (2009) Photo of waste rock piles at Delaware mine.  Retrieved July 28^th ,2011 from: http://www.mindat.org/photo-248417.html
 
Geology.com (2012) Copper Mineral Properties. Retrieved November 20^th, 2012 from: http://geology.com/minerals/copper.shtml
 
 Rose, B. (2011) MiTep ESI. Retrieved July 28^th ,2011 fromhttp://www.geo.mtu.edu/~raman/SilverI/MiTEP_ESI-1/Welcome.html
 
 Schaetzl, R. (n.d.)  Michigan’s Copper Deposits and Mining. Retrieved July 28^th,2011  from http://www.geo.msu.edu/geogmich/copper.html