The Empire strikes back EarthCache

This cache has been archived.

Geocaching HQ Admin: It has now been over 30 days since Geocaching HQ submitted the disabled log below and, unfortunately, the cache owner has not posted an Owner maintenance log and re-enabled this geocache. As a result, we are now archiving this cache page.

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Hidden : 4/23/2008
Difficulty:
1.5 out of 5
Terrain:
1.5 out of 5

Size: Size: other (other)

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Geocache Description:


Empire Mine State Historic Park is the site of one of the oldest, largest, deepest, longest and richest gold mines in California. In existence for more than 100 years, the mine produced 5.6 million ounces of gold before it closed in 1956. (5.6 million ounces of gold is equivalent to a box seven feet long, seven feet high, and seven feet deep filled with gold.) It is estimated that this represented only 20% of the available gold...80% remains.

By the time of the mine in 1956, an incline depth of 11,007 ft. had been reached. The 367 miles of shafts, drifts,and large caverned-out scopes were fully electrified, continually pumped, and renowned for maintaining a phenomenal degree of personal safety. It was a good mine to work in and a recognized training for every phase of mining.

The Empire Mines are part of the Grass Valley mining district with the following geologic features: an elongated body of granodiorite is in the central portion of the district. This body is five miles long in a north-south direction and 1/2 to two miles wide. It is intrusive into older metamorphic rocks and itself is cut by various dike rocks. Immediately east and west of the intrusion arc dark greenstones classified as metadiabase and metadiabase porphyry (so-called "porphyrites"), and continuing to the northeast are amphibolite schist, serpentine, gabbro and diorite, and slate. Just north of the granodiorite and to the southwest are slates, phyllite, quartzite, and schist of the Calaveras Formation (Carboniferous to Permian). A number of intermediate to basic dikes are present also, as well as a few aplite and granite porphyry dikes. Overlying part of the district to the east and to the northwest are Tertiary gravels, in turn largely overlain by andesite.

This is the most heavily mineralized and richest gold district in the state with a very large number of productive veins in a relatively small area. The veins fall into two major groups: 1) those of the granodiorite-greenstone area, which have gentle dips, and 2) those of the serpentine-amphibolite area, with steep dips. The veins of the granodiorite area are either in the granodiorite or in the adjacent greenstone, entering the granodiorite at depth. One group of veins strikes north and dips gently (about 35' on the average) either east or west.

The veins usually range from one to 10 feet in thickness and consist of quartz with some calcite and ankerite. They fill minor thrust faults. Many veins contain several generations of quartz. There are numerous northeast-striking, vertical or steeply-dipping fractures or "crossings" that commonly are boundaries of ore shoots. The' ore contains free sold and varying amounts of sulfides, chiefly pyrite. Present in smaller amounts are galena, chalcopyrite, arsenopyrite, sphalerite, and pyrrhotite. Galena is commonly associated with gold.

To log this cache, answer the following questions via email:

( It is not necessary to enter the park to complete the requirements for this earthcache)

1) At N39°12.437 / W121°02.731 describe the object at this location providing some detail as to it's size, diameter, color and purpose.

2) At N39° 12.418 / W121°02.801 What was the price of gold in each of these years: 1854, 1920, 1956 and the current price (the day you visited the park)?

3) Name 3 types of flowers and/or trees located near the park or in the park at the Bourn Gardens.

4) Post a picture of yourself and/or your caching party with your GPS using a part of the park as the background. Be creative!

References:

Tales from the Mines, Oakland Museum of California (visit link)
Empire Mine (visit link)
California State Parks (visit link)

Additional Hints (No hints available.)



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