Galena Curves Earthcache EarthCache
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Terrain:
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Size: 
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in our disclaimer.
As an earthcache, there is no “box” or “container” to discover. Rather, with this cache, you discover something about the geology of the area. For more info, consult www.earthcache.org
For paperless cachers, the logging requirements are at the beginning of the description.
There is a trail map / geological brochure to the self-guided trail at the trailhead, though at times, the box runs empty. I would suggest printing out the following brochure to assist in your geological discovery.
(visit link)
The trail is uneven and narrow, therefore not handicap accessible.
Logging Requirements:
Send the answers to #1-#6 to me through my geocaching profile. DO NOT post the answers to any logging requirements on this site.
1. List the name “GC**** Galena Curves Earthcache” in the first line of your email. Also, list the number of people in your group.
2. Which direction is the anticline headed at point #5?
3. What direction is the syncline headed at point #6?
4. Based on your viewing at points 5 & 6, how would you define anticline and syncline?
5. Which point (give me a #) best shows the contact area where the galena vein was once located?
6. At which point (give me a #) did you seen quartz, the milky white indicator mineral?
7. (Now considered optional by GC.com) Post a picture of yourself and/or your GPS with your log that shows you at one of the stops (a number in the pic would be nice). DO NOT show any of the pertinent information in your picture!
I will only respond if you have incomplete logging requirements. Go ahead and log your cache
Geology:
Pequea Silver Mine is located 4 miles south of Lancaster along the Pequea Creek. Silver occurs in galena which is concentrated in quartz veins and along joints in the Vintage dolomite just below the Conestoga phyllitic limestone. The Pequea silver mine was worked from before the Revolutionary War to 1875. A minor amount of mining was done about 1900.
Galena deposits often contain significant amounts of silver as included silver sulfide mineral phases or as limited solid solution within the galena structure. These argentiferous galenas have long been the most important ore of silver in mining.
The Pequea silver mine, is a well-exposed case study of structural and hydrothermal localization of ore bodies, The ore that was mined here is termed argentiferous galena and it was "hosted" by quartz veins in Cambrian Vintage dolomite just below its contact with Cambrian-Ordovician Conestoga phyllite. In other words, just below the "line" between the two rock layers, there is visible quartz, and when miners saw this quartz, they knew that the main ore body was close at hand, since the quartz was an "indicator mineral" for the presence of this ore.
The ore filled in the space in the double thurst fault that occurs from here to the south 1.2 miles. The impermeable phyllite (the lower rock layer) made it possible for the ore (in solution) to collect UNDER the folds and ABOVE the phyllite, in "veins."
Walking the trail (there are metal numbers attached to the rock):
Stops 3 through 8 follow the ore veins through several folds that crop out in the valley wall. These include two upfolds, or anticlines, separated by a downfold, or syncline. Stop 3 is probably the best surface location for viewing both the upper and lower ore veins. (The cross section of Figure 4 includes this location as its upper portion.) At this stop, the lowest place on the south wall of the cut exposes Vintage dolomite overlain by Conestoga phyllite. The top of the cut exposes a bit of the upper dolomite. Here, the path is in the excavated mass of that upper dolomite, visible in the gopher hole along with its north-dipping cover of black Conestoga phyllite. The gopher hole connects with the rear portion of the mine, note that the
dip of the beds is toward the north, similar to that of the mine adit indicating our location on the north limb of the northernmost fold, an anticline
Detailed Geology:
In Cambrian times this area was the edge of an ancient ocean. The city of Lancaster lay at the edge of a great limestone bank, somewhat like the barrier reefs of Australia today. North of Lancaster the thick bedded, shallow water limestones, we see today, were deposited in the quiet marine backwaters. To the south of Lancaster, are the thin-bedded sandy and muddy limestones and black shales of the Conestoga Formation. These are the continental slope deposits of material washed or collapsed into deeper water from off the limestone bank. Along Silver Mine Road is an outcrop of one of the submarine slide materials. This contains boulders of the shallow water limestones which slid off the bank and down the submarine slope into this area. The Vintage Dolomite constitutes the shallow water deposits which were later overwhelmed and covered by the black shales and limestones of the Conestoga Formation. The deeper ocean waters were rather stagnant so that organic carbon was preserved to cause the deep blue color of the Conestoga limestones and the black color of its shales. The stagnant waters also preserved some of the sulphur, iron, lead, zinc, and silver collected by primitive animals living in those seas. This is probably the original source for the pyrite cubes (iron sulfide) that occur throughout the area, as well as the ore minerals.
Around the mine, the most abundant mineral is milky white vein quartz, the host material for the ore. The chief ore was galena, a lead sulfide. Characteristics for its identification: a silvery metallic luster and a fracture or cleavage into tiny cubes. Galena from this mine included a large number of silver atom. These silver atoms warped the crystal structure and caused pronounced curvature of the galena’s cleavage surfaces. When the Pequea ore was smelted, a significant amount of silver was also recovered. Analyses are reported to have included 10 to 16 ounces of silver to the ton, or about $50 per ton at present prices. Unfortunately for modern mineral collectors, the mine was so thoroughly worked in its day and the old dumps were so thoroughly picked over by later mineral collectors that finding even a tiny fragment of galena is now quite rare. Small amounts of sphalerite (zinc sulfide) also occur in the ore.
The two most abundant host or country rocks are: (1) massive, light gray dolomite of the Vintage Formation (Dolomite is a magnesium-rich limestone.) and (2) black, limey phyllites and limestones of the Conestoga Formation (Phyllite is a recrystallized shale.) Both formations were deposited in the sea between about 500 and 450 million years ago. From about 450 to 250 million years ago these dolomite and shale formations were folded and fractured at great depth. During this time hot waters moved through them to emplace the quartz and galena. During deformation, the dolomite was brittle and fractured to provide openings for the hot waters whereas the shale flowed and acted as a seal. For this reason the galena bearing quartz veins are now concentrated in the dolomite where the hot waters were trapped just beneath the impermeable shale cover. Since that time erosion has removed the former mountains to expose these deeper roots of the once mighty Appalachians.
History/Extraneous Information:
“The existence of ore in the Pequea area was known in colonial times, but the bulk of the workings visible today probably dates from around the time of the Civil War. An 1863 stock prospectus for the “Lancaster Lead Company” was issued in an attempt to raise $250,000 to begin major mine operations. Extensive and ongoing exploration in 1863 by the sinking of a number of surface shafts was described in the prospectus, but no mention was made of the main underground workings or of the open-cut excavations. Only the northerly dip or inclination of the veins was mentioned, indicating that folding had not been recognized as of that date. Apparently, the stock was sold and most of the present underground workings as well as the surface strip mining around the folds were completed soon thereafter, possibly as part of the lead supply for Civil War musket balls.” (DCNR pamphlet v 36.1 online PDF)
Congrads to MidnightsRaiders on FTF (First to Finish logging requirements) on 9/18/2011.
Resources:
(visit link)
Additional Hints
(Decrypt)
Uvxr pbhagre pybpxjvfr (jvqr genvy "ebnq" svefg)