MJC Geology of the Central Motherlode

The 2013 edition of Modesto Junior College’s Geology of the Central Motherlode Class. Professor Garry Hayes led his students to an above-ground tour of the Kennedy Mine in Jackson, CA and into the depths of California Caverns near San Andreas, CA. The mine was at one time the deepest mine in the world (5,912ft) before getting shuttered during WWII and produced over 1.5 million ounces of gold. The caverns are cut out of marble created by metamorphosed coral reefs that once got scraped onto California 300 million years ago. Enjoy the photos.
First stop of the day - The Ione formation, just outside of, you guessed it, Ione, CA (HWY 88). High water tables have flooded this old quarry that holds 40-50Ma rocks that contain tropical fossils in clay-rich sediments. This was at one time a large delta or swampy floodplain for huge rivers streaming out of what is now Nevada and Idaho before the Sierra Nevada existed. The quarry used the clay for kitty litter. : ione formation Garry had a very captivated audience comprised of many geology newbies. It was great to see so many folks take an interest in their local surroundings. Second stop of the day - The historic Kennedy Mine. At one time the deepest mine in the world. Several of the 6-foot diameter old pulleys that once hoisted ore hoppers to the surface.
Detail of cable pulley. It looks like 2 or 3 inch cable was used on the pulley. A docent from the Kennedy Mine Foundation gave us a great introduction to the mine complex with a short period film that showed how the mining was done. Note the large map of shafts and runs showing the ultimate depth of 5,912 feet! Two gift shop volunteers. I think the furry one is checking to make sure no gold is stuck to its coat. Photo of the entire Kennedy Mine crew from 1914.
Part of the iron head frame that replaced the original wooden frame that burned. Looking up towards the top of the head frame. Another view of the head frame. I rather like this view.
Students model the method used for getting to work thousands of feet below the surface. Records show that more than 9 men fit in this bucket at a time! An ore cart - donkeys would have pulled the carts to the hoists, which were then brought to the surface. The ore hopper at the base of the head frame. Raw ore was filled into larger ore carts and hauled by donkey to the stamp mill 100 yards down a trestle. Ore bucket.
Remnants of the trestle. RJH9932 One final view of the head frame, ore hopper and trestle to the stamp mill. Remnants of the stamp mill. This mill used 100, 1000lb iron drums to pulverize ore into rubble the size of sand. 24hrs a day, seven days a week. The crushed ore was then run over a bed of mercury. GOld in the ore bonded with the mercury to create an amalgam that could be easily harvested.
The 1908 mine offices. The next stop on our trip - Kennedy Tailing Wheels Park. The Kennedy Mine was ordered to keep its polluted slurry of tailings out of the local watersupply and thus had to ship the toxic sludge a half mile away, upa nd over two hills. The solution tog etting the slurry over the hills? These giant tailings elevators. They picked the sludge off the bottom and lifted it 40 feet to a flume. Three wheels were used to get the slurry to the reservoir. this was the last wheel and had been recently enclosed in a new capsule thanks to over $600K in fundraising. Another view of the neat housing unit.
The newly paved trail up to the last tailings wheel. RJH9949 The sludge reservoir. Note the concrete dam in the center of the photo. Most of the tailings were removed and re-processed in the using cyanide to reclaim another $500K. The best stop of the day was our tour of California Caverns.
This would eventually be our exit. Safety first! Time to put on the loaner "hard" hats. This crack in the marble was discovered in 1849. The old courtroom.
Our first view of some of the speleotherms. In a nutshell, when water tables were much higher, underground water that was slightly acidic flowed through and dissolved massive amounts of marble (which was itself the metamorphic remains of 300Ma reefs). Once the water levels dropped and the cave became exposed to air, acidic surface water percolated through the remaining marble and would deposit small amounts of calcite as drops dripped to the floor of the cave. Here's a better sense of scale. Cave drapes. RJH9981
Cave bacon! Yum! Garry helps show scale of the cavern. I don't quite recall the purpose of this room. They all had some old-timey significance. Some of the stalactites that had been broken-off by earlier tourists had actually started to regrow!
Another shot of regenerating soda straws. Cave drapes. Cool! Look at all the brittle soda straws! RJH0013
According to tour-dude, this was the purest stalagmite in the cave. The reason? The jungle room wasn't discovered until the late 1980's and has been managed to do as little harm to the room as possible. Some helectites and stacks of "ice cream" scoops. Calcite peppers? I remembered to take a selfie for once. I look a little thin and pale due to a short but violent illness the previous several days.
One last shot of soda straws. Ok, one really last shot of soda straws. RJH0030 RJH0033
Tour dude shows us a native american "jail" entrance. Apparently several skeletons were discovered in the room. The last stop of the day was at the Carson Hill outcrop near New Melones. We were there to check out the hydrothermally-emplaced quartz. The vein is in the oak shadow, but it contains lots of gold. The metamorphic slates and conglomorates (old sea floor) had the quartz intruded into it nearly 100Ma. And a few cute Zephyr pics to end the trip.
And a few cute Zephyr pics to end the trip. RJH9818 RJH9822 RJH9849
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