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Minerals
Social climber
The Deli
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Yeah, we like to open a lot of cans around here, but this is one that I would like to wait on. There is some rather heated controversy going on these days with regard to how plutons form, complete with blatant attacks. I just don’t want to get myself in trouble. But don’t worry, there isn’t much that I’d rather discuss than the geology of Tuolumne Meadows, especially when there are folks who are interested and will listen!
I didn’t see that you added a second paragraph to your above post at first.
“…working on a scheelite-bearing Skarn deposit outside of Mina, NV (Gunmetal mine).”
NO WAY!!! Now you’re talkin’!!! I LOVE that area! It’s my county! Mineral County! Mina, Luning, and Soda Springs Valley… all of that area east of Hawthorne – it’s so cool out there. Need to get back soon! Spent a bunch of nights at the old Dunham Mill site (below Gunmetal mine) last winter and checked out the Desert Scheelite mine and Good Hope mine. I didn’t make it all the way up the hill to the Gunmetal mine – need one of my dirt bikes for that!
You gotta love skarns… and all of the cool minerals that form when magma intrudes limestone (Luning formation in this case) and cooks the piss out of it! There’s more garnet than a sandpaper manufacturer knows what to do with! We have so many skarn deposits here in Nevada, and no shortage of old mines that exploited them. I love it!
From Geology and Mineral Deposits of Mineral County, Nevada, by Donald C. Ross, 1961, p. 74:
“The Gunmetal mine near the east base of the Pilot Mountains and some of the mines of the Santa Fe district (T. 8 N., R. 35 E.) have had production, chiefly during and after WWII. These properties are developed in scheelite-bearing tactite bodies which formed from limestone along or near contacts with granitic rock. Most are low-grade deposits, but locally they contain ore that averages 1 percent or more of WO3.”
(tactite = older term for skarn, for those who don’t know)
Scheelite:
http://en.wikipedia.org/wiki/Scheelite
WHAT…? Mines are dangerous???
Chrysocolla (hydrated copper silicate), Desert Scheelite mine
Chrysocolla:
http://en.wikipedia.org/wiki/Chrysocolla
The view east: Mine dump and Kibby Flat, from Desert Scheelite mine
Look familiar, Tradster?
Hey Tradster, that is a cool image! So, the image covers 360° of the borehole walls? Minor faults? What do you see in that image?
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Jaybro
Social climber
Wolf City, Wyoming
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You guys is lax on yer Forams! would ostracods, or conodonts be better?
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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The view east: Mine dump and Kibby Flat, from Desert Scheelite mine
Look familiar, Tradster?
Minerals: looks familiar in that your photo is typical of basin & range terrain with alluvial fans & playa lake but it was so long ago I couldn't say if I've been to that particular area. What I recall is that when we were UV lampin' the outcrops near the Gunmetal mine at night you could see the lights of Tonopah off in the distance to the southeast. The mine was an hour commute on gravel roads east of Mina where we were staying. Here's the location of the Gunmetal mine on a Google map.
I was working with a mining geologist from Missoula, Montana who had done 2 tours of duty as a marine in Nam. He was intense...heavy drinker and chain smoker. He had his vices & I had mine. I respected him for serving even though I opposed the war. Anyway the adit to the mine was located right on a contact between granite and limestone. The contact metamorphic zone or skarn consisted of a solid layer of garnets several feet thick that contained scheelite & molybdenite. I wish I had photos from back then but I didn't even own a camera. It was a summer job while I was in grad school at UC Davis.
Have you ever been in the Pine Creek mine?
Hey Tradster, that is a cool image! So, the image covers 360° of the borehole walls? Minor faults? What do you see in that image?
Yes the image covers 360 degrees. It shows relatively flat lying interbedded siltstone and claystone offset by a steep NW-dipping fault with minor offset. The steep fault forms a sinusoid pattern on the image and the bottom of the sinusoid points in the direction of the dip azimuth (NW). If it was a vertical fault and the borheole was vertical, the pattern would be 2 parallel lines. If you know the borehole diameter(6")you can estimate the dip magnitude using simple trigonometry (i.e. the vertical distance between the top & bottom of the sinusoid (~30")form 1 leg of a right triangle and the borehole diameter forms the other leg). It appears to be a high angle (arctan of 30/6 = 79 degrees)reverse fault because the beds are lower in the foot wall than the hanging wall...correct?
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Jaybro: bring it on...how about some diatoms, radiolarians
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Jaybro
Social climber
Wolf City, Wyoming
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Let me check the pelagic, and get back to you...
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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While you're down there check the biogenic ooze
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brotherbbock
Trad climber
Alta Loma, CA
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It is obviosly Schmegmatite.
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sgarlick
climber
North Conway, NH
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Wow, great thread and amazing photos!
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Jaybro
Social climber
Wolf City, Wyoming
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I favor the globigerinal ooze, part...
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guyman
Trad climber
Moorpark, CA.
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Cool can o worms opened up here.
Dipper, The second photo looks like the stone at New Jack City, a popular destination for supertopians...... :>)
And Minerals, please keep up with the info, I really like studying the stone.
Have you seen the "Sand Stone Intrusion" on Power Dome at Courtwright Res?
Just wondering.
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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here are some examples of biogenic ooze that was deformed during subduction
subduction is friction between the sheets that can lead to orogeny
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Mighty Hiker
climber
Vancouver, B.C.
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Yaaaaaay! More geoporn. And not a creationist or politician to be seen.
I worked in geological exploration a few summers, so can sort of follow it.
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Yes the Pine Creek mine (also a skarn deposit) is located off HWY 395 near Bishop. When I visited the mine we rode for a couple of miles in an ore cart until there was ~8,000 ft of rock above us.
There's only 3 things in a mine...rock, steel, & flesh...flesh always loses out.
Yes, the folded Franciscan chert in the photos above is most likely soft sediment deformation.
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50
climber
Stumptown
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Tradster - Great photos of the ooze. Looks like the California coast. Possibly the Son-o-ma Beach area north of San Francisco?
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Exactly right 50...the annotations on those photos are, of course, intended to be humorous.
As you know Franciscan knockers make good sea stacks.
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jfailing
Trad climber
A trailer park in the Sierras
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Sweet thread - anyone ever scoped the Poleta Formation? I mapped part of this sucker for my senior exit requirement at UCSC. It is a complicated maze of multi-generational folding and faulting - chaotic enough to tear your hair out...
Tradster - I love that quote, though I've always known it simply as "They say that subduction leads to orogeny..." Also, where is the entrance to the Pine Creek mine? I climb up there all the time - it's interesting to note the series of paved sidewalk terrace things from the old mining days. I think you can see them on google earth.
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dipper
climber
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Topic Author's Reply - Jan 6, 2010 - 01:45am PT
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Thanks for all the info on the rocks.
For the fools amongst us, like myself, that want to learn it, can you mark your made up stuff as humorous?, so I know what to attempt to commit to memory and what to have a chuckle over.
Here are some dikes. Is the goo that filled the cracks aplite? I saw that term mentioned above.
Is that similar to plagioclase feldspar? Forgive my spelling and thanks for all the insights.
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BASE104
climber
An Oil Field
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God, if you want to hear some horror storys of difficult geology, I got em. They all involve wasting a very large amount of money. But we always blame the engineers.
And there are places that are so chopped up that they make those folds in the picture above downright friendly.
Those shiny things in the lava tubes look like casts of something smooth...like a gas.
You see that stuff all the time in turbidite outcrops. Not vesicles, but flute marks. Tells you which way the flow direction came from.
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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jfailing - the Pine Creek mine is an enormous mine that can only be accessed by permission and escort from the mining company that operates it. Not sure if it's still active. When I was there in the late-1970s on an economic geology field trip from UC Davis I think Union Carbide operated the mine.
Many schools hold their field camp in the Poleta Folds area...the geology there is so complicated it challenges anyone who tries to make sense of the chaos.
I did my field camp in the northern foothills of the Avawatz Mts, south of Death Valley National Monument. We mapped a deformed sequence of Quaternary deposits that formed the flanks of a fault bounded anticlinal structure with a pre-Cambrian granite-gneiss core. This is a tectonically active area with vertically dipping Quaternary playa lake and evaporite deposits situated at the convergence of the Death Valley and Garlock fault zones.
Vertically-dipping Quaternary alluvial fan deposits
Quaternary playa lake & evaporites in the foreground and light colored, pre-Cambrian granite-gneiss at about the middle of the photo. The view is looking north into Death Valley from the foothills of the Avawatz Mts.
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jfailing
Trad climber
A trailer park in the Sierras
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BASE - so what's the most structurally complex area you've dealt with? Expensive eh? Sounds like oil... I did some mudlogging in Elk Hills near Bako - not too structurally difficult, but cool stratigraphy!
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