Showing posts with label route 6. Show all posts
Showing posts with label route 6. Show all posts

Tuesday, April 25, 2017

From the Road: Some Nice Gneiss

Every time I drive Highway 6 between Idaho Springs and Golden, Colorado—and I almost always take that route when heading east, rather than the section of I-70 between Idaho Springs and the hogbacks—I try to get a few photos of the great gneiss forming the canyon walls. If I'm going eastward, it can be hard to stop because I'm almost there. This time, in the fall of last year, I was heading west, but I still found it hard to stop, partly because of traffic and unexpected road work. Nevertheless, I managed to make a few pullouts that were rewarding.

The first shot is typical of the biotite gneiss that underlies much of the region: darker bands with more mafic minerals, and lighter bands composed almost entirely of felsic minerals.
Here's a little more of that same biotite gneiss showing complicated deformation.
The geology of the area, seen below in a cutout from a USGS map, looks a little complex! Our first two photos (the two easternmost dots that are rather close together) are in what is mapped here as Xb: Proterozoic biotite gneiss.
Map courtesy USGS (Kellogg et al, 2008).
A little farther into Clear Creek Canyon, I pulled over and grabbed a couple shots of this second roadcut (single dot to the west, above), primarily because of all the light-colored dikes and masses. These rocks are probably what is mapped as Xh: hornblende-plagioclase gneiss and amphibolite.

All of the rocks we're looking at today are thought to have originated as sedimentary and volcanic rocks that were deposited in a basin 1780 to sometime after 1750 Ma (million years ago), as per this pamphlet accompanying the map.
A shot of the entire roadcut. 
Somewhat darker gneiss is above somewhat lighter gneiss in this roadcut. The darker portions may qualify as amphibolite, which is part of the Xh unit.
The same gneiss, zoomed in a bit.
I noticed what looks like a little folding while I was processing these photos, so I drew in a few lines. The rocks look darker inside the fold nose, and there has been a lot of injection of the light-colored material, which might include felsic dikes like aplite or pegmatite, and also might include some quartz veins. I really don't know how common quartz veins are within these gneisses, and the roadcut is too close to the often busy, narrow and windy, two-laned U.S. Route 6 for safe examination.

If you want to see more of these rocks, here is Robin Rohrback's set of gigapans of the roadcuts along this stretch of Highway 6, along with gigapans of hand samples of the gneiss.

Reference:
Kellogg, K.S., Shroba, R.R., Bryant, Bruce, and Premo, W.R., 2008, Geologic map of the Denver West 30’ x 60’ quadrangle, north-central Colorado: U.S. Geological Survey Scientific Investigations Map 3000, scale 1:100,000, 48-p. pamphlet.

Sunday, November 20, 2016

Links: The Sump, Nevada

This is about as close as I've gotten to The Sump, a place in Nevada that I had never heard of until I was doing some research into stops for our Death Valley trip of last February. And mind you, the declivity I've pointed out in the photo above is just the southern entrance to this apparently intriguing place. Fossils have been found here!

While trying to figure out if The Sump would be a stop along the way or the way back (it wasn't), I collected a few links. Most of the links show only one picture from the place; a few show more. I'll leave it to you to do more investigation (and visitation, I hope!). The links are listed rather randomly. Links about the fossils, in particular, are at the bottom.

The "Sump"—Strange Name but Amazing Place - Backyard Traveler by Richard Moreno

The Sump, Esmeralda County, Nevada - Eastern Mojave Vegetation (schweich.com)

The Sump Canyon paradise - Terry's World (Terry Wright, geologist)

The Sump (Esmeralda County, Nevada) - Weekend Wanderluster

The Fossils:
Hardy, F.C., and Bonde, J., 2015, Stomping Around the Sump: Miocene Pygmy Gomphothere from Esmeralda County, Nevada [also here], in Pennell, W.M., and Garside, L.J., eds., New Concepts and Discoveries: GSN 2015 Symposium Proceedings: Geological Society of Nevada, p. 929-937.

Sand and Bone - a photo slide show (in color): "Go along with a band of UNLV researchers as they uncover the skull of an extinct elephant-like creature that once roamed Esmeralda County."

Photo Essay: In the Footsteps of the Elephant -  VegasSeven (really nice B&W photos)

Friday, June 17, 2016

Friday Field Photo: Cannonball Chert

Back in my eastern Nevada field days, I was lucky enough to go on a stratigraphy tour that took me to several good examples of chert nodules in the mostly Pennsylvanian Ely Limestone.
Nicely spherical chert nodules in the Ely Limestone, with 2.5 lb sledge for scale.
In the 1950s and 1960s, R. A. Breitrick and J. E. Welsh described the detailed stratigraphy of the Ely Limestone in the area of Ely and the Robinson mining district (with Breitrick, at least, continuing to work in the area to this day). They divided the formation into mappable units, W through C, bottom to top. (Their units A and B have since been placed in the overlying Permian Riepe Spring Limestone.) The only summary of this stratigraphy I could find online is shown here (pdf; Maher, 1995, p. 22).

Several units within the Ely, notably units S, R, P, L, and F, contain cannonball cherts (although I'm not sure about the details of units T, U, V, and W: I can't find my field sheets in the mess my office is currently in!). Theses photos are most likely from S, R, or P (my thoughts).
Fairly large, sub-spherical chert nodule.
This is the best example I have of a chert nodule that is approaching "cannonball"  in size and shape. Apparently, cannonball chert nodules can weather out and end up looking a lot like loose cannonballs. An excellent example of a loose cannonball nodule can be seen here [pdf] on page 27 (Maher, 1995, Fig. 7C).

These photos were taken in the spring of 2007 on the northeastern slopes of Rib Hill, a location that might or might not be accessible from Highway 50 or Route 6 via a side road formerly known as S.R. 44 or S.R. 485 (the location might be behind a locked gate).

Tuesday, April 26, 2016

Death Valley Trip, Getting There: Coaldale, Black Rock, Lone Mountain, and the Boss Mine

Onward! Onward! How far will we get this time?
Coaldale, as seen in August, 2010.
With Boundary Peak still in view, MOH and I rounded the corner at Coaldale Junction, and pulled in briefly at Coaldale. This particular ghost town, which was first a small mining town and later a roadside waystation with a tiny population, holds a few minor memories for me, dating back to my early days at Northern Exploration Company in the late 70s and early 80s. For some reason, it always seems like a depressing place to stop, and I can rarely bring myself to take a photograph or to get out of my vehicle to take a close look. This time was no different, so I've uploaded a photo I shot back in 2010.

A few miles on, we pulled in at Black Rock, a spot which may originally have been just a little prospect pit in some black chert of the Ordovician Palmetto Formation, but which is now a semi-convenient place to stretch your legs (although it doesn't really offer much cover as a pit stop, and the Millers rest area and the town of Tonopah aren't too much farther down the road).
Coming to Black Rock from the west, Google Street View.
Lone Mountain as seen from Black Rock, looking ESE.
From the south side of Black Rock, we had a good view of Lone Mountain beyond the playa and salt flat of the southwestern end of Big Smoky Valley. A tiny bit of the Weepah Hills is in shadow off to the right (west).
A closer view of the southwest to northwest side of Lone Mountain.
In this photo, the lighter colored rock formation toward the right (west) is the ЄpЄ Reed Dolomite, which, as I noted earlier, is usually listed as Precambrian or Precambrian to Cambrian, and sometimes as Cambrian only. Here it's on top of a thin, dark section of Precambrian Wyman Formation. Underneath the Wyman, and to the left (east), the Cretaceous Lone Mountain pluton forms the bulk of Lone Mountain.

A couple ways in which the Cretaceous may have intruded the Precambrian so sharply and neatly are developed by Maldonado (1984) in the explanation of his map of the Lone Mountain area. I personally think the contact is structural: a low-angle fault (detachment, anyone?), and, in fact, the area is noted as being part of the Silver Peak-Lone Mountain detachment system (Oldow et al, 1994) or Silver Peak-Lone Mountain extensional (or core) complex (Oldow et al, 2009). Also, this map shows the contact as a detachment fault  (Hulen, 2008, between pages 4 and 5). In the few places that I've seen the Wyman-pluton contact on Lone Mountain, I've noted shearing, faulting, or other complexities—and along the north and west side of Lone Mountain, the top of the pluton looks somewhat planar from a distance, and other planar features (jointing?) are apparent from some angles. If you're driving by, a good place to pull off to see these planar features (I'm really not sure what they are) is at the turnoff to the dirt road going to the northern Gilbert mining district a few miles east of Black Rock  (Google Maps location).
Google Earth image from the perspective of between Black Rock and the turnoff to the northern Gilbert district, and up in the air a bit.
Approximate mapped contacts of the three major rock formations, from Maldonado, 1984.
The same image with a few pink lines added.
I'm not sure what the pink lines represent, other than that they are supposedly entirely within the Lone Mountain pluton. They may be joints in the pluton; they may be Tertiary lamprophyre dikes, as on the 1984 map. Another possibility is that the intrusive-sedimentary contact is mixed, like it is on Mineral Ridge, where Wyman and intrusive rock alternate near or just below the detachment fault (or detachment faults). Or maybe all three possibilities come into play. These are just a few ideas to take with you if you happen to go hiking in the area.

Turning back toward the highway, I stumbled across a few interesting rocks.
Breccia.
The rock is a veined and brecciated chunk of Ordovician Palmetto Formation—chert or siliceous mudstone to siltstone. While walking around, I wondered what the remnant of an old mine dump was all about. Maybe this rock holds a clue.
Here's a zoomed in view of the same rock, focusing in on the quartz vein right and center.
The quartz vein contains brown blades of a relict mineral that has now gone to iron-oxide and silica. Possibly the mineral was calcite, and if so, the resulting mineral or texture is often referred to as "bladed quartz" or "bladed quartz after calcite," or more properly, "quartz [or silica] after bladed calcite." The texture can be indicative that you're in the right part of an epithermal system to find an economic gold or silver deposit. Most of the quartz after calcite I've seen has been crystalline; this silica is microcrystalline.

In fact, several smallish gold deposits have been found in the immediate area, and one has been mined (so far only one deposit has been considered economic).
The Boss mine, a small gold deposit mined in the late 1980s, can be seen just across the road from Black Rock.
A zoomed-in view of the open pit area of the Boss mine.
The Boss produced about 32,000 ounces of gold from 600,000 tons of ore (Diner and Strachan, 1994). That would mean the ore grade was about 0.053 ounces Au per ton (o.p.t). The other deposits, including the Black Rock zone, are described here and here, along with the geology of the Boss mining area. Gold is reported to occur mostly in both Tertiary rhyolites and andesites.

And that will be it for today!

Location map

Related Posts (in order of posting):
Death Valley, "Super" Blooms, Turtlebacks, and Detachments
Death Valley Trip, Part 2: More of the Badwater Turtleback Fault
Death Valley Trip, Part 3: Northward, and over Daylight Pass
Death Valley Trip, Getting There: Wave Clouds beyond the Sierra
Death Valley Trip, Getting There: A Hike to Pleistocene Shorelines

Death Valley Trip, Getting There: Walker Lake, Road Stories, A Bit about Copper, and Some Folds near Luning

Death Valley Trip, Getting There: A Jeep Trail, Folds and Cartoons of Folds, Even More Folds, and Boundary Peak

Death Valley Trip, Getting There: Highway 95, Redlich, Columbus Salt Marsh, and Another View of Boundary Peak

Selected References:
Diner, Y., and Strachan, D.G., 1994, Geology of the Boss mining area, Gilbert district, Esmeralda County, Nevada: Econ. Geology v. 89, no. 5, p. 1176-1182.

Hulen, J.B., 2008, Geology and conceptual modeling of the Silver Peak geothermal prospect, Esmeralda County, Nevada: unpublished report for Sierra Geothermal Power Corporation, 23 p.

Maldonado, Florian, 1984, Bedrock geologic map of the Lone Mountain pluton area, Esmeralda County, Nevada: U.S. Geological Survey Map I-1533, 1:24,000.

Oldow, J.S., Elias, E.A., Ferranti, Luigi, McClelland, W.C., and McIntosh, W.C., 2009, Late Miocene to Pliocene synextensional deposition in fault-bounded basins within the upper plate of the western Silver Peak–Lone Mountain extensional complex, west-central Nevada: Geological Soc. America Special Papers 447, p. 275-312.

Oldow, J.S., Kohler, Gretchen, and Donelick, R.A., 1994, Late Cenozoic extensional transfer in the Walker Lane strike-slip belt, Nevada: Geology v. 22, no. 7, p. 637-640.

Strachan, D.G., 1988, Economic geology and exploration potential of the South Boss prospect, Boss gold mine, Esmeralda County, Nevada: unpublished report on file at Nevada Bur. Mines and Geology, 11 p. and notes.

Tuesday, March 1, 2016

Finding a Thesis: Arriving at Blind Spring Hill

With Mineral Ridge in my rear-view mirror, I stopped briefly at the basalt cinder cone, The Crater, which is located right on the side of the road just a few miles north of Silver Peak. From The Crater, I set my sights on Blind Spring Hill, which was last on my list of thesis possibilities. Blind Spring Hill is a ridge-like hill or small mountain that extends southward from the road between Benton and Benton Hot Springs, CA, and which hosts a small silver mining district, Blind Spring Hill mining district. Blind Spring Hill is about 30 miles north of Bishop, CA, and not far southwest of the California-Nevada state line.It was supposed to be my last stop.

I drove north on old 47 (now S.R. 265) to Blair Junction.
Blair Junction is the intersection between S.R. 265 (old 47) and Route 6 (cosigned with U.S. 95).
I turned left...and said goodbye to Mineral Ridge.
Mineral Ridge, looking south from near Blair Junction.
The domal shape of the Mineral Ridge core complex is easily seen looking south from U.S. 95–U.S. 6 if you're driving east or west along the south end of the Monte Cristo Range between Lone Mountain and Coaldale; in fact, the best angle to see the shape of the core complex really is from right about at Blair Junction, as in the above photo, which I took in 2010 when coming back from a trip to Fish Lake Valley. The pyramidal peak at the top of the dome is upper plate sitting atop of the Mineral Ridge detachment fault, which follows along and just above or just below the overall outline of Mineral Ridge. The fainter mountains seen through a low spot at the right end of Mineral Ridge is part of the Silver Peak Range south of Red Mountain, which is hidden from view at this angle. Rhyolite Ridge, also part of the Silver Peak Range, sits at the farthest right. The low, black hill on the horizon and left of center, almost hidden in the saltbush and shadscale is not The Crater. Rather, it's hill 4833, a low hill located along a paleo-beach in the south part of Big Smoky Valley (USGS TNM location). I've never stopped to check it out., but it might be made of tufa-cemented gravel related to a Pleistocene shoreline, or it could be something within the Tertiary Esmeralda Formation, which is broadly composed of shale, siltstone, and sandstone, with some interbeds of conglomerate, tuff, and tufa.

From Blair Junction, it's a little more than 6 miles to Coaldale Junction, where Highway 95 splits off from this section of conjoined Highway 6 to head north, and Highway 6 continues west toward California.
These old buildings are part of the site of Coaldale, which was active in its day.
Colorful, volcanic hills in the north part of the Silver Peak Range overlook the highway a little west of Coaldale and Coaldale Junction. I've driven by these hills many times but have never stopped. Uranium and coal occur in the area (Albers and Stewart, 1972).
Volcanic rocks south of Highway 6 near Coaldale Junction.
At Coaldale Junction, I turned off the Highway 95-6 combo, to continue west on Highway 6. From there, it's about 19 miles to the California border.

From the NV-CA state line, just north of the north end of the White Mountains, it's 7 miles to Benton and 8.5 miles to the north terminus of Blind Spring Hill.
Here's a good view of the White Mountains, looking south from close to the state line (Google Street View).

Boundary Peak, Nevada's highest mountain at 13,140 feet (4005 m), is the snow-covered peak above treeline on the left; Montgomery Peak, at 13,441 feet (4097 m), is California's higher peak just to its right. Boundary Peak is often considered a subsidiary peak to Montgomery Peak. Without Boundary Peak, Wheeler Peak, in eastern Nevada would be Nevada's highest mountain at 13,063 feet (3982 m). As for the White Mountains, Boundary Peak is practically a low hill: farther to the south, the Whites reach the even higher height of 14,246 feet (4342 m) at White Mountain Peak.

From U.S. 6 at Benton, I took California S.R. 120 toward Mono Lake and Lee Vining. Highway 120 is the road that ultimately goes over Tioga Pass to join Highway 49 on the other side of the Sierra Nevada near Moccasin Reservoir, about 30 miles northwest of the western entrance to Yosemite National Park. If you have never taken 120 over the Sierra, you should. If you’ve taken that route, I recommend driving 120 between Benton and Lee Vining, in either direction (I most commonly drive it from east to west). The route is typically closed in winter, so you might have to wait a couple months.
The section of Highway 120 route I'm recommending (Google Maps).

This rather obscure, back-country paved road will place the White Mountains either in front of you or in your rearview mirror, depending your direction of travel. You will either begin or end on Highway 395 at the south end of Mono Lake near Lee Vining, where you'll be at the north end of the flow-dome complexes of Mono-Inyo Craters and just south of Panum Crater. No matter which direction you end up traveling, you will be in for some great views, and you will be driving through some incomparable volcanic geology.

After getting on Route 120 at Benton, on my first journey ever through the area in 1976, I drove west toward the small outpost of Benton Hot Springs, which didn't look at all inviting to me. I didn't stop. At the time, besides being focused on completing my journey, I was plagued by my usual reservations about being observed by people while in the field, and I felt out-of-place and conspicuous. Despite these feelings, I probably did enjoy a lunch or two in Benton during my intermittent stay in the area (or was that later, when doing field work and reconnaissance for Former Mining Company?).

Because of my qualms or suspicions around people, rather than turning south at Benton Hot Springs, I almost certainly drove a couple miles farther to turn onto dirt. Without a doubt that turn is the way to go into the area if coming from the west, which I did at least once, maybe twice or three times.
This is the turnoff into the area, as seen from the west (Google Street View). The prominent mountains are the White Mountains. Blind Spring Hill is the low, inconspicuous range in front of the Whites.

My campsite, 14.5 miles from the state line on the dirt road I took and about 215 miles from home, was centrally located at about the middle of the hill’s western range front. I had a smallish tent, one large enough to sit or kneel in, but not tall enough in which to stand up. I had a sleeping bag, a cook stove, a small table, and  afolding chair.

Beyond camp, the dirt road steepened, zigged or zagged a little, and began its ascent of Blind Spring Hill’s western face to the numerous old workings. My 1976, light blue Opel sedan had easily traversed the dirt road from pavement to camp, but I could see I’d better walk up the road before committing the Opel to it. It’s a good thing I did, too. A 4WD would have been able to drive partway up the road, sliding around the gullies and dodging the gigantic boulders, but the road was completely washed out right at the top of the hill, so I would have had a long way to back down, something I wan't that proficient at in those early days of field work.

I walked up and took a look around.
The spliced Benton, Casa Diablo Mountain, Glass Mountain, and White Mountain Peak 15' quads, courtesy USGS.
The main part of the area, where all those prospects are, is bifurcated by two topo quads, and less than three miles from the corner of four quads. The area is right next to two paved roads and is 35 miles from a bar. This latter means that it doesn't quite make the criteria for being a good place to "find a mine" (and maybe that's why no one has, recently), although it is less than 30 airline miles from bars at Mammoth Lakes, so maybe...just maybe. (It's also less than 25 airline miles to The Boonies bar and cafe in Nevada's Fish Lake Valley—in case you were thinking of flying over the White Mountains!)
A strangely distorted view of a bar in Dyer, NV.
Blind Spring Hill, the last area on my list, was the most intriguing of all the places I’d visited. The mines were in granitic rock, which hopefully could be mapped into distinct plutons. I could learn some of the differences between weathering effects and the alteration effects that often accompany the fluids that shoot through and infuse the rocks during a mineralizing event. I stopped and looked at a few prospects on the way up the road, I looked around a few workings on the top of the hill, and I saw some promise. I had collected a good many rocks before I made it back to my camp at the base of the hill.

Note: I would now choose Mineral Ridge and the Mary Mine hands down over all the other areas I examined, perhaps barring the Betty O’Neal mine up near Battle Mountain. I’ve always had a lingering fondness for the Betty O’Neal, but would still choose Mineral Ridge. For one thing, it’s not located near Battle Mountain!!!

Selected Reference:
Albers, J.P., and Stewart, J.H, 1972, Geology and mineral deposits of Esmeralda County, Nevada [available for sale only]: NBMG Bulletin 78, 80 p

Related Posts:
Thesis: Finding an Area
Finding a Thesis: Battle Mountain to Austin to Gabbs
Finding a Thesis: Pole Line Road
Finding a Thesis: Pole Line to Belmont
Finding a Thesis: Klondyke District
Finding a Thesis: A Joshua Tree Aside
Finding a Thesis: Into the Palmetto Mountains
Finding a Thesis: Farther into the Palmetto Mountains
Finding a Thesis: A Bit O' Geology in the Palmetto Mountains
Future Stories from the Palmetto Mountains
Lida Summit Roadcut
Finding a Thesis: Next Stop, Silver Peak!
Finding a Thesis: Coming into Clayton Valley
Finding a Thesis: On the Southern Route to Mineral Ridge
Finding a Thesis: The Northern Route onto Mineral Ridge and a Little Geology
Finding a Thesis: Up to the Millsite and Back
Finding a Thesis: Views and Geography and ... Oh, What's That?
Finding a Thesis: A Cinder Cone Aside

Sunday, June 27, 2010

One & Two Years Ago Today: Trips to the Ovens

sign1sign2
Signs: Nevada Historic Marker #184 and Mining Charcoal
(Click to enlarge)

One year ago today, while some family types were visiting, we all packed up and drove to the Ward Charcoal Ovens, which are inside the Ward Charcoal Ovens State Historic Park, and aren't far off Highway 50 on a good, sometimes washboarded, graded dirt road.
The ovens, built in 1876 out of blocks of nearby quartz latite ash-flow tuff, are partially fenced, and it's difficult to get good pictures sans fencing. You can see some of the ash-flow tuff behind and between the two ovens. There are six ovens, here I'm only showing two. (More will be shown later.)
Looking closely at the first or easternmost oven, I spot something growing part way up the right side. What is it?
Maybe it's a weed?
Closer... It's a wildflower!
This is the kind of flower growing in between the blocks of the charcoal oven, a Penstemon, possibly this one.
The rest of our short visit became an excuse to take pictures of the penstemons, at least for me.
And more...
...and even more.

I've visited these ovens several times over the last three years, and have taken many pictures. In fact, one such visit was exactly two years ago today, when other family types were visiting. There must be something about June!
4 The lighting is usually a factor in the kinds of pictures one can take, and I'd say that morning and afternoon are probably best, rather than high noon. Fall before the snow flies might also be better than mid-summer, especially because the heat can seem hotter at the ovens than elsewhere in Steptoe Valley. Note another hill of ash-flow tuff behind the ovens; these hills are fun to hike.
inside1 It's difficult to get photos inside the ovens without using a tripod, but here are two of my best shots.
inside2 Charcoal darkens the walls, and there's been a little oxidation over the years.

Friday, February 26, 2010

Geology on the Road: Slate near Connors Pass, Highway 50

If you drive east of Connors Pass on Highway 50, to the location embedded in the map at the bottom of this post, you will come to this wonderful roadcut exposure of slate, along with many other wonderful roadcut exposures before and after this one (including a few faults, some shattered limestone, and much more slate). Watch for places to pull out while going downhill to the east (there are fewer places to pullout when going uphill to the west), and listen for the heavy truck traffic (and fast cars) when crossing the road. This part of Highway 50 overlaps with U.S. Route 6, an overall busier truck route.
I stopped here to get some garden rocks, but spent a lot of time - at this exposure and at others - checking out the geology. The phyllitic, calcareous slate (to slaty phyllite) is medium to dark gray, usually shiny, and before regional metamorphism it was either a thin-bedded shaly limestone or a limy shale (or both). It was assigned to the Lincoln Peak Formation by Drewes (1967), according to Hose and Blake (1970) - neither map is available online.
For this closer view, the hammer handle is parallel to lineation on the phyllitic slaty surface, and the hammer head is pointing parallel to some weak crenulations, which are stronger above and to the left of the hammer.
I love this shiny rock!
Here, I'm looking edge on at the slaty cleavage and parallel to the crenulations. Folding of the slaty cleavage is weak; there are a few cracks breaking through the slate at some of the crenulations - these may represent a weak or incipient crenulation cleavage. Looking edge on into the crenulations is difficult in the nearby roadcuts up and down the highway because the slate usually dips fairly steeply towards the road. This view requires considerable placing of face next to rock. Little crenulation folds like these can usually be seen only in float pieces.


View Highway 50 in Nevada in a larger map