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).

Friday Field Photos: Folded, with Lineation

This is a small glacial boulder of folded meta-argillite, possibly from the Precambrian McCoy Creek Group, which I found along the trail between Stella and Teresa Lakes, beneath Wheeler Peak in Great Basin National Park, close to last week's boulder. The greenish, coarser-grained layers accentuate and define the folding, which otherwise would be more difficult to see in the reddish or purplish gray layers.
Zooming in on the small boulder, I'm poining at some crude lineations, which my finger roughly parallels. The green bed at the top of the boulder is also lineated.
The lineation direction theoretically defines the direction of motion present during the tectonic event that created the lineations and possibly the folding. If we had some context, if this rock was part of an outcrop, we could look perpendicular to the lineation direction, instead of parallel to it the way we are now. While looking perpendicular to the lineation direction, the nature of the folding or of other micro- to meso-scale structures might tell us relative motion of beds during the lineation-forming event, for example top-to-the-east or top-to-the-west. Because this rock was part of a glacial moraine, it could tell us very little about the tectonic events it had been exposed to during the course of the last 540 million years or so. (GSA Geologic Time Scale.)

Friday Field Photo: Cross Bedding in Quartzite

This small quartzite boulder, found in morainal deposits between Stella Lake and Teresa Lake below Wheeler Peak in Great Basin National Park, shows cross-bedding defined by dark purplish to reddish laminations. Up appears to be to the left. Without a stratigraphic context it's hard to say whether this quartzite is part of the late Precambrian McCoy Creek Group (pCMc) or the possibly late Precambrian to mostly early Cambrian Prospect Mountain Quartzite (Cpm), but most slopes uphill from this spot are in the Prospect Mountain Quartzite. Depositional environment was likely nearshore to offshore marine.

Friday Fault Photos: Fault Scarp at Fairview Peak, Nevada

On that same gray day in early December that MOH and I found flow-banded rhyolite, brecciated rhyolite, tuff, fossils, and Earthscope, we made our way up the wide, gravelled, but unmarked road to the fault scarp on Fairview Peak. The unmarked road we took is here (Google Street View); the main road marked by the BLM "Earthquake Faults" sign is here. We took the unmarked road primarily because I'd never driven it. I don't know which road is best; the unmarked road goes by a strange government installation with warning signs and a robot that may come out onto the road every now and then, judging by tracks we saw.

The view in the first photo above looks southward from a parking area the end of a graded loop road, shown here in Street View. This same loop road is also shown on the second Google Earth image of my fault line post.
We walked uphill to stand on the fault, and were surprised to see a second fault scarp uphill from the main scarp. The photo looks straight down the main scarp, left of center; the second scarp is uphill and to the right.
We then walked SSW along the fault scarp to an area where the scarp cuts through bedrock rather than just cutting alluvial fan material. This is one of the most photographed parts of the fault, simply because it's so close to the loop road. To the left (east) of the east-dipping fault scarp, you can see a little valley overgrown with straw-colored bunch grass. The valley or gully is partly erosional and partly due to a small downdrop east of the main scarp. This downdrop appears to be down-to-the-west, opposite to the down-to-the-east main scarp. A similar downdrop can be seen in the USGS photo below, a photo which at first glance appears to have been taken at the same site (it may not be the same site).

USGS Photograph of the scarp formed on Dec 16, 1954, taken by H. Benioff.

The man is standing in a gully created by the juxtaposition of the main, east-dipping scarp (here it's some 2+ meters high), and a smaller, vertical to west-dipping cut to the left of the man. The USGS picture may show the same section of the fault that I photographed; it may be a different section. I know, for example, that there's a nice exposure visible if you drive (or hike) up a lousy, very steep, two-track road located north of the good, not-so steep loop road. I think the USGS photo shows what looks like a steep, second scarp above and west (right) of the main one; that second high scarp is not seemingly present at the loop-road site, and the trees and bushes don't look quite right to me. (Two Google Earth images at the bottom of this post show the loop road and lousy road.)
This is the view from that southern exposure of the scarp, with MOH for scale, looking back to the NNE, toward the little parking area at the end of the road.
Here's a similar view looking northeast along the sharp, V-shaped valley, which was in part formed by down-dropping along its right (east) edge, similar to the doubly faulted valley in the USGS photo. There may be a technical term for this second, opposing scarp or faulted valley, a term I don't know.
There's a great view to the northeast from the fault scarp (photo enlarges nicely), making the short hike well worthwhile. The Desatoya Mountains are the blue, snow-covered mountains on the right; the Clan Alpine Mountinas are the brownish to bluish mountains in front of them to the left and in the center. On our day's journey, we started near the southernmost visible part of the Clan Alpine Mountains. The EarthScope observatory we saw earlier is in the low hills of that southern, brownish part of the Clan Alpine Mountains.
The loop road. The scarp we walked to is the whitish, slightly bent part of the scarp where it crosses a little, tree-covered hill southwest of the loop. North is to the right.
The barely visible, steep, two-track road that leads to another well exposed scarp can be seen when this Google Earth image is enlarged. This road is not recommended for travel because of turning around problems at its steep upper end.

Friday Fault Photo: Fairview Peak, NV, Fault Line

I captured this Google Earth image of the east face of Fairview Peak, with north to the right and the scale bar on the left showing 4112 feet, and then set about drawing the fault scarp created by the 1954 Fairview Peak–Dixie Valley earthquake. The location of the fault line (in magenta) is somewhat approximate in places, and I've left gaps where the trace is unclear. Identifying the fault line on Google Earth is complicated by the fact that two or more scarps occur in some areas. The line, as drawn, has not been field checked.

An example of the scarp, as seen in an oblique Google Earth image.

The scarp angles across the hill above the loop road near the center, and above the linear road to the left.

Images below are broken into two halves and shown with north to the right (first two images), and then with north up (second two images). These images enlarge fairly well, with the horizontal (north=right) images being best in enlargement and the vertical images (north=up) being best on the blog.

North half of the Fairview Peak strip with north to the right.

South half of the Fairview Peak strip with north to the right.

Two images: north and south half of the Fairview Peak strip with north up.

Can't really say why I did this. I was just fascinated by the fact that you can take Google Earth, rotate the eye view to oblique and — especially after a visit to the area (early December) — can easily identify the fault scarp(s) in most places.

Related Posts:
Where in the West - March
Fairview Peak, Nevada
Friday Fault Photos #6

Friday Fault Photo: Where's the Fault?

It's great to see faults with nice outcrops, but not all faults expose themselves well.

This fault, partly hidden by trees (and now totally under snow), shows a nice linear outcrop pattern but nowhere does the actual fault surface crop out, though I suspect the fault plane lies less than 5 feet to the left of the above exposure of brecciated limestone, possibly within a foot or so. Likewise, the fault contact between the two (or more) faulted rock formations is not exposed, at least not in this area. Instead, one can follow a roughly linear outcrop of limestone — sometimes brecciated, sometimes veined or marbleized — and one can find a bit of fault breccia float and a trace of slickenside float here and there where the fault goes under cover. So far, there is no indication as to which way the fault actually moved, though one can assess relative motion and deduce a couple possibilities.

Some faults with large displacements show no surface outcrop at all, at least across broad areas, but instead can be found in relative low spots such as valleys. I found this to be particularly true back east where exposure is not as good as it is in the west, but it can happen anywhere. In fact, some geologists swear by an axiom stating that the faults that actually crop out on the surface are small faults (apparent offset I'd guess of less than a hundred feet or certainly less than 50), and that large faults rarely crop out. I can't say that I buy in to this way of thinking. Some very large faults with huge offsets and some large faults with large offsets have great exposures, some don't. Likewise with small faults. Many of the faults I find in the field are, indeed, small faults with offsets of 5 to 50 feet or so, and that's because there are a lot of faults in the Basin and Range, and they range in size from tiny to very large (as measured by amount of offset).

Many times, small faults are not mapped because they are considered insignificant. If they are part of a larger fault zone, however, they may be cogent to what you are trying to figure out. For example, several en echelon or sub-parallel faults with small displacements can, across a wide fault zone, offset stratigraphy, ore deposits, and faults and other structures in a way that will leave you wondering what is going on, possibly causing you to bend contacts where they don't actually bend. Of course, the scale of mapping has something to do with how many small faults you can show on your map, and you may have to lump several small faults as one fault trace.

Friday Field Photos: Mystery Cracks

I posted this photo elsewhere just recently, and got a little feedback as to what the irregular to polygonal cracks on the surface of these columnar-jointed basalt faces might be. Here are a few more photos. At this point, MOH and I had turned around on our Winnemucca-to-the-Sea Highway journey (turned from going toward Winnemucca to going away from Winnemucca), in order to spot a pullout to view the cracks better, and also to get a better look at the nearby Deep Creek Falls. (Okay, we really turned around to look at the falls.)
From the south side of Highway 140 right below the falls and a little less than 3 miles west of Adel, Oregon, here's the best roadcut I saw of the basalt: other roadcuts are in tight, narrow turns with no nearby pullouts.
A closer view.
The columns are weathering into somewhat rounded, rectangular to irregular shapes, which at times look like stacks of flattened pancakes and other times look like hoodooish sentinels watching over the road. Outcrops up the hill show the same patterns, exposures at the falls look merely columnar. So far, the consensus is that the basalt is undergoing incipient spheroidal weathering.

Additional ideas are welcome!

Location:

View Bend OR to Winnemucca NV in a larger map

Trip report to be continued...

Friday From the Road: Long Valley, Northeastern Nevada

The long road through Long Valley, Nevada (MSRMaps).

View Eastern Nevada in a larger map

A Friday Field Update

...on a Saturday evening.

As many of you may have guessed, and as some of you may know, I've recently started working a fairly intense schedule and have been unable to do much of anything online without detracting from my sleep time. The schedule includes the 10-hour days that are usually expected of field geologists (in mineral exploration, at least), and it currently includes an unspecified length of time. One likely scenario would be to work about 20 days and then to take about 10 days off. I described a few typical schedules a couple years ago, though I didn't describe several currently popular options, including the 4 and 3 or the 8 and 6. From the 8 and 6, one might extrapolate a schedule of 16 days on and 12 days off, but I haven't seen that in place anywhere. Anyway, the upshot is that I'm "in the field" — that is, I'm not working at home, and I'm not working in an office. One definition: the field is the everywhere that you do geology — whatever kind of geology you happen to do — and that geology is usually, although not always, done out there away from town and away from home.

This particular job is a little unusual in that I really don't know how long it will last: there is plenty of work to be done, but is there enough money to do it? In my experience, this has been a bit of a problem during the last couple years, at least for some exploration companies. I personally have been fortunate during my long career to work through some fairly flush times, and also to work through leaner times with companies that maintained a healthy exploration budget. No exploration = no mining down the line, so it's a good thing (IMO) for companies to maintain a healthy exploration budget.

Recently, many of the larger companies — the few existing majors in particular — have devoted a fair portion of their time and money toward buying already proven or nearly proven reserves, and they've dedicated the rest of their time and money toward exploring on site, an M.O. sometimes called "brownfields exploration." In the last several years, brownfields exploration has largely been conducted at the expense of stepping outside the mine area, outside the property, and — heaven forbid! — at the expense of actually doing some well conceived "greenfields" or even "grassroots" exploration. (That is not true, by any means, in all cases, and the trend may be changing.) So if you, as an exploration geologist, don't know exactly where you want to drill because you are thinking of stepping outside the box, you might not find anyone willing to fund the mapping and sampling necessary to go find or prove up the next big one. The next big one might well be what will keep the current operation going.

Disclaimer: I haven't yet devoted any of my own time or money to this type of exploration, either, though many of my career-long colleagues have.

Friday from the Road: The Road to Gabbs

Before going off onto another part of the old story, here are a few more pictures from the road to Gabbs, that is, from Middlegate Junction at Highway 50 south to Gabbs on S.R. 361.

This particular stretch of highway is unusual for Nevada because it passes into three counties in short succession, although not all the way through any of them. The road starts in one county, passes through another, and then passes into yet a third – an unusual feat given the relatively large to huge size of most Nevada counties.
Leaving Old Middlegate Station at 1:30 pm that spring day two years ago, I came to this first county sign 20 minutes later at almost exactly 1:50 pm. I was about to enter Mineral County, having driven about 15.7 miles on S.R. 361.
The sign on the other side of the road facing back to the north indicates that I just came through Churchill County.
A little short of five minutes later, I arrived in Nye County, the largest county in Nevada – and third largest county in the U.S., not counting boroughs in Alaska.
About 10 or 15 minutes later, a side road heading east toward Lodi Valley came into view. Lodi Valley runs north-south between the Lodi Hills in the left middle ground and the Paradise Range in the background.

The Lodi Hills was the site of my first submittal evaluation back in the late 1970's or early 1980's. Whether the submittal was for uranium or gold is something I no longer remember. I do remember a large quantity of quartz vein material, both lying around as float and jutting out as outcrop. I also remember something about barely making it uphill through newly fallen snow.
I drove off the road a little ways to get a good look at the nicely graded gravel road into Lodi Valley – okay, it's a little bit washboarded, but doesn't look too bad .
Just past that turn-off, the main part of the Downeyville mining district comes into view to the east. Downeyville is an old silver-lead-zinc-gold district, which had more zinc production than anything else, though the historic records are spotty. It's also an old ghost town. Directions and a couple pictures here.
About 29 miles south of Highway 50, one of the several signs for Ione that you can see scattered here and there around west-central Nevada comes into view, pointing off to the east. If you turn onto the side road, you'll be on S.R. 844, the Ione Road, formerly known as S.R. 91. Follow the road and you'll go over Brunton Pass, down into Ione Valley, and from there onward to Berlin-Ichthyosaur State Park, and then north to Ione. Gas is not necessarily available in Ione, check local sources or fill up in Middlegate or Gabbs.
Then, at 2:15 pm, almost 31 miles and less than an hour from Highway 50 – and closer to a half hour not counting photo stops – I arrived at the signs for north Gabbs.

An aside: There are lots of signs pointing toward Ione in central and west-central Nevada. Generally, the town seems to be about 20 to 50 miles from wherever you happen to be. I'm not sure I've ever been there, although I've been as close as Berlin-Ichthyosaur. Maybe someday I'll do a post about the many roads to Ione and the many signs pointing the way. I'll have to do a lot more sign collecting and backroad travel to get them all.

One Year Ago Today: A Stop in Baker, NV

One year ago today, after a rousing snowshoe trip, MOH and I stopped at this establishment in Baker, Nevada (one of very few establishments in Baker, Nevada).
I love the colors of the place, and could probably spend all my time taking pictures.
If you ever stop by, be sure to notice that you can see the Snake Range detachment fault from the front of the building, just under and north of the main sign. The fault can also be seen on the banner of this blog and in a couple other posts. (And the fact that you can see the fault in this photo makes this One Year Ago post also qualify as a Friday Fault Photo post.)
After going inside, you can have a meal in a cheery room...
...or, if you've a mind to, you can have one of a couple fine draft beers. Mmm... makes me thirsty. Bye!

Disclosure: This is not a paid-for restaurant review, just a random blog post.

Friday Field Finds: An Old Trommel

While out wandering around a couple years back, probably on our way to or from Great Basin National Park, MOH and I ran across this rusty specimen in Spring Valley on the western flank of the southern Snake Range, not far below the ghost town of Osceola. Osceola is the center of the Osceola mining district, which largely produced placer gold. Although most reports talk about the district as though it's dead, activity is ongoing, and we often see a small recovery operation or two when we drive by on Highway 50.
This is a trommel—smaller ones can be seen here—once used as part of a placer gold recovery operation. Trommels wash the dirt and gravel and separate the coarser material from the finer material before the fines and gold are put through some kind of concentrator like a sluice box. This trommel is now only good for its scenic and historic value; here it's framing the Schell Creek Range across Spring Valley. Black Mountain is the prominent mountain and South Schell Peak can barely be seen to the west (left) in the distance [MSRmaps location].

Silva, Michael, 1986, Placer gold recovery methods: CDMG Special Report 87, 31 p.

Friday from the Road: There & Back Again

I'm just going to throw out a few photos from my most recent road trip, which was to and from the NWMA convention last week. None of these pictures were taken on a Friday, but that doesn't matter to my way of thinking (which, admittedly, could be distorted by a slight fever).
On the way there, just after coming into Edwards Creek Valley, the guy ahead of me put on his breaks suddenly, so I slowed down, thinking I might get a glimpse of a coyote. Instead, off in the distance, I saw some smoke rising from a low spot in the Desatoya Mountains.
As I drove along, the wind was picking up in the valley. The smoke coming from a canyon to the south swirled a bit near the ground, then rose straight upward to spread out horizontally at an atmospheric layer not that far above ground level.
I eventually stopped and got this picture. The colors around the edges of the smoke fascinated me - and then my mind went on a tangent and I wished that the smoke could be from a little basalt flow erupting along a range front fault instead of a brush fire caused by who-knows-what. The canyon is probably the canyon of Edwards Creek. The truck ahead of me pulled over when they got cell service and called in the fire, which presumably stayed small, because I couldn't find anything about it online.
On the way back, I got this shot looking southwest down Big Smoky Valley toward Kingston Canyon, with the setting sun just about to go behind the Toiyabe Range.
A little farther to the east, the sagebrush bushes in Antelope Valley were a glowing golden orange, and the shadows were a deep greenish blue. The photo looks northeast toward the distant Roberts Mountains on the right and the closer Simpson Park Mountains on the left.