Things You Find in the Field: Broken Fire Assay Crucible

When wandering out and about in the field sometime back in April, when the air still had quite a chill, and the snow had not completely gone, I came upon some bits and pieces of history: a few remains from fire assaying. This was a small site, not necessarily the location of an actual assay lab, maybe just a place where someone had dumped some miscellaneous debris.
Here's the biggest, most distinctive chunk I found: part of the bottom of a fire assay crucible, a crucible used in fire assay for gold and silver.
The inside has a thin coating of what was once fused ore and flux, now cooled to a greenish glass.
I think the bottom of the crucible holds a vague clue to the manufacturer of the crucible, and hence to its age, but not one I know how to decipher.

Fire assay / cupellation at Wikipedia - a fairly abbreviated description of the fire assay process.

What is Fire Assaying? - a more complete description.

A Textbook of fire assaying - by Edward Everett Bugbee, the classic and complete text on fire assaying. I used a 1933 edition of Bugbee when doing fire assays for my thesis.

The Weekend Effect

It's the weekend, and not much has been going on at work, which is why weekends are nice. The weekly crowd leaves, has days off, and it's oh, so quiet. Very few emails are sent down the pike on a weekend, very few phone calls come in.

It doesn't matter whether I'm even there or not: no emails, no phone calls, no voice messages. :)

If one is in the field, actually out hiking around, mapping, taking samples, checking out localities, even driving to drill rigs, the weekend effect is still noticeable. These days, people generally assume that you can be reached by cell phone and email, even when you are in the field concentrating on rocks. Consequently, they call you, email you, leave messages, possibly bugging the hell out of you while you are trying to get things done, trying to have some peace, trying to commune with the rocks (perhaps non-geologists won't understand the "commune with rocks" aspect of the job). I don't usually see these messages (and I don't always hear my phone, especially if I'm at a rig or am banging away emphatically on some recalcitrant outcrop) — until lunch, when I sit down on a rock, or on the ground leaning against an outcrop or my backpack if a suitable sitting rock is not handy. I can then check my phone for emails, missed calls, phone messages — providing that I'm within range, which is not always the case in Nevada. (Thankfully.) In other words, the weekend effect is still in place when I'm out in the field: I'm unlikely to get any field-disturbing interruptions because the weekday crowd is off work, not around.

I'm not sure if the younger generations** realize, what with all the connectivity of today, that many of us got into geology for the solitude and great outdoor getaways — not just for the opportunity to work at scenic, possibly remote field sites, but also for the resulting benefit of getting away from people, from offices, from everything. We didn't get into it to sit behind computers* looking at simulations of rocks and their rocky relationships; we got into it to get out there and actually see, bang on, and map the rocks. (Many of us did, anyway.) I know geologists who are still moderately uncomfortable with computers, and some who've grown into them over the years, gradually and painstakingly. I know geologists who, if they are ever in the office or at home for more than a week or two, just go stark raving nuts and have to leave: they need to get out and get away from offices, bosses, memos, house and home and all that entails — and now, with constant connectivity, they need to get away from emails, cell phones, voice messages, text messages, and the constant on-call nature that these things are bringing to the field geologist who happens to own a cell phone. (I do know at least one geologist who doesn't own a cell phone; I know others who only use them while on the job; I know one or two who never answer, letting all calls ring through to voice mail.) I (fortunately?) can't always hear my cell phone, even if I have it turned to the max. My loss of hearing is the result of being around drill rigs before ear plugs were de rigueur, and from driving down dirt roads with the side window open. My job has given me relief from the current on-call nature of the job.

Anyway, I hope it's a good weekend for you, wherever you happen to be. Me? I've been weeding the garden and will later have a beer — indoors, away from the skeeters.

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P.S. This same weekend effect can be created — to some degree, and in some places — by working on holidays, although 3-day weekends in the Mojave and some other field locales can be an absolute drag (to say the least).

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* I have nothing against computers (as you might have guessed), and I did own the first IBM-compatible portable computer — the giant, 28-lb Compaq, which could barely be crammed into the overhead compartment for airline travel — but when I got into geology, the closest one could get to a computer was the batch room, where one could turn in stacks of punch cards. The associated keypunch and printout rooms were located part way across campus, miles, it seemed from the batch room. Consequently, most students never saw the mainframe, which was hidden away somewhere, maybe in the closed area behind the batch room attendant, who was possibly a computer science major making a few bucks.

** Updated: I hope it's understood that I have nothing against any of the younger generations, but want to merely note some differences between now and back then. When I first went out into the field, if anyone wanted to get in touch with me, they had to get in a 4WD and drive many miles from any town, or they had to rent a light plane or helicopter and fly out, or - never done - they had to get on a horse and ride out to see me. A more normal practice was for me to drive 10 to 30 miles after a day of field work to call the office from a pay phone, or, if I was too far out, to see my boss back in the office 10 days down the line.

For many years, we saw very few young geologists coming into mininig and minerals exploration, so few that I can probably count the ones I know of now middle years on two hands. The severe lack of younger geologists, who would now be in their twenties or early thirties, was lamented quite frequently by my collegues and I. More recently, in the last 5 years in particular, I have met several fine and enthusiastic younger geologists in meetings, working at remote mines, and on geology field trips. I've also met a lot of geologists of varying ages and broadly divergent fields online through blogging and other related activities.

And maybe I have an unusual point of view, having done most of my work in Nevada and other relatively remote parts of the west, where some cell companies can't, today, provide reliable service even 10 miles from our smaller towns or 10 to 30 miles off our major highways.

A Favorite Word: Detachment

While working every day for the past 17 or 18 days, whatever, I've been thinking on and off about what my favorite geological word might be, while also writing up an internal report that includes a large number of definitions. I was having a hard time writing anything at all for the blog, being thoroughly overloaded by words and definitions, and couldn't focus well on more words, favorite or otherwise.

Finally, though, I thought of one! (Well, actually I though of two others, but I won't digress... ha! Oh, and at least two other great words have already been used: mylonite and welded tuff.)

The word: Detachment, more specifically Detachment Fault. The entire post envisioned a couple nights ago, "Detachment: See header photo." (That's the one up there, above this blog post.)

I have gone a little beyond that short, terse post, but won't really get into a definition, which would involve a low-angle normal fault of regional extent, probably created by, or during a period of, what is sometimes known as "extreme extension."

Official AGI definition for detachment fault.

Detachment Fault: a good geological mystery book.

A number of Detachment Quotes.

My posts labeled "detachment" (there are only 20 so far, including this one).

Detachment fault on Facebook (it has no friends!)

The Northern Snake Range décollement or detachment fault as seen from Great Basin National Park.

This post has been submitted to Accretionary Wedge #35: What's Your Favorite Geology Word?

Cathedral Gorge II: The Hike

After coming out of of "the cathedrals" at Cathedral Gorge, MOH and I went on a little hike.
The trail goes north up the gorge, from the CCC Picnic area (facilities and water tower built by the CCC in the 1930s) to Millers Point, a one way distance of about a mile (MSRMaps location).
Fascincating textures can be seen in the Pliocene Panaca Formation along the way. Here, differential erosion of harder, thin sandstone layers interbedded with softer mudstone layers have created interesting mini-columns and maybe even some little mini-cathedrals hidden in the shadows.
My hand is straddling two sandy layers and a mudstone layer sandwiched in between. A curious jigsaw-like texture has developed over the mudstone. Essentially these are tiny gullies or rills created by water running down the outcrop.
We've now made it into the beginning of the steep, northern end of the trail, and I've turned around to look southward down the gorge.
Steep: The northern part of the trail is steep, especially in this section of hand-built stairs held up by partially eroding railroad ties. Beyond these wooden steps are metal stairs that go from ledge to ledge over the steepest sections of the trail.
Instead of hiking the stairs all the way to Millers Point, we stopped on one of the middle ledges. Columns capped by sandstone can be seen from several vantage points along this northern stretch of the trail. The scale of these hoodoo-like features is difficult to appreciate: they are often smaller than similar erosional features at Cedar Breaks, for example. These are maybe two hundred feet high at most.
This is one of several holes eroding into the broad ledge we were standing on. I peered in, but couldn't lean out far enough to see anything, so tried holding the camera out as far as possible, having it do the peering for me.
I wondered if this hole could be the top of one of the cathedral-like columns we had seen from below while wandering around near the picnic area (first post).
An overexposed photo showed me that this hole only goes down a few feet (railroad ties for scale).
Some of the other "holes" and irregular erosional features near the edge of the ledge may indeed go downward to become cathedral-like inner columns, but I really didn't want to check them out too closely!
Now I've jumped two or three hundred feet upward and two or three years back in time to show this photo taken from Millers Point. The broad ledge we were on is below; the stairs to the right along with a smaller set of stairs down on the ledge (barely visible on the far left part of the ledge) give some sense of scale to the columns and gorge, and to the broad plain into which the gorge has been eroded. The bentonitic, tuffaceous clays, silts, and sands of the Panaca Formation — essentially water-laid tuffs, diatomaceous in places — were deposited in a closed, Pliocene-aged basin. The source of the tuffaceous material is reportedly the Caliente caldera complex south of Caliente, NV — way off in the distance on the far right — which was active in latest Oligocene to middle Miocene time, from about 24 to 13 Ma.

The Panaca Formation reminds me somewhat of the Triassic Chinle Formation, a partly bentonitic formation seen on the Colorado Plateau at the Painted Desert. Possibly the Panaca will look like the Chinle in the far future, if it has the good fortune to be preserved, rather than being eroded as it is now, southward into Meadow Valley Wash, from there southward into the Muddy River (formerly into the Virgin River), and from there into the Colorado. We are outside the Great Basin!
We finally headed back toward the CCC picnic area, just beyond that final rise of sand highlighted by the early afternoon sun.
Gratuitous sand photo. And darn! I forgot to collect any!

Some References:
Rowley, P.D., Nealey, L.D., Unruh, D.M., Snee, L.W., Mehnert, H.H., Anderson, R.E., and Gromme, C.S., 1995, Stratigraphy of Miocene ash-flow tuffs in and near the Caliente caldera complex, southeastern Nevada and southwestern Utah: in Scott, R.B. and Swadley, WC, eds., Geologic Studies in the Basin and Range - Colorado Plateau transition in southeastern Nevada, southwestern Utah, and northwestern Arizona, 1992, U.S. Geological Survey Bulletin, 2056-B, p. 43-88.

Rowley, P.D., Snee, L.W., Mehnert, H.H., Anderson, R.E., Axen, G.J., Burke, K.J., Simonds, F.W., Shroba, R.R., and Olmore, S.D., 1992, Structural setting of the Chief mining district, eastern Chief Range, Lincoln County, Nevada, in Thorman, C.H., ed., Application of structural geology to mineral and energy resources of the central and western United States: U.S. Geological Survey Bulletin 2012, p. H1-H17.

Nevada-Utah series so far (in trip-time order):
Cathedral Gorge I
Cathedral Gorge II: The Hike (this post)
May Utah Trip to be Continued
Cross-Bedded
More Cross Bedding
Bighorns on the Overlook Trail

Recent Hike: Water in the Desert

On our late May trip through central Nevada (May 27th), we stopped at our usual spot — the Cold Springs Pony Express Station — to do a bit of hiking and biking. MOH went ahead on his mountain bike...
...while I stayed behind, hiking uphill slowly, looking for wildflowers. I found a few, not as many as a couple years ago, not as many as on May 31st of last year. We might have been late for the biggest bloom, we might have been early. I noted a large amount of cheat grass, more than was around with wildflowers in late April two years ago, more than was present with lupines and other wildflowers one year ago. Possibly the wet, cool spring gave the cheatgrass an advantage.
I finally came to the station ruins, which crudely mimic the distant cliffs of welded ash-flow tuff — boulders of that same ash flow tuff form the walls of the ruins.
And then, surprise! Running water! The creek that goes by the station is usually dry when we stop, though sometimes it's been muddy, and it was marshy with nearly stagnant water a year ago (May 31st, 2010). This time, the creek was in full flow, all the way from its source somewhere above the mouth of the canyon about a mile uphill, and down to the station and beyond. I'm not sure how often this creek was in flow during the 1970s and 80s; Pony Canyon creek or wash is shown as intermittent on the 1982 Cold Springs 7.5' topo map.

Water running past the Cold Springs Pony Express Station, looking west toward the Clan Alpine Mountains.

And onward it goes, heading downstream toward the juniper in the middle distance toward the left.
Meanwhile, MOH has biked up to the head of the alluvial fan south of Pony Canyon and is now coasting back down.
There he goes down the trail, past phlox and other flowers, over miscellaneous pieces of ash-flow tuff, back to the parking area where the Prius awaits us both. I still have about a mile to go, walking all the way.

P.S. People who don't live here may not understand the fascination that "desert" dwellers have for running and standing water. Driving by puddles after a rain I'm wont to say, "Oh, look! Water!!" It's variably surprising or unusual depending on the exact locality and time of year, but always worth noting.