Deskcrop: Dumortierite and Dumortierite-Sericite Schist

These various rocks had been lying around on my kitchen table for weeks when I decided to photograph them together, along with a Bailey's glass filled with wine and an empty Alaska cup. Clockwise from the Bailey's glass: dumortierite-sericite schist with rose-colored dumortierite, greenish dacite porphyry from the Osgood Mountains, reddish volcanic rock from the Midas area, and lavender dumortierite schist.

The dumortierite-sericite schist is a from the Champion Mine area, located in the Rochester mining district of the Humboldt Mountains, Pershing County, Nevada.

Dumortierite-sericite schist, composed mostly of dumortierite, sericite (AKA fine-grained muscovite), quartz, and possibly andalusite.

Sheen from the fine-grained, clear to white sericite (muscovite) on foliation planes and disseminated in the schist.

Lavender dumortierite schist.

I found this one piece of lavender dumortierite schist on the ground below the chute of the ore bin between the upper and lower Champion Mine workings.

Dumortierite has been mined for use in making refractory ceramics such as those used in spark plugs. It is sometimes used as a gemstone (or rock), and the blue varieties have sometimes been used to make fake lapis lazuli.

By the way, these rocks are currently unlabeled. Andrew Alden has a good post up recommending that everyone label their rocks and minerals (with name and location or provenance). I will be able to label precisely all but the reddish volcanic rock.

Related Posts:
Friday Photo: Dumortierite
The Road to the Champion Mine
Rock Walls at the Champion Mine Lower Workings
Dumortierite at the Champion Mine, Nevada
Upper Champion Mine Workings

Selected Reference:
Mackay School of Mines staff, 1928, A bulletin by the Mackay School of Mines staff on the mineral dumortierite, University of Nevada Bulletin, vol. 22, no. 2: Nevada Bureau of Mines and Geology Bulletin 8, 47 p., including 1 oversized page.

Twelve Months of LFD (2012)

I missed this retrospective meme last year, but here it is, back again, as per DrugMonkey:

The rules for this blog meme are quite simple.
-Post the link and first sentence from the first blog entry for each month of the past year.
I originally did this meme, after seeing similar posted by Janet Stemwedel and John Lynch.  Prior editions include 2011, 2010, 2009 and 2008.

Previous takes on this Twelve Month meme at LFD were posted for 2008, 2009, and 2010. As usual for LFD, I've also added the accompanying first photo of the month, where there was one with the first post of the month.

January:
I went on my first walk of the year earlier today, out along a creek in Anchorage, AK.

February:
I thought I'd back up to a time a week before our stop at The Geographic Center of Nevada, a time just prior to our soak at Spencer Hot Springs. 

March:Upon getting out of the truck at the north end of the Monitor Valley playa, it became rapidly clear to me that it was very cold. 

April:
I thought I'd actually have time over my 5-day break to get caught up on some blogging, but that hasn't been the case, and things aren't looking all that great for the coming 8- or 9-day work week and the break following that, so I'm posting a few views from the new area.

May:
Just a quick post showing a photo I took about two weeks ago at 5:50 am, on my early morning ride to work. 

June:
Yesterday I received an email while at work telling me that there was a hummingbird moth in one of our two pots of chocolate mint, which are sitting outside on the front porch. 

July:
These stitched photos were taken about three weeks ago near the site of Preble (just off the map to the west).

August:
These relatively small pinnacles are located in the canyon of Midas Creek, just north of the town of Midas, Nevada.

September:
Besides the obvious greenish feldspar, the countertop rock is composed of black pyroxene, gray metallic minerals (magnetite or ilmenite are likely, but I didn't bring my magnet, magnetometer, or portable xrf), and pyrite.

October:
In the morning after I wake up—while I'm drinking my first, second, and maybe third cup of coffee—I often think of things to write for the blog, how to write them, maybe even what pictures to use.

November:

I got to thinking after taking another looking at my arc photos, that this shot may show a weak tangent arc above the also weak 22 degree halo around the sun.

December:
We came in from the east or north, depending on how you view the direction of I-80 as it traverses the entire north-south length of the west flank of the Humboldt Range from Florida Canyon to Limerick Canyon northeast of Lovelock.

Upper Champion Mine Workings

Now we've turned the corner from the lower workings of the Champion dumortierite mine area and are looking straight up the old, now impassable road that once led all the way to a prosepct at the top of the hill. The dump for the uppermost prospect — with small juniper tree growing on it — is barely visible on the far left end of the uppermost outcrops in the left part of the photo, just beyond and behind the reddish brown, cliffy outcroppings of the middle foreground.

After hiking up the wash a little ways we came to this old ore bin, which is still connected to the upper workings by cables.

Looking inside the ore bin via the chute.

I looked inside the ore bin to see if there was still any ore. What I found, besides a few patches of thin snow, were a few small pieces of purplish blue (or lavender) dumortierite, which I'll show later. These chips, and a few similar ones lying around on the ground below the chute, were a different color than the standard purplish red (or rose) dumortierite I've always seen in the area, and it made me wonder if the bluish color indicated anything significant to the miners, or if it was just a chance find on my part, or if it indicated a possibility that the upper workings were entirely in the purplish blue variety of the mineral.

An adit next to the ore bin. 

A few of the cables going from the upper workings to the ore bin are bolted into the outcrop above the adit.

Closer view of the opening to the adit, its door more than half open.

Looking at the upper workings from the ore bin, the cables strung overhead.

At this point, we decided our hike and prospecting of the area was done for the day, so we didn't make it up to the upper dumps. We saved the area for later.

Instead, we had this view of the upper workings when we stopped at the Humboldt Queen (mentioned here) before driving on to Rochester Canyon.

Google Earth view of the entire Champion Mine area.

Related Posts:
Friday Photo: Dumortierite
The Road to the Champion Mine
Rock Walls at the Champion Mine Lower Workings
Dumortierite at the Champion Mine, Nevada

Dumortierite at the Champion Mine, Nevada

Here we are, back at the lower workings of the Champion Mine, standing on the second wall, looking at a funny, corrugated outcrop. If I look at this outcrop with a tilted head, I might imagine a sideways, not-quite-upside-down Nevada with corrugations of the Basin and Range forming large-ish mountain ranges (or I might imagine caterpillars crawling).

Closeup of the corrugated outcrop.

Most of the outer edges of the corrugations are terminated by planar, thin rinds of fibrous, purplish-red dumortierite. I'm not really sure what created the shape of the corrugations, but I'm thinking that they might be structural in origin, combined with some incipient cavernous or spheroidal weathering.

Thin rinds of dumortierite on schistose, Triassic rhyolite.

Fibrous to bladed dumortierite up close.

The orientation of the fibers or crystals reminded me of the slickenlines one might see on a slickensided fault surface, but I didn't have time to really check out this possibility by taking a lot of orientations with my Brunton.

Dumortierite in irregular veins cutting the Rochester Rhyolite.

Veins and a vein breccia.

Nice vein of fibrous dumortierite.

I'll have some more photos of dumortierite and dumortierite-sericite schist later, and soon, we'll head up towards the upper Champion Mine workings.

To be continued...

Rock Walls at the Champion Mine Lower Workings

We had just started up the hill to the lower workings of the Champion Mine in the Rochester mining district, Nevada.

Three rock walls.

The lower workings are a mess of mine dumps, scattered junk, and locally heavy brush amidst three well-defined rock walls below a cliff of Rochester Rhyolite.

Corner of the lower of the three walls.

The rock walls are built of dumortierite-sericite schist from outcrops of the Triassic Rochester Rhyolite, part of the larger Koipato Group of Triassic volcanic and volcaniclastic rocks. I'm guessing that the walls were possibly used to provide flat places for mining activities near the workings on the very steep slopes, rather than as foundations for shelters, buildings, or mills: we found no signs of such structures.

View from the lower wall, looking WSW down Rolands Canyon.

The second or middle wall as seen from below.

The third or upper wall, medium brown in the upper left of the photo.

Standing on the second wall, the third, or upper wall becomes apparent, high on the slope, nearly blending into the cliffy outcrops of Rochester Rhyolite. The funny, corrugated, white to beige or orange-brown outcrop at the far end of the flat platform contains dumortierite in fibrous masses, which we'll see in a later post.

View from the upper or third wall, with the first and second walls below.
My jeep is no longer visible.

Now we've gone back to the bottom of the hill, and are looking straight upward at all three walls.

From just above the jeep parking location, only the first and second walls can be seen.

But, before we had made it all the way back to the parking area to drive away toward continued adventures, MOH and I had turned and walked up the very old, impassable road to briefly investigate the upper workings.

To be continued...

The Road to the Champion Mine

We came in from the east or north, depending on how you view the direction of I-80 as it traverses the entire north-south length of the west flank of the Humboldt Range from Florida Canyon to Limerick Canyon northeast of Lovelock.

The Oreana–Rochester exit from the north on I-80.

We took Exit 119, turning off onto the Oreana–Rochester road, a paved road that goes up Limerick Canyon to Spring Valley Pass and the turnoff to the Coeur Rochester Mine.

The I-80 underpass near Oreana.

Go straight ahead, under the underpass, do not turn left back onto the freeway, unless you'd prefer to go to Rye Patch or points north.

The junction of the Limerick Canyon and Rochester Canyon roads.

To get to the Champion Mine, stay left at this junction, on the paved Limerick Canyon road. Don't take the dirt road to the right, which goes to Rochester Canyon. After the junction, you will take the first dirt road to the left, a fairly decent alluvial fan road. The right turn onto the road to the Champion Mine is marked below in my newly added location section, above the blog tags or labels (if clicked, the location will open in Google Maps).

No trespassing sign.

The dirt road up Rolands Canyon to the Champion Mine is a narrow, high clearance road with lousy turnouts in case you happen to meet someone coming up or down. You'll pass a small No Trespassing sign, which is there because of the spring and an old, not presently used (AFAIK) trailer at the cottonwood tree.

Rolands Canyon should be Rowlands Canyon, named after R. H. Rowland, who had some claims in the area of the Humboldt Queen Mine and Humboldt Queen Canyon back in the 1920's (NBMG Bull. 8, p. 10). Humboldt Queen Canyon is not named on topo maps of the area, but lies between Rolands Canyon and Limerick Canyon (MSRMaps location; USGS TNM Viewer topo).

We took a little side road to the Humboldt Queen, which gave us this view of the spring...

...and this view of the Champion Mine, high on the hill above Rolands Canyon.

A long time ago, on one of my first mineral collecting and mine visiting trips in Nevada, I went to a dumortierite prospect or old mine high on the western range front of the Humboldt Range up some long and narrow — and I thought rough — 4WD road. A long-time grad student with plenty of Nevada and 4WD experience was driving; he exhorted me to always drive with my thumbs on the outside of the steering wheel when traversing backcountry dirt roads.

Most 4WD trucks (all?) lacked power steering back then, and if you hit a rut or rock, the steering wheel could twist radically, and thumbs could get sprained, or worse. (Ford introduced power steering in trucks in 1959 (or 1954?); it became an option in their 4WD trucks in 1979 (or standard by 1977?).)

I still drive with my thumbs outside the wheel on dirt roads.

View of the main Champion Mine workings from a very old road.

The road to the Champion Mine has few pullouts in its steepest and curviest spots, and someone coming downhill when we were going up had to (begrudgingly, it looked like), back up and pull over into a large bush-tree to let us continue going uphill. (A Rule of the West: Drivers going uphill have the right of way on dirt roads, although it seems like very few people know that these days.)

When MOH and I walked up the part of the road that is now completely impassable, I thought the old road, now washed out and heavily overgrown, looked like it hadn't been used for at least 50 years. (But it's been quite a while since I actively knew the ages of old roads and had a lot of practice with road-age estimation.) And when I couldn't identify a road going right to the main dumps, I was became convinced that this wasn't the same dumortierite mine I went to back in '76. (Air photos do indicate a road going to the upper dump, coming in from the direction I remember, so it *is* possibly the same mine.)

Current end of the road, as seen from some lower workings.

And so, we had reached the end of the road and turned around and parked leaving room for someone else to turn around if they came up while we were hiking and prospecting. And we had hiked up the old, overgrown road and climbed the hill to look at the lower workings.

To be continued...

Friday Photo: Dumortierite

Dumortierite with unknown greenish mineral.
Champion Mine, Rochester District, Nevada.