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Author Topic: Need an expert identification....  (Read 8940 times)

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Offline diamond jim

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Need an expert identification....
« on: November 02, 2014, 08:07:50 PM »
The wife and I were driving through a rough area of northern Nevada last weekend. I spotted a 10" rock by the two-track as we went by. I noticed it had a greenish cast, which made me back up and take a closer look. The rock in that country is either rhyolite, or basalt, and is dark brown or reddish brown. This rock is definitelky an anomaly, and looks like iot might be a lamproite, though I'm more hopeful than sure on that. Any help to clarify would be greatly appreciated. The rock can be scratched with a knife blade, but not easily. A drop or two of muriatic acid had no obvious effect. A freshly broken face has no special odor....just sort of a dusty smell.
Jim





Offline EMF

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Re: Need an expert identification....
« Reply #1 on: November 03, 2014, 08:53:00 AM »
It is tuff, ash and larger pyroclasitic fragments welded together by the residual heat of the eruption, and is most likely of the same composition as that of the surrounding igneous rocks of the same age.  However, you'll need to do further analysis to determine the possibility of it being a lamproite tuff. See what any geological maps show about the area where found, examine the rock sample itself for positive indicators of it being lamproite. Are lamproite pipes geologically possible where the rock was found? If the pipes are posssible and the rock is a lamproite tuff, then it is time to try tracing out the source of the rock and doing some dry washing for indicator minerals in the area. One way or another, tuff luck.

Offline diamond jim

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Re: Need an expert identification....
« Reply #2 on: November 03, 2014, 06:15:50 PM »
Yup. Looks like I'm just going to have to go down there and get after it. Looks like I've got another job of surveying anthills ahead of me. The good thing is I actually enjoy that kind of prospecting. The area definitely could have lamproite pipes, or kimberlite. That whole northeast corner of Nevada is fairly close to the boundary of the craton that underlies Canada's, Wyoming's, and Colorado's diamond areas. As far as I know, however, no lamproites have been found in that area, though I seriously doubt anybody has looked very hard, if at all. The edge of the craton extends mostly north from Wells, NV, trending a little easterly, and goes clear up to the Canadian border, and beyond. I appreciate the ideas. I may crush the large piece of the stone, and see if it has any chrome diopside, or garnets. I'll keep the forum posted on any results....thanks again,
Jim  

Offline EMF

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Re: Need an expert identification....
« Reply #3 on: November 03, 2014, 09:34:57 PM »
What mystifies me is the origin of the diamonds found in California. Where they have been found is always downslope from an ultramafic rock body, but we are nowhere near any cratons, and no pipes have ever been found here. I know of one diatreme, but it is in the Coast range, really far from any craton. I might prospect it someday, but diamonds are unlikely.

Offline diamond jim

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Re: Need an expert identification....
« Reply #4 on: November 03, 2014, 10:17:19 PM »
What mystifies me is the origin of the diamonds found in California. Where they have been found is always downslope from an ultramafic rock body, but we are nowhere near any cratons, and no pipes have ever been found here. I know of one diatreme, but it is in the Coast range, really far from any craton. I might prospect it someday, but diamonds are unlikely.
Yes...also near Coos Bay, OR. Has to be something to do with the subduction zone, but hasn't been proven. Maybe CA's diamonds were brought up with the orogeny that produced the Sierras? Or maybe they were in the old tertiary rivers and were carried from kimberlite/lamproite pipes that are now completely eroded away, and gone.
Jim

Offline EMF

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Re: Need an expert identification....
« Reply #5 on: November 04, 2014, 10:03:11 AM »
I've been thinking their origin may be linked to the exhumation of slabs from subduction zones. Diamonds have been found in Asia that came about that way, but so far it is the only reasonable conjecture I can come up with lacking cratons and pipes. I would love to do some serious prospecting for them in the Sierra Nevada, but the diamond bearing areas there are taken up by private property and one gold mine. The Klamath mtns. afford more opportunity because most of the finds were on Federal land, but most of the diamonds found there so far were not gem quality.

Offline diamond jim

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Re: Need an expert identification....
« Reply #6 on: November 04, 2014, 11:11:44 AM »
Speaking of prospecting for diamonds....Dan Hausel showed, in his writings, that a couple  of diamonds were found in extreme SW Montana, which is also along the edge of the craton. Chris (wife), and I went up there in early Oct. I assumed the stones were found at gold mines. The research showed a fairly substantial gold operation had taken place on Jeff Davis Creek. When we got there, we were surprised to find that two operations were currently running for gold. I got lucky, and ran into two friends of one of the owners (smaller, and older operation). They introduced me, and he and I hit it off right from the start. Spent 3 hours talking. His is a great story, but I don't have time to write it now. He's currently getting $800-1,200/day off his place, and figured he had a 50 year supply of gravel left. The gravel is two hundred feet deep, and has never been tested at depth. I'll be back there next summer to run some of his tailing piles for gems.
The source of the placer has never been found. I'm thinking they're digging in an old, maybe tertiary, riverbed. If so, the source of any diamonds is long gone, but there could be diamonds in that old riverbed. The Creek is about 6,000' -8,000 elevation.
Jim

Offline EMF

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Re: Need an expert identification....
« Reply #7 on: November 04, 2014, 12:32:29 PM »
Well, the sources of diamonds have a deep reach into the earth, so if the local source there was not covered in sediment, or tectonically folded up, there should be an abraded remnant somewhere in the vicinity. Any geological mapping that shows ultramafic bodies of small area could give some hints about drainages to prospect.  I have seen a small circular ultramafic body on a geological map very close to one of the places where diamonds were found in the foothills of the Sierra Nevada, just screaming to be investigated, but the real estate developers got there first.

Offline diamond jim

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Re: Need an expert identification....
« Reply #8 on: November 04, 2014, 01:56:53 PM »
Well, the sources of diamonds have a deep reach into the earth, so if the local source there was not covered in sediment, or tectonically folded up, there should be an abraded remnant somewhere in the vicinity. Any geological mapping that shows ultramafic bodies of small area could give some hints about drainages to prospect.  I have seen a small circular ultramafic body on a geological map very close to one of the places where diamonds were found in the foothills of the Sierra Nevada, just screaming to be investigated, but the real estate developers got there first.
No chance at all? Not even "downstream" a bit? That's a real bummer. In this area, there is so much country, the geologic maps are far from detailed. The government just doesn't have enough manpower to cover it all, so a lot of assumptions are made based on the surrounding geology. It's very possible to find a small intrusive body that nobody knows about. I know of one place in Idaho, near the Utah border, where there are wheelbarrow-sized boulders of mica schist, along with big, rounded and very smooth, watermelon sized cobbles. This only covers an area about 200 yards in diameter. In all that area, this is the only place it occurs. I think the cobbles were rounded by being tumbled by an intrusive body. There are no rivers within 20miles. The cobbles are chert, quartzite, and other hard material. Creek that drains the are is full of small garnets, and possibly other gems. Eventually, I'll get the jig in there and see what's really in that creek. I know there's no gold. Keep at it, you never know where the next strike will come from.
Jim

Offline EMF

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Re: Need an expert identification....
« Reply #9 on: November 04, 2014, 07:34:17 PM »
Yeah, not much of a chance. I just checked my maps again, along with Google Earth, and it is totally private land there, with people living by the road next to the creek that comes down through the formation and then under the highway. But the prime areas to check are accessed by a hike through exposed country that is all private property.  It's not the first interesting looking place to prospect that I had to rule out due to lack of access.

First I look at the history and the geology, then I have to see if the good looking places are available. In that part of the state most of the good places have been picked over either with development or claims. Not much opportunity for a prospector unless he lives in the area and knows it well.

The Klamaths are mostly undeveloped and much of it is open to mineral entry, more suited to my interests. When I can be there my gold claims have kept me busy, but I do look forward to making some time to hunt for diamonds in the area. I found one eight years ago in a sample of black sand I was examining with a microscope, about ten times the diameter of one of the hairs on my head. I had a memory of it being brown somehow, but I just dug it out and looked again, and it is a light pink in color. There is more to be discovered about diamond sources than the science so far acknowledges, I believe. First you start with the concentated sediments in a drainage, and then follow the trace.