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GeneralStunning gold specimen

14th Feb 2017 17:45 UTCLarry Maltby Expert

Gold, Famatinite, Bismuthinite

Florence Mine, Goldfield, Goldfield Mining District, Esmeralda County, Nevada, USA

Uploaded by Jon Aurich

This stunning gold specimen was up-loaded this morning. Would some of our geologists please comment on its formation?

Is the center area quartz?

Is the gold deposit sequential?

Is the gold band a replacement like copper banded agate?

14th Feb 2017 19:33 UTCWayne Corwin

what does a streaktest show?

14th Feb 2017 20:21 UTCHolger Hartmaier 🌟

From the photo alone I can't tell if this is a nodular type formation (i.e. an "agate") or a tight folded vein. The gold mineralized zone looks remarkably consistent and conformable. Some close-ups of the gold mineralized zone would be interesting to look at to see what the bordering mineralogy consists of and the associated structure. Certainly very unusual. I've never seen anything like this before.

14th Feb 2017 22:28 UTCKyle Beucke 🌟

I have been reading about the Goldfield district. See:

https://archive.org/details/geologyoredeposi6667rans

Much of the rich ore consisted of altered volcanic rock fragments coated with bands of fine-grained quartz, gold, bismuthinite, copper sulfosalts (famatinite, goldfieldite, etc.), etc. Each band represents a successive stage of deposition.

Based on the descriptions in the literature, I would guess that this specimen consists of a core of altered (silicified) volcanic rock coated with a band of gold (+quartz?), then that in turn coated with dark sulfides (bismuthinite, copper sulfosalts?), and possibly later bands as well.

The gold was described as being very fine-grained, and in rich ore was so dense that the quartz had the color of yellow paint (but without metallic luster, because the gold was in tiny grains within the quartz).

Kyle

14th Feb 2017 22:35 UTCKyle Beucke 🌟

To reiterate, I think the deposition sequence is from the inside (immediately surrounding the presumed altered rock fragment) out. A closeup of the gray, inner core might show a trace of the texture of the volcanic rock (shapes of phenocrysts).

Kyle

14th Feb 2017 22:48 UTCGregg Little 🌟

Reading the description for the sample indicates that the deposit is epithermal. This means that the ore formation occurs in relatively shallow (less than 1 km) and cooler (less than 300 degrees C) depths in hydrothermal waters associated with volcanic, and by inference, underlying plutonic terrains. The heat sets up a convection system the drives mineral/element bearing fluid through a plumbing system (fractures and veins).

There will be zonation of the minerals (deposited in layers) in the fractures, or any type of opening, as the characteristics of the ore bearing fluid changes; for example pH, sulfur activity, oxidizing to reducing, temperature, elements or compounds in solution, etc. The gold layer represents the fluid conditions at that time, the core material (quartz?) represents a different stage of the fluid's composition. The gold is probably not replacement but primary ore deposition.

14th Feb 2017 23:27 UTCGregg Little 🌟

If the core material is not mineralization as indicated by Kyle (silicified host rock) then the zonation development still holds but instead is coating the fragments (breccia?). The host rock and surrounding country rock also goes through various types of alteration of which quartz is prominent in the mineral assemblages.

I think Kyle is right and although the picture is blurry when zooming in, there appears to be relic structures (phenocrysts?) in the fragment as well as preserved fractures and an alteration halo (lighter rim) forming a border around the outer portion of the fragment.

15th Feb 2017 05:10 UTCVolkmar Stingl

Looks in some way artificial to me.

15th Feb 2017 07:27 UTCUwe Ludwig

Thanks Volkmar that you said it. I was be in awe for a shitstorm when outing my oppinion in this case. This specimen looks definitely not natural. Welcome if anybody could convince me that this is not artificial.

Rgds.

Uwe Ludwig

15th Feb 2017 08:29 UTCDale Foster Manager

Perhaps before making suggestions of 'fake', you should go and take the time to familiarise yourselves with the other 49 uploaded images of the gold ore from the Florence Mine.

15th Feb 2017 10:08 UTCMarcus Voigt

54 Mineral Pictures

1 is from Kevin Ward

53 are from Jon Aurich = "Au-Rich" ?

:-S

15th Feb 2017 11:16 UTCPeter Slootweg 🌟

Good point Dale. But i must admit that my initial reaction was the same as Volkmar's. Very cool specimen! Never seen anything alike. (tu)

15th Feb 2017 11:27 UTCDale Foster Manager

Gold, Famatinite, Bismuthinite, Alunite

Florence Mine, Goldfield, Goldfield Mining District, Esmeralda County, Nevada, USA

Uploaded by Jon Aurich

Gold, etc.

Florence Mine, Goldfield, Goldfield Mining District, Esmeralda County, Nevada, USA

Gold, etc.

Florence Mine, Goldfield, Goldfield Mining District, Esmeralda County, Nevada, USA

Gold, etc.

Florence Mine, Goldfield, Goldfield Mining District, Esmeralda County, Nevada, USA

Gold, etc.

Florence Mine, Goldfield, Goldfield Mining District, Esmeralda County, Nevada, USA

Some of the other pictures showing the Florence Mine ore - intriguing material but doesn't look fake to me.

15th Feb 2017 11:45 UTCReiner Mielke Expert

Doesn't look fake to me. Looks like gold deposited around a fragment of rock.

15th Feb 2017 13:41 UTCDavid K. Joyce Expert

I've seen similar textures from veins/deposits at other Nevada gold mines, albeit not nearly as rich. It's for real.

David K Joyce

15th Feb 2017 14:21 UTCRory Howell

The goldfield district was famous for this mineralization and was one of the most famous and richest gold districts. The ore was extremely rich when it was encountered (hundreds, sometimes thousands of ounces per ton), but was very discontinuous - it was described as "raisins in a pudding" where the high grade pods were small but extremely rich. High-grading by miners was a serious problem because of the grades, and a lot of the material that is on the market probably came from either company geologists collecting unique pieces, or from high graders. The material is sold by the gram and is quite expensive as most is made into cabochons for jewelry.

Goldfield is a very interesting semi-ghost town with many hundreds of shafts over a 4-5 mile area and at one time was one of the largest towns in Nevada - you would not know it now as much of the original town was destroyed by fires and flash floods.

15th Feb 2017 15:04 UTCTony L. Potucek Expert

The Goldfield district produced an average of 1 troy oz. of Au per ton of ore mined over the life of the district. It is one of the richest gold districts ever mined in the world, based on average grade. Yes, the high grade did indeed look like those photos. The gold is intimately associated with the famatinite etc. sulfide rims around the altered volcanic fragments. In 1984, several geologists and I were allowed to enter the Florence Mine by the owner, Mrs. Martin Duffy, who still lived near the headframe. Our goal was to reach an area near the White Rock shaft off the 7th level of the Florence Mine. In 1948, Newmont mined that area and obtained 14,000 oz of Au from 28,000 tons of ore (0.5 opt average). The ground was taking weight and all timbers were cracked and snapped like broken match sticks, even where reinforced with steel and more lagging. In addition to samples taken, we retrieved Mr. Duffy's overalls, pipe, etc., at the request of Mrs. Duffy. During the Tucson show (Feb. 4), I gave a talk on this trip to an informal group of mining artifact collectors, and I also included underground trips into Delamar and Candelaria, Nevada. It was well attended, and I have to admit, a nice trip down my memory lane.

tlp

15th Feb 2017 16:37 UTCUwe Ludwig

Interesting, I'm convinced now that this amazing specimens are natural.

However (may be I read it over), it is not clear for me how these pieces are generated.

Were there at first empty quartz geodes which have been filled with the gold layer and later completely filled with a next generation of quartz or were there quartz noodles which got a layer of gold and which are later empeded with quartz?

Rgds.

Uwe Ludwig

15th Feb 2017 17:07 UTCKyle Beucke 🌟

Greetings Uwe,

This ore appears to be formed through deposition of gold, sulfides, and fine-grained quartz in layers over fragments of altered volcanic rock (that blotchy gray stuff in the "core" should be altered rock). Successive bands have different compositions, which is why the ore is so cool looking (black bands over, i.e. later than, gold bands, etc.).

Ransome (see link I posted above) wrote about these textures, mineralogy, etc. in great detail.

Kyle

15th Feb 2017 17:10 UTCLarry Maltby Expert

Very interesting specimen! Great comments all.

Kyle, thanks for the reference to the book. I was able to read parts of it until I got timed out. I have added another photo with two arrows pointed to what looks like dissolution channels in the altered rhyolite. Particles of gold have penetrated the rhyolite in these channels. The overall appearance of the rhyolite looks bleached and significantly dissolved. In fact I wonder if the dissolution of the rhyolite created the space between the chunks into which the mineralization progressed. Possible replacement.

Some of the other photos showing the matrix seem to illustrate this point.

15th Feb 2017 17:22 UTCKyle Beucke 🌟

Hello Larry,

Good point. Not an expert, but this is a high-sulfidation epithermal deposit. The "high-sulfidation" part is significant. It implies a greater input of magmatic volatiles and a much more acidic alteration fluid. Porosity resulting from leaching is more significant in these deposits, and ore deposition (supposedly later than alteration) is supposed to take advantage of this open space resulting from leaching. "Vuggy silica" is the extreme product of the alteration; it is basically a sponge of residual silica after the feldspar, etc. is dissolved from volcanic rock. Gold, copper sulfosalts, etc. in high-sulfidation deposits are often concentrated in the "vuggy silica." Lots of deposits in Chile, etc. like this.

Kyle

15th Feb 2017 17:37 UTCRory Howell

Quickie geology of Goldfield district

http://data.nbmg.unr.edu/Public/MiningDistricts/2160/21600019.pdf

15th Feb 2017 17:48 UTCLarry Maltby Expert

Kyle,

I follow your posts regularly because I know that you study hydrothermal deposits in geological settings that are much different from what we have in Michigan.

I have added a photo of an agate from the St. Louis Mine in Calumet, Michigan to illustrate the power of hydrothermal solutions to dissolve quartz. It would be difficult and dangerous to do this in a lab but nature seems to have no problem.

This is a Tom Rosemeyer agate that shows the dissolution of the outer quartz band and the replacement by copper suspended in recrystallized quartz.

15th Feb 2017 17:54 UTCLarry Maltby Expert

Rory,

Thanks for the info. I will get into it later today.

Larry,

15th Feb 2017 21:17 UTCKyle Beucke 🌟

Some similar textures from same district:

Photograph on this USGS page:

https://pubs.usgs.gov/of/2005/1258/

And from Ransome 1909:

16th Feb 2017 00:43 UTCPaul Brandes 🌟 Manager

Don't forget, there is a wonderful mini description of the Goldfield District on the Mindat Goldfield page itself:

https://www.mindat.org/loc-3894.html

16th Feb 2017 04:43 UTCJim Gawura

The state of Nevada has a very nice website that contains a lot of information on old mining districts. This is a link to the home page, http://www.nbmg.unr.edu/. Click, minerals and energy, mining, mining districts. type in Goldfield for district and your off. A lot of info. Anything listed that has a blue number on the far left is a hot link. USGS PP 66 can be found here https://pubs.er.usgs.gov/publication/pp66. Dive in and good luck.

Happy trails,

Jim

16th Feb 2017 05:42 UTCPhilip Persson Expert

Wow, wonderful specimens. As other have alluded to, this is a classic low-sulfidation epithermal mineralization texture. These types of veins form proximal to silicic volcanic rocks like rhyolites and dacites and typically gold will crystallize at the 'boiling horizon' where precious metal-bearing fluids decompress and devolatilize to the point where gold-bearing complexes with chlorine, OH etc are no longer stable and thus native gold precipitates. The banded appearance is another hallmark of low-sulfidation epithermal systems and is caused by repeated sequential precipitation of minerals on walls of a faulty or fracture surface that is repeatedly opened, mineralized, closed, etc over and over. If you cut a cross-section of a pipe at a geothermal powerplant in Iceland or New Zealand, you will actually see identical textures and mineral assemblages with even some little black squiggles that are very rich in Ag, Au etc. What is not well understood now, however, is why gold (and often silver) will often form such discrete 'bands' in larger, otherwise barren epithermal veins... this will take more lab work and understanding of P-T conditions of ore fluids at time of crystallization, as well as reaction kinetics of au precipitation. Anyways, great ore, I'd love to own some at some point from this mine! :)

cheers,

Phil Persson

Denver, Colorado

16th Feb 2017 06:17 UTCKyle Beucke 🌟

Hello Phil,

I am not a geologist, but Goldfield is considered to be a classic high (not low) sulfidation epithermal deposit. Abundance of alunite alteration (as opposed to adularia and sericite) and presence of enargite and luzonite/famatinite are some of the distinguishing characteristics. That being said, I have seen it described in the literature that the gold stage in high sulfidation deposits is often linked to a later, lower-sulfidation fluid than that responsible for the earlier alteration.

Again, not my field of expertise, but one hypothesis for sporadic Ag-rich bands in otherwise barren quartz (this time in low sulfidation deposits) was put forth by Wilkinson et al. 2013. They found evidence that pulses of magmatic brine are responsible for mineralization in a system otherwise dominated by meteoric water.

It is truly incredible ore, and not surprising it was often highgraded!

Kyle

16th Feb 2017 13:51 UTCDavid K. Joyce Expert

Uwe, if you look at the photo of the hand holding the banded fragment of high grade ore? This is the natural form of the ore. The mineralization is undulating. If you physically slice that specimen horizontally, through gold and examine the result, the slices will exhibit round or curved aggregates of mineralization. Most of the sawn samples shown in the pictures are sawn slices, that were sawn parallel to the wall of the vein to produce the dramatic rounded-curved-appearing slices of mineralization.

My thoughts, anyway!

David K joyce

16th Feb 2017 17:15 UTCLarry Maltby Expert

I have up-loaded a photo from the USGS paper that Kyle provided with a link. For the purpose of conversation I have exaggerated the color and contrast.

Phillip,

I was interested in your comment that the area between the “islands” of primary rock, opened and closed multiple times in sequence. Meaning, I think, that the primary host rock fractured in a random pattern allowing hydrothermal solutions to enter the fractures and dissolve away some of the primary rock leaving a mineral deposit based on the chemistry of the solution. The process would then repeat with another sequence of dissolution and the precipitation of a different mineral based on the changing chemistry of the solution. Each time that this occurs, the gap between the “islands” widens and the “island” gets smaller.

This seems to be a reasonable explanation of formation of the above specimen. It also infers that the gold was deposited late in the sequence because the gold borders the “islands” in their final size and shape.

20th Feb 2017 02:29 UTCGregg Little 🌟

I find the discussion around the sequence of mineralization somewhat confusing in that it appears to be opposite to the deposit description and samples pictures shown here. The literature describes, "Mined ledges are distinguished by nested heterolithic breccias that display upward clast displacement, and multiple encrustations of clasts by quartz, alunite, kaolinite, Cu-As-Sb-Ag-Bi-Sn-Te-S minerals, and gold.".

In the samples shown, the edges are sharp, corners angular and interiors nearly unmineralized by gold. I would contend that the country rock breccia fragments are altered (quartz, allunite, kaolin, etc.) and often have alteration selvages but in general not leached, dissolved, corroded or reduced to any extent. This would then indicate that the native gold, in contact with the clast, was early in the ore mineralization stage. Although there is some mention in the literature of clast replacement, the main mode of formation is encrustation which indicates the altered clasts were encrusted earlier rather than later by gold which was then followed by the latest stage void filling by gangue minerals.

20th Feb 2017 03:51 UTCKyle Beucke 🌟

Gregg,

I too think the gold looks like an early layer deposited on the rock fragments, with later minerals being deposited on that (for instance, some photos seem to show needles of what might be bismuthinite deposited on (later than) the gold). Ransome describes ore specimens with varying sequences of ore mineral deposition. In contrast to what we see in these photographs, he suggests that gold and quartz (without copper sulfosalts) was usually one of the later bands. I suppose fracturing (through tectonic means or hydrothermal explosions) at different times during the lifetime of the hydrothermal system could result in different sequences of mineralized bands appearing at different places.

Kyle

20th Feb 2017 09:46 UTCGregg Little 🌟

Kyle;

I think you are right there as well, this is a complex ore deposit system. My point was that encrusting ore deposition was the primary mechanism as indicated by the literature. The samples from the Florence and Mohawk Mines seen in this discussion show the encrusting deposition as apposed to leaching of the breccia fragments exteriors making room for gold deposition at a later stage.

I did leave in that part of the abstract statement "nested heterolithic breccias that display upward clast displacement" ("AGES AND GEOCHEMISTRY OF MAGMATIC HYDROTHERMAL ALUNITES IN THE GOLDFIELD DISTRICT, ESMERALDA CO., NEVADA", USGS poster session by Peter Vikre, Robert Fleck and Robert Rye) as an acknowledgement of other modes of ore deposition. It seems "elevated fluid flow velocities" can be determined from the mineralization distribution indicating "episodic and dynamic degassing from a magma chamber directly beneath the main district". Other ore samples if they didn't go to the processing plant probably show the complexity with multiple encrustations and breccia clast replacement occurring in this very dynamic hydrothermal process. The poster also describes alunite and microcrystalline quartz as replacing the breccia clasts as well as the ore minerals. Note that words in quotations are from the USGS poster.

15th Mar 2017 04:42 UTCJon Aurich

I'm the owner of the specimen and the Mine that it came from, as I see by the questions raised on this specimen, not many are familiar with this species of ore. The ore is not enhanced or fake, if you go to my site, you will find many different species of Epithermal ore that has come from the Florence Mine. Jon Aurich Google Plus.

15th Mar 2017 05:14 UTCJon Aurich

Generally, on this ore from the Florence, the center kernel or brecciated piece that the band of gold is around will be either Dacite or Milltown Andesite, the gold is of a high fineness, (840 - 860) and the particle size is around 300 mesh and mixed with a Cryptocrystalline Quartz. The high grade ore of the Florence is almost always associated with Famatinite and Bismuthinite, some of the Bismuthinite has well defined Needles, some of the needles are around 3/8 of an inch long, some Specimens have large amounts of Alunite and others are sparce. This ore is of highly acidic Sulphide.

15th Mar 2017 05:22 UTCJon Aurich

I do have a great name !!!!

15th Mar 2017 05:39 UTCJon Aurich

Another fine specimen

15th Mar 2017 05:52 UTCJon Aurich

My watch fob.

15th Mar 2017 09:44 UTCJohan Kjellman Expert

Jon,

I checked out your site and have a question. I see that you have many pieces in old jewelry. They are old right? If so, how come you know the different localities, is it something that has been in your family long time?

thanks

15th Mar 2017 16:16 UTCJon Aurich

Hello, The watch fob and one ring are totally original, from around 1907. The other rings are antique, but I took out the original cabs and custom made the High Grade for them, I thought the specimens look better in antique settings. Most of the specimens that you see, I have found, they were found on old tailing piles or backfills inside the Mines themselves, since some of the old Lease era drifts were abandoned and the miners were using candles, their cobbing of ore from waste underground wasn't 100% efficient, so the abandoned backfills would carry High Grade in them. Some specimens that I have from restricted areas, ( Government sites) were found in a map drawer that belonged to The Goldfield Consolidated Mines Company, in it were numerous High Grade specimens that were labeled. High Grade Gold Specimens from Goldfield are very rare and the only property to obtain them currently is the Florence Mine.

16th Mar 2017 06:11 UTCJon Aurich

Florence Mine, Goldfield Nevada.

16th Mar 2017 06:14 UTCJon Aurich

Florence Mine.

16th Mar 2017 06:20 UTCJon Aurich

The Famous Florence Mine.

16th Mar 2017 21:24 UTCJon Aurich

Goldfield

18th Mar 2017 14:38 UTCLarry Maltby Expert

Jon,

The last specimen that you show above is one of the best to illustrate a possible mode of formation. I have been studying hydrothermal brecciation with regards to the hydrothermal alteration that I see in the basalts of Michigan’s Keweenaw Peninsula. I came across a professional paper on “Hydrothermal Breccia Pipe Structures”. Figure 1, shows an excellent illustration of a hydrothermal pipe structure in cross section. It favors the encrustation theory especially near the top of the pipe.

http://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=1188&context=geologia

I spent a considerable amount of time going through your website. The combination of gold specimens and the historical artifacts that you have found was really interesting. My wife and I have always been interested in western history. Much or our travel in the west was to historical locations.

19th Mar 2017 03:28 UTCJon Aurich

Hi Larry, when you ever come through Nevada, call me ahead of time and I can maybe meet you here at the Florence Mine, I live in Vegas but come up regularly on the weekends. You may find it interesting to come up with your 10 power lense and maybe find some pieces of Epithermal High Grade Gold on the tailing piles yourself.......

19th Mar 2017 04:24 UTCJon Aurich

Florence Mine

19th Mar 2017 12:28 UTCLarry Maltby Expert

Hi Jon,

I would love to meet up and prowl the Florence with you but age related problems with my wife’s health has confined us to home. In our younger days we would be making plans to road trip to Nevada this summer to meet with you. We have always been big fans of the “road trip”. During our trips over a sixty year period, I have taken thousands of pictures mostly colored slides. Currently I spent my free time digitizing and restoring some of these old photos to upload them into the Mindat data base. It has been a good way to continue enjoying my hobby.

I have learned a lot from the comments on this thread.

Thank for the invite, Larry,

20th Mar 2017 18:34 UTCJon Aurich

Hi Larry, I'm sorry to hear that you and your wife cannot come out to Nevada, I guess that we should have met years ago, you would have enjoyed the mines here in Goldfield. I will continue to add more specimens to the site so that you can enjoy it that way..... Thanks for the interest in this type of ore that is unique. Talk soon, Jon.

22nd Mar 2017 13:01 UTCTony L. Potucek Expert

Hi, Jon,

In 1984, I sampled the Florence Mine with a couple of other geologists. Mrs. Martin Duffy was residing at the Florence Mine at the time and granted permission for us to enter the Florence and cross over into the White Rock Shaft ground via the 7 Level. We encountered two underground barricades, which we had to breach in order to gain access to ground last mined by Newmont in 1948. Mrs. Duffy requested that we bring up her late husband's work overalls and pipe, which we did. I would surmise that Mrs. Duffy has passed by now. Who lives in the house near the shaft nowadays? Thanks.

best regards, tlp

22nd Mar 2017 17:54 UTCJon Aurich

Hello Tony, I remember when Ruth gave you access, she was very cautious of it and as I can remember. I wish that the barricades were up as I cannot tell if someone is accessing the seventh level of the Florence from what was known as White Rock, in the main shaft of the Florence above the seventh level about 100' of platforms and ladders have collapsed, so I have no (man way) access to the seventh level and White Rock has no access above the seventh.... my family and I Have two residences, the Florence is one of them, and we also have a friend that watches the place when we are not there. Ruth has been gone about 15 years now. The house and the Hoist House have been restored, the Rustler #2 Mine which are the headframe and buildings outside the gate are about 50% restored now. Go to: Jon Aurich Google plus. And you will see hundreds of Nevada historic items and current photographs of the Florence and Rustler mines. Thanks, Jon.

23rd Aug 2018 05:47 UTCJon Aurich

Goldfield Nevada. This great specimen was from the Nixon, Wingfield and Sweeney Lease of the Florence Mine. Like the famous Engineers Lease, the ore was mainly High Grade with very little low grade material.... This specimen was the famous 1/2 - 1 ounce per pound Gold ore!!

24th Aug 2018 20:54 UTCJon Aurich

Goldfield Nevada. Here is another rare specimen from Goldfield. The Gold is plentiful on this one.

24th Aug 2018 22:23 UTCJeff Weissman Expert

Jon, again, very interesting photos and context - but, what are the sizes of these?

24th Aug 2018 22:27 UTCJon Aurich

The first one is 3 1/2” x 2” x 1/4” and the other is 1 1/2” x 5/8” x 5/8”.....

3rd Nov 2018 15:38 UTCJon Aurich

. Goldfield Nevada. Bonanza Ore. This amazing high acid Sulphide Gold Specimen is from the famous Goldfield mining district. From about 1906 - 1910, Goldfield was the largest populated city in Nevada, aided greatly by the fabulous high grade ore that was mined there. Some of this ore, like the one pictured above , assayed around one ounce of Gold to the pound ! This specimen contains Quartz, Famatinite, Goldfieldite, Dacite, Bismuthinite, Cryptocrystalline Quartz, Alunite and Native Gold. 3” x 1 3/4” x 1/4”..

6th Apr 2019 05:22 UTCJon Aurich

Goldfield Nevada. Bonanza Ore. High Grade Epithermal Gold Specimen. Here is another exceedingly rich Native Gold. Some of the incredible ore assayed at over 2,800 of Gold per ton !!

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