Silver Reef Utah

The Petrified Forest Cave story recorded by the Pioche Record January 1, 1881 - tells of

The petrifications of course were mined for their silver thus destroying the remarkable trees.

Most of the silver etc. was found with wood and vegetation, making this a great tale, but it probably isn't true.



wchsutah.org/towns/silver-reef8.pdf

We visit Silver Reef on occasion but never spent time looking for rocks. An acquaintance told me her father still mines Silver there, not a lot but it is there. She pointed me to a wash with some yard rock, went back recently and it's posted, "Private Property" and "For Sale" It's fun to go "behind the Reef", walk and explore the old foundations, visit the Cobb Mine. Wish I knew more about Geology, has to a fascinating area. There is a really nice Museum there, well worth a visit. Here's a link to some of my photos.

winpics.fototime.com/Silver%20Reef%20Mine%20Area-%20Leeds%20Utah

Of interest to rockhounds is the agate layer in the area.







Don wrote about "Lunch Break Agate."
forum.rocktumblinghobby.com/thread/59343/lunch-break-agate

Silver Reef jail.

www.stgeorgeutah.com/news/archive/2017/08/27/silver-reef-day-the-boom-bust-and-rebirth-of-a-ghost-town-anomaly/#.XA7BozF7n9I

We aught to give it a proper name.

I offer "Silver Reef Agate" as that is where the layer seems to be the thickest and most colorful.

citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.1011.9133&rep=rep1&type=pdf

COMMENTS REGARDING ORE GENESIS AT SILVER REEF, UTAH
by RICHARD V. WYMAN

The most recent publication on the geology of Silver Reef is that by Paul Dean Proctor (1) in which he hypothecates an origin of the silver mineralization from the leaching of Triassic volcanic tuffs, and transportation of the metals as sulfates to the seat of syngenetic deposition within the Silver Reef sandstone.

The following comments are intended principally to refute the arguments presented by Proctor, rather than let his work stand uncontested. Additional facts based upon the work of the recent operators add weight to the epigenetic origin of the orebodies from hypogene solutions.

ARGUMENTS FOR SYNGENETIC ORIGIN ANSWERED
On page 121 Proctor lists eleven points that must be considered in any theory of origin. Most of these points as presented tend to favor a syngenetic origin. They are as follows:
1.) The occurrence of silver chloride in association with copper carbonates and minor amounts of uranium-vanadium minerals and some selenium.
2.) The known areal distribution of minor silver and copper content in the St. George basin.
3.) The localization of commercial ore deposits in light colored sandstones inter- bedded-with red sandstone and shales of the Triassic Chinle formation.
4.) The common association of the metallic minerals with plant remains.
5.) The concentration of silver and copper minerals in stratigraphic units within the sandstone member.
6.) The association of silver, and to a lesser extent, copper with clay galls.
7.) The paragenetic sequence of deposition of the different minerals in the deposits.
8.) The absence of the associated intrusive rocks with the mineral deposits.
9.) The lack of silicification, sericitization, typical ore textures, and other accompaniments of hypogene deposition.
10.) The absence of recognizable feeder channels for the different orebodies.
11.) The occurrence of silver- and gold-bearing chalcocite-pyrite concretions in the bentonitic shale 310 feet below the Silver Reef sandstone.

The assemblage of metals described in item 1 should also include iron, which is especially prominent as spongy limonite associated with the uranium ores. Otherwise there is no difference of opinion as to the presence of the metals.

The assemblage could fit an epigenetic origin from hypogene solutions just as well.

In item 2 above, Proctor implies a wide areal distribution of metals in the Silver Reef. There are a few other deposits of this type known in the Santa Clara, St. George, and Hurricane areas. However, the deposits are isolated from one another, small, and not necessarily in the same stratigraphic position. In fact, minor amounts of silver and copper are known from the Shinarump up through the Dakota in the general area.

Item 3 is an undisputed fact. The light color, however, crosses bedding planes and spreads out from fractures and jointed areas. The light color described by Proctor as the Leeds Sandstone is also believed to be an alteration phase rather than a sedimentary facies. The relation of alteration of this type to ore mineralization is direct and significant, and can be used as a guide to favorable areas on a district basis, although it is too general a guide to be used for locating specific ore shoots.

Item 4 is only half true. To this should be added, "the occurrence of silver in the absence of plant remains," and "the occurrence of plant remains in the absence of any metals." The experience in the district was that plant remains were not a good indication of mineralization. Much of the silver ore lacks plant remains, and in one case--the 200 level of the Cobb mine-- charified plant remains occur unmineralized only a few feet from a com- mercial silver body that contained no plant remains. Organic material was much more important in localizing uranium, as would be expected from the conditions required for its precipitation as described by Garrels (2).

Items 5 and 6 are explained as the result of selectivity based on structural or chemical favorability. Similar selectivity in limestone sections has been noted in many mining districts where one bed is favored for some reason. In the Silver Reef district, the favored bed is not always in the same strati- graphic position within the sandstone, and there are also instances of several mineralized beds lying over one another.

Item 7, the paragenetic sequence, can be explained satisfactorily on the basis of epigenetic hypogene mineralization.

Item 8 is only partly true. There are no known igneous rocks other than recent basalts in the district. But the huge igneous mass of Pine -Valley Mountain lies within 6 miles to the north. This has been described by Cook (3) as a laccolith intruded beneath a blanket of ignimbrites. In many mining districts the granitic mass ascribed as a source of the metal is farther than this.
Nothing is known of the presence or absence of igneous rocks underneath the district. In particular, it is possible that the Virgin Anticline itself may contain a Iaccolithic mass that has not been exposed by erosion.

Item 9 is not true. A halo surrounding the ore deposits is mildly silicified. In particular, the individual quartz sand grains are extended by authigenic overgrowths to form a quartzitic rock.
It is notable that the stope backs stand well for this reason. Development of sericite is seen within the ore. At greater distance from the ore alteration in the form of bleaching, hydration of hematite, and removal of iron may be considered as a "normal" accompaniment of ore deposition.
To use the apparent lack of "typical" ore texture as supporting the syngenetic theory in an un-typicaI deposit is not a logical argument.

Item 10 is not true. In mining the Big Hill orebodies, the relationship of ore to feeders was clearly shown. There was even a zoning of metals away from the feeders, which was quite convincing. The feeder channels consist of strong fractures of small displacement of a few inches or a foot. Minor distribution was along joints from that introduced along the feeders.

In the Big Hill mine the zoning is as follows:

A central zone of high- grade uranium and much limonite iron surrounded by a zone of silver-bearing uranium ore.
Farther out and surrounding this zone is a broad area of silver ore with little or no uranium.
This gradually decreases in grade to an economic limit.
There is some increase in copper in the peripheral area.

In following the faults that are described as feeders, as they leave the uranium area they are still distinctly related to mineralization, and contain high-grade silver ore on both sides, decreasing outward until another feeder is approached.
A very prominent feeder is located on the Buckeye Reef where all of the mined orebodies appear related to it.

I refer to the fault illustrated by Proctor in Plate VIII, page 58. This fault was even stoped as a vein within the Buckeye Mine. On the White Reef, a strong system of through going fractures is related to the Cobb-Newton mine, and another to the Barbee-Walker. On the East Reef each of the several small ore showings has a similar structural locus.



Item 11 describes the concretions on Fire Clay Hill. It should be noted that this hill is in the center of the eroded Leeds Anticline, and only a few hundred feet from some of the biggest producers of the district. It is not surprising to find mineralization there. In fact, this can be used as an argument favoring a hypogene origin of the ore, as there is no evidence that these concretions are syngenetic.

Of the above comments, the most important favoring an epigenetic origin are those concerning the alteration of the sandstone, and the presence of structures to channel the ore solutions. Additional structural controls of deposition have been noted since the earliest days of the camp; some of them are:

1.) Location of the district on the nose of the Virgin Anticline.
2.) Location of the principal producing area of the district on the Leeds Anticline.
3.) Location of orebodies underneath clay beds, and in highly fractured areas, especially near faults of small displacement.

The control of mineralization by structures that were formed during Laramide or Tertiary time is sufficient evidence that the orebodies as they appear today are epigenetic. These same structural controls were used successfully to locate unoxidized black uranium and sulfide mineralization below the zone of vadose circulation, which throws still greater doubt upon the theory that these bodies were formed by secondary enrichment of a widespread low-grade mineralization.

Proctor states that the silver was derived from the leaching of the Bentonitic Shale member of the Chinle. On page 21 he lists analyses of these shales. The two highest assays were 0.10 oz Ag and the rest were "trace" or none. All samples were taken within the mining district. The thickness of the bed is 10 to 13 feet.

If the tiny amount of silver present were leached with 100 percent efficiency and moved by surface streams in solutions and reprecipitated 100 percent within the Silver Reef sandstone, then in order to account for the quantity of silver from recorded production plus that remaining in low-grade ores and dumps, a total of 6 square miles of the shale would have had to have been leached.

All of these conditions are highly improbable. In addition, the fact that the Silver Reef itself averages more than 0.10 oz Ag per ton, and is 100 feet or more in thickness, calls for the additional leaching of 10 square miles of the bentonitic shale for each square mile of the Silver Reef sandstone, assuming complete leaching.
There is no evidence that the bentonitic shales normally contain as much as 0.10 oz Ag, as again, all samples were taken within the mineralized district, and only 310 feet below the known "reef" mineralization.
Of the 6 samples, two had no silver, two had a trace and two had 0.10 oz Ag. This is very little upon which to base a theory of genesis.
If the bentonitic shales formerly existed in larger volumes, then there should be evidence of the presence of large quantities of redeposited bentonite within the Silver Reef. In fact there is none, or so very little that it is of distinctly minute importance.

CONCLUSION

The theory of genesis of the Silver Reef mineralization from a syngenetic process is doubtful on the basis of the evidence. The theory of genesis from the leaching of underlying bentonitic shales appears impossible from a logical approach, as well as from the field evidence.

An epigenetic origin for the orebodies fits the facts, and is especially substantiated by the presence of related alteration and a relation of orebodies to post-Chinle structures. A hypogene origin for the ore solutions appears most logical in view of the epigenetic origin, presence of igneous activity in the general vicinity, and stratigraphic distribution of the known mineralization. Solutions in their migration were controlled by permeability and ore deposition by chemical favorability of the beds as well as structure.

The ore solution must have been capable of carrying silver, copper, uranium, vanadium, gold, selenium, and sulfur. Further reconstruction of the nature of the ore solution would be a worthwhile step in the study of the ore genesis.

ACKNOWLEDGMENTS

The ideas advanced above have been the opinion of the writer for a number of years, and were the result of geologic studies at Silver Reef during the years of 1954 to 1957 when employed by Western Gold and Uranium, Inc. as Chief Geologist and General Superintendent.

I wish to acknowledge the stimulating conversations on the subject with other geologists who have been over the ground with me and encouraged me to record my observations for publication.
INTERMOUNTAIN EXPLORATION COMPANY ST. GEORCE, UTAH •April 4, 1960

REFERENCES
1. Proctor, Paul Dean, 1953, Geology of the Silver Reef (Harrisburg) Mining District: Utah Geol. and Min. Survey Bull. 44.
2. Garrels, R. M., 1953, Some thermodynamic relations among vanadium oxides and their relation to the oxidation states of the uranium ores of the Colorado plateaus: Am. Mineralogist, v. 38, p. 1251-1266.
3. Cook, Earl F., 1956, Geology of the Pine Valley Mountains, Utah: Utah Geol. and Min. Survey Bull. 58.

Good post Dave. I didn't know that the silver ore was also found with uranium at silver reef.

I agree that the two last pieces are almost identical to some of my AZ Pet Wood. Fascinating information.

I've visited that little museum and enjoyed it. If anyone is going by there it's worth the time to stop and see.