Thursday, August 26, 2010

Preparation For Gold Prospecting Trips


Claim post on Federal Minerals. I often get questions about claim staking,
but I'm as confused as you are. Please contact the US Bureau of Land
Management for information and hope they provide you with the correct
facts.
While completing my latest book with my son (who is also a geologist) I thought some information would be useful for those who are interested in learning some hints for prospecting. As a prospector, you need to learn about maps. Topographical maps provide information on geography and show locations of hills, valleys, mountains, roads, trails, creeks and towns. Geological maps show rock outcrops in relationship to the geography and likely will have locations of mines, prospect pits, trenches, tunnels, veins, faults, shear zones and folds. Geological maps also provide information on types of rocks.


Know what areas are open to mining claims. Much Federal land is open to claiming, but some is closed to claims. To find out what is open, visit you local BLM (Bureau of Land Management) office. State land cannot be claimed but often can be leased. Private land cannot be claimed unless it has Federal Minerals under the private surface. One problem with mining claims is that new claims are constantly filed, and at the end of the fiscal year, others are not renewed thus claim maps change. One way to access claim information that is mostly up-to-date is to access the BLM GeoCommunicator website (sorry, the BLM apparently decided to eliminate claim information on their website recently). This can also be found by doing a Google Search for "BLM GeoCommunicator". Just like the government, this site does not always work and it is also very slow.

Gold nugget found in Rock Creek, South Pass.
The BLM attempts to keep information up to date on this site, but like anything the government does, it is not always correct. So use it as a general guide for mining claims and claim activity then you need to follow up with research in the county courthouse. When prospecting in the field, watch for claim posts as these provide information on claim locations, although just because there are claim posts in the field, this does not mean that the claim is active or even legal.

Other sources that are excellent for prospecting include Google Earth and Virtual Earth. These provide aerial photos over areas of interest as does the GeoCommunicator. With the aerial photos and associated maps on these programs, relationships between geology, topography, mines, prospects, roads and drainages can be seen from the air prior to visiting a area of interest.

Schedule a trip to the Hidden Hand gold mine and vicinity in the Lewiston district of the South Pass greenstone belt in the southern Wind River Mountains in western Wyoming. The legal description of the Hidden Hand mine is SE section 5, T28N, R98W and map coordinates are 42o25’30’N; 108o32’39”W. Thus if you examine the Radium Springs quadrangle and find section 5 with the Hidden Hand mine labeled on the map, it is located in the southeast quarter of that section. Or by using the map coordinates, you should be able to zero right in on the mine with Google Earth.

Inside the power house at the Vulture Gold Mine ghost town, Arizona.
Topographical maps that cover this area include 2 degree sheets (scale 1:100,000) and 7.5 minute sheets. The 2 degree sheets are especially useful. These can be neatly folded and carried in a shirt pocket, glove compartment, or day pack. They represent general maps covering broad regions that are great for planning field excursions and contain information on roads and geography. For greater details, 7.5 minute quadrangles (scale 1:24,000) are invaluable. Topographical maps are available at some sporting goods stores, outfitter stores, the WGS, US Geological Survey (USGS), University of Wyoming Geology Library and local colleges and libraries. The WGS and USGS will also have geological reports and geological maps, many which can be ordered on-line or over the phone.

The WGS and USGS websites should have topographic map indexes. First find a 1:100,000 scale (2 degree) topographic index for the state. Now search the coordinates T28N (vertical scale) and R98W (horizontal scale). These coordinates intersect within the boundaries of the South Pass 1:100,000 scale topographical map. This is the first map you need for your excursion. Often there is a companion 1:100,000 scale BLM map on Land Status. The South Pass Land Status map will be useful as it gives general information on location of private, public and state lands. These Land Status maps also have a layer of topography sitting under the land status designations.

Next, examine the 1:24,000 scale (7.5 minute) topographic map index. The coordinates of the Hidden Hand mine places it within the Radium Springs quadrangle near the top of the map. The map to the north is the Atlantic City map which may also be useful. Search for geological maps on the WGS website: geological maps provide important geological relationships associated with the mine, such as rock types, nearby structures such as faults, shear zones, folds. The necessary geological maps are found by searching the Map Series page on the website. This part of the WGS website is poorly organized, so you will need to dig through the list of maps. After digging, you will find a geological map of the Radium Springs quadrangle (Hausel, 1988e). Other geological maps in this area that will be of use sooner or later include Atlantic City (Hausel, 1989), Miners Delight (Hausel, 1992e) and South Pass City (Hausel, 2007). Next find the Report of Investigations page on the website. Search for Report of Investigations 44 (Hausel, 1991a). This report will be useful as it is a detailed discussion of the geology and gold at South Pass. Another report that will be useful when learning geology and rock types of the area is Reprint 49 (Hausel and Love, 1992). This will be found on the Reprint page on the WGS website. The reprint was put together for a past Wyoming Geological Association field trip guide and describes important rock outcrops and will lead you on a personal field trip through South Pass. One more page that might be of interest is the Bulletin page. This has a group of books that contain general information on mineral deposits statewide - Bulletin 68, 70, 71, and 72.

A 7.5 ounce nugget found in tributary of Rock Creek, WY

The Hidden Hand mine is located about 8 miles east, southeast of Atlantic City along the Lewiston road (also referred to as the Oregon trail road) south of both the Lewiston ghost town site and Strawberry Creek. The mine is on a patented claim. Patented claims are claims filed under the 1872 mining law that had enough value the government allowed the claimants to purchase the property at a fair market price. This was done in the 19th century to try to stimulate interest in mining and development of the West (something the government today no longer does - now they just discourage development and protect bugs, flowers and dirt). Today, it is impossible to patent claims. Although I never had access problems to this mine because it sits in the middle of BLM ground surrounded by vast, empty, wasteland, it could easily be blocked off. There is a very disturbing trend that non-mining people buy patented mining claims and then close it off because they feel they have something of value when they have little to nothing other than coyote pasture. This is what has happened to many of the diamond deposits in the State Line and Iron Mountain districts. If it isn't the democrats stealing our future, it's the government stealing our land. Have you seen what the legislature did to the Carissa mine? This once potentially productive gold mine (it likely has more than a million ounces of gold in the ground) is now Wyoming's version of Disneyland.

When this district was mapped (Hausel, 1986c) I stayed in a tent near Lewiston for much of one summer and did not see another person all summer. But that was 25 years ago. Maps that cover this area include the Radium Springs 7.5 minute (1:24,000 scale) topographic and geological maps.

Now if you examine Google Earth, you should see distinct foliation (closely spaced lines) in the Miners Delight Formation metagreywacke that trend to the northeast. The rocks in this area are folded, faulted and turned on end. Also noticeable is the alignment of the Burr Mine with the Hidden Hand mine and this trend parallels regional foliation. A nearly east-west to northeasterly trending line of vegetation is visible southwest of the Hidden Hand that represents a cross-cutting shear zone that intersects the primary shear at the Hidden Hand. There are several prospect pits and a number of backhoe trench scars (some remain open, others are reclaimed) cut perpendicular to the primary shear zone.

A portion of the Radium Springs Geological Map near the Hidden Hand mine by the author showing shear zones and mines in this part of the South Pass greenstone belt. Greenstone belts are famous for gold in veins and shear zones.

A few things to note on the map: (1) the mine is located at the intersection of a group of shear zones (wiggly lines). At least 5 shear zones (faults) are apparent in the field and on aerial photos. Because of this, the mine shaft sits in highly brecciated and incompetent rock. (2) The mines (black and white squares) and prospect pits (x’s) line up on the map and on aerial photos as these essentially follow the shear structures that are buried under a few inches of dirt. (3) The Hidden Hand shear zones are offset along faults (dark, solid bold lines) to the south (where they appear to terminate) and to the north at Strawberry Creek. (4) A few hundred feet of the shear structures continue under much younger rock and dirt labeled as Tu along the bank of Strawberry Creek. Thus there is likely some gold sitting under Tu. (5) Strawberry Creek and Burr Gulch likely accepted much of the eroded gold eroded during the past, thus downstream from these shear zones (to the east) would be a very good place to prospect for placer gold.
 
The shaft was sunk on a 10- to 30-foot-wide, N40oE-trending, 62oNW-dipping shear in chloritized, hematitic metagreywacke (the normally black rocks actually have a slight reddish to greenish hue due to rock alteration) The shaft was 110-feet deep and the shear was explored by at least 640 feet of drifts prior to 1926. Ore from the 30-foot level was reported to run as high as 75 opt Au (ounces per ton in gold). In 1916, about 1000 tons of ore with an average grade of 4 opt Au were reportedly stockpiled. Some specimen-grade material assayed 3,100 opt Au (since there are only 32,000 ounces in a ton, this indicates that this specimen contained 9.6% gold). I must point out that such high assays must be questioned and are suspect.

Samples of altered metagreywacke that I collected from the dump contained only trace gold (Hausel, 1989). This discrepancy suggests one of a two possibilities: (1) the reported assays were exaggerated or (2) that the property developed a reputation for producing excellent gold specimens that the mine dump was thoroughly picked over by collectors over the years. Little information about this district and mine has been published and the mine workings are inaccessible, thus it is difficult to provide much in the way of conclusions. In addition, the explored structure at the Hidden Hand mine exhibits considerable brittle deformation – something that is more typical of Laramide faulting (post gold mineralization) in this region.

When looking at the Hidden Hand or other prospects, mines and districts, try to learn as much as possible. Soon you will become an expert prospector. If a prospect has a vein, try following the vein on the surface: look for minerals that are described in the area. Try to visualize the vein in three-dimensions. What does the vein look like at depth, how far does it go into the earth: five feet, 500 feet or 5,000 feet? Does it pinch and swell at depth? Does it pinch to 1 inch, is it faulted at depth, does it swell to a giant vein? Of course you can’t be certain, but sometimes there are things around you that give you clues as to what might happen at depth. One minable gold vein in Yellowknife, Canada that I looked at several years ago was only 1 foot wide on the surface, but at 100 feet deep, it is 8 feet wide and rich in gold! What angle does the vein project downward into the earth?

Outcrop of the distinctly dipping Vulture vein.
Now it’s time to call on the wisdom of Albert Einstein because we need to take a trip back into geological time. If we could step into a time machine and go back about 50 million years, what would the vein and surrounding topography look like? How far in the air would the vein (and surrounding country rock) have projected before erosion leveled the terrain to its current level: 20 feet, 200 feet or 2000 feet? Where did all of the gold in the eroded quartz vein go? If the level of erosion was 2000 feet, there could be considerable gold in the nearby creeks, gulches and draws. Is the vein folded? Folds in quartz are often great places to look for gold enrichment known as ore shoots.



Limonite-stained gossan found in glory hole near the Vulture vein 
in Arizona.
As an example, look some photos I took of the Vulture gold mine in Arizona. The vein provides an excellent example of a dipping vein. The photo was taken along its strike (or trend) such that from the point the picture was taken, the vein continues perpendicular to the surface of the photo. Off in the distance is a wooden structure which represents part of the old headframe where a decline shaft was sunk along the vein. The dip of the vein or angle that it projects from the surface into the ground follows the flat surface along the left edge of the vein: here it dips about 40 degrees. But not only is the vein of possible interest. When you walk around this mine area, several things of interest pop up. To the right of the photo is a glory hole of altered rock that is gossaniferous and stained by tawny yellow to brown limonite that likely has some gold. This sits below the quartz vein. Sitting adjacent to this pit and on top of the rock unit is some eluvial and alluvial material that past gold miners thought might be of interest as they dug an adit into the material. In Arizona, there are lots of eluvial gold deposits that eroded from adjacent gold deposits (many are hidden today).  Also, by walking around the area, other things of interest include rehealed breccias (the angular rock fragments have been cemented together with silica rich material). These probably contain gold and in some of the rich porphyry copper districts in Arizona, similar breccia pipes are good indicators of mineralization at depth. And the possibility of older rocks in the Vulture area containing structurally controlled gold may be worth checking because the old vulture mill sits on old, folded schist and gneiss.
 

Adit (tunnel) dug into eluvial and alluvial material. Many gold deposits in Arizona and some in Wyoming were found in alluvial and eluvial material, but few of these were ever explored at depth.
Quartz breccia on the Vulture property is worth looking at as many breccias in Arizona (as well as elsewhere) provide a clue to former high-pressure mineralized and gaseous fluids at depth that erupted because of the gas under pressure.
Folded schist that forms the foundation of the Vulture mill.

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