Gold was first discovered in the placer deposits of La Porte and Poverty Hill in 1850. Mining claims were laid out in 100-foot squares, and were operated as independent hydraulic mines. At Poverty Hill, there were several such operations and mining was carried on in this manner until 1884, when the Sawyer decision put an end to hydraulic operations. Poverty Hill was one of the 13 original mines enjoined.
Map of California Gold Mining Districts
Posted June 26, 2008 in Gold Mining
The channel was mined at two locations at Poverty Hill: the extreme north end at Slate Creek and at another point to the south where the channel turned east. These early ‘49-er hydraulic operations opened up the channel at these two points and allowed a thorough cross-sectional characterization both at the north limit and at a point 4,000 feet due south of the north limit. A. J. Oyster and Company, in July 1940, started a bucket-ladder dredge operation at a point halfway between the two prior hydraulic diggings, stripping the ground down to 30 feet above bedrock. They worked south to the pond that filled the old pit until the operation was shut down by the War Powers Act of 1941. Gold at that time was $35.00 per ounce, refined. Channel grade is about 100 feet to the mile. The history of early operations to the north and south of the Poverty Hill properties on this channel indicate very consistent values. To the north, at the Secret Diggings mine, records indicate a value of 45 cents per cubic yard as recovered by hydraulic mining. At Barnard’s Diggings to the north, average values of 55 cents per cubic yard were reported. To the south at Fair Play and Union Hill average values of 35 cents were reported. (Barneveld). These values are at the old price of gold which was $20.67 per ounce, refined. The channel was mined over an average width of 800 feet and cleaned down to bedrock wherever possible. Channel width is relatively consistent although at times ranging up to 1200 feet. Average depth of the channel to bedrock is 100 feet varying from a minimum of 80 to a maximum of 140 feet.
The deposit is characterized by uniformly fine gravel consisting essentially of white quartz pebbles. The channel is well stratified clay-bound sand and gravel and is readily washed. The percentage of rocks over six inches in diameter is negligible. Tests and operations to date indicate that values in the upper gravels run about five cents per cubic yard and that the concentration of pay is in the 20 feet of bank immediately above the bedrock, with the greatest values actually on or within a few feet of bedrock. The bedrock is decomposed and easily dug to a depth of five or six feet.
Based on historical values and the enhanced recovery methods we plan to employ, an average gold value of 3.5 pennyweight (pwt) /cu yd of excavated material is expected. As explained below this value is based on:
Poverty Hill is traversed by a main branch of the Tertiary Yuba River. Historical yields are documented at $2/cu yd within 5 to 6 feet of bedrock. This is the deposit from which White Rock Mining and Milling plans to extract gold and other heavy metals underground. Miners were able to sell gold for $16/oz at that time so this figure is equivalent to 2.5 pwt/cu yd. At today’s gold price of $1600/oz, this amounts to $200/cu yd.
To separate gold from the gravel, previous operations employed simple gravity separation techniques using equipment fabricated with easily available materials along with crude mercury amalgamation. White Rock Mining & Milling will be using a proprietary gravimetric separation process and no chemicals. We anticipate significantly enhanced recovery.
By employing an underground pneumatic/hydraulic mining process designed for the unique features of this site, efforts can be focused on the gravels immediately above the bedrock where the gold concentrations are known to be highest. Also, the irregular surface of the bedrock itself is known to contain an abundance of solution cavities. These are simply potholes, 1 to 6 feet in depth, where gold concentrations are much greater than the surrounding placer deposits. The underground pneumatic/hydraulic mining process will allow thorough cleaning of these cavities and with the use of MineLab’s GPX 5000 metal detector, we will leave no precious metals behind.
The area was mined by hydraulicking and drifting during and after the gold rush. Mining started up again in the area during the 1930s and early 1940s including an attempt to work the Poverty Hill pit with a bucket-line dredge. Lindgren estimated in 1911 that, at Poverty Hill, 2.25 million yards had been removed and 5 million yards were ultimately available, while at Scales and Mt. Pleasant, 4.05 million yards had been excavated and 60 million yards were ultimately available.
The geology of the area surrounding the proposed project is typical of much of the northern Sierra region. It consists of pre-Tertiary formations which are largely meta-volcanic in origin. The most detailed geologic description available is that done by Henborg (1966) and the gravity study by Merriam and Merriam (1986).
The geologic units present within the project area are the tertiary auriferous (gold-bearing) gravels and the partially eroded Penman volcanic and mud flows underlain by the Calaveras formation. The latter is the oldest rock present and referred to as the basement rock of the region. It is a hard, dark blue-green to gray meta-sedimentary rock. The auriferous gravels were deposited during the early Tertiary period (more than 50 million years ago) into numerous river channels cut into the Calaveras sedimentary rock by ancient, pre-Sierran streams which drained the relatively flat terrain of the region during the moist tropical period when rainfall is thought to range upward from 100 inches daily.
A segment of one of these partially buried, gravel-filled channels (the La Porte Channel) runs through the project area and is the object of the proposed mining operations. The maximum thickness of the gravel within the project area, including an upper low grade layer, is on the order of 120 feet and averaging 90 feet. After deposition of the gravel, large volumes of volcanic flow material (mud and broken rock) from the Penman formation successively covered the region’s channels and valleys, including the La Porte Channel. Physically, this deposited material is yellowish-brown, fairly soft, and sandy to clayey in texture and contains scattered fragments of harder volcanic rocks (andesite rhyolite). However, this flow material is not present on the project site due to erosion throughout the more recent Holocene epoch.
No constraining geologic hazards, such as large landslides or active earthquake faults, have been observed within or closely adjacent to the project area boundaries.
The project site is in an area that has been subject to extensive mining activities commencing with the California Gold Rush and up to the mid-20th century. Mining activity at the site has been well documented through U.S.G.S. reports, California state mineralogist reports, geological studies, township surveys, and patents, dating from the 1860’s to the present. Gold values have been well documented.
Historical Downieville during the gold rush.
Picture from the Bancroft Library, UC Berkleley. http://www.calisphere.universityofcalifornia.edu/themed_collections
All the required permits were previously obtained in 1998, which included the following:
These permits can be updated and resubmitted for expedited approval. In support of the previous permitting activity, studies documenting the flora and fauna of the area were carried out as well as archeological surveys. No endangered species nor sites of archeological importance were located in the area of the proposed mining activity. All paperwork has been maintained on file.
Today the proposed project area consists of recreation and watershed management areas and presents an attractive mountainscape of second growth timberland. The area is replete with un-reclaimed mining pits, spoils areas and gravel borrow pits. A survey conducted in 1987 found that no prehistoric or early historic artifacts of archaeological significance were located on the project site and recommended archaeological clearance. (Jensen & Associates Archaeological Consulting and Research).
Helms Deep Mine camp area
Soils within the project area are generally one foot or less in depth and range in composition from sandy to rocky clays to rocky sands. They are mostly light brownish-gray in color, except in the top few inches where decomposing forest duff has darkened them to a deeper brown. In the un-reclaimed pit areas, soils are generally absent.
Vegetation consists primarily of a Sierra mixed conifer forest system. As noted above, the project site is composed of highly disturbed landforms. Plant species native to the forest ecosystem occupy the relatively undisturbed areas and are successfully re-colonizing the disturbed portions. Very few non-native species have been identified in the area.
Wildlife species present within the project include black tail deer, gray squirrel, Douglas squirrel, snowshoe rabbit, and various bird species. No rare or endangered species are known to frequent the area.
Climate of the Poverty Hill area, including the subject site, is typical to that of the western slope of the Sierra Nevada Range, with relatively high winter precipitation and dry summers. Most of the precipitation occurs during November through March. The majority (65-75%) of the precipitation between December and March falls as snow. Evaporation always exceeds precipitation during the period between June and September, and usually between May and December, also.
Hydrology - Surface waters on the site are concentric, with the exception of Gold Run Creek, which runs down from Poverty Hill to the west, crossing the old hydraulic pit 700 feet south of the idle pond and 1300 feet north of the south pond. Neither of those two ponds have inflows or outflows of surface water. Ground water near the site is contained by the bedrock of the extinct river channel in the area, which forms a long trough trending north to south with a grade of two percent. The old river was turned to the east at the approximate location of the current south pond by encountering a more resistant diorite pluton that had intruded into and altered the bedrock. The formation of the Sierras during the latter part of the Tertiary Period tilted the easterly flow of the old channel back to the west. Hence, the ground water now flows back and into the south pond at a 2% grade, joining the ground water from the north. From there it percolates to the west over the lowered rim of bedrock, forming many springs some distance away. A great deal of the ground water is lost to evaporation.