Gold Run Mining District, Placer Co., California, USAi

Regional Level Types
Gold Run Mining District	Mining District
Placer Co.	County
California	State
USA	Country

Location and History: This is a Au-Ag-Pt mining district in north-central Placer County in secs. 3, 4, 9, 10, 15 & 16, T15N, R10E, MDM, the vicinity of and south of the town of Gold Run. Discovered in 1849. Extensive Tertiary channel gravels extend from here south to Indiana Hill and the North Fork of the American River. Much of the output in the district has come from the vast Stewart hydraulic mine, which is traversed by U.S. Interstate highway 80 across its north end. The area was first placer-mined in 1849, and the town was founded in 1854 by O. W. Hollenbeck. The town was originally called Mountain Springs. From 1865 to 1878 approximately $6,125,000 in gold was shipped from the express office here. The town thrived due to the extensive neighboring hydraulic mining operations until the mid-1880's when the Sawyer Decision curtailed hydraulic mining debris disposal. Mining on a moderate scale continued until about 1915, with considerable production reopened in 1908. There was minor work here in the 1920's and 1930's.

NOTE: Clark (1970a) considers this a separate district; however, the USGS MRDS database presents it as being incorporated into the Dutch Flat District (under Dutch Flat District file) to its N but provides an MRDS file as a separate district.

The early mining claims of this district were worked by about 40 small companies, but in later years they came under the ownership of few larger companies, of which Stewart Gravel Mines was the largest. Other large operators were Nicholls Estate Company, J.L Gould, and the Gold Run Ditch & Mining Company.

By 1873, the Gold Run deposits had been worked down to a level where the natural outlets were becoming choked with tailings. A 4,000-foot bedrock drain tunnel was constructed to allow working of lower deposits. Little has been recorded concerning the later hydraulic mining, but one run of 60 days resulted in a production of $64,564.81 (period values) from 237,400 yards of the cemented bottom gravel in a place not previously drifted. This yielded an average $0.27/yard (period values) for a depth of 80 feet, where considerable dynamite and black powder were used for blasting and 2,000 miners inches of water under 450 feet of head was employed.

The cemented "blue lead" gravels occupying the deep trough under the huge deposit of loose and finer material worked by hydraulic mining was extensively drift mined from the south end of the district at Indiana Hill where the river canyon exposed the deposit. The Indiana Hill Blue Gravel Mining Company worked these deposits from 1854. They erected an 8-stamp mill for crushing the cemented gravel in 1864. Between 1872-1874, the company produced 19,997 carloads, which yielded $75,422.47 or an average $4.71/ton (period values). By 1874, the company was working the bottom gravel by drifting through an adit then 1,600 feet long. They were then breasting a face 110 feet wide and taking out from 6-7 feet of gravel inclusive of the bedrock picking. They employed 25 men who extracted from 40-50 1,600 pound carloads every 24 hours. In places, a height of 10 feet was breasted. The previous production of the claim was estimated at $125,000 (period values). Between December 1, 1874 and August 21, 1875 the Indiana Hill Cement Mill and Mining Company produced $56,446.47 (period values) at an operating cost of $24,000 (period values). From 1876 to the end of January 1879, Indiana Hill Placer Mine produced $152,225.90 (period values). Details of later production are lacking, but the total is reported to be about $750,000 (period values)for the Indiana Hill mines.

In 1911, James Stewart acquired much of the property and did some underground drifting. Mining on a moderate scale continued at Gold Run until about 1915, with considerable production reported in 1908. Minor work was conducted on the deposits in the 1920's and 1930's.

As of 1936, 1,000 feet of the main Gold Run channel bottom had been worked entirely to bedrock beginning at the lower end of Indiana Hill, and a surface pit about 1,600 feet long by 2,000 feet was worked out completely. In addition, most of the top gravel is gone from the rest of the claims and the bottom has been drifted to an extent not exactly known. The upper gravel was ideal for hydraulicking, with no overburden or very large boulders.

Geology: The deposits are located on a major Tertiary channel of the American River that enters the area from the south and continues north to Dutch Flat. The gravel deposits are more than a mile wide in an east-west direction, three miles long in a north-south direction, and up to 400 feet deep. The lower cemented blue gravel yielded as much as several dollars per cubic yard (period values). The upper gravels contain quartz with clay and sand and averaged 11 to 17 cents (period values) per cubic yard, while the top gravels ran to four to five cents (period values) per cubic yard. Bedrock is slate in the west portion and gabbroic rock to the east.

Regional geologic structures include the Melones Fault Zone, the Foresthill Fault, and the Gills Hill Fault. Local structures include the Foresthill Fault.

Throughout most of the Gold Run District, only the basement rocks of the Calaveras Complex and the overlying Eocene auriferous gravels are present. While thick sections of Oligocene to Pliocene Valley Springs and Mehrten Formation rocks are present to the south in the districts of the Forest Hill Divide, and northwest in the Scotts Flat District, they have been largely lost to erosion at Gold Run.

The main body of basement rocks within the district consists of a belt of north-northwest-trending steeply dipping, slate, argillite, amphibolite, phyllite, chert, and metavolcanic rocks of the Calaveras Complex. Gabbroic and serpentinite intrusions are common. The Foresthill Fault, a steep easterly dipping thrust fault trends north-south through the district and cuts the Calaveras Complex. To the east of the district, the Melones Fault Zone (Clark, 1960) separates the Calaveras Complex from partially to completely serpentinized peridotite of the Feather River Peridotite Belt.

Basal Eocene auriferous gravels: Due to localized erosion of the Valley Springs and Mehrten Formations, the Gold Run and neighboring districts were known for their immense bodies of exposed auriferous gravel. The district produced from extensive auriferous channel gravels deposited by a tributary to the Tertiary Yuba River. Pebble imbrication and cross-bedding indicate this tributary flowed northward through the Gold Run District before turning sharply southwest in the neighboring Dutch Flat District. The tributary then flowed southwesterly, crossing the present Bear River about a mile west of Dutch Flat, and then flowed 2-3 miles through the You Bet District where it was mined at the Christmas Hill and Little York Diggings. It then turned sharply north and flowed through the Red Dog and Hunt's Hill areas to its confluence with the Yuba River near North Columbia.

In some places, the Eocene gravels at Gold Run are more than a mile wide in an east-west direction, but average between 600 and 1000 yards wide. They extend for about 4 miles in a north-south direction from Indiana Hill to Dutch Flat. They achieve a maximum thickness of 400 feet and can be divided into lithologically and texturally distinct units. The lower unit, or blue lead of the early miners, rests directly on bedrock, and contains most of the gold, yielding as much as $9/yard. It is generally confined to the wide channel troughs on bedrock and buried under thick sections of upper gravel. Underlying bedrock is slate in the western part of the district and gabbroic rock in the east. Bedrock is in part polished and hummocky with slates being in part soft and decomposed. Upper gravels contain abundant quartz with sand and clay and averaged only 11 to 17 cents per yard. Much of the district output came from the upper gravels in the vast Stewart hydraulic mine, which is currently traversed by Interstate 80. Channel grade was as much as 10 feet in 100 feet in the Gold Run and Dutch Flat area.

The lower gravels are generally immature and composed of bluish-black slate and phyllite of the Calaveras Complex, weathered igneous rocks, and quartz. Chlorite, amphibole, and epidote mineral grains are also common components. Lower gravels are generally well-cemented; they were extensively drift mined in neighboring districts and at the south end of the district where the river canyon exposed the deposit at Indiana Hill.

The upper gravels form the majority of the Eocene gravel deposits and, unlike the lower gravels, are well-exposed in cliffs and bluffs cut into the old river channels. Their thickness varies significantly within the district. These gravels are much finer, with clasts seldom larger than pebble size and characterized by an abundance of clay and silt beds. Large-scale cross-bedding and cut-and-fill features are common. Upper gravels are mature; quartz predominates, and the heavy-mineral content consists almost exclusively of zircon, ilmenite, and magnetite.

Due to localized erosion of the Valley Springs and Mehrten Formations, the Gold Run and neighboring districts were known for their immense bodies of exposed auriferous gravel. The district produced from extensive auriferous channel gravels deposited by a tributary to the Tertiary Yuba River. Pebble imbrication and cross-bedding indicate this tributary flowed northward through the Gold Run District before turning sharply southwest in the neighboring Dutch Flat District. In some places, the Eocene gravels at Gold Run are more than a mile wide in an east-west direction, but average between 600 and 1000 yards wide. They extend for about 4 miles in a north-south direction from Indiana Hill to Dutch Flat. They achieve a maximum thickness of 400 feet and can be divided into lithologically and texturally distinct units. The lower unit, or blue lead of the early miners, rests directly on bedrock, and contains most of the gold. The lower gravels are generally well-cemented and immature, composed of bluish-black slate and phyllite of the Calaveras Complex, weathered igneous rocks, and quartz. The upper gravels, which form the majority of the Eocene gravel deposits in this district, are of varying thickness, much finer, and mature. Quartz predominates, and the heavy-mineral content consists almost exclusively of zircon, ilmenite, and magnetite.

Mineralization is placer Au-Ag-Pt deposits (Mineral occurrence model information: Model code: 119; USGS model code: 39a; BC deposit profile: C01. C02; Deposit model name: Placer Au-PGE; Mark3 model number: 54), hosted in Tertiary unconsolidated sand & gravels. The ore bodies are irregular in form. Controls for ore emplacement included mechanical accumulation on irregular bedrock riffles and within river- and stream-channel lag gravels, bars, and point bar deposits. Local rocks include Paleozoic marine rocks, undivided, unit 6 (Northwestern Sierra Nevada).

Commodity information: The average value of upper gravels = $0.08 per cubic yard (period values). The average value of lower gravels = $0.30 per cubic yard (period values). Lower gravels yielded as much as $9.00 per cubic yard (period values)($35.00 ouce/Au).

Ore materials:: Native gold as fine to coarse gold and nuggets (.900 fine).

Gangue materials: Quartz and metamorphic gravels. Accessory minerals include magnetite, ilmenite, zircon, pyrite, amphibole, epidote, chlorite, and siderite.

Workings data: Workings included surface and underground openings.

Hydraulic Mining: Hydraulic mining methods were first applied in 1852 to the Yankee Jims gravels in the Forest Hill District of central Placer County. Its use and methods quickly evolved to where it was applied to most exposed Tertiary gravel deposits. Hydraulic mining involved directing a powerful stream of high pressure water through large nozzles (called "monitors") at the base of a gravel bank, undercutting it and allowing it to collapse. The loosened gravels were then washed through sluice boxes. The remaining tailings were indiscriminately dumped in the nearest available stream or river. Large banks of low-yield gravel could be economically mined this way. In some cases, adits were driven into the exposed face and loaded with explosives to help break down the exposure. One of hydraulic mining's highest costs was in the ditches, flumes, and reservoirs needed to supply sufficient volumes of water at high pressure. A mine might have many miles of ditches as well as dams and reservoirs, flumes, and tunnels. Hydraulic mining flourished for about 30 years until the mid-1880s when the Sawyer Decision essentially brought it to a halt.

Drift Mining: While limited mining of the Tertiary channel gravels by means of shafts and adits commenced soon after their discovery, underground mining flourished after the Sawyer Decision. Drift mining involved driving adits and tunnels along or close to the lowest point in the bedrock trough of an ancient channel and following it upstream along the bedrock surface. Some deeply buried drift mines were originally accessed through vertical shafts requiring timbering, headframes, hoisting, and pumping equipment. Larger shafts were seldom over 3 compartments Smaller mines often had single compartment shafts as small as 2 x 5 feet. Since considerable water was associated with the gravels, it was a serious problem in deeper shafts and costly pumping was required. By the 1890s, due to drainage problems and the expense of hoisting, most major drift mines were accessed through tramway and drain tunnels driven into bedrock below the channels.

Channels were usually located by gravel exposures on hillsides and terraces. Exposures of upstream and downstream gravels were called "inlets" and "outlets," respectively. Where a ravine or canyon cut into, but not through an old channel, the exposure was called a "breakout."

The preferred method of developing an inlet was to tunnel through bedrock under the channel at such a depth and angle as to break through into the bed of the channel providing natural drainage. The overlying gravels could then be accessed directly through the tunnel or by periodic raises and drifts. Development of an outlet involved following the bedrock channel directly into the hillside, the incline of the bedrock providing natural drainage. The tunnel entrances were usually in or near a ravine or gulch to aid in waste-rock disposal.

Prospecting and developing a breakout was more difficult, since the exposed gravel could be in the basal channel or hundreds of feet up on the edge of the channel, making it impossible to locate a prospect tunnel with any certainty. The surest method of prospecting was to run an incline on the pitch of the bedrock. Another method was to sink a vertical shaft on the presumed channel axis. The former method proved superior since it involved less subjectivity and often uncovered paying bench gravels on edges of the old stream. Once the bed of the channel was located, it was prospected by drifts and cross cuts to ascertain width, direction, grade, and the location, extent, and quality of pay.

Prospecting also included projecting the grade and direction of existing channel segments for distances up to several miles. Thus having determined a potential location, a prospect adit or shaft was driven to evaluate it. This was a common method of finding old channels where there were no surface exposures.

Access tunnels were driven in bedrock to minimize timbering and ensure a stable roof, through which upraises were driven to work the placer gravels. Tunnels were generally run under the lowest point of the bed of the channel in order to assure natural drainage and to make it possible to take auriferous gravels out of the mine without having to hoist it.

The main drifts were kept as straight as possible and in the center or lowest depression of the channel. To prospect the width of the channel, crosscuts at right angles to the drift were driven on each side to the rims of the channels or the limit of the paying lead. These were timbered and lagged in soft gravels, but not to the extent of the main drift. In wide pay leads, gangways paralleled the main tunnel to help block out the ore in rectangular blocks. In looser gravels, timbering was required and the main difficulty was preventing caving until timbering was in place. The looser gravels were excavated with pick and shovel. Up until the late 1800s, most workings were driven by hand, then later by machine and pneumatic drills.

Working drifts in the gravel beds and pay leads themselves were larger than the bedrock tunnels and usually timbered due to their extended and long-term use. In wide gravel deposits, as a precaution against caving, gravel pillars from 20 - 40 feet wide were left on each side of the drift. When the main access tunnel was in bedrock following the line of the channel, pillars were not required, as the tunnel in the gravel was only for temporary use in mining the ground between its connections with the bedrock tunnel. Raises to access the gravel were made every 200 - 400 feet as necessary.

The breaking out of gravel (breasting) was done from the working faces of drifts. Usually, 1-2 feet of soft bedrock and 3-4 feet of gravel were mined out to advance the face. When the gravels were well-cemented, blasting was required. Otherwise the material could be removed with picks. Boulder sized material was left underground and only the gravels and fines were removed from the mine.

Bedrock swelling was a frequent problem. Tunnels on and within bedrock were sometimes affected by the upward swelling of the bedrock. In these cases, heavy timbering was required and the tunnel floor had to be periodically cut and lowered to keep the tunnel open.

Soft or fractured slates were the most favorable bedrock. The surface was usually creviced and weathered enough that gold could be found to a depth of 1 foot in the top of the bedrock. Where sufficiently weathered and soft, this upper bedrock layer could be easily removed. If the surface of the bedrock was too hard to be worked, it was cleaned thoroughly, and the crevices and surface were worked with special tools to remove every particle of gold.

According to the gravel's hardness, they were either washed through sluices or crushed in stamp mills. Much of the gravel was so highly cemented it had to be milled several times. Stamp mills with coarse screens were also found to be suitable for milling cemented gravel. For soft and uncemented gravels, a dump, sluices, and water supply under generally low pressure comprised the entire surface workings.

Ventilation of mines was accomplished by direct surface connection through the use of boreholes and the mine shafts and tunnels. It relied on natural drafts, drafts by fire, falling water, or blowers. Within the mines, arrangements of doors were often used to direct the flow of air through the tunnels, drifts, and breasts.

Ore was removed by ore cars of various capacity determined by available power and tunnel size. In smaller mines, small cars were often pushed by hand. In larger mines using horsepower or trains, larger two ton cars could be brought out in trains of 5-10 cars.

Production information: The best estimate of production from the Gold Run District is only approximate since old mines had very few estimates of gravel produced. Evidence given by government investigators (1891) indicate 84,750,000 cubic yards had been mined. The later and more careful work of Gilbert in 1908 led him to believe the earlier figures should be increased by 51%. If this correction is applied to the Gold Run District it would indicate a total of about 128,000,000 cubic yards removed. Unfortunately there are no good estimates of yield. Estimates of average yield have ranged from $4.82/ton (period values) for the upper low grade gravels. Other estimates for unspecified gravel grades range from $0.08 - $0.15/ton (period values).

References

Other Databases

Link to USGS MRDS:	10310621

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