Mother Lode District

California - Gold, Geology & Prospecting

Shorty pans for gold - sketch by Dan Hausel

Gold was initially found by Spanish prospectors along the Colorado River between 1775 and 1780, but it was the later discovery of the precious metal at Sutter’s Mill in 1848 that produced one of the most important events in the history of the western US and led to a major gold rush that enveloped California with thousands of prospectors and merchants swarming to the Californian gold fields and settling large regions of the West. Gold was soon found in many locations that included Grass Valley, Jackson-Plymoth, Hammonton, Folsom, Columbia, La Porte, Oroville, Nevada City, Alleghany, French Gulch, Bodie, Sierra City, Angels Camp, Jamestown, Placerville, Carson Hill, Magalia, Big Oak Flat, Forest Hill, Mojave, Iowa Hill, Rand, Soulsbyville, Snelling and Polker Flat. It soon became evident that a major gold belt unparalleled in North America occurred in the north-central portion of the state east of Sacramento and west of the State’s elbow.

This belt, known as the Mother Lode, was outlined by gold discoveries in quartz veins in a region about 4 miles wide and 170 miles long that reached north from the Sixteen-to-One mine at Alleghany to Mormon Bar in the south. The precious metal was found in quartz veins in phyllite, schist, slate and greenstone. The more productive veins were discovered along at contacts between two different rock types. Where extensive erosion occurred, major placers formed downstream in Holocene and Tertiary gravels. Broad zones of mineralization found in weathered lodes that were hydraulically mined.

The Mother Lode was legendary for its incredibly rich pockets of gold. The richest contained crystalline gold within the Alleghany-Downieville region 75 miles northeast of Sacramento. In the 1920s, a pocket intersected at the Sixteen-to-One yielded nearly 95,000 ounces of gold! At today’s gold price, this one pocket would be worth $105 million! Another pocket found about the same time produced >45,000 ounces. Other mines in the Mother Lode belt noted for rich pockets included the Oriental, Alhambra, Four Hills, Keltz, Bonanza, Kate Hardy, Carson Hill, North Fork, Kenton, Angels, Green Emigrant, Finnegan, St. Patrick and Plumbago. But those of the Allegany district were especially rich (Clark, 1970).

Sketch by Dan Hausel

Some pockets showed enrichment of iron, others did not. Many of the rich pockets were small but found at or adjacent to serpentinite-slate contacts. In some, quartz-mariposite (a green mica) was found. Near serpentinites, many of the quartz veins split or were bent. Such structures produced gold pockets in some cases. Other high grade pockets were found at vein intersections or in shears.

Another variety of pocket veins were termed ‘Seam Diggins’ that were essentially a form of stockworks. These were found at Placerville, nearly 50 miles to the south of the sixteen-to-one mine and close to Sutter’s Mill. Most were mined by hydraulic methods because of the broad zones of gold mineralization with numerous crisscrossing quartz veinlets. Not only did the veinlets contain precious metal, locally some fractures contained gold. Possibly the largest seam was mined at Georgia Slide north of Georgetown (8 to 10 miles north of Sutter’s mill). The seam in amphibolite, was nearly one mile long and as much as 400 feet wide (Ralph, 2010). Today, such deposits would be likely mined by open pit. Many of the veins produced rich pockets cut by iron-rich fault offsets.

View PDF: Description of the Mother Lode District

Still Mining Gold in the Golden State

By Andrew Alden, KQED Science Contributor - MAR. 7, 2013

Since California became a state in 1850, it has had a gold industry: sometimes booming, sometimes just thriving and sometimes under its own version of Prohibition. Lately California gold has become an endangered species. The last producers in the Mother Lode are down to less than a handful, but it looks like the industry is ready to resume.

Gold was always known in the mountains of California, even before James Marshall famously spotted nuggets in his new millrace near Coloma on 24 January 1848. But Marshall’s find sparked the first serious flush of gold production as thousands of men waded into the Sierra Nevada rivers, sifting the gravel with their pans and sluices. They’ve been there ever since, ranging from weekend panners to elaborate syndicates. It was the syndicates that ruined things for everyone else with their notorious hydraulic methods. Before the courts shut down the industry in 1884, operations progressed from the gravel terraces of the Central Valley into the mountains, where hydraulickers stripped large swaths of land of their woods and soils and sent the waste sediment downstream to smother the farmlands of the Central Valley.

Hydraulic mining was banned from discharging waste into the Sacramento River. That left two ways to keep doing it. One was to strip other rivers instead, most notably the Trinity River, where the practice lasted into the mid-1900s. The other was to dredge Central Valley gravels without affecting the river. The huge gravel beds laid down in the Valley by the Yuba and Feather rivers, where the first gold dredger set to work in 1850, nurtured a long-lasting industry based on floating dredges. The last of these, Yuba Gold Dredge No. 17, is still at work there today. By digging up one side of a pond and depositing the waste on the other, the great dredge slowly travels across the gravel fields east of Yuba City collecting enough powder-fine gold to pay for itself. The sand and gravel can be quarried again and sold later as aggregate.

Yuba Gold Dredge No. 17 works its way across the Deep Reserve Area on behalf of Cal Sierra Development Inc., digging gravel with a belt of buckets (seen below the control room at center), sifting out fine-grained gold and heavy minerals, and dumping the rest out the stern with its high stacker (left). Launched in 1918 and refurbished twice, it makes the damnedest noise you ever heard. Photos by Andrew Alden

The hard-rock mines of the Sierra Nevada, hundreds of them, produced the majority of California’s gold and populated the region with strong communities. Without them the Mother Lode country would be a thinly peopled land of loggers like the northern Coast Range. The death blow to this industry was a federal wartime order in 1942 that halted all work. For the next five years the shafts filled with groundwater and the workers dispersed, making it uneconomical to reopen any but the richest deposits. Over the next decades the slow decline in the value of gold squeezed out what mines could be revived, and then the regulatory climate shifted to give nature a little more say.

Today, Carson Hill Rock Products, south of Angels Camp, still digs the fabulous ground that yielded the 195-pound Calaveras Nugget in 1854. But its main business is the green-veined decorative rock called mariposite. I am told that the operators keep their eye out for gold as they go, but produce it from the richest pockets only as a byproduct and thus avoid many of the regulations imposed on a gold mine.

Mariposite rock is named for the green phyllosilicate mineral mariposite, a variety of phengite.

The steady—apparently permanent—high price of gold today is driving a few long-standing efforts to reopen large-scale gold mining in the Sierra. Foremost of these is the Lincoln Mine project, in Amador County between Jackson and Plymouth, where the Sutter Gold Mining company has methodically gotten all its permits in order and anticipates starting to produce ore for real this spring.

But one little mine, started in 1896, still runs as an artisan operation: the Original Sixteen to One Mine, up in Sierra County in the hamlet of Alleghany. Its business model today is based solely on specimen gold, doing its work by hand and making no toxic waste. If you ever run across decorative California gold like this, with visible metal in creamy quartz, you’re surely looking at the mine’s output.

A small cabochon of gold quartz rests on serpentinite, a rock closely associated with the Mother Lode

Occasionally the miners hit a jackpot, like this specimen called “The Whopper,” that can pay for more than a year’s expenses all by itself.

Photo courtesy Mike Diggles, U.S. Geological Survey

The Original Sixteen to One Mine will let you spend a day in the mine with the miners for $400, lunch included. There’s no word on the website on whether you can keep what you find, but other rewards in Alleghany include Casey’s Place and, if you make an appointment, the Underground Gold Miners Museum.

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