Friday, May 31, 2013

The Giant King gold mine

Looking towards the mine portal within the Giant King mine.
In 2012, I visited the Giant King mine near the town of Washington and walked a small portion of the property (Figure 1).

Figure 1. Looking down a 40o slope above the
Giant King Mine.
The Giant King is in the Washington District of Nevada County a short distance from the town of Washington (~200 residents), and 14 to 16 miles east of Nevada City and Grass Valley. The claim maps provided by the mine owners indicated the mine has 480 acres of contiguous claims within 24 unpatented lode claims that enclose the Giant King and much of the Alpha hydraulic mine (Figure 2).

The Giant King mine lies along the Melones Fault Zone (MFZ) that includes the Mother Lode trend to the south and the 16-to-1 Mine to the north. Gold was recovered from both placer and lode deposits throughout this belt. Total gold production from California to date, has been approximately 118 million ounces – more than most countries in the world.

Figure 2. Lode claim map. The Alpha mine
lies on the eastern edge of the claims block.
A few hundred diamonds were also found nearby. Many were recovered from placers in the Oroville area 40 miles to the west-northwest. The Cherokee and French Corral gold placers in the Oroville region also yielded diamonds: Nevada County lies upslope from these. Other gems (benitoite and sapphire) were identified in a placer 25 miles to the north of the Giant King mine (Hausel, personal field notes). A possible source for such gems would be aluminous serpentinite and a source for diamonds has been postulated as tectonically emplaced, mantle-derived serpentinized peridotites (serpentinites) similar to those discovered at Beni Bousera in Morocco (Erlich and Hausel, 2000). Whether such high-pressure serpentinites exist in the Washington district was not investigated.

History & Geology
According to Western Mining History, the Washington district (which includes the Giant King mine) was caught up in the great California gold rush during the second half of the 19th century, and placers in the Middle Yuba River immediately downstream from the Giant King were mined for gold. The Omega and Alpha hydraulic mines were opened in the middle 1850s and worked on a major scale through the 1880s.

Lode mining began in the 1850s and continued until about 1915. There was renewed activity during the 1930s. The nearby Red Ledge mine was worked for gold and chromite. The Red Ledge produced some visible gold. According to a brief summary at, the gold-quartz veins at Red Ledge were in sedimentary rocks close to a contact with serpentinite (author’s note – this geology is similar the Giant King). At the Red Ledge, mariposite was reported to be associated with altered serpentinite as well as in close proximity to gold; and this appears to be a very important indicator of gold at the 16 to 1 mine north of the Giant King mine. Mariposite is distinctly colored, chrome-bearing mica.

Western Mining History’s website further describes the Washington district as being underlain by slate, schist and quartzite of the Blue Canyon Formation. A serpentine body one to two miles wide crops out in the central portion of the district. The Relief quartzite (Carboniferous) and amphibolite lie to the west and granodiorite to the east. The serpentine is a south extension of a belt that passes north-northwest through Alleghany and Goodyear's Bar in Sierra County to the north. Tertiary andesite overlies the main ridges to the north and south.

Figure 3. Geological map of the Giant King mine area (Saucedo and 
Wagner, 1992). The central purple band is serpentinized peridotite in 
the Melones fault zone. The light-blue band to the east is slate of 
the Shoo Fly complex (the primary host for the Giant King mine). 
To the west of the MFZ (light-blue band) are Calaveras Complex 
rocks (includes chert and argillites).
The auriferous Tertiary channel gravels at Alpha and Omega are part of the main channel that extends west and north to Relief and North Bloomfield. Jarmin (1927) estimated that, at Omega, 13 million yards were mined and yielded 13.5 cents in gold per yard. Lindgren (1911) estimated that 40 million yards remained. The quartz veins contain small but rich ore bodies, similar to those of the Alleghany district to the north, but are not as plentiful.

Except for arsenopyrite, sulfides are not abundant. 
Figure 4. Narrow fault with offset veins.
Following discovery of quartz veins in Washington Creek (a tributary of the Yuba River) in 1891, development of the Giant King mine and mill began. Some gold was mined on the property, which was closed during World War I and World War II. The history of the mine and events can be reviewed at the Giant King Mine’s website.

The mine was dug in metasedimentary rocks (slate) along the edge of the MFZ of the California gold belt (Figure 3). The Giant King encloses three main veins referred to as the Queen Vein, Central Vein, and King Vein in this report. Minor veins also occur in the mine and some may have potential as unrecognized mineralized zones. These need to be investigated for gold content. Recommendations are summarized in the last section of this report.

Based on the geological map compiled by Saucedo and Wagner (1992), the primary host for the Giant King is the northerly-trending Shoo Fly Slate. The slate is dark-gray, fissile, clayey metamorphosed sedimentary rock that weathers brown to tan and has strong foliation likely paralleling original sedimentary bedding. The rock units are tilted in the mine and sit on edge and may even be overturned locally. The slate is folded with several minor faults with only apparent minor offset (Figure 4). No major offsets were observed on any fault in the mine. The Slate lies in contact with serpentinite of the MFZ a very short distance west of the mine portals (the contact is likely marked by Washington Creek). 

Figure 5 Gold districts in the Sierra Foothills
California (from Sillitoe, 2008) (MFZ = Melones
fault zone) (BMFZ = Bear Mountains fault zone).
The MFZ is an important structure recognized in the Mother Lode district to the south, where it represents a major fracture of the foothills fault system of the western Sierra Nevada Mountains separating Mesozoic rocks to the west from Paleozoic rocks to the east. It is likely a conduit that tapped auriferous solutions at great depth during tectonic deformation in the geological past. Gold and silica (quartz) rose from these depths in the Mother Lode district as illustrated by some mines in the district that reached depths as great as 5,000 feet. It is likely that much of this gold was derived from the serpentinites of the MFZ.

Along the northern portion of the MFZ (and in the vicinity of the Giant King mine), this suture cuts Paleozoic stratigraphy exposing Paleozoic rocks on both sides of the fault. Movement along the MFZ is complex and may include both strike-slip and dip-slip components (Cebull and Russell, 1979).

The MFZ is likely important in controlling emplacement of gold-quartz veins in the Alleghany and the Mother Lode districts to the north and south of the Washington district, and should also be a gold target in the Washington district (Figure 5).

Figure 6. King vein (shear zone) exposed in mine drift.
Photo taken at manway connecting Lower Tunnel
(No. 1) to Middle Tunnel (No. 2).
The MFZ is mapped immediately west of the Giant King mine portals. Even so, the Lower Tunnel cuts a distinct shear zone characteristic of the MFZ that could represent a narrow off-shoot of the MFZ near the mine face. This shear encloses several; narrow, vertical quartz veins that were followed by a north-northeasterly drift for a short distance (Figure 6). The drift likely was the last development in the mine prior to closure during World War II and it does not appear that this suture was sampled or tested for gold (see Recommendations). This structure is identified as the King Vein in this report (see Figures 6 and 8).

Figure 7. Location of 1911 channel sample in the
Central Vein in east stope of Tunnel 2. Note
the abundant quartz and limonite (tawny-colored stains)
in the mine rib. The limonite likely originated from
oxidation of primary sulfides.

Figure 8. Cross-section and sketch map of mine workings at the Giant King with my notes and vein projections. There appears to be three parallel veins (targets) in the mine as well as a lack of samples in the Upper and Lower Tunnels on both the Central and King Veins. The King Vein may have been cut in the Central Tunnel just past the dam near the mine face. Otherwise, it may be just beyond the mine face.
References Cited
Cebull, S.E., and Russell, L.R., 1979, Role of the Melones fault zone in the structural chronology of the North Yuba River area, Western Sierra Nevada, California: Geological Society of America, Bulletin, v. 90, no. 3, p. 225-227.
Erlich, E.I., and Hausel, W.D., 2002, Diamond Deposits - Origin, Exploration and History of Discovery. Society of SME. 374 p.
Hausel, W.D., 1998, Diamonds & Mantle Source Rocks in the Wyoming Craton with Discussions of Other US Occurrences. WSGS Report of Investigations 53, 93 p.
Hausel, W.D., and Hausel, E.J., 2011, Gold: Field Guide for Prospectors and Geologists (Part 1 Wyoming). CreateSpace (Self-Published), 366 p.
Silitoe, R.H., 2008, Special Paper: Major gold deposits and belts of the North and South American Cordillera: Distribution, tectonomagmatic settings and metallogenic considerations: Economic Geology, v. 103, p. 663-687.
Saucedo, G.J., and Wagner, D.L., 1992, Geological map of the Chico Quadrangle, California (1:125,000)

Central vein complex exposed in the Giant King mine.
Narrow banded vein with adjacent stockworks in the Giant King
mine back.
At least two generations of quartz veins visible in the back of the mine tunnel, Giant King mine, California.
Limonite-stained mine rib, Giant King gold mine, California.
Ribbon vein in mine back at the Giant King.

Historical Alpha and Omega placer near the Giant King mine. Placers like
always contain gold nuggets missed by former miners. These are great places
to use metal detectors. And who knows how many diamonds or benitoite
gems may lie in these gravels.