Idaho - Maryland Mine

Site Name

Primary: Idaho - Maryland Mine

---

Commodity

Primary: Gold
Secondary: Silver

---

Location

State: California
County: Nevada
District: Grass Valley

---

Land Status

Land ownership: Private
Note: the land ownership field only identifies whether the area the mine is in is generally on public lands like Forest Service or BLM land, or if it is in an area that is generally private property. It does not definitively identify property status, nor does it indicate claim status or whether an area is open to prospecting. Always respect private property.
Administrative Organization: Nevada County Planning Department

---

Holdings

Not available

---

Workings

Not available

---

Ownership

Owner Name: Emgold Mining Corp.
Home Office: 570 Granville St. Vancouver, British Columbia Canada VGC 3P1

---

Production

Not available

---

Deposit

Record Type: Site
Operation Category: Past Producer
Deposit Type: Hydrothermal vein
Operation Type: Underground
Discovery Year: 1865
Years of Production:
Organization:
Significant: Y

---

Physiography

Not available

---

Mineral Deposit Model

Model Name: Low-sulfide Au-quartz vein

---

Orebody

Form: Tabular

---

Structure

Type: R
Description: Wolf Creek Fault Zone, Gillis Hill Fault, Melones Fault Zone

---

Alterations

Alteration Type: L
Alteration Text: Ankeritic, sericitic, and pyritic replacement of wall rocks adjacent to veins

---

Rocks

Name: Serpentinite
Role: Host
Age Type: Host Rock
Age Young: Mesozoic
Age Old: Paleozoic

Name: Diabase
Role: Host
Age Type: Host Rock
Age Young: Mesozoic
Age Old: Paleozoic

Name: Granodiorite
Role: Host
Age Type: Host Rock
Age Young: Early Cretaceous

---

Analytical Data

Not available

---

Materials

Ore: Gold
Ore: Pyrite
Ore: Galena
Gangue: Quartz
Gangue: Calcite
Gangue: Chalcopyrite
Gangue: Sphalerite

---

Comments

Comment (Development): The Idaho-Maryland is the second largest underground gold mine in California behind the Empire Mine. The mine was located in 1865. The first period of mining extended from 1867, when the Idaho Quartz Mining Company was organized, until 1893. In 1867, a shaft was sunk to 300 feet and encountered a rich pay shoot (the eastern extension of the Eureka -Idaho Ore Shoot). The Idaho Quartz Mining Company worked this same pay shoot stoping it for a distance of 3500 feet along strike until 1893 when the eastern limit of the Idaho claims were reached. Total output up to this time was $11,638,000, with ore ranging $12.76 to $35.00/ton and averaging $20.00/ton. Most of the gold came from the Eureka-Idaho shoot, which averaged 2.5 feet wide yielded 1 ounce/ton. The Idaho Mine was developed by a shaft inclined at 70 degrees to the 1000-foot level and an inclined winze raking to the east, called the Canyon shaft, that bottomed at the 1600-foot level at a vertical depth of 2,180 feet. In 1893, in settlement of a dispute over the eastward extension of the Eureka-Idaho shoot, the Maryland Company acquired the Idaho Quartz Mining Company for $85,000. From 1893 until 1901, the Maryland Company operated the mine and produced $1,250,000 in gold. A winze was sunk from the 1,600- to the 1,900-foot level. However, in 1894, a fire destroyed the hoist and the mine was flooded and workings below the 1,600-foot level were not reclaimed. In 1901, partly because of the poor condition of the workings, the mine was closed. The mine remained idle until 1903 when it was bonded to the Idaho-Maryland Development Company, which worked it until 1914. The company succeeded only in reopening it to the 1600-foot level, and the $300,000 in gold they produced came mainly from old stopes and pillars left behind by the earlier operators. A fourth period of activity extended from 1918 to 1925, when the mine was operated by the Metals Exploration Company. At a cost far exceeding the $500,000 in gold it produced, the main shaft was extended downward 1,000 feet to the 2,100-foot level at a vertical depth of 2,000 feet. Drifts on the 2,000- and 2,100-foot levels were driven from the main shaft, the Dorsey winze, and a new winze was sunk 850 feet below the 2,000-foot level. Failing to find a new ore shoot, the company suspended operations in 1925. Control of the property changed hands in 1926 when Errol MacBoyle and Edwin Oliver created holdings that included the Idaho-Maryland, Brunswick, and Morehouse mines. Work resumed the same year under the Idaho- Maryland Mines Company. New ore was found and the mine entered a period of prosperity. During the three years 1930, 1931, and 1933, the mine produced $1,681,887. Total production for the period 1868 - 1933 was almost $16,000,000. From 1926 to 1942, the mine produced 650,000 ounces of gold from 1.1 million tons of ore. The mines were closed in 1942 due to enactment of the Federal War Production Board's Limitation Order L-208, but were reopened again in 1945. Production was hampered by depleted operating funds, rising costs, labor shortages, and negligible exploration. All mining ceased in 1957. At the time of closure, the mine was owned by Idaho-Maryland Industries. In 1983, Emgold Mining Corp., through its subsidiary Emperor Gold (U.S.) Corp., obtained a lease and option to purchase all mineral rights formerly held by Idaho-Maryland Industries. From 1993 to 2000, Emgold spent $7,000,000 evaluating the Idaho-Maryland properties. The project was put on hold for 1.5 years while the lease and option were renegotiated. The revised Agreement includes a mining lease and option to purchase the property consisting of 2,750 acres of minerals and minerals rights and approximately 37 acres around the old New Brunswick shaft. The term of the lease is 5 years commencing on June 1, 2002. As of March, 2004, Emgold had conducted a boring and assessment program, but has not yet commenced mining operations.

Comment (Commodity): Ore Materials: Free-milling coarse and fine gold in quartz (850 fine). Auriferous pyrite and galena.

Comment (Commodity): Gangue Materials: Quartz, calcite, chalcopyrite, sphalerite

Comment (Economic Factors): Total gold production from the Idaho-Maryland group was estimated by Clark (1970) at about $70,000,000.

Comment (Geology): An important structural feature in the district is a group of "crossing" vertical or steeply dipping fractures that strike northeast, about normal to the long axis of the granodiorite body. In places they are simple fractures; elsewhere they form sheeted fracture zones several feet wide. Some are tight, some are open and form watercourses, and few contain any quartz. Two main stages of primary or hypogene mineralization are recognized - 1) a hypothermal stage represented by one vein and one mineralized crossing, in which magnetite, pyrrhotite, pyrite, and specularite were deposited, and 2) a mesothermal stage, in which the gold quartz veins were formed. The mesothermal stage is further divided into two sub-stages - an older one, in which quartz is the principal gangue mineral, and a younger one, marked by the deposition of carbonates. Pyrite and arsenopyrite, deposited in the quartz stage, are the earliest sulfides of the gold-quartz veins. Sphalerite, chalcopyrite, and galena are somewhat later. No secondary or supergene minerals have been noted except limonite, calcite, and gypsum, which are being deposited in the oxidized zone. The distribution of gold in the ore shoots is extremely erratic and assays of adjacent vein samples commonly differ widely. Some ore shoots have a pitch length of several thousand feet, but most are much smaller. Adjacent to veins and crossing fractures, the wall rocks are generally highly altered. Ankerite, sericite, and pyrite have replaced the original rock-forming minerals. Lesser amounts of chlorite and epidote have been found. The wall rock has not been replaced by quartz. LOCAL GEOLOGY By far the most important vein in the Idaho-Maryland Mine was the Eureka-Idaho-Maryland vein. This vein strikes N 77? W and has an average dip of 70? SW, ranging between 50? and 80?. The hanging wall is composed of diabase and gabbro, and the footwall is serpentinite. All of the rocks are highly altered and contain abundant ankerite. Mariposite commonly occurs in the serpentinite. The famous Eureka-Idaho ore shoot had a pitch length of almost 1 mile and a breadth of 500 to 1,000 feet. The width of the shoot averaged 2.5 feet but reached 8 feet in places. The average gold content in the Eureka-Idaho shoot was 1 ounce/ton. Most of the gold was free gold, and much specimen ore came from this famous shoot. Between 1-2 percent of the ore was sulfides, pyrite being the most abundant. Lesser amounts of galena, chalcopyrite, and sphalerite are present. The sulfides yielded between 5 and 20 ounces of gold per ton.

Comment (Workings): A diagram of the Eureka-Idaho ore shoot is given in Johnston (1940, fig. 64). A detailed account of the underground workings of the Idaho-Maryland Mine is not available at this time.

Comment (Location): The location point selected for latitude and longitude represents the Idaho-Maryland Mine main shaft as shown on the USGS Grass Valley 7.5-minute quadrangle.

Comment (Geology): REGIONAL GEOLOGY The Idaho-Maryland Mine is the second largest underground gold mine in the Grass Valley District. The Idaho-Maryland and the Empire-North Star Mine, located to the south, are the two largest-producing underground gold mines in California. The district is located in the northern portion of the Sierra Nevada Foothills Gold Belt. This belt averages 50 miles wide and extends for about 150 miles in a north-northwest orientation along the western slope of the Sierra Nevada range. The Foothills Gold Belt roughly coincides with the Foothills Metamorphic Belt, which can be subdivided into four major lithotectonic belts: Western Belt, Central Metamorphic Belt, Feather River Peridotite Belt, and Eastern Belt. The Grass Valley District lies within the Central Belt, where in the Grass Valley area it is marked by an 8-mile-wide north-trending assemblage of two accreted terranes that range from Late Triassic to Late Jurassic in age. The Central Belt is bounded on the east and west by regional-scale tectonic suture zones; the Wolf Creek Fault Zone on the west and the Gills Hill Fault/Melones Fault Zone on the east. The oldest rocks in the area are those of the Carboniferous-Triassic metasedimentary Calaveras Complex. Originally clastics, these rocks were converted to schistose or slaty rocks during the Late Paleozoic orogeny and locally into a contact-metamorphic biotite gneiss by intruded granodiorite during Late Mesozoic time. The slates of the Jurassic Mariposa Formation, which outcrop in a small part of the area, are relatively unaltered. Igneous rocks in the district include granodiorite, diabase, porphyrite, amphibolite schist, serpentinite, gabbro, diorite, quartz porphyry, and various dike rocks (Johnston, 1940). The veins of the Grass Valley and neighboring Nevada City districts are not connected with or continuations of the famous Mother Lode vein system to the south. The last veins of the Mother Lode end about 20 miles to the south. Also, the Grass Valley veins differ in general character from those of the Mother Lode. Generally, the Grass Valley veins are narrower and produce a higher-grade ore than those of the Mother Lode. The veins trend in two primary directions. One set trends N-S (dipping E or W), and the other trends E-W (dipping N or S). The major feature of the Grass Valley District is a body of Lower Cretaceous granodiorite and diabase five miles long from north to south and half a mile to two miles wide (probably the apex of a larger batholitic mass). It which is intruded into older sedimentary and igneous rocks, including diabase of the Mesozoic-Paleozoic Lake Combie Complex, and is itself cut by various dike rocks. Gold-quartz veins cut the granodiorite and diabase (and in some cases, serpentinite) throughout the district. Most of the veins strike generally north, parallel to the intrusive body, and display gentle dips averaging 35?. Others strike northwest, parallel to a diabase contact with the granodiorite. The veins fill minor thrust faults that occur within fracture zones of various width and degree of fracturing. The maximum measured reverse displacement is 20 feet (Johnston, 1940). In all veins, quartz is the principal vein material and occurs in four textural types: 1) Comb quartz that forms crustifications and lines vugs, 2) massive milky quartz with a granular texture that displays many sharp crystal faces and has not undergone deformation, 3) sheared quartz developed with little or no dilation of the vein fracture and commonly showing ribbon or shear-banding structures, and 4) brecciated quartz formed where vein movement dilated the interwall space (Johnston, 1940). Gold occurs in quartz and in sulfides, principally pyrite. Although specimen ore has been found, most ore from the district occurs as fine and coarse free-milling gold in ores averaging between 0.25 to 0.5 ounces per ton.

---

References

Reference (Deposit): Clark, W.B., 1970, Gold districts of California: California Division of Mines and Geology Bulletin 191, p. 53.

Reference (Deposit): Johnston, W.G., Jr., 1940, The gold quartz veins of Grass Valley, California: U.S. Geological Survey Professional Paper 194, 101 p.

Reference (Deposit): Koschmann, A.H., and Bergendahl, M.H., 1968, Gold-producing districts of the United States: U.S. Geological Survey Professional Paper 610, 283 p.

Reference (Deposit): Lindgren, W., 1896a, Geologic atlas of the United States - Nevada City Special Folio: U.S. Geological Survey Folio 29.

Reference (Deposit): Lindgren, W., 1896b, Gold-quartz veins of Nevada City and Grass Valley: Seventeenth Annual Report of the U.S. Geological Survey, Part 2, p. 1-262

Reference (Deposit): MacBoyle, E.M., 1919, Mines and mineral resources of Nevada County: Sixteenth Annual Report of the State Mineralogist, California State Mining Bureau, p. 1-270.

Reference (Deposit): Additional information on the Idaho - Maryland Mine is contained in File No. 331-9392 (CGS Mineral Resources Files, Sacramento)

---

California Gold

"Where to Find Gold in California" looks at the density of modern placer mining claims along with historical gold mining locations and mining district descriptions to determine areas of high gold discovery potential in California. Read more: Where to Find Gold in California.