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Esperanza Mine (Bright Hope Mine), Sulphur Creek, Black Oaks, West Mayacmas District, Mayacmas Mts (Mayacamas Mts), Sonoma Co., California, USA

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Latitude & Longitude (WGS84): 38° 48' 22'' North , 122° 50' 32'' West
Latitude & Longitude (decimal): 38.80611,-122.84222
GeoHash:G#: 9qbsu8mjb
Köppen climate type:Csb : Warm-summer Mediterranean climate

A former Hg mine located in the SE¼ sec. 10, T11N, R9W, MDM, on Sulphur Creek, 2.9 km (9,500 feet) SSW of Black Oaks.

Mineralization is hosted in serpentinite at a serpentine-sandstone contact.

Production data are found in: U.S. Bureau of Mines data.

Mineral List

4 valid minerals.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

Cretaceous - Jurassic
66 - 201.3 Ma

ID: 3190324
Mesozoic tectonic rocks

Age: Mesozoic (66 - 201.3 Ma)

Stratigraphic Name: Franciscan Complex

Comments: metamorphic protolith: mafic volcanics

Lithology: Shale

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Cretaceous - Jurassic
66 - 201.3 Ma

ID: 2791046
Franciscan melange

Age: Mesozoic (66 - 201.3 Ma)

Stratigraphic Name: Franciscan Complex

Description: Melange of fragmented and sheared Franciscan complex rocks.

Comments: Coast Ranges. Includes areas of Franciscan rocks specifically distinguished as melange on the Geologic Map of California. Includes parts of central and eastern Franciscan belts of Blake et al. (1988)

Lithology: Major:{melange}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]

Cretaceous - Jurassic
66 - 201.3 Ma

ID: 2597695
Central Belt of the Franciscan Complex, graywacke and mélange

Age: Mesozoic (66 - 201.3 Ma)

Stratigraphic Name: Franciscan Complex

Description: Massive to distinctly bedded, brown-, orange-, and white-weathering, green to gray, lithic wacke and dark-gray or black siltstone, shale, and slate, grading into mélange consisting of sheared argillite and graywacke matrix enclosing blocks and lenses of sedimentary, metamorphic, and volcanic rocks. Because contacts between coherent graywacke and mélange are gradational (derived from different amounts of shearing) and because of the size and amount of cover in the map area, it was not possible in this study to differentiate everywhere between coherent graywacke and mélange. Where observed, coherent graywacke masses within the unit are indicated on source map by a green hachure, while large observed blocks that are too small to map at 1:100,000 scale are indicated by diamonds (high-grade) and triangles (low-grade), and structural bodies known to be comprised primarily of mélange are mapped separately (fsr). Coherent graywacke bodies also locally include conglomerate, pebbly sandstone, and rare thin beds of red and white chert. Coarse clasts include black chert, quartzite, hornfels, granite, rhyolite, lithic wacke, blueschist, greenstone, green chert, marble, amphibolite, and quartz-mica schist. In many places, the graywacke contains conspicuous large chips of black and green shale. Coherent sedimentary rocks range from completely unfoliated to moderately foliated (Textural Zones 1-2A of Jayko and others, 1986). Late Jurassic (Tithonian) fossils have been found in both the coherent graywacke and the mélange matrix (Bailey and others, 1964; D.L. Jones, written commun.). Interbedded chert from the Asti quadrangle has been sampled, but not yet processed for microfossils. Interbedded chert in similar coherent graywacke in Marin County has yielded Late Jurassic to Early Cretaceous microfossils (Murchey and Jones, 1984). Chert pebbles from conglomerate have yielded Late Triassic to Early Jurassic microfossils (Seiders and Blome, 1984). Graywacke in this unit is distinguished from most other Franciscan Complex graywacke by its high lithic content. It is similar in composition to sandstone in Central Belt of Franciscan Complex (Kfgwy) but is significantly older, is in places more foliated, and lacks the depositionally underlying sequence of chert (KJfc) and greenstone (Jfgs)

Reference: Blake, M.C. Jr., R.W. Graymer, R.E. Stamski. Geologic Map and Map Database of Western Sonoma, Northernmost Marin, and Southernmost Mendocino Counties, California. U.S. Geological Survey Miscellaneous Field Studies Map MF-2402. [93]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License

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Bradley, W.W. (1918), Quicksilver resources of California, with a section on metallurgy and ore dressing: California Mining Bureau. Bulletin 78, 389 pp.: 186.
Bradley, W.W. (1938), Thirty-fourth report of the State Mineralogist: California Division Mines Report 34: 608.
Ransome, Alfred Leslie & J.L. Kellogg (1939), Quicksilver resources of California: California Division Mines Report 35: 353-486.
Bailey, Edgar H. (1946), Quicksilver deposits of the western Mayacmas district, Sonoma County, California: California Division Mines Report 42: 199-230.
Honke, Martin T., Jr. & Wm. E. Ver Planck, Jr. (1950), Mines and mineral resources of Sonoma County, California: California Journal of Mines and Geology: 46(1): 98-105.
Holmes, Jr., G.W. (1965), Mercury in California: in: U.S. Bureau of Mines Information Circular 8252.
Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 261, 274.
Pemberton, H. Earl (1983), Minerals of California; Van Nostrand Reinholt Press: 181.
Bailey, E.H., USGS, personal files.

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