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Last Chance vein (Baker Mines Company; Granite Mtn vein; Mayflower Mine), Cornucopia Mine, Cornucopia, Cornucopia District, Baker Co., Oregon, USA

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Latitude & Longitude (WGS84): 45° 1' 21'' North , 117° 13' 1'' West
Latitude & Longitude (decimal): 45.02250,-117.21694
Köppen climate type:Dsb : Warm, dry-summer continental climate

A former Pb-Cu-Ag-Au-Zn-Te-As occurrence/mine located in sec. 28, T6S, R45E, WM, 2.5 km (1.5 miles) NW of Cornucopia (site), on National Forest land. Owned by the Forest Industries Insurance Management Company. MRDS database accuracy for this location is not stated.

The Last Chance vein is one of several veins worked by the Cornucopia Mine. Others include the Whitman, Union-Companion, Wallingford and Valley View. Most of the production was from the Union-Companion and Last Chance veins.

Mineralization is hosted in rocks of the Canyon Mountain Complex (granodiorite of the Cornucopia stock, hornblendite, schist and hornfels). The ore body strikes N20E and dips 45W with a width of 2.13 meters and a length of 975.36 meters. Controls for ore emplacement
included pre-Tertiary faults that trend NNE. The deposit involves granodiorite stock and aplite dikes. The vein is mainly quartz with local inclusions of altered host rocks and gouge. The vein crops out at about 7,000 feet of elevation, about 2,500 feet horizontally NW of the Union-Companion vein and about 1½ miles NW of, and 3,000 feet above Cornucopia townsite. Local rocks include intrusive rocks (Cretaceous and Jurassic).

Related tectonic structures: Eugeosyncline.

Workings include underground openings. The vein has been developed and mined to a depth of 2,000 feet below the outcrop.

Mineral List

10 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

66 - 145 Ma

ID: 1496089
Nevadan Intrusives; Wallowa Batholith

Age: Cretaceous (66 - 145 Ma)

Description: Intrusive rocks; plutonic rocks; intermediate composition lithologies; mixed lithologies

Lithology: Major:: {tonalite}; Major:: {quartz diorite, mineralogy: hornblende biotite}; Major:: {trondjemite}

Reference: R.L. Smith, W.P. Roe (compilers). Oregon Geologic Data Compilation, release 6. State of Oregon Department of Geology and Mineral Industries. [20]

Maastrichtian - Rhaetian
66 - 208.5 Ma

ID: 2895444
Intrusive rocks

Age: Mesozoic (66 - 208.5 Ma)

Description: Hornblende and biotite quartz diorite (tonalite), trondhjemite, granodiorite, and small amounts of norite, in batholithic masses and large dikelike bodies. Includes Bald Mountain Tonalite and Anthony Lake Granodiorite of Taubeneck (1957), tonalite and trondhjemite of Wallowa batholith and Cornucopia stock (Taubeneck, 1964; Nolf, 1966), quartz diorite intrusion in the Snake River area (Morrison, 1963), quartz diorite and minor other intrusive rocks in the Caviness quadrangle (Wolff, 1965), quartz diorite northeast of John Day and southeast of Ironside Mountain (Thayer and Brown, 1964), quartz diorite in the Sparta and Durkee quadrangles (Prostka, 1962; 1967), and granodiorite and related rocks of the Pueblo Mountains (Roback and others, 1987). Rubidium-strontium and potassium-argon ages indicate an age range from about 94 to 160 Ma (Taubeneck, 1963; Thayer and Brown, 1964; Armstrong and others, 1976)

Comments: In OR291, unit includes three composite intrusions consisting of smaller individual intrusions that are chemically and petrographically distinct. The largest composite intrusion is the Bald Mountain batholith, which consists of the Elkhorn pluton (Lower Cretaceous and Upper Jurassic); Lower Cretaceous(?) granitic intrusions (granite of Clear Creek, granite of Anthony Butte, leucogranite of Dutch Creek, granite of Isham Spring); granodiorite intrusions (granodiorite of Indiana Mine Road, granodiorite of Beaver Meadow, tonalite of North Fork of Anthony Creek, granodiorite in Guard Station inlier; Upper Jurassic(?)-Lower Cretaceous), including quartz diorites (Upper Jurassic-Lower Cretaceous?; quartz diorite of Wolf Creek, quartz diorite of Guard Station inlier); lamprophyre (Lower Cretaceous or Upper Jurassic); and quartz gabbro (Lower Cretaceous or Upper Jurassic). The other composite intrusions are the North Fork and the Carney Butte stocks. The North Fork stock consists of the North Fork tonalite (Lower Cretaceous and Upper Jurassic), lamprophyre (Lower Cretaceous or Upper Jurassic) and granite (Lower Cretaceous or Upper Jurassic). The Carney butte stock consists of the granodiorite of Table Mountain (Upper Jurassic or Lower Cretaceous?), trondhjemite of Johnson Creek (Upper Jurassic or Lower Cretaceous), tonalite of Granite Meadows (Upper Jurassic or Lower Cretaceous?), diorite of Alexander Creek (Upper Jurassic?), gabbronorite of Carney Butte (Upper Jurassic?), and gabbronorite of Ridenor Canyon (Upper Jurassic?). Cretaceous and Jurassic diorite and gabbro intrusions are mapped as far north as the Umatilla River Basin (OR292) and include the Carney Butte stock

Lithology: Major:{quartz diorite,granitic,granodiorite}, Minor:{gabbro}

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]

Jurassic - Triassic
145 - 252.17 Ma

ID: 3192126
Mesozoic sedimentary and volcanic rocks

Age: Mesozoic (145 - 252.17 Ma)

Comments: Blue Mountains

Lithology: Conglomerate,limestone,sandstone,shale,chert

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]

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

This page contains all mineral locality references listed on This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.


Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Swartley, A.M. (1914), Ore Deposits in Northeastern Oregon, Oregon Bureau of Mines and Geology, Mineral Resources of Oregon: volume 1(8): 49-53.
Goodspeed, G.E. (1939), Geology of the Gold Quartz Veins of Cornucopia, A.I.M.E. Technical Publication 1035.
Brooks, Howard C., Len Ramp (1968), Gold and Silver in Oregon, Oregon Department of Geology and Mineral Industries Bulletin 61: 89-90.
Wiess, P.L., and others (1976), Mineral Resources of the Eagle Cap Wilderness and Adjacent area, Oregon, USGS Bulletin 1385-E: 39-41.
USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10102961 & 10176874.
U.S. Bureau of Mines, Minerals Availability System (MAS) file ID #0410010322 (and #0410010322).

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