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U.S. Borax Mine (Pacific West Coast Borax; Pacific Coast Borax Co.; Boron Mine; Boron open pit; U.S. Borax and Chemical Corporation Mine; Kramer Mine; Kramer pit; Baker Mine), Kramer Borate deposit, Boron, Kramer District (Kramer Borate District), Kern Co., California, USA

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Latitude & Longitude (WGS84): 35° 2' 40'' North , 117° 41' 40'' West
Latitude & Longitude (decimal): 35.0444444444, -117.694444444
Other regions containing this locality:North America

A B (borates)-As-Sb-clay occurrence/mine located in secs. 19, 23 & 24, T11N, R8W, MDM, approximately 7 miles NW of Kramer and 4 miles NW of Boron. Ownedr-Operated by the U.S. Borax (subsidiary Of Rtz Borax Ltd. Of Rtz Corporation PLC (London, UK), Home office = Los Angeles, California (until 1992).

The primary mineralization is borax, precipitated in a permanent shallow lake, fed from thermal (volcanic) springs rich in sodium & boron. Kernite was formed later upon deep (+1500 feet) burial and temperatures above 53 degrees C (Christ and Garrels, 1959). The sodium borates together with claystone are hosted as a core facies within the Middle Miocene (16 mybp) Kramer beds (Barnard & Kistler, 1967) and are completely enveloped by ulexite-bearing shales (Gale, 1946). Stratigraphic and structural studies indicate the Kramer borates were deposited in a small structural, nonmarine basin, elongated in an east-west direction and limited on the south by the Western Borax fault.
[Joe Siefke 2010]

Additional names which apply to this locality: Osborne shaft; Discovery shaft; West Baker Mine.

Workings at the site included underground workings that were subsequently subhumed by a large open pit operation. The workings have an overall depth of 182.88 meters, overall length of 2,000 meters and an overall width of 1,600 meters. The underground workings were employed from 1927 to 1957, when the open pit mining became more profitable. The above listed dimensions are for the open pit.

U.S. Borax operates the open pit, refinery and boric acid plant at the site. The waste to ore ratio is about 7:1 with almost 100% ore recovery. The waste to ore ratio is expected to increase as the pit expands to the SSW. On average, one train of 30 to 35 one hundred-ton cars aserves the mine. The mine operations are energy intensive.

Approximately 50% of the kernite is stacked in the pit, wetted with water, and left to hydrate to borax (usually takes a few weeks). Processing is described by O'Driscoll (1990).

In 1989, production averaged 3,000 to 3,500 short tons per day (O'Driscoll, 1990).

Reserve-Resource data are found in: Kistler, R.B., and Smith, W.C. (1975); Roskill Information Services Ltd. (1993).

Reserves and resources data: Type: in-situ (estimate year: 1975): total resources: 36,281,000 metric tons of ore at 25 weight percent B2O3. Estimate year: 1992: total resources: 127,000,000,000 metric tons at 27.7% weight percent B2O3. At 1990 mining rates, reserves were held to be adequate for 30 to 40 years (O'Driscoll, 1990).

Mineral List

Mineral list contains entries from the region specified including sub-localities

34 valid minerals. 4 (TL) - type locality of valid minerals.

Localities in this Region


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.


Minerals Notes and News (1948), Inderite discovered at Boron: Mineral Notes & News Bulletin 127: 12.

Frondel, Clifford & V. Morgen (1956), Inderite and gerstleyite from the Kramer borate district, Kern County, California: American Mineralogist: 41: 839-843.

Smith, George Irving, Hy Almond, & D.L. Sawyer, Jr. (1958), Sassolite from the Kramer borate district, California: American Mineralogist: 43: 1070.

Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 198, 227-228, 327.

Morgan, V. and Erd, R.C. (1969) Minerals of the Kramer borate district, California California Division of Mines and Geology Mineral Information Service: 22: 143-153, 165-172.

Kistler, R.B., and Smith, W.C. (1975), Boron and Borates, in: Lefond, S.J., editor, Industrial Minerals and Rocks (non-metallics other than fuels): New York, A.I.M.E.: 473-496.

U.S. Bureau of Mines (1979), Minerals Yearbook, 1978-1979, volume 1: 120.

Pemberton, H. Earl (1983), Minerals of California; Van Nostrand Reinholt Press: 238.

O'Driscoll, Mike (1990), “Minerals in the US Southwest - breaking rocks in the hot sun” Industrial Minerals, No. 272, p.59 (Ryan/Billie Mine; Ash Meadows Zeolite deposit: 78-79.

Roskill Information Services Ltd. (1993), “The Economics of Boron 1993, 7th ed.” London, Roskill Information Services Ltd., 156 pp.

USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10080426 & 10284982.

U.S. Bureau of Mines, Minerals Availability System (MAS) file #0060291052.

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