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Kate Hardy Mine (Hawn Mine; Derelict Mine; Kate Hardy Mine and mill), Old Mountain House, Alleghany District (Forest District), Sierra Co., California, USA

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Latitude & Longitude (WGS84): 39° 28' 41'' North , 120° 53' 15'' West
Latitude & Longitude (decimal): 39.4780555556, -120.8875
A former lode Au-Ag-Pb occurrence/mine located in the SW¼SW¼ sec. 29 & in the NW¼NW¼ sec. 32, T19N, R10E, MDM, 2.5 km (1.6 miles) S of Old Mountain House and about 2 miles WNW of Alleghany, on both sides of Oregon Creek (2 miles W of Forest), on National Forest land. The property comprises 35 acres. Owned/operated by the R. Flatland Company, California (1980). Intermittent production occurred thru 1956. MRDS database stated accuracy for this location is 100 meters. One of the earliest discovered mines. Production of Au ore was reported in 1949.

Mineralization is a vein deposit hosted in aplite, serpentinite, granite, gabbro, and diorite. The ore body strikes N23W and dips 78W at a thickness of 16.76 meters. The vein lies in black slate, cut by dikes of gabbro & serpentine. A post-mineralization vertical fault with a 25 to 30 foot offset to the N. Further S it may completely cut off the vein. The slate is mainly fissile & fine-grained. Vein lenses of quartzite. A massive green rock (tuff ?), or fine-grained gabbroic dike (?) occurs close to the vein. The serpentine mass crossing the entire district is 100 to 200 feet E here and small dikes from it extend nearly to the vein. The largest gabbroic dike crosses slate & serpentine and grades in short distance from olivine gabbro to diorite with porphyritic phase containing orthoclase. There are 3 outcrops of acidic intrusives: an aplite dike 4 to 8 feet thick; pyritized granite of mainly quartz and orthoclase. The vein cuts slate at a small angle and is tracable 1,000 feet nearly to Laua (??) contact. Quartz float indicates a N extension for about 1,200 feet of the vein. The vein changes to a zone of quartz stringers and silicified slate 100 feet thick. Early movement reversed, grooving pitches a few degrees S of the dip. Ribbon structure due to successive fissuring. Later quartz veining crosses earlier structure. Less altered than the Brush Creek Mine. A large number of small bunches of high-grade ore occur. High-grade shoots are generally vertical and end against prominent sheeting zones, which generally dip less than 10N, and is associated with coarse-grained arsenopyrite, and is more likely to be high-grade where it approaches serpentine. Local alteration includes carbonitization. Local rocks include Paleozoic marine rocks, undivided, unit 6 (Northwestern Sierra Nevada) and/or ultramafic rocks, chiefly Mesozoic, unit 2 (Western Sierra Nevada and Klamath Mountains).

Workings include unspecified surface and underground openings with an overall depth of 76.2 meters.

Analytical data results: Up to 4% sulfides-concentrate.

Mineral List

10 entries listed. 10 valid minerals.

The above list 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.


Logan, Clarence August (1929), Sierra County, Colusa County: California Mining Bureau. Report 25: 178.

Ferguson, Henry G. & R.W. Gannett (1932), Gold quartz veins of the Alleghany district, California: USGS Professional Paper 172: 89, 91, sketch map p. 90.

Averill, Charles V. (1942a), Mineral resources of Sierra County: California Journal of Mines and Geology, California Division Mines (Report 38): 38(1): 58.

U.S. Bureau of Mines Mineral Report (1949).

Carlson, D.W. & W.B. Clark (1956), Lode gold mines of the Alleghany-Downieville area, Sierra County, California: California Journal of Mines and Geology: 52: 253-254, 269.

Clark, Wm. B. (1970a) Gold districts of California: California Division Mines & Geology Bulletin 193.

Mine Safety and Health Administration (MSHA) (1980), MSHA file No. 0401285 (May, 1980).

Pemberton, H. Earl (1983), Minerals of California; Van Nostrand Reinholt Press: 33.

USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10086532, 10262502 & 10286589.

U.S. Bureau of Mines, Minerals Availability System (MAS) file #0060910243 & 0060910303.

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