Black Mountain Mine (Black Mountain group), Black Mountain, Poway, San Diego County, California, USAi

Regional Level Types
Black Mountain Mine (Black Mountain group)	Mine
Black Mountain	Mountain
Poway	- not defined -
San Diego County	County
California	State
USA	Country

A former As-Au mine located in sec. 5, T14S, R2W, SBM, 1.0 km (3,400 feet) NNE of Black Mountain (coordinates of record), on its N slope, and 7.6 km (4.7 miles) WNW of Poway, on state park land. Note the property is located within the Black Mountain Open Space Park and is closed to collecting. Alternate coordinates provided: 32°59'24"N, 117°06'40"W

According to 2009 article in the San Diego Union Tribune, "in the 1920s, there was a short-lived boom in white arsenic because it was an ingredient in a pesticide that attacked boll weevils, which were infesting Southern cotton crops. Frank Hopkins, an Escondido rancher, rodeo cowboy and actor, used his Hollywood contacts to fund an arsenic mine on the north slope of Black Mountain. Several years of cold winters and dry summers in the South effectively eliminated the boll weevils, so demand for white arsenic fell. The mine was abandoned in 1927, but its concrete dust chamber, shafts and oven remain."[1]

However according to a contemporaneous article, Mr. Hopkins and his partners may also have had interest in another mineral at this site - gold. According to a 1939 article, "known to be conservative" J.N. McLeod "a nationally known mining engineer", "obtained 150 samples from test holes and reports they assayed from $13.60 a ton at the extreme south end of the workings to $113 at the north end."[2] In 1939, the US Official gold price was set at $35 per troy ounce.

In 1926, the 180-foot-long concrete stack was constructed for processing the arsenic. The arsenic was mined, crushed, and heated to a vaporizing temperature. The condensed arsenic vapor was collected from the baffles inside the stack.[3] Downhill of the stack, is the mine's oven, a few collection bins (perhaps for cyanide leaching?) and collapsed outbuildings.

To the west of the oven and in front of what seems to be a collapsed mine adit, is a small pile of arsenopyrite ore, some with small, unremarkable pyrite crystals. Getting to the location also requires off trail bush-wacking, another activity frowned on by the park rangers, as dangers at this site include bees, ticks, thorns, mountain lions (2011 sightings), snakes, heat exhaustion and unstable structures.[4] And as readers of this website likely already know, elemental arsenic and arsenic compounds are classified as “toxic” and “dangerous for the environment” in the European Union under directive 67/548/EEC.

The Park is located in the geological area known as the “Poway Quadrant” which consists of rock units called “Santiago Peak Volcanics.” The Santiago Peak Volcanics comprise an elongate belt of mildly metamorphosed volcanic, volcaniclastic, and sedimentary rocks that crop out from the southern edge of Los Angeles Basin southward towards Mexico (California Division of Mines, 1975).

Local rocks include Mesozoic volcanic rocks, unit 4 (Peninsular Ranges) (per MRDS database).

Other Regions, Features and Areas containing this locality

References