Location
Oro Blanco Mountains north of the United States-Mexico boundary, T. 23 S., Rs. 10 and 11 E.
Topographic Maps
Ruby and Oro Blanco 15-minute quadrangles.
Geologic Map
Wilson, Moore, and O'Haire, 1960, Geologic map of Pima and Santa Cruz Counties, scale 1:375,000.
Access
From Nogales, about 25 miles northwest on State Highway 289 to Oro Blanco. Dirt roads and jeep trails lead south to placer areas.
Extent
The Oro Blanco Mountains are named for the fact that the placer gold found in the area is so alloyed with silver that it is silvery white. Placer gold is said to occur in almost every ravine and gulch, on many hillsides, and on surfaces where the soil is reddish from decomposed pyrite. Alamo Gulch and its neighboring gulches (T. 23 S., R. 10 E., Oro Blanco quadrangle) reportedly contained the richest placers; gold recovered from Alamo Gulch was valued at $16 per ounce (at $20.67 per oz).
Placers found at the mouth of Warsaw Gulch on California Gulch (also called Oro Blanco Viejo Gulch; sec. 29, T. 23 S., R. 11 E., Ruby quadrangle) containedgold valued at $10 per ounce (at $20.67 per oz). Most of the gold ranged in size from flour to small nuggets.
Production History
During the past century, most of the placer mining was done with crude implements and with an inadequate water supply. During the 20th century some large-scale placer mining has been attempted; most of these operations were unsuccessful, however, because of the fine size of the gold.
Source
The placers were derived from the numerous gold-silver-bearing veins in the Oro Blanco Mountains.
Literature
Bird, 1916: Notes placer-mining activity.
Blake, 1899: Location; extent of placer ground; character of placer gravels; placer-mining techniques.
Girand, 1933: Placer-mining techniques; activity in 1933.
Koschmann and Bergendahl, 1968: Placer production from 1896 to 1904.
Randolph, 1903: Placer-mining activity in 1902.
Wilson, 1961: Location; extent; areas of placer concentration; history; placer-mining activity during the period 1906-32; early production estimates.
