Trigo Mountains District (Cibola District), Trigo Mts, La Paz Co., Arizona, USA

Ref.: Wilson, E.D. (1933) Geology and Mineral Deposits of Southern Yuma County, Arizona. Arizona Bureau of Mines Bulletin 134: 72-73.

Farnham, L.L. & L.A. Stewart (1958), Manganese deposits of western Arizona, US Bureau of Mines Information Circular 7843: 78-82.

Parker, F.Z. (1966) The Geology and Mineral Deposits of the Silver District Trigo Mountains, Yuma County, Arizona. Masters Thesis, San Diego State College.

Keith, Stanton B. (1978) State of Arizona Bureau of Geology and Mineral Technology, Geological Survey Branch Bull. 192, Index of Mining Properties in Yuma County, Arizona: 179 (Table 4).

USGS & Arizona Bureau of Mines, and U.S. Bureau of Reclamation (1969), Mineral and Water Resources of Arizona, Arizona Bureau of Mines Bull. 180 (USGS Bull.871): 211-225.

Arizona Bureau of Mines file data.

A Mn-Au-Ag mining district located in T1-3S, R23-27W, in the northern and central Trigo Mountains.

Mineralization is varied: (1): Manganese oxides in lenticular shoots and bodies within fault zone breccias in Tertiary volcanics overlying Mesozoic schists; (2): Spotty gold in quartz-limonite fissure veins cutting Mesozoic schist, intruded by narrow granitic-porphyry dikes; and, (3): Gold placers deposits in washes below the area of the gold veins.

Original operations were on small gold veins and placers in the 1890's but manganese deposits received little attention until the 1950's when buying stations were established for low-grade material. Only about 52 tons of mined gold ore have been produced accounting for not more than some 62 oz. of gold and 10 oz. of silver. Placer operations may have produced some 323 oz. of gold with minor silver. The total production of manganese ore would be some 7,000 long tons of 40% or more Mn and 24,000 long tons of 20-30% Mn.