Abstract: Humate Deposits in New Mexico

C. T. Siemers, J. S. Wadell

Humates are the salts of humic acids, collectively, or the salts of humic acid, specifically; however, the term "humate" also is used as a lithologic term in reference to carbonaceous claystone or shale rich in humic matter (a collective term for completely decomposed organic matter containing humic acid and other components). Humate as a lithologic term is synonymous with "leonardite," a term used for soft brown coal-like deposits associated with lignite in North Dakota and the adjacent or nearby states of South Dakota, Montana, Colorado, and Wyoming. The Menefee Formation (middle unit of the tripartite Mesaverde Group) and Fruitland Formation (both Late Cretaceous age) of northwestern New Mexico contain abundant humate.

Humate beds in the upper part of the Menefee Formation in the southeastern part of the San Juan basin range from a few centimeters to greater than 2 m thick. The content of humic acids (collectively all alkaline extractable material) commonly ranges from 10 to 40 percent, by weight; humates containing in excess of 80 percent humic acids have been analyzed. Vertically and horizontally adjacent lithologies include barren (noncarbonaceous or nonhumic-rich) claystones, thin coal seams, and sandstone lenses; siderite nodules and concretions are present throughout humate-bearing intervals. Such deposits represent deposition in poorly drained and relatively well-drained deltaic swamps.

Three humate mining operations are active in the San Ysidro-Cuba area. All are extracting humates from the Menefee Formation and market the material principally as a "soil conditioner." The product is used extensively as an agricultural additive which may enhance soil productivity by increasing the water-retention capacity of the soil and improving its general physical characteristics, increasing the rate of decomposition of rocks and minerals to release nutrients, and acting as a carrier and retainer of plant nutrients including trace elements and soluble inorganic fertilizers.

As humates usually are associated with strippable coal deposits, it is suggested that they be added as soil conditioners to the surface material during the restoration phase of such strip mining.

AAPG Search and Discovery Article #90979©1975 AAPG – SEPM Rocky Mountain Sections Annual Meeting, Albuquerque, New Mexico