New Mexico Mineral Symposium — Abstracts

At the end of the last century, a time of intense exploration in New Mexico, remote areas of the territory were reached by prospectors, and more exotic resources were found. One of these was recorded by Carrera (in Prince, 1891): "There is said to exist up in the craggy peaks of the eastern slopes of the Organ Mountains large bands of lapis lazuli, a very valuable stone, made so both by its extreme rarity and matchless beauty." Farther east, in the Sacramento Mountains around 1904, an unusual blue-banded stone was quarried for building stone. The rock did not hold up to weathering and quarrying was halted. In both cases the blue mineral was misidentified and its significance unexplored.

The location of the lapis lazuli (lazurite (Na,Ca)_7-8(Al,Si)₁₂(O,S)₂₄[(SO₄),Cl₂,(OH)₂]) in the Organs was never properly reported in Prince (1891) and was repeated by Northrop (1944). When the area was mapped in some detail, Seager (1981) reported azurite present near the contact of the granite of Granite Peak with a roof pendant. Suspicious of the these early reports, the area was explored and lazulite MgAl₂(PO₄)₂(OH)₂, not lazurite or azurite, was found. The lazulite occurrence in the Sacramento Mountains was mapped in detail by the United States Geological Survey during the White Mountain Wilderness study, but lazulite was not identified. It was recently recognized during a reconnaissance geological trip.

In the Organ Mountains lazulite occurs in veins with muscovite (occasionally a dense blue-green variety), quartz, hematite, and jarosite hosted by a sericitized tuffaceous sandstone. The lazulite occurs in a roof pendant in close proximity to a pyritized zone in the granite of Granite Peak, the latest stage of granitic plutonism recognized in the Organ batholith. A red unidentified mineral is also associated with the lazulite.

At the Sacramento Mountains occurrence in Bluefront Canyon, the lazulite occurs in an altered quartzite. The rock contains corundum (v. sapphire) and alunite in addition to the quartz. The lazulite and corundum occur in bands that appear blue. The light-colored bands consist mostly of quartz. The blue bands of lazulite have reaction rims on their margins.

The origin of the lazulite is still under study. The geologic and mineralogic relationships suggest phosphate metasomatism associated with late-stage crystallization of a granitic magma gave rise to the lazulite veins. However, alteration of a phosphate-rich host rock is also possible. Porphyry-type molybdenum mineralization is in close proximity in both instances.
 

References:

1. Prince, L. B., 1891, Report of the Governor of New Mexico to the Secretary of the Interior, 1891,44 p., Washington, D.C.
2. Seager, W. R., 1981, Geology of the Organ Mountains and southern San Andres Mountains, New Mexico: New Mexico Bureau of Mines and Mineral Resources, Memoir 36, 97 p.