Famous Mineral Localities: The Erupcion/Ahumada Mine: Los Lamentos District Chihuahua, Mexico

MINERALOGY

The following minerals, except for pyromorphite, were described by Ransome (1927) and Foshag (1934). Few of them except wulfenite, descloizite, vanadinite and calcite have been found in recent decades. The wulfenite description presented here, of course, reflects the many excellent and interesting finds made since Foshag's time.

Anglesite PbSO^sub 4^

Anglesite formed the major ore mineral in the Erupcion mine and also occurred to a lesser extent in the Ahumada mine. Pure masses of fine-grained gray anglesite were found in the Erupcion mine, as well as coarse anglesite sand and gravel consisting of rough crystals to 1 cm in size. Banded nodules with a core of galena were abundant at one time. Perfectly formed but etched "floater" crystals to more than 6 cm in size were frequently found embedded in white gypsum or sulfur. In the lower levels, anglesite usually occurred as porous iron-stained masses.

Brochantite Cu^sub 4^^sup 2^+(SO^sub 4^)(OH)^sub 6^

Foshag (1934) reports seeing one small specimen of brochantite and gypsum from Los Lamentos. Copper minerals are almost entirely absent at the deposit.

Calcite CaCO3

Calcite is abundant as secondary crystals and thick, white, microcrystalline crusts associated with the ore minerals. It commonly covers limestone to form the matrix for wulfenite crystals. Simple, transparent rhombs occur in small cavities in massive calcite, and in association with wulfenite. It also occurs in a few places in stalactitic form, although stalactites and stalagmites are generally absent in most of the caves.

Cerussite PbCO3

Cerussite constituted an important part of the ore above the 5th level, especially as massive material and pulverulent cerussite sand. Below the 5th level it is replaced by wulfenite and vanadinite.

Descloizite PbZn(VO^sub 4^)(OH)

Descloizite was typically found in close association with vanadinite and wulfenite, and more rarely with calcite and willemite near the borders of the orebody. It is found in the Erupcion workings and the Ahumada workings, though in the former it is not associated with wulfenite or vanadinite. The small, bright crystals are black to dark brown or brownish green in color and very lustrous, usually forming drusy coatings on matrix. Spongy masses of lustrous crystals and irregular nodular masses were common. At least one pocket of wulfenite crystals showed coatings of descloizite that seemed to have formed at the expense of the underlying wulfenite, which was corroded.

Dolomite CaMg(CO^sub 3^)^sub 2^

Dolomite has been reported as the principal gangue mineral. It was formed by the alteration of limestone and has not been found as crystals. It ranges from gray to white and reddish. Chemical tests on a large number of specimens in the Smithsonian collection failed to show any dolomite; all dolomite-like material tested, both matrix and overgrowths, proved to be calcite (John S. White, personal communication).

Galena PbS

Galena occurs from the surface to the lower workings, mainly as remnant cores or nodular masses embedded in anglesite and cerussite, or encrusted with crystals of wulfenite. It is most abundant in thin stringers leading off from the main orebodies, and in the vicinity of the 7th level. Some cleavages contain crystals of sulfur.