About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 4. (April)

First Page: 760

Last Page: 761

Title: Geology of Sierra Pena Blanca Region, Chihuahua, Mexico: ABSTRACT

Author(s): Philip Goodell, Kenneth Carraway

Article Type: Meeting abstract


The Sierra Pena Blanca is a fault-block mountain range, extending 100 km in a north-south direction, and being up to 15 km wide. Paleozoic eugeosynclinal sediments constitute the southernmost part, and rocks are progressively younger to the north. Cretaceous basinal and reef carbonate facies are present, and are succeeded northward by lower Tertiary conglomerates, ash-flow tuffs, and volcaniclastics, ranging in age from 44 to 35 m.y. The area is at the boundary of the Chihuahua trough on the east and the Aldama platform on the west. Internally, the range has a repetition of significant northwest-trending, down-to-the-northeast faults. The Tertiary units show some variation in thickness and facies throughout the area. They illustrate an outflow environment, and some units uggest a caldera source on the west or southwest.

Significant uranium deposits occur near the base of the ignimbrite pile. The largest volume of ore is stratigraphically controlled at the base of a welded ash-flow tuff, the Nopal Formation. The Margarita deposit and northern El Curvo zone are examples of this type. Additional mineralization occurs in fractures and faults, as at Nopal 1 and 3. Some mineralization is also present in the underlying Cretaceous carbonate rocks, as at Domatilla, and Sierra Gomez.

Data were collected from drill holes in the Margarita deposits. To define the geochemical indicators a principal factor analysis was performed on the data, which consists of 30 samples with 28 chemical elements. Factor analysis reduced this data set to 8 latent variables or factors. The factors can be interpreted from the association of variables which have the highest factor loadings.

An eight-factor solution to the analysis indicated that certain trace elements, as well as some important major elements, could be used as possible geochemical indicators for this type of deposit. The positive trace elements defined are: MnO, Hg, B, Y As, Mo, F, and Cu. The multiple correlation coefficient

End_Page 760------------------------------

for these variable is as great as 0.9, but, individually, the correlation between uranium and the variables was no greater than 0.3. These elements individually have little significance but, taken as a suite, they are related to the uranium mineralization. Major and minor elements which are also related are MgO, CaO, CO2, Fe, and S. The deposit is interpreted as having been deposited from uraniferous ground waters between 100 and 200°C, migrating toward paleotopographic lows on the east. The uranium is believed to have been derived from the leaching of tuffs.

End_of_Article - Last_Page 761------------

Copyright 1997 American Association of Petroleum Geologists