Plateau, Arizona

Mineralised breccia pipes occur in Palaeozoic sedimentary rocks of the Colorado Plateau in northern Arizona (Weinrich, 1985). These pipes are usually circular or oval at suboutcrop, have horizontal dimensions that are typically a few tens of metres and vertical dimensions that may extend to 1000 m. They appear to have developed over solution-collapse structures resulting from karstic weathering of Lower Mississippian carbonate sediments between the Upper Mississippian and Triassic. The mineralisation, comprising pitchblende and sulphides of Fe, Cu, Mo, Pb and Zn, is found beneath a massive pyrite cap, several hundreds of metres below surface. Some of the ore bodies are, or have been, mined for uranium. Gangue minerals include calcite and dolomite. 

This technique was subsequently routinely adopted as an exploration tool in northern Arizona. However, prior to its adoption, a series of trials were carried out to determine its applicability and confidence levels in this environment. Of 14 prospects that were tested, 12 were subsequently drilled. From the soil-air CO2 data it was possible to predict correctly both the presence and tenor of the underlying mineralisation in 11 out of the 12 

Since the techniques described here measure transient fluxes of O2 and CO2 in soil air, it is hardly surprising that measurements are not always reproducible over long 

There is a substantial body of evidence to support the belief that the concentrations of O2 and CO2 in soil air can reveal the position of concealed mineralisation, even through considerable thicknesses of overburden. Surveys can be conducted using any one of several proven field and laboratory methods. The equipment required is, for the most part, inexpensive and readily available. 

However, there is a very wide range of concentrations of O2 and CO2 in the soil air of different environments. Also, measurements can vary markedly with the seasons. Thus it is extremely important when applying the technique in a given area to carry out local orientation tests in order to establish the true background and the contrast that may be expected. 

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Plateau, Arizona and Utah, U.S.A. It occurs as light yellow, soft encrustations in sandstones. It seems to represent a unique mineral group. 

In this example, individual plants of Lupinus sericeus Pursh were collected over a distance measuring approximately 1500 km, including most of the range of the species. hi practice, this amounted to a north-south transect running from the Alberta-British Columbia border to northern Arizona. Lupinus sericeus occurs from southeastern British Columbia and southwestern Alberta to the Kaibab Plateau in northern Arizona,... 

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