11 Economic Value

Pumice Deposits of the Klamath Indian Reservation, Klamath County, Oregon

Economic Value

Large volumes of pumice flow and pumice fall material on the Klamath Indian Reservation are potentially available for commercial exploitation. Tests of the chemical and physical properties of the pumice indicate that it is suitable, with some limitations, for use as an aggregate and as an abrasive. Preliminary tests indicate that it may also be suited for use as pozzuolana. Many factors, however, must be considered by prospective pumice producers.

The location of potential sites for pumice pits must be near available lines of transportation. In this respect, the pumice deposits in the northwest part of the Reservation are well situated, as subsidiary branch lines of the Southern Pacific Line and Great Northern Railway traverse this area. It is also served by U. S. Highway No. 97.

The thickness of the deposits must be considered in evaluating the pumice and in locating

1 Production figures published by Oregon State Department of Geology and Mineral Industries.

possible future pumice pits. Past experience in developing central Oregon pumice has shown that the top 2 to 4 feet of pumice must be discarded, because of the deleterious effect of contained soil and plant material. Experience has also shown that an adequate working face in pits must be maintained for low cost production; usually this working face needs to be 8 feet or more. The pumice, therefore, must be at least 10 or 12 feet thick, to be worked economically. Areas adjoining Klamath Marsh are underlain by pumice layers that are consistently 10 feet or more in thickness.

The most favorable sites for the development of the pumice are in the northwest corner of the Reservation in Tps. 29 and 30 S., Rs. 7 and 8 E. The deposits in this area consist of pumice flow, with some local layers of scoria. They are best suited for exploitation because they are thick and widespread and are readily accessible to transportation. Chemically they are acceptable for aggregate and possibly for pozzuolana. In its natural state, however, the material is poorly sorted and the individual pumice lumps are highly absorptive-and have little structural strength. These difficulties can be overcome, at least in part, by screening and processing.

To obtain a higher grade lightweight aggregate, fall pumice material could be mixed with the processed flow pumice, as an aggregate better sorted in size is formed by mixing the two types. The grains of pumice fall also would add to the strength and insulating qualities of the aggregate. Probably the most favorable place to develop the pumice fall deposits from an economic standpoint is in the southern part of T. 32 S. , R. 8 E. , but more detailed testing of the thickness of the deposits in this area would be necessary before quarry sites could be definitely located.

Lump pumice that can be used for a low-grade abrasive occurs only in the flow deposits. It must, therefore, be obtained from the northwest corner of the Reservation, but even in this area the distribution of lumps suitable for abrasive is so erratic that it is not possible to specify any localities that are particularly favorable for development.

The tremendous volume and adequate grade of pumice on the Reservation do not in any way guarantee that a new pumice operation can succeed. In recent years most of the pumice produced from central Oregon was used for lightweight aggregate, but the quantity used decreased during 1949 and early 1950, owing in part to wider use of haydite and other synthetic lightweight aggregates. Competition for this shrinking market is keen, and prospective pumice producers should have assurance of adequate and secure markets before making large expenditures for detailed exploration or equipment.

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