From foreword: This is a progress report describing four tungsten mines in the Republic of Argentina that were examined between October 1942 and May 1943. The work leading to this report was carried on by the Geological Survey, United States Department of the Interior, and Direcci6n de Minas y Geologia, Ministerio de Agricultura de la Republica Argentina. This work was part of a larger cooperative program sponsored by the Interdepartmental Committee on Scientific and Cultural Cooperation and was carried on under the auspices of the United States Department of State. It is hoped that this cooperative work will be continued, for it is not only of direct practical use to miners but of high scientific interest.