gems, olivine, peridot, Libya

Libya covers an area of about 1,600,000 square kilometers along the northern coast of Africa. It had a population of about 1,500,000 in 1964. Although most of Libya lies within the Sahara Desert, it spans three climatogeographic zones—the Mediterranean, a semidesert, and a desert zone that contains several fertile oases. The Mediterranean zone receives as much as 600 millimeters of annual rainfall and has a climate comparable to parts of southern Europe, but this gradually gives way to intense desert conditions southward. The present report is based on investigations conducted by the U.S. Geological Survey between 1954 and 1962, in cooperation with the Libyan Government, under the auspices of the Agency for International Development of the U.S. Department of State. Fieldwork focused on promising mineral deposits and geological reconnaissance to aid in evaluating the country’s mineral resources. Detailed sampling and studies were carried out on deposits of potential value, and general data were gathered on other resources. A topographic map of Libya was produced in 1960–61 and served as the base for a geologic map compiled in 1960–62; both maps were prepared in collaboration with private oil companies. Geologically, Libya is a cratonic basin on the northern edge of the African Shield. Precambrian igneous and metamorphic rocks occur in south-central, southeastern, and west-central Libya. Tertiary and Quaternary basalts and phonolites cover large areas in the central part of the country and smaller areas in the south-central and northwestern regions. Paleozoic rocks and Mesozoic continental deposits dominate the southern part of Libya below latitude 28° N. Mesozoic sedimentary rocks form the Hamada al Hamra plateau in the northwest and are largely overlain by a thin layer of early Tertiary sediments. Other Tertiary rocks occupy much of central and northeastern Libya and smaller areas in the south-central region. The narrow coastal plains are generally covered by Quaternary deposits; about one-third of the country is blanketed by sand dunes and gravel plains.