copper. Amazonite is present and was reportedly mined by the ancient Libyan civilization of Garamantes. Salt is mined today, and is an important source of income for the Toubou. The Soborom geothermal field, the name of which means "healing water", is known to locals for its medicinal qualities; its pools are rumored to cure dermatitis and rheumatism after several days of soaking. Mare de Zoui and its surroundings were rarely visited, aside from a nearby oasis. However, there are numerous small oases on the plains of Borkou, near Emi Koussi, which are extensively exploited. This water is thought to be sourced from the Tibesti Mountains, from where it flows underground before surfacing at these springs. Agriculture There are accessible oases to the west and north of the range. Where mosquitoes do not abound, they support several villages, such as Zouar where, by the 1950s, indigenous plant species had been largely replaced by some 56,000 date palms (Phoenix dactylifera). The dates are harvested between late July and early August. In winter, when reserves are depleted, it is not uncommon for the cores of the dates and the fiber of the palms to be ground into a paste and consumed. Some native palm species remain, such as the doum palm (Hyphaene thebaica), from which the hard yet vaguely-sweet fruit rinds are collected, ground and consumed, despite their low nutritional value. The banks of the enneris grow desert gourd (Citrullus colocynthis), which are collected in October to extract the bitter seeds which, after being washed, are ground to make flour. Women are customarily responsible for gathering wild grains on the tarsos in August. Horticulture is practiced on a small scale using traditional irrigation methods. The palm groves can also grow wheat, millet and maize, but the crops are spotty and sometimes swept away by flooding. in total, including barley, the Tibesti produced of cereals each year. On the plains of Borkou, some fields are irrigated, where cattle, goats and dromedaries can drink. In the 1950s, it was reported that goats and, more rarely, sheep numbered 50,000 heads, while 8,000 dromedaries and 7,000 donkeys were being raised in the range. Since the droughts of the 1970s and 1980s, dromedaries have come to dominate at the expense of cattle. Most animals spend the winter on the plateaus or in the high valleys. They descend into the lower valleys in February, just after the sowing of