Ghar Al Hibashi lava tube: the richest site in Saudi Arabia for cave minerals

Severallarge lava tubes have been explored and mapped in different lava fields around the Saudi Arabia.One of the largest is Ghar Al Hibashi, located in the Harrat Buqum-Na\Vasif lava field. It mainly consists of a hugerectilinear gallery (over 400 mlong and 15 m\Vide) the access to \Vhich is through a small vertical pit reaching aside cOlTidor. The cave \Vas long used as a shelter for bats, hyenas, \Volves and foxes. Therefore the entire cave11001', consisting of locally thick uncemented sand, is scattered \Vith a great amount of bones and coprolites,\Vhile some rather large guano deposits are also found. Some of these guano deposits caught fire, \Vhich partiallyburnt the bones overlaying them as \VelI. The only true speleothems consist of a fe\V small yello\V translucentstalactites. During three expeditions in 2003, a fe\V samples of secondary chemical deposits \Vere collected insidethis lava tube to be analysed from the mineralogical point ofvie\V. Despite the scarcity of these samples, at least19 different minerals have already been detected, most of \Vhich are related to the biogenic mineralization ofbones and guano deposits. Three of them, pyrocoproite, pyrophosphite and arnhemite are extremely rare O1'ganiccompounds strictly related to the guano combustion, \Vhich have been observed until no\V only in a fe\V caves inAfrica. Thanks to these findings Hibashi lava tube is not only the most important volcanic cave of Saudi Arabiabut also by far the richest mineralogical shelter of the country. Therefore this research, \Vhich is far from comingto an end, confirms the recently advanced opinion that amongst the different cave environments, volcaniccavities are very favourable for the development of different minerogenetic mechanisms.