ALBITITE AND LISTVENITE - NEW-TYPE OF DISSEMINATED GOLD DEPOSIT IN THE HIGHLY HYDROTHERMALIZED BIRIMIAN GREENSTONE-BELT OF BURKINA-FASO

The Loraboue prospect is located in the northern part of the Poura dis trict, in the Boromo greenstone belt (Burkina Faso). Gold mineralizati on occurs in albitized rock (albitite) and carbonatized ultrabasic roc k (listvenite), which represents a new type of ore deposit in Burkina Faso. The precipitation of gold can be achieved during the late stage of alteration inducing the crystallization of ankerite, quartz and mus covite in albitite, and ferroan-magnesite, fuchsite and quartz in serp entinized uitramafic rocks. Gold deposition Is linked to the formation of sulfides (mainly pyrite associated with quartz), itself controlled by the Fe/(Fe + Mg) ratio of the initial host-rock. This could explai n the higher Au contents of albitite (0.5 <Fe/(Fe + Mg) < 0.9 ; 5 to 1 250 ppb Au) than hydrothermalized ultrabasic rock (0.1 < Fe/(Fe + Mg) < 0.2; 10 to 200 ppb An). These unusual rocks could represent an attra ctive target for Au prospecting in the Burkina Faso.