PETROGRAPHY AND ALTERATION OF ORGANIC-MAT TER FROM THE BEDDIANE LEAD-ZINC-COPPER DEPOSIT (TOUISSIT-BOU BEKER, NORTHEASTERN MOROCCO)

Reflectance measurements and organic petrography were used to study al tered organic matter in the dolomitic Middle Jurassic Beddiane sequenc e hosting the Beddiane lead-zinc deposit. Organic matter occurs in the lower dolostone units of the formation where zinc sulfide mineralizat ion prevails. The upper units, where lead sulfide mineralization is do minant, contain lesser amounts of organic matter. The organic matter i n the Beddiane sequence consists of macerals, amorphous kerogen, and s olid bitumen. Inertinite and vitrinite are ubiquitous. The amount of e xinite increases toward mineralized areas but the ratio exinite/keroge n remains constant. Two types of vitrinite are considered on the basis of their reflectance: Vt(1) with low reflectance values (0.3-0.5%) an d Vt(2) with higher values (0.7-1.25%). The ratio Vt(1)/Vt(2) increase s and the reflectance values for Vt(1) decrease toward the zinc-prevai ling units. Organic matter associated with the mineralization exhibits features such as oxidation halos and desiccation cracks, together wit h a low-fluorescent exinite. The association of the kerogen content, t he trend in reflectance values, and the alteration features of the Mis sissippi Valley-type Beddiane deposit support the hypothesis that the regional flow of hot brines associated with the mineralization process was the cause of anomalous heating, that the occurrence of exinite ma ceral and its associated gas played a role in the ore deposition, and that the new chemical equilibrium reached by the zinc-dominant host ro ck after ore deposition is responsible for the suppressed reflectance values within and near the ore deposits.