RB-SR DATING OF SPHALERITE FROM THE CARBONATE-HOSTED JABALI ZN-PB-(AG) DEPOSIT (YEMEN)

The Jabali Zn-Pb-(Ag) deposit (12.6 Mt ore @ 8.9% Zn, 1.2 % Pb and 68 g/t Ag; Anonymous, 2009) lies about 110 km E of Sana'a (Yemen), at the SW-edge of the Late Jurassic/Early Cretaceous Sab´atayn basin. Mineralization is hosted by Upper Jurassic dolostones and comprises mostly smithsonite intimately intergrown with dolomite (Mondillo et al., 2011). This assemblage is thought to have been derived from the weathering of Mississippi Valley-type (MVT) sulfide ores, of which only residues are observed, consisting mainly of sphalerite, galena, and pyrite/marcasite. In absence of an absolute age, different genetic models have been debated for the origin of the sulfide ores. Al Ganad et al. (1994) assumed a relation of the mineralization with fluids circulating in a karstic network associated with Mesozoic rifting. Allen (2000) considered Jabali as a carbonate replacement deposit originated by hydrothermal circulation related to Tertiary igneous activity, associated with the Red Sea crustal extension (~22 Ma).

To solve this controversy, we investigated the Jabali sphalerite with the Rb-Sr method (crush-leach procedure, e.g. Nakai et al., 1993). The resultant age places sulfide mineralization into the upper Lower Cretaceous. This age is contemporaneous with the published timing for hydrocarbon generation and expulsion in the oil producing basins of Yemen (Ahlbrand, 2002; Csato et al., 2001; Alaug et al., 2012). We conclude that MVT-type mineralization originated at Jabali in close temporal relationship with tectonic extension and hydrocarbon generation in the Sab'atayn basin.

References

Ahlbrand, T.S., 2001. USGS Bull 2202-G

Al Ganad, I., Lagny, P., Lescuyer, J.L., Ramboz, C. and Touray, J.C., 1994. Miner Deposita 29, 44-56

Alaug, A.S., Leythäeuser, D., Bruns, B. and Ahmed, A.F., 2011. Iran J Earth Sci 3, 134-152

Allen, C.R., 2000. Unpub Rep, Cominco American

Anonymous. Mineral Resources of Yemen No, 1 Jan 2009

Csato, I., Habib, A., Kiss, K., Kocz, I., Kovacs, Z., Lorincz, K. and Milota, K., 2001. Oil Gas J 99, no.23, 68-74

Mondillo, N., Boni, M., Balassone, G., Grist, B., 2011. J Geochem Explor 108, 209-219

Nakai, S., Halliday, A.N., Kesler, S.E., Jones, H.D., Kyle, J.R. and Lane, T.E., 1993. Geochim Cosmochim Ac 57, 417-427