Abstract Paleoproterozoic (Rhyacian) gold deposits of the Loulo district in western Mali contain >17 million ounces (Moz) Au and form part of the second most highly endowed region within West Africa. The deposits are located within siliciclastic, marble, and evaporitic rocks of the ca. 2110 Ma greenschist facies Kofi series, which were folded and inverted between ca. 2100 and 2070 Ma, prior to gold mineralization. Deposits at Yalea and Gounkoto are located along discontinuous, low-displacement, albite- and carbonate-altered shear zones, whereas Gara is confined to a tourmaline-altered quartz sandstone unit. Lodes typically plunge gently to moderately, reflecting the attitude of folds in the adjacent rocks and bends in the host shear zones, both of which influenced their location. Gold mineralization in the Loulo district was broadly synchronous with emplacement of the Falémé batholith and associated Fe skarn mineralization, which intrude and overprint the western margin of the Kofi series, respectively. However, hydrothermal fluids generated during metamorphic devolatilization of the Kofi series rocks appear responsible for gold mineralization, albeit within a district-wide thermal gradient associated with emplacement of the Falémé batholith. The regional-scale Senegal-Mali shear zone, commonly cited as an important control on the location of gold deposits in western Mali, is absent in the Loulo district.

Abstract A deterministic computer program has been developed to simulate the stratigraphic evolution of two-dimensional transects across sedimentary basins. Clastic, carbonate, and mixed clastic-carbonate systems can be simulated. The main application of the program is to simulate basin stratigraphy using all available data as constraints. In this paper we concentrate on the simulation of carbonate systems and illustrate the following two specific applications of the program. (1) The history of sea-level fluctuations is reconstructed using the stratigraphy and geometry of carbonate systems as constraints. In a first example, the architecture of isolated Miocene carbonate buildups is simulated using sea-level curves similar to published eustatic charts. In a second example, the stratigraphic patterns at the margin of a Mesozoic cratonic carbonate basin are used to derive an estimate of the sea-level history. (2) Our understanding of the controls on carbonate platform architecture is improved by isolating individual processes. In this respect, we investigate the possible significance of isostasy in controlling the formation of intra- and inter-platform basins and in the initiation of carbonate pinnacles.