ORIGINAL PAPER A Brine Evolution Model and Mineralogy of Chemical Sediments in a Volcanic Crater, Lake Kitagata, Uganda Lichun Ma • Tim K. Lowenstein • James M. Russell Received: 6 January 2010 / Accepted: 6 August 2010 / Published online: 22 August 2010 Ó Springer Science+Business Media B.V. 2010 Abstract Lake Kitagata, Uganda, is a hypersaline crater lake with Na–SO 4 –Cl–HCO 3 – CO 3 chemistry, high pH and relatively small amounts of SiO 2 . EQL/EVP, a brine evaporation equilibrium model (Risacher and Clement 2001), was used to model the major ion chemistry of the evolving brine and the order and masses of chemically precipitated sediments. Chemical sediments in a 1.6-m-long sediment core from Lake Kitagata occur as primary chemical mud (calcite, magadiite [NaSi 7 O 13 (OH) 3 3H 2 O], burkeite [Na 6 (CO 3 )(SO 4 ) 2 ]) and as diagenetic intrasediment growths (mirabilite (Na 2 SO 4 10H 2 O)). Predicted mineral assemblages formed by evaporative concentration were compared with those observed in salt crusts along the shoreline and in the core from the lake center. Most simulations match closely with observed natural assemblages. The dominant inflow water, groundwater, plays a sig- nificant role in driving the chemical evolution of Lake Kitagata water and mineral precipi- tation sequences. Simulated evaporation of Lake Kitagata waters cannot, however, explain the large masses of magadiite found in cores and the formation of burkeite earlier in the evaporation sequence than predicted. The masses and timing of formation of magadiite and burkeite may be explained by past groundwater inflow with higher alkalinity and SiO 2 concentrations than exist today. Keywords Crater lakes  Alkaline lakes  Brine evolution  Mineralogy  Magadiite  Lake Kitagata L. Ma Institute of Mineral Resources, Chinese Academy of Geological Sciences, 100037 Beijing, China L. Ma  T. K. Lowenstein (&) Department of Geological Sciences, State University of New York, Binghamton, NY 13902, USA e-mail: lowenst@binghamton.edu L. Ma College of Resources and Environment, China Agricultural University, Beijing 100193, China J. M. Russell Department of Geological Sciences, Brown University, Box 1846, Providence, RI 02912, USA 123 Aquat Geochem (2011) 17:129–140 DOI 10.1007/s10498-010-9108-x