密西西比河谷型铅锌矿床

密西西比河谷型矿床为后生热液矿床。赋矿层位多，但一般不受主岩沉积相（变）控制。成矿温度并不一定象传统上认为的那样低。铅同位素组成可差异性较大（如J型铅），也可很均一，脉石矿物（方解石和白云石）的δ13C和δ18O明显低于主岩，而87Sr／86Sr值则相反。古老基底为其成矿金属十分重要的来源，硫主要来源于海相蒸发岩。蒸发岩硫酸盐中的硫可由基底中的Fe2+还原为还原态硫，成矿金属主要以硫氢配合物形式迁移，成矿流体的驱动力为构造应力（如由造山引起）和重力，近年其成矿年代方面的研究也取得重大突破。

THE MISSISSIPPI VALLEY-TYPE LEAD-ZINC DEPOSITS

The Mississippi Valley-type (MVT) lead -zinc deposits are the classic epigenetic hydrothermal ores. Generally, they are not controled by the sedimentary facies of the host rocks although they are stratafornd in nature. Both δ13C and δ18O values of cacite and/or dolomite are lower than those of the host rocks. However, the 87 Sr/86Sr ratios just show an opposite trend. The deposits may be heterogeneous (i. e., J-type lead) or homogeneous in lead isotopic composition. The old basement was one of the very important sources of meals involved in mineralizing, and sulfur mainly carne from evaporates. Sulfur in sulfides could com from sulfate reduction by Fe2+ in the basement. Bisulfide complexes are the important forms not only for Zn, Pb, etc., but also for sulfur in mineralizing soutions. Ore solution(s) may be driven from the recharge area by tectonic stress (often due to orogeny and/or rifting) and gravity through faults and/or fractures, Recently, significant progress has been made in the determination of metallogenic ages.