Modern Closed-Basin Potash Evaporites and Brine Evolution, Qaidam Basin, Qinghai Province, China

关于古钾盐蒸发岩的成因，从母水、沉积环境和形成时间等方面来看，很大程度上存在争议，因为没有详细描述现代含钾盆地。本文旨在研究中国西部柴达木盆地广泛发育现代层状钾盐(光卤石和钾盐)的钾盐成矿的地球化学和沉积学条件。该项目包括三个相互关联的部分：(1)利用计算机化的特定离子相互作用溶液模型，研究流入水的化学及其演化为卤水；(2)现代钾盐矿床的野外和岩石学研究以及伴生卤水的地球化学；(3)从两个岩芯(盐岩中的流体包裹体、孔隙流体化学、盐岩中的流体包裹体、孔隙流体化学、和岩石学)。许多古老的钾盐矿床缺乏海水蒸发岩序列所特有的硫酸镁盐。Hardie(1984)挑战了古代无镁钾盐蒸发岩的海洋成因，并提出了一种新的热液流入水模型，特别是对于那些形成于构造活动盆地中的水。对柴达木盆地的研究，以及最近的构造活动、不含镁的钾盐蒸发岩和大量的泉水流入，将使对古代钾盐蒸发岩起源的新假说得到验证。

The origin of ancient potash evaporites, in terms of parent waters, depositional environments, and timing of formation is controversial largely because no modern potash-bearing basins have been described in detail. The goal of this study is to document the geochemical and sedimentological conditions of potash mineralization in the Qaidam Basin of western China, where modern bedded potash salts (carnallite and sylvite) are widely developed. The project consists of three interrelated parts: (1) chemistry of inflow waters and their evolution into brines, using a computerized specific ion interaction solution model, (2) field and petrographic study of modern potash salt deposits and geochemistry of associated brines, and (3) Holocene-Pleistocene history of brine evolution and potash salt deposition from study of two cores (fluid inclusions in halite, pore fluid chemistry, and petrography). Many ancient potash deposits lack the MgSO4-salts that are characteristic of a seawater evaporite sequence. Hardie (1984, in review) challenged the marine origin of ancient MgSO4-free potash evaporites and proposed a new model involving hydrothermal inflow waters, especially for those formed in tectonically- active basins. Study of the Qaidam Basin, with recent tectonic activity, MgSO4-free potash evaporites, and major spring inflow, will allow testing of new hypotheses on the origins of ancient potash evaporites.