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

古代钾蒸发岩的起源，在母水、沉积环境和形成时间方面是有争议的，主要是因为没有详细描述过现代含钾盆地。摘要柴达木盆地是现代层状钾盐（光卤石和钾盐）广泛发育的地区，研究了该盆地钾成矿的地球化学和沉积条件。该项目由三个相互关联的部分组成：(1)利用计算机化的特定离子相互作用溶液模型研究入流水体的化学性质及其向卤盐的演化；(2)现代钾盐矿床的野外和岩石学研究以及伴生卤盐的地球化学特征；(3)通过岩心（岩盐流体包裹体、孔隙流体化学、岩心岩心）研究全新世-更新世卤水演化和钾盐沉积史；和岩石学)。许多古代钾盐矿床缺乏具有海水蒸发岩层序特征的mgso4盐。Hardie （1984, in review）对古无mgso4钾盐蒸发岩的海相起源提出了挑战，提出了一种涉及热液流入水的新模式，特别是那些形成于构造活跃盆地的热液流入水。对柴达木盆地近期构造活动、无mgso4钾盐蒸发岩和主要泉水流入的研究，将有助于检验古代钾盐蒸发岩起源的新假设。

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.