国内外古陆表海盆成钾条件对比——兼论华北成钾的可能性

克拉通古陆表海盆中的固体钾盐矿床占居全球钾盐资源总量的90%以上,其中最典型的2个巨型钾盐矿床是加拿大萨斯喀彻温和俄罗斯涅帕。为探究华北奥陶纪古陆表海盆的成钾可能性,对比分析了国内外同类型盆地的成钾条件,结果表明:萨斯喀彻温泥盆纪钾盐矿床的形成主要表现为巨量海水在稳定克拉通预备盆地的持续蒸发浓缩,进而迁移至相对活动的亚稳定构造区汇聚成钾盐矿床,其上覆盖着红层沉积,其成钾模式概括为"泪滴式";俄罗斯涅帕寒武纪钾盐矿床的形成过程总体表现为半封闭巨型蒸发台盆接受巨量海水的多次补给并持续蒸发浓缩,富钾卤水最终汇聚于受同沉积断裂控制的深坳中,形成巨型钾盐矿床,钾盐层系上覆为膏岩或灰岩等淡化沉积层,其钾盐成矿模式概括为"牛眼式"。华北奥陶纪古陆表海盆与形成上述2大典型钾盐矿床的盆地具有十分相似的构造古地理和古气候环境条件,且在华北西部的陕北盐盆已钻获厚1.22 m的钾石盐矿层和厚达64.7 m的钾石盐高矿化段,根据盆地特殊地质条件,建立了陕北奥陶纪盐盆的"复底锅"成钾模型。笔者认为,华北奥陶纪古陆表海盆完全可能形成一定规模的海相固体钾盐矿床,并对其中最有希望的陕北盐盆的钾盐资源潜力和找钾前景进行了分析讨论。

Comparative study of palaeo-epicontinental marine basin potash-forming conditions between China and foreign countries with special reference to potash-forming possibilities in North China

Solid potash deposits in craton epicontinental basins account for over 90% of the total global potash resources. The most typical cases are the two giant potash deposits in Saskatchewan of Canada and Niepa of Russia, respectively. To explore the potash formation possibility of Ordovician palaeo-epicontinental marine basins in North China, the authors made a contrastive analysis of the same type og basins in China and abroad. The results show that the formation process of the Saskatchewan Devonian potash deposit can be summarized as follows: a great amount of sea water evaporated continuously and concentrated in a stable cratonic preparation basin, and then the sea water migrated into relatively active metastable structure areas,leading to potash concentration which was later covered by red bed sediments for protection; this potash formation model is summarized as "tear drop" type. The formation of the Niepa Cambrian potash deposit is generally shown as follows: a semi-closed, giant evaporation basin accepted repeated supply of a huge amount of sea water and kept evaporation and concentration of sea water, and eventually K-rich brine converged in a deep platform depression controlled by synsedimentary faults, forming a giant potash deposit; potash formation was then covered by desalination sediments like karstenite or limestone instead of red bed, which, however, did not affect potash formation; this kind of potash formation model is summarized as "bull eye" type. Ordovician palaeo-epicontinental basins in North China have extremely similar tectonic palaeogeographic and climate conditions as the above 2 typical potash deposits on salification and potash concentration. In the Northern Shaanxi Salt Basin in the west of North China, 1.22 m thick sylvine ore horizon and 64.7 m thick highly mineralized sylvine layers have been detected; according to the special geological conditions of the basin, the "complex bottom pot" potash formation model in Northern Shaanxi Ordovician Salt Basin is put forward in this paper. It is thus held that marine solid potash deposits of some sizes are possibly existent in Ordovician paleo-epicontinental basins of North China, as shown by the contrastive analysis of the potash-forming conditions in China and abroad. In addition, some analyses and discussions are put forward for potash resources potential and prospect in the Northern Shaanxi Salt Basin.