Zhang Yu, Ma Lichun, Wang Kai
MNR Key Laboratory of Saline Lake Resources and Environments, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing, 100037, China.
China University of Geosciences (Beijing), Beijing, 100083, China.
Sci Rep. 2021 Nov 11;11(1):22077. doi: 10.1038/s41598-021-01278-3.
Nitrate deposits are rare worldwide, especially potassium nitrate deposits; furthermore, their genesis remains disputed. There is a rare salt-lake type potassium nitrate deposit in the Dawadi area of Lop Nor at the eastern margin of the Tarim Basin, and the ore bodies show coexisting solid and liquid phases. Additionally, there are large sulphate-type potash deposits in the adjoining Luobei Depression, south of the Dawadi area. To determine why there are two different types of potash deposits in adjacent depressions with similar climates, field geological surveys were conducted and samples collected. It was found that the Tertiary clastic layer at the periphery of the Dawadi deposit was rich in high-salinity brine, with nitrate contents of up to 495-16,719 mg/L, much higher than those in the Luobei Depression, 1-35 mg/L. Additionally, a type of deep hydrothermal (Ca-Cl) brine was found in the fault zones, with nitrate contents of up to 8044 mg/L, dozens of times greater than that of ordinary groundwater. Using comprehensive analysis and research, we concluded that the Dawadi and Luobei depressions belong to different hydrological systems with no connection between them; thus, the two deposits belong to different metallogenic systems. Furthermore, groundwater played an important role in the mineralization of the potassium nitrate deposit, and a deep source may have been an important source of the ore-forming materials. The fault system widely developed in Lop Nor provides favorable channels for deep hydrothermal recharge, and the groundwater and deep hydrothermal brine could provide the source for the nitrate mineralization in the Dawadi Depression through water-rock reactions.
硝酸盐矿床在全球范围内都很罕见，尤其是硝酸钾矿床；此外，其成因仍存在争议。在塔里木盆地东缘罗布泊的达瓦迪地区有一处罕见的盐湖型硝酸钾矿床，矿体呈现出固液相共存的状态。此外，在达瓦迪地区以南相邻的罗北凹陷有大型硫酸盐型钾盐矿床。为了确定为何在气候相似的相邻凹陷中会有两种不同类型的钾盐矿床，开展了野外地质调查并采集了样本。研究发现，达瓦迪矿床周边的第三系碎屑层富含高盐度卤水，硝酸盐含量高达495 - 16719毫克/升，远高于罗北凹陷的1 - 35毫克/升。此外，在断裂带发现了一种深部热液（钙 - 氯型）卤水，硝酸盐含量高达8044毫克/升，是普通地下水的数十倍。通过综合分析研究，我们得出结论，达瓦迪凹陷和罗北凹陷属于不同的水文系统，彼此之间没有联系；因此，这两个矿床属于不同的成矿系统。此外，地下水在硝酸钾矿床的成矿过程中起到了重要作用，深部来源可能是成矿物质的重要来源。罗布泊广泛发育的断裂系统为深部热液补给提供了有利通道，地下水和深部热液卤水通过水岩反应可为达瓦迪凹陷的硝酸盐成矿提供物质来源。
