Material source, sedimentary environment, and mineralization process of Shengzhou diatomite deposit in Eastern Zhejiang Province, China

The Shengzhou diatomite deposit, located in the Shengzhou-Xinchang basin, is recognized as one of the largest diatomite deposits in China. The scanning electron microscopy (SEM-EDS), mineral compositions and elemental geochemistry of the samples were analysed to identify the nutrient sources, depositional environments, and mineralization process. Through scanning electron microscopy, the predominant diatom species observed are <i>Aulacoseira granulata (Ehrenberg) Simonsen</i> and <i>Cyclotella shengxianensis Huang and Cai</i>. The results of X-ray diffraction (XRD) analysis results indicate that the mineral composition of diatomite mainly consists of opal-A, quartz, clay minerals, feldspar, carbonate minerals, and pyrite. The results of XRF and ICP-MS analysis show that the content of SiO₂ ranges from 59.11% to 69.44%, and the trace nutrient elements such as Mo, U, V, Co, Ni, Cu, and Zn are enriched. The correlation of geochemical composition between diatomite and Cretaceous volcanic rocks in the study area indicates that the weathering of volcanic rocks provides nutrients for diatom growth. Multiple geochemical indicators (Sr/Ba, V/Cr, Ni/Co, U/Th, V/(V+Ni), C-value, CIA, and Sr/Cu) and palaeontological evidence indicate that the diatomite was formed in a freshwater, oxic, and hot-humid environment. As the diatomite is susceptible to denudation, the overlying basalt may protect the deposit.

嵊州硅藻土矿床位于嵊州-新昌盆地，是中国规模最大的硅藻土矿床之一。通过对样品进行扫描电子显微镜（SEM-EDS）分析、矿物组成分析及元素地球化学分析，旨在揭示其营养物质来源、沉积环境及成矿过程。扫描电子显微镜观察显示，优势硅藻种类为<i>颗粒直链藻（Aulacoseira granulata (Ehrenberg) Simonsen）</i>和<i>嵊县小环藻（Cyclotella shengxianensis Huang and Cai）</i>。X射线衍射（XRD）分析结果表明，硅藻土的矿物组成以蛋白石-A（opal-A）、石英、黏土矿物、长石、碳酸盐矿物及黄铁矿为主。X射线荧光光谱（XRF）与电感耦合等离子体质谱（ICP-MS）分析结果显示，SiO₂含量介于59.11%至69.44%之间，且Mo、U、V、Co、Ni、Cu、Zn等微量营养元素富集。研究区硅藻土与白垩纪火山岩的地球化学组成相关性分析表明，火山岩风化作用为硅藻生长提供了营养物质。多种地球化学指标（Sr/Ba、V/Cr、Ni/Co、U/Th、V/(V+Ni)、C值、化学蚀变指数（CIA）、Sr/Cu）及古生物证据表明，该硅藻土形成于淡水、有氧、湿热环境中。由于硅藻土易受剥蚀，上覆玄武岩可能对矿床起到保护作用。