This paper provides a comprehensive review of the sinter deposits, formed largely of opal-A, that are form around hot springs and geysers throughout the world. The discharge aprons around hot springs and geysers are commonly characterized by spectacular discharge aprons that are covered with variegated microbial mats and ornate arrays of siliceous sinters that commonly contain well-preserved microbes and trace elements such as Cs, Ag, and Au. Although precipitation of opal-A, the principal component of these sinters, is controlled primarily by water temperature and pH, other factors such as evaporation, water composition, and the resident biota may also exert an influence. Opal-A is formed of heterometric arrays of microspheres (up to 6 μm diameter) and up to 20% free water and hydroxyls. Cryogenic opal-A, characterized by irregular-shaped plates, may form in cold climates as precipitation occurs between ice crystals that develop as the spring water freezes during periods of low air temperatures. Rapid opal-A precipitation commonly produces well-preserved silicified biota (e.g., cyanobacteria, fungi) that can potentially provide information about the environmental conditions under which they grew. In many cases, however, identification of the silicified biota in terms of extant genera/species is difficult because many of the features needed for precise taxonomic identifications are not preserved. During the early stages of diagenesis, meniscus and isopachous opal-A cements may reduce the porosity and permeability of the opal-A. Subsequent loss of water and transformation of the microspheres occurs as the opal-A develops into the lepispheres that characterize opal-CT. Given that opal-A, opal-CT, and opal-C are defined on X-ray diffraction analyses criteria, the full array of physical changes that accompanies each stage in this diagenetic progression is poorly understood and open to debate. Equally, the processes and time frames that govern these diagenetic transitions are still poorly constrained. Although much is known about the siliceous sinters that form in spring environments, much remains to be learnt about the environmental factors and parameters that control all facets of their geological evolution.

本文对世界各地围绕温泉和间歇泉形成的主要由蛋白石A组成的烧结矿床进行了全面回顾。温泉和间歇泉周围的排放围裙通常以壮观的排放围裙为特征，这些围裙上覆盖着杂色的微生物垫和华丽的硅质烧结物阵列，通常包含保存完好的微生物和微量元素，例如Cs，Ag和Au。尽管这些烧结矿的主要成分蛋白石A的沉淀主要受水温和pH值控制，但其他因素（例如蒸发，水成分和生物群落）也可能会产生影响。蛋白石-A由微球（最大直径为6μm）和多达20％的游离水和羟基的异质性阵列形成。低温蛋白石A，其特征是板形不规则，在寒冷的气候中，冰晶之间可能会发生沉淀，而冰晶之间会发生沉淀，而冰晶在空气温度低的时期结冰时会结冰。蛋白石-A快速沉淀通常会产生保存完好的硅化生物区系（例如，蓝细菌，真菌），从而可能提供有关其生长环境条件的信息。然而，在许多情况下，很难根据现存的属/种来鉴定硅化的生物区系，因为未保留精确分类学鉴定所需的许多特征。在成岩的早期，半月板和等渗的蛋白石A水泥可能会降低蛋白石A的孔隙率和渗透率。随着蛋白石A的发展，成为蛋白石CT的特征性的皮球，随后水的流失和微球的转变发生了。鉴于蛋白石A，蛋白石CT和蛋白石C是在X射线衍射分析标准上定义的，人们对该成岩过程中各个阶段所伴随的物理变化的完整了解甚少，尚有争议。同样，控制这些成岩性转变的过程和时间框架仍然受到严格限制。尽管人们对春季环境中形成的硅质烧结物知之甚少，但关于控制其地质演变的所有方面的环境因素和参数仍有很多知识要学习。