Mineralogical and textural changes accompanying ageing of silica sinter
Mineralogical and textural changes accompanying ageing of silica sinter
复制标题
二氧化硅烧结矿老化过程中矿物学和结构的变化
DOI：
10.1007/s001260050005
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发表时间：
2000
影响因子：
4.8
通讯作者：
K. A. Campbell
中科院分区：
文献类型：
--
作者：
N. Herdianita;Patrick R.L. Browne;K. A. Rodgers;K. A. Campbell
摘要 二十九个硅烧结矿样品的年代从现代到中新世，记录了矿物学和结构的时间变化。首次沉积时，烧结物主要由蛋白石 A 的非晶球体（直径<1-8μm）组成，表现出不同程度的密堆积。颗粒密度范围为 1.5 至 2.1gcm−3，总水量为 4–10wt%，孔隙率为 35–60%。尽管球体可能覆盖有一层额外的二次二氧化硅薄膜，但沉积后一万年的变化很小。在接下来的 10,000 到 ∼50,000 年中，二氧化硅逐渐结晶，变成结晶度较差的蛋白石-CT 和/或蛋白石-C；薄叶片晶体（lepispheres）的球形颗粒取代了蛋白石-A颗粒并聚结成微葡萄状聚集体（直径约10–30μm）。杏仁纤维簇与鳞球一起出现。随着二氧化硅晶格有序度的增强，总水含量降至<7 wt%，颗粒密度增加至∼2.3 g cm−3，孔隙率降低至<30%。在含有其他材料（例如方解石、硫、明矾石、植物残骸）的二氧化硅烧结体中，从蛋白石-A 到蛋白石-C 的变化发生在较短的时间内（约 50 年）。超过 50,000 年的烧结矿已重结晶为微晶石英。随着石英结晶作用在约 20,000 年开始，总水量 <0.2 wt%，颗粒密度接近石英 (2.65 g cm−3)，孔隙率 <4%。二氧化硅种类和结构的逐渐变化产生了烧结矿的老化剖面，这可以作为地热系统和/或地表热活动已减弱或停止地区的浅成热液矿床的古水文学的指南。
Abstract Twenty nine samples of silica sinter, ranging in age from modern to Miocene, record temporal changes in both mineralogy and texture. When first deposited, sinters consist largely of noncrystalline spheres (<1–8 μm diameter) of opal-A exhibiting varying degrees of close-packing. Particle densities range from 1.5 to 2.1 g cm−3, total water 4–10 wt%, and porosities 35–60%. Changes over ∼10,000 years following deposition are slight although the spheres may be invested by an additional film of secondary silica. For the next 10,000 to ∼50,000 years, the silica incrementally crystallises to become poorly crystalline opal-CT and/or opal-C; spherical particles of thin-bladed crystals (lepispheres) replace opal-A particles and coalesce in microbotryoidal aggregates (∼10–30 μm diameter). Amygdaloidal fibrous clusters occur with lepispheres. As silica lattice ordering becomes enhanced, total water content drops to <7 wt%, particle density increases to ∼2.3 g cm−3, and porosity reduces to <30%. The change from opal-A to opal-C takes place over a briefer periods (∼50 years) in silica sinters that contain other materials (e.g. calcite, sulfur, alunite, plant remains). Sinters older than ∼50,000 years have recrystallised to microcrystalline quartz. With the onset of quartz crystallisation at ∼20,000 years, total water is <0.2 wt%, particle density approximates quartz (2.65 g cm−3), and porosity is <4%. The progressive changes in silica species and texture yield ageing profiles for sinters that may serve as guides to the paleohydrology of geothermal systems and/or epithermal ore deposits in areas where surface thermal activity has declined or ceased.