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Mineralogical and textural changes accompanying ageing of silica sinter
Herdianita N.R.a,b, Browne P.R.L.a, Rodgers K.A.a, Campbell K.A.a
a Department of Geology, University of Auckland, New Zealand
b Department of Geology, Institute of Technology Bandung, Indonesia
[vc_row][vc_column][vc_row_inner][vc_column_inner][vc_separator css=”.vc_custom_1624529070653{padding-top: 30px !important;padding-bottom: 30px !important;}”][/vc_column_inner][/vc_row_inner][vc_row_inner layout=”boxed”][vc_column_inner width=”3/4″ css=”.vc_custom_1624695412187{border-right-width: 1px !important;border-right-color: #dddddd !important;border-right-style: solid !important;border-radius: 1px !important;}”][vc_empty_space][megatron_heading title=”Abstract” size=”size-sm” text_align=”text-left”][vc_column_text]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.[/vc_column_text][vc_empty_space][vc_separator css=".vc_custom_1624528584150{padding-top: 25px !important;padding-bottom: 25px !important;}"][vc_empty_space][megatron_heading title="Author keywords" size="size-sm" text_align="text-left"][vc_column_text][/vc_column_text][vc_empty_space][vc_separator css=".vc_custom_1624528584150{padding-top: 25px !important;padding-bottom: 25px !important;}"][vc_empty_space][megatron_heading title="Indexed keywords" size="size-sm" text_align="text-left"][vc_column_text][/vc_column_text][vc_empty_space][vc_separator css=".vc_custom_1624528584150{padding-top: 25px !important;padding-bottom: 25px !important;}"][vc_empty_space][megatron_heading title="Funding details" size="size-sm" text_align="text-left"][vc_column_text]Acknowledgements This study was a part of the NZODA study award provided by the Ministry of Foreign Affairs and Trade (MFAT), New Zealand. Funds were contributed by the University of Auckland Research Committee. We thank Drs Kevin Brown and Ritchie Sims, and Svetlana Danilova, Yan Jing, Rod Martin and Karen Sannazzaro for assistance and/or fruitful discussions. Louise Cotterall and Andrea Afaro assisted with the figures. The manuscript was considerably strengthened by the helpful commentaries of Drs Graetsch and Renaut during refereeing. K.A. Rodgers is Research Associate, Australian Museum, Sydney, NSW 2000, Australia, and Kathleen A. Campbell is Research Associate in Geology, California Academy of Sciences, Golden Gate Park, San Francisco, CA 94118, USA.[/vc_column_text][vc_empty_space][vc_separator css=".vc_custom_1624528584150{padding-top: 25px !important;padding-bottom: 25px !important;}"][vc_empty_space][megatron_heading title="DOI" size="size-sm" text_align="text-left"][vc_column_text]https://doi.org/10.1007/s001260050005[/vc_column_text][/vc_column_inner][vc_column_inner width=”1/4″][vc_column_text]Widget Plumx[/vc_column_text][/vc_column_inner][/vc_row_inner][/vc_column][/vc_row][vc_row][vc_column][vc_separator css=”.vc_custom_1624528584150{padding-top: 25px !important;padding-bottom: 25px !important;}”][/vc_column][/vc_row]