Alteration of volcanic rocks and genesis of kaolin deposits in the Sile region, northern Istanbul, Turkey; I, Clay mineralogy

• Published in: Clays and clay minerals Vol. 51; no. 6; pp. 675 - 688
• Main Authors: Ece, O. Isik, Nakagawa, Zenbe E, Schroeder, Paul A
• Format: Journal Article
• Language: English
• Published: Boulder, CO Clay Minerals Society 01-12-2003; The Clay Minerals Society
• Subjects: andesites; Andesitic Suite; Asia; clay mineralogy; clay minerals; Coal Beds; Crystalline rocks; Dta; Dysaerobic; Earth sciences; Earth, ocean, space; Exact sciences and technology; Experimental petrology; FTIR; FTIR spectra; gibbsite; goethite; hydrothermal alteration; igneous rocks; illite; infrared spectra; Istanbul Turkey; kaolin deposits; Kaolinite; kaolinization; Lacustrine Basin; lacustrine environment; lake sediments; Metallic and non-metallic deposits; metasomatism; Middle East; Mineralogy; oxides; sed rocks, sediments; Sedimentary petrology; sediments; SEM; SEM data; sheet silicates; Sile Turkey; Silicates; smectite; spectra; Suluklu Turkey; TEM; TEM data; Turkey; Useful material except metal geology; volcanic rocks; Weathering; Middle East; Turkey; illite; Lacustrine Basin; oxides; kaolinite; feldspar; clay mineralogy; pyrite; Dysaerobic; Coal Beds; Andesitic Suite; goethite; mineral deposits, genesis; FTIR; sheet silicates; silicates; framework silicates; K-feldspar; sulfides; iron sulfides; volcanic rocks; alkali feldspar; quartz; weathering; igneous rocks; leaching; transport; anatase; paragenesis; smectite; DTA; hydroxides; gibbsite; Asia; kaolin deposits; clay minerals; kaolinization; SEM; underclay; TEM; sediments
• DOI: 10.1346/CCMN.2003.0510610
• EISSN: 1552-8367
• ISSN: 0009-8604

The Sile Region contains discontinuous, cyclic, thin coal beds and industrial clay deposits that were accumulated in lacustrine basins which received extensive volcanoclastic sediments due to transport of highly weathered calc-alkaline volcanic rocks. The Suluklu area has the largest kaolin deposit in this region. Cyclic kaolinization depended on the degree of leaching of Si and alkalis in cyclic swamp environments and, therefore, kaolinite contents vary in each discontinuous lens-shaped clay bed and underclay within the basin. The kaolins comprise disordered kaolinite, illite, smectite, gibbsite, quartz, pyrite, anatase, K-feldspar and goethite. Depth-related changes in the distribution of clay minerals, associated with coal beds, are indicative of organic acid-mineral reactions. Kaolinite crystallization initiated at the edges of sericitic mica sheets in mica sheets in the form of composite kaolinite stacks. The small size (<1 µm), morphology and poor crystallinity of kaolinite crystals suggest that kaolinization post dated transportation. Primary or secondary origins of particles can be determined from the stacking sequences of kaolinite particles using high-resolution transmission electron microscopy images. Kaolinite stacks always contain a small amount of illite, but smectite is only present in the middle and upper levels. Gibbsite is a main constituent of refractory bauxitic clays locally found as discontinuous lenses and exploited from the lower level of the basin. Genesis of kaolin deposits took place in two stages: first, there was in situ weathering of the oldest andesitic agglomerates, tuffs and ashes at the base of the lacustrine basin coupled with discharge of shallow thermal waters which were initiated by local hydrothermal alteration; second, surface weathering enhanced transportation of altered rocks from the surrounding hills into the lacustrine basin. Kaolinization took place in cyclic swamp environments, as indicated by the presence of cyclic thin- to thick-bedded coals that provided necessary humic and fulvic acids for the post-depositional alteration of altered volcanic rocks to kaolin in dysaerobic, relatively low-pH conditions in saturated groundwater zones.