DIAGENETIC QUARTZ AND AMORPHOUS SILICA IN NEW-ZEALAND COALS

New Zealand coal seams (Late Cretaceous-Miocene, lignite-semi-anthraci te) contain numerous and varied occurrences of diagenetic quartz and a morphous silica. Early diagenetic silicifications include: sub-horizon tal and laterally extensive, quartz-mineralized bands; micro- and mega scopic, euhedral quartz crystals, dispersed or concentrated in layers; and silicified in situ tree stumps. Late diagenetic forms include: su b-horizontal, quartz-mineralized bands, mostly < 1 m in length; and fr acture-infillings. The origins of the silica remain uncertain but leac hed basement rocks and coal measure sediments, and siliceous phytolith s within the coal-forming plants, are possible sources. The silicifica tion of coal seams may have significant implications for exploration, mining and geological studies.