Preliminary Volcanic stratigraphy of the Khao Noi volcanic, Tha Takiap District, Chachoengsao Province, eastern Thailand

Abstract

The Khao Noi volcanics (study area) is in Tha Takiap district, Chachoengsao Province. This volcanics is part of the Lampang Volcanic Belt, a potential host rocks for mineralization especially gold and antimony epithermal style. Based on field investigation and drill core logging, the volcanic sequence at Khao Noi has a thickness of 150 meters. The lowest unit (sedimentary unit-Unit 3) which forms as a basement for the Khao Noi volcanics sequence is characterized by laminated limestone, laminated sandstone, limestone breccia, and laminated mudstone. The volcanic sequence can be divided into two units namely, 1) Mafic-intermediate volcanic unit (Unit 2) consisting of plagioclase-phyric andesite, monomictic andesitic breccia, and 2) Felsic volcanic unit (Unit 1) comprising of crystal-rich pumice breccia, lithic-rich pumice breccia, and quartz-phyric andesite. The contact between Unit 2 and Unit 1 is sharp contact and compositionally change from mafic-intermediate to felsic composition. The Khao Noi volcanic architecture is mainly composed of mafic to felsic volcanic succession reflects in eruption style, proximal and distal from sources, depositional environments, and emplacement processes, relatively shallow marine which dominant below wave-base submarine to the subaerial setting. After the formation of the Late Carboniferous sedimentary unit (Unit 3), Unit 2 was deposited with predominantly of andesite and subsequently followed by the deposition of volcanics Unit 1. The volcanic facies architecture comprises interfingering proximal and distal facies association related to four main volcanic types; (1) Submarine andesite includes plagioclase-phyric andesite facies and monomictic andesitic breccia facies. (2) Shallow mafic-intermediate intrusions comprise plagioclasephyric basalt and aphyric trachyte. (3) Submarine pumice pyroclastic surge comprises crystal-rich pumice breccia facies and lithic-rich pumice breccia facies, and (4) Syn-eruptive intrusion of quartzphyric rhyolite facies.