Geology and geochemistry of The Nang Ann prospect, Noen Maprang District, Phitsanulok Province, Central Thailand

Abstract

The Nang Ann prospect is situated approximately 35 km northeast of the Chatree gold-silver deposit in central Thailand. It is located in Ban Mung Subdistrict, Noen Maprang District, Phitsanulok Province. The mineralization at this site primarily consists of iron-copper reduced skarn, which is hosted in Late Permian-Early Triassic volcaniclastic rocks belonging to the Chatree volcanic complex. The oldest rock formation in the central part of the prospecting area is Permian limestone. In the northern part, there is a prevalent occurrence of polymictic rhyolitic sandstone and breccia, while the central part mainly contains unmineralized microdiorite. The host volcaniclastic rocks primarily comprise polymictic rhyolitic sandstone and breccia. Additionally, siltstone and quartz-phyric rhyolite intercalate within the sequence of host rocks. These rocks exhibit varying degrees of alteration, particularly in the sections intersected by diamond drill cores. The geochemistry of the intrusives in the area can be classified into two suites: the intermediate to mafic suite and the felsic suite. The intermediate to mafic suite includes andesite/basalt and basaltic andesite/andesite, suggesting a primitive magma source associated with within plate or ocean ridge origin. The felsic suite comprises dacite, trachy-andesite, and rhyodacite/dacite, indicating a magma source related to fractional crystallization in a volcanic arc setting. Both suites are identified as part of the calc-alkaline magma series.