Mineralogy and Petrography of Skarn in Khao Lek Area, Nong Bua District, Nakhon Sawan Province, Northern Thailand
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Abstract
Khao Lek deposit is located at District Nong Bua, Province Nakhon Sawan. The deposit is hosted in Permian limestone of Tak Fa Formation and Late Permian-Early Triassic volcanic rocks. The Permian limestone was metamorphosed to calc-silicate and marble. The volcanic rocks unit ranges in composition from basaltic andesite to basalt. Skarn is better developed in limestone than volcanics protoliths. In limestone skarn zonations represented by garnet skarn, pyroxene skarn, garnet-pyroxene, pyroxenewollastonite. In contrast, in volcanics protolith, only pyroxene skarn has been identified. Hence, most of pyroxene skarn occurs as veinlets or infilled vugs. In addition, skarn also occurs in few meters wide dioritic dyke hosting in limestone (marble). This endoskarn shows similar zoning to major skarn. Skarns also display mineralogical variation for example garnet skarn in which in the western part of the zone is represented by dark brown, medium- to coarse-grained associated with calcite whereas, at the eastern part garnet is reddish brown to yellowish green closely associated with pyroxene. This is consistence with composition obtained from EPMA analyzes suggesting that garnet at proximal has composition of spessartite-grossularite-andradite series and at the distal become andradite. These reflect source of fluid and type of protolith and proximal and distal from source intrusion. Similar to pyroxene where diopside represent pyroxene hosted in volcanic whereas, pyroxene hosted in or close to limestone protolith is represented by ferroaugite. These are likely reflected the influence of type of protolith. Other prograde skarn minerals identify at Khao Lek include biotite, tremolite, hornblende and quartz. Magnetite orebody is likely replaced the major endoskarn which was emplaced along ENE-WSW major fault as a dyke. This magnetite mineralization could well be formed during retrograde skarn formation as by cross cutting of quartz-chlorite-sulfides and epidote-chlorite ± calcite and calcite vein/veinlets and their associated hydrothermal alteration seem to have closed link to magnetite mineralization. These three veining systems are responsible for retrograde skarn alteration at the Khao Lek. The skarn at Khao Lek can be classified as calcic skarn based on its mineralogy. When consider in terms of ore deposits that are hosted by skarns, this deposit can be classified as skarn deposit. It is classified as iron ± copper skarn deposit which is based
on the dominant metal i.e., Cu, Au, Pb-Zn, Fe, Mo, W and Sn.
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Copyright © 2008 Department of Geology, Faculty of Science, Chulalongkorn University. Parts of an article can be photocopied or reproduced without prior written permission from the author(s), but due acknowledgments should be stated or cited accordingly.
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