International Geologiical Congress - Oslo 2008

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MPM-01 General contributions to mineralogy

 

Occurrence and mineralogy of the sericite ore deposit in the Precambrian granitic rock from Bonghwa, south Korea

 

Jiho Oh, Pusan National University (Republic of Korea)
JinYeon Hwang, Pusan National University (Republic of Korea)
SangMo Koh, Korea Institute of Geoscience and Mineral Resource Geology and Geo-infotmation Division (Republic of Korea)
Sejung Ji, Korea Institute of Geoscience and Mineral Resource Geology and Geo-infotmation Division (Republic of Korea)
Kyuwon Kwack , Pusan National University (Republic of Korea)
Hyomin Lee, Pusan National University (Republic of Korea)
 

 

The sericite ore deposits formed in the Precambrian granitic rock at the Bonghwa, Kyungsangbuk-do, South Korea. The geochemical and mineralogical characteristics of sericite occurred in Daehyun and Seonghwang mine were analyzed using petrographic microscope, XRD, EPMA, XRF and ICP-MS. An alteration mechanism was also studied.

Sericitization occurred within the granitic rock by hydrothermal alteration. From the careful study on the occurrence and mineral assemblage, four alteration zone were clearly identified: 1 Zone A: Unaltered rock (quartz + feldspar) 2 Zone B: weakly altered rock (quartz + feldspar + sericite) 3 Zone C: moderately altered rock (quartz + sericite) 4 Zone D: strongly altered rock (sericite). These zones reflect progressive hydrothermal alteration process. The breakdown of orthoclase, plagioclase and mica occurred at early stage of alteration, and abundant sericite formed as alteration intensity increased. Smectite and chlorite/smectite interstratified clay minerals partially formed in fractures zone are considered to be formed later by secondary alteration and/or weathering process.

All sericites belong to 2M1 polytype and their mineralogical and geochemical properties are close to illite. The sericite ores show various colors such as bluish green, pale green, and blackish green, but the characteristics of major element compositions and crystal structures are not different. The trace element analysis, however, indicates that the difference in color attribute to the abundance of Cr and Ti: bluish green colored sericite are enriched in Cr and blackish green colored sericite enriched in Ti.

The formations of sericite ore deposit in the granitic rocks are closely relate to fracture system such as fault and joint. It is considered that the sericite ore deposits in this area were formed by very simple hydrothermal alteration occurred along the fracture zones in granitic rocks with absence of other hydrothermally altered minerals such as kaolin and pyrophyllite.

 

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