평해지역 온정화강암 중 미량원소와 광화작용의 관계에 대한 지화학적 연구

A geochemical study on trace elements of the Onjong granite in relation to mineralization, Pyeonghae area

The variations of certain major and trace elements of the Onjong granite mass was studied on the basis of petrological and geochemical characteristics and compared with those of the Eonyang-Yucheon granite masses in order to investigate the geochemical differences of the granitic rocks in relation to mineralization between Pb-Zn ore district and Pb-Zn-Mo-W ore district in Kyeongsang basin. The Onjong granite mass is classified into granodiorite and monzo-granite, and the Eonyang-Yucheon granite masses into monzo-granite by the Streckeisen’s diagram. Between both granite masses there are clear differences in contents of certain major elements and lithophile trace elements. The former have high contents of Ca (2.94%), Mg (1.66%) and Sr (365 ppm), and low contents of K (3.52%), Na (3.51%), Rb (116 ppm), Ba (640 ppm) and Li (18.9 ppm), whereas the latter have high contents of K (4.02%), Na (4.28%), Rb (145 ppm), Ba (695 ppm) and Li (19.3 ppm), and low contents of Ca (1.42%), Mg (0.43%) and Sr (161 ppm). Except for Mo, there are not clear differences in chalcophile trace elements between two granite masses: the Onjong granite mass has higher Mo content (7.1 ppm) than that (1.7 ppm) of the Eonyang-Yucheon granite masses, but Pb and Zn contents are similar between the Onjong granite mass (Pb=8.7 ppm, Zn=37.1 ppm) and the Eonyang-Yucheon granite masses (Pb=7.8 ppm, Zn=39.8 ppm). Ca and Sr contents of the Onjong granite mass (Ca＞1.5%, Sr＞270 ppm) are higher than those of the Eonyang-Yucheon granite masses (Ca＜1.5%, Sr＜270 ppm), and Rb/Sr, Rb-Rb/Sr and K-Rb/Sr ratios are clearly distinguishable between the Onjong granite mass(Rb/Sr＜0.51, Rb-Rb/Sr＞250 and K-Rb/Sr＞5.2) and the Eonyang-Yucheon granite masses (Rb/Sr＞0.51, Rb-Rb/Sr＜250 and K-Rb/Sr＜5.0). Thus, variations of certain major and trace elements and ratios are applicable as geochemical index to distinguish the types of mineralization of the ore districts related to the Cretaceous granitic rocks in the Kyeongsang basin.