Abstract
The Daejang mine is one of the representatives of Cu-Pb-Zn-(Ag) vein deposit related genetically to late Cretaceous granitoid in Korea. Sericite from an alteration halo of the mine yielded a K-Ar date of $95{\pm}3.5Ma$. Based on macrostructures of vein filling, three major mineralization stages (I, II and III) are distinguished by tectonic breaks. Major ore constituents are arsenopyrite, pyrite, pyrrhotite, sphalerite, chalcopyrite, galena, boulangerite, with small amounts of Ag-bearing tetrahedrite, pyrargyrite, native bismuth, marcasite, siderite, ankerite, gudmundite and calcite. Characteristic feature of each mineralization stage and compositional variation of sphalerite and arsenopyrite are discussed in relation to the genetic environments. The FeS contents of sphalerites are 20.5~14.9 mole % in stage I, 17.9~11.9 mole % in stage IIA, 17.0~9.2 mole % in stage IIB, and 6.9~4.7 mole % in stage III. Their results are indicative of decreasing FeS contents during mineralization process in sphalerite coexisting with sulfur-rich sulfide assemblages, such as monoclinic pyrrhotite and pyrite, and is agreement with the conclusions shown by Scott and Kissin(1973). The composition of arsenopyrite decrease also in As content from stage I to stage III, and the compositional variation correlate with position of the associated minerals in the paragenesis. Temperature and pressure of the mineralization are determined as $250{\sim}430^{\circ}C$ and 4.0~0.3kb respectively, based on the chemistry of the minerals.