Reactions that involve biotites, amphiboles, pyroxenes and olivines place significant constraints on the intensive variables of magmas that crystallize to form granitic rocks. Fe₂+-bearing minerals such as magnetite, ilmenite, olivine, pyroxene, amphibole, biotite, and allanite constrain oxygen and sulfur fugacities. All (OH)- bearing phases place constraints on H₂O fugacities, especially if anhydrous reactants are present. Exchange reactions of (OH)- with halogens also place additional constraints on magma properties. Late stage subsolidus reactions commonly recrystallize these minerals and make interpretation more difficult.
Intensive parameters change during the history of a given magma. Sequences of crystallization, coupled with the composition of minerals, can record devolatilization reactions, increases in volatile constituents, and temperatures of magmas crystallizing to form plutons.
The intrinsic properties of a magma may reflect the source region, but may also change significantly during the history of a given magma. Reactions involving hydrous minerals in the source region place strong constraints on the initial water content of magmas. In regions of repeated crustal melting, early granitic magmas will be more hydrous than subsequent ones.

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Electron microprobe analyses of olivine, chromite, pentlandite, and pyrrhotite in 51 samples representing a 753-foot section of mineralized drill core from the ultramafic basal cumulates of the La Perouse layered gabbro reveal that cumulus processes were complex and dominantly of a mechanical, sedimentary nature.
Analyzed olivine grains are rounded and of clearly cumulus origin. Chromite occurs predominately as rounded 100- to 250-micrometer grains trapped within these olivine grains. Pentlandite and pyrrhotite occur both within interstitial (net-textured) sulfide aggregates and as phases exsolved from droplets (to 150 micrometers) of immiscible sulfide melt that were trapped in growing cumulus olivine.
Compositions of olivine grains range from Fo _77.5 a to Fo _82.5 and by as much as 1.7 mole percent Fo within a single thin section. Cr/(Cr+Al) for chromite most commonly falls in the range 0.23 to 0.56; Mg/(Mg+Fe₂+) in the range 0.20 to 0.45; and Fe ³⁺/(Fe₂++Fe ³⁺) in the range 0.10 to 0.25. Within a thin section Cr/(Cr+Al) may differ by as much as 0.24 among individual chromite grains. Ni/(Ni+Fe+Co) for pentlandite typically ranges between 0.33 and 0.48, may differ by over 0.1 for grains within individual thin sections, and is typically distinct for interstitial and included grains.
All analyzed minerals show compositional ranges within individual samples that can best be explained by accumulation from a number of distinct magmatic environments. Wider compositional variation and the repetitive nature of this variation are revealed by the full sample suite. Active processes such as multiple injection, convective overturn, and/or density currents are considered essential to evolution of the studied rocks.

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The southern half of Korean peninsula is composed geologically of Geyonggi-Yeongnam massif of Precambrian, Ogcheon group of age unknown, Joseon group of Cambro-Ordovician, Pyeongan group of late Carboniferous to Permian, Daedong group of late Triassic to early Jurassic, Gyeongsang group of Cretaceous, Yangbuk arid Yeonil groups of Tertiary, and alkaline volcanics of Quaternary. Three groups of granites are distributed in the peninsula, that is, Triassic granite series (Songrim granite series), Jurassic granite series (Daebo granite series) and Cretaceous granite series (Bulgugsa granite series). In the southern half of Korean peninsula, the latter two are widespread.
The mineral deposits related to Daebo granite series are many hypothermal to mesothermal Au-quartz veins known as Korean-type gold vein. These are distributed in NNE direction. The majority of metallic and nonmetallic mineralizations in the southern half of the Korean peninsula is considered to have been formed associated with the Cretaceous granite series. The vein-type deposits are mainly emplaced in the Cretaceous sediments and intermediate volcanics in the Gyeongsang basin. Economically important skarn type deposits are found along the same horizon between shale and upper limestone of Cambro-Ordovician formation in the Taebaegsan area. The southern half of the Korean peninsula can be divided into three metallogenic provinces of Gyeonggi-Yeongnam province, Ogcheon-Taebaegsan province and Gyeongsang province.

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Almost one hundred granitic rocks of Cretaceous age distributed in the Gyeongsang basin, Korea, were studied petrographically and geochemically. The petrographical data of the rocks represent that they have been evolved from quartz diorite to alkali-feldspar granite, and have been crystallized rapidly at relatively shallow level with a high temperature. The geochemical data show the trend of talc-alkaline magma (PEACOCK'S index of 59) occurred at compressional plate boundaries. The variations of major elements contents and Sr isotopic composition of the rocks denote that the magma was essentially derived from the mantle or igneous sources.
The mineralizations associated with the granitic magmatism seem to be controlled in particular by circular or radial structures resulted from volcano-plutonism in the basin. The mineralized zones are recognized (1) in the sedimentary rocks, (2) in the volcanic rocks, (3) in the granitic rocks, and (4) within the breccia-pipes in volcanic and granitic rocks, and Precambrian basement.

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Recognition of the importance of chlorine complexing in enhancing the solubility of metal sulfides in aqueous solution has led to the view that the chlorine content of intrusive rocks could govern the ability of a magma to separate a metal-rich hydrothermal phase. Relatively high chlorine contents were obtained for apatites, biotites, and amphiboles from Cretaceous granitic rocks in South Korea, whereas the same minerals from the Jurassic granitic rocks are essentially chlorine-free.
The distribution coefficient for chlorine-hydroxyl exchange between apatite and biotite depends on biotite composition and the distribution coefficient for fluorine-hydroxyl exchange between apatite and amphibole depends on amphibole composition. Detailed consideration of amphibole chemistry shows predominance of edenitic and tschermakitic substitution schemes, as well as coupling between substitution of Ti in octahedral sites and Al in tetrahedral sites.
Although the most of the Cretaceous granitic rocks in the Kyongsang basin belong to the magnetite-series, the Jurassic granitic rocks belong in part to the magnetite-series and in part to the ilmenite-series. For the Jurassic granitic rocks, Fe/(Fe+Mg) for biotites and amphiboles increased with an increase in host-rock SiO₂ content; for the Cretaceous granitic rocks in the Kyongsang basin, Fe/(Fe+Mg) for the same minerals decreased with an increase in host-rock SiO₂. It is suggested that the trend followed by Fe/(Fe+Mg) for mafic minerals with increasing host-rock SiO₂ was largely dependent on the presence or absence of early magnetite crystallization in these magmas.
From the mode of occurrence and textures of the granitic rocks and from the chemistry of rock-forming minerals, especially of mafic silicates, it is suggested that the Cretaceous granitic rocks in the Kyongsang basin are high level intrusions compared to the Jurassic granitic rocks. If hydrothermal transport of base metals in chloride complexes is accepted, it is suggested that most of hydrothermal base metal deposits in South Korea were associated with the Cretaceous granitic magmas. Sulfur isotopic composition of base metal deposits in South Korea also supports this conclusion.

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Report of 68 new chemical analysis data of granitic rocks collected during a preliminary field trip from Chungju to Busan through non-metamorphic part of the Ogcheon folding belt, Ryongnam land and Gyongsang basin is presented. Special attention is paid to characterize chemical composition of Jurassic and Cretaceous granites of the country. The studies hitherto performed show:
(1) Chemical evolution examined from (Na₂O+K₂O), total Fe as Fe₂O₃ and MgO variation of Jurassic granite is identical to that of Cretaceous one.
(2) For rocks having the same AL₂O₃/(AL₂O₃+total Fe as Fe₂O₃+MgO) index, Jurassic granite is less siliceous than Cretaceous one.
(3) Remarkable differences between Cretaceous and Jurassic granites are found in their petrographic texture and the sequence of crystallization of the constituent minerals.
Features enumerated above suggest that the two groups of granite separated by their ages differ also each other in their modes of emplacement.

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The characteristics of mineral deposits of granitic affinity in Japan, of mostly Cretaceous and Miocene age, have been well established by recent work. In the Korean peninsula, the Jurassic Daebo and Cretaceous Bulgugsa granitic activities are recognized, and Au-Ag, W-Mo-Bi, Cu-Zn-Pb, Fe(-Cu) and F deposits are formed in genetical association with these activities. Some geologic evidence, besides K-Ar age determination data, suggests that major Korean W-Mo-Bi, Cu-Zn-Pb and F mineralization occurred in Cretaceous time. This tentative conclusion makes it possible to correlate the metallogenic features of Japan and Korea for Cretaceous time. The distribution pattern of Cu and Zn-Pb deposits in both countries seems to be related to the present erosion level, that is, Cu is associated with plutonic activity, while Zn-Pb is with hypabyssal to effusive activity. Major fluorite deposits tend to be formed in shallow environments, perhaps related to subaerial volcanic activity. No clear correlation of W-Mo mineralization could be obtained between the two countries. To get the exact position of the southwestern Japan arc in Cretaceous time, reconstruction of the arc relative to the Korean peninsula is attempted (Fig.4). The arc arrived at its present position by clockwise rotation around the Hokusatsu bend in Tertiary time as a result of the opening of the Japan Sea.

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Jurassic and Cretaceous granitoids are compared in the two areas. The Jurassic Daebo granitoids are dominantly composed of the ilmenite-series and are different from the Jurassic Funatsu granitoids in the Japanese side. The Cretaceous granitoids in the peninsular interior are of the ilmenite-series and weakly magnetic magnetite-series. The cretaceous granitoids of the Gyeongsang basin are predominantly magnetite-series granitoids with no clear separation in the distribution of two types of granitoids, whereas the oceanic side of the ilmenite-series and the marginal sea side of the magnetite-series pair is distinct in the similar volcano-sedimentary basin in the Japanese side.
The Gyeongsang basin is essentially a tungsten province and the wolframite deposits are generally associated with scheelite and molybdenite. These minerals occur separately in the Japanese side. The split-off part of the Gyeongsang basin has not been observed in the northern Kyushu and the western Chugoku districts. It is suggested that magmatism of the Gyeongsang basin occurred in a stable continental margin environment successive to the development of subsided basin in a tensional tectonic setting, whereas that of the southwestern Japan occurred in a floating island arcs where parallel lineaments were developed. The southwestern Japan may have been located at some distance from the Gyeongsang basin during the Cretaceous or Paleogene time.

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Sulfur isotopic composition has been examined on 22 hydrothermal ore deposits in the southern Korean peninsula, dealing with mill materials or composite specimens. The δ³⁴S (CDT) values range from -1.4 to +12.7 per mil, but mostly fall in the narrow range between +2 and +7 per mil irrespective of varying loca-tion and feature of the deposits. The positive δ³⁴S trend resembles the trend of the magnetite-series ore sulfurs in Japan, and is consistent with the fact that most of the studied deposits formed in relation to Cretaceous to Paleogene granitic activities having magnetite-series characteristics.

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Twenty-five Jurassic granitoids, 13 Cretaceous granitoids and 7 metamorphic rocks were analyzed for trace amounts of tin. Jurassic and Cretaceous granitoids of the general ilmenite-series terrain of the continental interior are poor in tin ranging from 0.3 to 3.3 ppm in general. Some stocks, dikes and altered granite contain 2 to 12.8 ppm Sn. The basement metamorphic rocks are also low in tin (average 1.1 ppm). These low contents may be related to the general paucity of tin ore deposits in southern Korea. The magnetite-series, Cretaceous granitoids in the Gyeongsang basin are extremely low in tin (average 0.9 ppm). No tin deposits may be expected associated with the granitoids, but Cretaceous granitoids of the continental interior are different being richer in tin than the Gyeongsang basin granitoids; those of the Taebaegsan area need to be examined in terms of the tin geochemistry.

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The Shinyemi skarn deposit occurs in lower Paleozoic limestone close to Mesozoic felsic intrusives in the Taebaegsan area. Phlogopite occurring in the zinc-lead orebody is dated at 75 Ma. Thus the mineralization is related to the late Cretaceous Bulgugsa magmatic activity. The age is close to that of the No.2 Yeonhwa zinclead deposit, but slightly younger than the age of the Sangdong tungsten deposit.

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FeS, MnS and CdS contents of sphalerites from fourteen Korean hydrothermal deposits, are measured by an electron probe microanalyzer. The results are summarized in Table 2. Relatively MnS-rich sphalerites are found in the deposits where sphalerites are enriched in FeS molecule. Sphalerites from Zn-Pb deposits are characterized by high MnS and low CdS contents. Sphalerites from W deposits are high in CdS contents but those from Cu and/or Fe deposits are low in MnS and CdS contents.

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