Showing papers in "Mining geology in 1987"
TL;DR: In this paper, three lines of evidence which support the magmatic hydrothermal origin of kuroko deposits are evaluated, based on oxygen and hydrogen isotopic study, and they conclude that sea water cannot be the sole source of the kuroco ore solution.
Abstract: Three lines of evidence which support the magmatic hydrothermal origin of kuroko deposits are evaluated. (1) Mineralization of kuroko deposits took place around 15 Ma, at the same time as several other geologic episodes including a major shift in the tectonic stress field, a peak of bimodal volcanic activity, and a maximum degree of subsidence. The style of eruption of rhyolite changed from lava flows, acid hyaloclastites, and lithic tuff breccias before mineralization to extensive post-ore pumiceous pyroclastic flows. In an analogy with the Yellowstone caldera, absence of pre-ore basalt directly below the known kuroko deposits suggests that contemporaneous acidic magma existed at a depth of a few kilometers with the potential to release magmatic fluid. Basalt lava is often seen in the hanging-wall sequence of kuroko deposits; it extruded after the acidic pluton had solidified subsequent to mineralization. The post-ore pumiceous pyroclastics could have been produced by violent submarine eruptions similar to those related to the formation of Valles type calderas from resurgent acidic magma. Apparently such an abrupt release of material from the magma chamber was not suitable for conditions to develop and form kuroko deposits. (2) Based on oxygen and hydrogen isotopic study, sea water cannot be the sole source of the kuroko ore solution. Metals cannot be leached from footwall volcanic rocks, because an outward flow of hydrothermal fluids within the volcanic units is deduced from wall-rock alteration study. In addition, the notable homogeneity of isotopic compositions of ore minerals rules out the possibility that the ore metals were largely derived from basement rocks by leaching. (3) The rhyolitic magma which was contemporaneous with ore deposition had a large potential to result in separation of a metal-rich aqueous solution during its crystallization. This aqueous phase would have been a very efficient ore-forming solution, even after dilution by convecting sea water. This magmatic hydrothermal model of kuroko deposits is more consistent with the observed geological features than other models. Statement of the Problem Like many other volcanogenic massive sulfide deposits (hereafter termed massive sulfides), Japanese kuroko deposits are regarded strata-bound or time-bound in a broad sense. The reason for the exclusive occurrence of kuroko deposits within a volcano-sedimentary sequence of the Hokuroku district (Fig.1) Fig.1 Distribution of pumice, basalt, and mudstone type kuroko deposits (See text for explanation of each type of deposits). The numbers correspond to the deposits shown in Fig. 3. The first two types of deposits tend to occur in the eastern part of the region, whereas the mudstone type kuroko deposits tend to occur in the Japan Sea side of the Honshu Island, where the intensity of acidic volcanism was weak. The kuroko deposits cluster in Hokuroku (deposits 1, 2, 5, 6, 7) and Aizu (3, 4) districts. The Green Tuff region is shaded. Received on April 19, 1986, accepted on November 16, 1986. * Mineral Deposits Department , Geological Survey of Japan. 1-3, Higashi 1 chome, Yatabe, Tsukuba 305, Japan.
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TL;DR: Chalcopyrite blebs and lamellae intergrown with sphalerite, which are similar to those in natural ores, were experimentally formed at the condition of the temperature =400•Ž and the PH2O=400 kgf/cm2 by reacting Ferich sphalite with Cu-bearing aqueous solutions as mentioned in this paper.
Abstract: Chalcopyrite blebs and lamellae intergrown with sphalerite, which are similar to those in natural ores, were experimentally formed at the condition of the temperature =400•Ž and the PH2O=400 kgf/cm2 by reacting Ferich sphalerite with Cu-bearing aqueous solutions. This fact verifies a hypothesis that chalcopyrite inclusions in Febearing sphalerite are replacement product. Analytical results by electron microprobe analyses for the reacted sphalerite intergrown with chalcopyrite have proved that replacement mechanisms are not so simple and that copper substitutes not only zinc but also iron in sphalerite at an advanced stage of replacement.
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TL;DR: The Jeoneui Au-Ag mine in South Korea was reported to have a boiling pressure of <150 bars, corresponding to depths of 700 and 1,800m assuming lithostatic and hydrostatic loads.
Abstract: Electrum-galena-sphalerite mineralization of the Jeoneui Au-Ag mine was deposited in three stages of quartz and calcite veins at temperatures between 350•Kand 180•Ž from moderate salinity fluids (4 to 14 wt%NaCI eq). Evidence of boiling indicates pressures of <150 bars, corresponding to depths of 700 and 1,800m assuming lithostatic and hydrostatic loads. Au-Ag deposition was likely a result of boiling, coupled with declining temperatures. Sulfur isotope compositions of sulfides indicate an igneous source with a ƒÂ34S value near 4•ñ. Measured and calculated hydrogen and oxygen isotope values of ore-forming fluids suggest significant meteoric water involvement. Comparison of the Jeoneui Au-Ag deposits to similar shallow Cretaceous Au-Ag deposits and a deeper Jurassic Au system reveals an inverse relationship between depth and water-to-rock ratios in Korean Au-Ag vein deposits. This indicates significant differences in the postmagmatic evolutions of these granite-related gold-bearing hydrothermal systems and may be indicative of the manner in which Au and Ag are scavenged from cooling
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TL;DR: In this paper, the ages of five W-Mo deposits in South Korea were determined using eight specimens from five mines in the Gyeongsang basin, and the results for sericites from the Cheongyang W mine were around 80 Ma, and are almost same as those of the Daehwa WMo and Sangdong WMo-Bi deposits.
Abstract: K-Ar ages were determined on eight specimens from five W-Mo deposits in South Korea. Muscovites purified from tungsten ore and pegmatitic quartz vein of the Ssangjeon W deposits give ages of Proterozoic. Although biotite in pegmatitic quartz vein of the Ogbang W mine yields much younger age, the occurrences of the deposits in both mines are so similar that the Ogbang deposits seem to have been formed at almost the same time as the Ssangjeon deposits. Muscovites from the Garisan W-Mo and Jangsu Mo deposits give ages of about 170 Ma, and confirm wide distribution of W-Mo mineralization at early Jurassic time. The results for sericites from the Cheongyang W deposits are around 80 Ma, and are almost same as those of the Daehwa W-Mo and Sangdong WMo-Bi deposits. In South Korea, W-Mo mineralization is prior to Au-Ag mineralization in Jurassic time, whereas vice versa in Cretaceous time. At the northeastern end of the Ryeongnam massif,tin (•`1800 Ma), tungsten (•`1500 Ma) and gold (•`1100 Ma) mineralizations are overlapped in Proterozoic time. Introduction The Korean peninsula is famous for its large production of tungsten as well as gold. In South Korea, for example, the Sangdong mine is one of the most productive tungsten mines in the world. In his excellent pioneer work on the metallogeny of South Korea, KIM (1971) thought that most W-Mo deposits were formed in Jurassic time with genetical relation to Daebo granitic rocks. Recent age determinations, however, have revealed that some major W-Mo mineralizations are related genetically to Cretaceous Bulgugsa granitic activity. They include such as the Sannae W-Mo (65 Ma; FLETCHER and RUNDLE, 1977), Ilgwang Cu-W (66-81 Ma; FLETCHER and RUNDLE, 1977), Sangdong W-Mo-Bi (81-84 Ma; FARRAR et al., 1978), Shinyemi Zn-Pb-Mo (75 Ma; SATO et al., 1981), Daehwa W-Mo (89 Ma; SHIBATA et al., 1983) (88 Ma; So et al., 1983a) (85 Ma; KANEOKA et al., 1983), Geumseong Mo (157-179 Ma; SHIBATA et al., 1983), and Garisan (171 Ma; KIM and SEO, 1986) deposits. The first two deposits are situated in the Gyeongsang basin, which is covered by thick accumulations of Cretaceous sedimentary rocks with intermediate volcanic rocks. One more occurrence of tungsten is known in the basin, that is, the Ulsan Fe-W deposits. Although no direct age determination has yet been carried out, the deposits are thought to have been formed with genetical relation to Gadaeri granodiorite (PARK and PARK, 1980), which is dated as 58 Ma (LEE and UEDA, 1977). Those given above are all the data so far appeared in the literature, on the formation age of W-Mo deposits in South Korea. Formation age data on Au-Ag deposits in South Korea have been also accumulated in recent publications, and three epochs, Precambrian, Jurassic and Cretaceous, are clearly recognized (SHIMAZAKI et al., 1986). In the present paper, five W-Mo deposits situated out -Received on July 4, 1987, accepted on October 8, 1987* Geological Institute, Fac lty of Science, Univ rsity of Tokyo, Hongo, T ky 113, Japan.** Geological Survey of Japan, Higashi 1-1-3, Tsukuba,lbaraki 305 Japan.*** Department of Earth Sciences, Coll ge of Educa-tion, Seoul National U iversity, S oul 151, Republic ofKorea.** Depa tment of Min ral Deve opment E gineeri g, Faculty f E gineeri g, U iver it of Tokyo, Hongo, Tokyo 113, Japan.Keyw rds: K-Ar ag , W-M deposits, K rea Precam-br an , Jurassic, Cretaceous, Metallogeny.
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TL;DR: In this article, the authors employed the Rayleigh fractionation model to simulate the crystallization of granitic melts and suggested that the granitic rocks of Southwest Japan were mainly differentiated by fractional crystallization.
Abstract: To understand the mode of differentiation of the granitic magmas of Southwest Japan, neutron activation analyses have been made to measure the REE abundance of the granitic rocks. We employed the Rayleigh fractionation model to simulate the crystallization of the granitic melts. Since the model calculations fit the observed REE data for the granitic rocks well, it is suggested that the granitic rocks of Southwest Japan were mainly differentiated by fractional crystallization. On the basis of the model calculations, it is also suggested that the granitic rocks with a large negative Eu anomaly found near some tungsten deposits are residues of an extremely differentiated magma.
TL;DR: The Tochibora ore deposits of the Kamioka mine are mainly composed of skarn type lead and zinc ore bodies which replace a part of tightly folded limestone beds.
Abstract: The Tochibora ore deposits of the Kamioka mine are mainly composed of skarn type lead and zinc ore bodies which replace a part of tightly folded limestone beds. The deposits are classified into four types; 1) pyrometasomatic lead and zinc deposit (so-called Mokuji deposit), 2) mesothermal replacement lead and zinc deposit (so-called Shiroji deposit), 3) silver deposit and 4) disseminated type lead and zinc deposit described in this paper. Features of the disseminated type mineralization have been disclosed by recent exploration activities as follows: (1) The mineralization does not appear in limestone but in Inishi rock and gneiss. (2) There is a strong structual control of the mineralization by weak zones such as fold axis planes and intru sion boundaries of aplitic dykes. Directions and inclinations of ore shoots of the disseminated type deposits are not always concordant with those of the pyrometasomatic deposits. (3) The disseminated type deposit consists of epidotized-chloritized ore and silicified-sericitized ore with a small amount of argentiferous silicified lens. (4) Genetical stages of wall rock alteration recoginized by the sequence of mineralization are as follows; early stage: epidotization-chloritization of Inishi rock and gneiss, late stage: silicification-sericitization of epidotized-chloritized Inishi rock and gneiss. Studies of fluid inclusion, wall rock alteration and mineral assemblage on the Tochibora ore deposits including the disseminated type mineralization were useful to make a conceptual genetic model for the ore deposits.
TL;DR: The fluorite from veins in the Takatori tungsten deposit, central Japan, has a distinct 87Sr/86Sr composition ranging from 0.7260 to 0.7270.
Abstract: The fluorite from veins in the Takatori tungsten deposit, central Japan, has a distinct 87Sr/86Sr composition ranging from 0.7260 to 0.7270. This ratio is significantly higher than the initial 87Sr/86Sr ratio of the granitoids (0.7095-0.7136) in the Tsukuba and Yamizo areas probably related to the ore formation but rather approaching that of the wall sandstone (0.7250). Sr content in the wall sandstone composed mainly of quartz, feldspars (alkali feldspar+plagioclase) and sericite, shows a strong positive correlation with Na content, indicating that the Sr is mostly included in feldspars. The Sr content in the wall psammitic rocks decreases successively toward the vein from 200 ppm to several tens ppm with the increasing degree of sericitization of feldspars. Therefore, it is presumed that the Sr in the mineralizing fluid is essentially derived from feldspars in the nearby wall rocks through the sericitization.