Kuroko-type Deposits Research Articles

Kuroko-type deposits in the Middle-Cretaceous marginal basin of central Peru

Barite, massive sulfide, and siliceous stockwork deposits of Kuroko type in the Lima region are associated with the Casma Group, a sequence of submarine volcanic rocks of Middle Cretaceous age. These deposits were formed in an ensialic marginal basin with predominantly basaltic to andesitic fill. Volcanic-hosted deposits occur in the entire region; sediment-hosted deposits are restricted to the eastern Casma volcanic facies, which intercalate with limestones and shales deposited on a shelf platform adjacent to the marginal basin. In most cases, mineralization is spatially associated with dacitic domes and tuff breccias with zones of quartz-serieite alteration; the latter have locally been dated at 116 to 106 m.y. by the K/Ar method. Strata-bound deposits of bedded barite, pyrite, sphalerite, and pyrrhotite overlie the feeder zones.The most important deposits of this kind are Leonila-Graciela and Juanita, with 4 million tons of produced barite and 2.5 million tons of production plus reserves of massive sulfide ore. They are located in a roof pendant of folded strata intruded by two plutons of the Coastal batholith. Contact metamorphism of hornblende-hornfels facies affects both ore deposits and wall rocks. K-Ar ages on hornblende-biotite pairs from the granitic rocks indicate that they were emplaced 82 and 65 m.y. ago. Whole-rock ages on postmetamorphic dikes vary between 31 and 39 m.y.P-T conditions for contact metamorphism of hornblende-hornfels facies at Leonila-Graciela are estimated at 2.1 to 2.6 kb and 300 degrees to 500 degrees C on the basis of sphalerite geobarometry, stratigraphic reconstruction, metamorphic mineralogy, and interpretation of discordant K/Ar age patterns. Mole percent FeS in sphalerites increases in a prograde sense from the actinolite zone at Juanita to the biotite-muscovite zone at Gracicla. In massive sulfide specimens it varies correspondingly from 15.4 + or - 0.2 to 17.6 + or - 0.7. Sphalerites from siliceous stockworks show the same trend with 14.7 + or - 0.4 mole percent FeS and 17.6 + or - 1.1 mole percent FeS. Metamorphic equilibration was reached only in the biotite-muscovite zone at Graciela. This is demonstrated by the homogeneity of high mole percent FeS values detected in sphalerite, which coexists in mutual contact with pyrite and hexagonal pyrrhotite.

Geodynamic setting of Early Devonian kuroko-type sulfide deposits in the eastern Klamath Mountains (Northern California) inferred by the petrological and geochemical characteristics of the associated island-arc volcanic rocks

In the West Shasta copper-zinc district, Kuroko-type massive sulfide deposits are present in Early Devonian volcanic rocks consisting of the Copley Greenstone and the overlying Balaklala Rhyolite. The Copley Greenstone is composed of pillow lava (mainly basalts with subordinate andesites) and pyroclastic deposits. High Mg andesites occur near the top of the 1,800-m-thick volcanic succession. The Balaklala Rhyolite, 1,000 m thick, consists of highly siliceous rhyolite flows, conglomerates, and tuffs. Both units were deposited in a submarine environment. The sulfide deposits are localized in the rhyolitic flows of the upper part of the middle unit of the Balaklala Rhyolite.Petrological and geochemical data show that these lavas belong to a tholeiitic suite formed in an immature island arc. At the close of Copley eruptions, the island arc underwent rifting and tectonic extension. This is suggested by the presence of boninites, a feeder dike system for the Balaklala Rhyolite, and bimodal volcanism. The extensional environment is similar to that classically observed in the domain of the Kuroko massive sulfide deposits. This rifting led subsequently to the development of a back-arc basin represented by the Trinity basalts associated with an ophiolitic sequence.

Volcanogenic sulfide deposits in the southernmost Appalachians

Volcanogenic massive sulfide deposits in the southernmost Appalachians of east-central Alabama and west-central Georgia are associated with metamorphosed submarine basalts and felsic rocks of the Ashland, Wedowee, and Talladega lithotectonic terranes. These three terranes lie between the Brevard fault on the south and the Talladega-Cartersville and Hayesville faults on the north. The oldest sulfide deposits occur in a regional setting characterized by a thick sequence of metamorphosed Eocambrian to lower Paleozoic continentally derived clastic and intercalated submarine metavolcanic rock. The metamorphosed clastic rocks represent the basal section of a rifted margin prism, whereas the metavolcanic rocks represent rhyolites, andesites, and basalts which were probably erupted along rift zones of a spreading back-arc basin. Most of the volcanogenie massive sulfide deposits are localized within metavolcanic rocks and are rare or absent in the enclosing or interbedded metasedimentary rock. The youngest sulfide deposits occur in the distal part of a volcanic arc sequence of the Talladega terrane, which terminated sediment deposition and volcanic activity in the region. Talladega terrane sulfide deposits appear anomalously young (Devonian) respective to other deposits in the eastern United States.Three types of massive sulfide host rock associations have been recognized in the southernmost Appalachians; Kuroko-type deposits associated with predominantly felsic volcanic assemblages, Anyox-type deposits associated with predominantly mafic volcanic assemblages, and Besshi-type deposits associated with interbedded assemblages of clastic sedimentary and mafic volcanic rocks.

鉱石面からみた三波川帯・田老帯・グリーンタフ地域の層準規制型硫化物鉱床

The stratabound-type sulfide deposits in Japan are divided into two types; the Besshi-type deposit and the Kuroko-type deposit, on the basis of their geological and mineralogical aspects and isotopic characteristics. The “Kuroko” deposit is a polymetallic sulfide-sulfate deposit genetically related to submarine calc-alkaline acid volcanic activity of Neogene Tertiary. All of the Kuroko deposits occur in the so-called Green Tuff region. The nature of deposits changes downward from the stratiform deposit to the disseminated and/or the stockwork deposits. Meanwhile, the Kuroko deposit can be generally divided into the following four zones according to the mineral assemblage of ores; Quartz-hematite zone, Kuroko (black ore) zone, Oko (yellow ore) zone, and Keiko (siliceous ore) zone in stratigraphically descending order. The main hypogene minerals constituting the sulfide ore are pyrite, chalcopyrite, sphalerite, galena, minerals of tetrahedrite group, marcasite, bornite in decreasing order with quartz and barite as gangue minerals. Gypsum-anhydrite ores are well developed in the Kuroko deposit closely associated with sulfide ores. Besshi-type deposit, that is to say, the bedded cupriferous iron-sulfide deposit, is well known in the Sambagawa metamorphic belt, and the deposits of allied type occur in the non-metamorphic Palaeozoic terrains and in the Shimanto belt. Besshi-type deposit is usually associated with submarine basic volcanic materials, and are modified by later metamorphism and deformation. The ore minerals consist chiefly of pyrite, chalcopyrite, sphalerite and of less amount of bornite. A negligible amount of galena is one of the most significant features of ore. Magnetite or hematite layers occassionally interbedded in the cupriferous pyrite layers, are worthy of notice of the connection with the fugacities of S2 and O2 during ore deposition. Taro deposit, Kuroko-type deposit of the early Cretaceous age, occurs in the Taro belt of northeast Japan, being genetically related to submarine calcalkaline acid volcanic activity. The sulfide minerals consist chiefly of pyrite, chalcopyrite, sphalerite, and galena. Barite is rather less in amount than that in the Neogene Kuroko deposit. Small lenticular masses consisting of gypsum and calcite is poorly deleloped below the stratiform sulfide deposit. The ore deposit is comparatively monotonous in mineral assemblages, and variety of minerals is far less than that in the Kuroko deposit. However, alabandite occurring in the hanging wall side is noteworthy for studing the physico-chemical condition of ore deposition. In this paper, all of the minerals from the above-mentioned deposits are listed up, and some of them are described about their chemical compositions, and also mineral assemblages, in order to offer useful information on the investigation of physico-chemical environments of ore formation. Moreover, the texture and structure of ores from the deposits are briefly summarized.

The Formation of Kuroko-Type Deposits Viewed within the Broader Context of Ore Genesis Theory

The Formation of Kuroko-Type Deposits Viewed within the Broader Context of Ore Genesis Theory

Kuroko-type deposits in Vanua Levu, Fiji

Abstract Minor Kuroko-type deposits occur within a group of acidic volcanic rocks in northeast Vanua Levu, Fiji. Six prospects are described and their relationship to each other and the associated volcanic activity discussed. Variations exist between deposits formed at or near the surface around exhalative centres and those occurring at depth as epigenetic vein and stockwork deposits. Fijian volcanism and ore deposition seem to be closely associated with a tensional—transform regime of regional dimensions rather than subduction. The ore fluids are thought to have separated from cooling felsic magma and mixed with seawater on their way to the surface.

Identification of ore-deposition environment from trace-element geochemistry of associated igneous host rocks

Synopsis The tectonic environment of formation of volcanogenic massive sulphide deposits and porphyry tin and copper deposits can be identified from the geochemical characteristics of the associated igneous rocks. The ‘stable’ trace-element geochemistry (involving Ti, Zr, Y, Nb, Cr and rare-earth elements) and geology of metabasalts related to 12 massive sulphide deposits indicate that the deposits studied fall into four distinct classes. (1) Cyprus-type, including Cyprus, Oman and Betts Cove, possibly formed during the early stages of back-arc basin development; (2) Løkken-type, including Løkken and York Harbour, possibly formed at back-arc basin spreading centres; (3) Joma-type, including Joma, Røros and Bidjovagge, possibly formed in a small ocean of Red Sea type; and (4) Gjersvik-type, including Gjersvik, Buchans, Noranda and Lynn Lake, possibly formed during an early stage of island arc evolution (Gjersvik), later during island arc evolution (the Buchans Kuroko-type deposit) or in a Precambrian setting (Noranda and Lynn Lake). Deposits related to major ocean ridge crests appear to be small and relatively uncommon, perhaps because relatively few favourable sites for ore deposition exist in such environments. The environment of intrusion of acid-intermediate igneous rocks can be deduced by use of diagrams based on the element Nb (e.g. SiO 2 versus Nb). On this basis, tinbearing granites can be classified either as within-plate magmas (Nigeria) or as magmas from evolved volcanic arc settings (e.g. Bolivia, Cornwall and Indonesia); the latter group can be further subdivided geologically into postorogenic and back-arc extensional settings. Although the continental crust may play a significant role in the formation of tin deposits, the geochemical data presented here suggest that partial melting of tin-enriched mantle above a subduction zone may be the single most important genetic factor.

Experiments on the hydrothermal alteration of mordenite rocks in sodium carbonate solution, with reference to analcimization around kuroko deposits

In this paper, an attempt is made to estimate the formation environment of the analcime alteration zone in Miocene tuffs around Kuroko(Black ore)-type mineral deposits. Natural mordenite tuff and mordenite-opal tuff of Miocene age were subjected to alteration in sodium carbonate solution (1 molar; 0.25 molar) at 100 degrees to 300 degrees C and 30 to 110 kg/cm 2 for 2 to 20 days using a test-tube-type reactor. When these were treated at 150 degrees to 200 degrees C, analcime (NaAlSi 2 O 6 .H 2 O) was formed as an alteration product. At 300 degrees C, most of the analcime was decomposed with the elapse of time. In the dilute solution (0.25 molar) at 300 degrees C, analcime was secondarily altered to albite. Albite formed more readily in the mordenite-opal tuff (high-silica tuff) than in the mordenite tuff.On the other hand, mordenite and mordenite-opal tuffs showed no remarkable changes when treated at 200 degrees C in sodium chloride solution and artificial sea-water environments. Even though treated in Na-bearing reaction solution, they did not always produce analcime. It is possible to estimate from the present experiments that the alkalinity of the reaction solution is a significant controlling factor in analcimization, and the possible formation temperature of the analcime zone cannot exceed 200 degrees C. It also appears probable that the analcime zone around Kuroko-type mineral deposits is formed by the interaction of an alkaline interstitial solution and the precursor zeolite-bearing acidic pyroclastic rocks. These interstitial solutions might have been heated by submarine volcanism and/or exhalative activities which accelerated analcimization.

Chemical composition of ore-forming solution responsible for the Kuroko type mineralization in Japan

On the basis of available mineralogical and geochemical data for the Kuroko type deposits in. Japan, an attempt has been made to calculate the concentrations of some elements in the ore-forming solution responsible for this type of mineralization. The result reveals that the abundances of elements in the hydrothermal system are fairly close to those observed in the present-day ocean water.

Sulfide Ore Deposits in Relation to Plate Tectonics

The dynamics of lithospheric plate motions, as denned by plate tectonic theory, appear to exert a fundamental control on many geologic processes, including sulfide ore deposition. An analysis of basic types of sulfide ore deposits, in relation to various plate tectonic regimes reveals a systematic pattern. The calc-alkaline magmatism apparently generated via the subduction process at convergent plate boundaries gives rise, under favorable circumstances, to Kuroko-type (conformable massive sulfide) deposits in submarine volcanic environments, and Cordilleran-type (postmagmatic) ore deposits in epizonal plutonic environments. Porphyry copper deposits, an important subclass of Cordilleran-type deposits, exhibit a remarkable spatial relationship to present or former convergent plate boundary regimes. Certain copper-nickel deposits occurring in ultramafic extrusive or penecontemporaneous intrusive rocks also appear to be related to plate convergence. Sulfide ore deposits generated at divergent plate boundaries...

EXPERIMENTAL HYDROTHERMAL ALTERATION DIRECTLY RELATED TO THE FORMATION OF GYPSUM-ANHYDRITE ORES AT LOW TEMPERATURE AND PRESSURE

Synthetic anorthite was subjected to alter in aluminum sulfate solution at low temperature and pressure. Gypsum, anhydrite, kaolinite and boehmite were obtained as the alteration products. When the alteration products were treated again in magnesium chloride solution, montmorillonite was formed under certain limited conditions. The chemical reaction involved is described as follows; 3(CaSO4•2H2O)+24H4SiO4+10Al(OH)3+2MgCl2=3[Ca0.83Si8(Al3.34)Mg0.66O20(OH)4]+2CaSO4+60H2O+4HCl+H2SO4 The relation between Ca-sulfate mineralization and simultaneous alteration observed in Kuroko-type deposits was discussed on the basis of the present experiments.

About the paper ?volcanic activity related to the formation of the Kuroko-type deposits in the Kosaka district, Japan?

About the paper ?volcanic activity related to the formation of the Kuroko-type deposits in the Kosaka district, Japan?

Sulfur isotope study of Kuroko-type and Kieslager-type strata-bound massive sulfide deposits in Japan

Sulfur isotope data of sulfide and sulfate minerals from the Kuroko-type deposits of the Miocene age (63 samples of mill concentrates and 48 separate specimens) and from the later Paleozoic so-called Kieslager-type deposits (20 samples of mill concentrates and 11 separate specimens) are reported. The data of sulfides from the Kuroko-type deposits can be divided into two groups, i.e., a lower δ34S group of which deposits in the Ohdate area are representative and a higher δ34S group characterized by deposits in the Kosaka district. A remarkable difference between the Kuroko-type and the Kieslager-type is that the average sulfur isotopic fractionation factor between sulfides and contemporaneous sea-water sulfate is slightly larger in the Kuroko-type deposits than in the Kieslarger-type deposits. Based on the same logic as developed in the previous paper (KAJIWARA, 1971), the difference between the two groups of the Kuroko-type deposits as well as between the Kuroko-type deposits and the Kieslager-type deposits is most likely due to the difference in oxidation state at the time of their deposition, the first mentioned of each pair being higher in oxygen fugacity of ore formation. Similarly, it is also concluded that the “volcanic type” deposits of SANGSTER (1968) are relatively higher in the depositional oxidation state than the “sedimentary type” deposits.

Volcanic activity related to the formation of the Kuroko-type deposits in the Kosaka district, Japan

In the Miocene Kosaka formation of NE-Japan, submarine volcanic sedimentary deposits of the Kuroko-type occur. This formation consists mainly of volcanics which erupted in a submarine environment. The “Kosaka Volcano” was built up by nine or more volcanic events of a single eruptive cycle. The mode of eruption during a representative single eruptive cycle changed as follows: The Uwamuki tuff breccia is a contact product between dacitic magma and the sea water. Dacitic magma pushed the Motoyama dacite dome upward, as a result of the decrease in vesicularity and perhaps also in temperature. Next, a steam explosion occurred at a flank of this lava dome. The hydrothermal activity which began in this steam explosion center is responsible for the formation of the Kuroko-type Cu-Zn-Pb-mineral deposits. Similar examples of a single eruptive cycle as at Kosaka are also found in Quaternary terrestrial volcanoes of Japan.

黒鉱および黒鉱鉱物の微量成分

In the Green Tuff region, detailed comparison of published and new analyses leads to the following conclusions about the distribution of minor elements in ore minerals, especially sulfide minerals:(1) In xenothermal type deposits such as the Ashio mine, Bi, In, Sn and Co show high contents, and in epithermal vein deposits the contents of these elements decrease, while in Kuroko type deposits they show extremely low Contents.(2) In Kuroko type deposits, As, Sb, Ge, Ga, Hg, TI, Ag, and Mo, which are rarely detected in vein deposits, show high concentration. Besides, enrichment of W, U, and V is in the oxide bed of Kuroko type deposits.(3) These elements are closely similar to the elements which form volatile compounds of volcanic emanations at low temperature.(4) If the distribution of minor elements in ore minerals has close connection with the conditions of ore formation, it is considered that enrichment of these elements in Kuroko type deposits deals with volatiles in volcanic emanation.During the recent years many are becoming to believe that the Kuroko type deposit is of a submarine exhalative sedimentary origin by detailed field observations in the Kuroko area.Conclusions about the distribution of minor elements in ore minerals in the Kuroko type deposits support the exhalative sedimentary origin.

EFFECT OF ACCESSORY ELEMENTS ON THE UNIT CELL EDGE OF β ZnS MINERALS

Sixty sphalerite samples were collected from various mines in Japan. Ore deposits of Oe (Hokkaido), Toyoha (Hokkaido), Namariyama (Akita Prefecture), Nikkatsu (Akita Pref.) and Kuroiwa mines (Fukushima Pref.) are vein type deposits, those of Hanawa (Akita Pref.), Yoshino (Yamagata Pref) Yonaihata (Fukushima Pref.) and Kidogasawa (Tochigi Pref.) mines are so-called Kuroko type deposits, while Hitachi mine is a Kieslager type deposit. From the results of chemical analyses and X-ray measurements on sixty sphalerite samples, it has been recognized that natural β ZnS minerals consist of the β1 sphalerite and β2 sphalerite. The unit cell edges in β1 sphalerites are determined by Fe, Mn and Cd content dissolved in this minerals, and the equations of relation between unit cell edges and FeS content in this minerals are shown a0=5.4103+0.000717 X and a0=5.4124+0.000349X. a0 is in Angstrom unit and X is mole % FeS, and both these equations are continuous. The solubility of Mn in β1 sphalerite increase with an increasing FeS content, so that it is a function of the temperature and pressure as well as the variation of FeS content. The correlation between Fe and Cd is random, but the variation of Cd solubility is constant. From the variations of Fe, Mn and Cd content, β1 ZnS system is divided into β1 (Zn, Fe, Cd)S and β1 (Sn, Fe, Mn)S system. Also the equation of β2 sphalerite is shown by a0=5.4093+0.000290X.