MINING GEOLOGY, 28, 267•`276, 1978

Sub-types and Their Characteristics of Kuroko-type Deposits*

Ei HORIKOSHI** and Naotatsu SHIKAZONO***

Abstract: The Kuroko-type deposits in the Hanaoka-Kosaka district are divided into three sub-types based on the ratio of major base metals in a single unit deposit. The ratio of copper to lead and zinc increases in order of the "B", "C" and "Y" sub-types. There is the north-southerly lateral zoning of these sub-type deposits in the Hanaoka and Kosaka districts.

•¬ D values are distinctly high in the "B" sub-type deposits. •¬34S values are distinctly high in the "C" sub-type

deposits and iron contents of sphalerite are low in the "Y" sub-type deposits. The higher •¬D values of "B" sub-type

deposits occurring in the central part of basins may indicate sea-water as the predominant source for ore fluids.

Using iron contents of sphalerite and •¬34S values of pyrite the possible depositional environments of three sub-type

deposits were estimated on fo2-pH diagram. In conclusion, each ascending ore fluid responsible for different sub-type deposits was different in geo- chemical nature. This suggests that the chemical and physical changes of ore fluid circulating in a hydrothermal system are important for the cause of differences among three sub-types of the Kuroko-type deposits.

ores, and describe briefly their occurrence and Introduction geochemical characteristics, and discuss the In terms of a hydrothermal sedimentary possible cause. This paper concerns mainly theory the schematic section of a single unit with three sub-types in the Hanaoka-Kosaka of Kuroko-type deposits was first proposed by district, the northern part of Akita Prefecture. Horikoshi (1960). Thereafter, many schematic Black Ore Sub-type sections were proposed and modified slightly with the progress of investigations. There is, HIRABAYASHI(1908) defined first the however, no fundamental difference among Kuroko-type deposits as follows: Black ore the schematic sections appearing in 1970's. (Kuroko) is a compact mixed ore composed For example, the section published by of sphalerite, galena and barite. Furthermore, HORIKOSHI(1976) is essentially identical with he mentioned that Kuroko is usually accom- SATO'S (1970). It seems that the general panied with chalcopyrite and pyrite in addi- feature of a single unit of Kuroko-type deposits tion with the above minerals, and contains gold has been established among geologists, espe- and silver. According to HIRABAYASHI'Sdef- cially in Japan. inition, the Kuroko-type deposits are mineral It is possible, however, to classify the deposits composed mainly of the black ore. Kuroko-type deposits into more sub-types on It seems likely that his definition was affected the basis of some factors. Papers with this line by the economic value of ore in the Kuroko appeared already (HORIKOSHI,1965; URABE, deposits. The ore at that time was mined only 1974a. HORIKOSHIand OHMOTO,1978). The for silver contents of black ore, especially of the authors will classify the Kuroko-type deposits weathered ore. Therefore, the present yellow into three sub-types on the basis of constituent and siliceous ores, if any, were not regarded * Received May 20, 1978. as the economic ore. There are, however, ** Department of Earth Sciences, Toyama University, the Kuroko-type deposits composed exclusively Gofuku, 930 Toyama. of black ore. These mineral deposits are *** Geological Institute, University of Tokyo, Hongo, designated the Black Ore sub-type in the 113 Tokyo classification of this paper. Keywords: Kuroko, Classification, •¬D, Sphalerite, Ore fluid The Shakanai No. 1 deposit in the Shakanai

267 268 E. HORIKOSHI and N. SHIKAZONO MINING GEOLOGY:

siliceous ores are not exactly known, because the Doyashiki deposit is accompanied by many satellite deposits. It may be more than 10 million tons. The quantity of black ore is roughly equal to yellow or siliceous ore. The second largest deposit of Kuroko-type is probably the Motoyama deposit of this sub- type in the Kosaka mine. A part of the deposit was already eroded away, when the deposit was discovered in 1861. However, about 7 million tons of ore were mined until 1946, when the mining was ended. The ore contains 2.3 million tons of black, 1.1 million tons of yellow and 3.7 million tons of siliceous ores. That is to say, this mineral deposit consists of roughly equal quantities of black, yellow Fig. 1 Available data on the Cu, Pb and Zn ratio of and siliceous ores (Fig. 1). total ore in a single unit deposit in the Hanaoka- A part of geology of the Composite Ore Kosaka district, marked with three sub-types. sub-type is exhibited strikingly in the abandoned open-pit of the Motoyama deposit. mine is a good example for this type and was The Uchinotai-nishi deposit of the same excellently described by KAJIWARA(1970a). sub-type was, however, better described by There are more mineral deposits of this sub- HORIKOSHI(1969) and HORIKOSHIand SATO type in the Hanaoka-Kosaka district. The ore (1970). The hydrothermal activity responsible of Black Ore sub-type deposits consists pre- for the mineralization of the Composite Ore dominantly of galena and sphalerite compared sub-type deposits was mostly preceded by the to chalcopyrite (Fig. 1). Ore deposits of uplift of lava dome and the subsequent steam this sub-type are usually not directly associated explosion. with lava dome. It is known, however, that dome-shaped dacite occurs below some of Yellow Ore Sub-type this sub-type deposit (KAJIWARA, 1970a; Some of the Kuroko-type deposits consist URABE, 1974b; TANIMURA et al., 1974). predominantly of pyrite containing a little Total ore quantity of a single unit deposit is quantity of chalcopyrite. In this paper the generally small, about one million tons. mineral deposits composed predominantly of Composite Ore Sub-type pyrite, either with an economical value of chalcopyrite or not, are called the Yellow Ore Mineral deposits of this sub-type are sub-type, though the yellow ore means usually often called typical Kuroko-type deposits. SATO copper ore (Fig. 1). (1970), HORIKOSHI(1976) and others published Generally speaking, mineral deposits of their schematic sections of Kuroko-type copper-rich Yellow Ore sub-type occur above deposits referring to the general geology of lava dome or lava flow. While copper-poor this sub-type. The most characteristics are deposits occur mostly in pyroclastic rocks and that, from the economic point of view, the are associated with a lot of gypsum. The major Kuroko-type deposits belong to this Matsumine deposit in the Hanaoka mine is sub-tune. typical of the Yellow Ore sub-type, whose It seems that the largest Kuroko-type deposit geology was described by ITO et al. (1974). is the Doyashiki deposit of the Composite Ore The Matsuki and Takadate deposits in the sub-type in the Hanaoka mine. The total ore Matsuki mine also belong to this sub-type quantity and ratio of black, yellow and (KURODA,1978). Many pyrite-rich ore bodies 28(4), 1978 Sub-types and Their Characteristics of Kuroko-type Deposits 269 associated with a large quantity of gypsum ern part of the Hanaoka district were mined ore were mined in the Hanaoka mine many years ago. Hence, their forms and (TAKAHASHIand SUGA, 1974). It seems likely characteristics are slightly obscure. However, that these ore bodies are composed of several mineral deposits in the other area are mostly unit deposits of this sub-type. well documented. Figure 2 shows the distribu- tion of different sub-types of the Kuroko Areal Distribution deposits in the Hanaoka district. Roughly Hanaoka and Kosaka are the most produc- speaking, the "Y" sub-type deposits are tive Kuroko mining districts. Probably more distributed in the westernmost zone and the than 30 single units of Kuroko-type deposits "B" sub -type deposits are in the easternmost were already discovered and exploited. These zone of the district. The "C" sub-type de- deposits include all sub-type deposits men- posits occur between both zones. No mineral tioned in the preceding chapters. Hence, both deposit has been found in the western area districts are suitable to investigate the areal beyond the Tsutsumizawa fault. distribution of different sub-types of the In Figure 2, Kuroko-type deposits are Kuroko deposits. The authors will use the projected on the upper surface contours of abbreviations in the following sentences: "B", M1 mudstone occurring below mineral deposits sub-type for the Black Ore, "C" for the (TAKAHASHIand SUGA, 1974). M1 mudstone Composite Ore and "Y" for the Yellow Ore. shows weakly subsided trough-like structure. Mineral deposits located at the northwest- The axis is located between the "C" sub-type and "B" sub-type zones, and dips slightly to the southeast. This structure is slightly disturbed in the northern part, because large lava domes associated with the "C" sub-type deposits intruded in the area. The Hanaoka formation, in which most mineral deposits occur, becomes thicker to the east in the district. Furthermore, some pyroclastics in this formation moved down to the east as far as their flow directions were confirmed (HORIKOSHI, 1966; TAKAHASHIand SUGA, 1974). HORIKOSHI(1966) described, however, the field evidence that a tuff breccia moved to the east and was dammed up along the eastern zone over the Shakanai No. 1 deposit. It seems likely that the trough-like form of the sea floor existed already at the stage, when mineral deposits were formed. Mineral deposits from the Shakanai No. 1 to the Matsuki occur in crater-like depressions. This occurrence is indicated by mudstone distributed in the restricted areas on or above the mineral deposits (HORIKOSHI,1965; 1966; KURODA, personal communication). Figure 3 shows the areal distribution of "B" and "C" sub -type deposits in the Kosaka Fig. 2 Distribution of three different sub-types of the district. The "Y" sub-type deposits have not Kuroko deposits in the Hanaoka district. The top of M1 mudstone is also shown to visualize the structure yet been found in the district. It seems that of country rocks. two zones characterized by the distribution 270 E. HORIKOSHI and N. SHIKAZONO MINING GEOLOGY:

Fig. 4 •¬D values available in the Kuroko-type

deposits. Legend is the same as Fig. 2. Note three

values from the "B" sub-type deposits. Those three

•¬ D were obtained in the different districts, in the

Hanaoka, Kosaka and the midst of Hanaoka-

Kosaka districts.

•¬D Values

It seems likely that the geochemical para- meters can also offer the important clue to investigate the cause of three different sub-

types. HATTORI (1977) measured the •¬D values of fluid inclusions from the Kuroko-type deposits. The •¬D values of fluid inclusions in

barite are commonly variable. However, the •¬ D values of fluid inclusions in sulfide minerals and quartz fall within a narrow range in the same deposit (HATTORI, 1977). These •¬D

Fig. 3 Distribution of two different sub-types of the values may not be much different in a single Kuroko deposits in the Kosaka district. "Y" sub-type unit of mineral deposits, though the numbers deposits have not yet been discovered in the area. of measurement are still a little. OHMOTO and The top of pre-Tertiary basements is contoured RYE (1974) published also the •¬D values of showing some depressed structures. fluid inclusions in sulfide minerals of the

Kuroko deposits. Thus, altogether 20 •¬D of each sub-type deposit run north-southernly values of fluid inclusions are available at in the Kosaka district as well as in the Hanaoka district. Pyroclastic rocks in the Kosaka present from the Kuroko deposits. Figure 4 shows the •¬D values of fluid in- formation, in which all mineral deposits occur, clusions from the Kuroko-type deposits, marked become thicker to the east, and probably with three sub-type proposed in this paper. moved from the eruptive centers to the east The data were obtained from the Kuroko (HORIKOSHI, 1969). These evidences may indicate that the sea at that time became deposits in the Hanaoka and Kosaka districts deeper to the east. Figure 3 shows also the except one from Fukazawa of the "B" sub-type top of the pre-Tertiary basements. Mineral located in the midst of Hanaoka-Kosaka district, in the central part of so-called deposits, either "B" or "C" sub-types, occur Hokuroku basin. The figure shows that the above the crater-like depressions of basements. •¬D values from the deposits of "B" sub-type These depressions are about 1 km in diameter. are distinctly higher than the •¬D values from The Shinsawa deposit was a sole example the other two sub-types. The difference be- for the "B" sub-type in the midst of Hanaoka- tween the data from the "C" and "Y" sub- Kosaka district, so-called Hokuroku basin. types is not so clear. The •¬D values from the Recently the Tsunokakezawa deposit in the "Y" sub -type Fukazawa mine and mineral deposit in the , however, seems to be slightly higher than the •¬D values from the "C" Ezuri mine were discovered and exploited. sub-type. These two also belong to the "B" sub-type. 28(4), 1978 Sub-types and Their Characteristics of Kuroko-type Deposits 271

Figure 5 shows sulfur isotopic data of Sulfur Isotopic Data separated pyrite as the commonest sulfide

There is an inconsistency among the mineral published by KAJIWARA (1971) and sulfur isotopic data from the Kuroko-type KAJIWARA and DATE (1971), marked with deposits. The sulfur isotopic data of mill three sub-types. The 834S values of pyrite in concentrates fall within a remarkably narrow the "C" sub-type deposits are higher than range indicating the rather uniform average the •¬34S values of pyrite in the "Y" and "B" value in each single unit deposit (KAJIWARA sub-type deposits. The 534S values of pyrite and DATE, 1971). Nevertheless, these data from the "Y" sub-type seem to be slightly are systematically lower, about I to 2•ñ, higher than those from the "B" sub-type. than the •¬34S values of sulfide minerals KAJIWARA and DATE (1971) are in a separated from the layered ores and reported different opinion that the •¬34S values from the Kuroko deposits in the Kosaka dis- by the same authors. The higher values should be obtained from mill concentrates at least trict are higher than those in the Hanaoka for pyrite. Because KAJIWARA (1971) showed district. Because all sulfur isotopic data that the •¬34S values of pyrite increase toward from the "C" sub-type were obtained in the lower part of a single unit deposit, in which the Kosaka district. The sulfur isotopic data have not yet been available from the Uwamuki pyrite predominantly occur, the inconsistency between sulfur isotopic data from two sources deposits of "B" sub-type in the Kosaka is certainly more than analytical errors. district. The other data are probably from the "Y" and "B" sub -types in the Hanaoka dis- Furthermore, SMIRNOV et al. (1968) published trict. KAJIWARA and DATE'S data include the extremely low values for pyrite in black ore. AULT and KULP'S data (1960) seem to three •¬34S values of pyrite in the Doyashiki belong to the group of lower values. Their deposit of "C" sub-type in the Hanaoka samples were collected, however, from gypsum district. The main Doyashiki deposit was, ore in the Ochiaizawa ore bodies, the Hanaoka however mostly mined out, when their sam- mine. The wide variation of sulfur isotopic ples were collected in about 1969. Further- more, the mine calls the main Doyashiki of data for pyrite associated with gypsum was "C" subtype and the satellite deposits of "Y" reported in the Shakanai No. 1 deposit by KAJIWARA (1971). These causes are beyond subtype together the Doyashiki deposits (for the purpose of the present paper. For those example, TAKAHASHI and SUGA, 1974). In reasons the authors can not summarize all Figure 5 the data from Doyashiki are marked sulfur isotopic data from the Kuroko deposits. with the "Y" sub-type.

The authors will re-examine only the data of Iron Contents of Sphalerite separate minerals published by KAJIWARA Recently, many analytical data on the (1971) and KAJIWARA and DATE (1971) referring to three sub-types of the Kuroko Kuroko constituent minerals have been ac- deposits. cumulated. Sphalerite has been studied by many workers and is useful for the restriction of the chemical environment of ore deposition. Iron contents of sphalerite from replacement siliceous ores and fissure-filling vein ores are much higher than those from layered ores (TAKAHASHI,1963, 1966; SATO, 1969; URABE, Fig. 5 •¬34S values available in the Kuroko-type 1974b; MUKAIYAMAet al., 1974; URABE and deposits. Legend is the same as Fig. 2. The values SATO, 1978). That is to say, iron contents of from the "C" sub-type is higher than the others.

However, they are obtained in the Kosaka district, sphalerite generally increase downward in

where no data is available from the "B" sub-type a single unit of mineral deposit (URABE and

deposits. SATO, 1978). Therefore, the authors will 272 E. HORIKOSHI and N. SHIKAZONO MINING GEOLOGY: summarize data only from the layered ores. than sphalerite from the "C" and "B" sub-type Iron contents of sphalerite from the layered deposits. Iron contents of sphalerite from black ore of Uwamuki, mainly the No. 4 the "B" sub-type deposits show very wide deposit (URABE, 1974b), are about 0.0 to range. The avearage value, however, is 2.0 mole %, mainly less than 0.5 mole %. The probably lower than that from the "C"sub- slightly higher values were obtained from type deposits. sphalerite in the No. 1 deposit of Shakanai Filling Temperatures and Salinities (KAJIWARA, 1970b). The values are in a range from 0.15 to 2.5 mole %. NISHIYAMA Filling temperature of fluid inclusions in (1974) also analyzed sphalerite from the quartz appears to be most reliable in Kuroko- similar localities and indicated that sphalerite type deposits. The filling temperature of from the layered black ore cotains a relatively fluid inclusions in barite usually is highly low quantity of iron, ranging from 0.2 to variable (Lu, 1969; TOKUNAGAand HONMA, 0.4 wt. % (0.3 to 0.7 mole %). Those two 1974). The data from sphalerite are still mineral deposits belong to the "B" sub-type scanty. Quartz sample can hardly be collected of Kuroko deposits. Iron contents of sphalerite in black and yellow ores. Therefore, most of in layered black ore from the "B" sub-type data are obtained from fluid inclusions in vein- deposits seem to he about 0.1 to 0.2 mole % formed quartz of siliceous ore. For this reason, on an average, though the values attain more the authors will summarize the data of filling than 2 mole %. On the other hand, sphalerite temperature of quartz reported from siliceous from layered black ore of the "C" sub-type ore regardless of their occurrences. The filling deposits contains a little more iron than temperature of these samples shows the slight sphalerite from the "B" sub-type deposits. temperature gradient with depth (Lu, 1969; Sphalerite from the Uchinotai-higashi deposit MARUTANIand TAKENOUCHI,1978). of "C" sub-type contains about 0.3 to 0.6 TAKENOUCHI (1977) reported the data of mole % iron (Lu, 1969). Sphalerite from filling temperature in three sub-types of the Uchinotai-nishi deposit of "C" sub-type Kuroko deposits: Uwamuki No. 4 of "B" contains from 0.1 to 0.6 mole % iron (URABE sub-type, Uchinotai-nishi of "C" sub-type and SATO,1978). Sphalerite from the Daikoku and Matsumine of "Y" sub-type. They range deposit of "C" sub-type, Ainai mine , contains from 280•Žto 325•Ž, 280•Ž to 330•Ž and about 0.0 to 1.5 mole % iron (WATANABE , 270•Žto 340•Ž, respectively. Most of data unpublished, cited in URABEand SATO,1978) . are concentrated in about 300•Ž. The data Extremely higher value of iron contents as from the Shakanai No. 1 deposit of "B" sub- observed in the "B" sub-type deposits has type was published by TOKUNAGA and HONMA not yet been reported. Some sphalerites from (1974). It is in a range from 197•‹•Žto 293•Ž the Matsumine deposit of "Y" sub-type in with a mean value of 215•Ž. In the case of the Hanaoka mine are analyzed in this study . "C" sub -type deposits the filling temperature

Sphalerite analyzed were collected from is from 225•Ž to 305•Ž in the Uchinotai- the layered black and yellow ores and not higashi deposit, Kosaka (Lu, 1969), and from the siliceous and vein parts . The data from 200•Ž to 284•Ž with a mean value of obtained indicate that iron contents of sphal- 245•Ž in the Uchinotai-nishi, Kosaka erite from black ore are less than the detection (TOKUNAGA and HONMA, 1974). TOKUNAGA limit by electron microprobe analyzer . The and HONMA (1974) published the data of values from 0.0 to 0.2 mole % were obtained filling temperature in the Yokodawara deposit from layered yellow ore. of "Y" sub-type. It ranges from 229•Ž to Summarizing the iron contents of sphalerite 268•Ž with a mean value of 248•Ž. previously published and new additional TAKENOUCHI (1977) published higher data from Matsumine values as a whole, compared with the data by "Y" s , sphalerite from the ub-type deposits contains low iron TOKUNAGAand HONMA(1974). It seems likely 28(4), 1978 Sub-types and Their Characteristics of Kuroko-type Deposits 273 that the localities of samples are main cause occurring in the central part of a basin show for these different values of filling temperatures the higher •¬D values, close to SMOW. It may (URABE,personal communication). Therefore, suggest that the sea-water is more responsible the authors cannot point out the difference of for their ore fluids. It is reasonable to con- filling temperatures among three sub-type sider that the land at the stage of mineraliza- deposits. tion existed near the margin of a basin, rather Only a few cooling experiments were carried than in the center of a basin. Therefore, it is out until now. Lu (1969) and MARUTANIand probable that small amounts of the meteoric TAKENOUCHI(1978) measured the freezing water were involved in the formation of "Y" point depression for fluid inclusions. The data and "C" sub-type deposits. It is possible to are concentrated in a solution of about 3 consider, moreover, that the lower •¬D values weight percent of NaCl equivalent, ranging of the "C" sub-type deposits associated closely from 2 to 5 weight percent. No distinct differ- with volcanic centers may indicate the slight ence was detected among three sub-types. contribution of magmatic water to the ore fluid. Possible Cause of Three Sub-types Based on the iron contents of sphalerite and •¬34S values of pyrite , the authors can estimate Table 1 shows a summary of geological the possible foe pH range of different sub-type and geochemical characteristics on three deposits at constant temperature, ionic different sub-types of the Kuroko deposits. strength, total dissolved sulfur content and This table may indicate possible causes of •¬34S of ore fluid (KATIWARA , 1971; OHMOTO, the different features in the Kuroko deposits, 1972; SHIKAZONO, 1976, 1978). The difference though geochemical data are still scanty. in iron contents of sphalerite was observed It seems likely that the ratio of major between the "Y" sub-type, and the "B" and base metals in the Kuroko deposits changes "C" sub -type deposits. The similar difference laterally in a small basin such as Hanaoka in •¬34S values for pyrite was also obtained and Kosaka, and also in a large basin such as between the "C" sub-type, and the "Y" Hanaoka-Kosaka, i.e., so-called Hokuroku and "B" sub-type. The estimated ranges for basin. It is possible to consider that the three sub-types are shown in Figure 6. different physicochemical environments in The estimated field for the "C" sub-type the different depth of the sea involved the deposits are far from kaolinite field, compared feature of mineral deposits. GUBER and with the "Y" sub-type deposits. It was OHMOTO (this issue) suggested, however, that observed, however, that the main Doyashiki the depth of the sea at that time was deep and Senryu of "C" sub-type deposits are enough to suppose rather homogenized en- overlain by kaolinite layer (HORIKOSHI,1966). vironment. The authors consider that •¬D While sulfide minerals associated with kaolinite values of three sub-types reveal a clue to the were reported in the Matsumine deposit of lateral zoning. One of the possible inter- "Y" sub-type (SHIROZU, 1974) and the pretations of the •¬D variation is that the Uwamuki No. 1 deposit of "B" sub-type mixing degree of the meteoric water and (MATSUKUMAet al., 1974). It has to be noted sea-water is different in ore fluids of these that Figure 6 does not show precisely the sub-types. Because the "B" sub-type deposits chemical limitation of three sub-types, because Table 1 Characteristics in Three Sub-type Deposits. Figure 6 is constructed by assuming several parameters as constant. Nevertheless, this figure indicates the slight difference in foe and pH of three sub-type deposits. One of the probable cause of this difference is the oxida- tion reaction of hydrogen sulfide to sulfate ions. If free oxygen is supplied to the system, pH 274 E. HORIKOSHI and N. SHIKAZONO MINING GEOLOGY:

Fig. 6 Estimated fo2-pH ranges for three sub-type Kuroko deposits. An fo2-pH diagram constructed for tempera-

ture =250•Ž, ƒ°S=10-2.5 mole/kg¥H2O, Ionic strength=1, MK+= 0.2 mole/kg . H2O and •¬34total, in

solution=+20•ñ. Iso-FeS mole percent contours for sphalerite, iso-•¬34S contours for pyrite, the stability rela-

tions in some minerals and the boundary between the predominance fields of oxidized sulfur species (NaSO4-)

and reduced sulfur species (H2S) are given.

decreases with the reaction of H2Saq + 2O2= fluids before the precipitation of the ore SO•¬- + 2H+. Probably, the fo2 and pH of forming minerals and before the mixing with ore fluid for the "Y" sub-type deposits are more sea-water reflect the feature of each sub-type controlled by the above reaction than those deposits. for the other types. It is difficult to know, In order to confirm this tentative hypothesis, however, the place where this reaction occurred. it is highly desired to obtain more systematic If the fo2-pH ranges estimated for three geochemical data on the Kuroko-type deposits. sub-type deposits do not change remarkably Furthermore, it should be emphasized that, during the ore deposition, it could be con- from geological, geochemical and hydrody- sidered that base metal contents are con- namical point of view, the chemical and siderably different among ore fluids responsible physical evolution of ore fluids from sources for three sub-type deposits. Because solubilities to depositional places is very important to of sulfide minerals are affected by fo2 and pH, investigate this problem. especially in the predominance field of oxidized Acknowledgements: The authors are sulfur species. The authors consider at present deeply grateful to Prof. H. OHMOTO,Pennsyl- that the mixing of sea-water and ascending vania State University, Dr. T. URABE, Uni- solution above the sea-water-sediments inter- versity of Tokyo, and Dr. S. IsHIHARA,Geol- face is not so important for controlling fo2 ogical Survey of Japan, for discussions and and pH during the formation of Kuroko comments contributed to this paper. deposits. Consequently, the authors consider that the geochemical characteristics of ore 28(4), 1978 Sub-types and Their Characteristics of Kuroko-type Deposits 275

Genesis, University of Tokyo Press, Tokyo, 367 •`

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黒 鉱 鉱 床 のサ ブ タイ プ とそ れ らの特徴

堀越 叡 ・鹿園 直建

要 旨:花 岡 ・小 坂 地 域 の黒 鉱 鉱床 を,重 金 属元 素含 有 量 こ とを示 して い る の で あ ろ う.閃 亜 鉛 鉱 中 の 鉄含 有量 と の違 い に も とづ き,3つ の サ ブ タ イ プ に わ け た.Cu/Pb 黄鉄 鉱 の〓34Sを も とに して,3つ の サ ブ タイ プ の生 成環 +7nは"B","C","Y"の 順 で ふ え て い く.花 岡 ・ 境 がfo2-pH図 上 で も とめ られ た,こ れ らの こ とか らそ 小坂 地 域 で これ らの サ ブ タイ プ の 南 北 の水 平 方 向 の ゾー れ ぞれ の サ ブ タ イ プ をつ くっ た上 昇 鉱 液 の 化 学 的性 質 が ニ ング が み られ る . 異 な っ て い た とい う こ とが結 論 され た.つ ま り,黒 鉱鉱 〓 D値 は"B"サ ブ タイ プ で高 い .〓34S値 は"C"サ ブ 床 の3つ の サ ブ タ イ プ の違 い を生 じた原 因 と して,熱 水 タ イ プ で 高 い.閃 亜 鉛 鉱 中 の鉄 含 有 量 は"Y"サ ブ タイ 系 を循 環 す る鉱 液 の化 学的,物 理 的 変 化 が 重 要 で あ る と プ で 低 い,ベ イ ズ ンの 中 心 に あ る"B"サ ブ タイ プ の〓D 思 わ れ る. 値 は高 い が,こ の こ と は,海 水 が鉱 液 の 主 な起 源 で あ る