MINING GEOLOGY, 33 (3), 137•`147, 1983

Some Characteristics of the Oxidation Zone of Sulfide Deposits in Lower Yangtze Area, Southeast China

Wenda LI

Abstract: The characteristics of zoning and processes of oxidation of disulfide-rich ore deposits in Lower Yangtze area, Southeast China, are representative to the warm and humid area in medium latitude zone. The distinguishing features are (1) *1 gossans extended to a great depth due to the slow uplift of the area during the long process of oxidation; (2) the existence of a subzone of current secondary sulfide enrichment due to the rapid decomposition of Cu sulfide ore in the upper part, which makes Cu intensively migrating downward; (3) the assemblage of secondary native copper, cuprite and their further oxidized products, tenorite and , is an evidence of the ever-existence of ancient secondary sulfide enrichment; (4) carbonate and silicate are the prominant oxidation products of Pb-Zn ore deposits. The contrasts of the characteristics of sulfide ore oxidation in Lower Yangtze area to that of the arid Northwest China are also clarified in this paper.

occur in every mine. The pyrite or Cu-bearing Introduction massive pyrite bedded stratigraphically

The Lower Yangtze area is located in warm can be correlated with C1 to C2 beds and humid zone of medium latitude in (Gaolishanian to Huanglungian), it comprises Southeast China. The oxidation zone of sulfide chiefly disulfide (pyrite, melenikovite and ore deposits in this area is well developed. subordinate marcasite) with or without

The basis that determines the characteristic pyrrhotite. In those disseminated ore of Cu- features of the zone of oxidation includes the bearing skarn or magnetite type, disulfides are mineralogical composition, texture-structure subordinate constituents, while Pb-Zn sulfides of the ore as well as the climate and physio- are rare in Cu-bearing pyrite or pyrite deposits graphic history of the region in question. except some local small pockets. On the Cu ore deposits in this area (Fig. 1) consist other hand, a fair amount of chalcopyrite and of 1) Cu-bearing massive pyrite bed, 2) pyrite may be present in Pb-Zn (Cu) deposits. Cu-bearing skarn and magnetite type ore The abundance of disulfide is the essential deposits, with replacing Cu vein type deposits factor that controls the development of the near the metasomatic zone, 3) mineralized process of ore oxidation in the Lower Yangtze intrusive bodies, some of them are known area (Li et al., 1980). as porphyry copper deposits such as in Other factors influenced the characteristics Chengmenshan Mine. These three types of Cu of current development of oxidation zone are : deposits may be called "Three In One (or (1) annual precipitation, generally in a range Thrinity)" deposits, but the third one does not 1000 to 1500 mm, evaporation is greater than the precipitation except in rainy season; Received on January 6, 1983, accepted on March temperature varies with seasonal change, the 30, 1983. * Nanjing Institute of Geology & Resources, maxium is 37•‹ to 40•Ž in late July to early 534 East Zhongshan Road, Nanjing, China August, and the minimum -11•‹ to -12•Ž Keywords: Supergene zoning, Limonite gossans, Oxi- in the late January; (2) the regional dation zone, Lower Yangtze area. topography is mountanous to hilly, the *1 Limonite used in this paper refers to those mixtures of iron oxides & hydroxides without accurate min- physiographical history (BARBOUR, 1935) eralogical identification as customarily used among reveals that this region had suffered uplift and field geologists. subsidence for several times, but now it is in

137 138 W.D. LI MINING GEOLOGY:

Fig. I Geology and distribution of ore deposits in the Lower Yangtze area, Southeast China. slow subsidence; (3) Neotectonic movement is limonite. Gossans capping the ores of copper chiefly shown by post-ore faults which bearing skarn or magnetite are less developed revived even after the ore exposure oxidized and often sporadically distributed. While on (LI et al., 1980). the Pb-Zn deposits where pyrite occurs only as a subordinate mineral component, extensions Zoning of their gossans vary through a wide range, and Typical profile of the oxidation zone in the their depth of oxidation zone generally lies at discussed area consists of the following four 20 to 30 m below surface. The locally subzones: abnormal depth of oxidation is usually related Subzoneof Gossan (Z1) to fractural zone of post-ore deposition. Gossans of the massive pyrite or cupriferous Oxides and hydroxides of iron, the chief pyrite ore deposits are developed along the constituents of gossans, reveal somewhat zoning dipping host beds with an inclined depth down effect. In the upper part of gossans there to more than 350 m below the surface. The appear much more hydrogoethite, orange- lower limit of vertical depth from the surface yellow in color, and a little below, more varies within the range from 60 to 150 m, turgite, cherry red in color, then it is succeeded average of which about 80-90 m. Ore bodies of by the grant accumulation of mixtures of small extent are even oxidized completely into goethite and hydrogoethite, chestnut brown in 33(3), 1983 Oxidation of Sulfides in Lower Yangtze Area 139

Fig. 2 Cu, Pb and Zn contents of gossans in the Lower Yang- tze area. (Numbers denote ore deposits and mineralized local- ities.) color. Occassionally, an alternative and dis- Subzoneof SecondaryOxides (Z2) continuous interbedding of orange-yellow Beneath the gossan there exists an irregular hydrogoethite and cherry red turgite occurs and localized subzone of secondary oxides in the upper gossan. There is almost no derived from an ancient secondary sulfide exception that oxides and hy- subzone by reoxidation. Its thickness varies droxides which form the so-called "mangano- from 0 to 5 m. It chiefly consists of pitch-colored iron hat" are present in Pb-Zn ore deposits. limonite with native copper, cuprite and It is hardly to find out any supergene Cu, their further derivation malachite, occassionaly Pb or Zn derived from the chief with delafossite (c.f. PABST, 1946; Li et al., constituents of primary ores by naked eyes in 1980). Chalcocite was found as relics locally in the gossan of massive pyrite or cupriferous this subzone. Chemical analysis and minera- pyrite deposits, but chemical analysis reveals logical study testified that the pitch-colored that it contains a fair amount of Cu, Pb and limonite is a colloidal mixture of predominant Zn (Fig. 2). Our study proves that Cu, Pb and goethite with subordinate tenorite. Zn content of gossans can be used as a criterion The occurrence of this subzorie reveals that to justify the kind of ore if they reach to a the ancient secondary enriched Cu-sulfide has certain limit (Ore Oxidation Research Group, been subjected to destroy by reoxidation, the 1966). present localized subzone of secondary oxides 140 W.D. LI MINING GEOLOGY: is only a remnant of the former (c.f. ANDERSON, thickness varies from 0 to 5 m, locally exceeding 1955). 10 m. Typical supergene enrichment phe- Subzoneof DisintegratedSulfides (Z3) nomena in two of cross-cuts are illustrated as This is the uppermost part of the primary in Fig. 3 (ZHOU, 1965). ore subjected to strong oxidation and decom- The deposition of supergene sulfides is position. Sulfides here disintegrate and become related to the detention effect of ground water loose and sandy. It directly underlies the circulation caused by the impermeability of gossan except where the subzone of secondary foot-wall beds. The sites where supergene oxides is present between them. The thickness sulfides enriched are much nearer to the foot varies from 0 to 10 m, occassionally exceeding wall bed, they occur almost parallel with the 10 m. Here, the intense oxidation and leaching latter. The elevations they existed vary with make the useful elements of ore going into different ore deposits, most of them occur solution, moving down to the lower part and above the 0 m level, but in Tongkuanshan reacting with primary sulfides to form a new Copper Mine it sets on 35 to -25 m levels. The subzone of secondary sulfide enrichment; interface between this subzone and its therewith, a new formation of supergene underlying primary ore is irregular, it is not minerals is going on intensively, a great uncommon that the former cuts into the number of hydrosulfates are deposited thereby, latter. newly formed limonite settled down by As to the copper bearing skarn and magnetite hyrolysis could be observed locally. The type ores, the supergene enrichment is repre- cupriferous massive pyrite ore on the stope sented by the accumulation of large amount of wall not seldomly ignited due to the strong copper carbonates at certain levels. and rapid oxidation. The principal part of Due to the detention effect on groundwater this subzone lies between 35 to-25 m relative circulation along the impervious foot wall to the sea level in Tongkuanshan Mine, but beds dipping in a medium angle (45•‹ nearly) they occur chiefly above the sea level in all in Tongkuanshan Copper Mine, the oxidation other deposits. The boundary between this profile shows a lateral zoning character. subzone and its underlying cementation zone The most notable feature of the oxidation is vague in most cases, because sooty chalcocite zone of Cu-bearing massive pyrite ore deposits has already sparsely appeared among sandy in the Lower Yangtze region are that the sulfides, and hydrosulfate is also present in gossans extend to a much more depth than the underlying subzone even though in much usually expected, and the existenc of a subzone smaller amount. of secondary oxides representing an ancient Subzoneof SecondarySulfide Enrichment (Z4) supergene sulfide enrichment. It seems to be a It developes in various degrees in all copper- result of a long period of uplift of this region bearing massive pyrite deposits. Obviously, since post-Pliocene (BARBOUR, 1935). Judging its time of formation is not so long enough as from the remnant terraces of present physio- to make the supergene sulfide having a graphy, this region had suffered fluctuation greater thickness. Only by the time not very several times, but it reflected on the profile of far from regional uplift in the nearest past oxidation zone only by an uplift after the might it begin. The sooty supergene chalcocite formation of subzone of ancient sulfide accumulated in pockets or lenses, distributed enrichment-as indicated by the reoxidation of sporadically within the scope of this subzone. the ancient supergene sulfides, and by sinking Observation of polished sections indicates that down not far back from the present-as most the replacement of primary sulfides by of the gossans situated far below the present supergene chalcocite and covellite scarcely ground-water table. tends to have completed. Supergene enrichment increased the grade of ore from I weight Development percent to as much as 20 weight percent. The Characteristic features of zoning of sulfide 33(3), 1983 Oxidation of Sulfides in Lower Yangtze Area 141

Fig. 3 Phenomena of secondary sulfide enrichment of Tongkuanshan Copper Mine. (Two crosscuts at 5 m level.) Z1-gossan subzone; Z2subzone of secondary oxide enrichment; Z3-subzone of disintegrated and loose sulfide; Za- subzone of secondary Cu-sulfide enrichment; Zp-primary ore. ore oxidation recorded the regularity of supergene migration and deposition of major chemical elements comprising the ores under conditions of regional climate, geomorphology, and water table changes. Each subzone and its component minerals represent a definite stage in the whole oxidation processes. When the pyrite-rich ore body exposed to the surface, it began to oxidize and gave rise to free sulfuric acid. As soon as it had been present, oxidation of sulfides went on with accelerated rate, the acidity of oxidizing solution increased rapidly and the concentra- tion of Fe2+, Fe3+, Cu2+, SO24-, etc., raised a high peak. Data of analyses of groundwater samples at 35 m level were representatives of the character of such solution in the intense oxidation zone (corresponding to the upper part of disintegrated sulfides, Table 1, Fig. 4). The rapidity of oxidation was also shown by Fig. 4 Variation of average Fe2+, Fe3+, Cu2+, SO24- the great intensity of sulfate mineral formation. ionic concentration and pH value of mine water at A great amount of sulfate minerals of iron, different levels in Tongkuanshan Mine. 142 W.D. LI MINING GEOLOGY:

Table 1 Chemical composition and pH value of the therewith shoud be changeable from time to mine water in Songshushan-Laomiaoji deposits in time. The sulfate minerals, however, existed Tongkuanshan Mine (Unit of ion concentration: very temporarily, they vanished soon after they mg/1) had appeared in those comparatively arid part in the stope. It is impossible to form stable precipitants as in the arid regions of Northwest China (Tu et al., 1963). Just because of it, the major component elements of sulfide ore largely migrated downward, forming supergene sulfide enrichment in the lower part by reaction with primary sulfides; and due to the same reason, the sulfide ores were quickly destroyed, and instead, gossans grew up downward rapidly. However, this did not mean a through oxidation of sulfides, there remained sparsely dispersed small relic particles of sulfides in gossans as observed under microscope. While in those ore deposits lacking in disulfide, the role of this stage was much less important. Data according to Tongkuanshan Mine Company * Number in parenthesis denotes number of samples In those ore deposits such as copper-bearing ** Unit: milligram equivalent skarn and magnetite type as well as in Pb-Zn copper, aluminium, magnesium and other or polymetallic ore deposits of disseminated elements were observed in those strongly and vein type in carbonate rocks, the forma- oxidized parts of ore. The ferrous sulfates tion of carbonate minerals immediately suc- (melanterite, holotrichite, siderotil) predomi- ceeded the sulfate stage. While in those deposits nated over the ferric one. Part of ferric sulfates rich in disulfides, i.e. in pyrite or Cu-bearing (chiefly copiapite) was derived from ferrous pyrite deposits, the formation of carbonate sulfates. The transformation of sulfate from minerals was commonly weak or even absent ferrous to ferric might be observed within a few due to the apparent reason that the acidity of days in parts of mining stopes of good air solution did not favour to the formation and circulation. Newly settled limonite in associa- precipitation of carbonates. This is proved by tion with hydrosulfate was also noted in some the rarity of malachite and azurite in gossans mining pits. of Cu-bearing massive pyrite deposits. The Analyses of groundwater samples from 5 m presence of a few amount of malachite or level show that the Cu2+ ion concentration azurite in present gossan is nothing but an reached to a highest peak (average of 25 oxidation product belonged to another samples: 2482 mg/1) and it reveals that there supergene geochemical cycle (e.g. native went on a strong decomposition of copper copper and cuprite in secondary oxides minerals above that level; while the Fe3+ ion subzone transformed into malachite in the concentration had a sudden fall, that might be air). However, the supergene enrichment of a result of the high concentration of Cu2+ ion copper in those Cu-bearing skarn or magnetite which had promoted the hydrolysis of ferric type ore took place mainly at carbonate stage. sulfate (Fig. 4). The formation of limonite in the sulfate Because of the frequent rainfall and alterna- stage was discontinuous and sporadical in tive warm and cold seasonal temperature keeping with the seasonal change of ionic change, ionic concentration of the solution concentration and relative proportions among might show a much wavy character, so the Fe2+, Fe3+, Cu2+, SO24- and others. The formation and precipitation of sulfate minerals hydrolysis of ferric sulfate in large scale was 33(3), 1983 Oxidation of Sulfides in Lower Yangtze Area 143 only possible when sulfide ore body had been silicic acid had hardly any chance to combine nearly wiped out by oxidation, no supplement with copper to form silicate. The very few of sulfuric acid was available and the solution Cu2+ ions in solution during this period might haddgradually became more dilute. possibly go into the crystal lattice of certain The colloidal precipitants of iron oxide and sillicates as isomorphic mixtures or adsorped hydroxide hydrolysed from ferric sulfate would by clayey minerals. Nontronite, a variety of be transformed by a series of successive changes, high iron content, found as veinlets in gossans, i.e. leaching, transportation, dehydration and contains copper as much as 1.1 %, while X-ray further oxidation, such as shown in texture- analysis and DTA failed to discover any trace structure and mineralogical composition. The of independent copper minerals. manganese, for example, which has settled in Other silicates in gossans •¬ the hydro- iron oxides and hydroxides as colloidal and aluminium silicates (hydromica, kaolinite and isomorphic mixtures, was then separated from holloysite) and the hydromagnesium silicates

the latter in the basified medium, and formed (sepiolite) •¬ are mostly products independant minerals. We often found manga- in connection with gangue minerals. nese oxides and hydroxides attached on the Phosphorous, arsenic, molybdenum and stalactitic limonite surface or in the latter's other elements generally present in country colloform cavities, they generally existed in the rocks and ores might have already entered into upper part or at the top of gossans. Besides, a solution in their low valence when the oxida- series of transitional species from manganous tion media still kept for weakly acidic to to manganic with decreasing in depth from acidic condition (Tu et al., 1963). They

the surface had been noted. Hematite and precipitated in high valence in forms of turgite (SMIRNOV,1945) were probably the complex salt only after the media completely result of further oxidation and dehydration of basified. Skorodite, beudantite, turquois and goethite (GAKHALE,1961a, 1961b); they are wulfenite occurred in gossans were evidently present often in the upper part or near the formed after the formation of oxides and surface of gossans, occassionally in the colloform hydroxides of iron and manganese, most

cavities of goethite. probably later than the formation of silicates. As compared with those of the arid region As to the thin leaves of native gold in of Northwest China (Tu et al., 1963), hematite limonite cavities, the author considers that with turgite never formed independent accu- they were the final oxidation products pre- mulation, they existed only in the upper part cipitated from solution with complex salt in of gossans sporadically, vast accumulations are which gold had combined with chlorine. the goethite and hydrogoethite; besides, The essential features of development stages hematite in contrast with turgite is even much in oxidation of different kinds of ore deposits are

less in quantity. given in Table 2. In the Pb-Zn ore deposits, the formation of silicate succeeding that of oxide and hydroxide A Comparison is quite distinct. Hemimorphite occurs as The development of oxidation zone of crusted veinlets cut across the limonite and sulfide ore deposits in Lower Yangtze area may forms mamillated grains in the pore-space of be representative to most part of Southeast colloform limonite. Monheimite altered into China and show specific features contrast to limonite and hemimorphite around its margin that of Northwest China. The following was noted at an outcrop of polymetallic ores. discussion is chiefly on comparison of the Copper silicate is very rare. This may be characteristics of sulfide ore oxidation between explained by that when the oxidizing medium deposits in Southeast China and those in North- became basified, during which silica began west China, the data of the latter is based on to dissolve in a large quantity, there remained the works of Dr. Guangzhi Tu et al. (1963).

very few Cu2+ ions in solution, so that the (1) Solution produced by oxidation of 144 W. D. LI MINING GEOLOGY:

Table 2 Development stages of oxidation zone of sulfide ore deposits in the Lower Yangtze area (Li et al., 1980)

sulfide ore in the arid Northwest China underground especially those from intensely generally has a pH value 1-3 and higher total oxidized part, pH value may be lower than a degree of mineralization several thousand mg/l, unit, commonly 2-4; total degree of mineraliza- whereas the water analysis from the disulfide- tion reaches several thousand mg/l, few rich ore in Lower Yangtze area, the pH value analyses may be as high as above 10,000 mg/l. and total degree of mineralization vary greatly. However, with increase of depth, the pH value Value of pH of the surface spring in the mine goes up gradually, total degree of mineraliza- area is 6-7, degree of mineralization generally tion decreases. So it is hardly to say that the lower than 100 mg/1; while the mine water solution produced by oxidation in sulfide ore 33(3), 1983 Oxidation of Sulfides in Lower Yangtze Area 145 is necessary higher in pH value and lower in unfavorable to the formation of carbonate, total degree of mineralization in view of the while in the latter area the sulfate stage went rich rainfall in the discussed area. on very slowly due to the stability of sulfate (2) The essential factor controlling the minerals on the surface. As to the process of oxidation process is the abundance of disulfide oxidation of Pb-Zn ore deposits, carbonate and both in South and Northwest China. In the silicate stage are more important than in the Lower Yangtze area, the frequent rainfall does Cu-bearing massive pyrite ores, smithsonite and not impede the solution in the early stage of hemimorphite which are rarely found in North- oxidation with growing acidity and concentra- west China (Tu, 1964) are much more common tion of free sulfuric acid as well as ionic content in Lower Yangtze area. of Fe2+, Fe3+, Cu2+ etc. The seasonal change (5) K, Na, Ca, Mg in oxidized zone are of rainfall may cause a strong undulation of largely leached out under the climate condi- their concentration. The hydrosulfate stage tion such as in Lower Yangtze area, except differs from that of the arid region by its Fe2O3 and SiO2 preserved in the gossan. Most limited mineral species and their transient exposures of the pyrite and Cu-bearing pyrite feature. Sulfates can not accumulate to huge ore deposits in Lower Yangtze area are at amount as those in Northwest China. However, the oxide-hydroxide stage, the sulfate stage can sulfate stage in South China does exist as long as only be observed where sulfide ores are not yet the sulfide ore exists. In the arid region of demolished. Most of the exposures of oxidized Northwest China, sulfate produced by oxida- Pb-Zn ore deposits are at the carbonate or tion of sulfide ore may occur up to the surface silicate stage. As compared with the arid exposure, while those in South China generally region of Northwest China, it is a problem occur in the lower part of the subzone Z3 and related to the rate of oxidation. The hydro- the upper part of subzone Z4, and never sulfate minerals as an early oxidation product observed on the surface (c.f. Fig. 4). are relatively stable on the exposure, so it (3) As to the vertical zoning in the humid protects the primary ore from further oxidation, and warm area, subzone of gossan is extremely the speed of development in contrast to that of developed, it reaches 100-200 m below surface. the humid and warm area in South China (c.f. BROWN,1971) is never found in it. (including Kuangdong, Guangxi and Yunnan In most of the Cu-ore deposits in Lower Provinces) is rather slow. A comparison of the Yangtze area, native copper, cuprite and essential features of oxidation between the tenorite as well as relics of chalcocite are sulfide ore deposits in Lower Yangtze area common, this assembladge may be correlated and that in arid region of Northwest China is with the subzone of native sulfur and gypsum given in Table 3. in the Cu deposits where secondary sulfide Acknowledgement: The present paper is a suffer a reoxidation due to the downward brief of the past collaborative work on the movement of water table (Tu et al., 1963). In project of "Evaluation of gossans and oxidized our case, it is also true that native copper- outcrops in Lower Yangtze area". Here I cuprite assemblage represents the occurrence of express my thanks to the colleagues in Nanjing a subzone of ancient secondary sulfide enrich- Institute of Geology and Mineral Resources ment. Beneath this subzone is the disintegrated for their doing field work and laboratory work and loose sulfide, the thickness of which is with me, and excuse me for not listing their much greater than that of the Cu deposits in names (that will be too long to this paper). Northwest China. Geologists of the field prospecting teams (4) Carbonate minerals are rare but occur provided me with their data of gossan analyses, both in the Lower Yangtze area and Northwest among them are the senior geologists: Mr. China. The difference is that in the former area Enbang HUANG of the Prospecting Team of sulfate stage directly passed into oxide- Northwestern Jiangxi Province and Mr. hydroxide stage due to strong acidic condition Zhihua ZHOU of the Tongling Copper Mining 146 W. D. LI MINING GEOLOGY:

Table 3 Characteristics of the oxidation zone of sulfide ore deposits in humid and warm region contrast to that of arid region. 33(3), 1983 Oxidation of Sulfides in Lower Yangtze Area 147

Company, I owe a great deal to them. Li, Wenda et al. (1980): Studies on the oxidation zone of

The author also wishes to express his sulfide ore deposits and evaluation of their gossans in the middle-lower Yangtze Area. Geological sincere gratitude to Dr. Bingxi ZHANG, former Publishing House, Beijing (In Chinese). Professor of the Peking Geological College and PABST, A. (1946): Notes on the structure of delafosite. now advisor of the Ministry of Geology and Amer. Mineralogist, 31, 539•`546. Mineral Resources, and Dr. Guangzhi Tu, SMIRNOV, S. S. (1945): Oxidation zone of sulfide ore the Director of the Institute of Geochemistry of deposits. Geological Publishing House, Beijing Chinese Academy of Science, for their critical (In Chinese, Translated from Russian). reading of the original manuscript. Tu, Guangzhi et al. (1963): Characteristics of the

development of sulfide ore oxidation under arid References and extremely arid climate condition. Acta ANDERSON, J. (1955): Oxidation of copper sulfides and Geologica Sinica, 4, 361•`377 (In Chinese with

secondary sulfide enrichment. Econ. Geol., 50th English abstract).

Aniv. volume, 324•`340. Tu, Guangzhi (1964): A preliminary study on supergene BARBOUR, C. B. (1935): Physiographic history of the paragenesis of Pb-Zn minerals in the oxidation Yangtze. Geol. Memmoir, Ser. A, no. 14, Geol. zone of some Pb-Zn polymetallic ore deposits in

Surv. China. China. Symposium of the 1st Session on

BROWN, J. B. (1971): Jarosite-goethite stabilities at Mineralogy, Petrology and Geochemistry, Geologi-

25•Ž, 1 atm. Mineral Deposita, 6, 245•`252. cal Society of China, 441•`443 (In Chinese).

GAKHALE, K. V. G. K. (1961a): Studies on the oxida- ZHOU, Zhihua (1965): Characteristic features of the tion of magnetite. Econ. Geol., 56, 863•`971. oxidation of a copper ore deposits in Anhui. GAKHALE, K. V. G. K. (1961b): Studies on the oxida- Syposium of the Anhui Subdivision of Geological

tion of goethite. Econ. Geol., 56, 1058•`1062. Society of China, 4, No. 3-4 (In Chinese).

GARRELS, R. M. and CHRIST, C. L. (1965): Solution, Research Group of Sulfide Ore Oxidation (1966):

minerals and equilibrium. Harper and Raw. Some criteria on the evaluation of gossans in the Li, Wenda (1964): On the evaluation of gossans and Middle-Lower Yangtze area. Geology of China, their research problem. Geology of China, no. No. 1, 15•`22 (In Chinese). 11, 12•`19 (In Chinese).

揚子江 下流 域 の硫化物鉱床酸化帯 の特徴

李 文 達

要 旨: 揚 子 江 下 流 域 の硫 化 物 鉱床 にみ られ る酸 化 帯 と る. 硫 化 物 二 次 富 化 帯 とは,中 緯 度,温 暖 湿 潤 地 域 にお け る (3) 二 次 的 な 自然 銅,赤 銅 鉱 が み られ,そ れ らが,さ 酸 化 一 二 次 富 化 作 用 の代 表 例 とみ る こ とが で き,そ の特 ら に孔雀 石,黒 銅 鉱 に酸 化 し てい る こ とは,地 質 時 徴 は 次 の よ うに ま とめ られ る. 代 にお け る銅 二 次 富 化 作 用 の存 在 を意 味 す る. (1) 褐 鉄 鉱 や け は 長 時 間 に亘 る緩 慢 な隆 起 の結 果 深 く (4)鉛 亜 鉛 鉱 床 の 酸 化 帯 生 成 物 は炭 酸 塩,珪 酸 塩 鉱 物 発 達 す る. で あ る. (2) 上 部 の銅 硫 化 物 の急 速 な 分解,銅 の 下 方移 動 に よ 揚 子 江 流 域 と非 常 に乾 燥 して い る 中 国北 西 部 の鉱 床 酸 り,二 次 硫 化 物 富 化 帯 が 限 られ た ゾー ン に 発 達 す 化 帯 の特 徴 の比 較 につ い て ものべ た.