By Sergey M. Rodionov1, Alexander A. Obolenskiy2
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Liaoxi Metallogenic Belt ofBanded Iron Formation (BIF, Algoma Fe) andAu in Shear Zone and Quartz Vein Deposits(Belt LX) (Northeastern China)This Archean metallogenic belt is hosted in marine volcaniclastic and sedimentary basins and greenstone belts of West Liaoning-Hebei-Shanxi terrane in the Sino-Korean Craton in the western Liaoning Province. The belt is 100 km long and ranges up to 50 km wide. BIF deposits occur in the Xiaotazhigou Formation of the Archean Jianping Group and are hosted in mafic volcanic rock and in mafic and felsic volcanic and sedimentary rock. Au deposits occurs in the Archean Jianping Group and are hosted in microgneiss and marble. The most significant deposits in the belt are the Baoguosi Fe and Paishanlou Au deposits. Baoguosi Banded Iron Formation (BIF, Algoma Fe) DepositsThis BIF deposit (Xu Guangsheng, 1993) occurs in the middle member of the Xiaotazhigou Formation of the Archean Jianping Group. The formation consists of: (1) lower migmatitic biotite-plagioclase gneiss intercalated with plagioclase amphibolite and magnetite quartzite; (2) middle migmatitic biotite-plagioclase gneiss intercalated with granulite, magnetite quartzite and amphibolite; and (3) upper interbedded gneissic migmatite and migmatitic plagioclase amphibolite. The deposits are stratiform and layered. Mainly two types of ores exist. One type is magnetite quartzite type and the other is as hematite pseudomorph quartzite type. The deposit minerals are mainly of magnetite and quartz. Secondary minerals are hematite, pyrite, tremolite, actinolite, chlorite, and biotite. Typical deposit structures are gneissic, banded, and massive, and typical deposit textures are medium-to coarse-grained, crystalloblastic and xenomorphic granular crystalloblastic. Alterations are chlorite, biotite, sericite, and carbonate alteration. The deposits are interpreted as a metamophosed Archean sedimentary sequence. The deposit is large with an average grade of 33.78% Fe, 0.015% S, 0.01% P for magnetite quartzite; and 35.81% Fe, 0.015% S, and 0.01% P for hematite quartzite. Reserves are 107.9 million tonnes. Paishanlou Au in Shear Zone and Quartz Vein DepositThis deposit (Shen Baofeng and others, 1994) consists of 13 lensoid deposits that range up to 1000 m long along a mylonite schistosity. The shear zone trends east-west for 20 km and ranges from 2 to 4 km wide. The deposit in the shear zone is 3000 m long and 250 to 460 m wide and forms veinlets and disseminations in altered mylonite. The deposit minerals are gold, electrum, pyrite, and chalcopyrite, and the gangue minerals are quartz, feldspar, ankerite, sericite, chlorite, and others. The diameter of gold grain is 0.001 to 0.015 mm, and the average Au fineness is 929. Pyrite forms two stages. The early stage fine and Au-bearing and occurs along the mylonite schistosity. The late stage is coarse-grained, barren, and occurs as fine veinlets cutting the mylonite schistosity. The deposit alteration zones are: an internal zone of zone of pyrite and sericite; an intermediate zone of ankeritie; and an outer zone of chlorite. The host rocks are the Archean Jianping Group composed of microgneiss and marble. The Paishanlou deposit is the largest of several deposits that occur along the east-west-trending shear zone. The deposit is large with reserves of 25.88 tonnes Au and an average grade of 4.00 g/t Au. Origin and Tectonic Controls forLiaoxi Metallogenic BeltThe belt is hosted in the Liaoxi greenstone belt. The BIF deposits are interpreted as as forming in a rift along a Late Archean continental margin (Shen Baofeng and others, 1994). The eastern Archean Liaoning-Hebei-Shanxi terrane (Liaoxi area) that hosts the Liaoxi metallogenic belt deposits consists of the following major units: (1) a greenstone belt (Xiaotaziguo, Dayinzi and Waziyiu formations; and (2) tonalite, trondhjemite-granodiorite, and others rocks. The Au depositsare interpreted as forming during retrograde metamorphism to greenschist facies and associated thrusting. REFERENCES: Xu Guangsheng, 1993; Shen Baofeng and others, 1994. Liaoji Metallogenic Belt ofBanded Iron Formation (BIF, Algoma Fe),Volcanogenic Zn-Pb-Cu Massive Sulfide(Kuroko, Altai types), and Au in Shear Zoneand Quartz Vein Deposits(Belt LJ) (Northeastern China)This composite Late Archean metallogenic belt is hosted in marine volcaniclastic and sedimentary basins and greenstone belts of the Jilin-Liaoning-East Shandong terrane in the Sino-Korean Craton. The belt contains numerous BIF deposits in the Anshan-Benxi area, some volcanogenic Cu-Zn massive sulphides, and Au shear zone and BIF deposits in the Liaobei and Jiapigou areas. The belt extends northeast from the eastern Liaoning Province into the northeastern Jilin Province, and is about 1000 km long and 100 km wide. The deposits in the belt are hosted in the supracrustal rocks of the Anshan, Qingyuan, and Longgang Groups that are metamorphosed at amphibolite facies. These groups are derived from a sequence of mafic, intermediate, and siliceous volcanic rock and clastic sedimentary rock formed in small volcanic and sedimentary basins along an ancient continental margins. Because of the ancient geologic units and lack of detailed data, several mineral deposit types are combined into a composite belt. Large BIF deposits in Anshan-Benxi area have been the main source of ore for the Anshan Steel Company. The significant Fe deposit is at Gongchangling. The volcanogenic Cyprus Cu-Zn massive sulfide deposit at Hongtoushan well-known deposit. Au deposits in the Jiapigou area are related to ductile shear zones. Gongchangling Banded Iron Formation Deposit (BIF, Algoma Fe)This deposit (Cheng, Yuqi others, 1994) consists of several layers in host metamorphic rock of the Archean Anshan Group occur in a anticlinorium that was intruded and reworked during two periods of granite plutonism at about 2,100 to 2,300 Ma, and 1,700 to 1,900 Ma. The host metamorphic rocksx ared biotite microgneiss, amphibolite, mica schist, biotite gneiss, and garnet-chlorite schist that are derived form volcanic and sedimentary units. There are one to eight deposit beds, and individual deposit beds range from several meters to several tens of meters thick and from several hundred meters to 1 km long. Textures in the deposit layers are banded, paragneissic, and massive, and the ore minerals are coarse-grained magnetite, quartz and minor amphibole. Moderate amount of rich ores, with over 509% Fe consist mainly of magnetite, maghemitite, graphite, quartz, garnet, cummingtonite, pyrite, and pyrrhopyrite with mainly massive textures and local porous textures. There are two different interpretations for the origin of the Fe-rich ores: formation during hydrothermal reworking of lean ore, or enrichment of primary siderite (BIF) beds during regional metamorphism. The metamorphic age of the Anshan Group, that hosts the Gongchangling Fe deposit, 2,500 to 2,650 Ma. The age of the source rocks is probably older than 2,800 Ma (Cheng Yuqi, 1986). The deposit is large with reserves of 760 million tones and an average grade of 32.82% Fe. Hongtoushan Volcanogenic Zn-Pb-Cu Massive Sulfide (Kuroko, Altai type) DepositThis deposit (Zhang Qiusheng and others, 1984a, b; Ge, Chaohua and others, 1989) consists of chimney, vein, and stratiform deposits hosted in the lower and middle parts of the Hongtoushan Formation of Archean Anshan Group. The Hongtoushan Formation consists of biotite-plagioclase-gneiss and amphibole-plagioclase gneiss, with intercalations of felsic gneiss and magnetite quartzite. Ore mainly consists of pyrite (50%), pyrrhotite (20%-30%), chalcopyrite (1%-10%), sphalerite (1%-15%), as well as small amount of galena, cubanite, and chalcocite. The ores are massive, brecciform, banded, and disseminated. Limited proximal wall rock alterations were developed, including silica alteration, sericite alteration, chlorite alteration, tremolitization and cordieritization. The deposit occurs at the southern margin of Tieling-Qingyuan uplift, north side of the Hunhe fracture zone. The deposit is medium-size with reserves of 471,500 tonnes Cu grading 1.72% Cu reserves of 688,400 tonnes grading 3.04% Zn. Jiapigou Au in Shear Zone and Quartz Vein DepositThis deposit (Xu Enshou and others, 1994) consists of sulphide-poor Au veins that occur in a northwest-trending belt that is concordant to a northwest-trending hosting shear zone. More than ten Au deposits occur in the northwest-trending shear zone that is 40 km long and ranges from 5 to 10 km wide. Ore minerals are pyrite, minor chalcopyrite, galena, sphalerite, scheelite, wolframite, pyrrhotite, siderite, and scarce sulfosalt minerals. Alterations consists of formation of quartz, sericite, carbonate, pyrite, and chlorite. Au/Ag ratio of the ores is high, and the Au fineness is 820. The deposit is hosted along the northern boundary of the Jilin-Liaoning-Shangdong tonalite, trondhjemite, granodiorite terrane of the North China Platform. The supracrustal rocks are mafic and intermediate volcanic rock and sedimentary rock metamorphosed to amphibole and local granulite facies. The oldest isotopic age is 3.0 Ga. Younger heating events occurred at mainly 2.5 to 2.6 Ga, and 1.9 to 1.6 Ga. Many workiers suggest that the supracrustals in the area comprise a greenstone belt (Cheng Yuming and others, 1996). The origin of the deposit is debated with some geologists interpreting the deposits as related to magmatism during the Hercynian and (or) Yanshan Orogeny. Hart and others (2002) show that the gold deposits in the Jiapigou district are about 220 Ma according to SHRIMP U-Pb zircon dating on syn-gold mineralization felsic dikes and 40Ar-39Ar dating on gold-related sericite (Y. Qiu, unpublished data, 2004).The deposit is large with reserves of 17 tonnes gold and an average grade of 5 to 10 g/t Au. Origin and Tectonic Controls forLaioji Archean Metallogenic Belt.The BIF and massive sulfide deposits in the belt are interpreted as forming during volcanism and sedimentation in an island arc. The Au shear zone deposits are interpreted as forming during retrograde metamorphism to greenschist facies. Shen Baofeng and others (1986) interpret that the greenstone belts in Northern Liaoning (Hunbei) area formed in a tectonic setting similar to of a modern active continental margin, while the greenstone belts in Anshan-Benxi and Jiapigou areas formed along a rift along a continental margins that was contemporaneous with regional metamorphsim, folding and thrusting. The Archean Jilin-Liaoning-East Shandong terrane that hosts the metallogenic belt consists of mainly of the following units: (1) tonalite, trondhjemite, granodiortie; and (2) gneiss and amphibolite. The major disticts in Anshan-Benxi area in the northern Liaoning and Jiapigou areas are hosted in the northern Liaoning and Jiapigou greenstone belts respectively. The U-Pb age of zircon in the trondhjemite (mylonite) is 3,804 Ma (Wu Jiashan and others, 1998). Hu Guiming and Wang Shoulun and others (1998) iinterpret the Jilin-Liaoning-East Shandong terrane as the Liaoji amalgamation terrane (block) that contains several small terranes. Some of these small terranes are interpreted as fragments of continental nuclei whereas others are interpreted as greenstone belts derived form oceanic crust. REFERENCES: Cheng Yuqi, 1986; Shen Baofeng and others; 1986; Wu Jiashan and others, 1998; Hart and others, 2002. |