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Geochemical characteristics of sedimentation and metamorphism of the Dongchuan copper deposit, Yunnan Province, China
Precambrian Research, 25 (1984) 135--136
135
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
GEOCHEMICAL CHARACTERISTICS OF SEDIMENTATION AND METAMORPHISM OF THE DONGCHUAN COPPER DEPOSIT, YUNNAN PROVINCE, CHINA
WANG KENAN
Bureau of Geology, Ministry of Metallurgical Industry, Beijing (People's Republic of China)
EXTENDED ABSTRACT Wang, K., 1984. Geochemical characteristics of sedimentation and metamorphism of the Dongchuan copper deposit, Yunnan Province, China. Precambrian Res., 25: 135--136. The Dongchuan copper deposit lies in the Kunyang Group of the Late Precambrian Sinian System in Yunnan Province. The deposit is stratiform and is restricted to transitional beds of argillaceous and arenaceous dolomites which lie between purple beds of slate and dolomite below and red dolomite above, and to algal beds at the base of the red dolomites. The copper ore minerals are bornite and chalcopyrite with minor chalcocite, covellite and enargite. The major stratiform sulphide minerals show a vertical zonation. F r o m the top downwards they appear in sequence chalcocite, bornite, chalcopyrite and pyrite. Silver, germanium and gold occur in useful quantities. The gangue minerals include dolomite, calcite, quartz, and minor pyrite, chlorite and sericite. Most of the Sinian sedimentary rocks in the area are enriched in copper to levels well above the Clark value, particularly the barren transitional beds which contain six times the Clark value. Germanium has been detected in the transitional beds, but is only enriched in chalcopyrite and enargite veins within the hanging wall dolomite. Silver is concentrated in copper minerals, and there is a positive correlation between copper and silver contents. The transitional beds have much lower FeS+/Fe 2+ ratios than the adjacent beds, indicating a relatively reducing environment in the transitional beds. Nearby Precambrian mafic intrusive rocks might be considered to be a source of copper for the ore deposit. Bi, Sb, Be, Ag, Ge and Mo all occur in significant quantities in the ore, but not in the igneous rocks. Conversely the Ni, V and Ti are enriched in the igneous rocks, but not in the ore. This suggests that these mafic rocks were not the source of copper. Sulphur isotope studies suggest that the sulphur in the copper sulphides was derived mainly by the biological reduction of marine sulphate. Although most of the copper appears to be of sedimentary origin, there was significant remobilisation during subsequent folding and metamorphism. Veins of quartz, calcite, dolomite and sulphide formed in tensional fractures. Copper occurs in all these veins, but the highest contents are in the sulphide veins which are up to ten times as rich as the stratiform deposit. The relative depletion of the ore beds adjacent to copper-rich veins suggest that the metamorphic transport of copper was on a local scale, for distances varying from several cm to more than 200 m. The mineralised veins occur mainly in the hanging wall and less c o m m o n l y in the footwall or in tectonic breccia zones. There are two types of mineralised vein: chalcocite and haematite; and enargite with minor chalcopyrite and bornite. The enrichment of germanium in the enargite veins is also a result of metamorphism. In the veins silver is concentrated in bornite and chalcopyrite, whereas gold is concentrated in enargite.
0301-9268/84/$03.00
© 1984 Elsevier Science Publishers B.V.
136 The Dongchuan copper deposit is considered to be of sedimentary--metamorphic origin. Copper was first precipitated during the deposition of marginal marine sedimentary rocks and was later mobilised and locally reconcentrated during metamorphism.
135
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
GEOCHEMICAL CHARACTERISTICS OF SEDIMENTATION AND METAMORPHISM OF THE DONGCHUAN COPPER DEPOSIT, YUNNAN PROVINCE, CHINA
WANG KENAN
Bureau of Geology, Ministry of Metallurgical Industry, Beijing (People's Republic of China)
EXTENDED ABSTRACT Wang, K., 1984. Geochemical characteristics of sedimentation and metamorphism of the Dongchuan copper deposit, Yunnan Province, China. Precambrian Res., 25: 135--136. The Dongchuan copper deposit lies in the Kunyang Group of the Late Precambrian Sinian System in Yunnan Province. The deposit is stratiform and is restricted to transitional beds of argillaceous and arenaceous dolomites which lie between purple beds of slate and dolomite below and red dolomite above, and to algal beds at the base of the red dolomites. The copper ore minerals are bornite and chalcopyrite with minor chalcocite, covellite and enargite. The major stratiform sulphide minerals show a vertical zonation. F r o m the top downwards they appear in sequence chalcocite, bornite, chalcopyrite and pyrite. Silver, germanium and gold occur in useful quantities. The gangue minerals include dolomite, calcite, quartz, and minor pyrite, chlorite and sericite. Most of the Sinian sedimentary rocks in the area are enriched in copper to levels well above the Clark value, particularly the barren transitional beds which contain six times the Clark value. Germanium has been detected in the transitional beds, but is only enriched in chalcopyrite and enargite veins within the hanging wall dolomite. Silver is concentrated in copper minerals, and there is a positive correlation between copper and silver contents. The transitional beds have much lower FeS+/Fe 2+ ratios than the adjacent beds, indicating a relatively reducing environment in the transitional beds. Nearby Precambrian mafic intrusive rocks might be considered to be a source of copper for the ore deposit. Bi, Sb, Be, Ag, Ge and Mo all occur in significant quantities in the ore, but not in the igneous rocks. Conversely the Ni, V and Ti are enriched in the igneous rocks, but not in the ore. This suggests that these mafic rocks were not the source of copper. Sulphur isotope studies suggest that the sulphur in the copper sulphides was derived mainly by the biological reduction of marine sulphate. Although most of the copper appears to be of sedimentary origin, there was significant remobilisation during subsequent folding and metamorphism. Veins of quartz, calcite, dolomite and sulphide formed in tensional fractures. Copper occurs in all these veins, but the highest contents are in the sulphide veins which are up to ten times as rich as the stratiform deposit. The relative depletion of the ore beds adjacent to copper-rich veins suggest that the metamorphic transport of copper was on a local scale, for distances varying from several cm to more than 200 m. The mineralised veins occur mainly in the hanging wall and less c o m m o n l y in the footwall or in tectonic breccia zones. There are two types of mineralised vein: chalcocite and haematite; and enargite with minor chalcopyrite and bornite. The enrichment of germanium in the enargite veins is also a result of metamorphism. In the veins silver is concentrated in bornite and chalcopyrite, whereas gold is concentrated in enargite.
0301-9268/84/$03.00
© 1984 Elsevier Science Publishers B.V.
136 The Dongchuan copper deposit is considered to be of sedimentary--metamorphic origin. Copper was first precipitated during the deposition of marginal marine sedimentary rocks and was later mobilised and locally reconcentrated during metamorphism.