Alunite 40Ar/39Ar and Zircon U-Pb Constraints on the Magmatic-Hydrothermal History of the Zijinshan High-Sulfidation Epithermal Cu-Au Deposit and the Adjacent Luoboling Porphyry Cu-Mo Deposit, South China: Implications for Their Genetic Association

被引:56
作者
Pan, Jun-Yi [1 ]
Ni, Pei [1 ]
Chi, Zhe [1 ]
Wang, Wen-Bin [2 ]
Zeng, Wen-Can [3 ]
Xue, Kai [3 ]
机构
[1] Nanjing Univ, Sch Earth Sci & Engn, Inst Geofluids, State Key Lab Mineral Deposits Res, Nanjing 210093, Jiangsu, Peoples R China
[2] Fujian Inst Geol Survey, Fuzhou 350013, Fujian, Peoples R China
[3] Zijin Min Grp Co Ltd, Shanghang 364200, Peoples R China
基金
国家重点研发计划;
关键词
INDIO-PASCUA BELT; STABLE-ISOTOPE GEOCHEMISTRY; FUJIAN PROVINCE; FLUID INCLUSION; GOLD DEPOSIT; MINING DISTRICT; SULFUR-DIOXIDE; VOLCANIC-ROCKS; TRACE-ELEMENT; IGNEOUS ROCKS;
D O I
10.5382/econgeo.4658
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
The large Zijinshan high-sulfidation epithermal Cu-Au deposit, together with the adjacent Luoboling porphyry Cu-Mo deposit, constitutes a major porphyry-epithermal ore district in South China. Current debate centers on whether the Zijinshan and the adjacent Luoboling deposits are cogenetic or represent separate ore-forming events, which is a question of importance for exploration in the district. In this contribution, the magmatic-hydrothermal history of the relationship between Zijinshan and Luoboling is reconstructed based on new alunite 40Ar/39Ar ages from Zijinshan and zircon U-Pb ages of ore-related intrusions from both deposits. This study has been complemented by S isotope analysis on the dated alunite to assess their origin. Three types of coexisting alunite and sulfide assemblages exist at Zijinshan, namely, (1) alunite-quartz-covellite cemented breccias; (2) alunite-digenite veins and (3) banded alunite-pyrite veins. Their field occurrences and S isotope features suggest a magmatic-hydrothermal origin for alunite-quartz-covellite cemented breccias and alunite-digenite veins, whereas the origin of alunite-pyrite veins is likely to be related to magmatic steam. Given the intimate textural coexistence between sulfides and alunite, four undisturbed 40Ar/39Ar plateau ages obtained from alunite-quartz-covellite cemented breccia and alunite-digenite vein-type alunite define the timing of Zijinshan high-sulfidation mineralization from 102.86 +/- 0.61 to 101.19 +/- 0.60 Ma. These agree with bracketing zircon U-Pb ages of pre-ore dacite porphyry at 104.8 +/- 0.9 Ma and 104.7 +/- 0.5 Ma and a zircon U-Pb age of a post-ore granite porphyry dike at 99.5 +/- 0.7 Ma. Combined with their field occurrences, the four alunite ages imply two discrete hydrothermal pulses and a possible time span of over 500 k. y. for the overall high-sulfidation mineralization. Two alunite samples from alunite-pyrite veins yield a slightly disturbed 40Ar/39Ar plateau age at 101.67 +/- 0.61 Ma and an apparently undisturbed age at 99.91 +/- 0.59 Ma, probably reflecting partial or complete thermal resetting related to the coeval granite porphyry dikes. At Luoboling, zircon U-Pb analysis yields an age of 133.6 +/- 1.1 Ma for a dark, ore vein-bearing quartz-diorite porphyry sample and confirms the petrographic observation that they are xenoliths of early wall rocks for the porphyry mineralization. A granodiorite porphyry sample with abundant A-veins is interpreted as an intermineral porphyry phase, dated at 106.5 +/- 1.4 Ma. This age is interpreted as the upper limit for porphyry Cu-Mo mineralization and agrees well with previously reported molybdenite Re-Os and biotite 40Ar/39Ar ages, which collectively suggest porphyry Cu-Mo mineralization and potassic alteration at Luoboling were formed within the interval between ca. 106 and 104 Ma. Taken together, the age of the Zijinshan high-sulfidation mineralization is substantially younger than the porphyry mineralization at Luoboling, and we conclude that there is no direct genetic link between the two deposits. However, the Zijinshan Cu-Au deposit is temporally associated with the deep porphyritic granodiorite, which gives zircon U-Pb ages from 102.1 +/- 0.8 to 101.8 +/- 0.5 Ma, overlapping with the alunite 40Ar/39Ar ages for the high-sulfidation mineralization. This finding has important implications for the ongoing exploration for the two mineralization types in the ore district and elsewhere. The large Zijinshan high-sulfidation epithermal Cu-Au deposit, together with the adjacent Luoboling porphyry Cu-Mo deposit, constitutes a major porphyry-epithermal ore district in South China. Current debate centers on whether the Zijinshan and the adjacent Luoboling deposits are cogenetic or represent separate ore-forming events, which is a question of importance for exploration in the district. In this contribution, the magmatic-hydrothermal history of the relationship between Zijinshan and Luoboling is reconstructed based on new alunite 40Ar/39Ar ages from Zijinshan and zircon U-Pb ages of ore-related intrusions from both deposits. This study has been complemented by S isotope analysis on the dated alunite to assess their origin. Three types of coexisting alunite and sulfide assemblages exist at Zijinshan, namely, (1) alunite-quartz-covellite cemented breccias; (2) alunite-digenite veins and (3) banded alunite-pyrite veins. Their field occurrences and S isotope features suggest a magmatic-hydrothermal origin for alunite-quartz-covellite cemented breccias and alunite-digenite veins, whereas the origin of alunite-pyrite veins is likely to be related to magmatic steam. Given the intimate textural coexistence between sulfides and alunite, four undisturbed 40Ar/39Ar plateau ages obtained from alunite-quartz-covellite cemented breccia and alunite-digenite vein-type alunite define the timing of Zijinshan high-sulfidation mineralization from 102.86 +/- 0.61 to 101.19 +/- 0.60 Ma. These agree with bracketing zircon U-Pb ages of pre-ore dacite porphyry at 104.8 +/- 0.9 Ma and 104.7 +/- 0.5 Ma and a zircon U-Pb age of a post-ore granite porphyry dike at 99.5 +/- 0.7 Ma. Combined with their field occurrences, the four alunite ages imply two discrete hydrothermal pulses and a possible time span of over 500 k. y. for the overall high-sulfidation mineralization. Two alunite samples from alunite-pyrite veins yield a slightly disturbed 40Ar/39Ar plateau age at 101.67 +/- 0.61 Ma and an apparently undisturbed age at 99.91 +/- 0.59 Ma, probably reflecting partial or complete thermal resetting related to the coeval granite porphyry dikes. At Luoboling, zircon U-Pb analysis yields an age of 133.6 +/- 1.1 Ma for a dark, ore vein-bearing quartz-diorite porphyry sample and confirms the petrographic observation that they are xenoliths of early wall rocks for the porphyry mineralization. A granodiorite porphyry sample with abundant A-veins is interpreted as an intermineral porphyry phase, dated at 106.5 +/- 1.4 Ma. This age is interpreted as the upper limit for porphyry Cu-Mo mineralization and agrees well with previously reported molybdenite Re-Os and biotite 40Ar/39Ar ages, which collectively suggest porphyry Cu-Mo mineralization and potassic alteration at Luoboling were formed within the interval between ca. 106 and 104 Ma. Taken together, the age of the Zijinshan high-sulfidation mineralization is substantially younger than the porphyry mineralization at Luoboling, and we conclude that there is no direct genetic link between the two deposits. However, the Zijinshan Cu-Au deposit is temporally associated with the deep porphyritic granodiorite, which gives zircon U-Pb ages from 102.1 +/- 0.8 to 101.8 +/- 0.5 Ma, overlapping with the alunite 40Ar/39Ar ages for the high-sulfidation mineralization. This finding has important implications for the ongoing exploration for the two mineralization types in the ore district and elsewhere. The large Zijinshan high-sulfidation epithermal Cu-Au deposit, together with the adjacent Luoboling porphyry Cu-Mo deposit, constitutes a major porphyry-epithermal ore district in South China. Current debate centers on whether the Zijinshan and the adjacent Luoboling deposits are cogenetic or represent separate ore-forming events, which is a question of importance for exploration in the district. In this contribution, the magmatic-hydrothermal history of the relationship between Zijinshan and Luoboling is reconstructed based on new alunite 40Ar/39Ar ages from Zijinshan and zircon U-Pb ages of ore-related intrusions from both deposits. This study has been complemented by S isotope analysis on the dated alunite to assess their origin. Three types of coexisting alunite and sulfide assemblages exist at Zijinshan, namely, (1) alunite-quartz-covellite cemented breccias; (2) alunite-digenite veins and (3) banded alunite-pyrite veins. Their field occurrences and S isotope features suggest a magmatic-hydrothermal origin for alunite-quartz-covellite cemented breccias and alunite-digenite veins, whereas the origin of alunite-pyrite veins is likely to be related to magmatic steam. Given the intimate textural coexistence between sulfides and alunite, four undisturbed 40Ar/39Ar plateau ages obtained from alunite-quartz-covellite cemented breccia and alunite-digenite vein-type alunite define the timing of Zijinshan high-sulfidation mineralization from 102.86 +/- 0.61 to 101.19 +/- 0.60 Ma. These agree with bracketing zircon U-Pb ages of pre-ore dacite porphyry at 104.8 +/- 0.9 Ma and 104.7 +/- 0.5 Ma and a zircon U-Pb age of a post-ore granite porphyry dike at 99.5 +/- 0.7 Ma. Combined with their field occurrences, the four alunite ages imply two discrete hydrothermal pulses and a possible time span of over 500 k. y. for the overall high-sulfidation mineralization. Two alunite samples from alunite-pyrite veins yield a slightly disturbed 40Ar/39Ar plateau age at 101.67 +/- 0.61 Ma and an apparently undisturbed age at 99.91 +/- 0.59 Ma, probably reflecting partial or complete thermal resetting related to the coeval granite porphyry dikes. At Luoboling, zircon U-Pb analysis yields an age of 133.6 +/- 1.1 Ma for a dark, ore vein-bearing quartz-diorite porphyry sample and confirms the petrographic observation that they are xenoliths of early wall rocks for the porphyry mineralization. A granodiorite porphyry sample with abundant A-veins is interpreted as an intermineral porphyry phase, dated at 106.5 +/- 1.4 Ma. This age is interpreted as the upper limit for porphyry Cu-Mo mineralization and agrees well with previously reported molybdenite Re-Os and biotite 40Ar/39Ar ages, which collectively suggest porphyry Cu-Mo mineralization and potassic alteration at Luoboling were formed within the interval between ca. 106 and 104 Ma. Taken together, the age of the Zijinshan high-sulfidation mineralization is substantially younger than the porphyry mineralization at Luoboling, and we conclude that there is no direct genetic link between the two deposits. However, the Zijinshan Cu-Au deposit is temporally associated with the deep porphyritic granodiorite, which gives zircon U-Pb ages from 102.1 +/- 0.8 to 101.8 +/- 0.5 Ma, overlapping with the alunite 40Ar/39Ar ages for the high-sulfidation mineralization. This finding has important implications for the ongoing exploration for the two mineralization types in the ore district and elsewhere.
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页码:667 / 695
页数:29
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