| Microthermometric measurement of fluid inclusions and its constraints on genesis of PGE-polymetallic deposits in Lower Cambrian black rock series, southern China |
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| 作者姓名： | WANG Min |
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| 作者单位： | [1]Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China [2]Department of Earth Sciences, Sun Yat-sen University, Guangzhou 510275, China |
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| 基金项目： | CAS，中国科学院资助项目，the project of State Key Laboratory of Organic Geochemistry;Chinese Academy of Sciences，教育部跨世纪优秀人才培养计划 |
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| 摘 要： | Systematic microthermometric measurements of fluid inclusions in the PGE-polymetallic deposits hosted in the Lower Cambrian black rock series in southern China were performed, and the results suggest: (1) there exist two types of fluid inclusions. TypeⅠis of NaCl-H2O system with low-medium salinity, and its homogenization temperatures (Th) and salinities are 106.9- 286.4℃ and ( 0.8- 21.8) wt%NaCl eq. respectively; TypeⅡ is of CaCl2-NaCl-H2O system with medium-high salinities, and its homogenization temperatures and salinities range from 120.1℃ to 269.6℃ and ( 11.4- 31.4) wt%NaCl eq., respectively. The typeⅡ fluid inclusions have been discovered for the first time in this kind of deposits; (2) two generations of ore-forming fluids were recognized. Characteristics of fluid inclusions in the PGE-polymetallic ores and carbonate-quartz stockworks in the underlying phosphorites are almost of no difference, they may represent ore-forming fluids at the main metallogenic stage. The peak value of homogenization temperature of those fluid inclusions is about 170℃, while their salinities possess a remarkable bimodal distribution pattern with two peak values of (27-31) wt%NaCl eq. and (4-6) wt%NaCl eq. On the contrary, fluid inclusions in the carbonate-quartz veins in the hanging wall may represent ore-forming fluids at the post-metallogenetic stage. The homogenization temperatures and the peak values of salinities are mostly 130-170℃ and (12-14) wt%NaCl eq., respectively; (3) nobel gas isotopic composition analyses in combination with the microthermometric measurements of fluid inclusions suggest that the ore-forming fluids at the main metallogenetic stage were probably derived from mixing of basinal hot brines with the CaCl2-NaCl-H2O system and seawater with the NaCl-H2O system; (4) in the Early Cambrian, the basinal hot brines were trapped in the Caledonian basins, which were distributed along the southern margin of the Yangtze Craton, and where giant thick sediments were accumulated, and expelled and migrated laterally along the strata because of the pressure caused by overlying sediments. The basinal hot brines absorbed Ni, Mo, V, PGE from the surrounding rocks and were transformed into ore-bearing hydrothermal fluids with the CaCl2-NaCl-H2O system and medium-high salinities, then ascended along faults and mixed with seawater of the NaCl-H2O system, and finally PGE-polymetallic deposits or occurrences were formed in the black rock series.
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| 关 键 词： | 华南地区 岩石 热盐水 同位素 PGE 地质学 |
| 收稿时间： | 8 June 2005 |
Microthermometric measurement of fluid inclusions and its constraints on genesis of PGE-polymetallic deposits in Lower Cambrian black rock series, southern China |
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| Wang Min,Xiaoming Sun,Mingyang Ma.Microthermometric measurement of fluid inclusions and its constraints on genesis of PGE-polymetallic deposits in Lower Cambrian black rock series, southern China[J].Chinese Journal of Geochemistry,2005,24(4):297-305. |
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| Authors: | Wang Min Xiaoming Sun Mingyang Ma |
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| Institution: | (1) Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 510640 Guangzhou, China;(2) Department of Earth Sciences, Sun Yat-sen University, 510275 Guangzhou, China |
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| Abstract: | Systematic microthermometric measurements of fluid inclusions in the PGE-polymetallic deposits hosted in the Lower Cambrian
black rock series in southern China were performed, and the results suggest: (1) there exist two types of fluid inclusions.
Type I is of NaCl-H2O system with low-medium salinity, and its homogenization temperatures (T
h) and salinities are 106.9 – 286.4°C and (0.8 – 21.8) wt% NaCl eq. respectively; Type II is of CaCl2-NaCl-H2O system with medium-high salinities, and its homogenization temperatures and salinities range from 120.1°C to 269.6°C and
(11.4 – 31.4) wt% NaCl eq., respectively. The type II fluid inclusions have been discovered for the first time in this kind
of deposits; (2) two generations of ore-forming fluids were recognized. Characteristics of fluid inclusions in the PGE-polymetallic
ores and carbonate-quartz stockworks in the underlying phosphorites are almost of no difference, they may represent ore-forming
fluids at the main metallogenic stage. The peak value of homogenization temperature of those fluid inclusions is about 170°C,
while their salinities possess a remarkable bimodal distribution pattern with two peak values of (27 – 31) wt% NaCl eq. and
(4 – 6) wt% NaCl eq. On the contrary, fluid inclusions in the carbonate-quartz veins in the hanging wall may represent ore-forming
fluids at the post-metallogenetic stage. The homogenization temperatures and the peak values of salinities are mostly 130
– 170°C and (12 – 14) wt% NaCl eq., respectively; (3) nobel gas isotopic composition analyses in combination with the microthermometric
measurements of fluid inclusions suggest that the ore-forming fluids at the main metallogenetic stage were probably derived
from mixing of basinal hot brines with the CaCl2-NaCl-H2O system and seawater with the NaCl-H2O system; (4) in the Early Cambrian, the basinal hot brines were trapped in the Caledonian basins, which were distributed
along the southern margin of the Yangtze Craton, and where giant thick sediments were accumulated, and expelled and migrated
laterally along the strata because of the pressure caused by overlying sediments. The basinal hot brines absorbed Ni, Mo,
V, PGE from the surrounding rocks and were transformed into ore-bearing hydrothermal fluids with the CaCl2-NaCl-H2O system and medium-high salinities, then ascended along faults and mixed with seawater of the NaCl-H2O system, and finally PGE-polymetallic deposits or occurrences were formed in the black rock series.
This work was supported jointly by the Project of Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry,
CAS (No. MSGLCAS03-4), the National Natural Science Foundation of China (Grant Nos. 40173025, 49928201), the project of State
Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (No. OGL-200301),
Trans-century Training Program Foundation for Talents by the Ministry of Education and the Visiting Scholar Foundation of
Key Labs in Universities by the Ministry of Education. |
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| Keywords: | fluid inclusion basinal hot brine noble gas isotope PGE-polymetallic deposits in black rock series southern China |
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