摘要
It is revealed that the protolith of gray-light brown potash-feldspar-leucogranulites and granulites in the 2nd formation of the LG in Tanyaokou deposit are quartz kerotophyre of synsedimentary eruption based on the following facts and features: (1) The rocks look compact and homogeneous without obvious crystals with naked eyes; (2) they contain blastoporphyritic or glomeroporphyritic and blasto-crystalloclastic crystals consisting of quartz with wavy extinction and albite with obvious alteration and deformation; (3) they also contain radiated and fibrous blasto-microspherulitic texture and swallow-tailed bifurcate and blasto-hollow-skeleton crystal texture, representing the rapid cooling characteristic of the magma during submarine volcanic eruption; (4) the major chemical compositions of the rocks are: SiO2 = 70.80%―76.00%, K2O (4.83%―6.22%)>Na2O(2.78%―3.80%), and K2O+Na2O = 8.63%―9.00%; and (5) their petro-chemical diagrams indicate that they are volcanic rocks. Together with the characteristic that they occur in the same sequence with potassic spilite (SiO2 = 46.12%―50.68%, K2O = 4.23%―5.93%>Na2O = 2.15%―3.14%, K2O+Na2O = 6.51%―8.08%), it can be confirmed that the vol-canics occurring in the 2nd Formation of the LG in Tanyaokou district are double-peaking potas-sic volcanic rocks. The discovery, together with the tuffs with ore minerals and the distribution of lead isotopic as well as the value of Co/Ni of pyrites >1 showing the obvious endogenic metali-zation, can prove that the Tanyaokou deposit is an untypical SEDEX-type deposit formed in the extension fault basin in the Mesoproterozonic aulacogen of the northern margin of the North China Platform, and its metallogenesis is related to the synsedimentary volcanic activities and the hydrothermal exhalation, and both the ore-forming material source and volcanics came from mantle or lower crust. These facts mentioned above, together with the meta-volcanic rocks (double-peaking) found in the Dongshengmiao and Huogeqi districts and the host stratigraphic sequence of LG, can further prove that the Mesoproterozoic aulacogen of passive continental margin of Langshan-Zhaertaishan area had been unevenly expanded. This provides some in-formation and new approaches for the study on tectonic-hydrothermal events in Lang-shan-Zhaertaishan aulacogen and their evolutionary process, hydrothermal dynamical source, the relationship between the volcanic activities and the ore-forming process, the regional ore-forming regularity as well as for the correlation with the similar deposits abroad.
It is revealed that the protolith of gray-light brown potash-feldspar-leucogranulites and granulites in the 2nd formation of the LG in Tanyaokou deposit are quartz kerotophyre of synsedimentary eruption based on the following facts and features: (1) The rocks look compact and homogeneous without obvious crystals with naked eyes; (2) they contain blastoporphyritic or glomeroporphyritic and blasto-crystalloclastic crystals consisting of quartz with wavy extinction and albite with obvious alteration and deformation; (3) they also contain radiated and fibrous blasto-microspherulitic texture and swallow-tailed bifurcate and blasto-hollow-skeleton crystal texture, representing the rapid cooling characteristic of the magma during submarine volcanic eruption; (4) the major chemical compositions of the rocks are: SiO2 = 70.80%―76.00%, K2O (4.83%―6.22%)>Na2O(2.78%―3.80%), and K2O+Na2O = 8.63%―9.00%; and (5) their petro-chemical diagrams indicate that they are volcanic rocks. Together with the characteristic that they occur in the same sequence with potassic spilite (SiO2 = 46.12%―50.68%, K2O = 4.23%―5.93%>Na2O = 2.15%―3.14%, K2O+Na2O = 6.51%―8.08%), it can be confirmed that the vol-canics occurring in the 2nd Formation of the LG in Tanyaokou district are double-peaking potas-sic volcanic rocks. The discovery, together with the tuffs with ore minerals and the distribution of lead isotopic as well as the value of Co/Ni of pyrites >1 showing the obvious endogenic metali-zation, can prove that the Tanyaokou deposit is an untypical SEDEX-type deposit formed in the extension fault basin in the Mesoproterozonic aulacogen of the northern margin of the North China Platform, and its metallogenesis is related to the synsedimentary volcanic activities and the hydrothermal exhalation, and both the ore-forming material source and volcanics came from mantle or lower crust. These facts mentioned above, together with the meta-volcanic rocks (double-peaking) found in the Dongshengmiao and Huogeqi districts and the host stratigraphic sequence of LG, can further prove that the Mesoproterozoic aulacogen of passive continental margin of Langshan-Zhaertaishan area had been unevenly expanded. This provides some in-formation and new approaches for the study on tectonic-hydrothermal events in Lang-shan-Zhaertaishan aulacogen and their evolutionary process, hydrothermal dynamical source, the relationship between the volcanic activities and the ore-forming process, the regional ore-forming regularity as well as for the correlation with the similar deposits abroad.
基金
The authors would like to extend their gratitude to the National Natural Science Foundation of China
the National Natural Science Foundation of China(Grant No.40172040)
the National Natural Science Foundation of China(Grant No.40234051)
the State Key BasisResearchDevelopment Plan ofChina(Grant No.G1999043215).
