| 其他摘要 | Mian-Ning-Lue triangle area in Shanxi Province is one of Cu-Au polymetal potential area in southwest of our country. In this area, there are hundreds of different type Cu, Fe, Pb, Zn, Au and Ag poly-metal ore deposits. Most deposits in this area, which are not in large scale, are related to intermediate acidity intrusive except the gold deposit Jianchaling and Lijiagou with large or super-large scale. Of these ore deposits, Tongchang copper deposit is the most prospective and representative. Its scale is medium and its potential reserve is a large one. This area is dotted with many Cu-Au polymetal ore deposits, but there is not a big one or a super one. Geology workers have done lots of essential geological work and struggled for ore-finding work for many years. There are some achievements for them. Whereas from nineteen nineties, the ore-finding work is becoming more and more difficult. This paper chooses the most representative and potential Tongchang deposit in the area Mian-Lue-Nin as the subject. Through fluid geochemistry and geochemistry of rock and S-ores, we synthesis and make contrast with ore deposit geology characteristic, geochemistry, isotope chronology and then we get some points as follow:
(1) After sinian period, this area upheaved and became continent because of the collision from Yangtz plate. According to the petrology geochemistry and deposit geochemistry, the metallogenic tectonic background of Tongchang ore deposits is collisional orogeny.
(2) The study of trace elements of the deposits suggests that the exhalation→migration→enrichment of Cu etc. metallogenic substances is one of the most important way to form copper mineralization and copper mineralized body. REE elements result indicates that the REE elements composition of ores of this area bears resemblance to the one of diorite, albitite and spilite. However there is some difference between them. REE model diagrams show that diorite and albitite support major substance for mineralization.
(3) The ore-bodies are fine controlled by two groups of NWW- and NEE-strike ductile shear zones. They are occurred in the internal-external contract belt of the north part of diorite intrusive or schistosity belt within the intrusive.
(4) The metallogenic fluid is generally low-temperature and low-salinity. There is probably CO2-rich fluid in it. Its metallogenic fluid system bears some resemblance to that of orogenic gold deposits.
(5) The major metallogenic age is possible between 200~230 Ma, which is just within Indo-Chinese period, according to the metallogenic tectonic background and metallogenic chronology. During this period, ocean basin of Mian-Lue-Yang underwent subduction and collision and thus Qinling orogenic belt formed.
Therefore, the author gets some points as follow. The metallogenic tectonic background of the copper deposits is collisional orogeny. The major metallogenic substances are diorites and spilites. Its fluid system is characterized by low-temperature, low-salinity and CO2-rich. Metallogenic age is within Indo-Chinese period. Its metallogenic model is: during Indo-Chinese period, many NWW- and NEE-strike ductile strike-slip faults formed, and at the same time Mina-Lue ocean basin closed, subducted and collisoned, and then formed duplex overturned folds, ductile-brittle thrust nappes and strike-slip faults. The successive activities of diorites supply the gas-liquid, thermal dynamic and partial Cu etc metallogenic substances and formed volcano metamorphic hydrothermal fluid. This kind of fluid mixed with meteoric water to form alk-rich (Na+,K+) and CO2-rich fluid system. As result of this mixed fluid, Cu etc metallogenic substances in the spilites dissolved out and formed into the low-temperature and low-salinity metallogenic hydrothermal fluid. The fluid flew along the two groups of NWW and NEE-strike, filled them and precipated in them, and formed copper metallogenic body. |
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