| 中国有色金属工业总公司矿产地质研究院 |
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| 引用本文：.1986.A Tentative Discussion On The Origin Of The Changpo Tin-Polymetallic Deposit, Dachang Ore Field[J].Mineral Deposits,5(3):87~96 |
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| A Tentative Discussion On The Origin Of The Changpo Tin-Polymetallic Deposit, Dachang Ore Field |
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| Abstract:The Changpo tin-polymetallic deposit occurs in the Upper Devonian marine carbonate rocks and silicious rocks and is controlled jointly by three factors, i.e., strata (D3), structures and magmatic rocks, bearing dual characteristics of the syndepositional deposit and hydrothermal one. According to modes of occurrence and mineral assemblages, it can be divided into two types of mineralizations: stratiform stanniferous sulfides and veinlike cassiterite-sulfides. The former has such characteristics of sedimentary deposits as being controlled by the strata, and possessing typical syndepositional structure, e. g., striped and laminated structure, as well as less developed wall rock alterations. In contrast, veinlike mineralizations are characterized by features of hydrothermal deposits, such as being governed by fracture systems and affected by tectonic activities, showing polystage pulsation and having typical hydrothermal wall rock alterations including sericitization, tourmalinization and fluoritization. The two types display distinct differences not only in geological characteristics, but also in mineral assemblages, metallogenic physical-chemical conditions and temperatures as well as ore-forming time. Nevertheless, there exist close relations between the two mineralizations: (1) they occur in the same spatial position; (2) they have similar vertical mineral zoning: pyrite in the upper part of the orebody and pyrrhatite in the lower; (3) δ34S values of pyrite and sphalerite are similar in the two types, being -4.5‰ - +1.3‰ in the pyrite and -7.1‰ - +0.2‰ in the sphalerite respectively. All this implies that these two mineralizations have intimate relationships and also obvious differences. On the one hand, they were formed in different ore-forming stages and diverse geological conditions; on the other hand, the stratiform mineralization was- superimposed and remolded by the late ore-forming hydrothermal fluids, i. e., veinlike mineralization, whose material sources in turn had something to do with the stratiform mineralization. Studies show that the stratiform mineralization is of sea-floor syndepositional type formed in Late Devonian whose formation was probably related to the eruptive sedimentation of the volcanic hot spring ascending along the deep-seated fractures. The metallogenic elements such as S, Sn, Pb and Zn were derived from the depth of the crust, and the veinlike mineralization resulted from the hydrothermal liquid of Yanshanian granitic magma. Under the action of the magmatic solution and the heat of the magma, the metallogen materials in the stratiform mineralization were activated and transported, and thus provided some ore-forming materials for veinlike mineralization, such as S, Sn, Pb and Zn. It is therefore concluded that the Changpo ore deposit is a composite-origin type formed both by syndeposition, i.e., eruptive deposition from volcanic hot spring at seafloor, and by superimposition-reformation of the magmatic hydrothermal fluids, and that this deposit must have evolved from the stratiform stanniferous sulfide mineralization. |
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