The Research Of Geology And Origin Law Of Tin Ore In The Dachang Guangxi

The thesis "The research of geology and origin law of tin ore in the Dachang Guangxi" is based on this discovery of neutral and basic volcanic rocks and combined with the school-enterprise project "Dachang tin ore-controlling law of the Devonian strata and mineralization prediction ", using the latest theory-the theory of hydrothermal sedimentary mineralization as the guide to start.The tin-polymetallic ore in Dachang located in the north end of Danchi fold belt of the southwestern edge of the Jiangnan archicontinent, is a remarkable large tin polymetallic deposits in the world, is China's important production and export base of tin. But with the many years of mining, mineral resources crisis arises, is the time that strengthen the research of prospecting. In the research of recent years of Dachang tin ore, after finding the sub-basalt in the "East Rock wall" (Li Xiao etc., 2009), but also found the neutral and basic volcanic rocks in the stratiform copper-zinc ore body and ore-hosted strata of the Tongken and Heishuigou mines in the Middle Devonian (Liu Chenming, etc.,2011), these new findings have impotant meaning to the origin of ore and research of prospecting and deep and surrounding exploration.On the origin of ore is concerned, those described in this article geological relations and practical information does not have any kind of decisive significance single-handed, but in general terms, they forcefully indicate that the layered ore body of Dachang ore field is formed in the contemporaneous thermal water depositional surroundings. However, these facts do not apply to those observably unconformity contact through strata veins and other contact metamorphic rocks and minerals. As confirmed by previous research, these ores are epigenetic, formed during the Cretaceous granite intrusion and relate with it. As with the massive sulfide deposit, if without distinction of thinking about all the various geological phenomena, the Dachang deposit, neither with is syngenetic, nor is epigenetic, because it both has syngenetic and epigenetic characteristics, but should be a recombination; the origin of ore in the Dachang is neither thermal water depositional nor the formation of magmatic hydrothermal fluids, it has both the characteristics of hydrothermal sedimentary mineralization (stratiform ore body), but also has the characteristics of magmatic hydrothermal (though layer veins), so that should be the formation with a variety of geological processes. These geological events began in the Precambrian mafic volcanic activity laid the material foundation for the development of the Hercynian Devonian volcano-thermal water sedimentation, end up with the hydrothermal alteration which relates with the granite at Yanshan period.Through the study of the thesis reached the following understanding:(1) Think that there is volcanic rocks in the Dachang mining area of middle Devonian, the volcanic rocks belong to basaltic-andesite rocks and calc-alkaline-alkaline series, formed in a continental rift environment. The Volcanic rocks are conformable contact with the surrounding upper and lower rocks, with a lot of classic sedimentary structure characteristics of laminar and stripe, the output position of the volcanic rocks contains a lot marine fossils of tentaculitoid, these evidences indicate that the eruptions environment of the volcanic rocks is sea facies.(2) To discuss the origin of the silicalite, think that the siliceous rocks built of the deposit is formed form the hydrothermal solution with chemical deposition method, which eruption from the benthoal hydrothermal solution circulation system, organisms may be involved in the formation of some siliceous rocks, but not the main factors, In addition, in some time that the thermal water deposition decrease, there may be a small amount of detrital material join to form a small amount of sericite clay shale and lamina stripe of the siliceous rocks construction. The siliceous sources of the silicalite should be part of the main benthoal hot brine circulation system and part of the the neutral and basic volcanic rocks dissolving in the sea or devitrification.(3) To re-expound the process of mineralization and rebuild mineralization mode, put forward "the fourth floor of a ladder" of deposit structure model and three metallogenic series of the deposit. Discuss the the origin relationship between the volcanic activity of the Sibao-Xuefeng period, Hercynian and Yanshan period with the mineralization, think the volcanic activity of the Hercynian, not only provides heat energy to drive the hot brine cycle for the thermal water sedimentary mineralization, but also provides material source for the mineralization.(4) Put forward that the origin of the tin ore in the Dachang should be:sea facies volcano-thermal water deposition-overlying and reworking later. Deposit should be formed in the various geological processes and the multi-stage at the specific geological environment, but also is the result of the upper crust evolution.