| The Western YunNan Laochang Ag-Pb-Zn ploymetallic deposit is the important mineral deposit in southern of the Southwest "Sanjiang" Metallogenic Belt, its genesis existes different understanding for a long time. Many scholars have studied the deposit from ore-forming geological background, ore deposit geology, ore-forming materials, ore-forming fluid sources and so on, but less on deposit trace element geochemical. So this article is based on detail geological work, to further explore the genesis of deposit by trace element geochemical characteristics.The deposit is located in LanCang Rift Valley which is southern section of the ChangNing-MengLian Rift Valley in BaoShan Micro Plate, western YunNan. It is in southern of "SanJiang" Drapes belong to the contact zone between Indian Plate with Eurasian Plate.After field survey, there are two ore-bearing rock series in mining area, they are shallow carbonate ore-bearing rock series And deep volcanic ore-bearing rock series.①The main ore-forming elements in shallow carbonate ore-bearing rock series are Ag, Pb, Zn, As and so on. Orebodies mostly show in shape, lens shape, pulse cystic, they are epigenetic features. this type of orebodies is one of the major orebody type in LaoChang deposit.②The main ore-forming elements in the upper part of deep volcanic ore-bearing rock series are Fe, Pb, Zn, Ag. They formed by volcanic effusion deposition and superimposed hydrothermal mineralization. The main ore-forming elements in the lower part are Cu, Fe, W, Sn, Mo, they are the orebody related to concealed granite porphyry.Deposit affected by the impact of volcanic effusion deposition and concealed granite porphyry invasion. So deposit showes zoning characteristics in horizontal and vertical. It showes close correlation with volcanic and fracture, and it also caused the characteristics of multi-phase mineralization and multiple sources forming materials.Trace element geochemical characteristics show that:①Pb, Ag are more enriched in each era strata, it’s possible to provide some Pb, Ag ore-forming materials. Granite porphyry is significantly enriched with Cu, Mo, Ag, Sn, Pb and Zn elements, especially Cu significantly enriched, so it’s main reason of the Cu mineralization.②Pyrite formed from low to high temperature conditions, which display the causes of sedimentary origin, hydrothermal origin and volcanic, and it display transformation trace. Galena and sphalerite formation is related to magmatic hydrothermal. Small amount of galena is related to sediment reworking, it prove that galena in the early phase of the mineralization and later magmatic hydrothermal effects on the original mineralization to enriched and transformed it.③Lead-zinc ore related to volcanic effusion deposition and granite porphyry intrusive, display mixing origin. Volcanic effusion deposition formed part of the massive sulphide orebody but the main mineralization is granite porphyry mineralization.It is concluded that the Western YunNan LaoChang Ag-Pb-Zn ploymetallic deposit is a multi-phase with the mineralization, it effected by volcanic effusion deposition and concealed granite porphyry hydrothermal mineralization. Early Carboniferous volcanic exhalation brought part of minerals such as Fe, Pb, Zn, formed several massive sulphide orebodies. Late granite porphyry intrusive brought minerals of Cu, Pn, Zn, Fe, W, Sn, and Mo, It enriched and transformed the original orebodies. Porphyry formed molybdenum and tungsten orebody itself, formed copper-molybdenum orebody with wall rock in deep department, formed silver-lead-zinc orebody in shallow department. Orogeny made mining area terrain uplift, weathering and eroding made carbonate rock on the top of mine exposed on the surface, meteoric water infiltrated through cracks in the carbonate-containing to ore belt. With the impact of concealed porphyry intrusive, heat source made groundwater was heating, cycling and continuously leached out mineralization substance from carbonate rocks, volcanic rocks and granite porphyry, it made orebody continued getting richer. In final, these effects created LaoChang Ag-Pb-Zn ploymetallic deposit. |
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