The Geologic, Geochemical Characteristics And Metallogeny Of The Main Pb-Zn Deposits In South Tianshan Orogenic Belt

Maanqiao, Huoshibulake and Salitashi Pb-Zn deposits, in South Tianshan orogenic belt, are hydrothermal exhalative-sedimentary-reformed deposits. The deposits, formed in hydrothermal exhalative-sedimentatary mineralizing processes, have the bed and bedlike ore body, and their ores have the simple metal mineral assemblage, baritic and silica rocks, fluorite and gypsum, band and lamelliferous ore structures, the mildew spherical, tubular, colloidal and organic fragmentlike textural pyrite. The Salitashi deposit, having the lentiform, tubular and nested ore bodies hosted in interstratal fracture zones, the brecciform ore structures, and dolomitizing zones stringing along with the factures, shows it has been shaped by refoming mineralization. The purple fluorite-sphalerite veins, cutting through the ore body and its wall rocks in the Maanqiao ore field and the quartz-sphalertie veins in altereted shales which lie in the contact zone between the shale and the graniteperphyry vein of Huoshibulake ore field, as well as the high temperature alteration indicate these two deposits have undergone the refoming mineralization relating to magmatic gases. But the refoming mineralizations of these tow ore deposits are comparatively weaker than the Salitashi deposit, and the hydrothermal exhalative-sedimentary is their main mineralizaition.Geochemical studies show that the wall rock alterations of these deposits are mainly calcification, but the Salitashi deposit is dominated by dolomitization. The rare earth elements distribution patterns of the samples, gotten from the main ore body and part of wall rocks of the Huoshibulake and Maanqiao are marked by LREE enriching, strong positive Eu and clearly negative Ce anomalies, which suggest these rocks and ores were deposited near the high temperature hydrothermal vents. Comparatively, the rare earth elements distribution patterns of the ore and wall rock samples from the Salitashi ore field show MREE enrichment and negative Ce and Eu anomalies, being similar to those of biogenic sedimentary carbonate. The ore and its wall rocks of the Maanqiao deposit were strongly enriched in Pb, Zn, As, Ba, Sb, Cd, and the magmatophile elements, the Co, Fe and Cu. The ores of main ore body of the Huoshibulake deposit, as minor element enriching coefficient showing, enriches intensively in hydrothermal active elements Cd, Sb, As and Hg, but deplete in Mn, and gained Pb, Zn, As, Cd, Sb, Ag, but lost Ba, B, Cr, Co and Ni, as the Isocon analyses showing, during its formation. The pelitic and calcic siltstones, the wall rocks of the lower ore body, enrich in Ba, Sn, As, Cd, Mo, F, Cr, Co and Ni, which suggest that the hydrothermal, forming the lower ore body, were mixed by magmatic gases. So, the upper and lower mineralizing layers were formed in tow different hydrothermal systems, the entire deposit was formed by polygenous hydrothermal exhalative-sedimentation activities. The Isocon analyses also shows that the altered quartz sandstone of the Salitashi deposit which enriches in Cd, As, Ba, Sb, Ag, Co, Ni and Fe, gained Pb, Zn, Cd, Ag, Co, but lost Mn, Zr, Ba, V and Cr during it alteration, the ore and its dolomitized limestones intensively enrich in Ag, Cd, As, V, Cr, Co, Ni and Cu also. These indicate that the earlier sedimentation, and the latter refoming mineralization and dolomitization of the Salitashi deposit have the strong relation to the deep magma degassing.The geochemical studies also show that not only the ores formed in earlier mineralization periods, but also parts of the carbonate and clastic wall rocks of these deposits are hydrothermal sedimentary genetic rocks.The homogeneous temperatures of the fluid inclusions of quartz-sphalerite veins of the Huoshibulake and the fluorite-sphalerite veins of the Maanqiao have a wide range with bimodal distribution, of which the temperature of the Maanqiao fluorite are 150～250℃and 270～370℃, and the Huoshibulake quartz are 130～250℃and 270～390℃, and there are homogeneous temperatures of few inclusions are higher than 410℃, even 500℃in these tow deposits, the measured salinity of ore-forming fluids of the fluorite veins and quartz veins are 11.93～21.82%Wt% NaCl and 2.90～7.71 Wt% NaCl, respectively, and the Laser Raman spectroscopic analyses on the fluid inclusion composition reveal that the gaseous phases of these tow types inclusions are mainly the lower molecular weight paraffin of methane, ethane and propane, and little of H₂S, N₂, CO₂ and CO. These make sure that their refoming mineralizing fluids are mixture of high temperature magmatic gases and lower temperature and high salinity oil hot brines.The earlier hydrothermal exhalative-sedimentary mineralization of the Salitashi deposit has happened in the extensional period of pre-collision befor orogeny. The earlier hydrothermal exhalative-sedimentary mineralization of the Huoshibulake and another mineralization of the Salitashi deposits were happened in deep faults controlled residual basins in the faults quiescence period of pre-collision befor orogeny. The Maanqiao Pb-Zn deposit formed in a rift basin during tectonic extension of the post-collision period. The refoming mineralization of these deposits was happened during the post-orogenic magmatism. The vein type mineralization of the Maanqiao was formed from the mixture of magmatic gases with basin oil hot brine and the boiling of ore-forming fluids, the mixture of aside magmatic gas with basin oil hot brine brought on the reformed vein type ores of the Huoshibulake during the irruption of granite porphyry veins. The tectonic activity and the process of hydrothermal contain deep magmatic gases, leached the metallogenic matters out of the primary exhalative-sedimentary mineralizing layers, removed them into favorable structural rooms and reformed the new ore bodies of the Salitashi ore finally.