| The discovery of Xiongcun district is an important ore prospecting breakthrough of Jurassic mineralization in the southern Gangdese metallogenic belt, Tibet, which is considered the only one island arc porphyry copper related to oceanic subduction. The NO.?, NO.? and NO.? copper-gold deposits and a plurality of mineralized bodies have been discovered in the Xiongcun district. The mineralogy research of ore-bearing porphyry will help us to studying the metallogenic process and guiding the regional prospecting. The selection of topics is based on full, which have important theoretical and practical significance. Through the detailed field investigation, geological mapping, drilling geological logging and prospecting mineralogy and genetic mineralogy research of rutile, biotite, tourmaline, apatite, the major research progresses are summarized as follows:(1) The alteration and mineralization characteristics of the NO.? and NO.? orebody are described in detail. The alteration of NO.? orebody are potassic alteration,phyllic alteration, propylitic alteration and the hydrothermal veins are quartz – sulfide veins, quartz – molybdenite – sulfide veins, biotite – sulfide veins, pyrite veins,chalcopyrite – pyrite – pyrrhotite veins, polymetallic veins.The alteration of NO.? orebody are potassic alteration, sodic-calcic alteration, phyllic alteration, propylitic alteration and the hydrothermal veins are Magnetite – sulfide veins, quartz – sulfide veins, gypsum veins, pyrite – chalcopyrite veins, pyrite veins, quartz – molybdenite –sulfide veins, actinolite veins, chlorite – sulfide veins, pyrite veins.(2) The mineral composition of the ore bearing porphyry was identified. The ore-bearing porphyry of NO.? orebody is quartz diorite porphyry. The primary minerals of Ore-bearing porphyry are mainly quartz and a small amount of potassic feldspar and mineral alteration are mainly potassic feldspar, andalusite, biotite,phlogopite, muscovite, sericite, rutile, calcite and accessory minerals are zircon, a small amount of apatite, sphene. The Ore-bearing porphyry of NO.? are hornblende quartz diorite porphyry and primary minerals are quartz, plagioclase, hornblende,alteration minerals are mainly green screens stone, chlorite, actinolite, sericite, with minor biotite, potassic feldspar, albite,tourmaline, anhydrite, calcite, accessory minerals are apatite, zircon, a small amount of sphene, ilmenite, magnetite.(3) System to carrying out the mineralogy and mineral chemistry of apatite, rutile,hydrothermal biotite, zircon, chlorite and estimate the rock emplacement depth. The average apatite melt equilibrium temperature of NO.? ore bearing porphyry is1119 ?, the crystallization temperature of rutile is distributed in 622-762 ?, the crystallization temperature of hydrothermal biotites is >500 ?,which reflect the potassic alteration temperature of NO.? ore body is high. The average apatite melt equilibrium temperature of NO.? ore bearing porphyry is distributed in 1150 ?-1160?(average 1155?), the crystallization temperature of amphibole is distributed in 617 ?-849 ?(average 705 ?), temperature span >200. The crystallization temperature of chlorite of NO.? ore bearing porphyry is distributed in 313?-371?(average 332?), which reflect the sodic-calcic alteration temperature of NO.? ore body is high and the crystallization temperature of hydrothermal biotites late pyrite and gypsum is distributed in 200 ?-300 ?, which formed in the late stage of mineralization. ?n addition, quantitative calculation crystallization pressure of NO.? ore bearing porphyry using hornblende aluminum pressure is 0.86 Kbar and emplacement depth is <3.26 km.(4) According to the apatite oxygen fugacity, amphibole oxygen fugacity, the characteristics of mineral assemblage, put forward the magma-fluid oxygen fugacity degree of No.? orebody is low, which is a reduced porphyry Cu-Au deposit and the magma-fluid oxygen fugacity of No.? orebody bearing porphyry is high,which is a oxidation type porphyry Cu-Au deposit. The Mn in apatite oxygen fugacity(logf O2) of NO.? ore bearing porphyry is distributed in-19.21~-16.41(average-17.71), reflect the magma crystallization oxygen fugacity is redox state. A large number hypogenic pyrrhotite formed in metallogenic process, no crystallization of gypsum, the SO3 content of apatite is <0.10%, the ore-forming fluids rich in CH4, N2, etc. organic gases,indicated the oxygen fugacity of magma-fluid evolution process of NO.? ore bearing porphyry are low and the NO.? ore bady is a reduced porphyry copper gold deposit.The Mn in apatite oxygen fugacity(logf O2) of NO.? ? ore bearing porphyry is distributed in-16.46~-10.72(average-12.67), the hornblende crystallization oxygen fugacity(logf O2) is distributed in-15.36 ~-12.70, the SO3 content of apatite is relatively low(<0.10%), reflected the oxygen fugacity of initial magma crystallization is reducing state and when amphibole crystallization, oxygen fugacity is graduallyincreased to NNO between MH oxygen fugacity buffer line, and higher oxygen fugacity make of Cu, Au in the residual phase enrichment. When the temperature,pressure, diagenetic-metallogenic system oxygen state changed or the occurrence of water rock reaction, oxidation states of sulfur translate reduced sulfur, resulting in the precipitation of massive accumulation metallic element.(5) The genetic mineralogical characteristics of the two main bodies are summarized and the evaluation of the ore bearing type based on the altered minerals and the accessory minerals is carried out. Two ore bearing porphyry discovered in Xiongcun district. The mineralization and mineralogical characteristics show difference in different bearing porphyry. The NO.? ore bearing porphyry have large amount of rutile, biotite, andalusite, A small amount of apatite. The rutile content of V2O5 high(average of 0.42%), big grain( long×wide more than 4500?m);hydrothermal biotites formed high temperature(>400?) and with rich magnesium,potassium, poor in calcium, high F characteristics; the Mg/Fe is 0.92~9.62, K/Na average 48.15, Ca O<0.10%, F>0.79%, indicating the high grade copper mineralization of quartz diorite porphyry. The NO.? ore bearing porphyry have a lot of chlorite, epidote, actinolite, apatite, and no rutile; high oxygen fugacity(logf O2=-15.36 to-12.70) of amphibole crystallization; high temperature of chlorite crystallization(313?-371?); chemical zoning in tourmaline and Mg/(Mg+Fe) and Cu, Au negative correlation, Fe and Cu, Au positive correlation can be used to indicating mineralization characteristics and prospecting for mineral deposits. |
PDF Full Text Request