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安徽金寨沙坪沟斑岩钼矿床是目前秦岭-大别钼成矿带中已探明储量最大的钼矿床.矿区侵入岩发育,岩性多样.锆石U-Pb同位素年龄表明均形成于燕山期,可分为早晚两期.本文以与钼成矿关系密切的第二期侵入岩为研究对象,通过侵入岩的精细显微岩相学观察和研究发现,属同源岩浆并经历相似演化历史的石英正长岩和花岗斑岩却先后结晶出两种相态的石英,石英正长岩中只产出他形的α相石英,花岗斑岩中结晶自形六方双锥的假β相石英斑晶,后者为β相石英相变而来的α相石英,但保留β相石英假象.结合锆石Ti温度、石英P-T相图和中酸性侵入岩Q-Aβ-Or-H_2O相图,认为石英正长岩和花岗斑岩具有较大的岩浆起源深度和相似的成岩温度,而石英正长岩中的α相石英反映其侵位结晶压力大于0.7GPa,花岗斑岩中的原始β相石英反映其结晶压力约为0.4~0.7GPa,花岗斑岩中随后结晶的基质则反映其形成压力小于0.05GPa.这一结果表明,花岗斑岩形成于至少两次快速减压作用之下,而这种减压作用对于岩浆-流体过程中成矿流体出溶、沸腾及矿质卸载和沉淀意义重大.花岗斑岩中β相石英在成岩之后的相变过程会产生体积差,可致使斑岩体及其围岩发育裂隙,这些裂隙是良好的导矿和容矿构造,有利于斑岩型矿床的热液蚀变和网脉状-浸染状矿化.可以认为,斑岩体中假β相石英斑晶是斑岩型矿床的成矿标志之一,其反映斑岩型矿床成矿系统通常形成于减压应力状态的构造背景中.
The Shapinggou porphyry molybdenum deposit in Jinzhai, Anhui Province is the most proven molybdenum deposit in the Qinling-Dabie molybdenum metallogenic belt at present. The intrusive rocks in the mining area are developed with various lithologies. The U-Pb isotopic ages of zircons are all formed in Yanshan Period, which can be divided into two phases in the early and late stages.According to the microscopic petrologic observation and study of intrusive rocks, the second phase intrusive rocks that are closely related to molybdenum mineralization are studied, and belong to the same magma and undergo similar evolution The historical quartz syenite and granite porphyry have successively crystallized two phases of quartz. Only quartz-like α-phase quartz is produced in the quartz syenite and the crystallized self-forming hexagonal double cone in the granite porphyry β -phase quartz porphyry, which is α-phase quartz transformed fromβphase quartz, but retains βphase quartz artifacts.Combined with zircon Ti temperature, quartz PT phase diagram and intermediate acid intrusive rock Q-Aβ-Or-H 2 O Phase diagram shows that quartz and granite porphyry have a large depth of magma origin and similar diagenetic temperature. However, α-phase quartz in quartz syenite reflects that the emplacement crystallization pressure is greater than 0.7 GPa, and granite porphyry In the original β-phase quartz reflects the crystallization pressure of about 0.4 ~ 0.7GPa, granite porphyry subsequently crystallized The results show that the formation pressure is less than 0.05 GPa. This result shows that granite porphyry is formed under at least two rapid depressurization processes, and this depressurization has an important effect on the dissolution and boiling of ore-forming fluids during magmatic-fluid processes And ore unloading and precipitation is of great significance.P-phase quartz granite porphyry in the diagenetic phase transformation process will have a volume difference, can cause the porphyry and its surrounding rock development of cracks, these cracks are good guide ore and ore Tectonism is favorable for hydrothermal alteration and reticulation-disseminated mineralization of porphyry deposits.It can be considered that pseudo-β-quartz quartz porphyry is one of the ore-forming markers of porphyry deposits, which reflects Porphyry metallogenic systems are usually formed in the tectonic setting of stress-relief state.