八方山大型多金属矿床热水沉积岩相特征与矿化剂组分关系

陕西八方山大型(金)多金属矿床赋存在于中泥盆统吉维特晚期的热水沉积岩相中。富SiO2酸酐型热水同生—交代沉积作用形成热水同生沉积微相(层状硅质岩)、热水同生交代微相(微晶石英岩及硅化灰岩);富Fe^2 - Mg^2 碳酸盐型热水同生沉积作用形成层状含铜硅质铁白云岩;在同生断裂附近,因热水液压致裂-隐爆作用形达含铜黄铁矿硅质铁白云石角砾岩;富Na^ 铝硅酸盐型／富Fe^2 、Mg^2 碳酸盐型热流体在同生断裂中形成热水充填微相(穿层脉状钠长石碳酸岩);低温热卤水(富F、Ba、B、As、Sb)形成热卤水同生沉积微相。矿质大规模沉淀的地球化学动力学因素为：在热水沉积成矿盆地中,在单一成分热水体系的温度、压力改变而发生快速化学沉淀;不同成分、性态的热水混合后,强烈的酸—碱作用及Eh-pH剧变等,触发热水体系失稳,引起矿质大规模沉积。[SiO2]和F可能是重要的矿化剂。

CHARACTERISTICS OF HYDROTHERMAL SEDMENTARY FACIES IN RELATION WITH MINERALIZER IN BAFANGSHAN POLYMETALLIC DEPOSIT

The Bafangshan polymetallic deposit occurs in the Middle Devonian Fengtai apart pull basin. Based on its sedimentology, mineralogy, petrology and geoc hemistry of the deposit, the geological geochemical characteristics of hydrothe rmal facies are described. Six patterns of these hydrothermal lithofacies were d efined, i.e., hydrothermal syn sedimentation microfacies, hydrothermal syn sed imentation replacement microfacies, mixing hydrothermal syn sedimentation micr ofacies, hydrothermal explosion and fluid pressure fracturing microfacies, hydr othermal filling replacement microfacies and hot brine syn sedimentary microf acies. Silicates with (FeO+Fe 2O 3+MgO) accounting for less than 10% and SiO 2 >70% may have resulted from hydrothermal syn sedimentation. Siliceous fer rodolomitites with (FeO+Fe 2O 3+MgO) accounting for more than 20% and SiO 2 30% to 50% were also derived from hydrothermal syn sedimentation in the subbas in. Ferrodolomitites were produced by Fe Mg Ca rich carbonate type hot water . Polymetallic ores were accumulated as a result of mixing of different componen ts. Ore forming materials were deposited in response to extensive chemical reac tions. F and [SiO 2] in hydrothermal fluids could serve as the mineralizers m ainly responsible for the transport of metallogenic materials.