块状硫化物矿石中硫化物的压溶和增生及成矿意义——以加拿大西部矿床为例

Pressure Solution and Overgrowth of Sulphides in Massive Sulphide Ores and Their Metallogenic Significance: Exemplified by Deposits of Western Canada

加拿大西部块状硫化物矿石普遍地发生过硫化物的压溶和增生。增生作用根据增生体的成分可以分为同质增生和异质增生 ,根据动力环境可以分为静态增生和动态增生。三晶嵌接结构可以是静态增生的产物。压溶和增生是块状硫化物矿床成岩和变质过程中的重要作用。脉石矿物的压溶可使原生矿石就地加富 ,硫化物的压溶可使成矿物质发生再活化。增生可促进矿质沉淀。富含硫化物的地层之所以能成为地球化学障而有利于后期热液叠加和层控矿床的形成 。

The Faro and Tom deposits in the Selwyn basin and the Cirque and Driftpile deposits in the Kechika Trough of western Canada are massive sulphide deposits occurring in Cambrian phyllites (Faro) and Devonian marine clastics, black shales and carbonates(Tom, Cirque and Driftpile), respectively. Sulphide minerals as well as gangues in these deposits have suffered intense pressure solution, and the sulphides have undergone multi_stage overgrowth. Overgrowths can be divided into syntaxial and antitaxial ones based on the compositions of overgrown minerals, or into static and dynamic ones based on the environments for overgrowth processes. Triple junction textures can also be formed under the condition of nonorientable stress, and hence are not unique products of annealing equilibrium. Pressure solution of gangue minerals will raise the ore grades, and can hence be applied to account for the appreciably higher metal quantity in ore mylonites than in surrounding massive ores within some deposits. Pressure solution of sulphide minerals will induce remobilization of metals, which are likely to be precipitated in other locations to form new orebodies. Overgrowth is capable of facilitating the unloading of ore materials from fluids. The overgrowth of sulphide crystal seeds is a possible mechanism for sulphide_bearing strata to act as geochemical barriers, which will be overprinted preferentially by late_stage fluids to produce stratabound mineral deposits.