斑岩型钼矿床研究进展与问题

Advances and Problems in Study of Porphyry Molybdenum Deposits

本文在简要介绍全球重要成矿带斑岩型钼矿床品位、储量、时空分布以及构造背景的基础上,着重归纳了斑岩型钼矿床中Mo在岩浆—热液演化过程中的地球化学行为特征以及Mo在成矿流体中的迁移与沉淀机制两个方面的研究进展。取得了以下认识:形成斑岩型钼矿床成矿岩浆氧逸度(f_(O2))变化范围较大,但一般大于铁橄榄石—磁铁矿—石英(FMQ)缓冲体系。斑岩钼矿床形成的主要受岩浆房的大小,大体积的岩浆流体能否高效聚集到浅部岩株或岩脉,岩浆中的挥发分(例如F)含量等因素的控制,但与成矿花岗岩和出溶流体中Mo的含量高低无直接关系。成矿流体的氧逸度与p H降低对辉钼矿沉淀具有关键作用。除此之外,温度与盐度降低对辉钼矿沉淀也有重要作用。流体的多阶段沸腾可能对提高Mo品位具有重要意义。此外,应加强岩浆结晶分异过程、岩浆热液转化过程Mo的地球化学行为研究。

Based on the brief introduction of characteristics of Mo grade, reserve, temporal and spatial distribution and tectonic setting on porphyry type of Mo deposits in this study, we focus on two aspects, the first is the geochemical behavior of molybdenum in the process of magmatic--hydrothermal evolution, the second is the precipitation mechanism of molybdenum. We propose that the oxygen fugacity of ore-forming magma from porphyry Mo deposits varies in a relatively wide range, but it is commonly higher than FMQ （fayalite--magnetite--quartz） buffer system. Furthermore, the formation of porphyry Mo deposits depend on many factors such as an enormous magma chamber, the concentration of giant-volume fluid in a small and shallow magmatic rock and the relatively high content of volatile in magma et al. Whereas it has no relationship with the Mo contents of ore-forming magma and initial fluids. In the ore-forming fluids, the decrease in oxygen fugacity and/or pH plays a vital role in the precipitation of molybdenite. Moreover, the temperature and salinity reduction also contributes to molybdenum deposition. In addition, multistage fluid boiling can be very important for enhancing molybdenum grade. Apart from hydrothermal stage, the studies in the process of magma crystallization differentiation and magmatic--hydrothermal transition should be strengthened.