Microscopy of gold ores and treatment products

Gold minerals and especially native gold can generally be identified very well by ore microscopy because of their distinctive optical properties. Nevertheless gold microscopy has its peculiar difficulties. Above all ranges the usually low gold content of the ores, which makes it often hard to find any gold in polished section. This can often be achieved only after time consuming studies of several sections. Another complicating factor consists in the frequently small sizes of gold particles, which require the use of high magnifications.

Gold tends to show an irregular distribution in the ore. This is the case on macroscopic and even more so on microscopic scale. The fact that gold cannot be detected in the very first section of an high grade ore must not lead to the conclusion that it occurs in a submicroscopic form, e.g. in sulphides. Once detected we shall find that there are local concentrations or clusters, often in association with specific properties of the ore such as siliceous or ferruginous parts or in zones of microfracturing. These environments can be looked after in order to observe microscopic gold more easily. If, however, no gold minerals can be found after the study of a reasonable amount of sections, electronoptical and microanalytical investigations should be considered. By using these tools submicroscopical or chemically bonded gold will generally be detected.