THE FRACTURE OVERLAPPING-COMPOUNDING CONTACT ZONE AND ITS CONTROL ON THE FORMATION OF HYDROTHERMAL FLUID-FILLING DEPOSITS

The fracture overlapping-compounding contact zone formed by superimpo- sition of fractures on the primary contact zone is a complex structural fra- ctured zone and usually also an ore-controlling structural zone. It often exhibits the features of polyphase activity and is of compressive （-shear） nature in the early stage and tensile nature in the late stage. Like hydrothermal alteration and mineralization, tectonic breccias of tensile origin in the late stage often exhibit distinct localized features throughout the zone, and the three often overlap each other in the same place. The shape of the orebody in a hydro- thermal fluid-filling deposit controlled by this zone is defined by the anato- mosing into a complex network of several veinlets of different attitudes, stages and generations and mechanical nature; so ore-accomodating structural space of this kind of deposit is not a general simple fracture space of tensile origin. In regard to the basic characteristics of the fracture overlapping-compo- unding contact zone and the hydrothermal fluid-filling deposits controlled by it, experiments by the clay model and photoelastic method were performed, and the process of its formation and evolution and mechanism of deformation, pa- rticularly the formation of the ore-accomodating structural space, are discussed in detail. From the above studies, the authors come to know that the formation of the tectonic breccias, hydrothermal alteration, mineralization and ore-acco- modating structural space locally occurring within the zone is all related to the polyphase activity of the zone and its special boundary conditions, and contro- lled by the mechanism of "rejuvenation" proposed by the authors, whose co- nnotation is different from that of general "rejuvenaion". On the basis of the above-mentioned theoretical analysis combined with the case histories of some ore deposits, the authors sum up some lawns governing the localization of the orebodies of the kind of deposit.