Abstract:

 This paper discusses the cooling process of magmatic rock mass during the formation of the skarn and skarn deposits in contact zone and their coupling conditions, taking the Tonglüshan CuFe deposit as an example. The host rocks of Tonglüshan ore body are quartz monzodiorite porphyry and the Lower Triassic Daye Group carbonate rocks, which are in the contact zone with the form of peninsular and islandchainlike residues and xenoliths. The ore body and skarn are closely coexisting. The contact boundary lines among main ore body, skarn, magmatic rock mass, carbonatite, and other ores are generally distinct.  On the basis of a large number of field observations and comprehensive study of existing data of the tectonic setting of intrusions and ore bodies, and considering the facts that the carbonatite residues were in peninsular or islandchainlike forms and the xenoliths were at a stable and closed state in a period after the consolidation of magma, we put forward a concept of cooling shrinkage lowpressure area. We pointed out that  a cooling shrinkage lowpressure area system was formed when the condensation shrinkage after the consolidation of magma was taking place, and the fluids were continuously gathered together and preserved in this area for a long time. The coupling of this cooling shrinkage lowpressure area system with the postmagmatic hydrothermal fluids presented an appropriate condition for the formation of skarn and skarn ore deposits, leading to the occurrence of the Tonglüshan deposit.

Key words: cooling shrinkage lowpressure area, supercritical fluid, critical transition, skarn, skarn ore deposits, Tonglüshan, Hubei Province