Origin Of Ore-host Fault System In Huangsha Tungsten Vein Deposit, Southern Jiangxi Province

The vein-type tungsten ore deposit in southern Jiangxi Province exhibit unique"five-storeyed type"morphological vertical as well as horizontal zonality (from top to bottom: thread-vein zone, veinlet zone, thin-vein zone, big vein zone and thinning-out zone).So far the research on the host structures in the vein-type tungsten ore deposits in southern Jiangxi Province has been focused largely on the control of the evolution of the regional structures, and rarely touched upon the important role played by granitic magma and the associated postmagmatic processes. This paper takes the belt of the Bajaoken Group ore vein as major object for studying the mechanisms of formation of the"five-storeyed type"morphological zonality by synthetic approach of combining laboratory experiments and field observations with theoretical analysis,the following results are obtained.Granite is the ore-forming parent rock; it is intimately related with the ore deposit in time, space and composition. The ore deposit is the product of deuteric solutions derived from magmatic crystallization. Judging from the emplacement of granitic magma, the lateral zonality of altered wall-rocks and the thread veins forming under high temperatures, it is highly probable that the mineralizing fluid in the early stage might evolve from supercritical fluids.The system of host structures is situated locally above the granitic rock body and distributed radially like branches of a tree. The ore belt shows conspicuous vertical and horizontal zoning which is not in harmony with regional structures. The distribution of ore-bearing quartz veins in the ore region, the internal structures of single quartz veins and the extremely high pressures of the mineralizing solutions all demonstrate that the host structures belong to hydraulic fracturing.It is well-known that the Kaiser effect of acoustic emission of rocks records the times of paleostructural activities. Detection by acoustic emission for samples taken from country rock of veinlet zone and big vein zone as well as granitic rock body shows that 4, 8 and 4 times of paleostructural activities occurred respectively, corresponding to the three zones. The 4 times of paleostructural activities presented by the country rock of veinlet zone and the granitic rock body having maximum values of principal stress equivalent to the modern geostress indicate that they represent regional paleostructural activities. The sample from country rock of big veins shows 8 times of paleostructural activities, among which 4 times (with smaller maximum values of principal stress) are consistent with that of country rock of veinlet zone and the granite, therefore they reflect the post-metallogenic regional paleostructural activities. The other 4 times of paleostructural activities occurred in country rock of big-vein zone corresponding to maximum values of principal stress equal to the extremely high pressures of mineralizing fluids most probably reflect the times of activities of hydraulic fracturing favorably for ore formation.In short, the genetic nature of host structures in the Huangsha vein-type tungsten ore deposit belongs to hydraulic fracturing, and the times of hydraulic fracturing is four which is consistent with the number of mineralizing stages of ore formation.