Relationship Between Intermediate-acid Dike Rock And Gold Mineralization Of The Zaozigou Gold Deposit, Gansu Province

Western Qinling is one of the important gold deposit areas of China, the time-spacedistribution of mineral resources within the areas has the characteristics ofdistribution into groups and belts. Zaozigou gold mine located in the Xiahe-Hezuo oreconcentration area of gold, with proved gold resources over150tons ending December2012,is a king-size gold deposit in the Western Qinling Belt.The Zaozigou mining area’s primary stratum are the fine-grained clastic rocks (part hasmetamorphosed to slate) intercalated with limestone of the Middle-Triassic Gulangdiformation and intermediate-acid dike rock. The exposed dikes, accounting for30%of the totalmining area, are mainly controlled by the NEE. There are many Mesozoic granitic intrusivemass around the mining area, which are dominated by Meiwu, Dewulu, Ayishan Pluton andlots of intermediate-acid dike rock. The gold ore bodies controlled by the NE, NW, NS andEW are hosted in the slate and porphyrite dikes, The mineralization styles of the Zaozigougold deposit can be classified into porphyry type and quartz-vein type: former’s ore mineralincludes gold+pyrite+arsenopyrite and little chalcopyrite, galena etc., with the pepper-and-saltand veinlet-disseminated structure; the latter’s ore mineral is the gold+stibnite, massivestructure. Under the effect of regional tectonics and multi-periods hydrothermal activity, orewallrock alteration mineral is heterogeneous which has no obvious zoning. From the faultzone or the contact zone between dikes and sedimentary stratum to the sides, the alterationgrows gradually weaker and the gold values also declines, showing the strong correlation.Evidences from the geological and geochemical characteristics of the deposit, rareelements and the stable isotope elements(H, O, S, Pb)etc. indicate that the closerelationships between ore-forming event and diorite-porphyrite. Porphyrite dikes andmineralization are all the serial tectono-magmatic evolutionary products of regional crust andmantle-crust interactions, thus, associating each other in time and space. Since the mineralsubstance of porphyrite dikes is not enough to form so large-scale gold mine, the ore fluid,sulphur and metallic substance are considered to be homologous with the porphyrite dikes. Most of the mineral substance originate from the under batholith which is the source ofporphyrite, and then transport to the shallow porphyrite dikes or the broken-rock zone. Bothof them have the same souce and genetic development.The forming age of (quartz) dioritic porphyrite which have the relation of mineralizationis about216Ma, which is a little later than the granitoids of Xiahe-Hezuo ore concentrationarea and belongs to the later Indosinian. It is obvious that the Indosinian movement of Qinlingorogenic belt, especially the magmatic activity and metallization of the later Indosinian’s post–collisional extensional stage. The quick changes of stress during the extensional stage causethe upwelling of asthenospheric and deep material. Isotopic information indicates that theore-forming process of Qinling is the migration of mantle material. It is advantageous for themineralization in the exchange and recycling of the material and heat from the upper mantle.The achievement which has been made shows that the western Qinling regional mainmetallogenic epoch is the Indosinian, and based on the phenomenon that the age of porphyrytype deposit’s forming age is a little later than porphyry’age or synchronous, indicating thatthe Zaozigou gold deposit was formed during the end of Indosinian and there are hugepotentials within the western Qinling orogenic belt for prospecting porphyry gold deposit ofthe end stage of the Triassic post-collisional extensional environment.Based on the above studies, the metallogenic evolution model of Zaozigou gold deposithas been preliminary established. The minerals dicovered within the exploration areas arelocated in the top position of porphyrite dikes, which indicates the bright prospect of the deepareas.