On The Metallogenic Mechanism And Model Of The Ashele Volcanogenic Massive Sulfide Copper Deposit, Xinjiang

The Ashele copper deposit in Xinjiang is a newly found marine volcanogenicmassive sulfide deposit in China. This dissertation for PH. D degree studies onthe metallogenic mechanism and the metallogenic model and some basic geologicalproblems related to mineralization, based on data of volcanic petrology, oredeposit and geochemistry and so on. A few of new results are followed as:1. Volcanic rocks in the Ashele mine are characterized by interbedded basic andacidic pyroclastic rocks, and made up typical bimodal pattern according togeological features and lithochemistry;2. The setting of rock-forming and ore-forming is of rifting. The distinctive features of volcanic rocks, especially the spilite, illustrates that mantle plumeor hotspot with small scale might be the essential origin of a series geologicevents such as the extension of crust, the interval eruption of submarine bimodalvolcanic rocks especially the increasing eruption of basic rocks, and theminerallization of Ashele mine;3. The characters of mineralization zones in the Ashele mine, mainly the No.1ore deposit, have been studied detailly; the orebody pattern(sedimental beddedores combined with stringer ores of hydrothermal origin) is also outlined; fourmetallogenic epoches are devided; the zoning of mineralization(including zonesof ores, elements, mineral assemblages and temperature of mineralization)have beendepicted; the main types of wall-rock alleration are characterized aspropylitization of basic rocks and pyritization-sericitization-silicification ofacidic pyroclastic rocks; the origin of ores and seven kinds of main mineralshave been studied; and the metamorphism and deformation of orebodies is thoughtmainly due to the shearing and the intrusion of subvolcanic rocks;4. The reserach of the distribution of copper and other metallogenic elements inorebodies and hostrocks demonstrates that the spilites of the Ashele Formation ofearly-to middle Devonian are the source of the Ashele copper deposit. Thesignificance of the low-sodium halo of sodic hostrocks to exploration andtheoritic research has been emphasized in this paper and published recently. Thestudies of siticeous rocks and iron-cherts show the evolution of the environmentof rock-forming and ore-forming. The geochemical studies of ore-forming fludies,lend and sulfur isotopes outline the genetic differences between the No.1 orebodyand the No. 2 orebody, and demonstrate further that the basic rocks are differentfrom the acidic rocks originally and that spilite is the source rock of metalelements but sulfur is mainly contributed by exhalation related to acidicvolcanosm;5. Disscussed the relationships between rift and copper deposits and therelationship between volcanism and ore-forming, and concluded that the Ashelemassive sulfide copper deposit is not only controlled by rifting environment butalso by the bimodal volcanic rocks of early-to middle Devonian. Themineralization parameters of physical-chemical condition have been calculatedbased on equilibrum analysis. The unique character of the Ashele copper deposit isgranted by comparing with other types of volcanogenic massive sulfide depositsuch as the Cyprus type, the Besshi type, and the Kuroko type, helping toestablish the descriptive model and the genetic model. The metallogenic mechanismhas been studied and the evolution of rifting-magmatism-mineralization has beenconcluded also;6. Finally, this paper inquires into the mechanism of exhalation and enrichmentof metal elements in a brine pool, interpretes the origin of zoning of massivesulfide deposits from a new point, and designs a chemical-dynamic model for theformation of massive sulfide deposits with different sources of metal elementsand sulfur in an open system or environment.