Comparative Study Of Typical Porphyry With Geological Characteristics And Geochemical Characteristics In Yidun Island

"Sanjiang" area is one of the world’s most complex orogenic belts, both experienced theTethyan tectonic evolution, Indian-Eurasian plate collision and strong transformation of plateauuplift, This area has complex geological structure, strong magmation, active ore-forming fluid andcomplicated mineralization.Located on the eastern edge of Tibetan plateau, due to the interaction of the Indian plate, thePacific plate and the Eurasian plate, western Sichuan shows significant complexity and diversityon the geological structure. Its unique and intense tectonic evolution-magmatic activity created avery favorable and specific metallogenic geologcial environment, making it an importantmetallogenic province.Preliminary studies in recent years show that Chang Tai-Xiangcheng is an important arc withCu-Pb-Zn-Ag polymetallic metallogenic belt, which is a complete metallogenic series from thesouth to the north, namely, genetic type from porphyry-type to subvolcanic-type and thenhydrothermal-type; combination of metallogenic elements from the copper polymetallic depositsto Cu-Zn polymetallic deposits and then Ag-Pb-Zn-Au polymetallic deposits; metallogenictemperature presenting significant downward trend from the south to the north. These regularitiesare remained to be deepen, especially it is essential to determine the mineralization andmineragenetic epoch through analyzing typical deposits.According to author’s research, some proporties of the granite in western Sichuan are similarto the adakite, which presents a strong exploration potential. The existing datum on western areagranite are not many, while tectonic activities are extremely intense and complicated in Yidunisland arc. Based on the diagenetic period result, the porphyry in western region are produced inIndo-Chinese epoch, not Yanshanian which is same with the other porphyry such as the southernsection of the Pulang porphyry and Xuejiping porphyry. It is the approximate diagenetic period ofthe southern and the northern Yidun island arc area that presents Changdagou deposits in thenorthern of Yidun island arc is Indo-Chinese epoch porphyry copper deposits, so do Pulang andXuejiping copper deposits in the southern Yidun island arc. In a way, the microscopic geologicalconditions to form porphyry copper deposits exist in the northern of Yidun island arc. In addition,characteristics of the porphyry in the whole Yidun island arc belt are same which indicates thatthere’re huge potentials for prospecting porphyry copper deposits in the north of Yidun island arc.However, there’re some doubts that whether the formation of Changdagou porphyry copper andsurrounding rich ore porphyry are related to some special geological events.Yidun island arc regions may exist symmetric distribution pattern of metal deposits whichfrom the north to the south is porphyry deposits–subvolcanic deposits-VMS-type deposits-subvolcanic deposits-porphyry deposits. But why symmetric phenomenon appears both in the north and the south different type deposits in Yidun island arc area? Hou ZQ believed that Yidunisland arc experiences once subduction motion while Li WC thought Yidun island arc experiencestwice. But author doesn’t think that these two theories gave good explanations to the depositsdistribution regular in Yidun island arc area. If once subduction motion results in once magmatism,what is the cause that the structure metallogenic environment of north-south and central are not thesame? If twice subductions result in twice magmatism, how to explain the symmetrical mineraldistribution phenomenon? Here the author offers a hypothesis that no matter how many times itdive, functions of some tectonic environment leads to dive angle, then brings about pressed arcenvironment in the northern area and the southern area and extensional environment in the centralregions. This series tectonism may explain the special deposits distribution in Yidun island arc.This kind of explanation is just an assumption without abundant proofs to prove that how can thefactors such as tectonic environment affect the metallogenic regularity in Yidun island arc.Moreover, Changdagou is the unique typical porphyry copper deposits in western Sichuan withoutwidely representative.Whether the western area has the macro geological conditions and the environment to formporphyry copper is the uppermost research questions in this article. After comparing the porphyryboth in the western area and the southern section of Yidun island arc through tectonics, formingtimes, petrology and geochemical, etc., typical porphyry characteristics are comprehensiveanalyzed in Yidun island arc, and mineral resources potentials and prospecting targets areevaluated in the work area. This article gives suggestions to mineral resources evaluation andoffers some new questions, assumption and direction for the future work.