Study on Stable Isotopic Characteristics of the Hongyuntan Iron Deposit of Eastern Tianshan and Their Implications for the Process of Mineralization

The Hongyuntan iron deposit in Qoltag area of Eastern Tianshan in Xinjiang has long been believed to be a marine volcanic type deposit.The metallogenic mechanism of this type deposit has been regarded as the enrichment of the early formed ore source bed by the later hydrothermal metasomatism.According to the study of stable isotopic characteristics of this deposit,a new opinion is proposed in this paper:Hongyuntan is a pyrometasomatic deposit,which was formed by the superimposition of the later focal skarnization of special volcanic rock sequence upon early extensive alkali metasomatism.The process of the mineralization can be divided into five stages:the formation of special volcanic rock sequence,alkali metasomatism,skarnization,production of magnetite and deposition of quartz and sulfide.During the process of the mineralization,the ore-forming fluid evolved continuously:at the stage of the formation of the quartz in Hongyuntan magmatic rock,the mixture with low D value fluid caused the depletion of 2H in the fluid which produced the quartz;in the course of the massive production of magnetite,the addition of low 18O fluid resulted in the depletion of 18O in the magnetite;during the deposition of massive quartz and sulfide,the ore-forming fluid inherited not only low σD but also low σ18O features,and thus the fluid differed from both magmatic fluid and metamorphic fluid.