The Characteristics Of Illite In The Sinongduo Low-sulfide Epithermal Deposit,Tibet

The epithermal deposits are one of the important types of metal deposits in the world.Many porphyry deposits and skarn deposits haven been found in the Gangdis Metallogenic Belt,However,researches which focus on the epithermal deposits are quiet few.The Sinongduo deposit was the first low sulfidation epithermal deposit which is found in Gangdis Metallogenic Belt.It is found that there is a certain spatial coupling between distribution of illite and the ore-hosted situation of low-sulfide epithermal deposit.As a result,On the basis of microscopic examination,shortwave infrared technique,X-ray diffraction analysis,electron microprobe analysis?EPMA?,this study chooses the Tibetan Sinongduo low-sulfide epithermal deposit as the research object,conducting research on the distribution,content,chemical composition and spectral features of illite minerals in low-sulfied epithermal deposits so as to obtain the mineralogical characteristics of illite as an indicator for low sulfidation epithermal deposit.1?The SWIR mineral spectral information provides geological insights into three sides:?1?Sericite,illite and montmorillonite are the main alteration minerals in the Sinongduo deposit;?2?Along the NE direction,Overall formed the features of mineral assemblage is as follows:Sericite?less kaolinite and illite??Sericite+illite+Montmorillonite?illite+Montmorillonite+Sericite?fewer?.In vertical direction,formed the features of mineral assemblage is as follows:Sericite?illite??illite+Montmorillonite?paragonite??Sericite?Sericite+illite?Montmorillonite??Sericite?Sericite+illite?Sericite?illite?;?3?The ore body mainly occurs in Sericite+illite+Montmorillonite alteration zonation of epithermal deposit,and IC of illite has a certain regularity.2?Under the microscopic mineral identification,the illite structure has been found such as flake,scale and rod aggregates.It coexisted with sericite,feldspar and montmorillonite.There are two main forms of illite minerals in the Sinongduo deposit:?1?Illite metasomatic sericite and feldspar;?2?Development of illite veinlets along with structural fractures.3?Through the study of illite mineralogy by X-ray diffraction spectrum,it is found that:?1?Illite minerals are mainly distributed in mineralized districts of cryptoexplosive breccia type and illite-montmorillonite mixed-layer minerals are mainly distributed in mineralized districts of hydrothermal vein type;?2?The mineral content of the illite-montmorillonite mixed-layer decreases gradually from the far end of the ore body to the proximal end in mineralized districts of hydrothermal vein type;?3?The mean value of Kübler is 0.288 in mineralized districts of cryptoexplosive breccia type,and is 0.320 in mineralized districts of hydrothermal vein type,which show that illite Crystallinity in mineralized districts of cryptoexplosive breccia type is better than in mineralized districts of hydrothermal vein type.In vertical direction,Kübler index decreasing from surface to depth in the far end of the ore body?BZK1301?BZK2901?,but had no obvious change in the proximal end of the ore body?BZK0022?,Which is show that the enrichment of metallogenic elements affects the formation and distribution of illite minerals;?4?There is a certain correlation between the crystallinity KI value of illite and ore body grade,The KI value of illite crystallinity is proportional to the Zn mineralization grade and inversely proportional to the Pb grade at shallow part of the drilling?<120m?,The change of KI value of illite was inversely proportional to the change of Pb and Zn grade in deep?>120m?.4?Through EPMA analysis,It is found that:?1?The proportion of contents of major chemical components of illite mineral is:Al₂O₃33%—36%,Si O₂48%—53%,K₂O 6%—10%;?2?The K⁺content of illite near the ore body is 0.76,which shows the characteristics of the charge enrichment between illite layers near the ore body.The K⁺content of illite at the far ore body end is 0.56,which is lower than the lower limit of the interlayer K⁺content of 0.6 standard,reflecting the characteristics of interlayer charge loss of illite at the far ore body end in Sinongduo deposit.