Geological characteristics and genesis of the Linxiang gold deposit in southern margin of the Zhenxun Basin
The Linxiang gold deposit is a typical fine disseminated gold deposit in the southern margin of Zhenan-Xunyang Basin,South Qinling.The distribution of its orebody is controlled by the EW trending fault,which occurred in the spotted phyllite of the Lower Devonian Xichahe Formation and the limestone interlayered with phyllite of the Middle Devonian Yanglinggou Formation.The ore genesis of Linxiang deposit remains controversial due to the inconsistency of ore-forming materials,and related viewpoints about its mineralization include hydrothermal sedimentation and later hydrothermal superimposition on an exhalative sedimentation.In this paper,pyrite and native gold in the Linxiang gold deposit were studied by in situ EPMA and LA-ICP-MS analysis of sulfur isotopes and trace elements,aiming to discuss the occurrence of gold,define the source of ore-forming materials and the genesis of the deposit.The results show that the gold in the Linxiang gold deposit is mainly composed of fissure gold and inclusion gold,with a little of micro-nano gold(Au0).The sulfur isotope in the Ⅱ mineralization stage ranges from 16.28‰ to 17.84‰ with an average value of 16.91‰;the sulfur isotope in the Ⅲ mineralization stage ranges from 15.19‰ to 15.68‰ with an average value of 15.51‰,which is similar to those in the Jinlongshan Carlin-type gold deposit.The metallogenic stage has the characteristics of stratigraphic sulfur,while the later stage has the mixture of magmatic sulfur.From the Py Ⅱ-Ⅲ stage,the Au,Ag,Cu,Pb,Zn,Pb,Bi and other ore-forming elements all showed increasing trends,while the content of As showed a decreasing trend,and the content of Co and Ni increased slightly.PyⅡCo/Ni ratios varied greatly,which may be related to the recrystallization of pyrite;and this value of most of PyⅢ was above 1.00,demonstrating that it is hydrothermal pyrite.The correlation between different elements is quite different,the ore-forming fluid is a mixed source,and it is speculated that it may be disturbed by magmatic hydrothermal events in the late main ore-forming stage.The loss of CO2 and the addition of CH4 in the gaseous components of the fluid inclusions in the main mineralization stage indicate that the fluid is immiscible.As a preliminary result,the Linxiang gold deposit is formed by the extraction of gold from minerals during the upward migration of atmospheric precipitation and metamorphic fluid along the tectonic fissure;the fluid immiscibility in the favorable part of the mineralization led to the precipitation of ore-forming materials,and the addition of magmatic hydrothermal fluid in the later period led to further enrichment of ore-forming materials.
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