Trace Element Geochemistry Characteristic Of Pyrite And Its Significance For Deposit Genesis From The Dongguashan Copper-gold Deposit In Tongling,Anhui

Dongguashan deposit is located in the depth of Shizishan ore fields in Tongling (AnhuiProvince) ore cluster region of the middle and lower Yangtze iron copper sulfur goldmetallogenic belt. It is a large copper gold deposit closely related to yanshan periodmagmatism with the structure in intersection of subprime anticline nuclear department fromTongling Shunan double syncline and Baocun Houshan Qingshan EW basement tectonics.In consideration of its unique geological characteristics and important economic value,many scholars have done extensive and in-depth research on the genesis for a long time.But there have not been unified understanding, whether there is born with sedimentarymineralization in the Carboniferous, or the Carboniferous born with deposition and yanshanperiod magmatic hydrothermal role in the process of deposit formed in contributionsmainly diverge. Therefore, further understanding of ore deposit in the region and todetermine the source of ore forming materials and the genesis have important theoreticalsignificance and practical value.Based on a comprehensive understanding of regional geological background andDongguashan deposit geological characteristic, this paper selected pyrite, which was themain ore mineral of the deposit to carry out rock observational study more deeply, and alsoused the theory of trace element geochemistry and LA ICP MS to analyze thecharacteristics of trace elements. Besides, the author combined with the results of previousstudies to investigate the source of ore forming fluids and ore genesis. According topetrography observations, Dongguashan ore deposit could be divided into colloidal pyriteand granular pyrite. The colloidal pyrite had laminated and hull like structure, some wereformed into fine grained texture by the late metamorphic recrystallization ofQuartz calcite veins. Granular pyrite often coexisted with pyrrhotite, showed aseuhedral-semieuhedral, medium fine grained texture. Analysis results and the data castfigure showed that colloid form pyrite and ballbraincd pyrite had different trace elementscomposition features, the former is poor in Co but rich in Ni, the later is opposite to theformer. In Co Ni content relationship chart, colloid form pyrite mainly distributed inmagma province and hydrothermal area,∑REE was lower in the two type pyrites, but the colloid form pyrite was a little higher than ballbraincd pyrite. According to this study, it isregarded that colloid form pyrite was formed by submarine syngenetic deposition, butdidn’t exclude the possibility of magmatic origin. Granular pyrite had two causes: one wascrystallization from yanshan period magmatic hydrothermal, the other was made formcolloid pyrite recrystallization. Pyrrhotite might be formed by yanshan period magmatichydrothermal. Combined with the predecessors’ relevant research, this paper consideredthat Dongguashan deposit was formed in the late Jurassic–early Cretaceous, metallogenicmaterials were mainly from yanshan period magmatic hydrothermal, and hydrothermalmineralization had the multi-stage characteristics. Late Paleozoic Carboniferoussedimentary limestone provided a favorable condition of surrounding rock and storagespace environment for transport and precipitation of minerals, and it might form a smallquantity of copper and gold bearing ore forming elements of depositional pyrite layer;Stratabound skarn type ore body on the top deposit and porphyry ore body in the deepdeposit were the same magmatic hydrothermal ore forming system, Dongguashan depositshould be a major stratabound skarn type copper porphyry gold deposit which was closelyrelated with yanshan period magmatic hydrothermal activity.