| The Shiquan Xunyang gold belt in southern Qinling Mountains,located in the north of Shiquan County and Xunyang County,Ankang City,is one of the important gold fields in Qinling Mountains area.From west to East,there are several gold deposits that have been exploited,such as Yang Ping Wan gold deposit,Huanglong gold deposit,Lu Ming gold deposit,Chang Gou Gold deposit and Lan Mu Gou gold deposit.In recent years,the discovery of a new gold deposit in Han Bin District Cigou-Zaoyang Ankang city is a major breakthrough in the exploration of gold deposits in this field.However,it lacks the research on the structural style of the ductile shear zone,the alteration of rock facies and the occurrence of metal minerals,and in the study of many gold deposits in the western section of the metallogenic belt,the detailed study of microstructure is rarely involved.This paper is based on the project of"the key basic geological research in the Shaanxi Shiquan and Xunyang gold deposit exploration area"from"the key basic geological survey and potential evaluation project,China Bureau of the Geological Survey”,carry out by Chang'an University.Based on the geological and mineral investigation in the mining area,the field route survey and the large scale exploration trough are carried out.The characteristics of the structure and alteration of the mining area are summarized and analyzed.The following understanding is drawn:?1?6 gold orebodies and 3 gold mineralization bodies in the strong altered black mica schist in the upper part of the first lithologic section of the Ordovician Donghe formation(Odh1-2)and controlled by the brittle-ductile shear zone have been trapped in the study area,And the natural gold particle size is 1.36mm-0.03mm,and most of the particle size is0.15mm-0.38mm.The forms of natural gold are mostly irregular,flaky,dendrite and so on.The natural mineral type of the ore is dipping and strong deformed pyrite-containing black mica quartz schist type.The mineral composition is simple.The main precious metal minerals in the ore are natural gold.The ore minerals are mainly pyrite,hematite,hematite and limonite,accounting for about 5%of the total minerals,and the gangue minerals are mainly quartz,sericite and biotite.Garnet,chlorite,carbonate minerals,etc.?2?In the study area,two BDSZ1 and BDSZ2 brittle ductile shear zones were identified along the NW direction,with a tendency of 45 degrees-65 degrees,a dip angle of 45-60degrees,a length of 2500m,and a width of 10-30m.The two ductile shear zones are consistent with the Cigou-Zaoyang fault F2,and the lithology in the shear zone is mainly the second layer(Odh1-2)dark gray black mica quartz schist in the first section of the Donghe formation.Strong brittle ductile deformation structure,S-C fabric,mylonitization,quartz lens,fold quartz vein,knee fold and interlayer crumple are also seen,and browning,silicification,sericite and carbonation are developed.The ductile shear zone is a moderate angle ductile thrust nappe shear belt,and some parts are superimposed by late extensional tectonics,showing structural traces falling on the upper plate.There are two lines in the brittle ductile shear zone,with the average value of 117°?25°?122°?26°respectively.The formation of the foliation is concentrated at 50 degrees 55 degrees,indicating the oblique thrust nappe structure.?3?The different parts of the brittle ductile shear zone generally develop different degrees of Sericite replacement,micro crumple,S-C fabric,quartz wave extinction,quartz deformable pattern,quartz mechanical double crystal,mylonitization,early quartz vein crumple,black mica rupture and deformation,stone particle boundary migration recrystallization,quartz static The ductile deformation,such as recrystallization,indicates that the brittle ductile shear zone has undergone many stages of metamorphism,such as high temperature metamorphism,high temperature and low stress stage,low temperature mineralization,low temperature brittle deformation and so on,at the temperature of 500-600degrees?low amphibolite facies?.?4?The fractal dimensions of the quartz grain boundary migration recrystallization of 7samples on the TC1901 probe section are 1.1512±0.049?1.1458±0.0506?1.151±0.0578?1.2572±0.1664?1.12±0.1016?1.1196±0.0464?1.0506±0.036,respectively,indicating that the metamorphic condition reaches the phase of the low amphibolite-granulite.The temperature is at 590-780 degrees centigrade.The metamorphic temperature shows a partial inconsistency,but it is in the range of 600-800 degrees.Using the method of quartz recrystallization grain size simulation to calculate the paleo differential stress,the 7 average paleo differential stress values obtained are:6.89 Mpa13.65 Mpa.?5?According to macroscopic and microscopic two aspects,the research on the brittle ductile shear zone in the study area has analyzed and summarized the mineralization process.The strong ductile shear formed a partial dilatation zone in the tectonic schist,which provided a channel for ore forming hydrothermal irrigation.The stronger the rock deformation,the higher the gold grade.The ductile shear deformation is many times,and the enrichment of the metallogenic hydrothermal solution is also multiple.Only in this way can the high grade ore be formed,and the gold content in the ductile shear zone is generally high,but the industrial grade can not be reached.Owing to the heterogeneity of the strong deformation expansion zone formed by the high strain zone,the ore grade is also uneven.?6?Some suggestions for ore prospecting are put forward.?1?the deep prospecting for the ductile shear zone,the development of the metallic minerals in the ductile shear zone in the study area and the development characteristics of the quartz vein with the filling tendency of 330 degrees in the post tensional fissures after the main metallogenic period and the three stage metallogenic model proposed by Chen Bailin?1998?,that is,the quartz vein type gold deposits are superimposed on the early fine net veins and mylonite type gold deposits.Therefore,the deep part still has fine vein type and mylonite type gold deposit,and the gold element comes from the deep part of the ductile shear zone.?2?The scope of the ductile shear zone epitaxy is only a small part of the whole Cigou-Zaoyang precheck area,and the unexplored region in the brittle ductile shear zone is the key area for the next prospecting. |
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