Structure-alteration Lithofacies Mapping And Prospecting Prodiction Of Hanyin Huanglong Gold Deposit In South Qinling

Huanglong gold deposit is located in the north of Hanyin County of Shaanxi Province,tectonic location is in the Shiquan-Shenhe Ductile Decollement Thrust-nappe Belt of the South Qinling.Formation in the mining area is mainly the lower Silurian Meiziya Formation(S1m),which has gone through many phases of structural deformation,metamorphism and magmatic action,ore-controlling structure and alteration,mineralization are complex.There is little igneous rocks in the mine area,only a number of intermediate-acidic magamtic dikes,however,there is little study on the relationship between the gold mine and ore-controlling structure,alteration,magamtic dikes.This paper based on the comprehensive research project of China Geological Survey Bureau,"Special Mapping and Prospecting Forecast in Shaanxi Shiquan-Xunyang Gold Mine Integrated Survey Area ",and taking the structure and alteration rock as the main research object,through the structure-alteration lithofacies mapping and combined with the rock slice identification,rock geochemical test and quartz vein fluid inclusions homogeneous temperature test,and other methods to study the relationship between ore-controlling structure,alteration rock,magamtic dikes and gold mineralization,and made the following understanding:(1)According to the mylonitization foliated degree,structural deformation intensity,quartz vein,fault,folds and joints of the rock mass in the mining area,and the scale and density of silicification,pyrite mineralization,ferritization,the content of biotite porphyroblast.Identify 3 brittle-ductile shear zones with strong deformation in the two structure-alteration lithofacies maps(1:10000 and 1:5000)of Huanglong mining area.The three brittle-ductile shear zones constitute the regional brittle-ductile shear zone RF4(DSZ2),from north to south,they are named RF4-1,RF4-2,RF43,and controlling the Huanglong gold deposit:Shuidigou section(RF4-1),Wangjiawan section + Xiaohuangdong section + Jingou section(RF4-2),Chayuangou section(RF4-3).The three brittle-ductile shear zones tend to NW,which are consistent with the gold ore bodies in each section.(2)The Strata underwent polyphase metamorphism within the mine area,among these,regional metamorphism,dynamometamorphism(Forming mylonites or mylonitic rocks)and hydrothermal metasomatism are more obvious,the major alteration lithofacies are sericitization,biotite phenocrysts crystallization,charring,pyritization,garnetization,silicified etc.In petrology,each alteration zone has different mineral assemblages and content;In geochemical aspects,the major elements Si,K etc.present regularly vary in different altered lithofacies and mineralized zone,the content of the trace element and rareearth element in the altered lithofacies and mineralized zone has less obvious distinction,the ore mineralization and the surrounding rock have substantially same pattern in rare earth elements and trace elements,indicating that the mineralization on the alteration lithofacies with great succession,the gold-related mineralization elements are more enriched in silicified zone,biotite phenocrysts crystallization zone,pyritization zone,garnetization and charring zone,It is shown that these rocks with high content of gold-related elements,which are not only related to mineralization,but also can become ore deposits.(3)Based on the 1:10000 and 1:5000 structure-alteration lithofacies mapping and typically geological section measurement,the ore-controlling structure-alteration lithofacies-mineralization map of drilling core logging and exploration lines,find that the regional brittle-ductile shear zone is an important ore-controlling structure in this area,further,the S2 foliation of the brittle-ductile shear zone is the ore-controlling structure.particularly,the change of the S2 foliation attitude often caused the change of the ore body attitude.The contact interface between the weak schist and the capable of strong meta-quartz sandstone is often the structure weak belts composed of the schist or its superimposed dynamic metamorphic rocks.In this multi-stage structure belts,it is easy to be superimposed on various size of fault fracture and the fractured alteration zones are often superimposed by the brittle-ductile shear zone and the hydrothermal mineralization enrichment,where the ore-forming hydrothermal solution can easily move and gather in multiple times.Biotite phenocrysts crystallization,charring,pyritization,silicification and garnetization are more closely related to gold mineralization,and biotite phenocrysts crystallization,biotite phenocrysts crystallization+charring,biotite phenocrysts crystallization+pyritization+silicification and other superposed alteration lithofacies are more favorable for gold mineralization in this area.(4)The granite diorite veins in the Guanyin River,in the north of the Huanglong gold mining area is basically the same as or similar to the occurrence of the surrounding rock(the occurrence of S2),the study on petrology and petrogeochemistry have shown that the magmatic veins are high in silicon,low in aluminum,depleted calcium and magnesium,alkali-rich,and enrich the LILE,such as Rb,Ba,Th and other incompatible elements such as Sr,loss of K,Ta,Nb and other elements,no Eu anomaly,rare earth element distribution pattern was steep right-leaning type,its diagenetic type should be type I according to the discriminant diagram,and it is the outcome of post-magmatic hydrothermal.The U-Pb isotopic age of zircon is 180.2±3.6Ma,which belongs to the early Jurassic and the early Yanshanian magmatic action,The chemical analysis of gold is 0.20×10-6 and 0.11×10-6.The southern Qinling entered the Intracontinental orogenic period during Late Indosinian-Early Yanshanian.Gao Huaixiong et al.(2015)measured the Rb-Srisotopic age of the pyrite in the Yangpingwan gold deposit in the northwest of Huanglong gold deposit,which is 208±0.88 Ma,and it is determined that the metallogenic age is generally the Late Triassic,and belong to the Late Indosinian,so the ductile shear zone,the S2 foliation and the magmatic rocks are formed in the Late Indosinian-Early Yanshanian period,which is consistent or close to the metallogenic age.Therefore,the magmatic action in Early Yanshanian may not only provide heat for the gold mine,and also may provide some gold.This paper analyzes the characteristics of outcrops and rock geochemistry of lamprophyre vein in Jingou,presumably,that the vein should be formed later than the S2 foliation,The mineral(mainly biotite)in the vein increased significantly,and the hydrothermal and thermal metamorphic superposition resulted in a significant increase in the mineral growth.The gold was not detected in the fresh samples of the lamprophyre vein.Combined with previous research data,that the lamprophyre vein may be favourable for gold superposition enrichment to provide heat,but whether provide gold,it need further study.