Indosinian Intermediate Acid Magmatism And Metallogenic Prognosis Of Gold Polymetallic Deposits In Balong Area,Qinghai Province

Indosinian period is the main metallogenic period in the middle part of East Kunlun.Balong area is located in the middle part of East Kunlun.It belongs to Bokalike-Xiangride Indosinian metallogenic belt and Xueshanfeng-Buerhanbuda Variscan-Indosinian metallogenic belt.It has excellent metallogenic geological conditions and good prospecting potential for gold and polymetallic deposits.Balong gold deposit and Qingshuihe copper-molybdenum deposit occur in Indosinian granodiorite,which indicates that Indosinian intermediate-acid intrusive rocks are important ore-forming parent rocks in the middle part of East Kunlun Mountains,providing important material and heat sources for mineralization and important magmatic rock conditions.Based on the study of regional geological background and metallogenic geological environment of Indosinian gold and polymetallic deposits in Balong area,the metallogenic geological conditions are analyzed,and the metallogenic model of gold and polymetallic deposits in Indosinian granodiorite is established.Combining with geophysical and geochemical characteristics of the study area,the prospecting indicators are extracted and the prospecting model is established.Determine the prospecting direction in the study area.The Indosinian intermediate-acid intrusions belong to calc-alkaline-alkaline rocks,and the high content of total alkali shows the characteristics of crustal source,belonging to type I granite.The U-Pb isotopic age of zircon in granodiorite is 229 +10Ma.Therefore,the intrusive rocks belong to the Late Triassic.The Ar-Ar isochron age of amphibole in the dikes is 222.2 +3.3Ma,indicating that the dikes in the bedrock also formed in the late Indosinian period.Therefore,the eastern Kunlun orogenic belt underwent two magmatic activities in the late Indosinian period,and the latter mantle-derived magma intruded into the former crustal granitic basement.The Indosinian magmatic activity in the study area is intense,which provides abundant material sources for mineralization.Later hydrothermal activity and fault structure make the ore-forming elements continuously enriched.In addition,the intermediate-acid intrusive bodies in the study area not only bring abundant ore-forming materials,but also provide motive force for the further migration and enrichment of ore-forming elements.Mineralization in the area has played an important role in promoting.From the discovered mineralization points and mineralization information,many mineralization points are closely related to dikes,especially the intermediate-acid dikes in late Indosinian,such as syenite,granodiorite,diorite and diorite porphyrite.Combined with the characteristics of geophysical and geochemical anomalies,the geological and metallogenic favorable areas eventually extracted the prospecting criteria.(1)The tectonic favorable area for the development of veins in Indosinian granodiorite is the best area for prospecting gold,silver,copper,lead and zinc minerals in the area;pyritization,chalcopyrite mineralization,limonization,epidote,kaolinitization and chloritization,which are associated with mineralization,are indicators of mineralization alteration prospecting;(2)The comprehensive geochemical anomalies in Indosinian granodiorite rock mass with large outlined anomalous area,high anomalous peak value,good combination of elements and obvious anomalous concentration zoning are the direct geochemical exploration indicators for prospecting.(3)The contact zone of positive and negative anomalies with low and gentle geomagnetic anomalies in Indosinian granodiorite is a direct geophysical indicator for gold polymetallic deposits.Based on the geological,geophysical and geochemical information and the prospecting model established,four gold polymetallic metallogenic prognostic areas have been delineated in the study area.It is considered that there is a great potential to search for structural altered rock type and hydrothermal type gold polymetallic deposits in the Indosinian intermediate-acidic rock mass in Balong area.