Study On Geological Characteristics And Enrichment Regularities Of Gold Mineralization In Laozuoshan Gold Deposit, Heilongjiang Province

Laozuoshan golds mothball resources are severity deficiency;some new resources m diposit is the second largest gold deposit in Heilongjiang province.The history of exploitation has lasted less than twenty years.Now,it ust be searched in order to increase reserves.Geotectonically, the Deposit lies at the east segment of Tianshan-Inner Mountain fold belt,the segment of Songliao basin,Lao zuoshan down-warping of southeast of Jiamusi upheaval which belongs to Jilin-Heilongjiang geosynclinal system.The strata outcropping in the region mainly include lower Proterozic Erathem Damahe Group,Mesozaic Erathem Gretaceous Period and Quaternary period from Archaeozic to Cenozoic.The magmatic rock is mainly Hercynian intrusive rock and Yanshan intrusive rock. Structure activity has the character of multi-period .The basement of Xingdong Group whose attitude is nearly EW is monoclinic structure. The Tertiary Period basalt change into platform. The nearly NE and NW trend fault develop well and Laozuoshan deposit was controled by the later.There are three equidistant gold belts,the east,the middle,the west belts,in the area with more than two hundreds orebodies.The metallogenic conditions are very advantageous in east and middle belts,so there is high industrival value.The ore minerals which devide into two types that one is vein-type the other is auriferous alterd rock type in Laozuoshan gold deposit are composed of natural gold,arsenopyrite, pyrite, marcasite, pyrrhotine, chalcopyrite, galena, sphalerite, malachite, scorodite; gangue minetals are mainly microcline, quartz, biotite, diopside, calcite,essonite,tremolite.Wall rock alteration are represented by silicification, sericitization, skarnition, potassium, minor in chloritization, carbonation and pyrophyllition, among these alterations, silicification, skarnification, arsenopyrite have the most intimately association with mineralization.The metallogenic function in Laozuoshan deposit can be divided into three periods: skatnization period ,hot liquid period and supergenetic oxidation period according to reconnaissance and study on slice.According to mineralassemblages and intercalated relationship, skatnization period can be divided into three metallogenic stages and hot liquid period can be divided into four metallogenic stages.Metallogenic physica-chemical conditions of Laozuoshan deposit reflect complexity of liquid according to the analyzing of fluid inclusions and the liquid has characteristics of high salinity,low density, middle-high temperature, middle-depth.We can see that orogeny play crucial role to the development of the deposit from the analyzing about Geodynamics Background. One side ,a large scale of ductile shear zone and brittle faults supplied channels and space for minerals deposition;the other side,intrusine rock in the diggings supplied heat energy to the moving of liquid, extraction and enrich mineral. In addition, by comparing geological characteristics between Laozuoshan and typical orogenic gold deposit, it shows that Laozuoshan gold deposit has typical orogenic features in physical and chemical conditions; therefore, it finally identified to be as middle-deep orogenic type gold deposit.There are 22 faults that controlled the ore body in the diggings among which F5 and F12 are the main ore conducting structure and host structure.In section,orebodies occurred in local extensional place when the ore-controlling fault dip steeper;in plane, orebodies occurred in local extensional place when the strike turn west In the diggings intrusine rock supplied heat energy and liquid.Xingdong Group Damahe Formation is the original source of gold,whose gold content is 15 times than earth crust abundance.On the base of the summarizion and studing on the metallogenic condition and the rules of enrichment, the method of geophysical exploration and chemic is adopted to prognosticate in deep in the diggings. There are 7 anomaly areas whose polarizability more than 2.5% and their strike is the same as regionaln structural line.By comparing and optimizing,we conclude that orebody in the NO.2 has the bigger potential of prospection below 120m and 80m middle. The evidences are as followings metallogenic center of the orebody in the NO.2 about thickness and grade show that the ore bodies extend in deep;the ore bodies located in the anomaly area of DHJ—2;it has the character of higg polarizability and low resistance in the place of 120m;the fault still extend in deep;all of these proved our prognostication.According to our analyzing,we designed a horizontal borehole-ZK24120-3 in 120m middle and ore body whose average thickness is 4.8m and average grade is 3.1g/t was discovered in 38.3 m drilling footage.