Mineralization Enrichment Regularity And The Genesis Discussion Of Xincheng Gold Deposit,Laizhou Shandong

Shandong laizhou Xincheng gold deposite which located in the north of Laizhou city Shandong province has a good connect with outside. Xincheng gold deposit located in the Sorthwest of Longkou- Laizhou fault structure. Jurassic period, as the Izawa Naiqi plate dive into Eurasia by the SE-NW, Northwest Jiaodong began to enter into an important orogenic-ore-forming stage.The strata exposed in Xincheng mine area is Cenozoic quaternary strata and Archean Jiaodong Group.The Magmatic rocks are widely distributed in Xincheng mine area, mainly are linglong adamellite and guojialing granodiorite which located under the main fracture.This paper analysis of Guojialing granodiorite thinks its foundation is 127±2Ma.Dikes such as lamprophyre and dioritic porphyrite are well developed. Structures are well developed in the Xincheng mine area,and Jiaojia-Xincheng fault is the largest scale。Jiaojia-Xincheng fault in mine area is 2000 m long and 40° trend, dip to NW, dip angle between 28°~34°.and has a continuous and stable principal section,this fault is the important ore-controlling and ore structure. Xincheng gold orebodys are all located in the footwall of the principal section.No. Ⅰ orebody and NO.Ⅴorebody is the main deposit body of Xincheng gold deposit, it is located in the footwall of the principal section and is NE37° trend, dip to SE, dip angle 30°.Ore types are mainly beresite and beresitizational granitic cataclasite. The main metallic minerals in the ore are pyrite, a small amount of chalcopyrite, galena, etc. The main nonmetallic mineral are quartz, sericite and residual feldsparh. The main ore textures are crushing structure and grain structure. Ore structures are mainly disseminated structure. Wall rock alterations are well developed, include potassium, phyllic, pyrite phyllic and carbonate-based, among them, pyrite phyllic has the most intimate relationship with gold mineralization. Sanshandao gold deposit is mainly experience two mineralization periods: hydrothermal mineralization periods and supergene oxidation periods, and the hydrothermal mineralization periods can be divided into four mineralization stages:Ⅰquartz- pyritestage, Ⅱ quartz- pyrite- gold stage, Ⅲ quartz- gold-polymetallic sulfide stage and Ⅳ quartz- carbonate phases, Stage Ⅱ and stage Ⅲ are main stage of gold-rich mineralization,Test analysis on fluid inclusions of ore samples show the ore-forming fluids are low salinity(0.87%~10.24%NaCleqv) and low density(0.71~0.99g/cm3)and rich in CO2, mineralization temperature is concentrated in 260~320°C, mineralization pressure ranges from 62~112MPa, while mineralization depth ranges from 6.34~9.23 km.Hydrogen and oxygen isotopes diagram shows ore-forming fluids derive mainly from deep mantle fluids, and accompanied by a small amount of magmatic fluids.Sulfur and lead stable isotope diagram shows that ore-forming materials derive mainly from mantle and Au derives mainly from upper mantle sources.Based on above cognition, and compared with the Jiaojia gold deposit in the same region, I hold that Xincheng gold deposit belongs to mesothermal vein-type gold deposit which is controlled by faults and mantle-derived fluids involved in mineralization.Xincheng gold deposit orebodys strictly controlled by Jiaojia-Xincheng fault, the intercepting effects of fault gouge made gold orebodys all located in the footwall of the principal section. Industrial orebodies strike easterly tendency and on the angle slows the local tensile parts, it shows in metallogenic period the ore-controlling fracture was a right-latera normal fault. Industrial minerals body side to the SWdirection, side angle about 45°. It was considered by integrated analysis that there is another mineralization enrichment segment in the deep of gold deposit.provide a theoretical foundation for the further prospecting work.