The Geological Setting Of Mineralization And Porphyry Metallogenic Series With Micro-disseminated Gold Deposits In Fengshan Orefield Of Hubei

Guided by porphyry metallogenic theories, This paper emphaticlly studies the metallogenic geology background, micro-disseminated (Carlin-type) gold deposits recovered recently and porphyry metallgenic series of Fengshan orefield in Hubei. Based on the mass field on-site survey and the work of predecessors? with laboratory comprehensive study, the paper established the pophyry metallogenic model, summed up the metallogenic regulation, and pointed out the direction of further prospecting . The main new views obtained are as follows :(1) Based on geological survey and comprehensive analysis of data, new views on the metallogenic geology background were gained. At early Triassic end, nappes orogeny occurred in the area formed nappe structure. The structural planes of fracture made by nappe faults controlled intrusion-metallization of Yanshanian magma. By drawing composite map, it is discovered that the shape of Fengshan intrusive body dosent like the shape of a mushroom, which was recognized by predecessors. Geological and geochemical researches conclude that orefield instrusions are products of homologous magma most of which derived from upper mantle. Magneto-telluric, remote sensing and driling data suggest the intrusive body have "two layer constructions".The upper layer instrusions are controlled by relaxed main fracture and dimbricate fault,and the lower layer is hidden instrusion controlled by relaxed main fracture.In ore-host strata,the black carbo-naceous,argillaceous and siliceous carbonatite faded universally, the relic black rocks contain a lot of micro orbicular and micro-fine disseminated pyrites (δ 34S-7.33~-7.39%) and organic carbon wich are benificious to minerallization.The data of REE, isotope and trace elements illustrate that the strata are ore-beds that suply metallic elements (special Au) for metallization.(2) Two micro-disseminated gold metallogenic belts are discovered and affirmed. Basicly finded out the geological and geochemical characters of this type gold ore, generlized its significance for prospecting and estimated its prospective reserves. Expounded the geologial characters of hydrothermal vein-typ gold polymetal deposits for the first time, and the gold occurrence of the mine is ascertained for the mining requirment.(3) Regarding orefield as a porphyry metallogenic system, studied the geochemical characters of Fengshan copper deposit with data of H,O,Pb,S isotope , REE, trace elements and compositions of the inclusions. The results of the study indicated that the metallogenic fluid mainly derived from meteoric water, and that the ore-forming resources not olny from the upper mantle and lower crust but laso from ore-beds. The fluid of convective circulation drived by thermal energy from magma extracts, transports and releases the metallogenic resources from ore-beds.(4) Demonstrated the temporal and spatial evolution of the skarn deposit, porphyry deposit, hydrothermal vein-type deposit and micro-disseminated deposits in the orefield and genetic relations between them for explaining that they are porphyry metallogenic series and establishing pophyry metallogenic model of the orefield.(5) According to the orefield metallogenic regulation summarized, pointed out that the sectors between Lijiawan and Jilongshan and some districts else of easterm Hubei and northwestern Jiangxi are all faverable for prospecting deposits and the sector between Fengshan and Jilongshan with a prospect for exploring large-scale Au-Cu deposit. On exploring the the southern mountain of Fengshan, two zones of geophysical and geochemical anomalies were discovered, the zones with mineralized alteration rocks parallel the southern minerallize belt of Fengshan deposit. Industrial ore bodies riched in Au-Cu and thick in width has been discovered in the first drill hole on the 7th exploratory line, this verified our revewer.