Genetic Mineralogy And Deep Prospects Of Anfangba Gold Deposit In Longnan, Gansu Province

AnFangba gold deposit which is in Longnan, Gansu province is situated in thesouthern West Qinling Indosinian fold belt, Diebu-Wudu overthrust tectonic belt.Based on the analysis of the geologyical background, the geologyical conditions ofmineralization and geochemical characteristics of Anfangba gold deposit, the paperappies theories and methods of genetic mineralogy and prospecting mineralogy, tostudy the typmorphic characteristics of pyrite in No I-8orebody, which is indicativeto the deep ore prospecting and ore-finding in this mining area.No I-8orebody that is controlled by NE trending fault zone has occurred incontact belt between striped limestone of Triassic and shale. The thermoelectriccoefficient of pyrite ranges between338.40μV/℃and+344.90μV/℃,and the mostthermal electricity type is P-type. There are three main forms of thermal electricityratio histogram: discrete type A histogram which is mainly distributed in the shallowore boday, single peak type B and double peak type C histogram which alternate witheach other in the deep ore body. The spatial distribution of thermal electricity ratiohistogram zone clearly, and has a better consistency with Au-grade.The result of17pieces of pyrite analyzed by decrepitation method show that thecurve has three types, which is typeⅠcurve-initial decrepitation temperature morethan230℃and no host peak temperature in the meso-low temperature, type Ⅱcurve-initial decrepitation temperature230℃~300℃and some smaller and weakerbursting peak in the medium temperature, type Ⅲ curve-initial decrepitationtemperature lower than200℃and some obvious bursting peak in the low temperature.The spatial distribution of the pyrite decrepitation curve indicated that type Ⅰcurve ismainly in the shallow ore bodies, type Ⅱ curve is almost in the center, and type Ⅲcurve is primarily in the deep.Through the comparative study of thermoelectric coefficient calculatedtemperature and decrepitation temperature of pyrite, it is a mesothermal-lowtemperature and epithermal type gold deposit.The former shows the mineralizationtemperature of pyrite centers on three temperature range: high temperature300~330℃, middle temperature200~280℃and low temperature120~190℃.200~280℃is the main mineralization temperature.The latter indicates decrepitationtemperature of pyrite was decreased as mineralization, decrepitation temperature of the first stage is340~380℃, the second stage is240~280℃, the third stage is200~230℃, and the late stage is160~200℃. The second and the third stage are themain mineralization stage.The trace elements Pb, Zn, W, Cu, Sb, Bi, As in pyrite are in close relationshipwith Au. Pb, Zn, Cu, Sb, Bi could be regard as ore-body halo indicative elements. Srand Ba in pyrite are the front halo indicator elements. The rear halo indicator elementsare Co, V, Cr, W. Analysis of the structure superimposed halo of the mine could beused to predict new target area for the prospecting.Based on the results, three primary target areas and a secondary target area hasbeen blocked out. In a word, the study on the basis of genetic mineralogy is of greatsignificance to the reserve increase of the mine.