呷村银多金属块状硫化物矿床银的赋存状态

Modes of Occurrence of Silver in Gacun Silver-Polymetallic Massive Sulfide Deposit

通过大量岩石、矿石光 (薄 )片观察鉴定、电子探针分析 ,首次查明呷村海相火山岩型银多金属块状硫化物矿床有硫砷铜银矿和硫砷铜矿两种硫盐矿物。研究表明 ,除硫化物外 (主要为方铅矿、闪锌矿、黄铁矿 ,其次为黄铜矿、毒砂、斑铜矿、硫铜银矿、螺硫银矿、磁黄铁矿等 ) ,硫盐矿物十分发育 ,主要有黝铜矿、车轮矿、硫砷铜矿、硫砷铜银矿等。该矿床中的银主要在喷流_沉积成矿阶段富集。

Located in Baiyu County of western Sichuan Province, the Gacun silver_polymetallic deposit is a typical marine volcanics_hosted massive sulfide deposit in Late Triassic (T 3) Yidun volcanic belt. The strata in this deposit are composed of marine volcanic rocks (andesite and rhyolite) and upper sedimentary rocks, and the ore occurs in marine rhyolites. The attitude of the ore is parallel to that of marine rhyolites. The authors studied ore minerals by observation under microscope and electron microprobe analysis. Samples included about 100 sections of polished ores and rocks. The ore minerals of Gacun deposit comprise mainly sulfides and sulfosalts. Three sorts of sulfosalts were first identified, namely pearceite, polybasite, enargite. Then ore minerals were determined, which turn out to be mainly galena, sphalerite, pyrite and subordinately chalcopyrite, arsenopyrite, bornite, stromeyerite, acanthite, pyrrhotite as well as many kinds of sulfosalts. Tetrahedrite, pearceite, enargite, boulangerite and bournonite are main sulfosalts. Silver mainly occurring or scattered in sulfosalts was found, being spread mostly in tetrahedrites, and partly in silver_minerals (pearceite, stromeyerite, acanthite, etc.) as well as a series of Ag_bearing fine vermiform minerals. Silver minerals and vermiform minerals were also found to be mainly existent along the margins or fissures of sulfosalts (tetrahedrite). It is therefore considered that the ore_forming process of the Gacun deposit can be divided into two stages. The sulfides and sulfosalts belong to early stage, whereas silver_minerals and vermiform minerals are of late stage. The results are of significance in understanding mineralization process,and provide an important information for the evaluation of the deposit.