西藏甲玛铜多金属矿床金矿地质特征及成矿作用

甲玛铜多金属矿床按照赋矿岩石不同,共包含产于矽卡岩中的与铜共生的金矿(化)体、产于板岩-角岩中的脉状金矿(化)体、产于大理岩中的脉状金矿(化)体以及产于玢(斑)岩脉中的独立金矿(化)体4种金矿化类型。矽卡岩中的金矿化较强,全矿区金品位×厚度基本都大于1 m.g/t,存在多个富金块段;板岩中金矿化主要分布在矿区外围破碎细粒黄铁矿化硅化板岩中,角岩中金矿(化)体以富含雄黄、雌黄为特征;大理岩中金矿化较弱,矿(化)体通常呈透镜状产出;玢(斑)岩中金矿化主要产于岩脉中的石英脉内。矿石中金的赋存状态主要以独立矿物和类质同像形式存在。独立矿物形式的金以自然金、银金矿存在于铜矿物、石英、黄铁矿等载金矿物内;类质同像形式的金主要存在于以斑铜矿、黄铜矿为代表的铜矿物中。金矿物赋存状态以粒间金、包裹金为主,其次为连生金和裂隙金。笔者以甲玛铜多金属矿床金的地质特征、分布规律及赋存状态为研究基础,推测甲玛金成矿作用与幔源C-H-O流体有关,并初步建立了甲玛铜多金属矿床金成矿模型。此外,提出了运用模型开展区域及矿区下一步找矿工作的建议。

Analysis on Gold Metallization in Jiama Copper Polymetallic Deposit,Tibet

According to the host rock,the gold ore bodies found in the Jiama copper polymetallic deposit contains four types,including those association with copper ore bodies in skarns,vein gold ore boides in the slate and hornsfels and in marble respectively and those ore bodies in porphyritic and porphyric dykes,such as produced in the skarn symbiosis with copper,molybdenum and silver,and the other three types respectively veining in the slate,hornsfels,and marble.Gold mineralization in skarn is stronger than that in other rocks.Its grade×thickness is over 1 m·g/t,and many gold-rich blocks are found in this type of gold mineralization;gold mine-ralization in the slate are mostly found outside the mine in crushed and fine pyrite-bearing silicified slate.Gold mineralization in the hornfels is featured by abundance in realgar and orpiment.Gold mineralization in marble is weak and only a few small lenticular ore body are found.Gold mineralization in porphoritic and porphyirc dykes are found in quartz veins.Gold has two occurrence modes: isomorphism and independent mineral.Gold of Independent mineral occurrence occurs as native gold and electrum in the gold-bearing copper minerals,quartz and pyrite.Gold of isomorphism occurrence mainly occurs in copper minerals such as bornite and chalcopyrite.Most gold occur in and between other minerals as intergranular or intragranular gold and some gold occur as accreted and fissure-filled gold.Take the geological feature of the gold deposits,the regularity of ore distribution and the occurrence mode of gold in the Jiama copper polymetallic deposits as its research base,the present paper suggests that the gold mineralization in the studied area probably related to the mantle derived C-H-O fluid,and has set up a preliminary metallogenic model for the Jiama copper polymetallic deposits.Besides,the paper also gives some suggestions under gandance of the model for prospecting gold in the deposits and in adjacent areas.