西藏甲玛铜多金属矿硫同位素地球化学研究

西藏墨竹工卡县甲玛铜多金属矿床位于冈底斯成矿带东段,Cu、Mo、Pb+Zn、Au、Ag均达大型规模,并伴生Co、Bi、W、Ni等多金属矿化。黄铜矿、斑铜矿、辉钼矿、方铅矿、闪锌矿、黝铜矿、辉铜矿等硫化物为主要的矿石矿物,硫酸盐矿物以硬石膏为主,含矿岩浆岩以花岗斑岩、二长花岗斑岩和花岗闪长斑岩为主。通过对甲玛矿区主要硫化物和硬石膏的硫同位素分析,并结合前人研究,甲玛矿区硫化物的硫同位素δ34S值变化于13.6‰～+12.5‰,平均值1.33‰(样品数86)、硬石膏δ34S值+0.5‰～+1.8‰,平均值+1.13‰(样品数3)、岩浆岩δ34S值0.7‰～0.2‰,平均值0.5‰(样品数3),与岩浆硫δ34S值0±3‰一致。闪锌矿-方铅矿-黄铜矿矿物对的硫同位素地质温度计,显示成矿温度为408～433℃,说明其形成时硫同位素处于平衡状态。冈底斯成矿带上的驱龙等斑岩型矿床中硫化物和岩浆岩硫同位素,均具有δ34S值变化范围小,平均值接近0值,与岩浆硫特征一致的特点,反映了甲玛铜多金属矿床具有矽卡岩-斑岩型矿床硫同位素地球化学特征,硫以岩浆来源为主。

Stable Isotopes Geochemistry of the Jiama(Gyama) Copper Polymetallic Deposit in Tibet

The Jiama(Gyama) copper polymetallic deposit in Maizhokunggar County of Tibet is located in the eastern part of the Gangdise metallogenic belt.The metal resources of Cu,Mo,Pb+Zn,Au and Ag have all reached the scale of the large-size deposit in association with Co,Bi,W and Ni.The main ore minerals include chalcopyrite,bornite,molybdenite,galena,sphalerite,tetrahedrite and chalcocite,with anhydrite being the main sulfate mineral.Granite monzogranite and granodiorite porphyries constitute the dominant ore-bearing magmatic rocks.Sulfur isotope analyses in combination with other available data indicate that δ 34 S values of sulfur isotope in sulfides are 13.6‰ +12.5‰,with an average of 1.33‰ for 86 samples,those in anhydrite are +0.5‰ +1.8‰,with an average of +1.13‰ for 3 samples,and those in porphyries are 0.7‰ 0.2‰ with an average of 0.5‰ for 3 samples,which are consistent with the magmatic sulfur value(0±3‰).Sulfur isotopic geothermometer of mineral pairs such as sphalerite-galena-chalcopyrite shows the temperature of 408～433℃,indicating that sulfur isotopes in these minerals were in an equilibrium state during their formation.δ 34 S values of sulfides and porphyries from Qulong and other porphyry copper deposits in the Gangdise belt all have a small range around zero,which is consistent to the feature of magma sulfur.All these sulfur isotope characteristics indicate that the Jiama(Gyama) copper polymetallic deposit had derived the sulfur isotope composition from magma source,similar to other deposits in the Gangdise porphyry copper belt.