摘要
德兴斑岩铜矿发育两种类型的石英脉(Q1型和Q2型)。Q1型石英脉与绢云母-绿泥石化伴随,是主成矿期的产物,由石英、黄铁矿、黄铜矿、少量方解石和绢云母组成;Q2型石英脉形成于成矿晚期,与硅化伴随,由石英和方解石组成。对两期石英脉进行了单矿物微量元素特征、氢氧同位素组成和流体包裹体测温等方面的研究。结果表明,Q1型石英脉中的石英(以下简称为Q1型石英)富Ti(>10μg/g),Q2型石英脉中的石英(以下简称为Q2型石英)Li含量极高(>300μg/g);Q2型石英脉的流体氢同位素值低于Q1型石英脉;虽然Q2型石英脉的形成晚于Q1型石英脉,但Q2型石英脉的形成温度明显高于Q1型石英脉。通过对Q1型和Q2型石英脉的地球化学对比,认为两种类型石英脉是由演化程度不同的岩浆分异出的流体形成的,大气降水的加入和岩浆脱气作用可能对流体化学特征有一定影响,两期流体的矿化特性不同。Q1型石英脉以交代方式形成,继承了岩浆成因石英的部分地球化学特征。
The genesis of two generations of quartz veins from the Tongchang porphyry copper deposit (TCD) was investigated through multiple geochemical studies. There occur two main types of quartz veins (Q1-and Q2-types) at the TCD. Q1-type veins, which are spatio-temporally associated with sericite-chlorite alteration, formed in the main copper mineralization stage. Veins of this type occur as the most important copper-bearing veins at the deposit, and consist of quartz, pyrite, chalcopyrite, and minor calcite and sericite. Q2-type veins are the products of the hydrothermal activity of later stage, and their formation accompanied intense silication. Veins of this type are copper-free and consist mainly of quartz, and occasionally, calcite occurs as a significant phase. Inductively coupled plasma-mass spectrometry analysis (ICP-MS) combined with isotope mass spectrometry and fluid inclusion microthermometry studies reveal distinct difference between the quartz veins of the two types.Oxygen isotopic compositions of Q1-type quartz are from 9‰to 10.5‰, fluid inclusion homogenization temperatures are about 120 to 200 ℃, and there is no evident difference between the Q1-type vein fluid (from -70‰to -55‰) and Tongchang primary magmatic water (-58‰) on hydrogen isotope compositions. Therefore, magmatic water is the most possible origin of the Q1-type vein fluid, though meteoric water cannot be ruled out completely. Titanium contents of Q1-type quartz are from 10 to 50 μg/g, which are obviously higher than those of typical hydrothermal quartz from other area but are similar with those of orthomagmatic quartz, and a negative correlation is recognized between its Ti contents and oxygen isotopic values. So veins of this type are likely formed not by fissure-filling but by primary rock alteration, during which magmatic characteristics was kept in various degrees.According to Li contents of Q2-type quartz (from 320 to 370 μg/g), which are much higher than those of Q1-type quartz, veins of this type are believed being formed by fluid derived from highly evolved magma. But the Q2-type vein fluid has hydrogen isotopic compositions (average -91‰) obviously lighter than those of Q1-type vein fluid and primary magmatic water of Tongchang and other places. It is deduced that the addition of meteoric water could not be regarded as the cause for that isotopic gap but magma degassing could be for the following two reasons. Firstly, no evidence of mixture has been identified from trace elements composition feature of Q2-type veins. Secondly, their fluid inclusion homogenization temperatures are fairly high (200 to 280℃).
出处
《地球化学》
CAS
CSCD
北大核心
2005年第4期53-61,共9页
Geochimica
基金
国家重点基础研究发展计划项目(G1999043209)~~
关键词
斑岩铜矿
石英脉
微量元素
氢同位素
氧同位素
德兴
铜厂
江西省
porphyry copper deposit
quartz vein
trace element
hydrogen isotope
oxygen isotope
Dexing
Tongchang
Jiangxi Province
