兰坪金顶铅锌矿方解石微量元素、流体包裹体和碳-氧同位素地球化学特征研究

Geochemical characteristics of trace elements,fluid inclusions and carbon-oxygen isotopes of calcites in the Jinding Zn-Pb deposit,Lanping,China

金顶铅锌矿矿床成因一直受到广泛关注,但至今没有达成共识,其重要原因之一是对矿床成矿流体性质和来源认识的局限。本文以金顶铅锌矿床成矿早期脉状方解石和晚期结核状方解石为研究对象,系统开展了微量元素、流体包裹体和碳-氧同位素地球化学研究,在此基础上探讨了该矿床成矿流体的性质和可能的来源。研究发现,虽然2种产状方解石都以轻稀土富集、轻重稀土显著分异、配分模式向右陡倾为特征,并且具有相似的Mg、Fe和Mn含量,但它们在微量元素、流体包裹体和碳-氧同位素地球化学特征上亦存在显著差异。脉状方解石相对于结核状方解石稀土元素总量较高,富集Co、Ni、(W)、Mo、Bi;脉状方解石流体包裹体显示相对高温高盐度的特征(Th>250℃,S>8.0%NaCleqv),而结核状方解石流体包裹体相对低温低盐度(Th<200℃,S<8.0%NaCleqv);脉状方解石的碳同位素组成(δ13CPDB=-22.95‰～-2.56‰)较分散,具有多源性,而结核状方解石碳同位素组成(δ13CPDB=-7.02‰～-6.18‰)相对集中,二者的氧同位素组成(δ18OSMOW=20.16‰～23.49‰)与沉积岩类似。综合分析认为,金顶铅锌矿成矿期脉状和结核状方解石虽然均属热液成因,但它们分别代表了2类不同性质的热液体系,早期成矿流体为多源的混合流体,成矿过程中可能有深源组分的加入,而晚期成矿流体以大气降水为主。

The metallogenic mechanism of the Jinding Zn-Pb deposit is always of catholic concern,but it cannot reach a consensus.One of important causes is ascribed to limiting understanding in ore-forming fluid properties and its sources.Therefore,systematic geochemical studies of trace elements,fluid inclusions and carbon-oxygen isotopes on vein calcites and nodule calcites,formed in early and late mineralization respectively,have been carried out to investigate the ore-forming fluid nature and its potential sources.It is discovered that both vein and nodule calcites are characterized by sharing sharp right-dipped chondrite-normalized REE patterns with LREE enriched and LREE-HREE distinctively differentiated,as well as similar Mg,Fe and Mn contents.However,distinct discrepancies exist between two kinds of calcite in trace elements,fluid inclusions and carbon-oxygen isotopes.Relative to nodule calcites,vein calcites have higher ∑REE and are rich in Co-Ni-（W）-Mo-Bi.Fluid inclusions in vein calcites show relative high temperature-high salinity（Th250℃,S8.0% NaCleqv）,while that in nodule calcites display relative low temperature-low salinity（Th200℃,S 8.0% NaCleqv）.Besides,carbon isotopes spread dispersively（δ13CPDB=-22.95‰^-2.56‰）,indicative of carbonic multi-sources for vein calcites,but concentrate（δ13CPDB=-7.02‰^-6.18‰） for nodule calcites.Two groups of oxygen isotopes（δ18OSMOW=20.16‰~23.49‰） resemble sedimentary rocks.To be comprehensively analyzed,vein calcites and nodule calcites,both due to hydrothermalism,represent two different hydrothermal systems：early ore-forming fluid resulting from multi-sources with deep components added in and late ore-forming fluid dominated by meteoric water.