南岭钼矿的岩浆岩成矿专属性初步研究

Preliminary Study on Metallogenic Specialization of the Granites Related to the Molybdenum Deposits in the Nanling Region

南岭地区钼成矿与花岗质岩浆活动关系密切,“成钼”岩体常呈小岩株或岩瘤状产出,出露面积多数＜3.5 km2,以钾长石花岗岩/普通花岗岩类-二长花岗岩类-花岗闪长岩类系列为主。根据近年来南岭地区钼矿及其相关花岗岩的最新研究成果初步总结了“成钼”岩体的成矿专属性。结果表明,南岭地区“成钼”岩体具有以下特征：（1）极强的时代专属性和地域差异性,即成矿岩体集中形成于燕山期的150~171 Ma、129~140 Ma和90~105 Ma 3个主要阶段。其中,高峰期为150~171 Ma,主要分布在南岭中东段的赣南、粤北和湘南地区。早白垩世岩体以南岭东段的闽西南地区为主（90~140 Ma）,其次为南岭西段（90~105 Ma）；（2）化学成分专属性不显著, SiO2含量范围较广（58.04%~78.68%）,呈双峰式分布（峰值分别为62%~70%和72%~78%）,但当岩体具有不同矿化组合时,其 SiO2含量、碱含量（K2O＋Na2O）、K2O/Na2O 比值和分异指数（DI）具有不同的特征范围,表现出一定的专属性：一般具不太高的 SiO2含量（65%~71%）、高碱（6%~9%）、高 K2O/Na2O比值（＞6）、高氧化态（磁铁矿系列）和适度演化（70＜DI＜90）的岩体对形成较大规模的（独立）钼矿最为有利；（3）富集Rb、Th、U、K、Pb、Nd等元素,亏损Ba、Sr、P、Ti、Nb、Zr、LREE等,具不同矿化组合的岩体稀土元素组成差异比较大：当与铜矿有关时,各时代岩体稀土元素配分曲线呈右倾,具有不明显的Eu负异常（0.6＜δEu＜1）；独立钼矿与含铜矿化岩体特征相似,但Eu负异常更不明显（0.8＜δEu＜1）；与钨、铅、锌、锡矿等相关的岩体稀土元素配分模式呈平卧海鸥状,具有明显的Eu负异常（δEu＜0.45）；（4）岩石成因类型可以是I型、A型和S型,以后两者为主,当岩体为I型花岗岩时,往往发育铜矿化,当有幔源物质参与成岩时往往对成钼矿十分有利。

Molybdenum mineralization is closely associated with granitic magmatism in the Nanling region. Ore-bering plutons generally occur as small stocks or bosses with outcrop areas of 6）, high oxidation state （magnetite series） and moderate DI （70〈DI〈90） commonly relate to large-scale （independent） Mo ore deposits;（3） The plutons are relatively enriched in Rb, Th, U, K, Pb, and Nd, but depleted in Ba, Sr, P, Ti, Nb, Zr, and LREE. REE compositions are different for ore-bearing granitiods of different ages with different combinations of metallogenetic elements. Chondrite normalized REE patterns of the rocks with Cu mineralization show right-dipping patterns with insignificant negative Eu anomalies （0.6〈δEu〈1）;Chondrite normalized REE patterns of the Mo mineralized rocks are similar to those of Cu mineralized rocks with even less significant Eu anomalies （0.8〈δEu〈1）; whereas the chondrite normalized REE patterns of the rocks associated with W, Pb, Zn, Sn mineralization show flat seagull shapes with obvious negative Eu anomalies （δEu〈0.45）;（4） Three genetic types （I-, A-, S-types） of ore-bearing granitiods were discerned, however, most of which are either A- or S-type. It is strikely noteworthy that the Cu mineralization commonly related to I-type granites, while mantle involvement in the granite magma processes is crucial for Mo mineralization.