皖南竹溪岭钨多金属矿床花岗闪长岩成因、成矿时代及成岩成矿背景研究

皖南宁国竹溪岭钨多金属矿床位于江南古陆斑岩-矽卡岩型钨矿带的东部,是近年来新发现的一个大型钨矿床。矿体主要产于燕山期黑云母花岗闪长岩与震旦系兰田组灰岩接触带。与矿化关系密切的黑云母花岗闪长岩具有似斑状结构,斑晶主要由更-中长石、石英和少量黑云母组成,基质由更-中长石、石英、钾长石、黑云母和少量角闪石组成。岩石化学分析结果表明,岩石具有高硅、富钾、低镁的特征,A/CNK 1. 0,Mg#=35. 2~37. 2,P_2O_5的含量为0. 17%~0. 21%,为高钾钙碱性弱过铝质花岗质岩石;富集Rb、K,亏损Nb、Ta、Zr和Ti;为90.4×10~(-6)~168.6×10~(-6),LREE/HREE为7.15~15.2,值为10.9~35.1,呈现轻稀土元素富集的右倾配分模式,具弱的Eu负异常,δEu=0.54~0.81。以上特征说明竹溪岭花岗闪长岩为I型花岗质岩,原始岩浆以壳源为主,可能有幔源物质混入。矿石中辉钼矿Re-Os模式年龄为140.4~142.7Ma,等时线年龄为140.2±1.5Ma(MSWD=0.50),与区域成岩成矿年龄基本一致,与北侧的长江中下游地区燕山期斑岩-矽卡岩型Cu-Au-Mo矿可能为同一构造事件的产物。

Study on perogenesis of granodiorite, metallogenic epoch and petrogenetic-metallogenetic setting in the Zhuxiling tungsten polymetallic deposit, southern Anhui Province, China

The Zhuxiling tungsten polymetallic deposit in southern Anhui Province is a giant deposit discovered within the Jiangnan Paleocontinent porphyry-skarn tungsten ore belt (JNB) in recent years. The orebody was generated in skarn, which formed the contacted zone between the Yanshanian biotite granodiorites and limestones of the Sinian Lantian Formation. Petrographic studies show that the biotite granodiorite which is closely associated with the mineralization have porphyritic structures, and phenocrysts are mainly composed of oligoclase-andesine, quartz and a small amount of biotite, and the matrix is composed of oligoclase-andesine, quartz, K-feldspar, biltite and minor amphibole. The whole rock chemistry suggests that the felsic stock is characterized by high Si, K, and low Mg, with A/CNK>1.0, Mg^#=35.2~37.2,P₂O₅=0.17%~0.21%. The felsic rocks belong to K-rich weakly peraluminous granodiorite, and are enriched in Rb and K, and depleted in Nb, Ta, Zr and Ti. Their total REE contents are 90.4×10^-6~168.6×10^-6, LREE/HREE=7.15~15.2, (La/Yb)_N=10.9~35.1, and exhibiting insignificant Eu negative anomaly. These features indicate that Zhuxiling granodiorite belongs to I-type granitic rocks and crustal source with an input of mantle material. The Re-Os isotopic dating of molybdenite shows that model ages range from 140.4Ma to 142.7Ma with the isochron age of 140.2±1.5Ma (MSWD=0.50), which is similar to the ages of the regional diagenesis and mineralization. The above information indicates the rock and tungsten polymetallic deposits in Jiangnan Orogenic Belt and porphyry-skarn Cu-Au-Mo deposits along the Middle-Lower Reaches of the Yangtze River may be formed in the same tectonic setting.